icru 38

Dose and Volume Specificationfor Reporting Intraeayitary Therapy in Gynecology 1. Introduction In 1978, the ICRU published Report 29, Dose Specification for Reporting Esternal Beam Therapy with Photons and Electrons (ICRU, 1978). The present report deals with the problem of dose and volume specification for reporting intracavitary therapy. The principal subject is dose and volume specification for the intracavitary treatment of cervix carcinoma. However, the concepts developed in this report are designed to be applicable to other types of intracavitary applications, such as uterine body, etc. Intracavitary therapy is often used in combination with externa! beam therapy and, therefore, the same terminology and definitions of terms are advocated. In particular, it would be desirable, whenever possible, to use the concepts of target volume, treatment volume and irradiated volume, as defíned for externa! beam therapy. However, due to the high dose-gradient around the sources (throughout the tumor and target volume), the specification of the target absorbed dose in terms of the dose absorbed either at one or severa! réference point(s) within the target volume is not considerad meaningful; therefore, the approach used in externa! beam therapy cannot be used. The problem of dose specification is still more complicated when two or more target volumes are identified, some being treated either by external, or by intracavitary therapy and some by both methods. Furthermore, attention should be -paid to the different time-dose patterns linked to each treatment method. Based on clínica! experience, different systems have been proposed for the treatment of cervix carcinoma. Three basic systems have been developed: the Stockholm system (Kottmeier, 1964)1, the París system (Lamarque and Coliez, 1951)1 and the Manchester 1 The references quoted are not the first references but those which seem to be the most comprehensive. system (Paterson, 1948)1. Most of the systems used throughout the world are derived from these three basic systems. As used here, the term "system" denotes a set of rules taking into account the source strengths, geometry and method of application in order to obtain suitable dose distributions over the volume(s) to be treated. For reporting, the system includes recommendations for specifying the application and possibly, as in the Manchester system, for calculating the dose rate (or dose) at specific points. Typical applications according to the Stockholm system and the histórica! Paris system are presented in Figures 1.1 and 1.2, respectively. In both systems, applications have been reported in terms of "mg-h" (milligram hours), i.e., the product of the total mass or radium contained in the sources (in mg) and of the duration of the application (in hours). The Manchester system (Paterson and Parker, 1934), derived from the origina! Paris system, initiated about 1920, was designed to deliver a constant dose rate to defined points near the cervix, irrespective of variation in size and shape of the uterus and vagina. In the Manchester system, an application was specified in terms of the "dose" in roentgens delivered at specific points such as points "A" and "B" (Figure 1.3). Points A and B are still widely used throughout the world, although their exact meaning and their definition have not always been interpreted in the same way in different centers and even in a given center over a period oftime. In particular, some centers relate point A to anatómica! references in the patient, others to the geometry of the sources. The different methods of definition provide different valúes for the calculated dose rate to point A. As a resuit, where a prescribed dose to point A is used to calcúlate the tota! time for an insertion, different valúes of time for which the oíd systems are not always suitable. this will be the location where there is least variation in the dose rate from one source axrangement to another one. It is opportune now to reconsider dose and volume specification for severa! reasons: (i) Introducüon radium is being progressively replaced by gammaray emitting substitutes ( I37 Cs. the Manchester system is based on a set of strict rules concerning the method of inserting the radium sources (in particular the choice of vaginal ovoids and their separation. On the other hand. . from which new information and relationships can be derived. (ii) new sets of sources are available. is also used but will not be discussed ¡n this document. will be obtained. and (iv) computers are routinely used for calculations and complete sets of intracavitary dose distribution in severa] planes axe nbw becoming available. (iii) SI units are now being widely used in the field of radiology.1. a neutrón emitter. 192Ir and 60Co)2. It is therefore important to gíve a precise deacription of the method used to calcúlate the dose rate at specific points. Assuming that the Manchester definition of point A is used. depending on the method used. and the relative strengths of the intrauterine and intravaginal sources). 2 Californium-252. Typical treatment of a cervii carcinoma with a radium application (uterus normal ¡n size an¿ shape). • B • Fig. ptnint A is defined aa a point 2 ci latera] to the centra] canal of the úteros and 2 cm up from the mucot membrane of the latera] fornix. The figure shows a typical application and the amounto radium in the two applicators aa well aa the dose-rate (Figure fron Walstam. in the axis of the uterus. ñor connection between vaginal an uterine sources (Pierquin. : . In a typical application. the two applicators are not fixec to each other.3. each application lastini for 27-30 hours. but fixed or semi-fued combinationa have been de veloped. 1. 1. the histórica] París system does not imply any fixed distant between the vagina] sources. but in special caaes other forms of vaginal ap plicators raay be used. The total activity used ¡s one of the loweat in use fu such treatments and implies a typical duration of the application ( 6-8 days.2. Point B i defined as being in the transverso axis through points A. As far as the method of application ¡s coi cerned. Fig. allow for application times of 10-18 hours at eact treatment. and their strength between 10 an 15 mg of radium. Classically.5). 2 or i applicationa are given with 3-week intervala. Defmition of points "A" and "B' In the claasical Mancheater sysUm. Introductlon Scm Fig. their linear activit being between 6 and 10 mg per cm. The Stockholm system. 1964). 1967). The histórica] París system. 5 cm froi the midline. the loadingí intrauterine applicators varied between 20 and 35 mgof radium an between 15 and 25 mg of radium for each vaginal ovoid. 1.1. The resulta) treatment time to get 8000 R at point A was 140 hours. Typically. the ratio of the total activity of the vagina] sourcí to the total activity of the uterine sources should b e l (with variation between 0.66 and 1. doae calculations are often made froi radiographs and point A ¡s taken 2 cm up from the fiange of the ii trauterine source and 2 cm lateral from the centra] canal as indicatí in the figure (Meredith. The vaginal applicatoi usually consista of a fíat box containing 60-80 mg radium (70 mg it the example shown). Typically. 1954). The vaginal applicator ¡s held against the cervix and latera fornices by careful and systematic gauze packing. In clínica] practice. Typical radium applicatioi for a treatment of cervix carcinoma consisting of: 3 individualizei vagina] sources (one in each lateral fornix and one central in front o the cervical 03). The intrauterine rod-shaped applicator is loaded with 53-81 mg radium (74 mg in the exnmple shown). Poasible variations of the París system ¡n elude: 2 vaginal sources (or only one) in case of a narrow vagina] cavitj only 2 intrauterine radium tubes (or only one) in case of short uteru! The active length of the sources ia usually 16 mm. using largei amounta of radium. 1 intrauterine source made of 3 radium tubes (¡n so called tándem position). Modificationa of the Stockholm method.1. The Manchester system. each point source is equivalent to a given le of the linear source. O 1 2 3 In many of the modern application devices. Typically.1 Treatment Techniques 2. The dose i: rected for oblique filtration (Dutreix and Wambersie. 2. source lengths or both. for instance. continuous low dose-rate irradiation can be replaced by fractionated high dose-rate irradiation. Thus. could be reduced to a few minutes (O'Connell et ai. Variations of the of movement.in the preparation of the sources. the characteristics of the sources used for intracavitary applications were similar and their activities were of the same order of magnitude. 1969. 2.1). for instance. These point sources may be of equal activity and equally spaced. In addition. 2. these include no contamination from leakage and less shielding in the case of 137Cs and 192Ir. 192Ir and 60Co may be accomplished according to two options. continuous or stepwise. Von Essen. The introduction of remote afterloading device clinical medicine (see Section 2. In other applications. the elementary radium tubes most frequently used were 1. 1973.1. 198 In the simple case where a linear source is simu by a series of regularly spaced point sources of activity. 1967). and a linear: length I = n£ and of total activity o = nao-The curves arel 2.3 Dose Ratos In conventional brachytherapy with radium t the dose rate at the point or surface where the d prescribed. thus simulating a uniform linear activity.2. Linear sources can also be simulated by moving sources of appropriate activity. 1967. Irradiation times ranging from 6 to 8 days. not only as far as normal tissue tolerance is concerned. and to improve the dose distribution by providing. greater flexibility in the selection of the relative source activities. 1966.1. Bjórnsson. Himmelmann e 1980.. Definition of Terms and Concepts Currently Used in Intracavitary Thcrapy 2. The linear source simulated b point sources is longer than the distance betwee extreme point sources (see Figure 2. 1980. with source strengths ranging from 5 to 20 mg of radium and a total Pt filtration of 1 to 2 mm (see Appendix). involving different activities or different sp in order to modify and improve the shape of the rel isodose surfaces (Cardis and Kjellman. These new types of source are designed to allow the use of new and better techniques of application.4 and 2 grays per houi common practice to refer to this type of treatmi low dose-rate brachytherapy.1. lies between 0. Busch et ai. Van der Laar.1.. but also for effects on the tumor. of the speec dwell times of the source at different positions modify the shape of the isodose surfaces (Hensch al.1 Radium Substitutes When radium was the only available radionuclide. Twiss and Bradshaw. The principal advantages of the replacement of the radium concern radiation protection. the increased specific activities available with artificial radionuclides and the technical possibility of making miniaturized sources. In the first option. more complex arrangements are Fig. with radium in the Paris system. below) ha.2 Simulation of Linear Sources used.1 for relative dose raU. 1969. At dista larger than half the spacing between the point sou the dose distribution around the point sources is si to that around . 1968). Comparison of dose distributions between ": sources of activity ao spaced by a distance E. The dotted lines result from a serie sources and the full lines from a linear source.a linear source of the same total ac (Dutreix and Wambersie. The replacement of radium by 137Cs. the large range of source activities at present available allows the therapist to modify completely the time-dose pattern of application. Chas eí ai. It should be stressed that such drastic changes in the time-dose pattern require a modification of the total dose and that the clinical experience accumulated over many decades with relatively low dose-rate radium applications can no longer be applied without careful evaluation. The same technique of application can then be applied and the clinical experience gained with radium remains fully relevant. linear sources are simulated by a set of point sources. the new sources (mainly 137Cs) are similar in aize and shape and have an output similar to radium sources.1. afterloading. 1977.4. The second option takes advantage of the ¡mproved technology.5 to 2. Busch.se. Joslin et al. 1980).2 cm long. 196¡ . 2. source insertion and removal are operated from a control panel distant from the patient. and it falls off continuously with distance from the sources. variations greater than ±10% are not deemed acceptable. it must be stressed that the treatment duration should always be clearly reported (see Section 4). For curative treatment.2 Volumes The definitions given in ICRU Report 29 for external beam therapy will be modified where necessary for intracavitary therapy situations. if present. Moreover. the dose is máximum adjacent to the sources and at the center of the treated volume. For any given situation. Afterloading techniques help to ensure the correct and safe positioning of the radioactive sources in the patient. after the position of the applicators has been radiographícally checked using dummy sources. ¡n particular. some advantage Is obtained by replaclng radium by 7-emitters of lower energy (the shielding problems are easier and the risk of contamination is also avoided). the target volume consists of the demonstrated tumor(s). The dose distribution can also be computed so that the position of the guides can be corrected if necessary before the sources are inserted. Outside the treatment volume the dose falls off more or less steeply. attention needs to be given to the problems of dose specification and dose-time relationships. very high dose rates. However. the dose falls off rapidly at the edges of the treatment volume and in the lateral directions (Fields 3 and 4) remains fairly constant at about 30% of the dose at the center of the treatment volume. according to a chosen plan and without exposure of the staff. the radiotherapist has to indícate which dose level defines the treatment volume. As already stressed. For example. in addition to facilitating the transfer of the sources to and from a shielded storage container. Ln Figure 2. The treatment sources are inserted later. the dose patterns differ substantially within the treatment volume as well as in healthy tissues distant from the treated región.2 Absorbed-Dose Pattern and Volumes /ented an opportunity for investigating different dose 'ratea and.1 Absorbed-Dose Pattern and Volumes Absorbed-Dose Pattern 2. unloaded applicators or guides are introduced into the patient cavities. the size of the treatment volume cannot be deduced from a simple inspection of the isodose pattern. thus eliminating exposure of the clinical staff.1. 2. Therefore. Although the dose gradient (dose change per unit distance) at the border of the treatment volume is similar for either technique. i.2 2. As already discussed. In remotely controlled afterloading techniques.. the term high dose rate refers to any dose rate higher than 0.4 Afterloading Techniques Modifications of application techniques in intracavitary therapy are often made for purposes of radiation protection. afterloading techniques as well as modifying their irradiation procedures. In this Report. In afterloading techniques. there may be more than one target volume.2. In general. médium dose rate and high dose rate are arbitrary and debatable. and any other tissue with presumed tumor.2c.e.2c: the absorbed dose has been arbitrarily normalized to 100% at a distance of 2 cm from the uterine axis in order to allow a comparison of the absorbed dose patterns. While either manual or mechanical afterloading techniques may be used for low dose-rate applications. the sources are automatically retracted into the storage container when the door of the patient's room is opened. pelvic irradiation with a 60Co "box technique" (see Figure 2. Afterloading is an important aspect of intracavitary therapy. treatment sessions of a few minutes duration. Consequently. With some of the more advanced devices. With intracavitary therapy. In external beam therapy. the clinical experience accumulated with radium techniques cannot be applied to new irradiation conditions without careful consideration. as more centers are now adopting The pattern of the absorbed dose to the soft tissue in intracavitary therapy differs from the dose pattern encountered in external therapy. This is particularly the case for treat- . between 2 and 12 grays per hour and we propose to refer to sucfiTdose rates as médium dose rates. Such definitions of low dose rate. remote afterloading techniques are mandatory for médium and high dose-rate applications in order to ensure good radiation protection of the staff.2. one aim is to reduce variations in dose over the target volóme. the main ¡mprovement in radiation protection derives from the introduction of afterloading techniques. although it usually refers to dose rates as high as 2 to 5 grays per minute.2 gray per minute (12 grays per hour). Afterloading techniques may be manual or remotely controlled. In this connection.2a) produces a dose distribution within the treatment volume which is ráther'flat. Sorne radiotherapists are now exploring intermedíate dose rates. as shown in Figure 2. 2. Target Volume The target volume contains those tissues that are to be irradiated to a specified absorbed dose according to a specified time-dose pattern. .. 13 y. 0 5 1 .Field No Size (cm x crn) 3 17x20 10x20 10x20 Weighting factors 37'/. 37'/.2b IRIDIUM WIRES ( s a m e r e f e r e n c e air kerma rales as radium lub'es ) correction made for oblique f ilt ration . 13'/. .h-1 RADIUM T U B E S uterina Subes 3 x 10 mg vaginal tubes 2 x l 5 m g f i l l r a t i o n 1 mm Pt 2. I . 10 cm 2..2a \ \0 70 50 30 20 70110 10 cGy. topography and tumor volume. Treatment Volume The treatment volume is defined as the volume enclosed by a relevant isodose surface selected by the radiotherapist. The border of the target área is indicated by the heavy dotted line. and encompasses at least the target vol- ume. 1982).3. 2. The dotted line refers to intracavitary therapy (Figure 2. 2.. larger than the treatment volume. independently of the dose distribution. in terms of the patient's anatomy. Reference Volume The reference volume is defined as the volume enclosed by the reference isodose surface.2c shows the dose variation along a lateral axis.2b shows a typical dose distribution ¡n an intracavitary application (IAEA.2. 2. It should also be stated whether this volume will receive treatment only by intracavitary application or will receive treatment by both modalities. In order to facilitate intercomparisons between radiotherapy centers. which receives an absorbed dose . along the beam axis 3 and 4). that part of the target volume which has to be irradiated by means of intracavitary application should be separately described. it is necessary to determine the dimensions of the reference volume.2c + 10 cm Fig. 2. Dutreix et al. Examples illustrating target volumes in patients with carcinoma of the cervix are given in Figure 2. Figure 3.2b. while others are treated mainly by external therapy.2a shows the dose distribution for an irradiation of the pelvis with a 60Co teletherapy machine and four fíelds—the so-called "box technique" (see ICRU Report 29. some target volumes may be treated partly or totally by an intracavitary application. depending on the extent of disease. The shaded áreas (2 cm wide) show the high dose-gradient regions beyond the border of each of the two treatment volumes.2 Absorbed-Dose Pattern and Volumes 100 i_ 01 n 'S 50 u O Q I -10 axis 2. The full line refers to external therapy (Figure 2. 1972. For reporting intracavitary therapy. Comparison of absorbed dose patterns between external and intracavitary therapy. The absorbed dose has been normalized to 100% at a distance of 2 cm from the uterine axis. The treatment dose level defming the treatment volume may be equal to or different from this reference dose level. The target volume(s) must always be described. In intracavitary therapy. ment of cervix carcinoma where. Irradiated Volume The irradiated volume is that volume. This is because of the steep dose gradient around the sources and the variation encountered in the techniques used.2.2a. For the purpose of reporting intracavitary treatment. The physical dimensions of the target volume must be given.4). it ia necessary to agree upon a reference dose leuel. it is not feasible to express the valué of the isodose surface enclosing the treatment volume as a percentage of the dose at any point within the treatment volume. along the AB axis). It is necessary to plan the treatment to include the target volume within the treatment uolume. 2.3.. The total reference air kerma is the sum of the products of the reference air kerma rate and the duration of the application for each source. ONLY 1NTRACAVITARY TREATMENT B. Definition of Terms and Concepts Curren/// Used In Mracaviiy Therapy A. in air. The plarmed. For this purpose this quantity is expressed in ^íGy-h" 1 at one metre. considered to be significant in relation to tissue tolerance. Examples of target volumes and treatment volumes. The target volume for brachytherapy will only include the major parts of the tumor volume. The almost pear-shaped target volume includes the entirety of pajpable and visible tumor as well as the whole uterus. The reference air kerma rate of a source is the kerma rate to air. Treatment of cervix carcinoma. COMBINED INTRACAVITARY AND EXTERNAL BEAM THERAPY Targzt volume Treatmsnt volume Targzl vdume oí inlra cavilary Inzalmcnt (cervix región* corpus) Trtalm«nl volume oí intracavitary treatment Field |\r \'^..g.3. corrected for air attenuation and scattering. Stage II.a). in an intracavitary application for cervix carcinoma. . ureters and possibly sigmoid colon. 50%) of the agreed dose level (see Section 3. To treat the rest of the tumor volume and further subclinical disease throughout the pelvis and the regional lymphatics. Organs at Risk Organs at risk are those radiosensitive organs in or near the target volume which would influence treatment planning and/or the prescribed dose. at a reference distance of 1 meter. 2. external beam Iherapy w i l l be used. The significant absorbed dose level can be expressed as a percentage (e.recommended that radioactive sources be specified in terms of "reference air herma rate".2.. the main organs at risk are rectum. A—Tumor volume {hatched): 4 cm X 3 cm X 2 cm. pear-shaped treatment volume encompasses the target volume. AdditionaJ methods such as combined surgery or combined external radiation may be used.3 Specification of Radioactivo Sources It is.x Target volume of exUrnal beam therapy Treatment volume of external beam Iherapy Fig. bladder.2.b. and brachytherapy will be used as boost therapy. B—Tumor volume (hatched): 9 cm X 5 cm X 4 cm. but will include the whole uterus. For example. Specification of an intracauitary application in erras of the "reference volume" enclosed by the reference isodose surface is proposed in this Report. it has been recommended that the target absorbed dose be the absorbed dose at one or more specification points which are representative of the dose distribution throughout the target volume. (ii) reference air kerma rates. etc. larget volume.2. 3. (iv) type of vaginal sources. The recommendations presented ¡n this Report must be considered a mínimum requirement for reporting. Instead of a target-dose specification. 3.1 The Sources (i) radionuclide. including the ñame of the manufacturen The description should include information on the following points: (i) rigid (or not). consequently with fixed known geometry (or riot) of the complete applicator. the reported parameters will be meaningful only to the extent that the technique of the particular intracauitary application has been completely described. a volume specification is recommended. free. (v) high atomic number shielding materials in vaginal applicator (or not). . Recommendations for Reporting Absorbed Doses and Volumes in Intracavitary Therapy 3. mean. fixed. i. the concepta of máximum. (ii) unidirectional or oscillating movement. (iv) speed in different sections of the applicator. ring. the specification of the target absorbed dose in terms of the absorbed dose at specific point(s). it is recommended that the applicator be described. 3. are not relevant.2. To avoid confusión.e. or both. or dwell times of the source at different positions. (ii) rigid uterine source with fixed curvature (or not). b) When moving sources are'used to simúlate a set of different sources in fixed position. as defined in ICRU Report 29 (ICRU 1978). These specification points could be established / with respect to the target volume or to the beam axes. the indication of the reference volume must be supplemented. -lowever..2 Description of the Technique It is recommended that the technique be described on the basis of the guidance given below. by the indication of the total reference air herma which. The mínimum target absorbed dose is the only useful concept and is. for radium treatments. in order to produce an appropriate dose distribution. apy due to the steep dose gradient in the vicinity of the sourcea. a record of absorbed dose at reference points related to organs at risk or to bony structures is recommended. for safety reasons.2.2 Simulation of Linear Sources a) When a linear source is simulated by a set of point sources. in the vicinity of the sources. i The situation is more difficult in intracavitary ther¡|. provided that there is no significant difference between the applicator used and the one described in the literature.1 Intro4uction As the absorbed dose to soft tissue from in traca vi tary applications is so highly fronuniform throughout the . 3. filtration. becomes less meaningful and a different approach is required. throughout the tumor or the target volume. loóse (semi-fixed). In addition. is proportional to the number of "mg-h". On the other hand. For externa! beam therapy. the activity of these point sources and their separation(s) must be índicated. The time-dose pattern shall also be clearly mdicated (see Section 4). but they imply the calculation of ipecific quantities to be determined for reporting. However. by definition. step distance). This report deals mainly with the treatment of cervix carcinoma for which the anatomical región of interest is similar for every patient and the possible variation in the position of the radioactive sources is limited.sufficient when a complete description has already been published. for other gynecological Lntracavitary situations the same philosophy can be adopted.3 The Applicator Reference to the applicator is. (iii) shape. i.. equal to the treatment absorbed dose level. (iii) connection between vaginal and uterine applicators. The present recommendations do not imply a modi: ication of the method used for the calculation of the treatment duration. median and modal target absorbed dose.3. but some of the numérica! valúes and definftions may need to be modified according to the type of application. the following indications are required: (i) type of movement (continuous or stepwise.). as the different isodose surfaces are cióse to each other. special sources (box.e. number and orientation of line sources. etc. Under these conditions. (iii) range of movement or oscillation. Plañe a is the "oblique" frontal plañe that contains the intrauterina device. the dose rate obtained at P from the actual distribution of sources differs by less than 4% from that obtained by assuming that all of the sources are located at C (Dutreix et ai. the use of total reference air kerma is proposed in this Report. dose pattern should be clearly stated (see Section 4.1. Dose Leuel An absorbed dose leuel of 60 Gy is widely accepted as the appropriate reference level for classical iow dose-rate therapy.2).3. they complement each other and it is recommended that they be combined.2. even if mílligrams of radium are replaced by the term "milligram-radium equivalent" which can be misleading (see Appendix).2. The time- Plane a Plañe b Fig.20 Gy = 40 Gy.3. the isodose level to be considered would be 60 . 3. It becomes increasingly difficult to use the product mg-h for specifying an intracavitary application with other radionuclides.1 Total Reference Air Kerma When radium was used exclusively.3 Recommendations for Reporting Three approaches are proposed to specify intracavitary application for cervix carcinoma. the simple calculation of the total reference air kerma does not allow one to derive. 3. i. the product of the "quantity of radioactive material" and the duration of the treatment was given as mínima! information. it is recognized that the combined dose does not nec- . For example. Ln addition. in particular.1. in the tumor or target volume) and.2 Description of the Reference Volume The description of the reference volume. The reasons for this approach are described in Sections 2..3. respectively. It is proportional to the integral dose to the patient and can also serve as a useful Índex for radiation protection of personnel.3. Geometry for measurement of the size of the pear-shaped 60 Gy isodose surface (broken line) ¡n a typical treatrnent of cervix carcinoma using one rod-shaped uterine applicator and 2 vaginal applicators. However.. the absorbed dose in the immediate vicinity of the sources (i.3.) and the wi'dth (dw) of the reference volume are measured in plañe a as the máxima! sizes parallel and perpendicular to the uterine applicator. of the absorbed dose delivered during treatment at distances from the sources down to 20-10 cm. to a reasonable approximation. As noted in Section 2. The thickness (d t ) of the reference volume is measured ¡n plañe b as the máxima! size perpendicular to the uterine applicator.1. The oblique sagittal plañe is obtained by rotation of the sagittal plañe around AP axis. it should be stressed that an accurate and simple relation cannot be derived between total reference air kerma and absorbed doses at speciñc pointa such as A and B (see Figure 1. Pla-ne b is the "oblique" sagittal plañe that 'contains the intrauterino device. When the distance of a point P from the center C of the volume occupied by the sources is larger than 2. When two or more intracavitary applications are performed. 2. the isodose level to be considered is the difference between 60 Gy and the dose delivered at the same location by external beam therapy. Nevertheless. is proposed for specification in reporting. Recommendatlons for Reportlng Absorbed Doses and Volumes In Intracavltary Therapy 3. This quantity is unambiguous and easy to calcúlate. the inverse square law applied to the total reference aír kerma allows evaluation.. When intracavitary therapy is combined with external beam therapy. even roughly.2. 3. The height (¿t. The oblique frontal plañe is obtained by rotation of the frontal plañe around a transversa axis. if a dose of 20 Gy were delivered to the whole pelvis by external beam therapy. the absorbed dose to consider is that resulting from all applications. and 3. This is the "concept of the mg-h".e.e. the tissue volume encompassed by a reference isociose surface. 1982).).5 times the largest dimensión of that volume. a. ) are obviously useful with respect to normal tissue tolerance limita.) have been proposed by Chassagne and Horiot (1977). The balloon must be • filled with 7 cm3 of radio-opaque fluid. the reference point is taken at the center of the balloon. 3.2. Reference Points Cióse to the Sources and Related to the Sources As such points are located in a región where the dose gradient is high. such as stereographic x-ray films. oblique perpendicular radiographs or transverse sections (CT scans). When other methods are used. (iii) the thickness (dt) is the "máximum dimensión perpendicular to the intrauterino source and is measured in the oblique sagittal plañe containing the intrauterine source.3 Recommendatlons for Reporílng / essaríly produce the same effect as a similar dose from f\j intracavitary therapy alone. The bladder reference point is obtained as follows. These dimensions are usually expressed in cm. the therapist has to indícate the dose level which | he believes to be equivalent to 60 Gy delivered at classical low dose rate and should clearly state this. The catheter is pulled downwards to bring the balloon against the urethra. Some are relatively cióse to the sources and related either to the sources or to organs at risk.3. Related to Organs at Risk The determination and specifícation of the absorbed dose to organs at risk (bladder. The following definitions apply to the case where the doses are calculated from two perpendicular radiographs. The definitions of d^. The posterior vaginal wall is visualized. | For intracavitary therapy at médium or high dose sí rates. others are relatively far from the sources and are related to bony structures. etc. 6. the reference point is obtained on an anterio-posterior Une drawn through the center of the balloon. On the frontal radiograph. A Foley catheter is used. AP and lateral. dv and d t are proposed Ln order to mínimize the number of calculations. such information-v/ül be meanmgful only to the extent that it is obtained and expressed in precise and well-codified ways. On the lateral radiograph. particularly if rigid source combinations are not used. Reference Volume: Description of the Pear-Shaped Volume When uterine source(s) are combined with vaginal sources. On the lateral radiograph. any inaccuracy in the determination of distance results in large uncertainties in the absorbed doses evaluated at these points. or when the uterine source is more heavily loaded at the lower end. 3. The point of reference for the rectal dose is obtained as follows. the tissue volume to be described presenta a pear shape with its longest axis coineident with the intrauterine source. The point is located on this line 5 mm behind the posterior vaginal wall. However. (i) Calculated Valúes: Reference points for the expression of the absorbed dose to the bladder and the absorbed dose to the rectum (see Figure 3. seem an appropriate means of characterizing an intracavitary application and/or of specifying the target absorbed dose. therefore. the Reference Points Relatively Cióse to the Sources but b. The volume estimated from the intersections of the surface of a pear-shaped volume on two conventional planes does not necessarily represent the size of the true reference volume. by means of an intravaginal mould or by opacification of the vaginal cavity with a balloon 7 cm3 point intrauterina sources intravag sourczs rectal refzrznce point Fig. rectum. . for most applications they do not differ from the máximum dimensions of the reference volume by more than 1 or 2 mm.3. (ii) the width (dw) is the máximum dimensión perpendicular to the intrauterine source and is measured in the same oblique frontal plañe. Such calculated absorbed doses do not. depending upon the technique.3 Absorbed Dose at Reference Points Several reference points are in current use. Such points are not recommended. The reference point is taken on this line at the posterior suxface of the balloon.1): (i) the height (d^) is the máximum dimensión along the intrauterine source and is measured in the oblique frontal plañe containing the intrauterine source. However.2. the calculations need to be modified. This reference volume is deñned by means of three dimensions (see Figure 3. an anteroposterior line is drawn from the lower end of the intrauterine source (or from the middle of the intravaginal sources). a. Determlnation of the reference pointa for bladder and rectum (see text). 4.3. The point of máximum rectal dose rate is noted and the distance "d" iri cm from the anaJ verge deduced.r a l « m«Ur Mílhod B Fig. either pre-loaded (low-act¡vity treatment) or manuaUy loaded with /oiu-activity sources idéntica! in design to those used during /it'g/i-activity after-loaded treatment. this reference point is at the lower end of the intrauterine source or at the middle of the intravaginal source(s). in particular the description of the reference volume encornpassed by the 60-Gy isodose surface. Distance is taken as a direct reading on the centra] tube at the anaJ verge. related to well-defined bony structures and lymph nodo áreas. in the cranio-caudal direction. ¡s particularly useful when intracavitary therapy is combined with external beam therapy. EXT for right and left external. at different points along the anterior rectal wall to ensure that no área of the rectal mucosa receives a dose above 3.. respectively). 1977) can be visualized on an AP and a lateral radiograph and related to fíxed bony structures. The midpoint of a line connecting these two points is used to estímate the dose to the low comrnon (labeled R. At the top of the trapezoid. 1967. Then a line is drawn from'the middle of-that line to the middle of the anterior aspect of L4. (ii) The peluic-wall reference point (Chassagne et ai.3. PARA).). A trapezoid is constructed in a plañe pasaing through the transverse line in the pelvic brim plañe and the midpoint of the anterior aspect of the body of L4. (O'Connell et al. the tolerance leve!. c. (ii) Monitoring of the Absorbed Dose Rate to the Rectum: An alternative to calculating the rectal dose is to measure the dose. necessitates the computation of complete dose distributions in seueral planes. EXT and L.5.4): A line is drawn from the junction of S1-S2 to the top of the symphysis..1972). Evaluation of the absorbed dose at reference points. An example is given in Figure 3. or dose rate. Recommendations for Reporíing Absorbed Doses and Volumes in Intracavitary Therapy Mslhod A Dos* .3. the highest points of the right and left acetabulum. as a mínimum . 1980). allowanee for the distance of the probé sensor from the vagino-rectal septum needs to be taken into account. Reference Points Related to Bony Structures (i) The lymphatic trapezoid is obtained as follows (see Figure 3. radio-opaque gauze used for the packing. However. COM and L. the pelvic-wall reference point is intersected by the following two lines: a horizontal line tangential to the highest point of the acetabulum.3. Method A: The measuring probé is moved relative to a rigid guide tube inserted into the rectum and held in position. This type of mensurement requires specíal care in positioning the measuring probé. This point is intended to be representative of the absorbed dose at the distal part of the parametrium and at the obturator lymph nodes (see Figure 3. COM) iliac lymph nodes (from Fletcher. On an AP radiograph. are joined and the lateral projection of the pelvic-wall reference point is located at the mid-distance of these points. the rectal dose is measured. It is also useful in helping to avoid an overdose when intracavitary therapy is to be followed by surgery. Method B: The measuring probé is moved so that the tip of the probé is moved along the mid-line of the recto-vaginal septum un til the point of máximum dose rate is reached. PARA and L. points 2 cm lateral to the midline at the level of L4 are used to estímate the dose to the low para-aortic área (labeled R. Following the insertion of the source applicators. a vertical line tangential to the inner aspect of the acetabulum. However. The dose-rate and distance are recorded. 3. On a lateral radiograph. A point 6 cm lateral to the midline at the inferior end of this figure is used to give an estímate of the dose rate to mid-external iliac lymph nodes (labeled R.Joslineía/. The respective planes for which the dose distribution is to be computed will depend on the technique and the particular clinical situation. Calculation of Dose Distribution The present recommendation. The major disadvantage of method "A" is that the probé tip cannot l'ollow dosely the surface of the anterior rectal wnll. On the AP radiograph. Measurement of the rectal dose rate. On the left is an anteroposterior view and on the right a lateral view. .3. 3. LATERAL X .R A Y FILM Fig.3 Recommendaüons for Reporting 2crrv R Symphysis Fig.-i.5. Determination of the lymphatic trapezoid (see text). AP X .R A Y FILM Determination of the right (RPW) and left (LPW) pelvic wall reference points (see text). 3. However.4.4. 3.2 Vaginal Sources Only When only vaginal sources are present. pre-calculated isodose surfaces can be obtained for given loadings of the applicator. In connection with uterine packing.4. While this additional information will be of valué ¡n assessing effects in any individual patient. width is the largest dimensión from right to le'ft ¡n an oblique frontal plañe through the main axis of the vagina. 3. two facts need to be noted: —width and thickness are usually located at the level of the uterine fundus (the pear-shaped volume is reversed). in order to determine the absorbed dose at any relevant anatomical point.b) in this simple case. In estimating the volume (Section 3. 1972).3.4 Uterine Packing (In Endometrial Cáncer) In some situations only one linear source is present: —in the case of a narrow vagina with a uterine source protruding into the vaginal cavity.4 Definition of the 60 Gy Reference Volume in Special Situations 3. Height is measured along the vaginal axis. Thickness is the largest dimensión in a direction perpendicular to the above oblique plañe. which gives the máximum dimensión. When practicable.3. it will also provide: (i) the possibility of comparing the methods of specification used in different centers and of evaluating their respective merits.4. Therefore. and is commonly shorter than the other two dimensions. width and thickness given in Section 3. the same definitions of height. width and thickness can be-given (IAEA. —height should be determined in the oblique frontal plañe. . ¡t is recommended that the dose distributions be computed ¡n two planea: the oblique frontal plañe and the oblique sagittal plañe both containing the intrauterine source. the width is equal to the thickness. pointa "A" and "B") with the methods recommended in the present Report.tion. 3. (iii) the possibility of deriving new clinical and radiobiological data and correlations which could improve treatment techniques and develop further the method of specifica.2. (ii) the possibility of comparing the rnethods of specification used in historical series (mg-h.3 Rigid Applicator Provided that there is a fixed connectíon between vaginal and uterine sources. Recommendations for Reporling Absorbed Doses and Volumes in Intracavilary Therapy requirement. it is recommended that dose distributions be calculated in additional sets of planes and that theae dosimetric data be correlated with that obtained from radiographs or CT sections.3. 3. pre-calculated dimensions of height.2 can be used.1 One Linear Source Only —in the case of vaginal irradiation with a central source from a cylindrical applicator. In each brachytherapy application. repair of potentially lethal lesions. but the duration of the application should be stated. Furthermore. Similarly. depend to a greater extent on dose rate. Time-Dose Pattern 4.1 Radiobiological Considerations Radiobiological effects often depend on dose rate but to a greater or lesser extent according to the actual level of the dose rate and the nature of the effect (Hall. Recommendations for Reporting Time-Dose Pattern Sufficient data on the effect of dose-rate on various tissues are not available at the present time. The possible importance of changes in time factora (dose rate) in determining the biológica! or clinical effect should not be underestimated since there may be a shell of tissues surrounding the sources where differences in dose rate may be significant (Van Limbergen et al. the time-dose schedule of the whole treatment should be reported. Therefore. reoxygenation. and. 1985). \. 4. The relationship between dose rate and tissue response in uivo is complex because many factors have to be taken into account such as cell distribution. there is necessarily both a marked dose gradient and a marked dose rate gradient as a function of distance from the sources. It can be concluded that any significant change in the source strength and the time-dose pattern should be made with the greatest care. when external beam therapy and intracavitary therapy are combined.2 . its role is probably a minor one in brachytherapy applications.4.. In addition. 1978). which are most relevan t. no correction factors for dose rate can be recommended. but becomes increasingly dependent on dose rate at lower rates. For example. For dose rates below about 1 Gy-h"1 survival again becomes independent of dose rate. the time between fractions is important in the case of fractionated high dose-rate intracavitary therapy. the duration of each should be reported. As far as cell proliferation is concerned. early tissue reactions alone should not be used to-select the prescribed dose since late reactions. Its location and thickness will vary with the total reference air kerma rate and the application time. as well as the time interval(s) between them. When more than one application is performed. for tumors. it is genefally observed for mammalian cells irradiated in uitro that for dose rates larger than about 1 Gy-min"" 1 survival is independent of dose rate. the doses delivered at the TABLE 5. the specification of the target absorbed dose as that dose observed at one (or several) reference point(s) within the target volume or cióse to the souxces.1 3. For a given method of application (source geometry and-relative loads). any method of specification will be meaningfui only to the extent that the treatment technique has been completely described. First.3c 3. ness of the volume enclosed in the 60 Gy isodose surface for cervix-carciñoma treatment by low dose rates.b 3.3.3.3.3b 3. the absorbed dose(s) at reference point(s) related to bony structures (lymphatic trapezoid and peluic-wall reference points) should also be reported. For higher dose rates a dose level lower than 60 Gy has to be selected. The following are proposed in this Report (see Table 5. as aJready pointed out in ICRU Report 29 (ICRU. due to the high dose-rate gradient.3.3. the total reference air herma should be stated.1).3.3b 3.2' 3.5. width and thick.3.1—List of data needed for reporting intracavitary therapy in gynecology Data Needed Páragraph DESCRIPTION OF THE TECHNIQUE USED . width. Third. TOTAL REFERENCE AIR KERMA (cGy at 1 metre) DESCRIPTION OF THE REFERENCE VOLUME — Dose level if not 60 Gy — Dimensions of the reference volume (height.3. the absorbed dose at reference points in organs at risk (rectum. bladder) should be determined (computed or measured) and expressed in well-codified ways to provide ádditional safety limita.a 3. Finally.2 3.3 3.2. thickness) 3. the time-dose pattern should be completely specifíed. Conclusions and Final Recommendations different tissues or organs are directly proporcional to the total reference air kerma.3c 4 9 10 10 10 11 11 11 12 12 15 ABSORBED DOSE AT REFERENCE POINTS Bladder reference point Rectal reference point Lymphatic trapezoid Pelvic wall reference point 11 TIME DOSE PATTERN . 1978).3. Second.2. In intracavitary therapy. Fourth. In addition. it is recommended that the reference volume be described in terms of the height. Under these conditions. the same approach to reporting as in external beam therapy cannot be recommended. does not appear to be meaningful. 93). (7) The total reference air kerma is the sum of the products of the reference air kerma rate and the duration of the application for each source. sources were specified in "milligram-radium equivalent". (2) When artificial radionuclides became available. Assuming that the sources are left in situ for 6 days (144 hours). the total reference air kerma is equal to 435 X 144 X 10-6 Gy or 6. (3) Due to the inñuence of self-absorption and filtration within the source and its sheath. The reference exposure rate in milliroentgens per hour at 1 meter was used (mR-h^-m 2 ) (Wambersie et al. 65 mg of radium yield a reference air kerma rate of 435 ^Gy-h~ 1 -m 2 . 0.5 mm Pt filtration.1 at 1 m. (4) In order to compare radium substitutes directly with radium itself. (1) When radium tubes were the only radioactive sources used in intracavitary therapy. 1970). This quantity is expressed in /iGy-h" 1 at 1 m. corrected for air attenuation and scattering. their strength was specified in terms of the mass of radium in mg contained ¡n the tube. but it could lead to some confusión with the expression "milligram-radium equivalent".873 cGy-R"1) and the correction for the difference in filtration (0.27 cGy at 1 m. Dutreix and Wambersie.4 mSv-h" 1 . NCRP. at one metre from the patient the dose equivalent rate will not exceed about 0. Dutreix. For example. the expression "equivalent activity" has also been used (IAEA. the sources were first specified in terms of their actiuity in mCi. a "point" source c. The radium equivalent mass (mg-Ra equivalent) of a source is the mass of radium filtered by 0.25 ± 0. . the Comité Trancáis pour la Mesure des Rayonnements lonisants (CFMRI.5 mm of platinum which leads to the same exposure rate as that from the radioactive source of interest at the same distance. the dose rate at a given distance from a typical 10 mg radium tube filtered by 1 or 2 mm of platinum is less than the dose rate delivered at the same distance by a 10 mg Ra equivalent source which was standardized to 0. The dose delivered to the sigmoid for example (assumed to be 10 cm from the center of the sources) is approximately 6. Therefore. produces an air kerma rate of 67MGy-h. The apparent actívity of a source was defíned as the activity of a point source of the same radionuclide which would deliver the same exposure rate in air at the same distance from the center of the actual source (the distance should be large enough so that the actual source can be considered as a "point source"). at a reference distance of one metre. This is because sources of different radionuclides with the same apparent activity will not give equivalent dose distributions.. 1975).5 mm platinum.APPENDIX Specification of Radioactive Sources Used in Intracavitary Therapy Only some aspects of the problem of the specifícation of sources will be reported here since this topic will be dealt with at length in a forthcoming ICRU Report and has been treated recently (Dutreix et al. the strength of a source was specified in terms of its output. we consider an application performed with 25 mg of radium as an intrauterine source and 40 mg of radium as the vaginal sources. 1967 and ICRU. for example (for radioprotection purposes). in air. (6) Recently. 1 mm Pt filtration. a source containing 10 mg of radium. produces an exposure rate of 8.e. 1982).27 Gy. Thus. If the radium tubes are filtered by 1 mm Pt. 1973.27 X 102 cGy or 6. The reference air kerma rate of a source is the kerma rate to air.. Instead of the term apparent activity. 1974.. exposure rate at a reference distance. the "contained actiuity" was of little practica! interest and the concept of "apparent activity" was ir\troduced.25 X 10~4 R-h^-m 2 . By way of example.10 R-rr 1 at 1 cm or 8. TaJWng Into account the conversión factor from exposure to air kerma (0. 1983) has recommended that radioactive sources be specified ¡n terms of "reference air kerma rate" ("débit de kerma normal dans l'air"). i. (5) Later. 1974.ontainfng 1 mg of radium. neglecting tissue attenuation and the tissue-kerma to air-kerma ratio. Documents Similar To icru 38Skip carouselcarousel previouscarousel nextBrachytherapyICRU 82ICRU 38ICRU 58 ICRU RecommendationsICRU 38ICRU 50ICRU 62Icru Report 50ICRU-16ICRU38ICRU 62[1]Radiation Oncology ACR 2010 in-Service Exam RationalesHandbook of the Physics of Radiation TherapyHandbook of Radiotherapy Physics Theory and PracticeDNB Radiotherapy Final Questions - Topicwise (2006-2012)Icru Report 74Practical Radiotherapy Planning, Fourth Edition0849315050ICRU 50 ICRU_33.pdfRaphex 2012.pdfQ U A N T E C SUMMARYHandbook of Treatment Planning in Radiation Oncology067 Intensity-Modulated Radiation Therapy - S. WebbRadiation Oncology Study GuideMore From Alvaro Rodrigo Oporto CauzlarichSkip carouselcarousel previouscarousel nextGlosario Rdtbreast cancer ttoFundamentos de Oncologia(Rmn) Ojeda MabelIcru Report 50Pricipios_Fisicos_TCTac Detect Ores Bast. ComplFundamentos PETfisica rx 20046809583-Cerveza-de-JengibreFooter MenuBack To TopAboutAbout ScribdPressOur blogJoin our team!Contact UsJoin todayInvite FriendsGiftsLegalTermsPrivacyCopyrightSupportHelp / FAQAccessibilityPurchase helpAdChoicesPublishersSocial MediaCopyright © 2018 Scribd Inc. .Browse Books.Site Directory.Site Language: English中文EspañolالعربيةPortuguês日本語DeutschFrançaisTurkceРусский языкTiếng việtJęzyk polskiBahasa indonesiaSign up to vote on this titleUsefulNot usefulYou're Reading a Free PreviewDownloadClose DialogAre you sure?This action might not be possible to undo. Are you sure you want to continue?CANCELOK