Journal of the ICRU Vol 4 No 2 (2004) Report 72 Oxford University Press
DOI: 10.1093/jicru/ndh024
EXECUTIVE SUMMARY This Report was originally intended to provide guidance on the specification and calibration of beta-ray sealed sources------planar, concave, and seeds------as used in brachytherapy, and on the determination of their relative dose distributions. In the beginning, the main interest was the use of these sources for ophthalmic radiotherapy. Because lowenergy photon sources exhibit similar absorbed-dose characteristics and have replaced the use of beta-ray sources in some cases, corresponding guidance on the dosimetry of low-energy photons has been included for comparison. During the drafting of the Report, there was a rapid expansion in the use of beta-ray sources for intravascular brachytherapy. Therefore, the scope of the Report was adjusted to pay due attention to the dosimetry for intravascular applications. The sources covered by this Report are indicated in Section 1 and include: (a) planar and concave sources of beta rays from 90Sr----90Y and 106 Ru----106Rh, mainly used for ophthalmic plaques; (b) seed and wire sources of beta rays from 90 Sr----90Y, 90Y, and 32P, and shell sources of 32P, for applications in intravascular brachytherapy; and (c) seed sources of low-energy photons from 125I and 103 Pd, for use in ophthalmic plaques and as interstitial implants. Section 2 presents details of the sources and their application in brachytherapy, and more data are collected in Appendices A and B. Section 3 discusses recommended methods for the specification and calibration of the sources, and Section 4 discusses the determination of relative dose distributions, by both calculation and measurement. A consistent formalism for the presentation of absorbed-dose distributions from a single source, applicable to both beta-ray and photon line (seed or wire) sources, is also introduced in Section 4. Section 5 considers dosimetry comparisons pertinent to the applications covered by this Report. On the basis of Sections 4 and 5, relative absorbed-dose distributions, or parameters for their calculation, for a few specified types of beta-ray and low-energy photon sources are presented in Section 6. Finally, Section 7 discusses briefly the quality control of dosimetry. The recommended method of specification and calibration of individual sources is in terms of the
reference absorbed-dose rate for beta-ray sources, and in terms of the reference air-kerma rate for low-energy photon sources. These quantities are used as the basis of the calculation of complete twodimensional dose distribution, while the third dimension is usually taken care of by the assumed symmetry and uniformity of the sources. The primary calibration of these sources forms a special case, because only one primary-standards dosimetry laboratory (the National Institute of Standards and Technology, NIST, in the USA) currently provides such calibrations. The techniques applied at the NIST are, therefore, presented in detail. A revised value of the air-kerma rate constant of 0.0355 m2 mGy h 1 MBq 1 is recommended for 125I and the value of 0.0361 m2 mGy h 1 MBq 1 is recommended for 103Pd, both values including photons of energy greater than 10 keV. Because accurate measurements of dose distributions for beta-ray and low-energy photon sources are often very difficult, it is important to compare measurements with calculations. Monte Carlo methods provide the most accurate results and are recommended for such calculations. Because a traditional method, the integration of beta-ray point-source dose functions or point kernels, has been widely applied for the calculations of dose distributions of clinical beta-ray sources, this approach and its limitations are also discussed in this Report. It is concluded that, for practical clinical sources in non-homogenous media, the integration of the beta-ray point-source dose functions, or point kernels, cannot generally provide results of sufficient accuracy. The consistent formalism for presenting singlesource dose distributions for line (seed and wire) sources, as recommended in this Report both for beta-ray and photon sources, is equivalent to the modular approach introduced for photon sources by the Interstitial Collaborative Working Group (ICWG) in the USA, and subsequently adopted by the American Association of Physicists in Medicine (AAPM), for both photon and beta-ray sources. Data compiled for the dosimetric constants required in this approach are given for the few individual source types specified in the Report. This compilation
ª International Commission on Radiation Units and Measurements 2004
DOSIMETRY OF BETA RAYS AND LOW-ENERGY PHOTONS FOR THERAPEUTIC APPLICATIONS
melanoma and endovascular brachytherapy are presented in Appendix B.2. Following the GECESTRO (Groupe Europe´en de Curiethe´rapie) recommendations for reporting therapeutic irradiations, patient doses should be specified in relation to anatomical reference points and volumes in order to allow one to compare the efficacy of different techniques.
represents up-to-date published consensus data, which are supported by a reasonable number of studies. The relative depth-dose data given for beta-ray planar and concave sources should be used only as reference data for comparisons with actual measurements on similar sources. Clinical examples illustrating the application of beta rays and low-energy photons for uveal
16
DOI: 10.1093/jicru/ndh024
EXECUTIVE SUMMARY This Report was originally intended to provide guidance on the specification and calibration of beta-ray sealed sources------planar, concave, and seeds------as used in brachytherapy, and on the determination of their relative dose distributions. In the beginning, the main interest was the use of these sources for ophthalmic radiotherapy. Because lowenergy photon sources exhibit similar absorbed-dose characteristics and have replaced the use of beta-ray sources in some cases, corresponding guidance on the dosimetry of low-energy photons has been included for comparison. During the drafting of the Report, there was a rapid expansion in the use of beta-ray sources for intravascular brachytherapy. Therefore, the scope of the Report was adjusted to pay due attention to the dosimetry for intravascular applications. The sources covered by this Report are indicated in Section 1 and include: (a) planar and concave sources of beta rays from 90Sr----90Y and 106 Ru----106Rh, mainly used for ophthalmic plaques; (b) seed and wire sources of beta rays from 90 Sr----90Y, 90Y, and 32P, and shell sources of 32P, for applications in intravascular brachytherapy; and (c) seed sources of low-energy photons from 125I and 103 Pd, for use in ophthalmic plaques and as interstitial implants. Section 2 presents details of the sources and their application in brachytherapy, and more data are collected in Appendices A and B. Section 3 discusses recommended methods for the specification and calibration of the sources, and Section 4 discusses the determination of relative dose distributions, by both calculation and measurement. A consistent formalism for the presentation of absorbed-dose distributions from a single source, applicable to both beta-ray and photon line (seed or wire) sources, is also introduced in Section 4. Section 5 considers dosimetry comparisons pertinent to the applications covered by this Report. On the basis of Sections 4 and 5, relative absorbed-dose distributions, or parameters for their calculation, for a few specified types of beta-ray and low-energy photon sources are presented in Section 6. Finally, Section 7 discusses briefly the quality control of dosimetry. The recommended method of specification and calibration of individual sources is in terms of the
reference absorbed-dose rate for beta-ray sources, and in terms of the reference air-kerma rate for low-energy photon sources. These quantities are used as the basis of the calculation of complete twodimensional dose distribution, while the third dimension is usually taken care of by the assumed symmetry and uniformity of the sources. The primary calibration of these sources forms a special case, because only one primary-standards dosimetry laboratory (the National Institute of Standards and Technology, NIST, in the USA) currently provides such calibrations. The techniques applied at the NIST are, therefore, presented in detail. A revised value of the air-kerma rate constant of 0.0355 m2 mGy h 1 MBq 1 is recommended for 125I and the value of 0.0361 m2 mGy h 1 MBq 1 is recommended for 103Pd, both values including photons of energy greater than 10 keV. Because accurate measurements of dose distributions for beta-ray and low-energy photon sources are often very difficult, it is important to compare measurements with calculations. Monte Carlo methods provide the most accurate results and are recommended for such calculations. Because a traditional method, the integration of beta-ray point-source dose functions or point kernels, has been widely applied for the calculations of dose distributions of clinical beta-ray sources, this approach and its limitations are also discussed in this Report. It is concluded that, for practical clinical sources in non-homogenous media, the integration of the beta-ray point-source dose functions, or point kernels, cannot generally provide results of sufficient accuracy. The consistent formalism for presenting singlesource dose distributions for line (seed and wire) sources, as recommended in this Report both for beta-ray and photon sources, is equivalent to the modular approach introduced for photon sources by the Interstitial Collaborative Working Group (ICWG) in the USA, and subsequently adopted by the American Association of Physicists in Medicine (AAPM), for both photon and beta-ray sources. Data compiled for the dosimetric constants required in this approach are given for the few individual source types specified in the Report. This compilation
ª International Commission on Radiation Units and Measurements 2004
DOSIMETRY OF BETA RAYS AND LOW-ENERGY PHOTONS FOR THERAPEUTIC APPLICATIONS
melanoma and endovascular brachytherapy are presented in Appendix B.2. Following the GECESTRO (Groupe Europe´en de Curiethe´rapie) recommendations for reporting therapeutic irradiations, patient doses should be specified in relation to anatomical reference points and volumes in order to allow one to compare the efficacy of different techniques.
represents up-to-date published consensus data, which are supported by a reasonable number of studies. The relative depth-dose data given for beta-ray planar and concave sources should be used only as reference data for comparisons with actual measurements on similar sources. Clinical examples illustrating the application of beta rays and low-energy photons for uveal
16
