PP05 Presentation Time: 4:36 PM

Purpose

This presentation shares highlights of the International Atomic Energy Agency (IAEA) Technical Report Series 492 Code of Practice on brachytherapy (BT) dosimetry.

Methods

This IAEA Code of Practice is addressed to both secondary standards dosimetry laboratories (SSDLs) and hospitals, not addressed to primary standards dosimetry laboratories (PSDLs), and is based on the use of well-type re-entrant ionization chambers. It applies to all BT sources with intensities measurable by such detectors. The dosimetry formalism, common procedures for reference dosimetry and for calibration, reference-class instrument assessment, and commissioning of well-type chamber system are described. This Code of Practice is aimed to enable common procedures to perform dosimetry of radioactive sources used in BT, excluding beta-emitting eye plaques/applicators as well as stranded seeds and mesh-type sources. Targeted radionuclide therapy and miniature electronic brachytherapy (eBT) devices were also excluded. It provides a description of the most accurate and sensitive calibration systems available at PSDLs and recommends suitable detectors and procedures for source strength measurements at SSDLs and hospitals.

Results

This Code of Practice consists of ten sections and six appendices. Following the introduction in Section 1 that frames the background and scope, Section 2 provides a description of the radioactive sources currently available for BT. The dosimetric quantities reference air kerma rate, air kerma strength and absorbed dose to water are discussed in Section 3, along with the dose-rate constant and other parameters important to dosimetrically characterize BT sources. Section 4 provides a detailed description of well-type ionization chamber instrumentation and defines the requisites for reference-class instruments. It also includes a description of HDR remote afterloaders. Section 5 contextualizes the dosimetry framework that defines dissemination of primary dosimetry standards down to the hospital level. Section 6 provides an overview of the available primary standards useful for BT calibrations. Their dissemination through the adoption of a well-type chamber dosimetry system is furthermore described. Section 7 defines the dosimetry formalism employed for the determination of the dosimetry quantities used herein. The general procedure to properly perform BT dosimetry with the well-type chamber is given in Section 8, along with a description of methods to check for short and long term stability of the measurement system. Section 9 deals with estimating uncertainties typically involved with source strength measurement of LDR and HDR sources. The way measured reference quantities are useful in the clinical practice for assessing the dose to the patient is outlined in Section 10. The main BT source categories and treatment delivery methods are briefly approached. Appendices are provided to complement the information given in the main body of the publication: Appendix I briefly mentions antiquated quantities and units that are not recommended to be used any more for dosimetry purposes; Appendix II provides insight into the present situation for dosimetry standards based on air kerma and absorbed dose to water; Appendix III provides a brief description of eBT devices and the current status of their dosimetry standards; Appendix IV provides insight into some detector systems different from the well-type ionization chamber that might be used for BT dosimetry; Appendix V describes the formalism found in the AAPM Task Group 43 Report, which is commonly used for dose distribution calculation in interstitial and intracavitary BT; Appendix VI introduces the theory for estimating measurement uncertainties.

Conclusions

Guidance and recommendations for BT dosimetry in relation to identified good practices are presented for international harmonization.