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American Brachytherapy Society recommendations for clinical implementation of NIST-1999 standards for 103palladium brachytherapy

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Abstract

Purpose: Recent important developments in palladium-103 (103Pd) dosimetry mandate a reevaluation of 103Pd brachytherapy prescribing practices.

Methods and Materials: The clinical research committee of the American Brachytherapy Society (ABS) convened a consensus session of brachytherapists and physicists to develop recommendations regarding future dose prescribing guidelines for National Institute of Standards and Technology (NIST-1999) calibrated 103Pd sources.

Results: The ABS recommends that clinicians attempt to reproduce the implant doses delivered and reported in the literature through the past decade.

Conclusions: The following should be immediately implemented for 103Pd dosimetry: 1) All practicing physicians, physicists, dosimetrists, and suppliers implement NIST-1999 air-kerma strength standard for 103Pd brachytherapy. 2) All treatment planning systems and dose calculation algorithms must be updated to reflect new dose rate constants. The AAPM-recommended validated value for Theraseed model 200 is 0.665 cGy h−1 U−1. The dose rate constant for the Mentor MED3633 seed is currently reported as 0.68 cGy h−1 U−1. This latter value and the values for seeds from other manufacturers are awaiting independent confirmation. 3) Physicians who previously prescribed 115 Gy for 103Pd monotherapy prostate implants should now prescribe 125 Gy. When using 103Pd as a boost following 45 Gy of external beam irradiation, 100 Gy should be prescribed instead of the previous 90 Gy.

It is critical that all three changes be implemented concurrently, because they are interdependent.

Introduction

Recently, there have been three important developments in palladium-103 (103Pd) brachytherapy dosimetry. First, several changes have been noted in apparent activity quoted by the manufacturer over the past several years (1). Second, in January 1999, the National Institute of Standards and Technology (NIST) implemented an air-kerma strength (Sk) standard for 103Pd brachytherapy sources (1). Lastly, there has been a change in the dose rate constant for 103Pd 2, 3. These developments mandate a reevaluation of 103Pd brachytherapy prescribing practices.

Section snippets

Methods and materials

During the Annual Meeting of the American Society of Therapeutic Radiology and Oncology (ASTRO) in November 1999, the American Brachytherapy Society (ABS), in cooperation with ASTRO, presented an informational symposium on recent issues relating to the NIST-1999 standard. Guided by the symposium audience comments and concerns, the Clinical Research Committee of the ABS convened a consensus session January 8–9, 2000 of brachytherapists and physicists to develop recommendations regarding future

Results

Since the introduction of 103Pd sources (Theragenics Corp., Norcross, GA) in 1987, the air kerma strength of 103Pd sources has been determined using a NIST traceable 109Cd source. Over the first 10 years, this standard, developed and maintained by the manufacturer, was consistent and stable to within about 2%. When the 109Cd source was changed in 1997, a 9% shift in the standard was noticed. The dose implications of this change were not fully determined until late 1999, when the AAPM developed

Conclusions

Due to the above considerations, the ABS recommends that the following be implemented for 103Pd dosimetry:

  • 1.

    All practicing physicians, physicists, dosimetrists, and suppliers immediately implement NIST-1999 air-kerma strength standard for 103Pd brachytherapy.

  • 2.

    All treatment planning systems and dose calculation algorithms must be updated to reflect new dose rate constants. The AAPM-recommended value for Theraseed model 200 is 0.665 cGy h−1 U−1. The dose rate constant for the Mentor MED3633 seed is

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