ABSTRACT
Brachytherapy dose distribution calculation has evolved from the simple use of charts to the TG-43 formalism. It depends on the physical and geometrical characteristics of each source, the position of the source relatively to the calculation point and on the medium composition. Its principles and limitations are presented as well as the different dosimetric systems associated with implementing rules and the definition of the prescribed dose. The new generation of algorithms and their contributions are discussed.
Subject(s)
Brachytherapy/methods , Radiometry/methods , Radiotherapy Dosage , Algorithms , Health Physics/organization & administration , Health Physics/standards , Humans , Imaging, Three-Dimensional , Monte Carlo Method , Neoplasms/radiotherapy , Radiometry/standards , Radiotherapy Planning, Computer-Assisted , Societies, Scientific/standards , United StatesABSTRACT
PURPOSE: Post-implant CT-based dosimetry is the only method of assessing the quality of permanent prostate brachytherapy. As a consequence of our permanent feedback with the preplanned technique, geometric and dosimetric criteria for optimal seed implantation are proposed and pre and post-implantation dosimetric results are presented. PATIENTS AND METHODS: In 2000 and 2001, one hundred and twenty patients with early stage prostate cancer were treated with transperineal I-125 preplanned brachytherapy (RAPID Strand, Amersham Health). The prescription dose was 145 Gy to the planning target volume. For the pre-planning and post-implant dosimetry the Variseed 6.7 version software was used (Varian Medical Systems). The D90, V100 and V150 values, the position of the dose peak [Dose] peak) and the full width at half maximum (FWHM) on differential dose volume histogram from both planned and post-implant dosimetry were compared for all patients. RESULTS: For preplanned dosimetry, the mean values for D90, V100, V150, [Dose] peak, FWMH were respectively of 199Gy, 100%, 70%, 220Gy, 113Gy. For post-implantation, these values became respectively of 157Gy, 90%, 62%, 220Gy, 194Gy. CONCLUSION: In our practice, differences are noted between preplanned and post-implant dosimetry parameters that should be anticipated to assure optimal definitive result. A working methodology both for performing the preplanned dosimetry and for evaluating the post-implantation dosimetric results is proposed.
