Quality assurance of treatment plans for interstitial and intracavitary high-dose-rate brachytherapy

Purpose Quality assurance for complex high-dose-rate (HDR) treatment planning has always been a challenge to the physics community because of the time constraint between HDR planning and the delivery of the treatment. This study proposes an efficient, precise, and easy method for checking the complex computer calculation. Methods and materials Posttreatment, three-dimensional dose–volume study was performed for 98 patients with 128 new treatment plans along with 30 library plans. Volumes covered by the 100% isodose line, source activity (Ci), total dwell time (s), and the prescription dose (100%) were recorded. Variation of RV defined as (irradiated time × activity/elongation factor × prescribed dose) with volume was studied for different catheter systems. Results Parametric fit of RV with volume for three different systems that cover most of the interstitial and intracavitary brachytherapy implants agrees within ±6%. Conclusions The excellent agreement of RV derived from this simplistic point source model with three-dimensional dose calculations for individual HDR treatment plans clearly establishes that for an implant with known number of catheters, the time needed to deliver a prescribed dose to a given prescription volume can be easily predicted.