Retrospective Analysis of Treatment Time Calculation Agreement Between TPS and Manual Method and Source Strength Verification for 13 HDR Ir-192 Sources In Flexitron Brachytherapy Unit: A Single Institute Experience

Abstract

Introduction: Source strength measurement and verification during every source exchange in high dose rate (HDR) Brachytherapy 192Ir is primary part of quality assurance program as recommended by national regulatory body Atomic Energy Regulatory Board, Mumbai, India. The purpose of this study was to evaluate RAKR (in-house measurement) of 192Ir using re-entrant well-type ionization chamber with stated RAKR values as provided by the manufacturer in source certificate and to check the accuracy of the Oncentra treatment planning system calculation with manual method of computation at different intervals for 13 HDR Ir-192 sources. Materials And Methods: We have retrospectively evaluate the in-house measured RAKR with the calibrated Standard Imaging HDR 1000 PLUS Well chamber /electrometer CDX 2000B for 13 HDR Ir192 sources with stated RAKR and the treatment time calculation accuracy of Oncentra TPS verified by manual method of computation using TG-43 formalism. Results: The study shows, that the measured RAKR and stated RAKR were well within the tolerance limits set by the national and international recommendations i.e. ±3 % for 13 HDR Ir192 sources. The verification of TPS treatment time calculation with manual calculation for single source as well as for multi-source lies within ±2%. Conclusions: There is good agreement between in-house measured and vendor quoted values of RAKR which shows that the chamber has been stable to better than ±3 % and manual calculations shows agreement with the TPS outcome within ±2% for 13 HDR Ir192 sources. The manual method of computation works reliably and reassures the TPS functioning.