Implementation of Pretreatment Patient – Specific Quality Assurance for Intensity Modulated Radiotherapy

Abstract

Clinical implementation of Intensity Modulated Radiotherapy (IMRT) has begun in Ghana, despite this advancement, to date, there has been no implementation of patient-specific IMRT verification Quality Assurance (QA) in Ghana. If this is not addressed, the degree of accuracy and dose conformity in our IMRT plans may not be realized clinically. The main objective of this study was to verify the actual dose that would be delivered to the patient during an IMRT treatment at the National Centre for Radiotherapy and Nuclear Medicine (NCRNM), based on implementation of patient – specific Quality Assurance for IMRT prior to external beam radiation treatment using Gamma Index method. Ten (10) IMRT plans were generated for a phantom study using 3, 5, 7 or 8 fields IMRT, based on clinical objectives for the treatment of 10 patients with varying prostate and head and neck cancers. The procedure involved linear accelerator commissioning, absolute dose determination, calibration of patient – specific QA device, IMRT treatment planning, plan verification for IMRT, treatment delivery and data analysis using the gamma index (3%/3 mm, threshold 5%) criteria with 95% passing rate. All prostate IMRT cases enrolled in the study passed the acceptance criteria, with values that ranged from 95.50 to 98.43%.The mean passing rate, based on the gamma index method (γ≤1) for treatment of each of the cases using the MatriXX was 96.82±1.22%, showing good compliance with the prescribed rates for all 5 cases.The mean value for the pass rate of the head - and - neck IMRT cases was 96.42±1.14% with one case failing the acceptance criteria of the gamma evaluation method, and the passing values ranged from 94.60 to 97.70%.

The reference doses calculated at TPS were accurately delivered by the medical linear accelerator, and the gamma criteria for acceptance were mostly satisfied by the selected cases throughout the research for both cancer sites under study. The measurements and the results demonstrated that the delivery equipment, the treatment planning system, the QA tools and their corresponding software were accurate and therefore acceptable for IMRT implementation at the centre. The analysis made demonstrated that these IMRT results were consistent with peer reviewed baseline data for a well-commissioned IMRT program.