Design and implementation of an anthropomorphic quality assurance phantom for intensity-modulated radiation therapy for the Radiation Therapy Oncology Group

Purpose: To design, construct, and evaluate an anthropomorphic phantom for evaluation of intensity-modulated radiation therapy (IMRT) dose planning and delivery, for protocols developed by the Radiation Therapy Oncology Group (RTOG) and other cooperative groups. Methods and Materials: The phantom was constructed from a plastic head-shaped shell and water-equivalent plastics. Internal structures mimic planning target volumes and an organ at risk. Thermoluminescent dosimeters (TLDs) and radiochromic film were used to measure the absolute dose and the dose distribution, respectively. The reproducibility of the phantom's dosimeters was verified for IMRT treatments, and the phantom was then imaged, planned, and irradiated by 10 RTOG institutions. Results: The TLD results from three identical irradiations showed a percent standard deviation of less than 1.6%, and the film-scanning system was reproducible to within 0.35 mm. Data collected from irradiations at 10 institutions showed that the TLD agreed with institutions' doses to within ±5% standard deviation in the planning target volumes and ±13% standard deviation in the organ at risk. Shifts as large as 8 mm between the treatment plan and delivery were detected with the film. Conclusions: An anthropomorphic phantom using TLD and radiochromic film can verify dose delivery and field placement for IMRT treatments.