SU‐E‐T‐357: Development of An Anthropomorphic Head Phantom for the Assessment of Proton Therapy Treatment Procedures

Purpose: Develop an anthropomorphic head phantom for the evaluation of proton therapy treatment procedures from simulation to treatment planning and treatment delivery. Methods: A head phantom was designed and constructed from materials tested specifically with proton beams to match stopping powers and Hounsfield Units of corresponding human anatomy. Separate MR (water‐filled)‐ and CT (polyethylene)‐compatible inserts were designed for imaging (including target delineation) and dosimetry verification. The dosimetry insert contained radiochromic film and TLD dosimeters. The phantom was imaged with MR to outline the target and fused with a CT image for the dose distribution calculation. Passive scattering and spot scanning treatment plans were designed using the Eclipse proton planning system per M.D. Anderson Proton Center's standard brain protocol. The phantom was irradiated according to each treatment plan three separate times. The dose distributions and absolute point doses determined with film and TLD were compared to calculated points, dose profiles and dose distributions, using a gamma analysis with pass criteria of 5%/3mm and 5%/5mm, to determine agreement and reproducibility. Results: The average passive scatter plan pixel pass rates were 91.9% and 97.4% for 5%/3mm and 5%/5mm criteria, respectively. The average lateral shift ‐ mean(standard deviation) ‐ was 2.5mm(1.8mm); the average longitudinal shift was −2mm(1.9mm); the average transverse shift was 1.7mm(2.8mm). The average spot scan plan pass rates were 90.4% and 98.4% for 5%/3mm and 5%/5mm criteria, respectively. The average lateral shift was 2.2mm (1.4mm); the average longitudinal shift was −1.6mm(1.1mm) on the inferior side and 3.1mm(4.3mm) on the superior side; the average transverse shift was −0.9mm(0.4mm). Conclusions: A proton head phantom made of proton suitable plastics was developed that can verify the agreement between treatment plans and measurement that can be used to credential proton therapy facilities for participation in NCI‐funded clinical trials. Work supported by PHS CA010953 and CA081647, awarded by NCI, DHHS and Massachusetts General Hospital Federal Share Funds.