Comprehensive and Efficient Validation of Beam Modeling for a Proton Therapy System: Practical Considerations.

IntroductionAccurate beam modeling is essential for ensuring safe and effective proton therapy delivery. Before clinical implementation, pencil beam scanning systems require thorough validation to confirm that calculated dose distributions reliably reflect measured performance. This work outlines a practical approach to achieving comprehensive and efficient validation.MethodsThe beam model for a pencil beam scanning system was configured in the treatment planning system (TPS). Beam data including integrated depth dose, lateral profiles in air, and absolute outputs for various energies were measured and entered into the TPS following vendor recommendations. Validation tests were performed according to AAPM TG 185 and insights from other proton centers, adapted to our clinical requirements, time constraints, and regulations. The validation incorporated test cases from AAPM TG 350 draft report and included: 1) rectangular field dose distributions in water, 2) PDD measurements, 3) planar dose measurements using the DigiPhant detector with TG 350 test plans and clinical cases, and 4) end-to-end tests in animal tissue. TPS-calculated dose distributions, obtained using either the proton convolution superposition or Acuros Protons algorithms, were compared with corresponding measurements. A peer review from an institute with a similar proton treatment machine validated the machine output and our validation process.ResultsFor rectangular targets with various ranges and modulation widths in water based on TG 185, TG 350 test plans, and clinical plans, ionization chamber and MatriXX PT planar dose measurements agreed with TPS calculations (point dose difference < 3%, planar dose 3%/3 mm > 95%). Range differences for animal tissues were within 3%. Independent peer output measurements agreed with our results within 1%.ConclusionTPS-calculated range and dose were in good agreement with measurements across multiple validation tests. The beam model for both PCS and Acuros PT has been validated and used clinically. Incorporating practical considerations is essential for achieving comprehensive and efficient beam commissioning and validation.