The first existing model has proven to be a successful predictor of output for our compact double-scattering proton therapy system. The new model performed comparably to the first model and showed better performance in some options due to a great degree of flexibility of a polynomial fit. Both models performed well using r. Either model with r thus can serve well as an output prediction calculator.

The purpose of this study was to investigate comparability of three output prediction models for a compact double‐scattered proton therapy system. Two published output prediction models are commissioned for our Mevion S250 proton therapy system. Model A is a correction‐based model (Sahoo et al., Med Phys, 2008;35(11):5088–5097) and model B is an analytical model which employs a function of r = (R’‐M’)/M’ (Kooy et al., Phys Med Biol, 2005;50:5487–5456) where R’ is defined as depth of distal 100% dose with straggling and M’ is the width between distal 100% dose and proximal 100% dose with straggling instead of the theoretical definition due to more accurate output prediction. The r is converted to ((R‐0.31)‐0.81 × M)/(0.81 × M) with the vendor definition of R (distal 90% dose) and M (distal 90% dose‐to‐proximal 95% dose), where R’ = R‐0.31 (g cm−2) and M’ = 0.81 × M (g cm−2). In addition, a quartic polynomial fit model (model C) mathematically converted from model B is studied. The outputs of 272 sets of R and M covering the 24 double scattering options are measured. Each model's predicted output is compared to the measured output. For the total dataset, the percent difference between predicted (P) and measured (M) outputs ((P‐M)/M × 100%) were within ±3% using the three different models. The average differences (±standard deviation) were −0.13 ± 0.94%, −0.13 ± 1.20%, and −0.22 ± 1.11% for models A, B, and C, respectively. The p‐values of the t‐test were 0.912 (model A vs. B), 0.061 (model A vs. C), and 0.136 (model B vs. C). For all the options, all three models have clinically acceptable predictions. The differences between models A, B, and C are statistically insignificant; however, model A generally has the potential to more accurately predict the output if a larger dataset for commissioning is used. It is concluded that the models can be comparably used for the compact proton therapy system.

Aim: The purpose of this study is to investigate the feasibility of proton arc therapy (PAT) using the double-scattering MEVION-S250 proton system. The treatment planning and dose delivery parameters from PAT were compared with conventional treatment planning techniques. Materials and methods: PAT was simulated with multiple conformal and fixed-aperture beams (5–15) using the MEVION-S250-double-scattering proton system. Conformal apertures were simulated with the Eclipse-treatment-planning system: (a) using a static single aperture that provides the best average conformal circular or rectangular apertures to cover the tumour from different angular views (SPAT), and (b) dynamic conformal apertures of the tumour shape at each irradiation angle that can be obtained from a multi-leaf-collimator system (DPAT). Results: The DPAT and SPAT plans provided superior dose coverage and sparing of normal tissues in comparison with conventional plans (CPT). The entrance normal tissue and skin doses (<40%) were lowered significantly by delivering dose from different directions over a wider angular view compared to conventional plans that have large entrance dose from only two fields. While the mean and minimum doses from PAT and CPT were comparable, the maximum doses from arc plans were lower than the maximum doses in conventional plans. The SPAT and DPAT plans had comparable dose parameters for regularly shaped targets. The heterogeneity index (HI) was superior in PAT plans which improved with increasing number of beams in arc plans for the different treatment sites. The conformality index (CI) depends on the treatment site and complexity of the shape of the planning target volume where for brain, pancreatic and lung tumours, PAT plans conformality was comparable and sometimes superior to CPT; and HI and CI were generally better in DPAT compared to SPAT. Conclusions: PAT plans have superior dose coverage and sparing of normal tissues compared to CPT plans using the MEVION double-scattering system as shown in this simulation study. Ideally, conformal proton arcs require beam shaping and dose delivery with the gantry moving; however, the MEVION double-scattering system lacks a multi-leaf collimator system and cannot deliver dose during gantry rotation. The single aperture conformal proton therapy technique is more time and cost effective compared with conventional techniques that are used currently with the MEVION proton therapy system because of the elimination of the need for patient-specific compensators. In present study, PAT was simulated with the MEVION double-scattering proton therapy system; however, it can be performed also with other proton therapy systems.

Purpose: To report the detailed commissioning experience for a compact double‐scattering Mevion S250 proton therapy system at a University Cancer Center site. Methods: The commissioning of the proton therapy system mainly consisted of ensuring integrity of mechanical and imaging system, beam data collection, and commissioning of a treatment planning system (TPS). First, mechanical alignment and imaging were tested including safety, interlocks, positional accuracy of couch and gantry, image quality, mechanical and imaging isocenter and so on. Second, extensive beam data (outputs, PDDs, and profiles) were collected and analyzed through effective sampling of range (R) and modulation width (M) from 24 beam options. Three different output (cGy/MU) prediction models were also commissioned as primary and secondary MU calculation tool. Third, the Varian Eclipse TPS was commissioned through five sets of data collections (in‐water Bragg peak scans, in‐air longitudinal fluence scans, in‐air lateral profiles, in‐air half‐beam profiles, and an HU‐to‐stopping‐power conversion curve) and accuracy of TPS calculation was tested using in‐water scans and dose measurements with a 2D array detector with block and range compensator. Finally, an anthropomorphic phantom was scanned and heterogeneity effects were tested by inserting radiochromic films in the phantom and PET activation scans for range verification in conjunction with end‐to‐end test. Results: Beam characteristics agreed well with the vendor specifications; however, minor mismatches in R and M were found in some measurements during the beam data collection. These were reflected into the TPS commissioning such that the TPS could accurately predict the R and M within tolerance levels. The output models had a good agreement with measured outputs (<3% error). The end‐to‐end test using the film and PET showed reasonably the TPS predicted dose, R and M in heterogeneous medium. Conclusion: The proton therapy system was successfully commissioned and was released for clinical use.

etiology of the disease. We observed statistically significant differences in survival between groups of patients with different expression of MCM7 and p16 in tumor cells (Table 1). Conclusion: The survival of patients with potential HPV viral etiology of the disease, characterized by high expression of the proteins p16 (IRS!8) and MCM7 (IRS!4), was worse than in the group of patients with low expression MCM7. It was also significantly better than among those with low percentage of p16 and high expression MCM7.