Exhibit Hall | Forum 3
Purpose: To demonstrate the clinical benefit from using a mini ridge filter (MRF) to reduce treatment time for deep inspiration breath hold (DIBH) patients and patients with large target volumes and superficial disease in cyclotron-based pencil beam scanning (PBS) proton therapy.
Methods: An MRF beam model was generated by simulating the effect of an MRF on our clinical beam data using an analytical algorithm, assuming a fixed snout position relative to isocenter. The beam model was validated with a series of comparisons between the simulated beam data and measurement. The model was used to generate several treatment plans in a water phantom and on patient image sets to further study the effect of the MRF and for comparison with physician-approved plans. Beam-on times were measured to demonstrate the reduction achievable with the MRF.
Results: Validation measurements show that the analytical algorithm accurately simulates the effect of the MRF on the Bragg peak range, width (FWHM), distal fall-off and spot size as a function of beam energy. The increase in FWHM ranged from 3.1 mm at 226 MeV to 6.2 mm at 70 MeV. The average and maximum reduction in beam-on time observed per field was 35.2 s (40%) and 79.7 s (55%). Treatment plans generated with the MRF beam model are dosimetrically comparable to the corresponding clinical treatment plans with significantly reduced beam-on times.
Conclusion: MRFs can be used to reduce treatment time in cyclotron-based PBS proton therapy without sacrificing plan quality. This is particularly beneficial for patients with large targets and superficial disease such as in breast cancer where treatment times are generally long. Lower treatment time leads to more accurate dose delivery by minimizing uncertainty due to intra-fraction motion. In addition lower treatment time can make DIBH treatment tolerable to more patients.