Room: Exhibit Hall
Purpose: The continuous line scanning method which is one of proton scanning methods can deliver the dose fast. The line scanning method has the two types of intensity modulation methods, current modulation method and scanning speed modulation method. The former method depends on performance of the ion sources but the response of ion sources is slow and not stable because of phenomena of plasma in ion sources. However, the latter method can deliver the dose with accurate and stable control as scanning speed is controlled by scanning magnets with beam current fixedIn the scanning speed modulation method, as beam currents are determined in accordance with the minimum weight in a given energy layer, the plans which have large dynamic range between maximum and minimum weight may make it difficult to deliver the dose fast.
Methods: To avoid making scanning speed slow, we tried to introduce sub-layer method. The sub-layer method is achieved by applying the higher beam current anew to the sub-layers generated by dividing an original layer with logarithm scale without changing the original scan weight map. We conducted performance test using test plans with box phantom to confirm the benefit of shortening irradiation time.
Results: The result for a given plan is showed. The original plan had about 96 times dynamic range and the irradiation time was 13.6 sec. This plan was divided to three parts and the dynamic ranges for each sub-layers were 4.58. The sum of irradiation time of three sub-layers was 1.39 sec. This results shows this method made irradiation time about 10 times shorter than the original plan.
Conclusion: The introduction of sub-layer method makes it possible to deliver the same dose distribution ten times faster than conventional scanning speed modulation method with single beam current.
Funding Support, Disclosures, and Conflict of Interest: The all authers are employees of Sumitomo Heavy Industries, Ltd.