Reducing Beam Delivery Time for Proton PBS Treatment with Breath-Hold Motion Management Technique
M Zhu*, A Stanforth, Z Diamond, Y Lin, K Langen, Emory University School of Medicine, Atlanta, GA
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PO-GePV-T-111 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: Breath-hold is an effective motion mitigation strategy to reduce tumor motion interplay effect with active scanning pencil beam proton therapy. This work explores the possibility of reducing beam delivery time by decreasing the number of energy layers or proton spots.
Methods: Ten plans were re-created in a commercial TPS for 5 esophageal and liver cancer patients, with the same parameters as the clinical plans (Plan_C), except for the energy layer spacing (ELS) or the spot spacing (SS). In Plan_C, ELS and SS were usually set to values smaller than the system default. For each Plan_C, a Plan_ELS was optimized with the energy layer spacing changed to the default, i.e., fewer number of energy layers, while keeping all other parameters unchanged. Similarly, a Plan_SS with setting the spot spacing to default. All 15 plans were delivered on a clinical PBS proton machine and the beam delivery time was recorded for each field.
Results: Compared with the Plan_C, both Plan_ELS and Plan_SS achieved the same target dose. The Plan_ELS also had near identical OAR doses, while Plan_SS had slightly higher doses to selected OARs. Recorded beam delivery times were 55.5±11.9 s, 43.6±9.0 s, and 53.7±10.7 s for Plan_C, Plan_ELS, and Plan_SS, respectively. Number of energy layers were reduced by 34.9±4.4% in Plan_ELS; as a result, the beam delivery times were 21.4±4.0%, or 12.0±3.7 s, less than Plan_C. The Plan_SS had 26.5±4.8% fewer number of spots, while the delivery times were reduced by 2.9±2.6% (1.8±1.7 s) compared to Plan_C.
Conclusion: Although the spot spacing setting only had a marginal improvement on beam delivery time; using less energy layers can significantly reduce the beam delivery time without compromising plan quality. Future investigation will focus on achieving the optimal trade-off between plan quality and beam delivery time.
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