Efficient Pencil Beam Scanning Proton Treatment for Cranial-Spinal Irradiation
M Zhu1*, A Stanforth2, W LePain2, M Pasha2, K Langen1, (1) Emory University School of Medicine, Emory Proton Therapy Center, Atlanta, GA, (2) Emory Healthcare, Atlanta, GA,
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Purpose: Pencil beam scanning (PBS) proton treatment delivery time is proportional to target size and can take several minutes for each field in cranial-spinal irradiation (CSI). This work investigates the possibility of improving beam delivery efficiency by increasing the minimum spot MU (MUmin) and energy layer spacing (ELS) during plan optimization without compromising plan quality.
Methods: Clinical plans for a pediatric and an adult CSI patient are included, where the MUmin is 1MU and ELS is 0.7. Two more plans were created for each patient; the MUmin was set to 3MU in both plans, while in the second plan, the ELS were set to 1.0 for the brain fields. All plans were optimized with the same objective functions used in the clinic plans. The 6 plans were subsequently delivered on a clinical proton PBS system; the beam-on time was recorded and compared.
Results: There is no visually detectible differences among the 3 plans for each patient and nearly identical CTV coverage and OAR sparing were achieved. The delivery time for clinical plans ranges from 2.79-5.14 minutes per beam. Increasing MUmin to 3MU reduced the beam-on time by 2.13±0.36 minutes (52.6±3.1%); while setting ELS to 1.0 saved additional 0.26±0.05 minutes (5.6±0.6%).
Conclusion: Increasing the MUmin reduces the beam delivery time without compromising plan quality and decreasing number of energy layers further improves treatment delivery efficiency, both decrease the waiting time for multi-room proton treatment facility and increase overall patient throughput.
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