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Dosimetric Evaluation of Conformal Aperture Multiple Beam Proton Therapy Without a Compensator Using Double Scattering MEVION-S250 System

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S Ferguson

S Ferguson*, S Ahmad , O Algan , T Herman , I Ali , Oklahoma Univ. Health Science Ctr., Oklahoma City, OK


SU-I-GPD-T-182 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To evaluate quantitatively dose parameters of proton plans with multiple conformal beams without compensator compared with conventional proton plans with 1-2 beams that used apertures and compensators.

Methods: Conformal plans were calculated with multiple aperture proton beams (5-7 beams) with gantry angle spread out of 20o-40o using Eclipse treatment planning system. These plans did not employ compensators to modulate proton beam intensity and used only range modulations provided by double scattering MEVION S250 proton system. A planning-target-volume (PTV) was used to consider patient setup and dose delivery uncertainties with proton beams. The performances of conformal plans were compared quantitatively with conventional plans based on PTV dose coverage and sparing of critical structures using, dosimetric parameters (Dmin,Dmax,Dmean,D95,D90,D50).

Results: Conformal plans provided superior dose coverage compared to conventional plans where the differences were in the PTV dose coverage. The average Dmin was 3-5% higher, Dmax was 2-3% lower and Dmean was nearly 1-2% higher in conformal plans compared to conventional plans. In addition, conformal plans provided superior skin dose sparing (20% less) and normal tissue sparing (10% less) in the beam path compared to conventional plans. For regular shaped PTVs, such as spheres and rectangles, pre-cut apertures can be used instead of customized patient specific apertures.

Conclusion: This study demonstrated that conformal proton beams without compensator provided superior dose coverage to the PTV; and sparing of normal tissues compared to conventional proton plans. The dose delivery times and accuracy were nearly equal in both approaches. In addition, conformal proton therapy could provide more cost and time effective treatment than conventional therapy which requires manufacturing customized apertures and compensators and changing them during dose delivery. If the MEVION system is equipped with a multi-leaf collimator creating conformal aperture beams then time, effort and cost for proton treatments will be reduced.

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