MO-F-213AB-01: Improving Dose Uniformity in Patch-Field Proton Therapy Using Beam Current Modulation

Medical Physics
Patrick M HillCharles D Bloch

Abstract

To improve the dose homogeneity in patch-field proton therapy using beam current modulation. MCNPX simulations were performed for various configurations of the Mevion S250 beamline. Spread-out Bragg peak (SOBP) dose distributions were calculated, and lateral and distal dose profiles were extracted for through- and patch-field targets at depths ranging from 5.0 to 27.5 cm. We define 'dose non-uniformity' (DNU) as the difference between the maximum and minimum dose relative to the prescription observed in a patched dose distribution. DNU was first calculated for dose distributions combining through-field lateral dose profiles and with patch-field distal dose profiles, assuming a 'standard' delivery with constant beam current. Distal dose profiles were then optimized using beam current modulation to better complement the lateral dose profiles when combined into a patched dose distribution. The DNU for optimized dose distributions was then calculated and compared to the DNU found for standard delivery. Using standard deliveries, DNU was 10% or less when patching lateral profiles 12.5-17.5 cm deep. Significantly greater DNU was observed for patches outside of this range, sometimes exceeding 35%. Using optimized distal profiles, DNU ...Continue Reading

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