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A Comparison of Single-Field Vs Multi-Field Delivery Uncertainty in Proton Therapy

K Grantham

K Grantham1*, E Klein2, (1)University of Missouri, Columbia, MO (2) Washington University, Saint Louis, MO

SU-E-T-444 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To evaluate of the impact of uncertainty on proton plan delivery when one field per fraction treatment regimes (SFPF) are used rather than delivering all planned fields for every fraction (MFPF).

Methods: A nominal proton treatment plan (NP) was created in Eclipse (Varian) to treat a spherical target to 54Gy using parallel-opposed fields. The fields created in the NP were applied to geometries with uncertainties introduced. Uncertainty was simulated for four scenarios: a 1cm shift in one of the fields for 10 of 30 fractions, a 5° rotation of the patient for 10 of 30 fractions, and unilateral introduction of 3cm of bone or air for 10 of 30 fractions. The full treatment was calculated using summed plans for the SFPF case is delivered and the MFPF case. The results of the SFPF and MFPF plan sums were compared to each other and the NP by calculating Dmax/min/mean along with V90,95,98,99,100%. Dmax/min/mean were also compared for an OAR placed contralateral to the introduced uncertainty.

Results: The cases for 5° rotations introduced, showed no significant difference from the NP. In all other cases, the introduced uncertainty degraded the treatment delivery with the most significant difference in the target Dmin. The SFPF treatments consistently showed a decrease in Dmin compared to the MFPF treatment. For the introduction of air and bone the SFPF treatments exhibit increases of 1.5% and 20% respectively. With bone introduced, V95 and V90 suffered an additional 3% and 4% for SFPF treatments. With air introduced, dose to the Dmax, Dmin, and Dmean were increased by 14, 16, and 20% respectively for SFPF treatments.

Conclusion: Tumor response and minimum target dose can be correlated. In the presence of uncertainty, SFPF treatment regimes may result in a decreased tumor response and increased OAR dose.

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