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Analysis of Recurrences in Lung Patients Treated with Protons

D Mirkovic

D Mirkovic*, P Yang, Z Belal, U Titt, CR Peeler, Z Liao, R Mohan, M.D. Anderson Cancer Center, Houston, TX


SU-I-GPD-T-97 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To assess the impact of approximations in analytical dose calculation method used in a clinical treatment planning system (TPS) on local control in lung patients treated with passively scattered proton therapy (PSPT).

Methods: We analyzed 13 patients with local failure from the proton arm of a prospective randomized trial comparing IMRT and PSPT. Dose distributions planned with TPS were compared with dose distributions computed with the corresponding data computed with a Monte Carlo method. The location of the local recurrence was determined for all patients using post treatment imaging and the contours of the recurrence region were registered to the planning CT. For both MC and TPS dose distributions, dosimetric indices based on a dose-volume histogram analysis were collected for the target and the recurrence volume for each local recurrence.

Results: We found that TPS consistently overestimated the mean target dose on average by 3%. The dose in the recurrence volume was also overestimated by TPS on average by 4% for all patients in the cohort.

Conclusion: Our results indicate that analytical dose calculation algorithms used in current treatment planning systems underestimate the scattering in the heterogeneous thorax geometry, which may lead to underdosage of the target by as much as 6%. This can be mitigated by using Monte Carlo dose calculation methods.

Funding Support, Disclosures, and Conflict of Interest: Supported by Cancer Prevention and Research Institute of Texas Research Award RP160232.

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