Program Information
Internal Neutron Analytical Model for Proton Therapy of Pediatric Patients with Intracranial Tumors
K Gallagher1,2*, P Taddei3 , (1) Oregon Health and Science University, Portland, OR, (2) Oregon State University, Corvallis, OR, (3) American University of Beirut Medical Center, Beirut, (4) The University of Texas MD Anderson Cancer Center, Houston, Texas
Presentations
SU-I-GPD-T-121 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: The purpose of this study was to produce a fast and universal model for estimating within a factor of two the equivalent dose from secondary neutrons originating inside patients’ bodies in proton therapy of pediatric intracranial tumors.
Methods: A double-Gaussian model of neutron equivalent dose (mSv) per therapeutic dose (Gy) as a function of distance from the field edge was analytically fit to the data of a 9-year-old girl for three fields with nominal energies of 160 MeV, 180 MeV, and 160 MeV. Two model-fits were performed--one for lower energy intracranial fields (140-160 MeV) and one for higher energy intracranial fields (>160 MeV). We used results from previously-published Monte Carlo simulations of intracranial proton therapy fields for a 9-year-old girl to train the model and those of a 10-year-old boy to validate the model. As a figure of merit, mean organ equivalent doses were calculated in organs at risk for subsequent malignant neoplasms and compared to those of the previous studies. Doses within the field were disregarded because they are small compared to therapeutic doses.
Results: Root-mean-square deviation values were small, at 0.245 mSv/Gy and 0.247 mSv/Gy for the lower energy and higher energy models, respectively. When applying the model to the 10-year-old boy’s treatment, the model overestimated the equivalent dose of the Monte Carlo simulations by approximately a factor of two for all organs at risk for subsequent malignant neoplasms with the exception of the testes, for which the model underestimated the Monte Carlo result by approximately 2%.
Conclusion: Our findings indicate that a computationally-efficient model can be used with sufficient accuracy to estimate the equivalent dose from secondary neutrons originating inside patients’ bodies in proton therapy of pediatric intracranial tumors. Because this model is independent of treatment facility, it can be applied in any proton therapy environment.
Funding Support, Disclosures, and Conflict of Interest: Funding is in part by the Fogarty International Center award K01TW008409, and the Portland Chapter of the Achievement Rewards for College Scientists. The content is solely the responsibility of the authors, and does not necessarily represent the official views of the sponsors.
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