Program Information
Dose Weighted Linear Energy Transfer Analysis of Critical Structures in Proton Therapy of Pediatric Brain Tumor Patients
F. Pirlepesov1*, J. Shin1 , V. P. Moskvin1 , J. Gray1 , Z. Li2 , C. Hua1 , A. Gajjar1 , M. J. Krasin1 , T. E. Merchant1 , J. B. Farr1 , (1) St. Jude Children's Research Hospital, Memphis, TN, (2) University of Florida Proton Therapy Institute, Jacksonville, FL
Presentations
SU-F-BRD-14 (Sunday, July 12, 2015) 4:00 PM - 6:00 PM Room: Ballroom D
Purpose: Dose weighted Linear Energy Transfer (LETd) analysis of critical structures may be useful in understanding the side effects of the proton therapy. The objective is to analyze the differences between LETd and dose distributions in brain tumor patients receiving double scattering proton therapy, to quantify LETd variation in critical organs, and to identify beam arrangements contributing to high LETd in critical organs.
Methods: Monte Carlo simulations of 9 pediatric brain tumor patients were performed. The treatment plans were reconstructed with the TOPAS Monte Carlo code to calculate LETd and dose. The beam data were reconstructed proximal to the aperture of the double scattering nozzle. The dose and LETd to target and critical organs including brain stem, optic chiasm, lens, optic nerve, pituitary gland, and hypothalamus were computed for each beam.
Results: Greater variability in LETd compared to dose was observed in the brainstem for patients with a variety of tumor types including 5 patients with tumors located in the posterior fossa. Approximately 20% - 44% brainstem volume received LETd of 5kev/μm or greater from beams within gantry angles 180°±30° for 5 patients treated with a 3 beam arrangement. Critical organs received higher LETd when located in the vicinity of the beam distal edge.
Conclusion: This study presents a novel strategy in the evaluation of the proton treatment impact on critical organs. While the dose to critical organs is confined below the required limits, the LETd may have significant variation. Critical organs in the vicinity of beam distal edge receive higher LETd and depended on beam arrangement, e.g. in posterior fossa tumor treatment, brainstem receive higher LETd from posterior-anterior beams. This study shows importance of the LETd analysis of the radiation impact on the critical organs in proton therapy and may be used to explain clinical imaging observations after therapy.
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