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An Auxiliary Minibeam Collimator for Preclinical Proton Radiotherapy

D Miles

D Miles1*, K Stantz1, V Moskvin2, J Farr2, (1) Purdue University, West Lafayette, IN, (2) St. Jude Children's Hospital, Memphis, TN


TU-H-CAMPUS-TT-1 (Tuesday, August 1, 2017) 4:30 PM - 5:30 PM Room: Therapy ePoster Theater

Purpose: In-vivo preclinical study is a necessity to advance our understanding of linear energy transfer (LET) and relative biological effectiveness (RBE)-variability in proton radiotherapy. However, typical clinical systems are unable to produce small field sizes at small depths required for high-precision small-animal studies. This work presents the design for an auxiliary proton minibeam collimator suitable for delivering preclinically-relevant radiation fields from a clinical proton beam radiotherapy system.

Methods: Monte-Carlo simulations were performed in FLUKA general purpose transport code using PRECISIO default parameters. The simulation geometry consists of a mono-energetic 5mm FWHM proton beam incident on a 3.4cm-thick PMMA range shifter, a 10cm-thick brass collimator, and a water phantom. Initial beam energies were varied between 70 – 85 MeV, and aperture diameters were varied from 250um – 2mm. Total dose, dose-averaged LET, and secondary photon and neutron energy fluences were scored in the target, and bio-effective dose was calculated using the MCDS model assuming aerobic conditions.

Results: At the tested energies, our collimator can deliver proton dose at ranges from 1 – 18 mm in water, with a lateral FWHM of roughly 1 mm for a 500um-diameter aperture. The MCDS model estimates an RBE of 1.4 at the Bragg peak across all simulations. The ratio of peak-to-entrance doses varies from 1.4 to 2.1, increasing with decreasing incident proton energy and increasing aperture diameter. Secondary neutrons and photons produced during nuclear interactions in the collimator contributed less than 0.6% of the physical Bragg peak dose for simulations with aperture diameter greater than 250um.

Conclusion: Our collimator can successfully shape therapeutic proton fields to field sizes and treatment depths suitable for preclinical small animal studies. Upon commissioning, this collimation system will be paired with robust immobilization tools and image-guidance techniques, and applied to preclinical dose and LET-painting radiation studies in mice.

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