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Radiation Therapy with Very High-Energy Electron (VHEE) Beams in the Presence of Metal Implants

C Jensen

C Jensen1*, B Palma1, B Qu1, P Maxim1, B Hardemark 2, E Hynning 2, B Loo1, M Bazalova1, (1)Department of Radiation Oncology, Stanford University, Stanford, CA, (2) RaySearch Laboratories, Stockholm, Sweden


SU-E-T-274 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To evaluate the effect of metal implants on treatment plans for radiation therapy with very high-energy electron (VHEE) beams.

Methods: The DOSXYZnrc/BEAMnrc Monte Carlo (MC) codes were used to simulate 50-150MeV VHEE beam dose deposition and its effects on steel and titanium (Ti) heterogeneities in a water phantom. Heterogeneities of thicknesses ranging from 0.5cm to 2cm were placed at 10cm depth. MC was also used to calculate electron and photon spectra generated by the VHEE beams’ interaction with metal heterogeneities. The original VMAT patient dose calculation was planned in Eclipse. Patient dose calculations with MC-generated beamlets were planned using a Matlab GUI and research version of RayStation. VHEE MC treatment planning was performed on water-only geometry and water with segmented prostheses (steel and Ti) geometries with 100MeV and 150MeV beams.

Results: 100MeV PDD 5cm behind steel/Ti heterogeneity was 51% less than in the water-only phantom. For some cases, dose enhancement lateral to the borders of the phantom increased the dose by up to 22% in steel and 18% in Ti heterogeneities. The dose immediately behind steel heterogeneity decreased by an average of 6%, although for 150MeV, the steel heterogeneity created a 23% increase in dose directly behind it. The average dose immediately behind Ti heterogeneities increased 10%. The prostate VHEE plans resulted in mean dose decrease to the bowel (20%), bladder (7%), and the urethra (5%) compared to the 15MV VMAT plan. The average dose to the body with prosthetic implants was 5% higher than to the body without implants.

Conclusion: Based on MC simulations, metallic implants introduce dose perturbations
to VHEE beams from lateral scatter and backscatter. However, when
performing clinical planning on a prostate case, the use of multiple
beams and inverse planning still produces VHEE plans that are
dosimetrically superior to photon VMAT plans.

Funding Support, Disclosures, and Conflict of Interest: BW Loo and P Maxim received research support from RaySearch laboratories. B Hardemark and E Hynning are employees of RaySearch.

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