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A Novel Intra-Beam Range Verification and Delivery Optimization for Particle Radiotherapy

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Y Zhong

Y Zhong*, W Lu , M Chen , Y Shao , UT Southwestern Medical Center, Dallas, Texas


MO-L-GePD-J(A)-4 (Monday, July 31, 2017) 1:15 PM - 1:45 PM Room: Joint Imaging-Therapy ePoster Lounge - A

Purpose: To develop a novel PET image based method to improve the accuracy of beam range verification and therapy targeting in particle radiotherapy.

Methods: A portion of therapy beams is selected from the original treatment plan to provide sufficiently high counts for PET imaging and accurate beam range verification. The selected beams target the middle region of the tumor to avoid beam overshooting, and the mid-tumor beam range measurements from PET images are used to verify the treatment plan and to enable adaptive modification of the remaining beam deliveries. Simulations were conducted on a digital human brain phantom based on CT images with a 5 cm diameter tumor inserted near the center. The phantom was irradiated with 104 MeV scanning proton beams (5x10⁹ protons, ~0.4 Gy). PET images (2mm resolution) with 43 cm trans-axial and 6.4 cm axial field-of-view was acquired for ~120 sec. An extra air or bone sphere of 2.5 cm diameter was inserted in front of the tumor to alter the beam range.

Results: PET based beam range measurement was accurate with error of 0.4 mm (MEAN) and 1.6 mm (Standard Deviation). The difference between the delivered and planned doses (~10 Gy) were evaluated. For cases without and with adaptive delivery, the Gamma-index (between plan and delivery) pass rates were 75.8%, 82.6% and 93.9%, 98.7% respectively with the Gamma-index criteria of 3% and 3mm for only target and organ-at-risk voxels.

Conclusion: The proposed new method significantly improves the beam range verification accuracy for adaptive beam delivery without compromising the dose distribution. This should lead to solving relevant fundamental technical problems and providing a practical solution to improve the targeting accuracy and therapy efficacy.

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