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Beam Characteristics of the First Clinical 360-Rotational Compact Scanning Pencil Beam Proton Treatment System and Differences From a Multi-Room System

C Shang1*, G Evans1, M Rahman1, L Lin2, (1) South Florida Proton Therapy Institute, Delray Beach, FL, (2) Emory Proton Therapy Center, Atlanta, GA

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
To present the proton beam characteristics of the first clinical, newly designed single-room ProBeam Compact™ proton therapy system (SRPT) and comparison against multi-room ProBeam™ system (MRPT).

Methods:
A newly designed ProBeam Compact™ with protons ranging from 70MeV to 220MeV was commissioned in late 2019. IDDs were scanned using 81.6 mm PTW Bragg peak chambers normalized by output factors at 15 mm WET and 1.1 RBE offset. The beam spot profiles were acquired using a planar scintillation device and were fitted by single Gaussian distribution for modeling Eclipse v15.6 treatment planning system. A pin-point ionization chamber measured field size correction factors at near surface. The dosimetric characteristics were compared against a recent beam data from MRPT. Independent end-to-end checks were performed by IROC via an output phantom and pelvic phantom.

Results:
In comparison, a marginally increased proton straggling in the Bragg peak region was found in high-energy proton beams of SRPT, accompanied by slightly elevated proximal transmission beam values. IDDs of SRPT showed 0.182 to 0.450 MeV broader Bragg peak (Rb80 - Ra80) from 140 MeV beams, peaked at 180 MeV with 0.65-0.79 mm extended distal falloffs (Rb20?80). The spot divergences are between 7.62 and 1.23 mrad, as seen in MRPT. No differences in beam spot sizes, proton particles/MU, and field size correction factors were identified. Dosimetry checks through IROC reported high passing scores of 1.00 and 1.04 or 96% respectively, the similar seen in 108 patient specific QA measurements for fields with or without range shifters.

Conclusion:
The comparison results demonstrate comparable proton beam characteristics from this first clinical ProBeam Compact™ with slightly increased proton straggling in higher energies, indicated by minimally widened Bragg peak and distal falloffs. None-compromised accuracy of its dose delivery was suggested per independent end-to-end tests and patient's specific beam QA's.

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Keywords

Protons, Commissioning, Pencil Beam Algorithms

Taxonomy

TH- External Beam- Particle/high LET therapy: Proton therapy – Development (new technology and techniques)

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