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Measurements of LET, Nuclear Halo, Energy and Angular Spectra of a Proton Spot Scanning Beam with a Hybrid Semiconductor Detector

S Charyyev1*, C Chang2, A Stanforth3,4, J Harms5, C Oancea6, L Lin7, (1) Emory University, Atlanta, GA, (2) Emory University, Atlanta, GA, (3) Emory University, Atlanta, GA, (4) Georgia Institute of Technology, Atlanta, GA, (5) Emory University, Atlanta, GA, (6) ADVACAM, Prague, CZ, (7) Emory Proton Therapy Center, Atlanta, GA


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

Room: AAPM ePoster Library

Purpose: There are numerous models of LET, nuclear halos, energy and angular spectra of proton spot scanning beams, but little data for these quantities has been measured due to inherent difficulty in the measurements. Therefore, we introduce an approach to measure these quantities with hybrid semiconductor pixel detector, AdvaPix-TPX3 (TPX).

Methods: A single proton pencil beam (PB) of 100 MeV is incident on a 256x256 square pixelized silicon detector with pitch of 55 µm. Data is taken in list mode where, for each proton, position, energy, time of arrival and track shape are measured. Other spectroscopic and directional information (i.e. LET, elevation angle, type) are extracted from detailed pattern analysis of the particle tracks. To avoid saturation of the detector and overlap of the proton tracks, 2 mm diameter aperture was used to further collimate the PB. Moreover, the detector was placed at 60 degrees to the incident beam for greater sampling of the proton range. In-water (at depths 0, 5, 7 and 7.5 cm) spot size, halo, LET spectrum and large angle scatter were measured to demonstrate potential clinical use of the proposed technique.

Results: All results from measurements are compared to simulated data using TOPAS. Spot size and halo, measured as 0.1% maximum signal, of the collimated PB varied from 0.73-1.75 mm and 6.87-13.58 mm for depths 0 and 7.5 cm, respectively. There was a discrepancy, up to 3.5%, in spot size and halo measurements between TPX and TOPAS. Measured LET varied as 1.4-6.2 keV/µm for 0 and 7.5 cm depths respectively. Specific pattern of the angular spectrum as a function of radius from spot center was not observed, prompting further investigation.

Conclusion: We introduced a novel detector and technique to measure beam parameters, allowing for increased confidence in beam modeling for treatment planning systems.

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LET, Energy Spectrum, Semiconductor Detectors


TH- External Beam- Particle/high LET therapy: Proton therapy – out of field dosimetry/risk analysis

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