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Session: Quality and Safety in Radiotherapy II [Return to Session]

Film-Less Quality Assurance (QA) of a Robotic-Arm Linac Using a Scintillation-Based Imaging System

M Ashraf1*, L Skinner2, X Gu3, L Xing4, L Wang5, (1) Stanford University, Palo Alto, CA, (2) Stanford University, Stanford, CA, (3) Stanford University, Dallas, TX, (4) Stanford University School of Medicine, Stanford, CA, (5) Stanford University, Stanford, CA


SU-F-BRA-3 (Sunday, 7/10/2022) 2:00 PM - 3:00 PM [Eastern Time (GMT-4)]

Ballroom A

Purpose: To develop and characterize a low-cost, rapid scintillator-based imaging system for quality assurance (QA) of a robotic arm linear accelerator, which would replace reliance on film dosimetry.

Methods: A scintillating sheet was used to capture surface profiles using a low-cost CMOS camera. A light-tight enclosure was 3D printed to block ambient light. The camera, equipped with a 12mm lens, was angled at 45 degrees with a direct line of sight of the scintillating sheet. A perspective image transformation with optical distortion correction was then employed to obtain a beam’s eye view image. Beams with fixed cones, Iris, and multileaf collimation (MLC) were imaged and compared to gafchromic film. A garden fence and a diamond-shaped pattern constructed using the MLCs were also imaged to assess the ability to resolve individual leaves.

Results: The limiting resolution of the optical system defined as the full-width half maximum of the line spread function, was measured to be ~ 0.3 mm. Field size, as measured by the camera-based system for fixed cone and Iris apertures, was within 0.1 mm of the values measured using film. Individual MLC leaves were successfully resolved and the average difference between expected leaf position compared to the optically measured position was 0.13 mm. Using a 2%/1mm gamma criteria, a 100 % passing rate was seen for relative central axis beam profiles for 10 mm and 5 mm Iris collimated beams. Low-energy scatter at the surface led to the optical response being higher outside the projected radiation field when compared to film data, but the effect was minimal for small fields (<10 mm).

Conclusion: The optical system presented here is a promising low-cost alternative to film and electronic portal-based imaging devices and will obviate the need for cumbersome and time consuming read-out procedure associated with film dosimetry.


Quality Assurance, Optical Dosimetry, Small Fields


TH- Radiation Dose Measurement Devices: scintillators

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