(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose:
To evaluate a commercial flat-panel imager fundamental property of proton signal responses, spatial accuracy and quenching effect and its application in IMPT plan patient-specific QA.
Methods:
The flat-panel signal linearity of 100, 150 and 200MeV proton were obtained for 6 gains settings (0.25, 0.5, 1, 2, 4, 8pF). The flat-panel spatial response was measured by irradiation of 100MeV proton 10x10cm2 beam through 6.3cm solid water then a high-precision perforated aluminum plate with holes in 1cm spacing. The flat-panel measured distances between the centers of adjacent spots were compared to the plate mechanical specifications. PDDs of 100, 150 and 200MeV protons were measured by the flat-panel with different thickness solid water slabs and compared to ones in water. The flat-panel quenching effect was quantified using peak-to-plateau ratios of PDD. A prostate PBS plan was measured at 0, 2, 5, 10 and 15cm depths in solid water using the flat-panel. The obtained images were converted to planar doses through counts-to-dose calibration and compared to corresponding planar doses from the treatment plan using gamma tests with different criteria.
Results:
The signal responses were linear in all gain settings. Sixteen of 18 linear fits had coefficient-of-determination greater than 0.9998 and the minimum was 0.999. The flat-panel measured inter-hole distances agreed with the plate specification to 0.1mm. The distal R80 of measured PDDs were within 1mm of those measured in water. However, lower peak-to-plateau ratios (under-response at pristine peak region) of the measured PDD indicated quenching effect of the flat-panel. The gamma test pass rates of prostate IMPT plan at the 5 depths were from 96.6% to 100% (3mm, 3%).
Conclusion:
The flat-panel signal response was linear and spatial response was accurate. The detector had quenching effect at pristine peak region of PDD. The IMPT plan patient-specific QAs are acceptable at the measured depths.
Keywords
Protons, Intensity Modulation, Quality Assurance
Taxonomy
TH- External Beam- Particle/high LET therapy: Proton therapy – quality assurance
Contact Email
