MENU

Click here to

×

Are you sure ?

Yes, do it No, cancel

Systematic Evaluations of a Flat-Panel Imager for Intensity-Modulated Proton Therapy (IMPT) Plan Patient-Specific QA

Z Su1*, S Rossomme2, W Hsi3, (1) University of Florida, Jacksonville, FL, (2) IBA Dosimetry (3) University of Florida, Jacksonville, FL,

Presentations

(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.

Download ePoster [PDF]

Keywords

Protons, Intensity Modulation, Quality Assurance

Taxonomy

TH- External Beam- Particle/high LET therapy: Proton therapy – quality assurance

Contact Email