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Methods and Device for Dose Based Proton Radiography

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E Bentefour

E Bentefour1*, D Samuel2, M Testa3, H Lu4, (1) Ion Beam Applications (IBA),3 Chemin du Cyclotron, Louvain la Neuve, Belgium, (2) Universite catholique de Louvain, Louvain-la-neuve, Walloon Brabant, (3) Massachussetts General Hospital, Boston, MA, (4) Massachusetts General Hospital, Boston, MA

SU-E-T-447 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
We report on the development of high spatial resolution, large active area proton radiography device that uses the dose measurement method for WEPL determination for both passive scattering (DS) and Pencil Beam Scanning (PBS).

Methods:
We used on the shelf appropriately CMOS sensor with an active area of 27mm x 22mm and active pixel size of 21.7 μm2. The read out electronics can record images at 2000 fps over 1024 x 1024 pixels. This technology is combined with an on the shelf QA device that uses 900cm2 gadolinium based scintillator and geometric optical system that focus the image on a 45 degree mirror on the above CMOS sensor. When placed behind the patient, the assembled device measures the 2D exit dose distribution. For DS fields, the method utilizes the periodic time dependence of the dose. By measuring the time-dependence of dose at each pixel and comparing it against a library of time-dependence patterns for all depths in water, the radiological path length to the point of measurement can be determined with millimeter accuracy. For PBS fields, the method uses test beam that contains a few scanning layers in depth with properly spaced ranges. Each layer has a known dose profile in water phantom. The ratio between the measured doses from each layer provides the WEPL information through the patient.

Results:
The assembled device achieved high performances as proton radiography device. The WEPL of large objects, up to 900cm2, are imaged, using both passive and active beams, with 0.6mm2 spatial resolutions and mm accuracy. The dose needed to achieve such performance is less than 1cGy for both DS and PBS.

Conclusion:
The assembled device proves to be a versatile proton imager. It has the potential for use as in-room tool for pre-treatment QA for patient WEPL verification.

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