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Derivation of Energy-Resolved Dose Functions Using a Flat-Panel Detector for a PBS System

C Finley1*, K Jee1 , T Zwart2 , G Sharp1 , W Huo1 , M Jones2 , K Huang2 , D Catanzano2 , J Cooley2 , S Rosenthal2 , H Lu1 , (1) Massachusetts General Hospital, Boston, MA, (2) Mevion Medical Systems, Inc., Littleton, MA


(Monday, 7/30/2018) 3:45 PM - 4:15 PM

Room: Exhibit Hall | Forum 9

Purpose: Imaging patients with protons would help to improve treatments for patients undergoing proton therapy by reducing the range uncertainties created during the conversion from Hounsfield Units (HU), acquired during patient CT, to relative stopping power (RSP), which is required for treatment planning. This study uses a unique pencil beam scanning (PBS) system from a proton therapy equipment vendor to generate proton images by taking energy-resolved dose (ERD) measurements with a proton beam and a flat panel x-ray detector.

Methods: A MatriXX (IBA Dosimetry) was first used to determine the optimal beam characteristics to produce images without overdosing the flat panel. A fluoroscopy panel (4030E, Varian Medical Systems, Palo Alto, CA) was scanned with 31 energy layers ranging from 100 to 230 MeV (corresponding to range of 8 to 33 cm). A piece of lead was placed in the beam line to increase the spot size and create a more uniform field. Varying thickness of solid water from 0 to 19.2 cm was imaged to build a calibration data set. Various phantoms were then scanned, including head, torso, and arm phantoms.

Results: Image acquisition worked reasonably well. The seventeen calibration images were used to build an empirical model of the ERD curves for the measured WEPLs. The model was used to interpolate between existing ERD curves in order to calculate ERDs for any desired WEPL. Proton images for the scanned phantoms were then derived from the extended ERD functions.

Conclusion: A fluoroscopy panel was successfully used to gather images using a proton PBS system. The calibration ERDs gathered with the flat panel were used to build a model of any ERD as a function of WEPL, which can be used to generate proton radiographic images.


Protons, Radiography


Not Applicable / None Entered.

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