Room: Exhibit Hall | Forum 9
Purpose: To develop a tool to evaluate the feasibility of proton transmission radiography for patients undergoing treatments at centers with proton therapy beams with a maximum energy of 235 to 250 MeV.
Methods: We are developing a python program which uses DICOM x-ray CT and RTION plan files to calculate the water equivalent thickness (WET) distribution needed to traverse previously treated proton patients along a treatment beamâ€™s axis. The PyDicom module in Python allows the program user to read only the necessary tags from the DICOM files to calculate the WET, meaning there is no need to anonymize the patient data before running the program. The algorithm utilizes Euler rotation matrices to step along a virtual ray defined by the gantry angle and the patient support angle. To account for beam divergence, each ray is rotated with respect to the effective source point such that it passes through points spaced 1 cm apart normal to the treatment beam at isocenter as defined by the aperture. At each step, the program reads the HU from the corresponding DICOM voxel and converts it to RSP. The RSP is then multiplied by the step size and all steps are summed to measure the total WET of the ray through the patient. The WET of each ray in a given field is then collected into a histogram for analysis.
Results: The program was verified on a solid cube of water and five tumor sites on six patients. The program successfully calculates the WET of divergent rays in a variety of conditions. In this limited sample size, four of the five tumor sites have low enough WET to image with protons.
Conclusion: A tool has been developed and validated that will offer insight into which patients can be proton radiographed with proton therapy beams.
Funding Support, Disclosures, and Conflict of Interest: This work was funded by Ion Beam Applications (IBA)