SU‐E‐T‐75: A Simple Technique for Proton Beam Range Verification

• Published in: Medical physics (Lancaster) 2015-06, Vol.42 (6Part12), p.3348-3348
• Main Authors: Burgdorf, B, Kassaee, A, Garver, E
• Format: Article
• Language: English
• Subjects: 60 APPLIED LIFE SCIENCES; BRAGG CURVE; DEPTH DOSE DISTRIBUTIONS; DOSIMETRY; Ion beams; IONIZATION; IONIZATION CHAMBERS; Linear equations; Multilayers; PHANTOMS; PROTON BEAMS; Proton therapy; Protons; PVC; QUALITY ASSURANCE; RADIATION DOSES; RADIOLOGY AND NUCLEAR MEDICINE; RADIOTHERAPY; VERIFICATION
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.4924436

Purpose: To develop a measurement‐based technique to verify the range of proton beams for quality assurance (QA). Methods: We developed a simple technique to verify the proton beam range with in‐house fabricated devices. Two separate devices were fabricated; a clear acrylic rectangular cuboid and a solid polyvinyl chloride (PVC) step wedge. For efficiency in our clinic, we used the rectangular cuboid for double scattering (DS) beams and the step wedge for pencil beam scanning (PBS) beams. These devices were added to our QA phantom to measure dose points along the distal fall‐off region (between 80% and 20%) in addition to dose at mid‐SOBP (spread out Bragg peak) using a two‐dimensional parallel plate chamber array (MatriXX™, IBA Dosimetry, Schwarzenbruck, Germany). This method relies on the fact that the slope of the distal fall‐off is linear and does not vary with small changes in energy. Using a multi‐layer ionization chamber (Zebra™, IBA Dosimetry), percent depth dose (PDD) curves were measured for our standard daily QA beams. The range (energy) for each beam was then varied (i.e. ±2mm and ±5mm) and additional PDD curves were measured. The distal fall‐off of all PDD curves was fit to a linear equation. The distal fall‐off measured dose for a particular beam was used in our linear equation to determine the beam range. Results: The linear fit of the fall‐off region for the PDD curves, when varying the range by a few millimeters for a specific QA beam, yielded identical slopes. The calculated range based on measured point dose(s) in the fall‐off region using the slope resulted in agreement of ±1mm of the expected beam range. Conclusion: We developed a simple technique for accurately verifying the beam range for proton therapy QA programs.