SU‐E‐T‐138: Range Verification for Proton Therapy Systems: A Multi‐Center Study

Purpose: Proton beams have finite range and spare normal tissues distal to the target. Accurate determination and routine verification of proton range are critical in proton therapy, but depends on measurement device and method and could vary with proton centers. The purpose of this study is to develop a consistent approach to cross verify range accuracy at various proton centers. Methods: Three Lucite blocks were manufactured, with water equivalent thicknesses (WET) of about 7, 9 and 12 cm. The exact amount of WET was determined using a multi‐layer ionization chamber (MLIC). Using various block combinations, we tested four beams of different proton ranges (9, 16, 21 and 28 cm). The block combination and proton beams were chosen so that the measured dose by the PPC was about 50% of the dose at the center of spread out Bragg peak (SOBP) for each beam. A parallel plane chamber (PPC) was used to measure the dose at the center of SOBP and immediately behind the block(s). Since proton beams have a very sharp distal falloff (∼10−20% dose change per mm), the PPC reading behind the blocks is very sensitive to range change, thus allowing accurate range verification. Results: A set of Lucite blocks with step‐by‐step instructions were developed for cross center proton range checks. Using these blocks and a commercial PPC, various ranges were measured and compared to MLIC measurement and nominal ranges. Such measurements were carried out for four treatment rooms at one center, and cross range checks at other proton centers are under way. Conclusion: A simple method has been developed to cross check proton ranges among various proton centers within sub‐millimeter accuracy. The same approach can also be used to check proton range consistency with time. The multi‐center range results would provide valuable data for range uncertainty assessment. © 2013, American Association of Physicists in Medicine. All rights reserved.

Duke Scholars

Author Tien Yin Wong Ophthalmology