Room: ePoster Forums
Purpose: In situations, where the high density implant canâ€™t be avoided, it is critical to identify its relative stopping power (RSP) before proton beam planning. Herein, we proposed a clinical workflow to estimate the RSP of the high density implants and incorporating it into the clinical practice.
Methods: The RSP of a hip implant system (DePuy Ceramax^TM) was investigated as well as several high density materials (Titanium, Tungsten, Platinum, and Al2O3). To estimate the RSP, we use: (1) the software package Stopping and Range of Ions in Matter (SRIM; www.srim.org) (2) the National Institute of Standards and Technology (NIST) online program PSTAR (https://physics.nist.gov) and (3) If a sample implant was available, the RSP was measured. The data calculated by SRIM must be verified by at least either (2), (3), or using both, before using it in clinical plans. During the entire treatment course, the implant location is closely monitored via daily CBCT. If any change was noted, the physician was informed to review the dosimetric effect and to decide whether a re-plan was needed.
Results: The RSP of the Titanium alloy stem and Ceramic cap of the hip implant system was calculated using SRIM. The result was less than 0.8% from the measured value (3.22 vs. 3.22 for the stem, 3.43 vs. 3.46 for the cap). The RSPs of other materials (Titanium, Tungsten, Platinum, and Al2O3) encountered in our clinic were estimated using SRIM and verified by PSTAR, and their discrepancies were within 1%.
Conclusion: The proposed clinical workflow is practically achievable, and clinically useful. This is especially important when the high density implant lie inside the target volume and therefore directing beams through target volume could be favored due to improved target volume coverage, plan complexity and robustness.