Click here to


Are you sure ?

Yes, do it No, cancel

Override of High-Density Implants and Validation of Their Dose Perturbation in Pencil Beam Scanning Proton Therapy

W Zheng*, X Li, J Vadas, D Yan, D Moore, K Les, C Stevens, P Kabolizadeh, X Ding, William Beaumont Hospital, Royal Oak, MI


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: Significant overestimation of the proton dose beyond the high-density implants could happen if material override is not appropriately handled. Herein, we proposed a workflow to override the material for high-density implants and validate their perturbation in PBS.

Methods: Several materials including a hip implant system (ceremic, Ti6Al4V) ( DePuy Ceramax™), a cement bone (Surgical Simplex® P), a PEEK spine spacer (polyetheretherketone) (ACIS®) and a Vitallium rod in a spine system (ES2®, Stryker) were investigated in this study. The relative stopping power (RSP to water) of the implants was calculated using software package SRIM ( with stoichiometry and factional mass density of the elements. Dose was then calculated with material override using Monte Carlo simulation and compared with the film measurements. Method I overrides the material based on water, setting effective mass density equal to RSP. Method II is to create a new override material with similar mean nuclear scattering cross-section, and mean excitation energy and an effective mass density matched to the calculated RSP interpolated in the TPS pre-calculated materials.

Results: The material override with nuclear scattering cross-section and RSP matching resulted in negligible discrepancy between the calculated dose and film measurements. In contrast, override simply based on RSP to water could lead to up to 18% higher calculated dose beyond the implant than the film measurements for Vitallium, 10% for ceramic, and 6% for Ti6Al4V implants. While for the materials dominantly made of organic elements, the dose discrepancy is negligible between two override methods.

Conclusion: We proposed a clinical workflow to override the high-density implants and validate their dose perturbation for the materials that are not provided in the proton planning system. Such an approach could provide a more accurate dose calculation in the presence of high-density implants that may be associated with local recurrence (Staab 2011).


Not Applicable / None Entered.


Not Applicable / None Entered.

Contact Email