Room: Exhibit Hall | Forum 7
Purpose: Improved dose conformality afforded by proton therapy may be especially beneficial in head-and-neck treatments where target dose coverage and OAR sparing may otherwise be in conflict using more typical modalities. Dental hardware, including amalgams, crowns, and implants whose properties are currently uncharacterized for proton therapy may cause dose perturbations, precluding safe delivery through these materials. We characterize common dental materials in terms of stopping power and dose perturbation to determine the potential for transoral head-and-neck treatment.
Methods: Amalgam stopping power was estimated using the SRIM application for a variety of clinically relevant stoichiometric weights of the most common elemental media (Hg, Ag, Sn, Cu). Similarly, stopping power was estimated for several of the most common materials found in porcelain-fused-to-metal (PFM) crowns and dental implants. Two experiments were designed. One to measure relative stopping power and one to measure dose perturbation through a custom phantom on a 2D dosimeter. Amalgams, PFM crowns (including porcelain materials of lithium disilicate and silicon dioxide, as well as a noble metal alloy), and both alumina and zirconia implants were included.
Results: SRIM calculated stopping power varied mostly with Sn content, varying from the mean at maximum by 8.35% for 100 MeV protons. Similar variations, however, were seen by varying Ag and Cu content (8.31% and 5.12%, respectively). For all studied PFM crown ceramics and metal alloys, mass stopping powers varied from the mean up to 6.5% and 1.9%, respectively. For validation, the most common PFM materials were measured. For implants, because mass stopping power varied up to 42%, the materials at each limit (zirconia and alumina) were selected for validation.
Conclusion: Delivery of proton beams through dental implants requires consideration of stopping power and dose perturbation. Further work determining the dosimetric effect and planning considerations is ongoing.