Room: AAPM ePoster Library
Purpose: The dosimetric effect of proton delivery through common dental materials is as yet unvalidated and uncharacterized, impeding ideal transoral head-and-neck treatment geometry. A 159.9 MeV proton spot was delivered through common compositions of amalgams, crowns, and implant materials. The change in the dose was characterized in terms of relative stopping power and geometric dose perturbation.
Methods: Crown and implant materials were selected in collaboration with Advanced Prosthodontics to represent a historical sampling of commonly employed hardware. Relative stopping power of each material was measured experimentally using a multi-layer ionization chamber (MLIC). Dose perturbation of the 159.9 MeV proton spot was characterized on film using a simple phantom, simulating en-face and edge-on delivery through each material. The films were oriented in both coronal and axial orientations to characterize perturbation in each spatial dimension.
Results: Relative stopping powers of the studied dental materials fell between 1.34 and 5.44, suggesting large potential effects on proton range with respect to water. Film measurements of each of the spots confirm a reduction in proton range and an upstream shift of the Bragg peak through each of the materials in both en-face and edge-on orientations. Axial film orientations show a shift of dose towards the proximal regions of the beam. Cold spots are also found immediately behind edge-on features. However, the dose exhibits a medial back-filling characteristic at greater depths.
Conclusion: Dose perturbation of single proton spots was observed. Delivery through each dental material resulted in shortening of the proton range, and general reductions in intensity. Further, more severe cold spots were found directly behind edge-on features. Beyond these cold spots, however, the dose was shown to back-fill medially.