Purpose: Proton dose perturbations from dental fixtures (e.g. amalgams, crowns, and implants) are unverified for clinical treatment plans. The effect of several treatment planning approaches for patients with installed dental fixtures is quantified. Four scenarios were measured and compared: (1) standard-operating procedure (SOP) treatment geometry (two anterior oblique and one posterior beam) with no fixtures in phantom; (2) SOP plan for patient with installed fixtures (e.g. spot delivery through fixtures prohibited); (3) SOP no-fixture plan delivered to phantom with installed hardware; (4) installed fixtures overridden and plan reoptimized without limitations for spot positions/delivery.
Methods: An anthropomorphic head phantom with removable maxilla, mandible, and tongue inserts was simulated and clinically representative treatment plans were generated, delivering 54 Gy dose to a base-of-tongue (BoT) clinical target volume (CTV). An approximately 1.5 mm depth central groove occlusal amalgam and a PFM crown were installed on separate maxilla inserts and tongue inserts were 3D printed accommodating either a microdiamond diode (PTW 60019: Frieberg, Germany) or several axial or sagittal oriented pieces of EBT3 film (Ashland: New Jersey, USA).
Results: For the amalgam, case (3) delivered to a SFO BoT treatment plan resulted in a dose shadow parallel with the field delivering through the fixture. The dose shadow corresponded to an approximately 12% decrease in dose directly behind the amalgam. Dosimetric losses were local, dropping to a 1% deviation from control within 1 cm of maximum in the direction of the affected beam. Further, the microdiamond diode, which was not set up directly in line with the amalgam, measured effectively no change in delivered dose.
Conclusion: For SFO BoT plans, amalgams do perturb the beam, resulting in a shadowing effect, reducing the dose directly behind the amalgam in the direction of the affected beam. Losses were observed to be largely local to the implanted fixture.