High-energy electron and photon therapy to the parotid bed: radiation dose perturbations with a titanium mandibular implant.
Adjuvant radiation therapy to the parotid bed is commonly administered following surgical resection using either a pair of angled wedged photon beams or an ipsilateral mixed-beam portal of electrons and photons. The present study seeks to determine the optimal parotid bed treatment technique in the presence of a titanium mandibular implant by investigating perturbations in the dose distribution deep to this implant for a 15-MeV electron beam and a 6-MV photon beam. A titanium mandibular plate was embedded in a tissue-equivalent phantom, and irradiated with 15-MeV electrons, and 6 MV photons. Radiation doses behind the plate were measured with both thermoluminescent dosimeters and radiographic film. With 15-MeV electrons, there is a clinically significant decrease in the dose beyond the titanium plate, which is most important at 5-mm and 10-mm depths (18-27%). With 6-MV photons the dose at the deep interface of titanium and tissue is reduced by between 15 and 18%, but rapidly drops to < 5% at a depth of 5 mm. In adjuvant treatment to the parotid bed, when the clinical target volume includes tissue positioned deep to a titanium implant, significant underdosage occurs with ipsilateral beam arrangements, especially when electrons are used.
Menard
C M
CM
Department of Radiation Oncology, Manitoba Cancer Treatment and Research Foundation, Winnipeg, Canada. umskorac@cc.umanitoba.ca
Bews
J
J
Skoracki
R I
RI
Chowdhury
A D
AD
D004583:Electrons; D008334:Mandible / Q000601:surgery*; D010306:Parotid Gland / Q000528:radiation effects*; D019047:Phantoms, Imaging; D017785:Photons; D019736:Prostheses and Implants; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy; D014025:Titanium
D014025:Titanium