In vivo dose verification for photon treatments of head and neck carcinomas using MOSFET dosimeters

In vivo dosimetry was performed for the head and neck carcinoma patients during the treatment of a large photon field using MOSFETs. This study followed the protocols recommended by the European Society for Therapeutic Radiology and Oncology. A total of 32 portals belonging to 12 patients were under investigation. Results showed that the deviation between in vivo midline doses and planned target doses was partly due to the manual dose calculations in the treatment planning which used the patient geometric thickness rather than the radiological thickness. Other factors responsible for this deviation included the difficult positioning of MOSFETs on the face mask, the asymmetric positioning of MOSFETs on the left and right sides of the mask, and the asymmetric tissue inhomogeneities with respect to the body midline. To reduce the deviation contributed from these factors, in vivo midline doses were calculated by averaging the results for each bilaterally opposed portals and compared with corresponding planned target doses. This comparison showed that MOSFET dosimeters are suitable for in vivo dosimetry of the present study.