Three dimensional conformal postoperative radiotherapy for unilateral parotid gland cancer: A comparison of three different parotid gland irradiation techniques

Abstract

Introduction: Postoperative radiotherapy of the parotid gland could be achieved with various radiotherapy techniques. However they irradiate differently the surrounding organs at risk (OARs) in particular the cochlea, oral cavity & contralateral parotid causing significant increase in the risk of oral mucositis, xerostomia, and hearing deficits on the irradiated side.
Objectives: The aim of this study was to compare radiation doses received by target volume and different surrounding OARs using three different parotid irradiation techniques aiming to achieve the optimum technique which shows adequate target coverage and sparing of surrounding OARs during postoperative 3DCRT treatment of parotid gland cancer patients.
Methodology: Ten patients diagnosed as having parotid cancer were included in this study. They were subjected to CT simulation and scans were transferred to the treatment planning system. Target volumes and contralateral parotid, oral cavity, cochlea, spinal cord, brain stem, eyes, lenses and optic nerves were contoured. Three plans were done using (a) ipsilateral oblique wedged photon pair, (b) oblique wedged photon pair  and direct lateral field, and (c) ipsilateral mixed photon electron beams. For three plans, the dose volume parameters (DVPs) for target volume and surrounding OARs were compared and analyzed statistically.
Results: Target dose coverage was adequate and comparable for techniques 1 and 2. Technique 2 showed the best dose homogeneity and conformity and lowest max dose to PTV and to the whole body and although the dose to OARs was higher compared to technique 1 it was far lower than OARs tolerance. On the other hand, technique 3 showed unaccepted underdose & dose inhomogeneity within the PTV, the highest doses to OARs and the highest PTV max and body max dose.
Conclusion: The ipsilateral oblique wedged photon pair and direct lateral photon field technique is an optimal treatment technique for parotid cancer patients in comparison to other plans.

Keywords: Parotid gland cancer; 3DCRT; Postoperative radiotherapy techniques; Dose distribution