Dosimetric Evaluation of an Ipsilateral Intensity Modulated Radiotherapy Beam Arrangement for Parotid Malignancies
Purpose/Objective(s): We conducted a dosimetric comparison of anipsilateral beam arrangement for Intensity Modulated Radiotherapy (IMRT) with off-axis beams.
Materials/Methods:Six patients who received post-operative radiotherapy (RT) for parotid malignancies were used in this dosimetric study. Four treatment plans were created for each CT data set (24 plans): 1) ipsilateral4-field off-axis IMRT (4fld-OA), 2) conventional wedge pair (WP), 3) 7 field co-planar IMRT (7fld), and 4) ipsilateralco-planar 4-field quartet IMRT (4fld-CP). Dose, volume statistics for the PTVs and PRVs were compared for the four treatment techniques.Results: Wedge pair plans inadequately covered the deep aspect of the PTV. The 7-field IMRT plans delivered the largest low dose volumes to normal tissues. Mean dose to the contralateral parotid was highest for 7 field IMRT. Mean dose to the contralateral submandibular gland was highest for 7 field IMRT and WP. 7 field IMRT plans had the highest dose to the oral cavity. The mean doses to the brainstem, spinal cord, ipsilateral temporal lobe,cerrebellum and ipsilateral cochlea were similar among the four techniques.
Conclusions: For postoperative treatment of the parotid bed, 4-field ipsilateral IMRT techniques provided excellent coverage while maximally sparing the contralateral parotid gland and submandibular gland.