Is Sparing the Deep Lobes of Parotid Gland Necessary on Intensity Modulated Radion Therapy of Head and Neck Cancers?

Abstract

RT to the lymphatics of the neck is an essential component in squamous cell cancers of the head and neck (SCCHN). Radiation induced mouth dryness, thickening of saliva and taste alteration affects nutrition and performance status of the patients. Protection of parotid glands from radiation is an important task during RT planning. Contemporary methods such as intensity modulated radiation therapy (IMRT) ease the protection of parotid glands. Most of the recurrences are seen close to the spared deep lobe of parotid glands. Exclusion of the deep lobes for sparing with dosimetric analysis has not been studied in the literature. In this study, we evaluated treatment plannings of 13 patients with SCCHN. As a dosimetric analysis, we compared the applied IMAT and the virtual IMRT without delineation of deep lobe of parotid glands. The dose for lymphatic region was prescribed as 50-54 Gy. Superficial and/or deep lobe of parotid gland was constrained as 26 Gy. Without definition of deep lobe, the radiation for dose lymphatic region planning target volume (PTV) was achieved without any dose change in the primary or high risk regions. With definition of deep lobe, the mean dose of lymphatic region PTV (not less than 95%) decreased by 5.8% (2.9-3.1 Gy). In conclusion, exclusion of sparing of deep lobe of parotid gland prevents decrease of radiation dose in the lymphatic region. It would be a treatment rationale to avoid the dose drop in the metastatic side of the neck region or the site of high risk for recurrence next to the parotid gland.