Dynamic Changes of Major Salivary Glands During Head and Neck Intensity Modulated Radiation Therapy

Abstract

Normal tissue sparing strategies are becoming the standard for modern radiation therapy; without organ preservation the toxicity associated with external beam radiation therapy, such as xerostomia, adversely affects a patient’s long-term quality of life (QOL). Recently, clinicians have come to understand that there are significant changes to the head and neck (H&N) anatomic compartments induced by radiation therapy, despite efforts to spare normal structures. Herein, we propose an investigation of the anatomic and volume changes of the major salivary (parotid and submandibular) glands during treatment with concurrent chemoradiation. We further assess the volume changes of the deep and superficial parotid glands during our IMRT treatment. Our ultimate goal is to identify the timing at which radiation-induced changes to the salivary glands occur, the effects on saliva quality, and assess QOL, with the future goal to design an adaptive radiation therapy paradigm to maximize the quality of life of H&N patients. We retrospectively investigated 20 patients with recurrent or newly diagnosed squamous cell carcinoma of the H&N carcinoma treated with concurrent chemoradiation therapy. Assessed, were the volume and anatomic positions of the parotid and submandibular glands at the time of CT simulation, the 12th, 25th, and final fraction of image guided radiation therapy. We compared the total gland volumes, and then measured position translation to a bony reference (C2 dens). We utilized the embedded volume, distance, and dosing tools within the treatment planning software package. Cohort median age was 61 (3:1 male:female ratio). Fifteen patients were diagnosed with stage IVa H&N squamous cell carcinoma. There was a balance of left vs. right-sided disease. Patients received a minimum of 66 Gy, with a median dose of 70 Gy. Mean treatment package time was 44d; 85% of patients received concurrent chemotherapy. Median weight loss was 7.4%. CCRT vs. no chemotherapy resulted in a trend towards significant mean parotid gland volume loss (41.9 ± 19.4% vs. 35.2 ± 20.1%; P = 0.18). Volume loss was greatest by the first 12 fractions of treatment. For submandibular glands, our sample small sample size suggested a trend increased volume loss with CCRT. The glands exhibited a medial displacement of 5-8mm during the course of treatment. No differences in unstimulated/stimulated saliva output or pH were seen between the two groups. Our data suggests a connection with use of CCRT and salivary gland changes. Due to a small sample size, these differences were not statistically significant, however, we are increasing our study size in light of this important result. We wish to identify timing of gland changes, dose effect on saliva chemistry, and assess QOL to design an adaptive CCRT paradigm to maximize QOL.