Clinical target volume design of postoperative intensity-modulated radiotherapy for major salivary gland tumours according to surgical principles: an innovative method.

Abstract

No international consensus has been reached regarding delineation of postoperative intensity-modulated radiotherapy (PO-IMRT) clinical target volumes (CTV) for major salivary gland carcinoma (SGC). The purpose of this article was to report our experience according to surgical principles. Between June 2010 and June 2018, 54 consecutive patients were enrolled. Reserved tissues around the margin of resection that were less than 5mm from the invasive tumour edge before surgery were defined as high-risk clinical target volumes (CTV-HD), those less than 10mm away were defined as medium-risk CTV (CTV1), and those 10-20mm away were defined as low-risk CTV (CTV2), and were irradiated with 63-65Gy, 59.5-61Gy, and 45-54Gy, respectively. Target volume distributions of reserved tissues were analysed and actuarial estimates of overall survival (OS), recurrence-free survival (RFS) and distant metastasis-free survival (DMFS) were obtained with the Kaplan-Meier method. In parotid gland tumours, the percentages of defined CTV-HD in the styloid process, mandibular ramus, posterior venter of the digastric muscle, carotid sheath and stylomastoid foramen reached 34.29%, 25.71%, 54.29%, 40.00%, and 37.10%, respectively. The median follow-up was 33months (range, 5-98months). The 3-year and 5-year Kaplan-Meier estimates of OS, RFS and DMFS were 85.4% and 77.8%, 97.4%, and 97.4%, and 82.0% and 82.0%, respectively. It is feasible to delineate CTVs according to distances between various reserved tissues and the primary tumour edge before operation.