Parotid gland radiation dose‐xerostomia relationships based on actual delivered dose for nasopharyngeal carcinoma

Abstract

Xerostomia induced by radiotherapy is a common toxicity for head and neck carcinoma patients. In this study, the deformable image registration of planning computed tomography (CT) and weekly cone‐beam CT (CBCT) was used to override the Hounsfield unit value of CBCT, and the modified CBCT was introduced to estimate the radiation dose delivered during the course of treatment. Herein, the beams from each patient's treatment plan were applied to the modified CBCT to construct the weekly delivered dose. Then, weekly doses were summed together to obtain the accumulated dose. A total of 42 parotid glands (PGs) of 21 nasopharyngeal carcinoma patients were analyzed. Doses delivered to the parotid glands significantly increased compared with the planning doses. V20, V30, V40, Dmean, and D50 increased by 11.3%, 28.6%, 44.4%, 9.5%, and 8.4% respectively. Of the 21 patients included in the study, eight developed xerostomia and the remaining 13 did not. Both planning and delivered PG Dmean for all patients exceeded tolerance (26 Gy). Among the 21 patients, the planning dose and delivered dose of Dmean were 30.6 Gy and 33.6 Gy, respectively, for patients with xerostomia, and 26.3 Gy and 28.0 Gy, respectively, for patients without xerostomia. The D50 of the planning and delivered dose for patients was below tolerance (30 Gy). The results demonstrated that the p‐value of V20, V30, D50, and Dmean difference of the delivery dose between patients with xerostomia and patients without xerostomia was less than 0.05. However, for the planning dose, the significant dosimetric difference between the two groups only existed in D50 and Dmean. Xerostomia is closely related to V20, V30, D50, and Dmean.

Dosimetric impact of weight loss and anatomical changes at organs at risk during intensity-modulated radiotherapy for head-and-neck cancer

“…As expected, organs such as the parotid gland, optic nerve, and brainstem near the PTVs were partially irradiated by the primary radiation beams and received significantly diverse doses level than the planned doses. Increasing the doses received by parotid glands over the constraint doses may lead to xerostomia; these results are consistent with previous studies (Gabryś, Buettner, Sterzing, Hauswald, & Bangert, 2017;Hawkins et al, 2018;Lou et al, 2018;Mireștean, Buzea, Butuc, Zara, & Iancu, 2017;Richards et al, 2017;Vissink et al, 2010).…”

“…is essential to identify dosimetric changes and to ensure adequate doses within the constrained doses to target volumes and safe doses to normal tissues (Gabryś et al, 2017;Hawkins et al, 2018;Lee et al, 2010;Lou et al, 2018;Noble et al, 2019;Ren et al, 2015;Richards et al, 2017).…”

A Review on the Assessment of Radiation Induced Salivary Gland Damage After Radiotherapy

“…Saliva produced from “damaged” parotid and submandibular glands may show reduced levels of the constituents and subsequently affect the digestive and protective processes in the oral cavity. Previous studies have demonstrated that the severity of xerostomia were associated with the hypo-function of the salivary glands due radiation damage, which was found to be dependent on the amount of radiation dose delivered to the glands (16, 17). Because of this, submandibular gland (SMG)-sparing and parotid gland (PG)-sparing techniques have been suggested to minimize the damage of salivary glands in recent studies (18).…”

Deformable image registration for radiation therapy: principle, methods, applications and evaluation

“…Thus, an image that represents the current anatomy with reliable electronic densities is required. DIR has therefore been used to propagate the Hounsfield unit from the planning CT to the per-treatment imaging (e.g., CBCT or megavoltage CT (MVCT)), generating a pseudo-CT that allows the fraction dose distribution to be calculated [76,77].…”