Letter to the Editor: Serial Changes in Parotid Gland Volume and Symptoms After Radiation Therapy in Oropharyngeal Cancer

Dear editor,

We extend our congratulations to Jun et al. for their research investigating the sequential alterations in parotid gland volume (PGV) and examining the correlation between changes in volume and xerostomia after curative intent radiotherapy (RT) or chemoradiotherapy (CRT). ¹ This study analyzed 33 patients with oropharyngeal cancer who received either 67.5 Gy in 30 fractions as definitive RT or 63 Gy in 28 fractions as adjuvant RT after surgery. There were no statistically significant differences between the 3 post-RT PGV measures, but the mean PGV decreased from 23.30 mL pre-RT to 15.80 mL after 6 months, 15.93 mL after 1 year, and 16.67 mL after 2 years (all P < .001). Although the findings provide valuable insights into a significant but overlooked issue with profound implications for patients with head and neck cancer undergoing RT or CRT, we have one concern to be addressed by the authors.

The mean prescribed total RT dose was specified as 62.7 Gy (range: 60-67 Gy) for all patients, and this dose was used as a reference point for comparing with existing literature. Consequently, the authors came to the surprising conclusion that the radiation dose had no impact on the PGV measures. Regrettably, their data indicate that the authors failed to consider the dose-volume parameters for the parotid glands, the main determinants of the fate of parotid glands, and related toxicities after head and neck RT.^2,3 Because when intensity-modulated RT is used, it is nearly impossible for the parotid glands to receive the same doses as the prescribed doses for the primary tumor site and lymphatic regions. To clarify, the term “prescription dose” does not refer to the actual dose that the parotid glands will receive. Hence, such kind of finding can only be achieved through the use of 2 parallel opposing field RT techniques, without any dose-volume constraints on the parotid glands. ⁴ We believe it is crucial to thoroughly review and analyze the dosimetric data to determine the precise correlation between the mean and Vx (X Gy received by a specific percentage of the parotid gland(s)) doses and the serial PGV measurements. In addition to providing a solid foundation for future research, this type of analysis is highly significant because it can also be valuable in making more precise predictions about other difficult to manage toxicities, such as osteoradionecrosis of the jaw and radiation-induced trismus. Notwithstanding the aforementioned concerns, the findings of Jun et al. hold significant academic value, as they underscore the critical importance of implementing dose constraints in the RT or CRT of patients with head and neck cancers. This measure is crucial in mitigating the risk of long-term severe toxicities, thereby averting the adverse consequences associated with the administration of higher radiation doses to one or both parotid glands. ⁵ These endeavors may facilitate the development of prompt multidisciplinary preventive measures, such as salivary stimulation for xerostomia and temporomandibular joint exercises for radiation-induced trismus, and adaptive RT for both.