Top Line: Can salivary function be preserved by sparing parotid stem cells during head and neck radiation?
The Study: There is preclinical evidence that the parotid glands contain stem cells capable of regenerating salivary function after radiation. Stem cell rich (SCR) regions are felt to be located around the major parotid ducts. In this trial, patients receiving radiation (IMRT) for head and neck squamous cell carcinoma were randomized to parotid gland sparing with or without additional sparing of an oval-shaped SCR region near the parotid duct. In both arms, mean dose to the whole parotid was minimized while in the experimental arm plans were optimized to also minimize dose to the SCR region. Here’s where the study really took it to the next level. Two plans (standard and experimental) were generated for each patient, and both were approved for treatment. The patient and provider were blinded to the plan used. Over 100 patients were randomized and 88 were evaluated for the primary endpoint, however 65% of eligible patients were excluded due to insufficient baseline salivary flow. Mean parotid dose was similar between arms, but mean SCR dose was lower with SCR-sparing optimization. At 12 months, there was no difference in the proportion of patients with a >75% reduction in salivary flow with (2.8%) or without (4.8%) SCR sparing. And except for moderate-to-severe nighttime xerostomia at 6 months, there was no difference in any other xerostomia outcomes. In multivariable analysis, though, mean contralateral SCR dose was the strongest predictor of xerostomia.
TBL: In the setting of parotid-sparing IMRT for HNSCC, additional sparing of parotid stem cells did not significantly improve post-treatment parotid function. | Steenbakkers, Int J Radiat Oncol Biol Phys 2021