The results, Dr. Kyle Wang told Reuters Health by email, “suggest that clinicians should avoid the parotid glands when using whole-brain radiation. Most patients that receive this treatment have poor prognoses, and it’s important to maintain their quality of life.”
In a paper online November 29 in JAMA Oncology, Dr. Wang, of the University of North Carolina Hospitals, Chapel Hill, and colleagues note that WBRT is employed in “hundreds of thousands of patients who develop brain metastases every year.”
Numerous studies, they go on to say, have underlined the importance of limiting radiation dose to the parotid glands during head and neck radiation, but “the parotid glands are not typically delineated nor avoided during WBRT.”
To examine possible effects, the researchers enrolled 100 patients receiving WBRT for the treatment or prophylaxis of brain metastases. At baseline they completed the University of Michigan Xerostomia Questionnaire and a four-point bother score. They did so again immediately after WBRT and for up to six months thereafter.
Altogether results from 73 patients were eligible for analysis and 55 were evaluable at one month. The median volume of parotid receiving at least 20 Gy (V20Gy) was 47%.
The mean xerostomia score was seven points at baseline and was significantly higher following radiation, at 21 points immediately after WBRT, 23 at one month, 21 at three months and 14 points at six months.
The xerostomia score increased by 20 points or more in 19 patients at one month. This score was associated with parotid dose as a continuous variable and was 35 points in patients with parotid V20Gy of 47% or more. In patients with parotid V20Gy less than 47%, the score was only nine points, a significant difference.
At one month half of the patients who had a parotid V20Gy of 47% or more reported being bothered quite a bit or bothered very much by xerostomia compared to only 4% who had received a lower dosage. At three months, 50% of the higher-dosage group continued to be bothered compared to none of the lower-dosage group.
The team notes that patients are not only at risk for substantial acute salivary toxic effects but also may not live long enough to recover salivary function.
“In this study,” they point out, “the median survival of patients who received WBRT was only 8 months. Thus, patients who develop xerostomia after WBRT may live with this adverse effect for a considerable portion of their remaining life.”
And, said Dr. Wang, “A simple alteration of radiation technique may be able to prevent this side effect.”
Dr. Egle Milia of the University of Sassari in Italy, who has studied radiotherapy and xerostomia and was not involved in the study, said “selecting a group of xerostomic patients only using a questionnaire is not sufficiently rigorous.”
She noted that the authors observe that “the level of xerostomia is higher in comparison to that deriving from head and neck cancer (HNC) irradiation therapy even if the dose directed to the parotid in WBRT is less than in HNC.”
This, said Dr. Milia, could be explained because “secretion of saliva from the parotid is under the influence of the salivary centre in the medulla in the brain. So, irradiating the brain . . . might have had an influence on the nervous transmission of stimuli from the salivary reflex arc in the brain to the parotid gland,” adding brain toxicity to that directly affecting the parotid.
JAMA Oncol 2018.