Prevalence of hyposalivation and associated factors in survivors of head and neck cancer treated with radiotherapy

Abstract Hyposalivation and sensation of dry mouth (xerostomia) are one of the most common adverse effects in the treatment of patients with head and neck cancer. Objective: This study evaluates the prevalence of late hyposalivation and associated factors in survivors of squamous cell carcinoma of the oral cavity, oropharynx, hypopharynx, or larynx treated with radiotherapy with or without concomitant chemotherapy. Methodology: A cross-sectional study was conducted with 88 patients who had concluded radiotherapy at least three months before the study, at a referral center for the treatment of head and neck cancer in the Southern region of Brazil. Hyposalivation was evaluated based on the stimulated salivary flow rate using the spitting method. Multivariate analysis using binary logistic regression was performed to determine the associations between hyposalivation and clinical and demographic variables. Results: Hyposalivation was found in 78.41% of the sample and the mean radiation dose was 63.01 Gy (±9.58). In the crude model of the multivariate analysis, hyposalivation was associated with higher doses of radiation (p=0.038), treatment with concomitant radiotherapy and chemotherapy (p=0.005), and time elapsed since the end of radiotherapy (p=0.025). In the adjusted model of the multivariate analysis, hyposalivation was only associated with dose and time elapsed. Patient who received higher doses of radiation had a 4.25-fold greater chance of presenting hyposalivation, whereas a longer time elapsed since the end of radiotherapy exerted a 75% protective effect against the occurrence of hyposalivation. Conclusion: Hyposalivation is a highly prevalence late-onset side effect of radiotherapy in patients treated for head and neck cancer, with a greater chance of occurrence among those who received higher doses of radiation and those who ended therapy less than 22 months before our study. Concomitant chemotherapy and radiotherapy does not seem to increase the chances of hyposalivation compared to radiotherapy alone.


Introduction
Cancer of the oral cavity, pharynx, and larynx corresponds to approximately 4.6% of all cases of cancer worldwide. 1 In 2018, 834,860 new cases of cancer in these anatomic sites were diagnosed. 1 When anatomic sub-sites are analyzed, the incidence of cancer of the mouth and oropharnyx is higher, followed by cancer of the larynx and hypopharynx. 2 Due to demographic changes, the number of cases of lip, mouth, and pharyngeal cancer is expected to increase by 62%, reaching 856,000 cases annually by 2035.
Radiotherapy (RT) is widely employed in the treatment of head and neck cancer used as primary therapy, adjunct therapy to surgery, with concomitant chemotherapy (CT) or as palliative treatment. High doses of RT can negatively affect the soft and hard tissues of the oral cavity. 3 Patients with head and neck cancer are generally irradiated with high doses (50 to 70 Gy), 4 which side-effects include hyposalivation, trismus, and dysphagia; in hard tissues, the effects may be osteoradionecrosis and radiation caries -all of which have a late-onset. 3 One of the main problems resulting from radiotherapy in the head and neck region is the damage to glandular tissues, reducing the salivary flow. 5 Hyposalivation occurs due to cell death and fibrosis of the glandular tissue caused by radiotherapy, leading to a sensation of dry mouth (xerostomia). 6 Some studies suggest a significant increase in lateonset xerostomia in patients treated with concomitant chemotherapy and radiotherapy, 7 whereas other authors state that there is no strong evidence of the additive effect of chemotherapy concomitant to radiotherapy on hypofunction of the salivary glands. 8 In a systematic review, Jensen, et al. 8 (2010) found divergences in the literature regarding hyposalivation and xerostomia. According to some authors, the term xerostomia is often used as a synonym of hyposalivation, when it should only be used to indicate the perception of dry mouth reported by the patient. The inclusion criteria were men or women aged 18 years or older, presumably disease free who agreed to undergo the proposed examinations.
The sample size was calculated based on the difference in mean non-stimulated salivary flow between individuals exposed to a radiation dose of 50 Gy and non-exposed individuals in a previous study: 0.47 (SD: 0.31) and 0.28 (SD: 0.32), respectively. 9 Considering a 5% significance level and 80% power, as antihypertensive agents, antidepressant and others) 10,11 as well as data regarding the disease (tumor type and stage) and treatment (type and dose of radiation) were collected from the patient medical charts. Xerostomia (subjective assessment) was recorded based on the answer to the following question: "Does your mouth generally feel dry?" 12,13 Saliva collection and sialometry -stimulated salivary flow The participants were instructed not to eat, drink (except water) or smoke at least one hour prior to the saliva collection. Stimulated salivary flow rate was determined using the spitting collection method. 14 The mechanical stimulation of salivation was performed with a sterile rubber strip with a standardized size (2x2 cm). The collection lasted five minutes. All saliva collection procedures were held between 13:30 and 3:30 pm. The participant was seated comfortably on a chair and were instructed neither to speak nor interrupt the data collection process; otherwise, a new collection would be initiated. The saliva from the first minute was discarded to eliminate possible food scraps that could influence the weight of the saliva. Then, the participant expelled saliva into a previously sterilized and weighed universal collector at 60-second intervals.
The collection time was controlled with a chronometer.
The total quantity of stimulated saliva was determined based on weight measured using a precision scale (Balança Eletrônica Gehaka BG 200) expressed in grams. The total weight was divided by four (because the first minute was discarded) to obtain the salivary flow rate in grams per minute, which is similar to mL/ min. Hyposalivation was recorded if the stimulated salivary flow rate was less than 0.5 mL/min. 15

Radiation caries
Ring-shaped caries on the cervical third of the vestibular, incisal, occlusal, and lingual faces of the teeth were considered radiation caries, 4 which were detected through a visual clinical examination aided by a wooden tongue depressor with the patient lying on the dental chair. The clinical examinations were performed by two raters who had previously undergone training and calibration exercises. The calibration involved the examination of 20 images displayed on a computer screen one at a time, for which the raters marked "yes" or "no" on a chart. The procedure was repeated after 30 days. The Kappa coefficient was estimated for the determination of intra-rater and inter-rater agreement (K=0.79 to 1.00).

Statistical analysis
The data were analyzed descriptively, with the

Results
The response rate was 89.79% (88/98).   (Table 3). Hyposalivation was not associated with age, sex, location of primary tumor, or radiation caries.    Some studies offer information on threshold doses of radiation to avoid harm to the salivary glands and consequent occurrence of hyposalivation. Marks, et al. 19 (1981) found that a dose from 30 to 40 Gy was able to cause an accentuated reduction in salivary flow.    associated with radiotherapy on harm to the salivary glands leading to hyposalivation. 8 According to Chao, et al. 27 (2001), neither the treatment modality (with or without chemotherapy) nor the radiation technique (intensity-modulated radiation therapy [IMRT]  Nonetheless, no association was found between RT + CT and hyposalivation in the adjusted multivariate analysis, despite the fact that the crude analysis suggested such association. In the literature, the minimum cutoff point for total stimulated salivary flow ranges from 0.5 to 0.7 mL/min. In our study, hyposalivation was defined as a stimulated salivary flow rate of less than 0.5 mL/ min, as suggested by Sreebny 15 (2000). Considering the participants' mean age and the fact that more than half of the sample had comorbidities and/or used medications that could reduce salivary flow and, mainly, it is a sample composed of patients who had their head and neck irradiated, we found it more prudent to use the criterion that represented a more significant reduction in the total volume of stimulated salivary flow. Regarding xerostomia, different from other authors, 30 we used a tool easier to apply in order to assess this variable, 12,13 once the main purpose of the study was the objective assessment of hyposalivation.
This investigation has limitations that should be addressed. It was a cross-sectional study and no evaluations of salivary flow or xerostomia were performed in the pre-radiotherapy period. It was also not possible to measure the average radiation dose received in isolation by the parotid gland. Moreover, we did not exclude individuals who took medications that cause xerostomia, such as anti-hypertensive agents or antidepressants, or those participants who had some comorbidity that could cause xerostomia, such as diabetes. However, this possible bias was minimized by the inclusion of these independent variables in the statistical analysis. Comorbidities and xerostomic drugs that could reduce salivary flow had no statistically significant association with hyposalivation in both crude analysis or multivariate analysis adjusted for confounding variables.
Studies have demonstrated that IMRT produces less toxicity and fewer adverse effects compared to 3D conformal radiotherapy. 31,32 All individuals in the study had been submitted to the latter form of radiotherapy,

Conclusion
Hyposalivation is a significant late-onset side effect of radiotherapy, with a high prevalence rate among patients submitted to irradiation of the head and neck region. This condition is also dose dependent. Chemotherapy concomitant to radiotherapy does not seem to increase the chances of hyposalivation compared to radiotherapy alone.
A better understanding of the causes and factors that expose patients to a greater chance of having hyposalivation is essential to the development of