Radiation-induced Xerostomia is Related to Stem Cell Dose-dependent Reduction of Saliva Production.

PURPOSE: Previous studies have shown that the mean dose to the parotid gland stem cell rich regions (Dmean,SCR) is the strongest dosimetric predictor for the risk of patient-reported daytime xerostomia. This study aimed to test whether the relationship between patient-reported xerostomia and Dmean,SCR is explained by a dose-dependent reduction of saliva production. METHODS AND MATERIALS: In 570 patients with head and neck cancer treated with definitive radiation therapy (RT), flow from the parotid (FLOWPAR) and submandibular/sublingual (FLOWSMSL) glands, and patient-reported daytime (XERDAY) and nighttime (XERNIGHT) xerostomia were prospectively measured before, at 6 months, and 12 months after RT. Using linear mixed effect models, the relationship of the mean dose to the parotid glands (Dmean,par), Dmean,SCR, non-SCR parotid gland tissue (Dmean,non-SCR), submandibular glands (Dmean,sub), and oral cavity (Dmean,oral) with salivary flow and xerostomia was analyzed while correcting for known confounders. RESULTS: Dmean,SCR proved to be responsible for the effect of Dmean,par on FLOWPAR (P ≤ .03), while Dmean,non-SCR did not affect FLOWPAR (P ≥ .11). To illustrate, increasing Dmean,SCR by 10 Gy at a fixed Dmean,non-SCR reduced FLOWPAR by 0.02 mL/min (25%) after RT. However, if the opposite happened, no change in FLOWPAR was observed (0.00 mL/min [4%]). As expected, Dmean,sub was significantly associated with FLOWSMSL (P < .001). For example, increasing Dmean,sub by 10 Gy reduced FLOWSMSL by 0.07 mL/min (26%) after RT. Xerostomia scores were also affected by dose to the salivary glands. Dmean,SCR and Dmean,oral were associated with higher XERDAY scores (P ≤ .05), while Dmean,sub increased XERNIGHT scores (P = .01). For example, an increase of 10 Gy in Dmean,SCR raised XERDAY scores by 2.13 points (5%) after RT, while an additional 10 Gy in Dmean,subs increased XERNIGHT scores by 2.20 points (6%) after RT. Salivary flow was not only associated with radiation dose, but also with xerostomia scores in line with the salivary glands' functions; ie, FLOWPAR only influenced XERDAY (P < .001, 10.92 points lower XERDAY per 1 mL/min saliva), while FLOWSMSL affected XERDAY and XERNIGHT (P ≤ .004, 6.69 and 5.74 points lower XERDAY and XERNIGHT, respectively, per 1 mL/min saliva). Therefore, the observed relationships between dose and xerostomia were corrected for salivary flow. As hypothesized, Dmean,SCR only increased XERDAY scores via reducing FLOWPAR, whereas the effects of Dmean,oral on XERDAY and Dmean,sub on XERNIGHT were independent of salivary flow. CONCLUSIONS: Higher SCR region dose reduced parotid gland saliva production, subsequently resulting in higher daytime xerostomia scores. Consequently, this study supports the clinical implementation of stem cell sparing RT to preserve salivary flow with the aim of reducing the risk of xerostomia.

Prediction of Radiation-Induced Parotid Gland-Related Xerostomia in Patients With Head and Neck Cancer: Regeneration-Weighted Dose.

PURPOSE: Despite improvements to treatment, patients with head and neck cancer (HNC) still experience radiation-induced xerostomia due to salivary gland damage. The stem cells of the parotid gland (PG), concentrated in the gland's main ducts (stem cell rich [SCR] region), play a critical role in the PG's response to radiation. Treatment optimization requires a dose metric that properly accounts for the relative contributions of dose to this SCR region and the PG's remainder (non-SCR region) to the risk of xerostomia in normal tissue complication probability (NTCP) models for xerostomia. MATERIALS AND METHODS: Treatment and toxicity data of 1013 prospectively followed patients with HNC treated with definitive radiation therapy (RT) were used. The regeneration-weighted dose, enabling accounting for the hypothesized different effects of dose to the SCR and non-SCR region on the risk of xerostomia, was defined as Dreg PG = Dmean SCR region + r × Dmean non-SCR region, where Dreg is the regeneration-weighted dose, Dmean is the mean dose, and r is the weighting factor. Considering the different volumes of these regions, r > 3.6 in Dreg PG demonstrates an enhanced effect of the SCR region. The most predictive value of r was estimated in 102 patients of a previously published trial testing stem cell sparing RT. For each endpoint, Dreg PG, dose to other organs, and clinical factors were used to develop NTCP models using multivariable logistic regression analysis in 663 patients. The models were validated in 350 patients. RESULTS: Dose to the contralateral PG was associated with daytime, eating-related, and physician-rated grade ≥2 xerostomia. Consequently, r was estimated and found to be smaller than 3.6 for most PG function-related endpoints. Therefore, the contribution of Dmean SCR region to the risk of xerostomia was larger than predicted by Dmean PG. Other frequently selected predictors were pretreatment xerostomia and Dmean oral cavity. The validation showed good discrimination and calibration. CONCLUSIONS: Tools for clinical implementation of stem cell sparing RT were developed: regeneration-weighted dose to the parotid gland that accounted for regional differences in radiosensitivity within the gland and NTCP models that included this new dose metric and other prognostic factors.

Impact of sarcopenia on acute radiation-induced toxicity in head and neck cancer patients.

BACKGROUND AND PURPOSE: Sarcopenia is related to late radiation-induced toxicities and worse survival in head and neck cancer (HNC) patients. This study tested the hypothesis that sarcopenia improves the performance of current normal tissue complication probability (NTCP) models of radiation-induced acute toxicity in HNC patients. MATERIAL/METHODS: This was a retrospective analysis in a prospective cohort of HNC patients treated from January 2007 to December 2018 with (chemo)radiotherapy. Planning CT scans were used for evaluating skeletal muscle mass. Characteristics of sarcopenic and non-sarcopenic patients were compared. The impact of sarcopenia was analysed by adding sarcopenia to the linear predictors of current NTCP models predicting physician- and patient-rated acute toxicities. RESULTS: The cut-off values of sarcopenia in the study population (n = 977) were established at skeletal muscle index < 42.0 cm2/m2 (men) and < 31.2 cm2/m2 (women), corresponding to the lowest sex-specific quartile. Compared to non-sarcopenic patients, sarcopenic patients were more frequently smokers (61% vs. 48%, p < 0.001), had more often advanced stage of disease (stage III-IV, p = 0.004), higher age (67 vs. 63 years, p < 0.001) and experienced more pretreatment complaints, such as dysphagia (grade ≥ 2, p < 0.001). Sarcopenia remained statistically significant, next to the linear predictor, only for physician-rated grade ≥ 3 dysphagia (week 3-6 during RT, p < 0.01). However, sarcopenia did not improve the performance of these NTCP models (p > 0.99). CONCLUSION: Sarcopenia in HNC patients was an independent prognostic factor for radiation-induced physician-rated acute grade ≥ 3 dysphagia, which might be explained by its impact on swallowing muscles. However, addition of sarcopenia did not improve the NTCP model performance.

Parotid Gland Stem Cell Sparing Radiation Therapy for Patients With Head and Neck Cancer: A Double-Blind Randomized Controlled Trial.

PURPOSE: Radiation therapy for head and neck cancer frequently leads to salivary gland damage and subsequent xerostomia. The radiation response of the parotid glands of rats, mice, and patients critically depends on dose to parotid gland stem cells, mainly located in the gland's main ducts (stem cell rich [SCR] region). Therefore, this double-blind randomized controlled trial aimed to test the hypothesis that parotid gland stem cell sparing radiation therapy preserves parotid gland function better than currently used whole parotid gland sparing radiation therapy. METHODS AND MATERIALS: Patients with head and neck cancer (n = 102) treated with definitive radiation therapy were randomized between standard parotid-sparing and stem cell sparing (SCS) techniques. The primary endpoint was >75% reduction in parotid gland saliva production compared with pretreatment production (FLOW12M). Secondary endpoints were several aspects of xerostomia 12 months after treatment. RESULTS: Fifty-four patients were assigned to the standard arm and 48 to the SCS arm. Only dose to the SCR regions (contralateral 16 and 11 Gy [P = .004] and ipsilateral 26 and 16 Gy [P = .001] in the standard and SCS arm, respectively) and pretreatment patient-rated daytime xerostomia (35% and 13% [P = .01] in the standard and SCS arm, respectively) differed significantly between the arms. In the SCS arm, 1 patient (2.8%) experienced FLOW12M compared with 2 (4.9%) in the standard arm (P = 1.00). However, a trend toward better relative parotid gland salivary function in favor of SCS radiation therapy was shown. Moreover, multivariable analysis showed that mean contralateral SCR region dose was the strongest dosimetric predictor for moderate-to-severe patient-rated daytime xerostomia and grade ≥2 physician-rated xerostomia, the latter including reported alteration in diet. CONCLUSIONS: No significantly better parotid function was observed in SCS radiation therapy. However, additional multivariable analysis showed that dose to the SCR region was more predictive of the development of parotid gland function-related xerostomia endpoints than dose to the entire parotid gland.

Impact of sarcopenia on survival and late toxicity in head and neck cancer patients treated with radiotherapy.

BACKGROUND AND PURPOSE: Sarcopenia is emerging as an adverse prognostic factor for survival and complication risk in cancer patients. This study aims to determine the impact of sarcopenia on survival and late toxicity in a large cohort of head and neck squamous cell carcinoma (HNSCC) patients treated with definitive (chemo)radiotherapy ((C)RT). MATERIALS AND METHODS: HNSCC patients treated with definitive (C)RT from January 2007 to June 2016 were included. Sarcopenia was assessed from radiation planning computed tomography (CT) scans using skeletal muscles at level C3. The impact of sarcopenia on overall survival (OS) and disease-free survival (DFS) was evaluated using the Kaplan-Meier method. Multivariable association models were developed to assess the impact of sarcopenia on late toxicity. RESULTS: The study population was composed of 750 HNSCC patients. Cut-off values for sarcopenia were set at SMI < 42.4 cm2/m2 (men) and <30.6 cm2/m2 (women) corresponding lowest gender specific quartile. Sarcopenic patients had significantly poorer survival rates, especially those with lower performance status and locally advanced disease. In oropharyngeal cancer patients, survival was more determined by p16 status than by sarcopenia. In multivariable analysis, sarcopenia was associated with worse OS (HR 0.72, p = 0.012) and DFS (HR 0.67, p = 0.001). In multivariable association models, sarcopenia was associated with physician-rated xerostomia six months after treatment (OR 1.65, p = 0.027) and physician-rated dysphagia six and twelve months after treatment (OR 2.02, p = 0.012 and 2.51, p = 0.003, respectively). CONCLUSION: Sarcopenia in HNSCC patients receiving definitive (C)RT is an independent prognostic factor for worse survival outcomes and is associated with physician-rated toxicity.