Purpose: In this study, we investigated a novel dose-volumetric constraint for the parotid glands other than the mean dose constraint which is generally used as a dose-volumetric constraint for the parotid gland in the clinic.
Methods: A retrospective study was performed with 130 patients who received intensity-modulated radiation therapy (IMRT) for head-and-neck cancer. For all the patients, the mean doses of the bilateral parotid glands and the unilateral parotid gland were less than 25 Gy and 20 Gy, respectively, following the Quantitative Analyses of Normal Tissue Effects in the Clinic (QUANTEC) guideline. For each patient, volumes receiving more than 10 Gy (V10), V15, and V20 were calculated. After that, we calculated the volume that could divide the patients into two groups (a group with patients showing high probability of the Radiation Therapy Oncology Group (RTOG) Grade ≥1 toxicity for the parotid glands and the other group with patients showing less probability of the toxicity) with statistical significance (p-value < 0.05).
Results: When dividing the patients into two groups with criteria of 81.8% of V10, 27.6% of V15, and 18.2% of V20, the short-term toxicity rates of the groups below vs. above the criteria were 61.0% vs. 81.8%, 48% vs. 79.7%, and 47.6% vs. 78.0%, respectively. For the long-term toxicity rates, those were 25.0% vs. 48.5%, 7.2% vs. 36.2%, and 14.3% vs. 37.0%, respectively.
Conclusion: It seems that additional use of the dose-volumetric constraint, V15 less than 27.6%, during treatment planning for the head-and-neck cancer patients could reduce the RTOG Grade ≥1 toxicity rate of the parotid glands.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the Radiation Technology R&D program through the National Research Foundation of Korea funded by the Ministry of Science and ICT (2020M2D9A1093990 and 2020M2D9A1093992).
Tolerance Doses, Dose Volume Histograms