West Asia Organization for Cancer Prevention (WAOCP), APOCP's West Asia Chapter. Asian Pacific Journal of Cancer Prevention 1513-7368 24 11 2023 11 01 An Analytical Study to Determine Dose-Volume Threshold for Radiation Induced Hypothyroidism 3859 3866 90888 10.31557/APJCP.2023.24.11.3859 EN Kumar Pravesh Department of Radiation Oncology, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India. Pooja Sethi Department of Radiation Oncology, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India. 0000-0003-0663-6424 Sadish Kumar Kamalanathan Department of Endocrinology, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India. Manivannan Manavalan Department of Radiation Oncology, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India. Journal Article 2023 06 29 Objective: To determine radiation dose volume threshold in predicting the development of hypothyroidism in cancer patients following neck irradiation. Methods: This is a cross sectional follow up study for patients who had been previously irradiated, prior to enrolment in the study. We have done thyroid dose-volumetric analysis on 120 histologically proven cancer patients in the age group of 18-75 years who received neck irradiation as a part of their definitive or adjuvant radiotherapy with three-dimensional conformal or intensity-modulated radiotherapy technique (3D -CRT or IMRT) and completed at least six months post-radiotherapy. Primary tumor sites included carcinoma or lymphoma of the head and neck, breast, cervical, and upper thoracic esophagus, requiring neck irradiation. Results: The proportion of patients who tested positive for Radiation induced hypothyroidism (RIHT) was found to be 40%, with clinical hypothyroidism and subclinical hypothyroidism being 25.8% and 14.2%, respectively. Time to develop hypothyroidism peaks around two years. Mean thyroid gland dose (Dmean) >28 Gy, thyroid gland volume receiving 40 Gy dose (i.e. V40) >49% and age <50 years were found to be significant risk factors for the development of RIHT on binary logistic regression. RT dose >50 Gy and thyroid gland volume spared from 40 Gy (i.e. VS40) < 2.12cm3 were statistically significant predictors for RIHT on chi-square and (Receiver operating characteristic) ROC curve analysis respectively but not on regression analysis. Conclusion: Dose-volume threshold for the thyroid gland as Dmean <28 Gy and V40 <49% may prevent the development of RIHT. https://journal.waocp.org/article_90888_cdf5741d367e342b3eec776a2a8414b2.pdf