Thyroid V30 Predicts Radiation-Induced Hypothyroidism in Patients Treated With Sequential Chemo-Radiotherapy for Hodgkin’s Lymphoma

Purpose Hypothyroidism (HT) is a frequent late side effect of Hodgkin’s lymphoma (HL) therapy. The purpose of this study is to determine dose–volume constraints that correlate with functional impairment of the thyroid gland in HL patients treated with three-dimensional radiotherapy. Methods and Materials A total of 61 consecutive patients undergoing antiblastic chemotherapy and involved field radiation treatment (median dose, 32 Gy; range, 30–36 Gy) for HL were retrospectively considered. Their median age was 28 years (range, 14–70 years). Blood levels of thyroid-stimulating hormone (TSH), free triiodo-thyronine (FT3), free thyroxine (FT4), and thyroglobulin antibody (ATG) were recorded basally and at different times after the end of therapy. For the thyroid gland, normal tissue complication probability (NTCP), dosimetric parameters, and the percentage of thyroid volume exceeding 10, 20, and 30 Gy (V10, V20, and V30) were calculated in all patients. To evaluate clinical and dosimetric factors possibly associated with HT, univariate and multivariate logistic regression analyses were performed. Results Eight of 61 (13.1%) patients had HT before treatment and were excluded from further evaluation. At a median follow-up of 32 months (range, 6–99 months), 41.5% (22/53) of patients developed HT after treatment. Univariate analyses showed that all dosimetric factors were associated with HT ( p < 0.05). On multivariate analysis, the thyroid V30 value was the single independent predictor associated with HT ( p = 0.001). This parameter divided the patients into low- vs. high-risk groups: if V30 was ≤ 62.5%, the risk of developing HT was 11.5%, and if V30 was >62.5%, the risk was 70.8% ( p < 0.0001). A Cox regression curve stratified by two levels of V30 value was created (odds ratio, 12.6). Conclusions The thyroid V30 predicts the risk of developing HT after sequential chemo-radiotherapy and defines a useful constraint to consider for more accurate HL treatment planning.