Abstract
The aim of the present study was to compare radiation dose received by thyroid gland using different radiotherapy (RT) techniques with or without thyroid dose constraint (DC) for breast cancer patients. Computerized tomography (CT) image sets for 10 patients with breast cancer were selected. All patients were treated originally with opposite tangential field‐in field (FinF) for the chest wall and anteroposterior fields for the ipsilateral supraclavicular field. The thyroid gland was not contoured on the CT images at the time of the original scheduled treatment. Four new treatment plans were created for each patient, including intensity‐modulated radiotherapy (IMRT) and helical tomotherapy (HT) plans with thyroid DC exclusion and inclusion (IMRTDC(−), IMRTDC(+), HTDC(−), and HTDC(+), respectively). Thyroid DCs were used to create acceptable dose limits to avoid hypothyroidism as follows: percentage of thyroid volume exceeding 30 Gy less than 50% (V 30 < 50%) and mean dose of thyroid (TDmean) ≤ 21 Gy. Dose‐volume histograms (DVHs) for TDmean and percentages of thyroid volume exceeding 10, 20, 30, 40, and 50 Gy (V 10, V 20, V 30, V 40, and V 50, respectively) were also analyzed. The Dmean of the FinF, IMRTDC(−), HTDC(−), IMRTDC(+) and HTDC(+) plans were 30.56 ± 5.38 Gy, 25.56 ± 6.66 Gy, 27.48 ± 4.16 Gy, 18.57 ± 2.14 Gy, and 17.34 ± 2.70 Gy, respectively. Median V30 values were 55%, 33%, 36%, 18%, and 17%, for FinF, IMRTDC(−), HTDC(−), IMRTDC(+), and HTDC(+), respectively. Differences between treatment plans with or without DC with respect to D mean and V 30 values were statistically significant (P < 0.05). When thyroid DC during breast cancer RT was applied to IMRT and HT, the TDmean and V 30 values significantly decreased. Therefore, recognition of the thyroid as an organ at risk (OAR) and the use of DCs during IMRT and HT planning to minimize radiation dose and thyroid volume exposure are recommended.
Highlights
Breast cancer is the second most common cancer nowadays, after lung cancer.[1]
Some studies have reported the occurrence of RT‐induced hypothyroidism at high radiation doses (e.g., ≥30 Gy),[21,25] Dorri et al.[3] observed no significant differences in thyroid hormone levels before and after RT in breast cancer patients, further highlighting the contradictory findings regarding RT’s effects on thyroid function
During the Computerized tomography (CT) scan, each patient was in a supine position on a breast board, adjusted to achieve a flat chest wall with the head turned away from the side of treatment and the ipsilateral arm placed above the head
Summary
Breast cancer is the second most common cancer nowadays, after lung cancer.[1]. Surgery is one of the most clinically beneficial procedures for treatment of breast cancer. Thyroid gland is very sensitive, important and the largest pure endocrine gland in our body and more importantly its hormones play a very significant role in metabolism, development, growth, overall energy expenditure, and a large number of body organs functions.[7,8] Primary hypothyroidism is a well known side effect of curative RT in patients with head and neck cancer and Hodgkin lymphoma,[9,10,11,12] whose RT portals usually encompass the entire thyroid.[13,14,15,16] limited data are available regarding hypothyroidism in patients with breast cancer treated with locoregional RT wherein the treatment field includes only part of the thyroid.[17,18,19,20,21]
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