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. 2019 Jul;20(7):135-141.
doi: 10.1002/acm2.12668. Epub 2019 Jun 24.

Effect of dose constraint on the thyroid gland during locoregional intensity-modulated radiotherapy in breast cancer patients

Emel Haciislamoglu  1 , Emine Canyilmaz  1 , Sonay Gedik  2 , Ozlem Aynaci  2 , Lasif Serdar  2 , Adnan Yoney  1
Affiliations

Effect of dose constraint on the thyroid gland during locoregional intensity-modulated radiotherapy in breast cancer patients

Emel Haciislamoglu et al. J Appl Clin Med Phys. 2019 Jul.

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% (V30 < 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 (V10 , V20 , V30 , V40 , and V50 , 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 Dmean and V30 values were statistically significant (P < 0.05). When thyroid DC during breast cancer RT was applied to IMRT and HT, the TDmean and V30 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.

Keywords: breast cancer; dose constraint; supraclavicular radiotherapy; thyroid gland dose.

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Conflict of interest statement

The authors declare that there is no conflict of interest regarding the publication of this article.

Figures

Figure 1
Figure 1
The isodose distribution for the four plans in axial plane for a representative patient. Color‐wash threshold was set to 21 Gy. (a) IMRTDC(−); (b) IMRTDC(+); (c) HTDC(−); and (d) HTDC(+). IMRT, intensity modulated radiotherapy; HT, helical tomotherapy.
Figure 2
Figure 2
Dose‐volume histograms (DVH) comparison of the thyroid gland using FinF, IMRTDC(−), HTDC(−), IMRTDC(+), and HTDC(+) in a representative patient. IMRT, intensity modulated radiotherapy; HT, helical tomotherapy.
See this image and copyright information in PMC

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