Should we consider thyroid gland as an organ at risk in carcinoma breast patients receiving adjuvant radiation by conformal technique? A single institute dosimetric study.

BACKGROUND

The most common malignancy among Indian women is carcinoma of the breast. In the management of breast cancer (BC), radiation therapy (RT) is given to breast or chest wall and supraclavicular lymph nodal (SCLN) area, with at least part of the thyroid receiving RT dose.There is an increased incidence of hypothyroidism (HT) among BC patients after RT involving the SCLN area. Moreover, the incidence of HT in India is higher than in the West. The aim of our study is to dosimetrically evaluate the thyroid doses during RT for BC.

METHODS

This is a single institute prospective study (n = 131). Radiation was planned by three-dimensional conformal radiation therapy (3D-CRT) technique and dose-volume parameters for thyroid gland were noted.

RESULTS

The median thyroid gland volume was 7.4 cc. The median of the mean dose to thyroid gland was 2068 cGy, V10 was 42%, and V40 was 33%. In other studies, BC patients with smaller thyroid gland were more prone to HT (volume <8 cc). In our study, we have seen that the median thyroid volume was 7.4 cc.

CONCLUSION

Our study showed a lower mean dose to the thyroid gland and smaller volume thyroid glands than in the literature. As the incidence of HT is higher in India, compared to the west and our patients had small volume thyroid glands, they could be at higher risk of developing HT RT. So BC patients should be monitored for HT and should be given a dose constraint while planning RT.