Assessment of Thyroid Lobe Dose in Breast Cancer Intraoperative Radiotherapy

Background: Breast cancer is the most common cancer among women. Considering the fact that a high dose is delivered in a single fraction of IORT, the evaluation of the dose at sensitive organs like thyroid is necessary. Objective: The current study has aimed to evaluate the received dose to thyroid lobes in the breast IORT technique.Material and Methods: A total of ۴۹ women with breast cancer undergoing IORT were enrolled in this cross-sectional study with census sampling. Immediately after tumor resection, a single dose of ۲۰ Gray at the applicator surface was delivered using ۵۰KV X-ray by an Intrabeam machine. The thyroid dose was detected using thermoluminescent detectors (TLD) ۱۰۰ at the mid-thyroid line, left and right lobes. Results: The dose at the right and left lobes of the thyroid gland as well as the mid-thyroid line was found to be ۴۰.۱۸±۳۵.۴۴ mGy, ۳۵.۵۰±۲۷.۳۲ mGy, and ۴۰.۶۱±۳۲.۴۷ mGy, respectively. The right lobe received a significantly higher absorbed dose compared to the left lobe when the right breast was under IORT treatment. The same trend was seen with the left lobe and left breast under IORT treatment (P=۰.۰۰۰۱ and P=۰.۰۱۸, respectively). The applicator size showed non-significant effects on the absorbed dose at the thyroid gland. Also, the applicator depth had a non-significant inverse effect on thyroid dose. Conclusion: According to our findings, the absorbed dose at each thyroid lobe depends on the under-treatment side as well as the applicator size and depth (applicator upper surface distance from the skin).

Keywords:

Breast cancer , Intraoperative radiotherapy , Thyroid , Radiotherapy Dosage , Thermoluminescent Dosimetry