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Risk of Hypothyroidism in Women After Radiation Therapy for Breast Cancer

Authors
 Seo Hee Choi  ;  Jee Suk Chang  ;  Hwa Kyung Byun  ;  Nak-Hoon Son  ;  Chae-Seon Hong  ;  Namki Hong  ;  Ye-In Park  ;  Jihun Kim  ;  Jin Sung Kim  ;  Yong Bae Kim 
Citation
 INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS, Vol.110(2) : 462-472, 2021-06 
Journal Title
INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS
ISSN
 0360-3016 
Issue Date
2021-06
Abstract
Purpose: To study the hypothyroidism risk after adjuvant radiation therapy (RT) and the association of different RT targets with hypothyroidism risk.

Methods: We studied 4073 women treated with adjuvant RT for breast cancer from 2007 to 2016. The primary endpoint was hypothyroidism development after RT. Patients were divided and analyzed into 3 groups: whole breast (WB)-alone (n = 2468), regional node irradiation (RNI)-Lv.4 (n = 215; cranial border at the subclavian artery, according to the European Society for Radiotherapy and Oncology consensus guideline), and RNI-supraclavicular lymph node (SCL) (n = 1390; cranial border at the cricoid cartilage). In general, RNI-Lv.4 was used in the patients with high-risk pN0 and pN1 breast cancer. In auxiliary analysis, the mean thyroid dose was estimated in each group (total n = 600, 200 from each group). All the doses were converted to the equivalent dose in 2 Gy fractions (EQD2) with α/β ratios of 3.

Results: The median follow-up duration was 84 months (WB-alone, 84 months; RNI-Lv.4, 44 months; RNI-SCL, 91 months). The 3-year hypothyroidism incidence rate differed significantly between the RNI-SCL and WB-alone groups (2.2% vs 0.8%; Bonferroni corrected P [Pc] < .001) but not between the RNI-Lv.4 and WB-alone groups (0.9% vs 0.8%; Pc > .05). The Cox model revealed an adjusted hazard ratio of 2.25 (95% CI, 1.49-3.38) for RNI-SCL vs WB-alone, 1.69 (95% CI, 1.12-2.56) for adjuvant systemic therapies, and 2.07 (95% CI, 1.07-3.99) for age <60 years. In the subgroup analysis, the hypothyroidism risk became more prominent in patients aged <60 years. The mean exposure doses to the thyroid were 0.23 versus 1.93 versus 7.89 Gy (EQD2) for the WB-alone versus RNI-Lv.4 versus RNI-SCL groups (P < .001). No statistically different locoregional recurrence rates were seen between groups (5-year rate: <3%).

Conclusions: The risk of hypothyroidism increases after RNI-SCL for breast cancer but not after RNI-Lv 4. These data support routine contouring of the thyroid in the RNI setting, and future studies are required to develop optimal dose-volume constraints.
Full Text
https://www.sciencedirect.com/science/article/pii/S036030162034743X
DOI
10.1016/j.ijrobp.2020.12.047
Appears in Collections:
1. College of Medicine (의과대학) > Dept. of Internal Medicine (내과학교실) > 1. Journal Papers
1. College of Medicine (의과대학) > Dept. of Radiation Oncology (방사선종양학교실) > 1. Journal Papers
Yonsei Authors
Kim, Yong Bae(김용배) ORCID logo https://orcid.org/0000-0001-7573-6862
Kim, Jihun(김지훈) ORCID logo https://orcid.org/0000-0003-4856-6305
Kim, Jinsung(김진성) ORCID logo https://orcid.org/0000-0003-1415-6471
Byun, Hwa Kyung(변화경) ORCID logo https://orcid.org/0000-0002-8964-6275
Chang, Jee Suk(장지석) ORCID logo https://orcid.org/0000-0001-7685-3382
Choi, Seo Hee(최서희) ORCID logo https://orcid.org/0000-0002-4083-6414
Hong, Nam Ki(홍남기) ORCID logo https://orcid.org/0000-0002-8246-1956
Hong, Chae-Seon(홍채선) ORCID logo https://orcid.org/0000-0001-9120-6132
URI
https://ir.ymlib.yonsei.ac.kr/handle/22282913/184034
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