Radiation Oncology/Toxicity/Thyroid

Hypothyroidism

Head & Neck Cancer

U of Florida; 2005 PMID 15923797 -- "Thyroid function should be monitored following radiotherapy to the low neck." (Garcia-Serra A, Amdur RJ, Morris CG, Mazzaferri E, Mendenhall WM. Am J Clin Oncol. 2005 Jun;28(3):255-8.)
- Retrospective. 504 patients whose RT fields included the thyroid gland and defined as TSH >= 4.5 mIU/L.
- Outcome: 5-year hypothyroidism all patients 22% (42% in those patients with documented post-treatment TSH levels), 10-year 49% of all patients (74% in those patients with documented post-treatment TSH)
- Recommendations: Check Serum TSH q6 months for the first 5 years and yearly thereafter.

Cleveland Clinic; 2001 PMID 11753963 -- "Hypothyroidism: a frequent event after radiotherapy and after radiotherapy with chemotherapy for patients with head and neck carcinoma." (Mercado G, Cancer. 2001 Dec 1;92(11):2892-7.)
- Retrospective. 143 patients, H&N cancer, RT or chemo-RT. TSH measured regularly. Median F/U 4.4 years
- Outcome: 5-year hypothyroidism 48%, 8-year 67%. Median time-to-development 1.4 years
- Conclusion: Incidence of hypothyroidism higher than generally reported

MD Anderson; 2008 PMID 18213620 -- "Risk of hypothyroidism in older breast cancer patients treated with radiation." (Smith GL, Cancer. 2008 Mar 15;112(6):1371-9. doi: 10.1002/cncr.23307.)
- SEER analysis, 1992-2002. Stage 0-III breast cancer and cancer-free controls
- Outcome: 5-year incidence of hypothyroidism 14% identical among non-irradiated, irradiated with N0, and irradiated with 4+ LN. After adjustment for sociodemographic/clinical characteristics, no difference between irradiated N0 and irradiated 4+ LN (HR 1.04) but both groups significantly higher than non-irradiated patients (HR 1.21, SS)
- Conclusion: Development of hypothyroidism common in breast cancer survivors treated with radiation; SCV irradiation doesn't appear to amplify risks