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Cancer risks in thyroid cancer patients.
1Department of General Oncology, Radiumhemmet, Karolinska Hospital, Stockholm, Sweden.
British Journal of Cancer
|July 11, 1991
Summary
Thyroid cancer patients treated with radioactive iodine (131I) showed a slightly increased overall cancer risk. Higher doses of 131I correlated with elevated cancer risk, but specific cancer types were not definitively linked to high-dose exposures.
Area of Science:
- Oncology
- Radiology
- Epidemiology
Background:
- Thyroid cancer treatment often involves radioactive iodine (131I).
- Understanding long-term cancer risks associated with 131I therapy is crucial for patient management and radiation safety.
- Previous studies have yielded varying results regarding the carcinogenicity of 131I.
Purpose of the Study:
- To investigate the long-term cancer risks in patients treated for thyroid cancer with 131I compared to those treated by other means.
- To assess the relationship between radiation dose from 131I and the risk of developing subsequent cancers.
- To evaluate the consistency of cancer risk over time and explore potential dose-response relationships.
Main Methods:
- A cohort study involving 834 patients treated with 131I and 1,121 patients treated by other methods in Sweden (1950-1975).
- Record-linkage with the Swedish Cancer Register to identify new cancer diagnoses occurring more than two years after therapy.
- Calculation of standardized incidence ratios (SIR) with 95% confidence intervals (CI) to compare cancer risks between groups and assess dose-response relationships.
Main Results:
- Patients treated with 131I had a significantly increased overall standardized incidence ratio (SIR) for subsequent cancers (SIR=1.43) compared to those not receiving 131I (SIR=1.19).
- In females treated with 131I, elevated SIRs were observed for tumors of the salivary glands, genital organs, kidney, and adrenal gland.
- A significant trend of increasing cancer risk with higher activities of 131I was noted, particularly for doses >= 3,664 MBq (SIR=1.80). Organs receiving >1.0 Gy showed a significantly increased risk (SIR=2.59).
Conclusions:
- Radioactive iodine therapy for thyroid cancer is associated with a moderately increased risk of developing other cancers, particularly in organs receiving higher radiation doses.
- While no specific cancers were definitively linked to high-dose 131I, the observed trend suggests a dose-dependent risk.
- The findings support the current practice of extrapolating high-dose radiation effects to lower-dose situations for low linear energy transfer (LET) radiation, suggesting it is unlikely to underestimate hazards.