Abstract
OBJECTIVES: Our aim was to compare cancer incidence in a cohort exposed in childhood (1950-63) to a therapeutic dose of radiation in the North of Portugal and followed-up until the end of 2012, with the incidence rates for the same age and sex in the general population. METHODS: A population-based North Region cancer registry (RORENO) was used to assess which members of the cohort developed cancer. The association between radiation exposure and overall and specific cancer sites was evaluated using standardised incidence ratios (SIR). RESULTS: Over the full follow-up period, 3357 individuals of the 5356 original tinea capitis (TC) cohort (63%) were retrieved in the RORENO, and 399 new cancer cases were identified, representing an increased risk of 49% when compared with the general population (SIR = 1.49; 95% CI: 1.35-1.64). The risk was slightly higher in males than in females (SIR = 1.65; 95% CI: 1.43-1.89 vs SIR = 1.35; CI = 1.17-1.55). The risk was slightly higher in the individuals exposed to a higher radiation dose (SIR = 1.78; 95% CI: 1.22-2.51 for ≥630 R vs SIR = 1.46; 95% CI: 1.31-1.62 for 325-475 R). In females, there was an excess cancer risk in all cancers with the higher radiation dose (SIR = 2.00; 95% CI: 1.21-3.13 for ≥630 R vs SIR = 1.30; 95% CI: 1.11-1.51 for 325-475 R) which was not observed in males, and for combined dose categories significantly raised SIRs for thyroid and head and neck cancer, suggesting a possible higher radiosensitivity of females. An increased risk was also observed for some cancers located far from the irradiated area. CONCLUSIONS: The results suggest an association between radiation exposure and later increased cancer risk for cancers located near the radiation exposed area, mainly thyroid, and head and neck cancers. Further studies are necessary to disentangle possible non-radiation causes for distant cancers increased risk. ADVANCES IN KNOWLEDGE: This paper shows a possible association between childhood X-ray epilation and increased risk of cancer which was not previously investigated in the Portuguese TC cohort.