Second cancer after radiotherapy, 1981–2007

Abstract 

Background and purpose

Today, there is growing concern about radiotherapy induced secondary malignancies. We analysed the incidence and dose dependence of second cancer.

Material and methods

The study includes 12,000 one-year survivors of radiotherapy, treated between 1981 and 2007. For risk estimates a public databank on cancer in Germany served as reference. Contralateral second breast cancer, second oesophageal and colorectal cancer were analysed with retrospective dosimetry. GI-tract data were used for risk modelling.

Results

The incidence rate of second cancers (493 cases) was ∼1% per year. Contralateral breast cancer was the most frequent entity (relative risk RR=2.8). The scatter-dose gradient (2–3Gy) across the contralateral breast did not cause a detectable risk gradient. There was an increased risk for second head and neck cancer (RR=5.1) and for male oesophageal cancer (RR=5.8). For both entities, dose response modelling with case-control data predicted maximum curves with peak induction at 1–5Gy and positive excess absolute risk values at high doses.

Conclusions

A survey of second cancer after radiotherapy requires follow-up over decades. Preliminary dose response modelling albeit with low case numbers suggests an increased risk from multiportal techniques. To improve risk assessment, prospective out-of-field dosimetry and long-term multicentre data collection are recommended.

Keywords: Radiotherapy, Peripheral dose, Radiation risk, Follow-up study, Cancer epidemiology, Risk models