LAUSR

Purpose Radiotherapy of paediatric patients comes at the expense of increased secondary cancer risk. This study examines whether the use of a 1 mm lead shielding during volumetric-modulated arc therapy (VMAT) for paediatric brain cancer can reduce the secondary cancer risk for the thyroid and breast. Methods Coplanar 6 MV VMAT plans were prepared for two anthropomorphic phantoms resembling a 1-year and 5-year old girl, for two different PTV sizes (2 cm and 5 cm diameter), simulating post-operative radiotherapy of an ependymoma in the posterior fossa. Out-of-field doses to the thyroid and breast were measured using thermoluminescence dosimeters. The phantoms were subject to three fractions (1,8 Gy each), with and without 1 mm lead shielding of the torso. The measured doses were used to calculate lifetime attributable risks for cancer incidence, for the total treatment dose of 54 Gy, in accordance with the BEIR VII report. 1 Results Applying lead shielding yielded dose reductions of 8–18% for the thyroid and 12–18% for the breast. The results were statistically significant (Student’s t-test, significance level p  Conclusions Lead shielding of the phantoms resulted in a systematic decrease in the measured doses to the thyroid and breast, reducing the lifetime attributable risks for cancer incidence. The results hereby suggest that a 1 mm thick lead rubber blanket might be a clinically feasible solution for reducing the risk of secondary cancer in paediatric radiotherapy patients.