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Residual DSB in skin following a 4Gy dose were not significantly associated with risk of late adverse effects of breast radiotherapy, although exploratory analyses suggested an association in severely affected individuals. By contrast, a significant association was detected based on the in vitro response of lymphocytes.

Purpose: To evaluate the accuracy of an external immobilisation system in patients receiving radiotherapy for prostate cancer.Methods: Portal Imaging data were audited in 20 patients treated using an in-house immobilisation system and 20 patients treated using an indexed commercial immobilisation system (CombifixÔ). Individual and group random and systematic errors were calculated to determine the accuracy of set-up using skin marks alone and with a no-action-level protocol. Results:The initial results showed a larger systematic error in the CombifixÔ in the anterior-posterior direction (2.7 mm) compared with the in-house system (1.5 mm). The possible source of this was identified as the difficulty in accurately aligning the laser to a curved couch top prior to setting the isocentre height. A change in the process of setting the isocentre was introduced, and comparable baseline set-up accuracy was achieved. This was with a systematic error of 2.0 mm and a random error 1.5 mm of patient position set-up error with skin marks alone, and using the CombifixÔ. The systematic errors were further reduced to <1 mm with an off-line no-action-level protocol. Conclusion:Using the CombifixÔ system a high level of set-up accuracy was reproduced in routine daily practice.