Hypofractionated radiotherapy has the potential for second cancer reduction.
OBJECTIVE
A model for carcinoma and sarcoma induction was used to study the dependence of carcinogenesis after radiotherapy on fractionation.


METHODS
A cancer induction model for radiotherapy doses including fractionation was used to model carcinoma and sarcoma induction after a radiation treatment. For different fractionation schemes the dose response relationships were obtained. Tumor induction was studied as a function of dose per fraction.


RESULTS
If it is assumed that the tumor is treated up to the same biologically equivalent dose it was found that large dose fractions could decrease second cancer induction. The risk decreases approximately linear with increasing fraction size and is more pronounced for sarcoma induction. Carcinoma induction decreases by around 10% per 1 Gy increase in fraction dose. Sarcoma risk is decreased by about 15% per 1 Gy increase in fractionation. It is also found that tissue which is irradiated using large dose fractions to dose levels lower than 10% of the target dose potentially develop less sarcomas when compared to tissues irradiated to all dose levels. This is not observed for carcinoma induction.


CONCLUSIONS
It was found that carcinoma as well as sarcoma risk decreases with increasing fractionation dose. The reduction of sarcoma risk is even more pronounced than carcinoma risk. Hypofractionation is potentially beneficial with regard to second cancer induction.
Radiotherapy Hirslanden AG, Institute for Radiotherapy, Rain 34, Aarau, Switzerland. uschneider@vetclinics.uzh.ch
Uwe
U
Schneider
Jürgen
J
Besserer
Andreas
A
Mack
D019583:Dose Fractionation, Radiation; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008954:Models, Biological; D016609:Neoplasms, Second Primary / Q000209:etiology / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000209:etiology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D012307:Risk Factors