The single shot partial breast irradiation (SSPBI) trial was designed as a prospective Phase
II "single-arm study". The use of a single dose tumor bed is expected to be very effective in
terms of tumor control, but it could increase the incidence of radiation induced erythema.
Therefore, the investigators assumed that a decreased DNA repair capability, as well as a
reduced detoxification of the damage caused by oxidative stress could explain the increased
acute toxicity, i.e. a higher incidence of erythema after a single dose. For this reason the
investigators decided to investigate SNPs of genes involved in antioxidant and DNA damage
repair pathways such as GST, XRCC1, XRCC3 and RAD51.
The investigators assumed an erythema rate of 20% and 54% in patient groups at low and high
risk, respectively, (groups were identified based on the absence/presence of the above
polymorphisms alone or in combination), thus the minimum sample size was 56 patients with
α=0.05, 2-tailed test and a power of the study of 80%.