The value of the NSD formula in equation of acute and late radiation complications in normal tissue following 2 and 5 fractions per week in breast cancer patients treated with postmastectomy irradiation.

In 1978-1980, inclusive, all breast cancer patients referred for postmastectomy irradiation were treated by 2 fractions per week (73 patients) but due to a high incidence of late complications this fractionation schedule was changed from early 1981 to 5 fractions per week (66 patients) with dose adjustment according to the nominal standard dose (NSD) concept. The dose aim in both regimens was 1345 ret minimum target dose. This allowed a comparison of acute and late complications in the two patient groups treated to the same NSD value, but with different fractionation. The patients have been analysed with respect to acute and late reaction in the skin, subcutaneous tissue, lung and bone, as well as related complications, such as arm oedema and impairment of shoulder movement. Except for the acute skin reactions, all other endpoints could not be adequately predicted by the NSD formula. Thus, telangiectasia greater than or equal to grade 1 and skin fibrosis greater than or equal to grade 2 were found to be 75% and 67% in patients treated with the 2-fraction scheme versus 39% and 5% in patients treated with the 5-fraction scheme. In the 2-fraction regimen, a higher frequency of impairment of shoulder movement and arm oedema was found compared to the 5-fraction regimen, 38% versus 11% and 44% versus 33%, respectively. The acute lung reaction as well as late lung reaction were significantly more pronounced in the 2-fraction regimen than in the 5-fraction regimen (pneumonitis greater than or equal to grade 2, 43% versus 23%, and lung fibrosis greater than or equal to grade 2, 32% versus 17%, in the photon fields, respectively). Further, radiation-induced osteonecrosis in the ribs was significantly more frequent in patients treated with large dose per fraction (19% versus 2%). The data clearly demonstrates the danger by using the NSD formula in equation of two different fractionation schedules. This formula as well as other mathematical models can only be used with caution within the limitations defined by the underlying clinical and experimental data on which they have been derived.