Prophylactic low-dose post-operative orthovoltage radiotherapy in stage II breast cancer

Between the years 1974 and the beginning of 1977, 199 patients with stage II infiltrating duct carcinoma of the breast were treated with post-operative radiation, using a 250 kVp X-ray machine. Three treatment schedules were used consisting of 22, 26.2 and 29.6 Gy (2200, 2620 and 2960 rad) total tumour dose, calculated at 2 cm depth, with 5, 3 and 3 fractions a week respectively. The frequency of local recurrences, mainly in the chest wall, were 20.3%, 8.3% and 8.1% respectively. The latter two frequencies were not different from those reported for the commonly used high dose treatments of 45-60 Gy (4500-6000 rad) delivered either as given doses or tumour doses. An approximate 70% five year survival rate was similar in the three groups and does not differ from results observed with high doses. Low dose treatment is advantageous, because it has fewer complications and it can be delivered in a smaller number of sessions, making it more convenient to the patient, without loss of efficacy. The results presented of the low dose treatment may reflect the existence of an optimal dose level of radiation.