Prospective studies with the CRE formula of prolonged fractionation schedules.

Different dose schedules prospectively calculated with the Cumulative Radiation Effect (CRE) formula were used for irradiation of inoperable breast carcinomas. Fractionation with 2 X 260 rad and 2 X 450 rad twice a week, and total doses corresponding to CRE levels 1900 to 2300, were compared. The results showed that prolonged fractionation increased the tolerance of normal skin and the therapeutic ration with respect to early radiation reactions. Late reactions could not be assessed as yet because their development requires several years. With the prolonged course of treatment and 2 X 260 rad per week, no moist desquamation developed despite dose levels between 6800 and 9400 rad. Skin reactions were milder than those in the rapidly treated areas, indicating that the CRE formula cannot exactly predict acute skin reactions for very prolonged treatment schedules. The tumor regressed continuously during the irradiation schedule.