Office hours pulsed brachytherapy boost in breast cancer

Background and purpose: Radiobiological studies suggest equivalent biologic al effects between continuous low dose rate brachytherapy (CLDR) and pulsed brachytherapy (PB) when pulses are applied without interruption every hour . However, radiation protection and institute-specific demands requested th e design of a practical PB protocol substituting the CLDR boost in breast c ancer patients. An office hours scheme was designed, considering the CLDR d ose rate, the overall treatment timer pulse frequency and tissue repair cha racteristics, Radiobiological derails are presented as well as the logistic s and technical feasibility of the scheme after treatment of the first 100 patients. Materials and methods: Biologically effective doses (BEDs) were calculated according to the linear quadratic model for incomplete repair. Radiobiologi cal parameters included an alpha/beta value of 3 Gy for normal tissue late effects and 10 Gy for early normal tissue or tumour effects. Tissue repair half-time ranged from 0.1 to 6 h. The reference CLDR dose rate of 0.80 Gy/h was obtained retrospectively from analysis of patients' data. The treatmen t procedure was evaluated with regard to variations in implant characterist ics after treatment of 100 patients. Results: A PB protocol was designed consisting of two treatment blocks sepa rated by a night break. Dose delivery in PB was 20 Gy in two 10 Gy blocks a nd, for application of the 15 Gy boost, one 10 Gy block plus one 5 Gy block . The dose per pulse was 1.67 Gy, applied with a period time of approximate ly 1.5 h. An inter-patient variation of 30% (1 SD) was observed in the inst antaneous sourer: strength. Taking also the spread in implant size into acc ount, the net variation in pulse duration amounted to 38%. Conclusion: An office hours PB boost regimen was designed for substitution of the CLDR boost in breast-conserving therapy on the basis of the BED. Fir st treatment experience shows the office hour regimen to be convenient to t he patients and no technical perturbations were encountered. (C) 2001 Elsev ier Science Ireland Ltd. All rights reserved.