Biologic comparison of partial breast irradiation protocols.
OBJECTIVE
To analyze the dose/fractionation schedules currently used in ongoing clinical trials of partial breast irradiation (PBI) by comparing their biologically effective dose (BED) values to those of three standard whole breast protocols commonly used after segmental mastectomy in the treatment of breast cancer.


METHODS
The BED equation derived from the linear-quadratic model for radiation-induced cell killing was used to calculate the BEDs for three commonly used whole breast radiotherapy regimens, in addition to a variety of external beam radiotherapy, as well as high-dose-rate and low-dose-rate brachytherapy, PBI protocols.


RESULTS
The BED values of most PBI protocols resulted in tumor control BEDs roughly equivalent to a 50-Gy standard treatment, but consistently lower than the BEDs for regimens in which the tumor bed receives a total dose of either 60 Gy or 66 Gy. The BED values calculated for the acute radiation responses of erythema and desquamation were nearly all lower for the PBI schedules, and the late-response BEDs for most PBI regimens were in a similar range to the BEDs for the standard treatments.


CONCLUSIONS
Biologically effective dose modeling raises the concern that inadequate doses might be delivered by PBI to ensure optimal in-field tumor control.
Rosenstein
Barry S
BS
Department of Radiation Oncology, Mount Sinai School of Medicine, New York, NY 10029, USA. barry.rosenstein@mssm.edu
Lymberis
Stella C
SC
Formenti
Silvia C
SC
D001918:Brachytherapy; D001943:Breast Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D016014:Linear Models; D015412:Mastectomy, Segmental; D012062:Relative Biological Effectiveness