Biologically effective dose-response relationship for breast cancer treated by conservative surgery and postoperative radiotherapy.
OBJECTIVE
To find a biologically effective dose (BED) response for adjuvant breast radiotherapy (RT) for initial-stage breast cancer.


METHODS
Results of randomized trials of RT vs. non-RT were reviewed and the tumor control probability (TCP) after RT was calculated for each of them. Using the linear-quadratic formula and Poisson statistics of cell-kill, the average initial number of clonogens per tumor before RT and the average tumor cell radiosensitivity (alpha-value) were calculated. An alpha/beta ratio of 4 Gy was assumed for these calculations.


RESULTS
A linear regression equation linking BED to TCP was derived: -ln[-ln(TCP)] = -ln(No) + alpha(*) BED = -4.08 + 0.07 (*) BED, suggesting a rather low radiosensitivity of breast cancer cells (alpha = 0.07 Gy(-1)), which probably reflects population heterogeneity. From the linear relationship a sigmoid BED-response curve was constructed.


CONCLUSIONS
For BED values higher than about 90 Gy(4) the radiation-induced TCP is essentially maximizing at 90-100%. The relationship presented here could be an approximate guide in the design and reporting of clinical trials of adjuvant breast RT.
Plataniotis
George A
GA
Department of Oncology, Aberdeen Royal Infirmary, Aberdeen, United Kingdom. george.plataniotis@nhs.net
Dale
Roger G
RG
D000465:Algorithms; D001943:Breast Neoplasms / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D016014:Linear Models; D015412:Mastectomy, Segmental; D016012:Poisson Distribution; D011836:Radiation Tolerance; D018714:Radiotherapy, Adjuvant; D016032:Randomized Controlled Trials as Topic; D012062:Relative Biological Effectiveness