SU‐FF‐T‐488: Estimation of Alpha/beta Ratio for Benign Tumor of the Brain From Clinical Data

Purpose: To estimate a plausible α/β value for benign tumor of the brain from clinical data. Materials and Methods: Forty‐five articles published between 1997 and 2008 were selected for the analysis. These included publications on conventional external beam radiotherapy, fractionated stereotactic radiotherapy and stereotactic radiosurgery. Reports on combined radio‐chemotherapy were excluded. Three methods for α/β estimation were compared. These included two iso‐effect scheme matching, reciprocal iso‐effect dose plot and two‐step graphical matching. A 5‐year tumorcontrol rate (TCR) % was chosen as an end point for the analysis. The α/β values estimated by different methods were tested for their differences by t‐test. Results: The α/β values obtained from reciprocal iso‐effect dose plot, two iso‐effect scheme matching and two‐step graphical matching were 3.53 Gy (95% CI 2.08–4.98 Gy), 2.71 Gy (95% CI 2.67–2.75 Gy) and 2.67 Gy (95% CI 1.87–3.47 Gy), respectively. Statistical analysis showed no significant difference among α/β values obtained from these methods (p⩾ 0.14). Noteworthily, plausible estimate of α/β determined by the two iso‐effect scheme matching and two‐step graphical matching could be obtained only when the size of dose fraction differed by at least a factor of seven folds. Conclusion: The average α/β estimate (2.97 Gy, 95% CI 2.42–3.52) for benign braintumor obtained in this study was in remarkable agreement with the typical value of 2–3 Gy for the late responding tissue.