Estimation of the α/β ratio for lower lip cancer treated with interstitial HDR brachytherapy

BackgroundA standard linear-quadratic (LQ) model is now routinely used for clinical data analysis and the prediction of the clinical effect of radiotherapy. The typical α/β values suggested in the literature range from 10 to 20Gy for most tumours and early responding normal tissues, and from 2 to 5Gy for late responding tissues.AimThe estimation of α/β ratio values for planoepithelial lower lip cancer.Materials/MethodsThe clinical material is based on the records of 25 patients undergoing radical treatment with interstitial brachytherapy: 19 patients were administered brachytherapy exclusively and 6 patients were treated postoperatively. The following stage arrangement was applied: T1 in 15 pts, T2 in 9 pts, N0 in 24 pts and N1 only in one T2 patient. Radiotherapy was based on HDR brachytherapy using the interstitial technique. Patients with positive margins after surgery were qualified for postoperative brachytherapy. The dose was either specified at the reference 80% isodose according to the Paris System or points calculated 3-5 mm from the macroscopic tumour. The average total dose was 38.3Gy, the number of fractions being 7 and the fraction dose 5.3Gy. The overall treatment time was 12 days. The average follow-up period was 30 months. A standard probit regression in conjunction with a linear-quadratic model was used.ResultsThe estimated value of the α/β ratio for lip cancer was 12Gy (±3.72*10−10 95% CI).ConclusionsThe estimated α/β ratio is consistent with α/β ratios published for squamous cell head and neck cancers