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

Abstract

Background

A 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.

Aim

The estimation of α/β ratio values for planoepithelial lower lip cancer.

Materials/Methods

The 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.

Results

The estimated value of the α/β ratio for lip cancer was 12Gy (±3.72^*10⁻¹⁰ 95% CI).

Conclusions

The estimated α/β ratio is consistent with α/β ratios published for squamous cell head and neck cancers.