Local control in t3 laryngeal cancer treated with radical radiotherapy, time dose relationship: the concept of nominal standard dose and linear quadratic model

Abstract

In a retrospective study of the Dutch cooperative head and neck group 104 evaluable patients with a T3NxMO squamous cell carcinoma of the larynx were treated primarily with a full course of radiotherapy. The results of treatment are presented in terms of locoregional control. The actuarial 3-year local control rate was 53%. Regional control was 77% for node positive patients and 96% for NO patients ( p = 0.01). Surgical salvage was successful in 53% of cases with a local recurrence and in 3/8 regional recurrences, resulting in an ultimate locoregional control rate of 83% for NO patients and 68% for N+ patients. A uni- and multivariate analysis of local control rate versus total dose, nominal standard dose, and extrapolated response dose has been done. To calculate extrapolated response dose the linear quadratic equation was used, assuming an a/b of 10 and a potential doubling time of clonogenic cells of 3, 5, and 7 days. In multivariate analysis the extrapolated response dose with a potential doubling time of 5 days was the only independent prognostic factor for local control ( p = 0.069) and ultimate locoregional control ( p = 0.00 15). Nominal standard dose showed no dose-response relationship. Based on the S-shaped dose response curve, using the LQ model, several therapeutical options are discussed.