Determination of therapeutic gain factor for chemo-radiotherapy of head and neck cancers on the basis of linear quadratic model

An analysis of Head and neck cancer patients treated by radiotherapy (RT) alone (114 patients) and by chemoradiotherapy (RT + CT) (72 patients) was carried out. Dose Enchancement Factor (DEF) and Therapeutic Gain Factor (TGF) values were evaluated on the basis of Linear Quadratic model. Radiation doses for RT and RT + CT groups varied from 40 - 77 Gy and 35 - 71 Gy respectively. 750 - 100 mg per cycle of 5-FU (induction/concurrent) was used. ERD values were evaluated with (α(β)) values of 2.5 and 6 Gy for late complications and tumour response. ERD vs late complication rate and response rate curves were drawn for RT, RT+CT (7 cycles), RT+CT (6 cycles) and RT+CT (cumulative). DEF values for response rate were 0.95, 0.95 and 0.82 for the three RT+CT groups respectively. Similarly DEF values for late complication rate were evaluated as 0.87, 0.93 and 0.88. TGF values for RT+CT were found to be 1.09, 1.02 and 0.93. The TGF values indicates lack of significant influence of CT on the clinical outcome