Extrapolated response dose as a potential tool in radiotherapy and chemo-radiotherapy of head and neck cancers.

An analysis of head and neck cancer patients treated by radiotherapy (RT) alone (114 patients) and by chemo-radiotherapy (RT + CT) (115 patients) was carried out; the doses varied from 40-77 Gy and 35-71 Gy in RT and RT + CT groups respectively. The chemotherapy (CT) (induction/concurrent) drugs used were 5-FU, cisplatin, methotrexate either single or in combination. Extrapolated response dose values were evaluated with alpha/beta values of 10, 2.5 and 6 Gy for acute, late complications and tumour response, respectively. Dose enhancement factor (DEF) and Therapeutic gain factor (TGF) values were evaluated on the basis of ERD for patients receiving 5-FU RTCT (72 patients). 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 1.09, 1.02 and 0.93. TGF values indicated lack of significant influence of CT on clinical outcome. The correlation of ERD with late complication, response and status at last follow up (NED) was statistically significant for both groups (P < 0.01). ERD did not correlated with acute complication in RT group (P > 0.01). From the present analysis, in RT + CT treatments of head and neck cancers, an ERD value of 69 Gy is suggested as the limit for an acceptable 5% late complication rate.

Late radiation induced laryngeal oedema in the treatment of vocal cord cancer: analysis using the linear quadratic model.

The incidence of late complications for different size of dose per fraction is analysed in 208 cases with squamous cell carcinoma of the vocal cord. The series comprised 156 cases with T1 and 52 cases with T2 lesions. Radical radiotherapy was given with three different regimens having dose per fraction as 3.33, 2.5 and 2.25 Gy. There were 46 cases with persisting radiation induced laryngeal oedema. Using two different statistical methods, an alpha/beta value of 2.38 Gy of linear quadratic model was estimated for late complications of vocal cord. The analysis indicate the increased incidence of late complications with size of dose per fraction. Relevance of linear quadratic model for the prediction of late complication is demonstrated in the present study.