Small Cell Lung Cancer: The Influence of Dose and Treatment Volume on Outcome

The treatment of small cell lung cancer is clearly enhanced by the addition of radiation therapy. Survival increases modestly while local thoracic failure as first site of progression is reduced from approximately 60% when chemotherapy alone is used to 30% after combined modality therapy. The variables of radiation dose and treatment volume seem to be important in the successful management of this disease. Local chest control appears to increase as doses are escalated from low levels (25 Gy) to moderate levels (45 to 50 Gy(. With about one third of patients experiencing local chest progression, one can speculate that higher radiation doses might be of value. However, at this time there is no proof that increased dose or dose intensity bears out this promise. Indeed, increasing dose intensity of radiotherapy, eg, twice-daily treatment, increases esophagitis, perhaps reduces local failure, but has not improved overall survival. Using larger total doses or altered fraction schemes must still be considered to be under investigation. To increase dose in a safe manner, reduction in the volume covered by radiation portals will likely need to take place. Modern trials suggest that prophylactic treatment of the radiographically or clinically negative contralateral hilum and/or supraclavicular nodal regions may not be necessary for survival or local control. Importantly, reducing treatment volumes may permit increasing doses without exceding normal tissue tolerance. Also, reduced volumes pave the way for further clinical trials that improve radiation dose delivery by better target definition and more conformal therapy.