CCRT for non-small cell lung cancer: Sensitivity of clinical gains to organ tolerance restrictions

A method is described for allowing the entrance angles of beams to vary along the longitudinal axis of the target volume using a computer controlled radiation therapy (CCRT) treatment technique. The increase in tumor dose potentially available with this technique is evaluated for the case of a non-small cell carcinoma of the lung for which treatment is constrained by a clinically relevant tolerance condition. Tolerance is expressed in terms of that volume of unaffected contralateral lung allowed to receive > 20 Gy. The evaluation is repeated with small changes made to the constraining condition in order to explore the sensitivity of the dose gain to the definition of tolerance. For the chosen example, at least an additional 10 Gy could be prescribed to the tumor with the CCRT technique when the 20 Gy contralateral lung volume was held to less than 30%. A gain of 7 Gy was found when the 20 Gy volume was held to 27% and 1 Gy when the 20 Gy volume was reduced to 25%. CCRT treatment can result in a significant dose gain under a clinically relevant condition for tolerance. Its measured advantage strongly depends on the dose constraints specified. Sensitivity analysis is necessary to meaningfully evaluate the merits of alternative treatment techniques.