Radiotherapy for lung cancer: Target splitting by asymmetric collimation enables reduction of radiation doses to normal tissues and dose escalation

Purpose: This study was performed to develop a method of reducing the radia tion doses to normal thoracic tissues, increasing the target dose, especial ly in the primary radiotherapy of non-small cell lung cancer (NSCLC), and t o evaluate acute/subacute toxicity of dose escalation. Methods and Materials: From December 1998 to March 1998, the technique of t arget splitting has been applied to 58 patients. In this period, 30 patient s were treated with doses > 80 Gy (ICRU-specification, mean 85.1 Gy, range 80.1-90.2 Gy). The target volume is split into a cranial part (e.g., upper mediastinum) and a caudal part (e.g., primary tumor and middle mediastinum) . Both volumes are planned and treated independently, using conformal irrad iation techniques for both parts with half-collimated fields to prevent ove r- or underdosage in the junction plane. After fine-adjustment of the jaws, a verfication film, exposed in a polymethylmethacrylate (PMMA) phantom, de monstrates the homogeneity of dose in the entire target volume. For compari son With conventional techniques, planning to identical doses is performed for 5 patients. Dose-volume histograms (DHVs) for normal lung tissue are pr esented for both methods. Results: The irradiated volume of normal tissue of the ipsilateral lung can be lowered at dose levels greater than or equal to 65, greater than or equ al to 45 Gy, and greater than or equal to 20 Gy to values of 37% (range 25- 54%), 49% (range 46-54%), and 86% (range 55-117%), respectively. Other orga ns at risk, such as heart or esophagus, fan also be spared significantly. O nly 1 patient showed a transient grade 3 toxicity (pneumonitis), and there where no grade 4 acute/subacute side-effects. Two patients with Stage III A central tumors in close proximity to the large vessels died due to a pulmo nary hemorrhage 2 and 4 months after therapy, respectively. No patient deve loped esophagitis. Antimycotic prophylaxis for esophagitis and posttherapeu tic steroid prophylaxis for pneumonitis for several weeks were routinely us ed. Conclusion: The technique of target splitting by asymmetric collimation hel ps to increase conformation, and thus enhances the sparing of normal tissue s. It can be used whenever there is a marked difference in the shape of the planning target volume (PTV) in a cranio-caudal direction. This technique can principally be handled with 2D-planning systems, because it is coplanar . We consider target splitting as an important tool for dose escalation in the primary radiotherapy of NSCLC, that should also be used for other lung cancer patients necessitating moderate doses only. (C) 1999 Elsevier Scienc e Inc.