Results of multi-field conformal radiation therapy of non-small cell lung cancer using multi-leaf collimator beams

Purpose/Objective: Several radiation dose escalation studies suggest improvement in local-regional control and possible survival in patients with inoperable non-small cell lung cancer (NSCLC). Delivering doses greater than 60 Gy with conventional AP/PA and opposing off-cord obliques and addition of concurrent chemotherapy have resulted in higher normal tissue toxicity. We have developed a multi-field conformal technique using a multi-leaf collimator which allows better delineation of the target while sparing the normal tissues from receiving high radiation doses. Our objective was to evaluate the clinical end points including toxicity using the PFTs and SPECT scan, local-regional control, and survival. Materials and Methods: Treatment planning CT scans were performed in 45 patients with inoperable NSCLC to obtain image data for five field beams-eye view planning of treatment portals. The target volume (TV) was defined as the gross tumor volume (GTV) on CT scan plus a margin of 1-2.0 cm including regional involved lymphnodes (>1.0 cm). Each multi-leaf collimator was positioned from the GTV widest projection in the beams eye view. To minimize areas of overlap in normal lung, a minimum 30 deg. hinge incident angle was set between adjacent beams. The beams were purposely set un-opposed to minimize the integral dose to sections of the irradiated normal lung in the transit volume. Patients were evaluated with pretreatment PFTs and SPECT perfusion scans for baseline data. In several patients SPECT scans were used to identify and minimize the volume of functioning lung in the transit volume of each field. Dose/Volume histogram (DVH) analysis was carried out to evaluate the cumulative dose to lungs, heart, and spinal cord. Thirty patients were treated from 1/94 to 11/95. 64.5% these patients received concurrent chemotherapy (Taxol/Carboplatin or Cisplatin/VP-16). Median dose of radiation was 6080 cGy (5000- 6440 cGy) in 180 cGy fractions. Median follow-up was 0.45 years (0 - 1.93 years). Patients were routinely followed with CXR, PFTs, and SPECT perfusion scans at 1, 3, 6, and 12 months following radiation therapy. Acute and late normal tissue toxicity was graded using the RTOG scale. Results: The median survival was 0.99 years. 12.5% of patients receiving chemotherapy developed grade 3 or higher esophagitis as compared to no patients treated with RT alone. 6.8% of irradiated patients developed grade 1-2 pneumonitis. No patient developed grade 3 or greater pneumonitis. These toxicities were correlated with PFTs and SPECT scans. Of the 11 patients who had serial PFTs, one had a decrease in FEV1, FVC, and DLCO. This was correlated with a matched decrease in ventilation and perfusion on SPECT scan. In addition DVH analysis clearly showed a significant reduction in the volume of both lungs receiving doses in excess of 50% of the tumor target dose delivered by the five field conformal RT, compared to the conventional AP/PA and off-axis oblique fields generated by Virtual simulation. Conclusion: The preliminary data suggests that the decreased pulmonary toxicity with five field conformal irradiation of inoperable NSCLC should allow us to escalate dose to improve local-regional control and possible survival. Evaluation of quality of life using a dyspnea index as a subjective indicator of pulmonary function to correlate quantitative volumetric perfusion data obtained from SPECT scan to 3-D dosimetry is in progress