Predictors Of Pulmonary And Other Thoracic Complications After Lung Stereotactic Body Radiotherapy (Sbrt) For Primary Or Metastatic Lung Tumors: Dose-Volume Analysis

To analyze multiple dosimetric parameters for predicting pulmonary and other thoracic complications after stereotactic body radiotherapy (SBRT) for lung tumors. From 2005–2008, 61 patients were treated with lung SBRT for primary or metastatic tumors to a dose of 48 or 60 Gy in 4 or 5 fractions. Sixty-one percent had T1N0, 23% T2N0, and 2% T3N0 NSCLC, 15% had metastatic tumors. Normal tissue contours included: cord, brachial plexus, esophagus, bronchial tree and trachea, lungs, heart, aorta, plus ribs, and chest wall. All treatment plans were heterogeneously calculated and inversely optimized using direct machine parameter optimization (DMPO) allowing a single segment per beam for optimal target conformality; with a mean of 7 beams/plan using both coplanar and noncoplanar beams. Patients underwent baseline followed by serial pulmonary function tests at 6 weeks; 3, 6, 9, 12, and 24 months after SBRT. Toxicities were defined using CTCAEv3.0. Multiple dose–volume parameters for the lung (V5, V7.5, V10, V12.5, V15, V20, V25, V30, V35, V40, V45, V50, V55, V60, and mean lung dose [MLD]) were evaluated for association with pneumonitis and change in pulmonary function after SBRT. Median potential follow-up was 1.7 years. Eight patients (13%) developed RT pneumonitis: 5% Grade 1; 5% Grade 2; and 3% Grade 3. Using linear regression or chi-square analysis, no dose–volume parameter was found to be predictive of pneumonitis. Six patients (10%) developed rib fractures at a median of 1.8 years post-SBRT: 4 Grade 2; and 2 Grade 1. In those with rib fractures, the mean dose to 1 cc of rib was 59.9 Gy, mean V60 was 1.7 cc, mean V50 7.2 cc, and mean rib maximum dose was 65.4 Gy. A total of 6 patients (10%) developed chest wall myositis: 3 acute Grade 1; 3 chronic 1 each Grades 1, 2, and 3 at 0.8, 0.6, and 1 year post-SBRT. In those with chest wall myositis, the average chest wall maximum dose was 58.5 Gy, mean dose 19.2 Gy, V30 74 cc, V40 31 cc, V50 10 cc, V60 <1 cc, and dose to 1 cc of chest wall was 53.8 Gy. Ten percent of patients had Grade 1 fatigue and 3 had Grade 1 chronic fatigue. Thirty percent had Grade 1 acute skin toxicities and only 2% Grade 2. Using the RTOG SBRT Pulmonary Toxicity Scale 1 year post-SBRT, approximately 60% of all patients had no significant declines in FEV1 or FVC (Grade 0); 50% had no significant declines in DLCO. About one-third of patients had Grade 1 declines in FEV1 or FVC, while one-quarter had Grade 1, and just under one-third had Grade 2 declines in DLCO. Lung SBRT using 48–60 Gy was well-tolerated and associated with low rates of pneumonitis with no dosimetric parameters predictive of toxicity. Rib fractures and myositis were not uncommon and appear to be related to small-volume high-dose RT. Pulmonary declines were primarily Grade 1–2.