NORMAL TISSUE TOXICITIES OF STEREOTACTIC BODY RADIATION THERAPY FOR THORACIC MALIGNANCIES

Abstract

Purpose: Stereotactic body radiation therapy (SBRI) is a novel radiotherapeutic technique used to deliver a potent, locally ablative dose to deep-seated tumors in the body. In the last decade, it has emerged as a safe and effective treatment modality in the management of lung malignancies. However, data regarding the toxicities of such treatment regimens continues to evolve. We aim to evaluate the acute and chronic toxicities of patients treated with SBRT to the lung using the Novalis system at our institution. Materials: Between April 2006 and December 2009, we treated a total of 89 separate lung lesions in 78 patients with SBRT at Loyola University Chicago. Of these, 68 were primary lesions, 16 were metastatic disease and 6 were local recurrences. Sixteen tumors were considered central based on RTOG guidelines. A hypofractionated regimen was used with a median dose of 50 Gy (range 24-60) in 5 fractions (range 3-10) and median isocenter dose of 10.5 Gy (range 4-18 Gy). BodyFix (Medical Intelligence, Germany) patient immobilization was utilized during simulation and treatment. An lTV (internal target volume) approach was used with GTVs (gross tumor volumes) contoured on tidal volume inspiration and expiration CT scans and combined. For treatment planning, a uniform PTV (planning target volume) margin of 3-8mm (median 4 mm) was added to the lTV. Daily image guidance was performed using ExacTrac X-ray 6D Robotics (Brainlab, Germany). Isocenter verification was performed immediately prior to and at least once during the treatment course using conventional portal imaging. All treatment plans were available for review. Results: The mean follow-up for all patients is 13 months (range 2-41 months). Thirty-three patients had follow-up beyond 20 months. The estimated 2 year local control rate for lung tumors is 88%. For all plans, the median conformality index at the prescription dose was 1.32 with the prescription dose covering 98% of the PTV. The mean GTV and lTV for lung tumors were 24 cc and 34 cc. The median ipsilateral lung V20, V10 and V5 were 5, 10 and 18%, respectively. The mean D(1 cc) to the chest wall for peripheral lung lesions was 53 Gy. Among all lung patients treated, 9 experienced some form of acute lung toxicity six with a grade 1 cough and two with a grade 2 pneumonitis. Unfortunately, one patient experienced a lethal grade 5 acute pneumonitis complicated by an infectious process. Five patients developed acute esophageal toxicity, four with grade 1 and a single patient with grade 2 dysphagia. Fourteen patients experienced Grade 1-2 fatigue. Long term toxicity data was available for 75 patients. The SBRT treatment course was well-tolerated by the vast majority of patients. Eighteen patients experienced some degree of chronic lung toxicity with only 4 patients developing grade 2 symptoms and the remaining toxicities limited to grade 1 radiographic changes. Two patients developed chronic grade 1 chest wall toxicity. There was no incidence of rib fractures among treated patients. Each of the patients with chest wall toxicity had peripheral lung lesions with the PTV abutting or involving the chest wall. There were no observed long-term toxicities of the spinal cord, esophagus or skin in this cohort. Conclusions: In our experience with Novalis-based SBRT for lung tumors, patients have tolerated highly conformal hypofractionated regimens well, with minimal morbidity. Prior radiation therapy, central vs. peripheral tumor location and volume of irradiated tissues playa role in predicting for toxicity. Our rates of acute and chronic toxicity compare favorably to similar published series. We believe this may be in part due to our standard prescription method, 50 Gy in 5 fractions to the 90+% isodose line. Long-term follow-up is necessary to assess ultimate local control, survival and long term toxicity.