PD5-2-3: Translating research into routine clinical practice: image-guided lung stereotactic radiation therapy for unresectable patients with early stage lung cancer

Abstract

Stereotactic Body Radiation Therapy (SBRT) has emerged as a non-invasive treatment option for unresectable early stage non-small cell lung cancer (NSCLC), delivering very high radio-ablative doses of RT to the primary tumor. To ensure efficacy of treatment and patient safety, high precision planning and careful treatment delivery under vigilant quality assurance are needed. We present the evolution of SBRT practice at Princess Margaret Hospital with an emphasis on accuracy of treatment set up and verification using image-guided techniques. From Oct 2004 to Feb 2007, we treated 46 patients (pts) with T1T2N0MO NSCLC with SBRT (48 tumors were treated). RT schedule for peripheral tumors was 60 Gy/3 fractions over 2 weeks (for 29 tumors, 12 of the pts were part of the RTOG 0236 phase II study). When organ at risk tolerance doses were not achievable, either 54 Gy/3 fr (3 pts) or 48 Gy/4 fr (10 tumors, all T1) was employed. Central tumors were treated with a lower dose of 50 Gy/10 fr schedule (6 pts). 4DCT simulation was acquired in all but 9 pts who were too large for the scanner. All tumor and normal tissue contours and final plans are reviewed in weekly multidisciplinary SBRT rounds. On the treatment unit, cone beam CT (CBCT) is used for image guidance with therapist manually matching directly to the tumor, adjusting the patient's position for discrepancies >3mm. CBCT is performed for initial localization and repeated during treatment to verify the tumor position. We compared CBCT soft tissue (tumor) matching to bone matching (which would mimic matching used in conventional portal imaging). Patients are followed every 3 months with radiological and clinical assessment. Median pt age was 73 yrs (48-96); mean tumor size was 2.6 cm (range 0.7-5.7). Median follow-up is 10 mo (range 0-26 mo). Acute RT toxicity was generally mild with grade G1 fatigue the most common acute side effect (16 pts). There was 1 episode of G3 dyspnea possibly treatment related, but no other >G2 events. One pt developed G2 RT pneumonitis. 9 pts developed late chest pain at 3-21 mo post SBRT; 4 of those developed rib fractures in the RT field area, 11-21 mo post SBRT. In 38 evaluable pts (40 tumors), 6 CR and 24 PR were observed. There were no local failures in 36 pts with peripheral tumors, but 2 failures in pts treated with the lower 50 Gy/10 fr schedule. CBCT tumor matching compared to bone matching resulted in a mean difference of 6.8mm (±4.9), the difference was >13.9 mm in 10% of pts; this would have resulted in very significant tumor miss if portal imaging was used without proper visualization of the target. These results confirm that lung SBRT gives high rates (95%) of local control with the only local failures observed in the centrally-located tumors treated with lower dose of 50 Gy/10 fr. Acute toxicity is low; rib fracture is the most common late toxicity. CBCT greatly improves the accurate delivery of high radioablative doses of SBRT for early stage lung cancer.