Michael Warren Guiou MD, Presenter: Nothing to Disclose

Terence Williams MD,PhD, Abstract Co-Author: Nothing to Disclose

Simon Shek-Man Lo MD, Abstract Co-Author: Nothing to Disclose

Nina A. Mayr MD, Abstract Co-Author: Nothing to Disclose

SABR for early-stage non-small cell lung cancer (NSCLC) results in high local control (LC) rates of over 90%, when the biological equivalent dose (BED) exceeds 100 Gy10. These results have been extrapolated to justify SABR for oligometastatic disease to the lung from non-lung primary tumors, but dose response data for these lesions are elusive. We sought to compare LC for primary NSCLC vs. non-lung primary metastases treated with SABR.

Patients were immobilized using stereotactic body frame or vacuum cushion with or without compression depending on habitus, lung function or comfort. 4D-CT simulation was performed and SABR was delivered with 7-10 noncoplanar beams. Patients were followed 3-monthly with clinical exam and chest CT. Serial 3D volume of treated lesions was calculated. Local failure was defined as persistent increase in volume greater than 20%. Comparisons between groups were calculated using Kaplan Meier analysis. 

In 42 patients (33 primary NSCLC, 9 mets) 50 lesions (37 primary NSCLC, 13 mets) were treated. Most of the mets (11/13, 85%) originated from colorectal adenocarcinoma primaries. SABR regimens ranged from 5-18 Gy per fraction delivered in 3-5 fractions to the planning target volume . Mean BED was 81 ± 24 Gy10 with no significant difference between lung primaries and metastases (84 vs. 77 Gy10, p=0.4). Mean follow-up was 16±10 vs. 16±7 months for primary NSCLC and metastatic patients, respectively. LC at 2 years was significantly greater for primary NSCLC vs. metastases (87 vs. 54%, p=0.03). Comparing LC exclusively for adenocarcinoma histologies, LC was higher for primary lung than for metastatic adenocarcinomas (82% vs. 45%, p=0.034). No patient experienced Grade ≥3 toxicity.

Our results suggest that metastatic pulmonary lesions are more resistant to treatment with SABR than primary lung tumors, even when directly comparing LC for adenocarcinomas. The radiobiological and molecular underpinnings of this difference are unclear. SABR regimens tailored towards the primary vs. metastatic origin of lung lesions may be needed, as metastatic lesions likely require higher doses for tumor control.  

SABR is an emerging technology for the treatment of oliogmetastatic disease. Determining the optimal dosing regimen for metastatic lesions is of utmost importance to maximize clinical benefit.

Guiou, M, Williams, T, Lo, S, Mayr, N, Differences in Local Control for Primary Versus Metastatic Lesions of the Lung Following Stereotactic Ablative Radiotherapy (SABR).  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12037827.html