Is There a Dose Response Relationship With Stereotactic Body Radiation Therapy for Pulmonary Oligometastases?

Abstract

To determine whether there exists a dose-response relationship for pulmonary oligometastases treated with stereotactic body radiation therapy (SBRT). An Institutional Review Board (IRB)-approved registry of patients treated with stereotactic body radiation therapy (SBRT) was queried for patients with oligometastatic disease who were treated with SBRT to the lung between 2004 and 2014. Demographic information, comorbidities, size of lesion, number of pulmonary metastases, histology of primary cancer, PET SUV of lesion, use and timing of chemotherapy, and dosimetric parameters were recorded. Local failure was defined as persistent growth of the treated lesion on subsequent imaging, increasing SUV after treatment, or biopsy-proven recurrence. Local control (LC) and overall survival (OS) were calculated using actuarial analysis. LC was stratified by fractionation based on biological effective dose (BED) grouping (100-105 Gy vs 120-132 Gy vs 180 Gy). Cox proportional hazards regression was used to identify factors associated with LC and OS. Eighty-nine patients (pts) with 140 lesions were treated during this time period. The median age was 65.9 years (yr). Median follow-up was 24.6 months. 24 pts (28.1%) had colorectal primaries. Other common histologies were sarcoma (18 pts, 20.2%) head and neck (10 pts, 11.2%), and non-small cell lung cancer (8 pts, 9.0%). Breast, esophageal, GYN, melanoma, pancreaticobiliary, renal cell, thyroid, and other histologies comprised the remainder. Chemotherapy was not given in 21 pts (23.6%), pre- and post-SBRT in 31 pts (34.8%), pre-SBRT in 32 pts (36.0%), and post-SBRT in 4 pts (4.5%). 105 lesions (75.0%) were treated with BED 100-105.6 Gy, 13 lesions (7.8%) were treated with BED 120-132 Gy, 17 lesions (12.1%) were treated with BED 180 Gy. The overall 2 yr rate of LC was 79.5% (81.0% for BED 100-105, 50% for BED 120-132, and 91.3% for BED 180). Differences were not statistically significant. On multivariate analysis, colorectal primary was associated with worse LC (HR 2.92, 95%CI 1.200-7.092). Overall 2 yr OS was 68.7% (66.9% for BED 100-105, 81.8% for BED 120-132, and 75.7% for BED 180). Lower BED (100-105 Gy vs 180 Gy) was the only factor associated with worse OS on univariate analysis (HR 2.82, 95% CI 1.080-7.351). SBRT with higher BED trended towards improved LC and was associated with improved survival compared to lower BED. Colorectal oligometastases are associated with worse LC than other histologies. Further multi-institutional collaboration is needed to validate these findings and to determine optimal SBRT doses for oligometastases by histology.