Room: Exhibit Hall
Purpose: To retrospectively investigate tumor responses of lung Stereotactic Body Radiotherapy (SBRT) patients. To analyze the relation between optimal biologically equivalent dose (BED) and tumor responses for different SBRT prescriptions.
Methods: Treatment outcomes of multi-institutional lung SBRT patients were assessed with Computed Tomography (CT) follow-ups and max Standardized Uptake Value (SUV) from Positron Emission Tomography (PET). Compared the efficiency and accuracy between these diagnosis modalities, a tumor response criterion using post max SUV read from PET/CT taken around 3 months after treatment was introduced in this study. Biologically equivalent doses (BED) calculated using Î±/Î² of 10Gy were analyzed with assessments of tumor responses for different prescriptions.
Results: We found 3-month post max SUV could efficiently assess local tumor responses after lung SBRT. From our primary data for four SBRT prescriptions (9GyÃ—5, 10GyÃ—5, 11GyÃ—5, and 12GyÃ—4) historically recommended by RTOG, we observed that higher BEDâ‚?â‚€ and lower tumor volume would achieve a higher complete response rate. The highest complete response rate was observed for smallest tumor volume (PTVâ‚?áµ¥â‚‘ = 6.8cc) with higher BEDâ‚?â‚€ (105.6) of 12GyÃ—4 prescription. For 11GyÃ—5 prescription, the BEDâ‚?â‚€ (115.5) was the highest, but its complete response rate (58%) was lower than 79% of 12GyÃ—4 prescription. We observed the PTVâ‚?áµ¥â‚‘ was 15.5cc for 11GyÃ—5 group, which was more than double of the average of tumor volume of 12GyÃ—4 group. Modification of the linear quadratic model and dose escalation for patients with larger tumor volume were discussed.
Conclusion: We suggest 3-month post max SUV read from PET/CT should become standard tumor response assessment for lung SBRT. Although SBRT with prescriptions resulting in a BEDâ‚?â‚€ > 100 experienced favorable tumor responses for normal non-small cell lung cancer (NSCLC), escalation of BEDâ‚?â‚€ to higher levels, e.g. 150Gy, may be beneficial for patients with larger tumors undergoing lung SBRT.
Not Applicable / None Entered.