(Saturday, 4/7/2018)
Room: Foyer
Purpose: To compare tumor responses after lung Stereotactic body radiotherapy (SBRT) using maximum Standardized Uptake Value (SUV) from 18F-fluorodeoxyglucose (FDG) Positron Emission Tomography (PET) for different SBRT prescriptions.
Methods: Tumor responses among different SBRT prescriptions were compared by examining 48 treatments that used 4 different SBRT prescriptions. All SBRT patients were treated on 21iX and Trilogy machines (Varian Medical Systems, Palo Alto, CA) using RapidArc®. This study used a simplified tumor response criteria: (1) Complete Response (CR) — post max SUV (SUVpost) after SBRT in the treated tumor region was almost the same as the SUVs in the surrounding regions; (2) Partial Response (PR) — SUVpost was smaller than previous max SUV (SUVpre), but was greater than the SUVs in the surrounding regions; (3) No Response (NR) — SUVpost was the same as or greater than SUVpre. Some SUVpost reported as mild or favorable responses were classified as CR/PR. Biologically equivalent dose (BED�₀) calculated using an α/β of 10 Gy were used in the discussions.
Results: We observed that max SUVpost at or below 1.9 showed similar max SUVs in surrounding regions for patients treated with SBRT. SUVpost ≤ 1.9 was classified as CR. The 4 SBRT prescriptions of 45 Gy @ 9 Gy × 5, 50 Gy @ 10 Gy × 5, 55 Gy @ 11 Gy × 5, and 48 Gy @ 12 Gy × 4 had 29%, 40%, 58%, and 79% CR, respectively.
Conclusion: We found that 3 month post max SUV could efficiently assess local tumor responses after SBRT. The lung SBRTs treated at our institute had very favorable tumor responses. Comparing the tumor responses among different SBRT prescriptions historically used at our institute, SBRTs delivered with a BEDâ‚?â‚€ > 100 seemed to result in an improved rate of CR.
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