Using max standardized uptake value from positron emission tomography to assess tumor responses after lung stereotactic body radiotherapy for different prescriptions.

Abstract

PurposeTo retrospectively investigate tumor responses of lung SBRT patients for different prescriptions. To analyze the relation between optimal biologically equivalent dose (BED) and tumor responses.Methods and MaterialsTumor responses after lung SBRT were compared by examining 48 treatments used four prescriptions. This study used simplified tumor response criteria: (a) Complete Response (CR) — post max SUV (SUV post) after SBRT in the treated tumor region was almost the same as the SUVs in the surrounding regions; (b) Partial Response (PR) — SUV post was smaller than previous max SUV (SUV pre), but was greater than the SUVs in the surrounding regions; (c) No Response (NR) — SUV post was the same as or greater than SUV pre. Some SUV post reported as mild or favorable responses were classified as CR/PR. BED calculated using α/β of 10 Gy were analyzed with assessments of tumor responses for SBRT prescriptions.ResultsFor the prescriptions (9 Gy × 5, 10 Gy × 5, 11 Gy × 5, and 12 Gy × 4) historically recommended by RTOG, we observed that higher BED 10 and lower tumor volume would achieve a higher complete response rate. The highest complete response rate was observed for smallest tumor volume (PTV ave = 6.8 cc) with higher BED 10 (105.6) of 12 Gy × 4 prescription. For 11 Gy × 5 prescription, the BED 10 (115.5) was the highest, but its complete response rate (58%) was lower than 79% of 12 Gy × 4 prescription. We observed the PTV ave of 11 Gy × 5 prescription was more than double of the PTV ave of 12 Gy × 4 prescription. For the same lung SBRT prescription (BED 10 > 100) earlier staging tumor had more favorable local control.ConclusionWe demonstrated post max SUV read from PET/CT could efficiently and accurately assess tumor response after lung SBRT. Although SBRT with prescriptions resulting in a BED 10 > 100 experienced favorable tumor responses for early staging cancer, escalation of BED 10 to higher levels would be beneficial for lung cancer patients with later staging and larger volume tumors.