Room: AAPM ePoster Library
Purpose: Perfusion imaging has been shown to predict the response of tumors to radiotherapy. Perfusion imaging is especially pertinent to SBRT treatments given the vascular nature of ablative radiotherapy damage due to higher doses per fraction. The purpose of this study was to use CT Perfusion (CTP) imaging to assess longitudinal changes in pancreas and pelvic node SBRT patients.
Methods: Patients with pancreas (14) or pelvic nodal (9) tumors were treated with 27-33 Gy in 3 fractions on a prospective protocol. CTP scans were performed at simulation (SIM), 1 hour after the first fraction of radiation (1FX), and 6 weeks after treatment (6WK). Perfusion metrics calculated include blood flow (BF), blood volume (BV), and permeability/flow extraction product (FE). The median of each metric in the gross tumor volume was computed at each time point.
Results: Tumor response was observed immediately after ablative radiation delivery; all perfusion metrics significantly increased at 1FX compared to SIM (FE: 22.6 vs 14.4 mL/100mL/min, p=0.0003, BF: 57.9 vs 44.5 mL/100mL/min, p=0.002, BV: 4.4 vs 3.4 mL/100mL, p=0.004). In pelvic nodal tumors, these values returned to baseline at 6WK, but remained significantly increased (or trended towards significance) in pancreatic tumors (FE: p=0.09, BF: p=0.13, BV: p=0.04). No baseline differences were observed between pancreatic and pelvic nodal patients.
Conclusion: CT Perfusion imaging is a promising technique to understanding changes in vascularity for pancreas and pelvic nodal tumors treated with dose-escalated SBRT regimens. CTP imaging performed within 60 minutes of ablative radiotherapy reveals significant increases in blood flow and permeability. Significant differences were found in these same metrics between pancreas and pelvic node tumors 6 weeks after treatment, potentially due to superior local control in pelvic node patients. CTP imaging is a promising tool for assessing treatment response; future studies will compare CTP metrics with patient outcomes.