Room: Exhibit Hall | Forum 6
Purpose: The purpose of this study is to quantify the response of PET-defined tumor to pulsed-low-dose-rate (PLDR) radiotherapy through evaluation of CT HU values.
Methods: Image assessment was initiated for 10 patients (8 esophageal and 2 lung) on an in-house, IRB approved protocol where treatment is delivered via PLDR to decrease pre-surgical esophagitis. All patients underwent pre- (scan-1) and post-RT (scan-2) PET-CT scans that were fused based on boney anatomy. All PET volumes were delineated by an experienced Nuclear Medicine physician. The scan-2 PET volumes were transferred to the scan-1 CT (with air subtracted). The intersection of the scan-1 and scan-2 volumes were then evaluated on both pre- and post-RT CT scans. The average volumes and mean HU values were obtained for all.
Results: The average PET-defined gross tumor volumes decreased from 67.9cc for scan 1 to 21.7cc (68%) for scan 2. The decrease for esophageal patients only was from 82.7cc to 26.7cc (68%) and included 2 complete responders. The pre-treatment volume mean HU values decreased from an average of 25.5HU to 19.2HU with one of the lung cases demonstrating the only increase. 100% of the esophagus patients demonstrated an average decrease in pre-tx volume from 24.0HU to 14.8HU from scan-1 to scan-2. The esophageal patients post treatment volume mean HU values decrease from an average of 29.3HU to 19.9HU from scan-1 to scan-2, respectively, omitting the complete responders.
Conclusion: The above decrease in PET-defined gross tumor volumes and the decreases in mean HU values from pre- to post-treatment are indications of treatment effectiveness. The PET-based 25% complete response seen here for esophageal patients compares well with the 25% complete response rate for adenocarcinoma patients following surgery. Targeting areas of higher mean HU with this well-tolerated delivery technique may improve response rates.