2263 - Evaluation of ¹⁸F-FDG and ¹⁸F-FMISO PET Imaging for Biology-Guided Radiotherapy in Lung and Abdomen Cancer Patients

Purpose/Objective(s): Biology-guided radiotherapy (BgRT) on a PET/CT Linac is currently only FDA cleared for ¹⁸F-FDG guided treatment for lung and bone tumors. The aims of this study are to (1) assess ¹⁸F-FDG uptake in abdominal tumors to determine BgRT eligibility and (2) evaluate ¹⁸F-FMISO uptake in lung tumors to determine suitability of a hypoxia radiotracer for BgRT.

Materials/

Methods: Pre-treatment ¹⁸F-FDG and ¹⁸F-FMISO imaging data was retrospectively collected for both lung and abdominal radiotherapy patients. Image registration and contouring were completed in commercial software. A biology-tracking zone (BTZ) was delineated for each patient by expanding the PET-avid PTV volume by 2-5 mm. Images and structures were transferred to the BgRT planning software to determine if desired activity concentration (AC) and normalized target signal (NTS) met the required threshold values for treatment delivery.

Results: ¹⁸F-FDG data from 5 abdominal SBRT patients treated for various abdominal sites and ¹⁸F-FMISO data from 6 lung SBRT patients were evaluated. Four out of five abdominal patients demonstrated adequate tumor size and ¹⁸F-FDG uptake (AC = 5 kBq/ml, NTS = 2.7) to allow for BgRT treatment planning. SUV_max alone does not appear to correlate with suitability for BgRT, as patient 5 did not pass BgRT planning but also did not display the lowest SUV_max of the cohort. Patient 4 displayed a similar tumor size to patient 5 with significantly higher ¹⁸F-FDG uptake, indicating that small tumor size and lower SUV_max may signal patient exclusion from BgRT. For the lung SBRT cohort with ¹⁸F-FMISO data, only one patient demonstrated adequate FMISO uptake for BgRT treatment planning.

Conclusion: This study demonstrates the potential of utilizing ¹⁸F-FDG for the treatment of abdominal sites with BgRT, suggesting this technology can be extended to other treatment sites in addition to lung and bone. Furthermore, the data reveals a possible correlation between SUV_max values and tumor size with suitability for BGRT; smaller tumors necessitate higher SUV for BgRT delivery. ¹⁸F-FMISO data in this patient cohort was inconclusive. While the ¹⁸F-FMISO uptake in one patient provided adequate signal for BgRT treatment planning, further investigation is needed to determine feasibility of ¹⁸F-FMISO for BgRT delivery. Abstract 2263 – Table 1