Screen: 21
Emily Draeger, PhD
Yale University School of Medicine
New Haven, CT
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. SUVmax 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 SUVmax 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 SUVmax 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.
Patient Tx Site Tracer Tumor Size (cm) SUVmax BgRT Result AC (kBq/ml) NTS 1 GE Junction 18F-FDG 2.6 7.1 Pass 8.73 4.44 2 Esophagus 18F-FDG 2.3 12.7 Pass 12.98 7.33 3 Rt Adrenal 18F-FDG 3.5 7.1 Pass 14.25 7.80 4 Mesentery 18F-FDG 1.9 32.5 Pass 15.80 11.59 5 Abdominal Lymph Node 18F-FDG 1.5 11.5 Fail - - 6 Right Upper Lobe Lung 18F-FMISO 4.1 5.1 Pass 6.91 3.79 7 Left Upper Lobe Lung 18F-FMISO 2.2 4.2 Fail - - 8 Left Lower Lobe Lung 18F-FMISO 1.6 7.0 Fail - - 9 Right Upper Lobe Lung 18F-FMISO 2.5 6.1 Fail - - 10 Right Upper Lobe Lung 18F-FMISO 1.3 15.1 Fail - - 11 Right Lower Lobe Lung 18F-FMISO 5.3 13.1 Fail - -
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 SUVmax 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