G. Gibbard, K. A. Al Feghali, A. Maniyedath, and D. de Jong; RefleXion Medical, Inc., Hayward, CA
Purpose/Objective(s): Biology-guided radiotherapy (BgRT) relies on tumor emissions detected after FDG injection to control the radiotherapy beam during each fraction. A target’s Activity Concentration (AC) > 5 kBq/ml and Normalized Target Signal (NTS) > 2.7 are two key metrics for BgRT feasibility. The objective of this study is to determine the characteristics of cervical lesions (size, volume and PET metrics) for which a suitable BgRT treatment plan may be generated. Materials/
Methods: PET/CT image datasets of cervical cancer were obtained from TCIA. The diagnostic FDG PET/CT images of the cervical lesions were collected on the MIRADA Medical Imaging Software, and each PET was resampled to match the CT slice thickness required for import on the PET linac Treatment Planning System (TPS). The PET images were processed on the PET linac TPS to simulate PET images generated on the PET-linac which would be used to guide real-time delivery. The PET-delineated GTVs for the cervical lesions were provided via TCIA. PTVs and Biology-Tracking Zones (BTZs) incorporating the full range of motion of the GTVs plus a margin were generated by 5 and 10 mm isotropic GTV expansion, respectively, along with a background structure BTZ shell created by expanding the BTZ by 3 mm. The mean SUV (SUVmean) was calculated for each cervical lesion GTV, PTV, BTZ, BTZ shell, the bladder and uterus, and the maximum SUV (SUVmax) was measured for GTV, BTZ shell, the bladder and uterus in MIRADA. AC and NTS values were also measured on the PET linac TPS. GTV, PTV and BTZ volume, and GTV superior-inferior length (SIL) were recorded in MIRADA for all cases. Results: In total, 5 lesion datasets passed the AC and NTS metrics requirements upon conversion to a PET linac-equivalent PET. The SUVmean for GTVs, PTVs, BTZs, BTZ shell were 9.5 +/- 2.8, 7.0 +/- 2.5, 5.4 +/- 2.5, 3.0 +/- 2.5, respectively. The SUVmean for the bladder and uterus were 15.7 +/- 11.4 and 4.2 +/- 1.1, respectively. The ACmax for the GTVs and BTZ shells was 25.0 +/- 11.6, and 26.9 +/- 16.4 kBq/ml, respectively. The GTV, PTV and BTZ volumes, and GTV SIL were 30.5 +/- 21.2 cc, 70.4 +/- 35.6 cc, 126.3 +/- 53.5 cm, and 3.6 +/-0.6 cm, respectively. The TPS AC and NTS were 48.08 +/-18.16 kBq/ml and 4.54 +/- 1.30, respectively. Conclusion: This study reports on the tumor volumes, lengths, and SUVs of cervical lesions using diagnostic PET-CT scans that were resampled for cases meeting the AC and NTS thresholds for BgRT planning on the PET linac TPS. These initial findings could help in selecting patients for future BgRT studies for cervical lesions, although tumor proximity to the bladder and other FDG-avid OARs should also be examined. *Mayr, N., Yuh, W. T. C., Bowen, S., Harkenrider, M., Knopp, M. V., Lee, E. Y.-P., Leung, E., Lo, S. S., Small Jr., W., & Wolfson, A. H. (2023). Cervical Cancer – Tumor Heterogeneity: Serial Functional and Molecular Imaging Across the Radiation Therapy Course in Advanced Cervical Cancer (Version 1) [Data set]. The Cancer Imaging Archive. https://doi.org/10.7937/ERZ5-QZ59
