ESTRO 2024 - Abstract Book

S1808

Clinical - Lung

ESTRO 2024

was cleared for BgRT in early 2023 by FDA for bone and lung cancers and this report describes the workflow and outcomes of the world’s first patient treated with BgRT using the X1 system.

Material/Methods:

A 58-year-old female with EGFR-mutated lung adenocarcinoma, previously treated with SABR to a right lung tumor, exhibited isolated disease progression at this site. Local re-irradiation with SABR to a higher biologically effective dose than the prior treatment was recommended. The RefleXion X1 system, equipped with a 6 MV flattening -filter free (FFF) linear accelerator and onboard PET imaging, was employed for treatment given the pre-treatment PET avidity of this nodule was distinct from its surroundings. The patient underwent simulation in the supine position, including 4D-CT and PET scans to define planning volumes. The GTV was contoured on the end expiration, and a 5 mm margin was added to create PTV. The motion extent of the tumor was used to define an ITV and a 10 mm margin was added to ITV to create a Biological Tracking Zone (BTZ) (Figure 1). The SCINTIX system uses the BTZ to mask PET emissions coming from outside of the BTZ and only responds to the signals coming from within the BTZ. A PET simulation was performed using RefleXion X1 after injecting the patient with 15 mCi of 18 F-fluorodeoxyglucose (FDG), and the PET emissions captured with the system were used to create a BgRT plan with a prescription dose of 50 Gy in 4 fractions. In the day of the BgRT delivery, the patient was injected again with FDG and kVCT localization was performed, followed by a fast PET pre-scan at RefleXion X1 to evaluate the FDG uptake of the day. After visual inspection of the PET biodistribution, evaluation metrics such as Activity Concentration (AC) and Normalized Target Signal (NTS) were measured and compared to the BgRT limits of AC>5 kBq/ml and NTS>2. A backup SABR plan was also generated for a standard linear accelerator.

Figure 1: Transverse, sagittal and coronal slices of PET images acquired on RefleXion X1 where GTV, PTV and BTZ volumes identified.