ESTRO 2024 - Abstract Book

S3894

Physics - Image acquisition and processing

ESTRO 2024

Purpose/Objective:

18F-Fluorodeoxyglucose (FDG) PET/CT, which can target viable over necrotic tumor tissues and highlight lymph nodes for inclusion in treatment, is an indispensable tool for radiation therapy planning (RTP) of non-small cell lung cancer (NSCLC). However, it requires two imaging sessions: PET/CT in radiology and 4D-CT in radiation oncology. Tumor motion information is solely provided by 4D-CT, and none from PET/CT. To change this, we propose a new DDG PET/CT in a single imaging session to help assess tumor motion from both PET and CT without an external respiratory gating device (RGD), required in 4D-CT. The new DDG PET/CT can be completed in less than 15 mins of a whole body (WB) PET/CT imaging session. It reduces radiation exposure to the technologist because physical insertion of an RGD is not needed. Not only mis-registration and motion artifacts often encountered in PET/CT can be effectively eliminated in the new DDG PET/CT, tumor motion information can also be derived by both DDG CT (similar to 4D CT) and DDG PET (acquired in minutes), to assist gated RTP of NSCLC. For feasibility, the new DDG PET/CT was applied on 25 FDG WB PET/CT scans.

Material/Methods:

The new DDG PET/CT was based on a DDG PET, which calculates the respiratory signal (see figure) from principal component analysis of a series of short-time frames of dynamic PET data over 2 mins and a new DDG CT also acquired in less than 2 min, developed in house based on the CT density in the lungs and cross-sectional body outlines. Unlike 4D-CT, which relies on an external RGD of optical, strain gage or air bellows to provide the respiratory signals for selection of EI and EE (50% between two EI) for 4D-CT, DDG CT selects EI and EE based on the CT density and cross sectional body outlines, and was demonstrated to be more accurate than 4D-CT in selection of the EE phase of CT. Data acquisition of the new DDG PET/CT is less than 15 mins including 15 secs of free breathing (FB) CT followed by 2 mins per PET bed position and 5 bed positions in total for a coverage of 114.5 cm on a PET/CT scanner of 25 cm axial field of view LYSO detector. A cine CT of 5-sec duration per 2-cm couch position is acquired over the lung region and could be completed in 2 mins. The 5-sec cine duration was chosen to cover 97.5% of the normal respiration rate of patients age > 65 years. The short scan time of < 15 mins improves patient comfort and patient compliance during imaging and is about the same duration of a treatment session. The cine CT acquisition is identical to the one in 4D CT except without an external RGD and is easy to implement on PET/CT. Radiation exposure to the technologist is reduced because there is no need to manually introduce an RGD to the patient. Gated window selections of DDG PET at EI and EE are -10 to 15% and 30 to 80%, respectively. The portion of FB CT overlapping with cine CT is replaced by the average CT and DDG CT from cine CT for attenuation correction of PET and DDG PET data, respectively. The new DDG PET/CT was applied on 25 patient scans of FDG WB PET/CT. All patients were covered with a warm blanket due to cold temperature setting in the PET/CT room. Improvement on registration of PET/CT and motion correction of DDG PET/CT as well as range of tumor motion were assessed.

Results: