Total-Body Dynamic PET/CT Imaging of Proton-Induced Activity and Biologic Washout After Proton Therapy

Area of Science:

• Medical Imaging
• Nuclear Medicine
• Radiotherapy Physics

Background:

• Off-line PET imaging post-proton therapy faces challenges like transport delay and limited scanner sensitivity.
• Conventional scanners struggle with ultralow activity imaging and characterizing whole-body biologic washout.
• Evaluating proton-induced activity and its washout is crucial for in vivo treatment assessment.

Purpose of the Study:

• To assess if a near-room total-body PET/CT system can enable practical imaging of proton-induced activity after treatment.
• To evaluate the system's capability in characterizing whole-body biologic washout of this activity.
• To establish a foundation for future washout modeling and in vivo treatment assessment methods.

Main Methods:

• Phantom studies were conducted to evaluate total-body PET performance at ultralow activity using Monte Carlo simulations.
• Nineteen patients with solid tumors underwent off-line total-body dynamic PET/CT imaging post-proton therapy.
• Spatial correlation (DSC, NCC) between PET and MC results was quantified, and time-activity curves analyzed dynamic behavior.

Main Results:

• PET images demonstrated close spatial correspondence with Monte Carlo references under ultralow activity conditions.
• In patients, PET/MC agreement was high for stationary targets (mean DSC/NCC ~0.81-0.83).
• Dynamic total-body PET revealed whole-body washout and redistribution of activity, including enrichment in blood pools and organs.

Conclusions:

• Near-room total-body PET/CT provides interpretable imaging of ultralow activity post-treatment.
• Dynamic imaging effectively captures whole-body biologic washout of proton-induced activity via circulation.
• This technology supports future development of in vivo treatment assessment and washout modeling.