PET-Detectable Signatures of Very-High-Energy Electron Beams for Treatment Verification
Abstract
Purpose
Very-high-energy electron (VHEE) radiotherapy is an emerging modality that currently lacks established dosimetric verification protocols, motivating the development of real-time treatment monitoring methods. This work investigates the potential for positron emission tomography (PET) imaging for treatment beam visualization and dosimetric verification in VHEE radiotherapy.
Methods
Simple VHEE treatments were modelled for a pediatric glioblastoma and adult prostate patients with eight 200 MeV electron beams using TOPAS Monte Carlo. Dose deposition, prompt positron annihilation events, and production of PET-relevant β⁺-emitting radionuclides (¹¹C, ¹⁵O, ¹³N) from tissue activation were scored. Spatial distributions were analyzed to assess the potential for PET-based beam visualization and to evaluate correlations between dose and both prompt annihilations and β⁺ radionuclide production. Voxels were grouped by tissue type, and Pearson (r) and Spearman (ρ) correlation coefficients were calculated for all non-zero count voxels.
Results
Prompt annihilations and β⁺ radionuclide production were seen to visually correlate with dose. Mean prompt annihilation yield within the PTV was 11,700 counts per Gy·cm³ for the pediatric patient and 159,700 counts per Gy·cm³ for the prostate patient. The corresponding β⁺-emitting radionuclide production was 3,300 counts per Gy·cm³ and 23,100 counts per Gy·cm³, respectively. Strong correlations between prompt annihilations and dose were observed across tissue types. For the pediatric patient, correlations ranged from r = 0.849–0.940 and ρ = 0.862–0.920 for dose with annihilations per Gy, and r = 0.663–0.909 and ρ = 0.704–0.874 for dose versus β⁺ radionuclides per Gy. For the prostate patient, correlations ranged from r = 0.922–0.968 and ρ = 0.920–0.974 for annihilations, and r = 0.795–0.936 and ρ = 0.783–0.886 for β⁺ radionuclides.
Conclusion
VHEE radiotherapy produces a strong prompt annihilation signal with excellent correlation to delivered dose across tissue types, supporting PET-based treatment verification. Lower signal yields in pediatric brain tissue indicate location-dependent signal intensity.