Author: Guillermo Daniel Alvarez, Daniel Fino, Rocio Luz Gilli, Dorian Alexander Romero 👨🔬
Affiliation: School Foundation of Nuclear Medicine, INTECNUS Foundation, Nuclear Medicine and Radiotherapy Center of Southern Patagonia 🌍
Purpose: To evaluate the anatomical, functional, and molecular information from PET/MR images with F18-PSMA to identify intraprostatic lesions and delineate a boost in stereotactic body radiotherapy (SBRT) treatments with simultaneous integrated boost (SIB), following the hypo-FLAME protocol.
Methods: Twelve patients with suspected prostate cancer were studied, incorporating an experimental pseudo-diffusion MR sequence with 16 b-values to obtain IVIM and DKI pseudo-diffusion biomarkers. Acquisition sequences were set up for mpMRI and PET/MR protocols, and a Python program was developed to process pseudo-diffusion images, adjusting the signal with a three-step algorithm, segmenting the resulting image and storing it in DICOM format. Quantitative DCE biomarkers (Ktrans, kep and ve) were semi-automatically generated using the manufacturer's workstation. Biomarkers of cellular density, vascularization, and metabolism from F18-PSMA were registered and fused with tomographic images to simulate SBRT treatment plans with and without SIB, using the Halcyon v2.0 system.
Results: The pseudodiffusion sequence allowed obtaining perfusion biomarkers, being an alternative for patients with renal failure. PET/MR biomarkers showed greater sensitivity and specificity compared to MR alone, identifying lesions through PSMA overexpression. In the SBRT-SIB plan simulations, high doses were delivered to the tumor lesion with optimal prostate coverage without exceeding dose constraints for most OARs. However, an increase in low-dose exposure was observed in the anterior and posterior regions of the GTV, as well as an increased irradiated volume of the bladder, rectum, and urethra due to the urethra’s location within the GTV. It should be noted that the plan with SIB required more monitoring units.
Conclusion: This study showed the feasibility of using PET/MR together with pseudodiffusion biomarkers in SBRT-SIB treatments, a technique with the potential to define new treatment standards.