Demonstration of real‐time positron emission tomography biology‐guided radiotherapy delivery to targets
Authors: Oderinde Oluwaseyi M. , Narayanan Manoj , Olcott Peter , Voronenko Yevgen , Burns Jon , Xu Shiyu , Shao Ling , Feghali Karine A. Al , Shirvani Shervin M. , Surucu Murat , Kuduvalli Gopinath 
Published: March 2024

Background

Biology‐guided radiotherapy (BgRT) is a novel technology that uses positron emission tomography (PET) data to direct radiotherapy delivery in real‐time. BgRT enables the precise delivery of radiation doses based on the PET signals emanating from PET‐avid tumors on the fly. In this way, BgRT uniquely utilizes radiotracer uptake as a biological beacon for controlling and adjusting dose delivery in real‐time to account for target motion.

Purpose

To demonstrate using real‐time PET for BgRT delivery on the RefleXion X1 radiotherapy machine. The X1 radiotherapy machine is a rotating ring‐gantry radiotherapy system that generates a nominal 6MV photon beam, PET, and computed tomography (CT) components. The system utilizes emitted photons from PET‐avid targets to deliver effective radiation beamlets or pulses to the tumor in real‐time.

Methods

This study demonstrated a real‐time PET BgRT delivery experiment under three scenarios. These scenarios included BgRT delivering to (S1) a static target in a homogeneous and heterogeneous environment, (S2) a static target with a hot avoidance structure and partial PET‐avid target, and (S3) a moving target. The first step was to create stereotactic body radiotherapy (SBRT) and BgRT plans (offline PET data supported) using RefleXion's custom‐built treatment planning system (TPS). Additionally, to create a BgRT plan using PET‐guided delivery, the targets were filled with 18F‐Fluorodeoxyglucose (FDG), which represents a tumor/target, that is, PET‐avid. The background materials were created in the insert with homogeneous water medium (for S1) and heterogeneous water with styrofoam mesh medium. A heterogeneous background medium simulated soft tissue surrounding the tumor. The treatment plan was then delivered to the experimental setups using a pre‐commercial version of the X1 machine. As a final step, the dosimetric accuracy for S1 and S2 was assessed using the ArcCheck analysis tool—the gamma criteria of 3%/3 mm. For S3, the delivery dose was quantified using EBT‐XD radiochromic film. The accuracy criteria were based on coverage, where 100% of the clinical target volume (CTV) receives at least 97% of the prescription dose, and the maximum dose in the CTV was ≤130% of the maximum planned dose (97 % ≤ CTV ≤ 130%).

Results

For the S1, both SBRT and BgRT deliveries had gamma pass rates greater than 95% (SBRT range: 96.9%–100%, BgRT range: 95.2%–98.9%), while in S2, the gamma pass rate was 98% for SBRT and between 95.2% and 98.9% for BgRT plan delivering. For S3, both SBRT and BgRT motion deliveries met CTV dose coverage requirements, with BgRT plans delivering a very high dose to the target. The CTV dose ranges were (a) SBRT:100.4%–120.4%, and (b) BgRT: 121.3%–139.9%.

Conclusions

This phantom‐based study demonstrated that PET signals from PET‐avid tumors can be utilized to direct real‐time dose delivery to the tumor accurately, which is comparable to the dosimetric accuracy of SBRT. Furthermore, BgRT delivered a PET‐signal controlled dose to the moving target, equivalent to the dose distribution to the static target. A future study will compare the performance of BgRT with conventional image‐guided radiotherapy.