PET-Guided Radiotherapy Successfully Manages Lung and Bone Tumors

"We successfully treated the lung and bone tumors on the real-time PET signal, which guided our planning and the delivery," according to study investigator Rameshwar Prasad, PhD.

The use of SCINTIX, a novel PET-guided radiotherapy system, successfully demonstrated the ability to use biological information to guide the planning and delivery of radiotherapy in a small cohort of patients with lung and bone tumors, according to findings presented at the 2025 Society of Nuclear Medicine and Molecular Imaging Annual Meeting.

Of 14 patients who underwent treatment, data showed that the activity concentration (AC) generally decreased across 5 fractions of radiotherapy, with values of 61.3 kBq/mL per functional modeling (FM), 60.99 after fraction 1, 48.74 after fraction 2, 39.88 after fraction 3, 44.51 after fraction 4, and 33.49 after fraction 5. Additionally, the normalized target signal (NTS) values were 36.23, 30.42, 27.59, 24.68, 24.81, and 18.13 at each time point. Tumor sizes were 14,355 mm³, 9000 mm³, 9450 mm³, 8748 mm³, 4189 mm³, and 3391 mm³ at each respective period.

In a particular patient with a bone tumor in the lower spine who received a single fraction of radiotherapy at 12 Gy, the standard uptake value (SUV) was 7, the AC was 29.85 kBq/mL, and the NTS was 17. Additionally, the planning targeting volume 12 (PTV12) was 97.6% and all organs at risk met constraints, including the bowel at 8 Gy and Cauda Equina at 12 Gy. Treatment was conducted in 29 minutes for this patient.

In a discussion of a clinical case based on a patient with a lung tumor, presenting author Rameshwar Prasad, PhD, highlighted the ability to significantly reduce PTV with the use of the PET-based information system. He described how the platform can help avoid irradiation of healthy tissue near the tumor.

“We can include the biological information for the planning as well as the delivery of high-beam [radiotherapy]. We successfully treated the lung and bone tumors on the real-time PET signal, which guided our planning and the delivery,” Prasad, an associate professor of Radiation Oncology and faculty in the Department of Radiation Oncology’s Division of Medical Physics & Engineering at UT Southwestern Medical Center, stated in the presentation. “I personally feel there's a lot of potential in this system. However, we really need more trials and continued work, especially on the technical and the clinical front.”

Prasad and colleagues reported their institution’s initial experience with using the real-time PET-guided external beam radiotherapy platform for treating patients with lung and bone tumors. He contextualized these findings by highlighting how conventional radiotherapy typically relies on pre-treatment imaging via CT, MRI, or PET scans, which do not account for tumor motion during therapy. Additionally, conventional modalities carry a risk of irradiating healthy tissues based on setup uncertainties, and there is less ability to adapt to real-time changes in tumor biology.

The investigational PET scanner, SCINTIX, which consists of 64 total detectors across 2 arcs, was designed to obtain limited-time-sampled PET images that guide the delivery of radiotherapy. Furthermore, the platform’s PET subsystem actively gathers emission data throughout biology-guided radiotherapy (BgRT).

Investigators evaluated the use of SCINTIX based on 2 primary PET quantitative metrics: AC and NTS. AC was defined as a measure of how much signal was available to guide the treatment, which was scaled with injected doses and was evaluated at treatment planning. NTS was a measurement of the target contrast relative to the immediate background noise, with mandatory thresholds completed at the time of planning and delivery.

The assessment included a total of 27 patients who were evaluated for BgRT, with 14 undergoing treatment for a total of 54 fractions of radiotherapy. Moreover, investigators administered all radiation fractions without interruption or medical events while executing all treatment plans as intended.

Reference

Prasad R, Shen C, Banks T, et al. Real-time PET guided external beam radiation therapy: initial experience. Presented at: 2025 SNMMI Annual Meeting; June 21-24; New Orleans, Louisiana.