This prospective, open-label Phase I/II trial evaluates a PET/CT-guided planning strategy for radioactive seed implantation therapy in malignant solid tumors. The approach integrates metabolic information from PET/CT into brachytherapy planning to improve the accuracy of biological target volume delineation, enhance dose coverage, and support biologically informed dose delivery. Eligible participants are assigned to one of three arms: conventional CT-guided implantation, PET/CT-guided standard-dose implantation, or PET/CT-guided biologically optimized implantation. All participants undergo image-guided treatment followed by post-implant dosimetric verification and standardized clinical follow-up.
Primary endpoints include technical success rate, dosimetric superiority, and 6-month local control. Secondary endpoints include dosimetric indices (D90, V100, conformity index, homogeneity index), pain relief, quality of life (EORTC QLQ-C30), treatment-related adverse events (CTCAE v5.0), progression-free survival (PFS), failure-free survival (FFS), and overall survival (OS). Exploratory analyses will evaluate associations between baseline PET metabolic parameters (SUVmax, metabolic tumor volume) and clinical outcomes, assess the feasibility of SUV-guided dose painting, and compare the performance of tumor-specific tracers (such as PSMA and FAPI) with FDG for target delineation and treatment response prediction.
The central hypothesis is that PET/CT-guided planning-particularly when incorporating biological dose optimization-will achieve superior dosimetric performance and improved local control and survival outcomes compared with conventional CT-guided implantation.
Age ≥ 18 years.
Pathologically or clinically confirmed malignant tumor (solid tumor, lymphoma, or leukemia with a localized lesion suitable for radioactive seed implantation).
Tumor site accessible for image-guided implantation, with a target lesion visible on CT or PET/CT.
Life expectancy of at least 6 months.
Pregnant or breastfeeding women.
Uncontrolled infection or active systemic inflammatory disease.
Severe cardiopulmonary dysfunction that contraindicates interventional procedures (e.g., heart failure, severe COPD).
Coagulation disorders (INR > 1.5 or platelet count < 50 × 10⁹/L).
Parallel
CT-Guided Radioactive Seed Implantation
Procedure/SurgeryCT-guided implantation of 125I radioactive seeds for localized treatment of malignant tumors. The target area is delineated on contrast-enhanced CT images, and seeds are implanted according to a treatment planning system (TPS) with a prescribed dose of about 100 Gy. Post-procedure dosimetry will confirm D90, V100, and V150, as well as organ-at-risk (OAR) dose constraints.
PET/CT-Guided Radioactive Seed Implantation
Procedure/SurgeryPET/CT-guided 125I seed implantation performed using PET/CT fusion to support anatomical target delineation without SUV-based biological sub-volume definition. A standard uniform-dose treatment plan is implemented, and post-implant dosimetric evaluation is used to confirm target coverage and compliance with organ-at-risk constraints.
PET/CT-Guided Radioactive Seed Implantation (Biological Dose Optimization)
Procedure/SurgeryPET/CT-guided 125I seed implantation for the treatment of malignant tumors. The biological target volume (BTV) is defined using 18F-FDG PET/CT fused with planning CT to improve target accuracy and tumor coverage. The prescribed dose is approximately 100 Gy. Post-implant verification includes D90, V100, and OAR constraints.
Tumor-Specific PET/CT-Guided Radioactive Seed Implantation (PSMA/FAPI Subgroup)
Procedure/Surgery125I seed brachytherapy guided by tumor-specific PET/CT imaging. Tracers such as PSMA (for prostate cancer) and FAPI (for pancreatic, colorectal, and fibrotic tumors) identify biologically active regions for targeted dose escalation. High-uptake areas (SUVmax \> threshold determined by tracer characteristics) receive escalated doses of approximately 120-150 Gy through increased seed density or activity, while normal tissues remain within tolerance limits.
Technical Success Rate
Technical success is defined as post-implant dosimetry achieving D90 ≥ 90 Gy and V100 ≥ 85% without major intraoperative or immediate postoperative complications (CTCAE Grade ≥3).
Dosimetric Superiority of PET/CT-Guided Implantation
Comparison of mean D90 between PET/CT-guided and CT-guided groups. Superiority is defined as a ≥10 Gy improvement in D90 or ≥5% increase in V100 coverage.
Local Control Rate at 6 Months
Local control is defined as complete response, partial response, or stable disease per RECIST 1.1 criteria at treated sites on follow-up imaging.
Progression-Free Survival (PFS)
Time interval from treatment to progression or death, analyzed using Kaplan-Meier curves and log-rank test.
Failure-Free Survival (FFS)
Time from treatment initiation to the first occurrence of disease progression, death from any cause, treatment discontinuation due to toxicity, recurrence, or initiation of new anticancer therapy.
Overall Survival (OS)
Time from implantation to death from any cause, evaluated by Kaplan-Meier method.
Pain Relief Rate
Pain relief rate is defined as the proportion of patients achieving a clinically meaningful reduction in pain intensity, defined as either a ≥2-point absolute decrease or a ≥30% relative decrease from baseline, as assessed by the Visual Analogue Scale (VAS). The VAS is a 0-10 numeric pain rating scale, where 0 indicates no pain and 10 indicates the worst pain imaginable; higher scores indicate worse pain intensity.
Comparison of PET-GTV and CT-GTV
Differences in tumor volume and spatial overlap between PET-defined and CT-defined GTVs, evaluated by Dice similarity coefficient and centroid distance.
Predictive Value of Baseline Tumor SUVmax on PET/CT for Treatment Outcomes
To evaluate the predictive value of baseline tumor SUVmax measured on PET/CT for treatment outcomes, baseline SUVmax of the index lesion will be analyzed as a continuous predictor for 6-month local control using logistic regression and for progression-free survival (PFS) using a Cox proportional hazards regression model, with results summarized as odds ratios and hazard ratios with 95% confidence intervals.
Early Metabolic Response
Change in SUVmax (ΔSUVmax) from baseline to 4-6 weeks and its predictive value for 6-month local control using ROC analysis.
Feasibility of SUV-Guided Dose Painting
Proportion of high-SUV subregions (SUVmax \>5.0) achieving target D90 ≥120 Gy within organ-at-risk limits.
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Li Min
Lead sponsor
Jinan Military General Hospital
Sponsor institution
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