PET/CT-Guided Biological Target Volume Delineation and Dose Optimization for Radioactive Seed Implantation Therapy in Malignant Tumors

Summary

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.

Conditions

• Malignant Tumors

Interventions

PROCEDURE

CT-Guided Radioactive Seed Implantation

CT-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.

PROCEDURE

PET/CT-Guided Radioactive Seed Implantation

PET/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.

PROCEDURE

PET/CT-Guided Radioactive Seed Implantation (Biological Dose Optimization)

PET/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.

PROCEDURE

Tumor-Specific PET/CT-Guided Radioactive Seed Implantation (PSMA/FAPI Subgroup)

125I 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.

Sponsors & Collaborators

• Li Min

  lead OTHER

Principal Investigators

• Min Li, Dr.

Study Design

Allocation

RANDOMIZED

Purpose

TREATMENT

Masking

SINGLE

Model

PARALLEL

Eligibility

Min Age

18 Years

Sex

ALL

Healthy Volunteers

No

Timeline & Regulatory

Start

2026-01-31

Primary Completion

2027-06-01

Completion

2028-06-01

Countries

• China

Study Locations