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Published on: February 6, 2019
Defining Intraprostatic Gross Tumor Volume and Micro-boosting through Consensus: A Contour-Based Modified Delphi
Lucas C Mendez1, Costas Zamboglou2, Shafak Al-Uwini3
1London Health Sciences Centre, Western University, Canada.
Summary
Expert consensus was reached on key aspects of prostate radiotherapy gross tumor volume (GTV) micro-boosting, including imaging use and lesion eligibility. However, variability persists in complex cases, highlighting the need for standardized guidance in GTV micro-boosting.
Area of Science:
- Radiation Oncology
- Medical Imaging
- Prostate Cancer Treatment
Background:
- Advances in imaging, including multiparametric MRI (mpMRI) and PSMA-PET, enable precise identification of intraprostatic gross tumor volumes (GTVs) for prostate radiotherapy.
- This facilitates opportunities for GTV micro-boosting, a technique aiming to deliver higher doses to the identified tumor volume.
- However, significant variability exists among experts in patient selection, target delineation, and treatment planning for GTV micro-boosting.
Purpose of the Study:
- To characterize expert contouring variability in defining GTVs for prostate radiotherapy micro-boosting.
- To establish consensus guidance for GTV micro-boosting using a contour-based modified Delphi consensus process.
- To identify areas of agreement and disagreement among international experts regarding GTV delineation and treatment planning.
Main Methods:
- A two-part study involving international radiation oncologists with expertise in GTV micro-boosting.
- Part 1: A contouring exercise where participants delineated GTVs on two prostate cancer cases using mpMRI and PSMA-PET imaging, including a complex case with imaging discordance.
- Part 2: A two-round modified Delphi consensus survey addressing patient selection, imaging, contouring, and planning, with consensus defined as ≥75% agreement.
Main Results:
- Fifteen experts participated. Contouring agreement was high for simpler cases but lower for complex cases with imaging discordance.
- PSMA-PET-based GTVs were consistently larger than mpMRI-based GTVs.
- Consensus (≥75%) was achieved for 33% of statements, including using combined mpMRI sequences, eligibility of PI-RADS/PROMISE 4-5 lesions, preferring PSMA-PET tracers, and avoiding CTV margins with combined imaging. No consensus on SBRT micro-boosting outside trials or dose prescription.
Conclusions:
- Expert contouring variability exists, particularly for complex prostate cancer cases with imaging discordance.
- Areas of consensus were identified for GTV delineation and imaging selection, providing a foundation for standardized GTV micro-boosting protocols.
- Further research and consensus are needed for specific aspects like SBRT micro-boosting outside trials and optimal dose prescriptions.
