Author: Lau, Yu Ching
Title: Variations in tumor delineation and quantification on 18F-PSMA-1007 PET/CT for radiotherapy planning of prostate cancer
Advisors: Cai, Jing (HTI)
Yoo, Jung Sun (HTI)
Degree: DHSc
Year: 2022
Subject: Prostate -- Cancer -- Radiotherapy
Image-guided radiation therapy
Hong Kong Polytechnic University -- Dissertations
Department: Faculty of Health and Social Sciences
Pages: x, 129 pages : color illustrations
Language: English
Abstract: Image-guided radiotherapy utilizes information on medical images to personalize treatment plan and monitor response. Apart from tumor morphology, functional contours and metabolic parameters of tumors on positron emission tomography (PET) are becoming more useful for delineation of biological target volume, dose painting and evaluation of early treatment response. With outstanding sensitivity and specificity in lesion detection, 18F-PSMA-1007 has recently emerged as an important PET tracer that influences the clinical management of prostate cancer patients. Apart from manual drawing, different approaches using semi-automatic segmentation have been proposed for tumor delineation. However, functional parameters measured on static PET images are known to be affected by technical factors such as uptake time and lesion contouring which vary from patient to patient, from scan to scan, even within a single imaging center. Without considering the variations in PET imaging and their significance, using segmentation tools simply based on physical settings results in error propagation in the workflow which limits the potential utilities of metabolic information in personalized radiotherapy.
The goal of this study was to determine an optimal setting in clinical practice for reliable tumor delineation and quantification of prostate cancer lesions on 18F-PSMA-1007 PET/CT. This study evaluated the variations in metabolic parameters at different uptake time and the impact of functional contouring using gradient-based and threshold-based methods (threshold 30%, 40%, 50%, 60% and 70% of lesion SUVmax). Dual time-point clinical scans were reviewed retrospectively. Positive lesions were contoured separately on both time points using the segmentation methods. Lesions were categorized into four lesion types for analyses, namely intra-prostatic lesions, lymph nodes (LN), bone lesions and soft tissue lesions in pelvic region. Changes in tumor SUVmax, functional tumor volume (FTV) and metabolic tumor burden (MTB, defined as the product of SUVmean and FTV) were evaluated. Early and delayed images were aligned using automatic rigid alignment. Contouring consistency between the time points was determined by Dice similarity coefficient (DSC). Uptake patterns of lesions were investigated based on percentage changes in tumor SUVmax. Results revealed that performing scans at the delayed time point in this imaging protocol was associated with an overall 10-12% increase in tumor SUVmax. The overall change in FTV using gradient-based method was smaller than threshold-based method (median percentage change: gradient= 0.0% vs 30%= -8.6%, 40%= -8.8%, 50%= -7.6%, 60%= -12.0%, 70%= -11.6%). Although there was an overall increase in MTB using gradient-based method (median percentage change: gradient= 6.3% vs 30%= 4.7%, 40%= 2.3%, 50%= 1.9%, 60%= -0.5%, 70%= -2.0%), it was compatible with an increased tumor uptake while keeping FTV measurement consistent. Moreover, the contouring consistency of gradient-based method (DSC=0.5338) was comparable to threshold-based method using 60% (DSC=0.5358). In addition, gradient-based method demonstrated higher reliability in creating contours under challenging conditions such as low lesion contrast and presence of nearby intense lesion, which was particularly useful for intra-prostatic lesions. Furthermore, uptake patterns in different lesion types were similar. Only a small proportion of lesion showed a decrease pattern. Variations in tumor uptake caused by difference in uptake time should be taken into consideration when assessing disease progression or regression on follow-up scans. In this regard, FTV measured by gradient-based method may be of reference value. In conclusion, gradient-based method is recommended for tumor functional contouring on 18F-PSMA-1007 PET/CT.
Rights: All rights reserved
Access: restricted access

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