Physics Contribution
Comparison of [11C]choline Positron Emission Tomography With T2- and Diffusion-Weighted Magnetic Resonance Imaging for Delineating Malignant Intraprostatic Lesions

https://doi.org/10.1016/j.ijrobp.2015.02.004Get rights and content

Purpose

The purpose of this study was to compare the accuracy of [11C]choline positron emission tomography (CHOL-PET) with that of the combination of T2-weighted and diffusion-weighted (T2W/DW) magnetic resonance imaging (MRI) for delineating malignant intraprostatic lesions (IPLs) for guiding focal therapies and to investigate factors predicting the accuracy of CHOL-PET.

Methods and Materials

This study included 21 patients who underwent CHOL-PET and T2W/DW MRI prior to radical prostatectomy. Two observers manually delineated IPL contours for each scan, and automatic IPL contours were generated on CHOL-PET based on varying proportions of the maximum standardized uptake value (SUV). IPLs identified on prostatectomy specimens defined reference standard contours. The imaging-based contours were compared with the reference standard contours using Dice similarity coefficient (DSC), and sensitivity and specificity values. Factors that could potentially predict the DSC of the best contouring method were analyzed using linear models.

Results

The best automatic contouring method, 60% of the maximum SUV (SUV60) , had similar correlations (DSC: 0.59) with the manual PET contours (DSC: 0.52, P=.127) and significantly better correlations than the manual MRI contours (DSC: 0.37, P<.001). The sensitivity and specificity values were 72% and 71% for SUV60; 53% and 86% for PET manual contouring; and 28% and 92% for MRI manual contouring. The tumor volume and transition zone pattern could independently predict the accuracy of CHOL-PET.

Conclusions

CHOL-PET is superior to the combination of T2W/DW MRI for delineating IPLs. The accuracy of CHOL-PET is insufficient for gland-sparing focal therapies but may be accurate enough for focal boost therapies. The transition zone pattern is a new classification that may predict how well CHOL-PET delineates IPLs.

Introduction

Conventional treatment modalities for localized prostate cancer such as radical prostatectomy and radiation therapy aim to treat the entire prostate gland, with little consideration of the location of the malignant intraprostatic lesion (IPL), despite the fact that it is uncommon for localized prostate cancer to involve the entire prostate. One large prostatectomy-based study of predominantly Gleason 7 and pT2c cases found that the tumor involved a median of only 5% of the total prostate volume (1).

Conventional whole-gland treatments pose several problems. First, these treatments may not be necessary in lower risk patients and may result in unnecessary treatment-related morbidities (2). Second, whole-gland treatments may not treat IPLs aggressively enough in higher risk patients, resulting in a high likelihood of local recurrences 3, 4, 5. Focal treatments using modalities such as intensity modulated radiation therapy, focal brachytherapy, focused ultrasonography, and cryotherapy have been proposed as ways of overcoming these problems 2, 6, 7, 8. Lower risk patients who need more than active surveillance may be treated with focal therapy to treat the IPLs only while sparing the rest of the prostate gland 2, 8, 9. Higher risk patients may be treated by whole-gland treatment with a focal boost to IPLs to improve local control 9, 10, 11, 12. These focal treatments remain investigational and have not gained widespread acceptance.

One reason why these focal treatments have not been more widely adopted is that conventional imaging with modalities such as T2-weighted (T2W) magnetic resonance imaging (MRI) has not been reliable enough to localize IPLs (2). However, new imaging modalities such as [11C]choline positron emission tomography (CHOL-PET) (13), [11C]acetate PET (14), diffusion-weighted (DW) and dynamic contrast-enhanced MRI (15), and MR spectroscopy (MRS) 16, 17 may more reliably identify IPLs, potentially making focal therapies a more viable strategy.

CHOL-PET is a particularly promising imaging modality for identifying IPLs. CHOL is a radiotracer based on choline, an essential component of the cell membrane. Prostate cancer cells show changes in choline transport and choline kinase alpha expression, leading to an increased uptake of choline (18). However, CHOL-PET for localizing prostate cancer is currently controversial, with some studies showing high accuracy 13, 17 and others showing no advantages over T2W-MRI 16, 19.

The aim of this study was to compare the accuracy of CHOL-PET with that of T2W-MRI for delineating IPLs based on histopathological reference standards and to investigate factors that could predict the accuracy of CHOL-PET.

Section snippets

Study design and patient population

This study analyzed data from a prospective, single-institution study of 30 patients recruited between September 2008 and March 2011. Eligible patients included those with histopathologically proven prostate adenocarcinoma with intermediate to very high risk factors (20) who were medically and surgically suitable for radical prostatectomy.

All patients had standard diagnostic and staging investigations prior to recruitment, including serum prostate-specific antigen (PSA) concentration test,

Results

Twenty-one patients from the original cohort of 30 patients were included in the final analysis, as 6 patients did not have DW-MRIs and 3 patients had significant susceptibility artifacts (caused by prosthetic hips) on the DW-MRIs. Patient characteristics are summarized in Table 1. The mean DSC, sensitivity, specificity, and YI for each contouring method are listed on Table 2. Of the automatic contouring methods, SUV60 had both the highest DSC and the highest YI with values of 0.59 and 0.43,

Discussion

The main finding in this study was that both manual and automatic contouring using CHOL-PET was superior to manual contouring using MRI for delineating the IPL when correlated with its histopathological reference.

Automatic contouring using CHOL-PET was assessed in 2 previous studies. A pilot study of 8 patients reported SUV60 as the contouring method with the best correlation with histopathology (13). A similar study of 4 patients also reported SUV60 as the contouring method best correlated

Conclusions

CHOL-PET is superior to the combination of T2W and DW-MRI for delineating IPLs. The accuracy of CHOL-PET is insufficient for gland-sparing focal therapies, however, it may be accurate enough for focal boost therapies. The transition zone pattern is a new classification that may predict how well CHOL-PET delineates IPLs and may be used to more appropriately select patients for this scan.

Acknowledgments

The authors gratefully acknowledge the contributions of Graham Hepworth, Statistical Consulting Centre, University of Melbourne.

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    • Supported by grant 487916 through Cancer Australia, Prostate Cancer Foundation Australia, and Australian Government Department of Health and Aging; Australian National Health and medical research council practitioner fellow award 487907 (I.D.D.); and support from the National Institute for Health Research Royal Marsden/Institute of Cancer Research Biomedical Research Centre (V.K.).

    Conflict of interest: none.

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