Faculty Bibliography

INTRODUCTION/BACKGROUND:The increasing use of molecular imaging probes as biomarkers in oncology emphasizes the need for robust and stable methods for quantifying tracer uptake in PET imaging. The primary motivation for this research was to find an accurate method to quantify the total tumor uptake. Therefore we developed a histogram-based method to calculate the background subtracted lesion (BSL) activity and validated BSL by comparing the quantitative consistency with the total lesion glycolysis (TLG) in phantom and patient studies. METHODS:A thorax phantom and a PET-ACR quality assurance phantom were scanned with increasing FDG concentrations. Volumes of interest (VOIs) were placed over each chamber. TLG was calculated with a fixed threshold at SUV 2.5 (TLG2.5) and a relative threshold at 42% of SUVmax (TLG42%). The histogram for each VOI was built and BSL was calculated. Comparison with the total injected FDG activity (TIA) was performed using concordance correlation coefficients (CCC) and the slope (a). Fifty consecutive patients with FDG-avid lung tumors were selected under an IRB waiver. TLG42%, TLG2.5 and BSL were compared to the reference standard calculating CCC and the slope. RESULTS:In both phantoms, the CCC for lesions with a TIA ≤50ml*SUV between TIA and BSL was higher and the slope closer to 1 (CCC=0.933, a=1.189), than for TLG42% (CCC=0.350, a=0.731) or TLG2.5 (CCC=0.761, a=0.727). In 50 lung lesions BSL had a slope closer to 1 compared to the reference activity than TLG42% (a=1.084 vs 0.618 - for high activity lesions) and also closer to 1 than TLG2.5 (a=1.117 vs 0.548 - for low activity lesions). CONCLUSION/CONCLUSIONS:The histogram based BSL correlated better with TIA in both phantom studies than TLG2.5 or TLG42%. Also in lung tumors, the BSL activity is overall more accurate in quantifying the lesion activity compared to the two most commonly applied TLG quantification methods.

In patients with a clinical suspicion of recurrence after treatment for prostate cancer, imaging can be used to distinguish between local recurrence and metastatic disease. Multiparametric magnetic resonance imaging (mpMRI) of the prostate may be a valuable imaging modality for the detection and localization of local recurrence in patients treated for prostate cancer. In mpMRI, morphological T2-weighted images are combined with functional MRI techniques including diffusion-weighted imaging, dynamic contrast-enhanced imaging, and magnetic resonance spectroscopic imaging to improve accuracy. In this paper, the current status of imaging techniques used to detect and to localize tumor recurrence in patients treated for prostate cancer will be reviewed, with emphasis on mpMRI for local prostate cancer recurrence.

PURPOSE/OBJECTIVE:To assess radiotherapy (RT)-induced changes in the urethra and periurethral tissues after treatment for prostate cancer (PCa). METHODS AND MATERIALS/METHODS:This retrospective study included 108 men (median age, 64 years; range, 43-87 years) who received external-beam radiotherapy (EBRT) and/or brachytherapy for PCa and underwent endorectal-coil MRI of the prostate within 180 days before RT and a median of 20 months (range, 2-62 months) after RT. On all MRIs, two readers independently measured the urethral length (UL) and graded the margin definition (MD) of the urethral wall and the signal intensities (SIs) of the urethral wall and pelvic muscles on 4-point scales. RESULTS:The mean urethral length decreased significantly from pre- to post-RT MRI (from 15.2 to 12.6mm and from 14.4 to 12.9 mm for readers 1 and 2, respectively; both p-values <0.0001). Brachytherapy resulted in greater urethral shortening than EBRT. After RT, SI in the urethral wall increased in 57% (62/108) and 35% (38/108) of patients (readers 1 and 2, respectively). The frequency and magnitude of SI increase in pelvic muscles depended on muscle location. In the obturator internus muscle, SI increased more often after EBRT than after brachytherapy, while in the periurethral levator ani muscle SI increased more often after brachytherapy than after EBRT. CONCLUSION/CONCLUSIONS:After RT for PCa, MRI shows urethral shortening and increased SI of the urethral wall and pelvic muscles in substantial percentages of patients.

PURPOSE/OBJECTIVE:To evaluate the incremental value of using diffusion-weighted magnetic resonance (MR) imaging in addition to T2-weighted imaging for the detection of prostate cancer in the transition zone and the assessment of tumor aggressiveness. MATERIALS AND METHODS/METHODS:This retrospective HIPAA-compliant institutional review board-approved study included 156 consecutive patients (median age, 59.2 years) who underwent MR imaging before radical prostatectomy. Two readers who were blinded to patient data independently recorded their levels of suspicion on a five-point scale of the presence of transition zone tumors on the basis of T2-weighted imaging alone and then, 4 weeks later, diffusion-weighted imaging and T2-weighted imaging together. Apparent diffusion coefficients (ADCs) were measured in transition zone cancers and glandular and stromal benign prostatic hyperplasia. Areas under the receiver operating characteristic curves were used to evaluate detection accuracy, and generalized linear models were used to test ADC differences between benign and malignant prostate regions. Whole-mount step-section histopathologic examination was the reference standard. RESULTS:In overall tumor detection, addition of diffusion-weighted imaging to T2-weighted imaging improved the areas under the receiver operating characteristic curves for readers 1 and 2 from 0.60 and 0.60 to 0.75 and 0.71, respectively, at the patient level (P = .004 for reader 1 and P = .027 for reader 2) and from 0.64 and 0.63 to 0.73 and 0.68, respectively, at the sextant level (P = .001 for reader 1 and P = .100 for reader 2). Least squares mean ADCs (× 10(-3) mm(2)/sec) in glandular and stromal benign prostatic hyperplasia were 1.44 and 1.09, respectively. Mean ADCs were inversely associated with tumor Gleason scores (1.10, 0.98, 0.87, and 0.75 for Gleason scores of 3 + 3, 3 + 4, 4 + 3, and ≥ 4 + 4, respectively). CONCLUSION/CONCLUSIONS:Use of diffusion-weighted imaging in addition to T2-weighted imaging improved detection of prostate cancer in the transition zone, and tumor ADCs were inversely associated with tumor Gleason scores in the transition zone.

OBJECTIVE:Pelvic radiation therapy (RT) can influence fertility in female rectal cancer survivors. Data regarding its effects on the adult uterus are scant. This study aims to evaluate the uterus before and after RT, using dynamic contrast-enhanced MRI. METHODS:Eligible patients (n=10) received RT for rectal cancer, had an intact uterus and underwent dynamic contrast-enhanced MRI before and after RT. Seven patients were pre-menopausal. RESULTS:Patients received pelvic RT (median, 50.2 Gy) with concurrent 5-fluorouracil. Five patients were treated with intensity modulated RT (IMRT) and five with a three-field technique. The median D95 of the uterus was 30 Gy; D05 was 48 Gy; and V95 was 97%. The median cervical D95 was 45 Gy; D05, 50 Gy; and V95, 100%. Cervical dose was higher with IMRT than with three-field plans (p≤0.038). On T2 MRI, the junctional zone was visible in nine patients before and in one after RT (p=0.001). Median cervical length (2.3 vs 3.0 cm) and endometrial thickness (2.6 vs 5.9 mm) were reduced after RT (p≤0.008). In pre-menopausal patients, the volume transfer constant, K(trans), (0.069 vs 0.195, p=0.006) and the extracellular extravascular volume fraction, V(e), (0.217 vs 0.520, p=0.053) decreased. CONCLUSION/CONCLUSIONS:Pelvic RT significantly affected uterine anatomy and perfusion. Cervical dose was higher with IMRT than three-field plans, but no attempt was made to constrain the dose. ADVANCES IN KNOWLEDGE/CONCLUSIONS:Pelvic RT significantly affects the adult uterus. These findings are crucial to understand the potential consequences of RT on fertility, and they lay the groundwork for further prospective studies.