Accuracy of gross tumour volume delineation with [68Ga]-PSMA-PET compared to histopathology for high-risk prostate cancer.

BACKGROUND: The delineation of intraprostatic lesions is vital for correct delivery of focal radiotherapy boost in patients with prostate cancer (PC). Errors in the delineation could translate into reduced tumour control and potentially increase the side effects. The purpose of this study is to compare PET-based delineation methods with histopathology. MATERIALS AND METHODS: The study population consisted of 15 patients with confirmed high-risk PC intended for prostatectomy. [68Ga]-PSMA-PET/MR was performed prior to surgery. Prostate lesions identified in histopathology were transferred to the in vivo [68Ga]-PSMA-PET/MR coordinate system. Four radiation oncologists manually delineated intraprostatic lesions based on PET data. Various semi-automatic segmentation methods were employed, including absolute and relative thresholds, adaptive threshold, and multi-level Otsu threshold. RESULTS: The gross tumour volumes (GTVs) delineated by the oncologists showed a moderate level of interobserver agreement with Dice similarity coefficient (DSC) of 0.68. In comparison with histopathology, manual delineations exhibited the highest median DSC and the lowest false discovery rate (FDR) among all approaches. Among semi-automatic approaches, GTVs generated using standardized uptake value (SUV) thresholds above 4 (SUV > 4) demonstrated the highest median DSC (0.41), with 0.51 median lesion coverage ratio, FDR of 0.66 and the 95th percentile of the Hausdorff distance (HD95%) of 8.22 mm. INTERPRETATION: Manual delineations showed a moderate level of interobserver agreement. Compared to histopathology, manual delineations and SUV > 4 exhibited the highest DSC and the lowest HD95% values. The methods that resulted in a high lesion coverage were associated with a large overestimation of the size of the lesions.

Histopathology-validated lesion detection rates of clinically significant prostate cancer with mpMRI, [ 68 Ga]PSMA-11-PET and [ 11 C]Acetate-PET.

OBJECTIVE: PET/CT and multiparametric MRI (mpMRI) are important diagnostic tools in clinically significant prostate cancer (csPC). The aim of this study was to compare csPC detection rates with [ 68 Ga]PSMA-11-PET (PSMA)-PET, [ 11 C]Acetate (ACE)-PET, and mpMRI with histopathology as reference, to identify the most suitable imaging modalities for subsequent hybrid imaging. An additional aim was to compare inter-reader variability to assess reproducibility. METHODS: During 2016-2019, all study participants were examined with PSMA-PET/mpMRI and ACE-PET/CT prior to radical prostatectomy. PSMA-PET, ACE-PET and mpMRI were evaluated separately by two observers, and were compared with histopathology-defined csPC. Statistical analyses included two-sided McNemar test and index of specific agreement. RESULTS: Fifty-five study participants were included, with 130 histopathological intraprostatic lesions >0.05 cc. Of these, 32% (42/130) were classified as csPC with ISUP grade ≥2 and volume >0.5 cc. PSMA-PET and mpMRI showed no difference in performance ( P  = 0.48), with mean csPC detection rate of 70% (29.5/42) and 74% (31/42), respectively, while with ACE-PET the mean csPC detection rate was 37% (15.5/42). Interobserver agreement was higher with PSMA-PET compared to mpMRI [79% (26/33) vs 67% (24/38)]. Including all detected lesions from each pair of observers, the detection rate increased to 90% (38/42) with mpMRI, and 79% (33/42) with PSMA-PET. CONCLUSION: PSMA-PET and mpMRI showed high csPC detection rates and superior performance compared to ACE-PET. The interobserver agreement indicates higher reproducibility with PSMA-PET. The combined result of all observers in both PSMA-PET and mpMRI showed the highest detection rate, suggesting an added value of a hybrid imaging approach.

Oral manganese for liver imaging at three different field strengths.

RATIONALE AND OBJECTIVES: To study the magnetic resonance imaging signal intensity of the liver and gall bladder before and after ingestion of a new oral manganese containing contrast medium at three different field strengths. MATERIALS AND METHODS: Twelve healthy male volunteers (mean age, 24.9 years; range, 20-39 years) underwent abdominal magnetic resonance imaging (T(2)W COR, T(1)W COR, T(1)W TRA) at 0.23 T, 0.6 T, and 1.5 T before and after the contrast administration. The duration of fasting was identical before the two studies. Volunteers were randomized into two equal groups (n = 6) to ingest either half or full strength CMC-001 providing either 0.8 or 1.6.g MnCl(2) plus absorption promoters. The CMC-001 dose was dissolved in 400 mL water and ingested 2.5 hours before imaging. The resulting images were evaluated with regard to visualization of the liver and the gall bladder by three radiologists. The signal intensity of the liver was also measured. Blood and urine samples were collected before and after ingestion of CMC-001. RESULTS: The intake of CMC-001 caused a significant increase in the signal intensity of the liver at all three field strengths and at both dosages (up to 90%) on the T(1)W images. The internal structure of the liver was significantly better delineated. The bile in gall bladder was bright after ingestion of the low dose, but dark after the full dose. On the T(2)W images, CMC-001 lowered the signal intensity of liver with up to 30%. CMC-001 had a slight metallic taste, but of no importance according to the volunteers. No systematic adverse reactions caused by the contrast medium were registered. No changes in the blood levels of various routine parameters were measured. CONCLUSION: It is possible to increase the signal intensity of the liver significantly by oral intake of essential nutritional elements including manganese. The imaging window is more than 2 hours.