Prostate imaging: Contribution of PET PSMA and MRI.

Prostate cancer is the most common malignant tumour and represents the third cause of cancer-mortality in men. The management of prostate cancer has dramatically changed over the last decades, mainly due to improvement of diagnostic modalities and development of new therapeutic strategies. Imaging plays a key role in all the steps of prostate cancer management. In recent years, magnetic resonance imaging (MRI) and positron-emission tomography (PET) - computed tomography (CT) have emerged as two major tools for the detection of prostate cancer, tumour staging and treatment choice. Both MRI and PET-CT - using choline or prostate-specific membrane antigen (PSMA) as radiotracer - have become mandatory. This article presents the contribution of the latest advances in these two imaging techniques of prostate cancer and their future developments.

Optimisation of reconstruction, volumetry and dosimetry for 99mTc-SPECT and 90Y-PET images: Towards reliable dose-volume histograms for selective internal radiation therapy with 90Y-microspheres.

PURPOSE: In Selective Internal Radiation Therapy (SIRT), 99mTc-MAA SPECT images are commonly used to predict microspheres distribution but recent works used 90Y-microspheres PET images. Nevertheless, evaluation of the predictive power of 99mTc-MAA has been hampered by the lack of reliable comparisons between 99mTc-SPECT and 90Y-PET images. Our aim was to determine the "in situ" optimisation procedure in order to reliably compare 99mTc-SPECT and 90Y-PET images and achieve optimal personal dosimetry. METHODS: We acquired 99mTc-SPECT/CT and 90Y-PET/CT images of NEMA and Jaszczak phantoms. We found the best reconstruction parameters for quantification and for volume estimations. We determined adaptive threshold curves on the volumetric reconstruction. We copied the optimised volumes on the quantitative reconstruction, named here the "cross volumes" technique. Finally, we compared 99mTc-SPECT and 90Y-PET Dose Volume Histograms. RESULTS: Our "in situ" optimisation procedure decreased errors on volumes and quantification (from -44.2% and -15.8% to -3.4% and -3.28%, respectively, for the 26.5mL PET phantom sphere). Moreover, 99mTc-SPECT and 90Y-PET DVHs were equivalent only after the optimisation procedure (difference in mean dose <5% for the three biggest spheres). CONCLUSIONS: This work showed that a preliminary "in situ" phantom study was necessary to optimise volumes and quantification of 99mTc-SPECT and 90Y-PET images and allowed to achieve a reliable comparison between patient treatment planning and post implant dosimetry, notably by the use of the "cross volumes" technique. Methodology developed in this work will enable robust evaluations of the predictive power of 99mTc-SPECT, as well as dose-response relationship and side effects in SIRT treatments.

Liver Selective Internal Radiation Therapy with (90)Y resin microspheres: comparison between pre-treatment activity calculation methods.

Different methods to calculate (90)Y resin microspheres activity for Selective Internal Radiation Therapy (SIRT) were compared. Such comparison is not yet available and is needed in clinical practice to optimize patient specific treatment planning. 32 (99m)Tc-macroagregates (MAA) evaluations were performed, followed by 26 treatments. Four methods to calculate (90)Y-activity were applied retrospectively: three based on Body Surface Area and one based on MIRD formalism, partition model (PM). Relationships between calculated activities, lung breakthrough (LB), the activity concentration ratio between lesions and healthy liver (T/N) and tumour involvement were investigated, where lobar and whole liver treatments were analysed separately. Without attenuation correction, overestimation of LB was 65%. In any case, the estimated lungs' doses remained below 30 Gy. Thus, the maximal injectable activity (MIA) is not limited by lungs' irradiation. Moreover, LB was not significantly related to T/N, neither to tumour involvement nor radiochemical purity (RP). Differences in calculated activity with the four methods were extremely large, in particular they were greater between BSA-based and PM activities for lobar treatments (from -85% to 417%) compared to whole liver treatments (from -49% to 61%). Two values of T/N ratio were identified as thresholds: for BSA-based methods, healthy liver doses are much higher than 30 Gy when T/N < 3; for PM, tumour doses are higher than 120 Gy when T/N > 4. As PM accounts for uptake ratio between normal and tumour liver, this method should be employed over BSA-based methods.

Accuracy of 18-fluoro-2-deoxy-D-glucose positron emission tomography in the pretherapeutic detection of occult para-aortic node involvement in patients with a locally advanced cervical carcinoma.

PURPOSE: Patients with locally advanced cervical cancer (LACC) are usually treated with concurrent chemoradiotherapy. Extended-field chemoradiotherapy is indicated in case of para-aortic node involvement at initial assessment. 18-Fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography (18-FDG PET/CT) is currently considered to be the most accurate method of detection of node or distant metastases. The goal of this study was to evaluate the accuracy of PET at detecting para-aortic lymph node metastases in LACC patients with a negative morphological imaging. METHODS: Patients from five French institutions with LACC and both negative morphologic (magnetic resonance imaging, CT scan) and functional (PET or PET/CT) findings at the para-aortic level and distantly were submitted to a systematic infrarenal para-aortic node dissection either by laparoscopy or laparotomy. On the basis of pathological results, sensitivity, specificity, and positive and negative predictive values of PET/CT were assessed for para-aortic lymph node involvement. RESULTS: A total of 125 LACC patients (stage IB2-IVA disease with two local recurrences) fulfilled the inclusion criteria. All had an ilio-infrarenal para-aortic lymphadenectomy, either by laparoscopy (n = 117) or laparotomy (n = 8). Twenty-one patients (16.8%) had pathologically proven para-aortic metastases. Among them, 14 (66.7%) had negative PET/CT. Overall morbidity of surgery was 7.2%. All but one of the complications were mild and did not delay chemoradiotherapy. Sensitivity, specificity, and positive and negative predictive value of the PET/CT were 33.3, 94.2, 53.8, and 87.5%, respectively, for the detection of microscopic lymph node metastases. CONCLUSIONS: Laparoscopic staging surgery seems warranted in LACC patients with negative PET scan who are candidates for definitive concurrent chemoradiotherapy or exenteration.

Specificity of radioiodinated MIBG for neural crest tumors in childhood.

UNLABELLED: The high sensitivity of metaiodobenzylguanidine (MIBG) scintigraphy for sympathomedullary tumors such as neuroblastoma and pheochromocytoma is well documented. The specificity of MIBG scintigraphy for these tumors is also high but has been incompletely characterized for other neural crest tumors and non-neural crest tumors of childhood. METHODS: The medical records and MIBG scans of all children who had undergone MIBG scintigraphy for known or suspected neuroblastoma or pheochromocytoma were retrospectively reviewed at five major referral centers. Those patients found to have pathologies other than neuroblastoma or pheochromocytoma form the basis of this study. RESULTS: One hundred children with a total of 110 lesions met the inclusion criteria. All had negative MIBG scans except 1 of 2 children with infantile myofibromatosis, 1 of 2 with neuroendocrine carcinomas, 1 of 2 with pancreaticoblastomas and 1 of 10 with primitive neuroectodermal tumors. CONCLUSION: MIBG scintigraphy is highly specific for neuroblastoma and pheochromocytoma. Only 4% (4/100) of nonsympathomedullary tumors (non-pheochromocytoma and non-neuroblastoma) in childhood showed MIBG uptake, of which only 2% (2/100) were of non-neural crest origin.