We describe our initial experience with integrated whole-body Fluor-18-Fluordesoxyglucose-PET/MR imaging in children in a retrospective study of all 18F-FDG-PET/MR at our institution. 51 studies were carried out in 41 children (34 girls, 17 boys) with a mean age of 10.16 years (10 months-24 years). Primary diagnosis included rhabdomyosarcoma (n=18) and Osteosarcoma (n=5). The majority of studies (n=29, 57.9%) were performed for treatment response/restaging. All studies were diagnostic (technical success rate 100%). The mean effective dose was 5.25 mSv (2.1-11.5 mSv). Mean total imaging time was 80 minutes (42-138 minutes). Thirty-eight (74.5%) cases had an average of 2.2 additional MR sequences. 18F-FDG PET/MR is technically feasible for the evaluation of oncologic processes in children at a fraction of the radiation dose.
A total of 51 whole body 18F-FDG PET/MRI studies were carried out in 41 children (34 girls, 17 boys) between December 2016 and November 2017. The children’s ages ranged from 10 months to 24 years (mean age: 10 years 2 months). Primary oncologic indication included rhabdomyosarcoma (n =18), Osteosarcoma (n = 5), neuroblastoma (n = 3), Ewing sarcoma (n = 2), teratoma (n=2), as well as one of each of the following: Burkitt’s lymphoma, Adrenal Cortical Carcinoma, Cutaneous T-cell lymphoma, GIST Tumor, Medulloblastoma, Rhabdoid Tumor, Urothelial Carcinoma, Paraganglioma and Wilm's Tumor. Eight children were investigated for cancer predisposition syndromes (Li-Fraumeni-n=4, Neurofibromatosis 1-n=3, Ataxia-Telangiectasia-n=1); while 3 others had benign diseases (Castleman's disease-n=1, Gorham-Stout disease-n=1, Langerhans Cell Hitiocytosis-n=1) and one patient underwent PET/MR for the investigation of a paraneoplastic syndrome (autoimmune encephalitis). Sixteen (31.4%) studies were performed for initial investigation/staging of known lesions, 29 (57.9%) were performed for evaluation of treatment response/restaging. The remaining 6 (11.8%) studies were performed for suspected malignancy/surveillance.
All studies were diagnostic (technical success rate 100%). Thirty-two patients (62.7%) underwent general anesthesia, two (3.9%) patients receive deep sedation and 17 (33.3%) did not require either. The mean effective dose was 5.25 mSv (range: 2.1-11.5 mSv). Average time from injection to imaging was 70 minutes (range: 49-199 minutes).
Total imaging time range from 42 minutes to 138 minutes (mean: 80 minutes +/- 22 minutes). Thirty-eight (74.5%) cases had additional MR sequences requested by the radiologist averaging 2.2 additional sequences per case and with an average additional time of 15 minutes (range 5-50). The remaining 13 (25.5%) cases had no additional sequences.
Discussion
Our early experience shows perfect technical success in a wide variety of oncologic processes both for initial staging and treatment response/follow up with a major impact in effective dose between 58% and 71% lower than previously reported averages (12.5 mSv +/- 4.1 and 18.35 +/- 13.52 mSv) for 18F-FDG PET/CT[1,2].
We acknowledge that our protocol has more sequences than most previously published
protocols because it will allow us to determine which sequences are necessary
for localization and characterization of lesions. The additional goal of this
detailed protocol is to create a one-stop-shop imaging test that eliminates the
need for additional studies. Eliminating additional MR studies is of
particular importance in younger patients to decrease anesthesia/sedation time and
eliminate sedation visits. This preliminary series will be used to create
new, focused protocols. For example, DWI
adds time and may not be necessary in areas without disease. Additional out-of-protocol sequences, present in a majority
(74.5%) of cases and contributing to an average of 15 minutes per case, must
also be addressed to eliminate uncertainty of exact study duration. As we transition
more patients from PET/CT to PET/MRI, specifically tailored protocols that
allow us to maintain reasonable table times and patient throughput.
1. Klenk C, Gawande R, Uslu L, Khurana A, Qiu D, Quon A, Donig J, Rosenberg J, Luna-Fineman S, Moseley M, Daldrup-Link HE. Ionising radiation-free whole-body MRI versus (18)F-fluorodeoxyglucose PET/CT scans for children and young adults with cancer: a prospective, non-randomised, single-centre study. Lancet Oncol. 2014; 15(3):275-85.
2. Kim YY, Shin HJ, Kim MJ, Lee MJ. Comparison of effective radiation doses from X-ray, CT, and PET/CT in pediatric patients with neuroblastoma using a dose monitoring program. Diagn Interv Radiol. 2016; 22(4):390-4