3543 - Utility of ⁶⁸Ga DOTA-Octreotate PET/CT in Characterization of Pediatric Neuroendocrine Tumors

E. L. McKone¹, R. O. Kowalchuk¹, M. Dorr², J. D. Cameron³, M. A. Connors⁴, W. Allen-Rhoades⁵, P. J. Schoettler⁵, J. Rawwas⁶, D. R. Johnson⁷, G. B. Johnson⁷, A. Mahajan¹, S. K. Ahmed⁸, and N. N. Laack II¹; ¹Department of Radiation Oncology, Mayo Clinic, Rochester, MN, ²Department of Quantitative Health Sciences and Alliance Statistics and Data Management Center, Mayo Clinic, Rochester, MN, ³Department of Quantitative Health Sciences, Mayo Clinic, Rochester, MN, ⁴Mayo Clinic, Rochester, MN, ⁵Department of Pediatric Hematology/Oncology, Mayo Clinic, Rochester, MN, ⁶Childrens Minnesota Hematology Oncology, Minneapolis, MN, ⁷Mayo Clinic, Division of Nuclear Medicine, Rochester, MN, ⁸Department of Radiation Oncology, Mayo Clinic AZ, Phoenix, AZ

Purpose/Objective(s): Metaiodobenzylguanidine (MIBG) scintigraphy is standard for detecting metabolic tumor burden and radiotherapy (RT) target delineation in pediatric neuroendocrine neoplasms. However, MIBG scans are only 50% sensitive, with poor localization and spatial resolution. This is problematic for 3D RT planning, resulting in treating unnecessarily large volumes or inadvertent omission of areas that need RT. Most relapses occur in sites seen at baseline but not irradiated due to satisfactory chemotherapy response per MIBG. This suggests occult disease below the detection threshold of MIBG. We initiated a non-randomized prospective single institution trial of patients =30 years old with high-risk neuroendocrine neoplasms to assess the utility of FDA-approved ⁶⁸Ga-DOTATATE PET/CT in defining RT clinical target volume (CTV) compared to MIBG. Materials/

Methods: Patients were enrolled at initial diagnosis or later in treatment for primary metastatic or recurrent disease. Standard multimodality therapy was given before consolidative RT. RT volumes were standard-of-care and determined by post-induction MIBG. ⁶⁸Ga-DOTATATE PET scans were obtained at the time of RT planning. An institutionally approved unplanned interim analysis was performed after RT delivery. This included clinically blinded review of PET scans by 2 board certified Nuclear Medicine Radiologists and comparison to baseline scans and MIBG-determined CTVs. Patterns of failure will be assessed during an ongoing 2 year follow up.
Results: Eight patients with neuroblastoma of median age 3.5 years (all <18 years old; 4 female; 7 white) were analyzed. One patient enrolled after recurrence and had previous RT. All others enrolled during initial treatment. Results of PET scan analysis are shown on the table. The average (range) SUV max was 6.7 (2.5-33) for positive scans (n=6/8). At the time of interim analysis, only 2/8 patients are 2 years post-RT. Both are without evidence of relapse, including 1 with untreated PET-avid sites (n=4). Three relapses occurred <2 years post-RT, with 1 instance of radiographic progression in an untreated PET-avid site during maintenance therapy.
Conclusion: Results from this interim analysis suggest ⁶⁸Ga-DOTATATE may identify lesions not detected with MIBG. Although at least 1 participant in our ongoing study may have benefitted from utilization of ⁶⁸Ga-DOTATATE PET/CT for CTV delineation, multiple patients with untreated avid sites have not experienced relapse. Further efforts are required to define clinically meaningful findings on ⁶⁸Ga-DOTATATE PET.

Abstract 3543 – Table 1

	MIBG	PET DOTATATE
	Metastases in CTV	PET+ lesions	Summed mCurie Score	Overall Krenning Score*	Untreated PET+ Lesions	Any Relapse?	Relapse in Untreated PET+ site?	Follow-up of <1 year
Total Number	22	23	-	-	10	3	1	5
Median [range]	2.5 [1-6]	2 [0-7]	2.5 [0-14]	2.5 [1-4]	1 [0-4]	-	-	-
				*n=6 scans with Krenning score data