Dosimetry for 131 I-MIBG therapies in metastatic neuroblastoma, phaeochromocytoma and paraganglioma

Purpose Radiation dosimetry is a basic requirement for targeted radionuclide therapies (TRT) which have become of increasing interest in nuclear medicine. Despite the significant role of the radiopharmaceutical 131 I-metaiodobenzylguanidine (MIBG) for the treatment of metastatic neuroblastoma, phaeochromocytoma and paraganglioma details for a reliable dosimetry are still sparse. This work presents our procedures, the dosimetric data and experiences with TRT using 131 I-MIBG. Methods A total of 21 patients were treated with 131 I-MIBG between 2004 and 2008 according to a clearly defined protocol. Whole-body absorbed doses were determined by a series of scintillation probe readings for all 21 cases. Tumour absorbed doses were calculated on the basis of quantitative imaging for an entity of 25 lesions investigated individually using the region of interest (ROI) technique based on five scans each. Results Typical whole-body absorbed doses are found in the region of 2 Gy (range: 1.0–2.9 Gy) whereas tumour absorbed doses in turn cover a span between 10 and 60 Gy. Nonetheless this variation of tumour absorbed doses is comparatively low. Conclusion The trial protocol in use is a substantial advancement in terms of reliable dosimetry. A clearly defined modus operandi for MIBG therapies should involve precisely described dosimetric procedures, e.g. a minimum of 20 whole-body measurements using a calibrated counter and at least four gamma camera scans over the whole period of the inpatient stay should be carried out. Calculation of tumour volumes is accomplished best via evaluation of SPECT and CT images.