30th Annual Meeting of the BACR & 4th Annual Meeting of ACP - 10-12 April 1989

Measurements of M125IBG uptake in surgically excised samples of neuroblastoma from 6 patients were used to assess absorbed dose to micrometastases. Doses to achieve a 50% probability of cure were calculated using a simple analysis. Two categories were examined: (a) absorbed dose greater than 50% cure dose; (b) absorbed dose less than 50% cure dose. The number of patients falling into each category depends on the tumour size and on the radionuclide half-life in the tumour. For a 1 mm diameter tumour the number of category (a) patients increases from 0 (t1/2 = 1.2 days) to 4 (t1/2=8 days). MIBG is less effective for smaller tumours due to the reduced absorption of the beta-energy from 1311. For a 0.2mm diameter tumour the number of category (a) patients increases from 0 (t1/2=1.2 days) to 2 01/2=8 days). The use of mIBG in combination with total body irradiation (TBI) and autologous bone marrow rescue was investigated. For a 1 mm tumour the number in category (a) increases from 3 (t1/2= 1.2 days) to 5 (t1/2=8 days). For a 0.2mm tumour all 6 patients remain in category (a) for the full range of tumour half-times considered. Tumour doses with combined mIBG/TBI are significantly higher than achievable with either modality alone. Additionally, the two modalities complement each other as TBI is relatively more effective at eliminating small (< 1 mm) micrometastases and single cells whereas in mIBG is better for larger (>, 1mm) micrometastases.