Tumor Dosimetry in a Phase I Study of Lu(177)-DOTA-HH1 (Betalutin) - How hard does the magic bullet strike?
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- Institutt for fysikk 
Introduction: Antibody-radionuclide-conjugate therapy using the monoclonal antibodyagent 177 Lu-DOTA-HH1 (BetalutinTM ) developed by Nordic Nanovector, is a novel treatment of Non-Hodgkin s Lymphoma. A Phase I/II study is currently being conducted at Oslo University Hospital, the Lymrit-37-01-study. The main aim of this thesis was to develop and present a method to do dosimetric calculations on tumors in patients included in the study. Inhomogeneity of dose was investigated through dose rate maps and cumulative dose rate histograms.Method: Using imaging data from two SPECT/CT-sessions 4 and 7 days post-injection,activity in lesions was quantified. Volumes of interest (VOIs) were drawn by a nu-clear medicine specialist. VOIs were drawn with a margin around the imaged activityof the lesion, the novel VOISPECT -method. Cumulative activity was found through mono-exponential clearance of the activity. Patient specific masses from VOIs closely aroundthe tumors were used. Absorbed dose was found by the proposed S-factor, S,resultingin mean dose to the tumors. The activity quantification method was verified throughphantom measurements with hot spheres in attenuating material. The energy absorptionfactor was found using the dose calculation computer program OLINDA. Dose rate mapswere generated through the use of convolution of activity distribution and a voxel s-value kernel retrieved from a database.Result: A total of 17 tumors in 6 patients grouped in three dose levels were ascribeda mean dose. Mean doses ranged from 86 to 794cGy. Inter- and intra-patientdifferences were observed. The phantom experiment showed good accuracy, with relativeerrors in the order of 5% compared to true activity. A constant factor S ̄ to calculate thecumulative energy was found sufficient as long as tumor volumes are in the range 1mL to300mL. 16 dose rate maps and cumulative dose rate volume histograms were made, andD-values were found. Conclusion: The method presented was found to be successful in the calculation of mean tumor dose. A method to generate dose rate maps and cumulative dose rate histograms has also been found and presented.