Internal Dosimetry in Patients Undergoing a ¹⁷⁷Lu-[DOTA0, Tyr3] Octreotate Therapy

Abstract

Patients with inoperable neuro-endocrine tumours (NETs) often have symptoms (i.e. diarrhea...) that decrease their quality of life. Targeted radionuclide therapy (TRT) can be used to increase the quality of life for these patients by relieving symptoms and suppressing tumour growth. For NETs, ¹⁷⁷Lu-[DOTA0, Tyr3] (a radiolabelled somatostatin analogue) is used as TRT. The organs at risk for this TRT are the kidneys and bone marrow, therefore, dosimetry should be performed in these patients to avoid side effects of over exposure (<25 Gy for Kidneys and 2 Gy for bone marrow). The aim of the study was to acquire dose measurements for the Kidneys using Mathematica 8™ for residence times and OLINDA/EXM™ for absorbed dose. Three patients with varying cycles of therapy were selected. The absorbed dose to the kidneys and to the tumour was calculated. For this, whole body images were acquired (GE Infinia Hawkeye 1) at 2hrs, 3hrs, 5hrs and 23hrs post injection of the therapeuticum. Regions of interest (ROI) were drawn over the kidneys and the tumour (liver lesions). The area under the curve of %Injected Activity vs. Time for all time points for each organ was used to calculate the residence times according to the MIRD dosimetry scheme using Mathematica 8™. These residence times were inputted into the OLINDA/EXM™ dosimetry software which then calculated equivalent radiation dose which can be converted to absorbed dose by multiplying it with injected activity. The results showed doses of about 0.36 Gy, 1.6 Gy and 0.75 Gy for kidneys on respective cycles, 1.34 Gy, 0.78 Gy and 0.696 Gy for the respective tumour in the liver. Results indicate how dose limiting organs, and tumour sites can be evaluated using the Mathematica 8™ and OLINDA/EXM™. Planar conjugate imaging can be used for dosimetry. From the work that was done during this research, an individualized patient dosimetry system was setup at another hospital, which provides another novel technique that supports physicists to learn and hopefully be able to improve on this novel technique for enhanced patient treatment and importantly for the safety of all who work with these radionuclides.