Radiation absorbed dose calculation of Lu-177-DOTA-TATE therapy in patients with somatostatin receptor expressing tumors

Objectives During the last decade, Lu-177/Y-90 labelled somatostatin analogues, which preferentially binds to somatostatin receptors have been used extensively for the therapy of somatostatin receptor expressing tumours. The aim of the present study was to calculate radiation-absorbed doses in patients treated with Lu-177-DOTA-TATE in our department.

Methods The study population was composed of 27 patients, 14m, 13f, with a mean age of 55.3±12.9. For calculation of radiation absorbed doses a series of anterior-posterior whole body images were acquired for each patient at 4, 20, 44 and 68 hours after the therapeutic radiopharmaceutical administration. Blood samples at 0, 15, 30, 60, 180 min and 24, 48 and 68 hours after injection were obtained for bone marrow and whole body radiation dose calculations. For estimation of individual tumour doses, MIRD scheme with unit density sphere model was used. Tumour volumes were determined from CT images.

Results The administered Lu-177-DOTA-TATE dose was ranged from 8.0 GBq to 24.2 GBq (mean dose 15.1±4.5GBq). The number of treatment cycles were 2 in 12 patients, 3 in 12 patients, 4 in 2 patients and 5 in 1 patient. The calculated radiation absorbed dose to whole body, bone marrow and kidneys were 0.8±0.3 Gy (min 0.3 and max 1.4 Gy), 0.4±0.2 (min 0.1, max 0.9 Gy) and 13.5±4.2 Gy (min 2.0, max 22.5 Gy), respectively. The tumour doses were ranged from 5.1 to 628.3 Gy with a mean value of 110.3±115.1 Gy.

Conclusions This study suggested the Lu-177 DOTA-TATE therapy is a safe treatment technique and radiation absorbed doses to critical organs are within limits. Also it seems that radiation absorbed dose calculation is mandatory for planning the number of therapy cycles for each patient.