Characterisation of a planar dosimetry method estimating the absorbed dose to the bone marrow during 177Lu-DOTATATE treatment

• Aim: An image based method for bone marrow dosimetry, earlier presented by our research group, has shown a significant correlation between the absorbed dose to the bone marrow and haematological toxicity in 177Lu-DOTATATE treatment. The aim of this study was to further evaluate and optimise the method. Materials and Methods: 46 patients with advanced neuroendocrine tumours were treated with 177Lu -DOTATATE on 2-6 occasions. The patients were evaluated using the 4 planar gamma camera images collected at 2, 24, 48 and 168 hours after injection. The whole body was divided into a high- and a low uptake compartment, using a threshold based segmentation tool in the image platform PhONSAi, developed in-house. The segmentation tool starts by including the highest uptake focus and then gradually includes foci with lower and lower uptakes until a threshold is reached where the number of foci escalates. The threshold determines the proportion of the foci that is included in the two compartments. Visual inspection was used to determine the threshold valuewhere all high uptake tissues (i.e. kidney, spleen, liver and tumours) were included in the high uptake compartment. For thresholds around this value the activity in the two compartments was determined by the conjugate view method and the bonemarrow dose was calculated as a sum of the self and cross dose in the low uptake compartment and the cross dose from the high uptake compartment. Results: The visual analysis implies a threshold value of 10%of the maximum number of foci. A correlation was found between the absorbed bone marrow dose and haematological toxicity with p-values ranging from 0.001 to 0.02 for thresholds between 2 % and 25 %, the strongest correlation was found at 15 %. The mean absorbed bone marrow dose were 0.20-0.22 Gy per 7.4 GBq for threshold values between 10-25 %, and increased to 0.28 Gy for the lower values. No significant difference was observed in coefficient of variation (8.2-8.7 %) for the individual mean absorbed doses when varying the threshold value. Conclusion: The individual variation in absorbed dose is maintained at a low level when varying the threshold value for the determination of the compartment sizes. This implies that the method is stable for estimation of bone marrow doses and its correlation to haematological toxicity.

Subject headings

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Cancer och onkologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Cancer and Oncology (hsv//eng)

Publication and Content Type

vet (subject category)

kon (subject category)