Semi-automatic Segmentation Method for Determining 177Lu-DOTATATE Tumor Dosimetry

Meningioma

dosimetry, theragnostic

The aim of this study was to compare a semi-automatic segmentation method with manual reference segmentation to determine an overall tumor volume on post-therapy scintigraphy at D1 in patients treated with 177Lu-DOTATATE for meningioma or neuroendocrine tumor for dosimetric calculation.

The new wide-field solid-state cameras enable quantitative single-photon emission tomoscintigraphy (SPECT) acquisitions, particularly during internal vectorized radiotherapy treatments. These innovative treatments are mainly used in cancer therapy. They involve the injection of a radiopharmaceutical consisting of a vector specifically targeting the tumor cell - in this case, somatostatin analogues targeting somatostatin receptors - and a radioactive isotope emitting β- or α-radiation to kill the tumor cell, and γ-radiation for SPECT imaging - in this case 177Lu. These radiopharmaceuticals are currently prescribed at fixed doses for all patients. With the aim of personalized medicine, tumor dosimetry is essential for predicting efficacy and dose-response relationships at the individual level of this type of treatment. In view of the increasing therapeutic applications of these 177Lu therapies, the European Association of Nuclear Medicine (EANM) has recently issued recommendations on the dosimetry of 177Lu-labeled somatostatin analogues (Lutathéra®, 177Lu-DOTATATE), among others. Nevertheless, these recommendations are precise as regards dosimetry to organs at risk, but remain unclear as regards tumor dosimetry. Tumor dosimetry is therefore difficult to implement on a routine clinical basis. The efficacy of 177Lu-DOTATATE treatment has been demonstrated for neuroendocrine tumors in the NETTER-1 phase 3 study, and interesting results have been reported for the treatment of refractory meningiomas. Furthermore, a recent study showed that in patients with gastrointestinal neuroendocrine tumors treated with 177Lu-DOTATATE, tumor dosimetry could predict patient survival. In order to optimize a dosimetric approach in clinical routine, several steps are necessary: i) define a standardized manual or semi-automated segmentation method for determining the volumes of interest (tumor volume and/or organs at risk), ii) precisely quantify tumor or organs at risk volume activities over time, and iii) determine the doses absorbed by the tumor and/or organs at risk. An initial study was conducted in the department of nuclear medicine,to define a semi-automatic segmentation method for meningiomas treated with 177Lu-DOTATATE on pre-therapeutic 68Ga-DOTATOC positons emission tomography (PET), with the aim of predicting tumor dosimetry from pretherapeutic imaging. For this study, tumor segmentation will be performed directly on SPECT imaging carried out post-treatment on a 360° wide-field CZT camera to determine tumor dosimetry. The aim of this study is to compare a semi-automatic segmentation method with manual reference segmentation to determine overall tumor volume on post-therapy scintigraphy at D1 in patients treated with 177Lu-DOTATATE for meningioma or neuroendocrine tumor, with a view to dosimetric calculation.

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