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Abstract
Objective. Molecular radiotherapy is the most used treatment modality against malign and benign diseases of thyroid. In that context, the large heterogeneity of therapeutic doses in patients and the range of effects observed show that individualized dosimetry is essential for optimizing treatments according to the targeted clinical outcome. Approach. We developed a high-resolution mobile gamma camera specifically designed to improve the quantitative assessment of the distribution and biokinetics of 131I at patients’s bedside after treatment of thyroid diseases. The first prototype has a field of view of 5 × 5 cm2 and consists of a high-energy parallel-hole collimator made of 3D-printed tungsten, coupled to a 6 mm thick CeBr3 scintillator readout by an array of silicon photomultiplier detectors. The intrinsic and overall imaging performance of the camera was evaluated with 133Ba and 131I sources. In order to test its quantification capability in realistic clinical conditions, two different 3D-printed thyroid phantoms homogeneously filled with 131I were used. Both single view and conjugate view approaches have been applied, with and without scatter correction technique. Main Results. The camera exhibits high imaging performance with an overall energy resolution of 7.68 ± 0.01%, a submillimetric intrinsic spatial resolution of 0.74 ± 0.28 mm and a very low spatial distortion 0.15 ± 0.10 mm. The complete calibration of the camera shows an overall spatial resolution of 3.14 ± 0.03 mm at a distance of 5 cm and a corresponding sensitivity of 1.23 ± 0.01 cps/MBq, which decreases with distance and slightly changes with source size due to the influence of scattering. Activity recovery factors better than 97% were found with the thyroid phantoms. Significance. These preliminary results are very encouraging for the use of our camera as a tool for accurate quantification of absorbed doses and currently motivates the development of a fully operational clinical camera with a 10 × 10 cm2 field of view and improved imaging capabilities.
Highlights
Molecular radiotherapy (MRT) is a localized radiation treatment modality based on the internal delivery of a radiolabelled vectors, known as radiopharmaceutical, for the treatment of benign, malign and inflammatory conditions
The mean energy resolution (ER) measured in the useful field of view (UFOV), CFOV and CFOV together with the corrected overall ER are summarized in table 1
Characterization and calibration of the first prototype of a high-resolution mobile gamma camera with a 5 × 5 cm2 field of view (FOV) optimized to improve the quantitative assessment of the distribution and biokinetics of 131I after treatment administration
Summary
Molecular radiotherapy (MRT) is a localized radiation treatment modality based on the internal delivery of a radiolabelled vectors, known as radiopharmaceutical, for the treatment of benign, malign and inflammatory conditions. MRT is currently rapidly evolving thanks to the joint development of new tumor-seeking biomarkers and innovative radionuclides, which allow to selectively deliver cytotoxic radiation to cells while causing minimal toxicity to surrounding healthy tissues. Other applications are available in clinic, as the therapy of neuroendocrine tumors using 177Lu/90Y-somatostatin analogs (177Lu-Dotatate or 90Y-Dotatoc), the treatment of prostate cancer metastasized to bones using 223Ra-dichloride (Xofigo®) and the intra-arterial treatments of unresectable primary hepatocarcinoma and metastases with 90Y-microspheres (SIR-Spheres® or TheraSpheres®) (Ting et al 2009, Yeong et al 2014). New radiopharmaceuticals, including agents that target tumor-associated antigens over-expressed in different malignant tissues are currently tested in clinical trials, such as PSMA for the treatment of prostate cancer (Eyben et al 2018). Because of the higher relative biological effectiveness of alpha radiation, the interest in the development of therapies involving alpha emitters, such as 211At, 225Ac, 227Th, 213Bi, and 212Pb, is rapidly growing and first clinical trials show very promising results (Marcu et al 2018)
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