Development of a portable gamma imaging system for absorbed radiation dose control in molecular radiotherapy

Abstract : Targeted radionuclide therapy is still a developing area among the different treatment modalities against cancer. However, its range of applications is rapidly expanding thanks to the emergence of new radiopharmaceuticals labeled with beta or alpha emitters (peptides, ²²³ Ra alpha-therapy, ²²¹ As alpha- immunotherapy, ...) (Ersahin 2011). In that context, the large heterogeneity of absorbed doses and the range of effects observed, both in terms of toxicity and response, demonstrate that individualized patient dosimetry is essential to optimize this therapy (Strigari 2011). In clinical practice, patient-specific dosimetry of tumors and organs-at-risk (liver, kidney, ...) is image-based and rely on the quantification of radio- pharmaceutical uptake as a function of time. These images can be obtained from either a pre-therapy tracer study or from a previous therapy procedure. The detection constraints imposed by the treatment protocols are very different from those associated with diagnostic imaging. (Flux 2011 Konijnenberg 2011). Thus, conventional gamma cameras are not suited for detecting high activity of gamma emitters with energy below 100 keV (²²³ Ra) or greater than 300 keV (¹³¹ I, ⁹⁰Y ). Moreover, high activities of the injected tracer typically require isolation of the patient, making the use of standard imaging devices difficult. Finally, the availability of these devices is incompatible with an accurate temporal sampling of the kinetics of the tracer, which is a key parameter for the quantification of the absorbed doses. The objective of my thesis was precisely to propose new instrumental and methodological approaches aiming to strengthen the control of the dose released to patients during molecular radiotherapy. This is achieved by reducing the uncertainties associated to activity quantification (and therefore to the absorbed dose calculation) through the use of a compact and highly optimized imaging system. Specifically, the work consisted in the development and optimization of a miniaturized, high-resolution mobile gamma camera specifically designed to improve the individual quantitative assessment of the heterogeneous distribution and biokinetics of the radiotracer before and after treatment administration. The study was focused on the treatment of benign and malign thyroid disease with ¹³¹ I. The first prototype of the mobile camera, with a field of view of 5x5 cm², consists of a high-energy parallel- hole collimator, optimized with Monte Carlo simulation and made with 3D printing, coupled to a 6 mm thick continuous CeBr3 scintillator readout by a recent and well-suited technology based on arrays of Silicon Pho- tomultiplier (SiPMs) detectors. Its intrinsic properties, in term of energy and spatial response, have been tested with collimated point source of ⁵⁷Co and ¹³³Ba. The first feasibility prototype has been then calibrated with a line and five cylindrical sources filled with ¹³¹ I. The system calibration leads to an overall spatial resolution of (3.14±0.03) mm at a distance of 5 cm and a sensitivity that decreases with distance and slightly changes with source size. An average sensitivity of (1.23±0.01) cps/MBq has been found at 5 cm. In order to test the quantification capability of the camera, the first preclinical planar studies involved the use of different 3D-printed thyroid phantoms filled with ¹³¹ I, with and without nodules. Although corresponding to a relatively ideal, but realistic, clinical situation (no superimposition of background activity), the optimized imaging features of the camera leads to very promising results, with activity recovery factors that deviate of around 2% from the unity.
Complete list of metadatas

Cited literature [340 references]  Display  Hide  Download

https://tel.archives-ouvertes.fr/tel-02475983
Contributor : Abes Star <>
Submitted on : Wednesday, February 12, 2020 - 1:57:41 PM
Last modification on : Friday, February 14, 2020 - 1:36:24 AM

File

81526_TRIGILA_2019_diffusion.p...
Version validated by the jury (STAR)

Identifiers

  • HAL Id : tel-02475983, version 1

Citation

Carlotta Trigila. Development of a portable gamma imaging system for absorbed radiation dose control in molecular radiotherapy. Instrumentation and Detectors [physics.ins-det]. Université Paris-Saclay, 2019. English. ⟨NNT : 2019SACLS285⟩. ⟨tel-02475983⟩

Share

Metrics

Record views

29

Files downloads

3