Detection and discrimination of neutron capture events for NCEPT dose quantification

Medientyp: E-Artikel
Titel: Detection and discrimination of neutron capture events for NCEPT dose quantification
Beteiligte: Chacon, Andrew; Kielly, Marissa; Rutherford, Harley; Franklin, Daniel R.; Caracciolo, Anita; Buonanno, Luca; D’Adda, Ilenia; Rosenfeld, Anatoly; Guatelli, Susanna; Carminati, Marco; Fiorini, Carlo; Safavi-Naeini, Mitra
Erschienen: Springer Science and Business Media LLC, 2022
Erschienen in: Scientific Reports
Sprache: Englisch
DOI: 10.1038/s41598-022-09676-x
ISSN: 2045-2322
Schlagwörter: Multidisciplinary
Entstehung:
Anmerkungen:
Beschreibung: <jats:title>Abstract</jats:title><jats:p>Neutron Capture Enhanced Particle Therapy (NCEPT) boosts the effectiveness of particle therapy by capturing thermal neutrons produced by beam-target nuclear interactions in and around the treatment site, using tumour-specific <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{10}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>10</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>B or <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{157}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>157</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>Gd-based neutron capture agents. Neutron captures release high-LET secondary particles together with gamma photons with energies of 478 keV or one of several energies up to 7.94 MeV, for <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{10}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>10</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>B and <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{157}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>157</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>Gd, respectively. A key requirement for NCEPT’s translation is the development of in vivo dosimetry techniques which can measure both the direct ion dose and the dose due to neutron capture. In this work, we report signatures which can be used to discriminate between photons resulting from neutron capture and those originating from other processes. A Geant4 Monte Carlo simulation study into timing and energy thresholds for discrimination of prompt gamma photons resulting from thermal neutron capture during NCEPT was conducted. Three simulated <jats:inline-formula><jats:alternatives><jats:tex-math>$$300\times 300\times 300$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>300</mml:mn> <mml:mo>×</mml:mo> <mml:mn>300</mml:mn> <mml:mo>×</mml:mo> <mml:mn>300</mml:mn> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> mm<jats:inline-formula><jats:alternatives><jats:tex-math>$$^3$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>3</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula> cubic PMMA targets were irradiated by <jats:inline-formula><jats:alternatives><jats:tex-math>$$^4$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>4</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>He or <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{12}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>12</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>C ion beams with a spread out Bragg peak (SOBP) depth range of 60 mm; one target is homogeneous while the others include <jats:inline-formula><jats:alternatives><jats:tex-math>$$10\times 10\times 10$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>10</mml:mn> <mml:mo>×</mml:mo> <mml:mn>10</mml:mn> <mml:mo>×</mml:mo> <mml:mn>10</mml:mn> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> mm<jats:inline-formula><jats:alternatives><jats:tex-math>$$^3$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>3</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula> neutron capture inserts (NCIs) of pure <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{10}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>10</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>B or <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{157}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>157</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>Gd located at the distal edge of the SOBP. The arrival times of photons and neutrons entering a simulated <jats:inline-formula><jats:alternatives><jats:tex-math>$$50\times 50\times 50$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>50</mml:mn> <mml:mo>×</mml:mo> <mml:mn>50</mml:mn> <mml:mo>×</mml:mo> <mml:mn>50</mml:mn> </mml:mrow> </mml:math></jats:alternatives></jats:inline-formula> mm<jats:inline-formula><jats:alternatives><jats:tex-math>$$^3$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>3</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula> ideal detector were recorded. A temporal mask of 50–60 ns was found to be optimal for maximising the discrimination of the photons resulting from the neutron capture by boron and gadolinium. A range of candidate detector and thermal neutron shielding materials were simulated, and detections meeting the proposed acceptance criteria (i.e. falling within the target energy window and arriving 60 ns post beam-off) were classified as true or false positives, depending on their origin. The ratio of true/false positives (<jats:inline-formula><jats:alternatives><jats:tex-math>$$R_{TF}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>R</mml:mi> <mml:mrow> <mml:mi>TF</mml:mi> </mml:mrow> </mml:msub> </mml:math></jats:alternatives></jats:inline-formula>) was calculated; for targets with <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{10}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>10</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>B and <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{157}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>157</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>Gd NCIs, the detector materials which resulted in the highest <jats:inline-formula><jats:alternatives><jats:tex-math>$$R_{TF}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>R</mml:mi> <mml:mrow> <mml:mi>TF</mml:mi> </mml:mrow> </mml:msub> </mml:math></jats:alternatives></jats:inline-formula> were cadmium-shielded CdTe and boron-shielded LSO, respectively. The optimal irradiation period for both carbon and helium ions was 1 µs for the <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{10}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>10</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>B NCI and 1 ms for the <jats:inline-formula><jats:alternatives><jats:tex-math>$$^{157}$$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow /> <mml:mn>157</mml:mn> </mml:msup> </mml:math></jats:alternatives></jats:inline-formula>Gd NCI.</jats:p>
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