Proton computed tomography using multichannel gas detection technology

Patent metadata

Field	Value
Publication number	US-12455390-B2
Application number	US-202318222131-A
Country	US
Kind code	B2
Filing date	Jul 14, 2023
Priority date	Jul 15, 2022
Publication date	Oct 28, 2025
Grant date	Oct 28, 2025

Abstract

A Proton Computed Tomography (pCT) system utilizing proton beams for construction of 3-dimensional density maps of both test phantoms and living tissue. PCT is a much sought-after modality for treatment planning and validation at proton therapy treatment centers, as it would allow in situ imaging with the same beam that is used for the treatment. A pCT system according to the present invention includes gaseous detectors for tracking and energy reconstruction, a shutter system to extend dynamic range features while maintaining good energy resolution, and a method for determining proton energy from a forward-search algorithm utilizing segmentation of energy detector ionization signal readout. The gaseous detectors are Gas Electron Multiplier (GEM) based gaseous detectors.

First claim

We claim:

1. A method for creating tomographic images of a target Proton Computed Tomography (pCT), comprising:
directing a stream of protons toward a target;
measuring the proton trajectory of each proton before the target with a pre-tracker;
measuring the proton trajectory of each proton after the target with a post-tracker;
positioning a gaseous Time Projection Chamber (TPC) having a plurality of gas cells after the trackers to measure the proton energy after exiting the target by amplifying and measuring the profile of energy deposited along the proton trajectory through the TPC via the signal from ionization electrons liberated from proton energy loss in each gas cell;
a variable energy degrading shutter between the post-tracker and the TPC, said shutter extending the dynamic range of the TPC and maintaining good energy resolution in the TPC;
said shutter including a shutter encoder;
recording data from the shutter encoder in the data stream for automatic correction of the energy loss in the shutter; and
determining the proton energy by a search algorithm to determine the best match for the energy loss profile along the proton trajectory (dE/dx), with the stopping energy as the seed value for the search range.

2. The method of claim 1 , wherein the TPC comprises:
a series of absorbers equally spaced in order to divide the TPC into said plurality of gas cells, each of said cells including an inert gas therein;
one or more Gas Electron Multiplier (GEM) layers; and
applying an electric field to each of said gas cells to drift ionized electrons from each gas cell to the one or more GEM layers.

3. The method of claim 2 , wherein the TPC comprises an electronic readout layer for receiving electrons from the one or more GEM layers: said readout layer having segmentation along the proton direction in order to determine the energy loss profile.

4. The method of claim 3 , comprising:
said electronic readout layer including a plurality of segmented electrodes on a PCB;
an induced electric pulse generated by the electrons via induction; and
front end electronics for amplifying and processing the electric pulse and sending the resultant data on each pulse to a computer for further processing.

5. The method of claim 2 , comprising:
the absorbers are equally spaced; and
the absorbers are plastic film absorbers.

6. The method of claim 5 , comprising the film absorbers are constructed of MYLAR®.

7. The method of claim 4 , comprising:
the total integrated charge of each induced electric pulse is proportional to the number of ionized electrons produced; and
the total number of ionized electrons produced in each cell is proportional to the energy lost in that cell by protons passing through the gas.

8. The method of claim 7 , comprising grouping clusters of signals from each cell to determine the energy deposited in each cell.

9. The method of claim 8 , comprising determining the energy of the proton entering the TPC by measuring the stopping distance along the proton trajectory and the profile of the energy lost along the proton track.

10. The method of claim 2 , wherein the TPC comprises:
a chamber including a top plate with an inner surface; and
a plurality of grooves for accepting said absorbers.

11. The method of claim 2 , comprising said electric field applied to said gas cells 1 kV/cm.

12. The method of claim 1 , wherein the shutter comprises inserting one or more absorbers of different thicknesses before the TPC.

13. The method of claim 12 , comprising the encoder to record the thickness of said one or more inserted absorbers.

14. The method of claim 2 , wherein each of said absorbers in said series of absorbers are 0.3 mm thick MYLAR®.

15. The method of claim 14 , wherein said TPC comprises 50 of said gas cells having a total length per cell of 1 cm.

16. The method of claim 15 , wherein said TPC comprises an energy range up to 48 MeV for protons stopping in the TPC.

17. The method of claim 16 , wherein said TPC comprises a reconstructed energy resolution of less than 300 keV on average across the energy range based on fitting the energy loss profile and a measurement resolution of 10% per cell not including the energy straggling.

18. The method of claim 17 , wherein said absorbers in said TPC stops protons with less than 1 MeV kinetic energy.

Assignees

• Jefferson Science Ass Llc

Inventors

• Christy M Eric
• Keppel Cynthia

Classifications

• A61B6/032

  Transmission computed tomography [CT] · CPC title

• G01T1/1641

  Static instruments for imaging the distribution of radioactivity in one or two dimensions using one or several scintillating elements; Radio-isotope cameras · CPC title

• G01N2223/107

  protons · CPC title

• A61N5/1038

  taking into account previously administered plans applied to the same patient, i.e. adaptive radiotherapy · CPC title

• A61N5/1049

  for verifying the position of the patient with respect to the radiation beam · CPC title