SU-F-J-200: An Improved Method for Event Selection in Compton Camera Imaging for Particle Therapy

Journal Article · Wed Jun 15 00:00:00 EDT 2016 · Medical Physics

DOI:https://doi.org/10.1118/1.4956108· OSTI ID:22634796

Mackin, D; Beddar, S ^[1]; Polf, J; Draeger, E ^[2]; Peterson, S ^[3]

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1. UT MD Anderson Cancer Center, Houston, TX (United States)
2. University of Maryland School of Medicine, Baltimore, MD (United States)
3. University of Cape Town, Rondebosch, Cape Town (South Africa)

Purpose: The uncertainty in the beam range in particle therapy limits the conformality of the dose distributions. Compton scatter cameras (CC), which measure the prompt gamma rays produced by nuclear interactions in the patient tissue, can reduce this uncertainty by producing 3D images confirming the particle beam range and dose delivery. However, the high intensity and short time windows of the particle beams limit the number of gammas detected. We attempt to address this problem by developing a method for filtering gamma ray scattering events from the background by applying the known gamma ray spectrum. Methods: We used a 4 stage Compton camera to record in list mode the energy deposition and scatter positions of gammas from a Co-60 source. Each CC stage contained a 4×4 array of CdZnTe crystal. To produce images, we used a back-projection algorithm and four filtering Methods: basic, energy windowing, delta energy (ΔE), or delta scattering angle (Δθ). Basic filtering requires events to be physically consistent. Energy windowing requires event energy to fall within a defined range. ΔE filtering selects events with the minimum difference between the measured and a known gamma energy (1.17 and 1.33 MeV for Co-60). Δθ filtering selects events with the minimum difference between the measured scattering angle and the angle corresponding to a known gamma energy. Results: Energy window filtering reduced the FWHM from 197.8 mm for basic filtering to 78.3 mm. ΔE and Δθ filtering achieved the best results, FWHMs of 64.3 and 55.6 mm, respectively. In general, Δθ filtering selected events with scattering angles < 40°, while ΔE filtering selected events with angles > 60°. Conclusion: Filtering CC events improved the quality and resolution of the corresponding images. ΔE and Δθ filtering produced similar results but each favored different events.

• OSTI ID: 22634796
• Journal Information: Medical Physics, Vol. 43, Issue 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-2405
• Country of Publication: United States
• Language: English

Related Subjects

60 APPLIED LIFE SCIENCES
61 RADIATION PROTECTION AND DOSIMETRY
ALGORITHMS
ANIMAL TISSUES
BIOMEDICAL RADIOGRAPHY
CAMERAS
COBALT 60
ENERGY ABSORPTION
FILTERS
GAMMA RADIATION
GAMMA SPECTRA
IMAGES
PARTICLE BEAMS
PATIENTS
RADIATION DOSE DISTRIBUTIONS
RADIATION DOSES
RADIOTHERAPY
SCATTERING
CDZNTE SEMICONDUCTOR DETECTORS