Measurement and calculation of characteristic prompt gamma ray spectra emitted during proton irradiation

Polf, Jerimy; Peterson, Stephen W.; McCleskey, M.; Roeder, B. T.; Spiridon, A.; Beddar, Sam; Trache, L.

doi:10.1088/0031-9155/54/22/n02

Cited by 87 publications

(84 citation statements)

References 14 publications

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“…The energy resolutions for both the HPGe and CZT baseline CCs are less than 5% for incident gammas with energies above 2 MeV, and we found this resolution adequate for identifying major peaks in the incident gamma energy spectrum. As shown by Polf et al 3,4 the PG spectrum emitted during proton therapy may be clinically useful as means of studying the elemental composition of the irradiated tissue.…”

Section: Discussionmentioning

confidence: 99%

The effects of Doppler broadening and detector resolution on the performance of three‐stage Compton cameras

et al. 2012

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Purpose:The authors investigated how the characteristics of the detectors used in a three-stage Compton camera (CC) affect the CC's ability to accurately measure the emission distribution and energy spectrum of prompt gammas (PG) emitted by nuclear de-excitations during proton therapy. The detector characteristics they studied included the material (high-purity germanium [HPGe] and cadmium zinc telluride [CZT]), Doppler broadening (DB), and resolution (lateral, depth, and energy). Methods:The authors simulated three-stage HPGe and CZT CCs of various configurations, detecting gammas from point sources with energies ranging from 0.511 to 7.12 MeV. They also simulated a proton pencil beam irradiating a tissue target to study how the detector characteristics affect the PG data measured by CCs in a clinical proton therapy setting. They used three figures of merit: the distance of closest approach (DCA) and the point of closest approach (PCA) between the measured and actual position of the PG emission origin, and the calculated energy resolution. Results: For CCs with HPGe detectors, DB caused the DCA to be greater than 3 mm for 14% of the 6.13 MeV gammas and 20% of the 0.511 MeV gammas. For CCs with CZT detectors, DB caused the DCA to be greater than 3 mm for 18% of the 6.13 MeV gammas and 25% of the 0.511 MeV gammas. The full width at half maximum (FWHM) of the PCA in theẑ direction for HPGe and CZT detectors ranged from 1.3 to 0.4 mm for gammas with incident energy ranging from 0.511 to 7.12 MeV. For CCs composed of HPGe detectors, the resolution of incident gamma energy calculated by the CC ranged from 6% to 1% for gammas with true incident energies from 0.511 to 7.12 MeV. For CCs composed of CZT detectors, the resolution of gamma energy calculated by the CC ranged from 10% to 1% for gammas with true incident energies from 0.511 to 7.12 MeV. For HPGe and CZT CCs in which all detector effect were included, the DCA was less than 3 mm for 75% and 68% of the detected gammas, respectively, and restricting gammas to those having energy greater than 2.0 MeV increased these percentages to 83% and 77% for HPGe and CZT, respectively. Distributions of the true gamma origins and the PCA after detector characteristics had been included showed good agreement on beam range and some loss of resolution for the lateral profile of the PG emission. Characteristic energy lines were evident in the calculated gamma energy spectrum. Conclusions: The authors found the following: (1) DB is the dominant source of spatial and energy resolution loss in the CCs at all energy levels; (2) the largest difference in the spatial resolution of HPGe and CZT CCs is that the spatial resolution distributions of CZT have broader tails. The differences in the FWHM of these distributions are small; (3) the energy resolution of both HPGe and CZT three-stage CCs is adequate for PG spectroscopy; and (4) restricting the gammas to those having energy greater than 2.0 MeV can improve the achievable image resolution.

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Section: Discussionmentioning

confidence: 99%

The effects of Doppler broadening and detector resolution on the performance of three‐stage Compton cameras

et al. 2012

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“…Anderson scanning beam proton therapy treatment nozzle. We incorporated the ability to calculate PG detection with a high purity germanium (HPGe) detector by adding the HPGe detector and BGO Compton-suppression shielding geometry and gamma scoring from a validated MC model developed by Polf et al (2009b) into the scanning beam model. Finally, the abilities to load patient CT data and model proton beam interactions within the patient were incorporated into the MC model providing the option to calculate prompt gamma emission from either a rectangular water phantom or a patient irradiated during scanning beam proton treatment delivery.…”

Section: Methodsmentioning

confidence: 99%

Detecting prompt gamma emission during proton therapy: the effects of detector size and distance from the patient

et al. 2014

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Recent studies have suggested that the characteristics of prompt gammas (PG) emitted from excited nuclei during proton therapy are advantageous for determining beam range during treatment delivery. Since PGs are only emitted while the beam is on, the feasibility of using PGs for online treatment verification depends greatly on the design of highly efficient detectors. The purpose of this work is to characterize how PG detection changes as a function of distance from the patient as a means of guiding the design and usage of clinical prompt gamma imaging detectors. Using a Monte Carlo model (GEANT4.9.4) we studied the detection rate (PGs per incident proton) of a high purity Germanium detector for both the total PG emission and the characteristic 6.13 MeV PG emission from 16O emitted during proton irradiation. The PG detection rate was calculated as a function of distance from the isocenter of the proton treatment nozzle for: (1) a water phantom irradiated with a proton pencil beam and (2) a prostate patient irradiated with a scanning beam proton therapy treatment field (lateral field size: ~6 cm × 6 cm, beam range: 23.5 cm). An analytical expression of the PG detection rate as a function of distance from isocenter, detector size, and proton beam energy was then developed. The detection rates were found to be 1.3 × 10−6 for oxygen and 3.9 × 10−4 for the total PG emission, respectively, with the detector placed 11 cm from isocenter for a 40 MeV pencil beam irradiating a water phantom. The total PG detection rate increased by ~85±3% for beam energies greater than 150 MeV. The detection rate was found to be approximately 2.1 × 10−6 and 1.7 × 10−3 for oxygen and total PG emission, respectively, during delivery of a single pencil beam during a scanning beam treatment for prostate cancer. The PG detection rate as a function of distance from isocenter during irradiation of a water phantom with a single proton pencil beam was described well by the model of a point source irradiating a cylindrical detector of a known diameter over the range of beam energies commonly used for proton therapy. For the patient studies, it was necessary to divide the point source equation by an exponential factor in order to correctly predict the falloff of the PG detection rate as a function of distance from isocenter.

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“…Prompt-gamma ray imaging appears as a good candidate to provide real-time information about the local dose both for proton [6], [7] and carbon ion [8] therapy. Indeed the prompt-gamma emission point distribution is tightly correlated to the dose distribution and the emission yields are of the same order of magnitude as the number of fragmentation events, which potentially constitutes a sufficiently intense source for in-beam single photon emission tomography.…”

Section: Introductionmentioning

confidence: 99%

Monte Carlo Simulations of Prompt-Gamma Emission During Carbon Ion Irradiation

Foulher

Bajard

Chevallier

et al. 2010

IEEE Trans. Nucl. Sci.

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Monte Carlo simulations based on the Geant4 toolkit (version 9.1) were performed to study the emission of secondary prompt-gamma rays produced by nuclear reactions during carbon ion-beam therapy. These simulations were performed along with an experimental program and instrumentation developments which aim at designing a prompt-gamma ray device for real-time control of hadrontherapy. The objective of the present study is twofold: firstly, to present the features of the prompt-gamma radiation in the case of carbon ion irradiation; secondly, to simulate the experimental setup and to compare measured and simulated counting rates corresponding to four different experiments. For each experiment, we found that simulations overestimate prompt-gamma ray detection yields by a factor of 12. Uncertainties in fragmentation cross sections and binary cascade model cannot explain such discrepancies. The so-called "photon evaporation" model is therefore questionable and its modification is currently in progress.

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Measurement and calculation of characteristic prompt gamma ray spectra emitted during proton irradiation

Cited by 87 publications

References 14 publications

The effects of Doppler broadening and detector resolution on the performance of three‐stage Compton cameras

The effects of Doppler broadening and detector resolution on the performance of three‐stage Compton cameras

Detecting prompt gamma emission during proton therapy: the effects of detector size and distance from the patient

Monte Carlo Simulations of Prompt-Gamma Emission During Carbon Ion Irradiation

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