The Experts below are selected from a list of 2304 Experts worldwide ranked by ideXlab platform

J Verburg - One of the best experts on this subject based on the ideXlab platform.

  • a full scale clinical prototype for proton range verification using prompt gamma ray spectroscopy
    Physics in Medicine and Biology, 2018
    Co-Authors: F Huesogonzalez, Thomas Bortfeld, Moritz Rabe, Thomas A Ruggieri, J Verburg
    Abstract:

    We present a full-scale clinical prototype system for in vivo range verification of proton Pencil-Beams using the prompt gamma-ray spectroscopy method. The detection system consists of eight LaBr3 scintillators and a tungsten collimator, mounted on a rotating frame. Custom electronics and calibration algorithms have been developed for the measurement of energy- and time-resolved gamma-ray spectra during proton irradiation at a clinical dose rate. Using experimentally determined nuclear reaction cross sections and a GPU-accelerated Monte Carlo simulation, a detailed model of the expected gamma-ray emissions is created for each individual Pencil-beam. The absolute range of the proton Pencil-Beams is determined by minimizing the discrepancy between the measurement and this model, leaving the absolute range of the beam and the elemental concentrations of the irradiated matter as free parameters. The system was characterized in a clinical-like situation by irradiating different phantoms with a scanning Pencil-beam. A dose of 0.9 Gy was delivered to a [Formula: see text] cm3 target with a beam current of 2 nA incident on the phantom. Different range shifters and materials were used to test the robustness of the verification method and to calculate the accuracy of the detected range. The absolute proton range was determined for each spot of the distal energy layer with a mean statistical precision of 1.1 mm at a 95% confidence level and a mean systematic deviation of 0.5 mm, when aggregating Pencil-beam spots within a cylindrical region of 10 mm radius and 10 mm depth. Small range errors that we introduced were successfully detected and even large differences in the elemental composition do not affect the range verification accuracy. These results show that our system is suitable for range verification during patient treatments in our upcoming clinical study.

  • a full scale clinical prototype for proton range verification using prompt gamma ray spectroscopy
    arXiv: Medical Physics, 2018
    Co-Authors: F Huesogonzalez, Thomas Bortfeld, Moritz Rabe, Thomas A Ruggieri, J Verburg
    Abstract:

    We present a full-scale clinical prototype system for in vivo range verification of proton Pencil-Beams using the prompt gamma-ray spectroscopy method. The detection system consists of eight LaBr3 scintillators and a tungsten collimator, mounted on a rotating frame. Custom electronics and calibration algorithms have been developed for the measurement of energy- and time-resolved gamma-ray spectra during proton irradiation at a clinical dose rate. Using experimentally determined nuclear reaction cross sections and a GPU-accelerated Monte Carlo simulation, a detailed model of the expected gamma-ray emissions is created for each individual Pencil-beam. The absolute range of the proton Pencil-Beams is determined by minimizing the discrepancy between the measurement and this model, leaving the absolute range of the beam and the elemental concentrations of the irradiated matter as free parameters. The system was characterized in a clinical-like situation by irradiating different phantoms with a scanning Pencil-beam. A dose of 0.9 Gy was delivered to a 5x10x10 cm^3 target with a beam current of 2 nA incident on the phantom. Different range shifters and materials were used to test the robustness of the verification method and to calculate the accuracy of the detected range. The absolute proton range was determined for each spot of the distal energy layer with a mean statistical precision of 1.1 mm at a 95% confidence level and a mean systematic deviation of 0.5 mm, when aggregating Pencil-beam spots within a cylindrical region of 10 mm radius and 10 mm depth. Small range errors that we introduced were successfully detected and even large differences in the elemental composition do not affect the range verification accuracy. These results show that our system is suitable for range verification during patient treatments in our upcoming clinical study.

  • mo ab bra 07 prompt gamma ray spectroscopy for range verification of clinical proton Beams
    Medical Physics, 2015
    Co-Authors: J Verburg, Thomas Bortfeld, J Seco
    Abstract:

    Purpose: We developed a pre-clinical prototype system for range verification of proton Pencil-beam scanning fields. The system was evaluated using phantom treatment plans delivered with a clinical dose rate. Methods: The absolute range of proton Pencil-Beams was verified through an optimization procedure, which matches energy- and time-resolved prompt gamma-ray measurements with models, based on cross sections for discrete prompt gamma-ray line excitations. Phantom experiments were performed with a pre-clinical prototype detector, using treatment plans delivered with a clinical Pencil-beam scanning system. The detector consisted of an actively shielded lanthanum(III) bromide scintillator. Tungsten was used to collimate the gamma-rays. To support high event rates, the detector readout featured custom amplifiers and an active voltage divider for the photomultiplier. The detector signals were acquired by fast analog-to-digital converters and processed using digital algorithms. The data acquisition was also synchronized with the Pencil-beam scanning and dosimetry systems. Results: We successfully acquired prompt gamma-ray spectra during the delivery of proton Pencil-Beams with a clinical beam current of 2 nA at the exit of the treatment head. The number of events in the primary detector ranged from 1 x 10⁶ to 2 x 10⁶ per second. In phantom experiments, non-uniform range errors were introduced by placing strips of plastic in the beam path. The magnitudes and positions of these range errors were correctly detected in two-dimensional range maps that were generated from the measurements. With our small scale prototype, a 1.0 mm standard deviation on the absolute range required about 5 x 10⁸ protons per delivered Pencil-beam. Conclusions: Prompt gamma-ray spectroscopy to verify the absolute range of proton Beams was demonstrated under clinical Pencil-beam delivery conditions. A 1 mm to 2 mm range verification accuracy for a field delivering 1 Gy, appears feasible with a full scale system. This work was supported by the Federal Share of program income earned on C06-CA059267, Proton Therapy Research and Treatment Center.

  • proton range verification through prompt gamma ray spectroscopy
    Physics in Medicine and Biology, 2014
    Co-Authors: J Verburg, J Seco
    Abstract:

    We present an experimental study of a novel method to verify the range of proton therapy Beams. Differential cross sections were measured for 15 prompt gamma-ray lines from proton-nuclear interactions with 12C and 16O at proton energies up to 150 MeV. These cross sections were used to model discrete prompt gamma-ray emissions along proton Pencil-Beams. By fitting detected prompt gamma-ray counts to these models, we simultaneously determined the beam range and the oxygen and carbon concentration of the irradiated matter. The performance of the method was assessed in two phantoms with different elemental concentrations, using a small scale prototype detector. Based on five Pencil-Beams with different ranges delivering 5 × 108 protons and without prior knowledge of the elemental composition at the measurement point, the absolute range was determined with a standard deviation of 1.0–1.4 mm. Relative range shifts at the same dose level were detected with a standard deviation of 0.3–0.5 mm. The determined oxygen and carbon concentrations also agreed well with the actual values. These results show that quantitative prompt gamma-ray measurements enable knowledge of nuclear reaction cross sections to be used for precise proton range verification in the presence of tissue with an unknown composition.

Narayan Sahoo - One of the best experts on this subject based on the ideXlab platform.

  • quality assurance of proton Beams using a multilayer ionization chamber system
    Medical Physics, 2013
    Co-Authors: S Dhanesar, Narayan Sahoo, M Kerr, Brad M Taylor, P Summers, Ronald X Zhu, Falk Poenisch, Michael Gillin
    Abstract:

    Purpose: The measurement of percentage depth-dose (PDD) distributions for the quality assurance of clinical proton Beams is most commonly performed with a computerized water tank dosimetry system with ionization chamber, commonly referred to as water tank. Although the accuracy and reproducibility of this method is well established, it can be time-consuming if a large number of measurements are required. In this work the authors evaluate the linearity, reproducibility, sensitivity to field size, accuracy, and time-savings of another system: the Zebra, a multilayer ionization chamber system.Methods: The Zebra, consisting of 180 parallel-plate ionization chambers with 2 mm resolution, was used to measure depth-dose distributions. The measurements were performed for scattered and scanned proton Pencil Beams of multiple energies delivered by the Hitachi PROBEAT synchrotron-based delivery system. For scattered Beams, the Zebra-measured depth-dose distributions were compared with those measured with the water tank. The principal descriptors extracted for comparisons were: range, the depth of the distal 90% dose; spread-out Bragg peak (SOBP) length, the region between the proximal 95% and distal 90% dose; and distal-dose fall off (DDF), the region between the distal 80% and 20% dose. For scanned Beams, the Zebra-measured ranges were compared with those acquired using a Bragg peakmore » chamber during commissioning.Results: The Zebra demonstrated better than 1% reproducibility and monitor unit linearity. The response of the Zebra was found to be sensitive to radiation field sizes greater than 12.5 × 12.5 cm; hence, the measurements used to determine accuracy were performed using a field size of 10 × 10 cm. For the scattered proton Beams, PDD distributions showed 1.5% agreement within the SOBP, and 3.8% outside. Range values agreed within −0.1 ± 0.4 mm, with a maximum deviation of 1.2 mm. SOBP length values agreed within 0 ± 2 mm, with a maximum deviation of 6 mm. DDF values agreed within 0.3 ± 0.1 mm, with a maximum deviation of 0.6 mm. For the scanned proton Pencil Beams, Zebra and Bragg peak chamber range values demonstrated agreement of 0.0 ± 0.3 mm with a maximum deviation of 1.3 mm. The setup and measurement time for all Zebra measurements was 3 and 20 times less, respectively, compared to the water tank measurements.Conclusions: Our investigation shows that the Zebra can be useful not only for fast but also for accurate measurements of the depth-dose distributions of both scattered and scanned proton Beams. The analysis of a large set of measurements shows that the commonly assessed beam quality parameters obtained with the Zebra are within the acceptable variations specified by the manufacturer for our delivery system.« less

  • verification of proton range position and intensity in impt with a 3d liquid scintillator detector system
    Medical Physics, 2012
    Co-Authors: L Archambault, Radhe Mohan, Narayan Sahoo, Falk Poenisch, Michael Gillin, D Robertson, A Lee, Sam Beddar
    Abstract:

    Purpose: Intensity-modulated proton therapy (IMPT) using spot scanned proton Beams relies on the delivery of a large number of beamlets to shape the dose distribution in a highly conformal manner. The authors have developed a 3D system based on liquid scintillator to measure the spatial location, intensity, and depth of penetration (energy) of the proton beamlets in near real-time. Methods: The detector system consists of a 20 x 20 x 20 cc liquid scintillator (LS) material in a light tight enclosure connected to a CCD camera. This camera has a field of view of 25.7 by 19.3 cm and a pixel size of 0.4 mm. While the LS is irradiated, the camera continuously acquires images of the light distribution produced inside the LS. Irradiations were made with proton Pencil Beams produced with a spot-scanning nozzle. Pencil Beams with nominal ranges in water between 9.5 and 17.6 cm were scanned to irradiate an area of 10 x 10 cm square on the surface of the LS phantom. Image frames were acquired at 50 ms per frame. Results: The signal to noise ratio of a typical Bragg peak was about 170. Proton range measured from the light distribution produced in the LSmore » was accurate to within 0.3 mm on average. The largest deviation seen between the nominal and measured range was 0.6 mm. Lateral position of the measured Pencil beam was accurate to within 0.4 mm on average. The largest deviation seen between the nominal and measured lateral position was 0.8 mm; however, the accuracy of this measurement could be improved by correcting light scattering artifacts. Intensity of single proton spots were measured with precision ranging from 3 % for the smallest spot intensity (0.005 MU) to 0.5 % for the largest spot (0.04 MU). Conclusions: Our LS detector system has been shown to be capable of fast, submillimeter spatial localization of proton spots delivered in a 3D volume. This system could be used for beam range, intensity and position verification in IMPT.« less

  • experimental characterization of the low dose envelope of spot scanning proton Beams
    Physics in Medicine and Biology, 2010
    Co-Authors: Gabriel O Sawakuchi, Radhe Mohan, Ronald X Zhu, Falk Poenisch, Michael Gillin, Kazumichi Suzuki, G Ciangaru, Uwe Titt, A Anand, Narayan Sahoo
    Abstract:

    In scanned proton beam radiotherapy, multiple Pencil Beams are used to deliver the total dose to the target volume. Because the number of such Beams can be very large, an accurate dosimetric characterization of every single Pencil beam is important to provide adequate input data for the configuration of the treatment planning system. In this work, we present a method to measure the low-dose envelope of single Pencil Beams, known to play a meaningful role in the dose computation for scanned proton Beams. We measured the low-dose proton beam envelope, which extends several centimeters outwards from the center of each single Pencil beam, by acquiring lateral dose profile data, down to relative dose levels that were a factor of 10(4) lower than the central axis dose. The overall effect of the low-dose envelope on the total dose delivered by multiple Pencil Beams was determined by measuring the dose output as a function of field size. We determined that the low-dose envelope can be influential even for fields as large as 20 cm x 20 cm.

  • monte carlo investigation of the low dose envelope from scanned proton Pencil Beams
    Physics in Medicine and Biology, 2010
    Co-Authors: Gabriel O Sawakuchi, Narayan Sahoo, Ronald X Zhu, Michael Gillin, G Ciangaru, Uwe Titt, Dragan Mirkovic, Radhe Mohan
    Abstract:

    Scanned proton Pencil Beams carry a low-dose envelope that extends several centimeters from the individual beam's central axis. Thus, the total delivered dose depends on the size of the target volume and the corresponding number and intensity of Beams necessary to cover the target volume uniformly. This dependence must be considered in dose calculation algorithms used by treatment planning systems. In this work, we investigated the sources of particles contributing to the low-dose envelope using the Monte Carlo technique. We used a validated model of our institution's scanning beam line to determine the contributions to the low-dose envelope from secondary particles created in a water phantom and particles scattered in beam line components. Our results suggested that, for high-energy Beams, secondary particles produced by nuclear interactions in the water phantom are the major contributors to the low-dose envelope. For low-energy Beams, the low-dose envelope is dominated by particles undergoing multiple Coulomb scattering in the beam line components and water phantom. Clearly, in the latter situation, the low-dose envelope depends directly on beam line design features. Finally, we investigated the dosimetric consequences of the low-dose envelope. Our results showed that if not modeled properly the low-dose envelope may cause clinically relevant dose disturbance in the target volume. This work suggested that this low-dose envelope is beam line specific for low-energy Beams, should be thoroughly experimentally characterized and validated during commissioning of the treatment planning system, and therefore is of great concern for accurate delivery of proton scanning beam doses.

Thomas Bortfeld - One of the best experts on this subject based on the ideXlab platform.

  • a full scale clinical prototype for proton range verification using prompt gamma ray spectroscopy
    Physics in Medicine and Biology, 2018
    Co-Authors: F Huesogonzalez, Thomas Bortfeld, Moritz Rabe, Thomas A Ruggieri, J Verburg
    Abstract:

    We present a full-scale clinical prototype system for in vivo range verification of proton Pencil-Beams using the prompt gamma-ray spectroscopy method. The detection system consists of eight LaBr3 scintillators and a tungsten collimator, mounted on a rotating frame. Custom electronics and calibration algorithms have been developed for the measurement of energy- and time-resolved gamma-ray spectra during proton irradiation at a clinical dose rate. Using experimentally determined nuclear reaction cross sections and a GPU-accelerated Monte Carlo simulation, a detailed model of the expected gamma-ray emissions is created for each individual Pencil-beam. The absolute range of the proton Pencil-Beams is determined by minimizing the discrepancy between the measurement and this model, leaving the absolute range of the beam and the elemental concentrations of the irradiated matter as free parameters. The system was characterized in a clinical-like situation by irradiating different phantoms with a scanning Pencil-beam. A dose of 0.9 Gy was delivered to a [Formula: see text] cm3 target with a beam current of 2 nA incident on the phantom. Different range shifters and materials were used to test the robustness of the verification method and to calculate the accuracy of the detected range. The absolute proton range was determined for each spot of the distal energy layer with a mean statistical precision of 1.1 mm at a 95% confidence level and a mean systematic deviation of 0.5 mm, when aggregating Pencil-beam spots within a cylindrical region of 10 mm radius and 10 mm depth. Small range errors that we introduced were successfully detected and even large differences in the elemental composition do not affect the range verification accuracy. These results show that our system is suitable for range verification during patient treatments in our upcoming clinical study.

  • a full scale clinical prototype for proton range verification using prompt gamma ray spectroscopy
    arXiv: Medical Physics, 2018
    Co-Authors: F Huesogonzalez, Thomas Bortfeld, Moritz Rabe, Thomas A Ruggieri, J Verburg
    Abstract:

    We present a full-scale clinical prototype system for in vivo range verification of proton Pencil-Beams using the prompt gamma-ray spectroscopy method. The detection system consists of eight LaBr3 scintillators and a tungsten collimator, mounted on a rotating frame. Custom electronics and calibration algorithms have been developed for the measurement of energy- and time-resolved gamma-ray spectra during proton irradiation at a clinical dose rate. Using experimentally determined nuclear reaction cross sections and a GPU-accelerated Monte Carlo simulation, a detailed model of the expected gamma-ray emissions is created for each individual Pencil-beam. The absolute range of the proton Pencil-Beams is determined by minimizing the discrepancy between the measurement and this model, leaving the absolute range of the beam and the elemental concentrations of the irradiated matter as free parameters. The system was characterized in a clinical-like situation by irradiating different phantoms with a scanning Pencil-beam. A dose of 0.9 Gy was delivered to a 5x10x10 cm^3 target with a beam current of 2 nA incident on the phantom. Different range shifters and materials were used to test the robustness of the verification method and to calculate the accuracy of the detected range. The absolute proton range was determined for each spot of the distal energy layer with a mean statistical precision of 1.1 mm at a 95% confidence level and a mean systematic deviation of 0.5 mm, when aggregating Pencil-beam spots within a cylindrical region of 10 mm radius and 10 mm depth. Small range errors that we introduced were successfully detected and even large differences in the elemental composition do not affect the range verification accuracy. These results show that our system is suitable for range verification during patient treatments in our upcoming clinical study.

  • mo ab bra 07 prompt gamma ray spectroscopy for range verification of clinical proton Beams
    Medical Physics, 2015
    Co-Authors: J Verburg, Thomas Bortfeld, J Seco
    Abstract:

    Purpose: We developed a pre-clinical prototype system for range verification of proton Pencil-beam scanning fields. The system was evaluated using phantom treatment plans delivered with a clinical dose rate. Methods: The absolute range of proton Pencil-Beams was verified through an optimization procedure, which matches energy- and time-resolved prompt gamma-ray measurements with models, based on cross sections for discrete prompt gamma-ray line excitations. Phantom experiments were performed with a pre-clinical prototype detector, using treatment plans delivered with a clinical Pencil-beam scanning system. The detector consisted of an actively shielded lanthanum(III) bromide scintillator. Tungsten was used to collimate the gamma-rays. To support high event rates, the detector readout featured custom amplifiers and an active voltage divider for the photomultiplier. The detector signals were acquired by fast analog-to-digital converters and processed using digital algorithms. The data acquisition was also synchronized with the Pencil-beam scanning and dosimetry systems. Results: We successfully acquired prompt gamma-ray spectra during the delivery of proton Pencil-Beams with a clinical beam current of 2 nA at the exit of the treatment head. The number of events in the primary detector ranged from 1 x 10⁶ to 2 x 10⁶ per second. In phantom experiments, non-uniform range errors were introduced by placing strips of plastic in the beam path. The magnitudes and positions of these range errors were correctly detected in two-dimensional range maps that were generated from the measurements. With our small scale prototype, a 1.0 mm standard deviation on the absolute range required about 5 x 10⁸ protons per delivered Pencil-beam. Conclusions: Prompt gamma-ray spectroscopy to verify the absolute range of proton Beams was demonstrated under clinical Pencil-beam delivery conditions. A 1 mm to 2 mm range verification accuracy for a field delivering 1 Gy, appears feasible with a full scale system. This work was supported by the Federal Share of program income earned on C06-CA059267, Proton Therapy Research and Treatment Center.

  • accounting for range uncertainties in the optimization of intensity modulated proton therapy
    Physics in Medicine and Biology, 2007
    Co-Authors: Jan Unkelbach, Timothy C Y Chan, Thomas Bortfeld
    Abstract:

    Treatment plans optimized for intensity modulated proton therapy (IMPT) may be sensitive to range variations. The dose distribution may deteriorate substantially when the actual range of a Pencil beam does not match the assumed range. We present two treatment planning concepts for IMPT which incorporate range uncertainties into the optimization. The first method is a probabilistic approach. The range of a Pencil beam is assumed to be a random variable, which makes the delivered dose and the value of the objective function a random variable too. We then propose to optimize the expectation value of the objective function. The second approach is a robust formulation that applies methods developed in the field of robust linear programming. This approach optimizes the worst case dose distribution that may occur, assuming that the ranges of the Pencil Beams may vary within some interval. Both methods yield treatment plans that are considerably less sensitive to range variations compared to conventional treatment plans optimized without accounting for range uncertainties. In addition, both approaches—although conceptually different—yield very similar results on a qualitative level.

Radhe Mohan - One of the best experts on this subject based on the ideXlab platform.

  • verification of proton range position and intensity in impt with a 3d liquid scintillator detector system
    Medical Physics, 2012
    Co-Authors: L Archambault, Radhe Mohan, Narayan Sahoo, Falk Poenisch, Michael Gillin, D Robertson, A Lee, Sam Beddar
    Abstract:

    Purpose: Intensity-modulated proton therapy (IMPT) using spot scanned proton Beams relies on the delivery of a large number of beamlets to shape the dose distribution in a highly conformal manner. The authors have developed a 3D system based on liquid scintillator to measure the spatial location, intensity, and depth of penetration (energy) of the proton beamlets in near real-time. Methods: The detector system consists of a 20 x 20 x 20 cc liquid scintillator (LS) material in a light tight enclosure connected to a CCD camera. This camera has a field of view of 25.7 by 19.3 cm and a pixel size of 0.4 mm. While the LS is irradiated, the camera continuously acquires images of the light distribution produced inside the LS. Irradiations were made with proton Pencil Beams produced with a spot-scanning nozzle. Pencil Beams with nominal ranges in water between 9.5 and 17.6 cm were scanned to irradiate an area of 10 x 10 cm square on the surface of the LS phantom. Image frames were acquired at 50 ms per frame. Results: The signal to noise ratio of a typical Bragg peak was about 170. Proton range measured from the light distribution produced in the LSmore » was accurate to within 0.3 mm on average. The largest deviation seen between the nominal and measured range was 0.6 mm. Lateral position of the measured Pencil beam was accurate to within 0.4 mm on average. The largest deviation seen between the nominal and measured lateral position was 0.8 mm; however, the accuracy of this measurement could be improved by correcting light scattering artifacts. Intensity of single proton spots were measured with precision ranging from 3 % for the smallest spot intensity (0.005 MU) to 0.5 % for the largest spot (0.04 MU). Conclusions: Our LS detector system has been shown to be capable of fast, submillimeter spatial localization of proton spots delivered in a 3D volume. This system could be used for beam range, intensity and position verification in IMPT.« less

  • experimental characterization of the low dose envelope of spot scanning proton Beams
    Physics in Medicine and Biology, 2010
    Co-Authors: Gabriel O Sawakuchi, Radhe Mohan, Ronald X Zhu, Falk Poenisch, Michael Gillin, Kazumichi Suzuki, G Ciangaru, Uwe Titt, A Anand, Narayan Sahoo
    Abstract:

    In scanned proton beam radiotherapy, multiple Pencil Beams are used to deliver the total dose to the target volume. Because the number of such Beams can be very large, an accurate dosimetric characterization of every single Pencil beam is important to provide adequate input data for the configuration of the treatment planning system. In this work, we present a method to measure the low-dose envelope of single Pencil Beams, known to play a meaningful role in the dose computation for scanned proton Beams. We measured the low-dose proton beam envelope, which extends several centimeters outwards from the center of each single Pencil beam, by acquiring lateral dose profile data, down to relative dose levels that were a factor of 10(4) lower than the central axis dose. The overall effect of the low-dose envelope on the total dose delivered by multiple Pencil Beams was determined by measuring the dose output as a function of field size. We determined that the low-dose envelope can be influential even for fields as large as 20 cm x 20 cm.

  • monte carlo investigation of the low dose envelope from scanned proton Pencil Beams
    Physics in Medicine and Biology, 2010
    Co-Authors: Gabriel O Sawakuchi, Narayan Sahoo, Ronald X Zhu, Michael Gillin, G Ciangaru, Uwe Titt, Dragan Mirkovic, Radhe Mohan
    Abstract:

    Scanned proton Pencil Beams carry a low-dose envelope that extends several centimeters from the individual beam's central axis. Thus, the total delivered dose depends on the size of the target volume and the corresponding number and intensity of Beams necessary to cover the target volume uniformly. This dependence must be considered in dose calculation algorithms used by treatment planning systems. In this work, we investigated the sources of particles contributing to the low-dose envelope using the Monte Carlo technique. We used a validated model of our institution's scanning beam line to determine the contributions to the low-dose envelope from secondary particles created in a water phantom and particles scattered in beam line components. Our results suggested that, for high-energy Beams, secondary particles produced by nuclear interactions in the water phantom are the major contributors to the low-dose envelope. For low-energy Beams, the low-dose envelope is dominated by particles undergoing multiple Coulomb scattering in the beam line components and water phantom. Clearly, in the latter situation, the low-dose envelope depends directly on beam line design features. Finally, we investigated the dosimetric consequences of the low-dose envelope. Our results showed that if not modeled properly the low-dose envelope may cause clinically relevant dose disturbance in the target volume. This work suggested that this low-dose envelope is beam line specific for low-energy Beams, should be thoroughly experimentally characterized and validated during commissioning of the treatment planning system, and therefore is of great concern for accurate delivery of proton scanning beam doses.

Michael Gillin - One of the best experts on this subject based on the ideXlab platform.

  • quality assurance of proton Beams using a multilayer ionization chamber system
    Medical Physics, 2013
    Co-Authors: S Dhanesar, Narayan Sahoo, M Kerr, Brad M Taylor, P Summers, Ronald X Zhu, Falk Poenisch, Michael Gillin
    Abstract:

    Purpose: The measurement of percentage depth-dose (PDD) distributions for the quality assurance of clinical proton Beams is most commonly performed with a computerized water tank dosimetry system with ionization chamber, commonly referred to as water tank. Although the accuracy and reproducibility of this method is well established, it can be time-consuming if a large number of measurements are required. In this work the authors evaluate the linearity, reproducibility, sensitivity to field size, accuracy, and time-savings of another system: the Zebra, a multilayer ionization chamber system.Methods: The Zebra, consisting of 180 parallel-plate ionization chambers with 2 mm resolution, was used to measure depth-dose distributions. The measurements were performed for scattered and scanned proton Pencil Beams of multiple energies delivered by the Hitachi PROBEAT synchrotron-based delivery system. For scattered Beams, the Zebra-measured depth-dose distributions were compared with those measured with the water tank. The principal descriptors extracted for comparisons were: range, the depth of the distal 90% dose; spread-out Bragg peak (SOBP) length, the region between the proximal 95% and distal 90% dose; and distal-dose fall off (DDF), the region between the distal 80% and 20% dose. For scanned Beams, the Zebra-measured ranges were compared with those acquired using a Bragg peakmore » chamber during commissioning.Results: The Zebra demonstrated better than 1% reproducibility and monitor unit linearity. The response of the Zebra was found to be sensitive to radiation field sizes greater than 12.5 × 12.5 cm; hence, the measurements used to determine accuracy were performed using a field size of 10 × 10 cm. For the scattered proton Beams, PDD distributions showed 1.5% agreement within the SOBP, and 3.8% outside. Range values agreed within −0.1 ± 0.4 mm, with a maximum deviation of 1.2 mm. SOBP length values agreed within 0 ± 2 mm, with a maximum deviation of 6 mm. DDF values agreed within 0.3 ± 0.1 mm, with a maximum deviation of 0.6 mm. For the scanned proton Pencil Beams, Zebra and Bragg peak chamber range values demonstrated agreement of 0.0 ± 0.3 mm with a maximum deviation of 1.3 mm. The setup and measurement time for all Zebra measurements was 3 and 20 times less, respectively, compared to the water tank measurements.Conclusions: Our investigation shows that the Zebra can be useful not only for fast but also for accurate measurements of the depth-dose distributions of both scattered and scanned proton Beams. The analysis of a large set of measurements shows that the commonly assessed beam quality parameters obtained with the Zebra are within the acceptable variations specified by the manufacturer for our delivery system.« less

  • verification of proton range position and intensity in impt with a 3d liquid scintillator detector system
    Medical Physics, 2012
    Co-Authors: L Archambault, Radhe Mohan, Narayan Sahoo, Falk Poenisch, Michael Gillin, D Robertson, A Lee, Sam Beddar
    Abstract:

    Purpose: Intensity-modulated proton therapy (IMPT) using spot scanned proton Beams relies on the delivery of a large number of beamlets to shape the dose distribution in a highly conformal manner. The authors have developed a 3D system based on liquid scintillator to measure the spatial location, intensity, and depth of penetration (energy) of the proton beamlets in near real-time. Methods: The detector system consists of a 20 x 20 x 20 cc liquid scintillator (LS) material in a light tight enclosure connected to a CCD camera. This camera has a field of view of 25.7 by 19.3 cm and a pixel size of 0.4 mm. While the LS is irradiated, the camera continuously acquires images of the light distribution produced inside the LS. Irradiations were made with proton Pencil Beams produced with a spot-scanning nozzle. Pencil Beams with nominal ranges in water between 9.5 and 17.6 cm were scanned to irradiate an area of 10 x 10 cm square on the surface of the LS phantom. Image frames were acquired at 50 ms per frame. Results: The signal to noise ratio of a typical Bragg peak was about 170. Proton range measured from the light distribution produced in the LSmore » was accurate to within 0.3 mm on average. The largest deviation seen between the nominal and measured range was 0.6 mm. Lateral position of the measured Pencil beam was accurate to within 0.4 mm on average. The largest deviation seen between the nominal and measured lateral position was 0.8 mm; however, the accuracy of this measurement could be improved by correcting light scattering artifacts. Intensity of single proton spots were measured with precision ranging from 3 % for the smallest spot intensity (0.005 MU) to 0.5 % for the largest spot (0.04 MU). Conclusions: Our LS detector system has been shown to be capable of fast, submillimeter spatial localization of proton spots delivered in a 3D volume. This system could be used for beam range, intensity and position verification in IMPT.« less

  • experimental characterization of the low dose envelope of spot scanning proton Beams
    Physics in Medicine and Biology, 2010
    Co-Authors: Gabriel O Sawakuchi, Radhe Mohan, Ronald X Zhu, Falk Poenisch, Michael Gillin, Kazumichi Suzuki, G Ciangaru, Uwe Titt, A Anand, Narayan Sahoo
    Abstract:

    In scanned proton beam radiotherapy, multiple Pencil Beams are used to deliver the total dose to the target volume. Because the number of such Beams can be very large, an accurate dosimetric characterization of every single Pencil beam is important to provide adequate input data for the configuration of the treatment planning system. In this work, we present a method to measure the low-dose envelope of single Pencil Beams, known to play a meaningful role in the dose computation for scanned proton Beams. We measured the low-dose proton beam envelope, which extends several centimeters outwards from the center of each single Pencil beam, by acquiring lateral dose profile data, down to relative dose levels that were a factor of 10(4) lower than the central axis dose. The overall effect of the low-dose envelope on the total dose delivered by multiple Pencil Beams was determined by measuring the dose output as a function of field size. We determined that the low-dose envelope can be influential even for fields as large as 20 cm x 20 cm.

  • monte carlo investigation of the low dose envelope from scanned proton Pencil Beams
    Physics in Medicine and Biology, 2010
    Co-Authors: Gabriel O Sawakuchi, Narayan Sahoo, Ronald X Zhu, Michael Gillin, G Ciangaru, Uwe Titt, Dragan Mirkovic, Radhe Mohan
    Abstract:

    Scanned proton Pencil Beams carry a low-dose envelope that extends several centimeters from the individual beam's central axis. Thus, the total delivered dose depends on the size of the target volume and the corresponding number and intensity of Beams necessary to cover the target volume uniformly. This dependence must be considered in dose calculation algorithms used by treatment planning systems. In this work, we investigated the sources of particles contributing to the low-dose envelope using the Monte Carlo technique. We used a validated model of our institution's scanning beam line to determine the contributions to the low-dose envelope from secondary particles created in a water phantom and particles scattered in beam line components. Our results suggested that, for high-energy Beams, secondary particles produced by nuclear interactions in the water phantom are the major contributors to the low-dose envelope. For low-energy Beams, the low-dose envelope is dominated by particles undergoing multiple Coulomb scattering in the beam line components and water phantom. Clearly, in the latter situation, the low-dose envelope depends directly on beam line design features. Finally, we investigated the dosimetric consequences of the low-dose envelope. Our results showed that if not modeled properly the low-dose envelope may cause clinically relevant dose disturbance in the target volume. This work suggested that this low-dose envelope is beam line specific for low-energy Beams, should be thoroughly experimentally characterized and validated during commissioning of the treatment planning system, and therefore is of great concern for accurate delivery of proton scanning beam doses.