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OC-0271: Production of high quality 11C beams for radiation therapy and PET-CT dose delivery verification
S104
ESTRO 33, 2014 The beam was calibrated according to IAEA TRS398 code of practice using a PTW Markus parallel-plate ionization chamber at 3 mm depth in water. Percentage depth dose (PDD) was measured with the same chamber in a water phantom at a Collimator-to-Surface Distance (CSD) of 100 cm, while a PTW SemiFlex ionization chamber was used to monitor the beam. Calibration curves of HDV2 and EBT3 Gafchromic film models were established at 3mm depth in a Solid WaterTM phantom using the same reference monitor chamber. Dose profiles were acquired at surface and 2 mm depths in Solid Water using HDV2 film. Results: The output at 3 mm depth in water was found to be stable within 5% at 4.8 Gy/sec. Figure 1a shows PDD measurement result with Bragg peak at 7.06 mm which is comparable to theoretical range of 7.08 mm in water according to NIST PSTAR database. Figure 1b shows calibration curves of EBT3 and HDV2 film models in proton beam compared to a typical EBT3 film calibration in 6 MV photon beam. Figures 1c and 1d show relative dose profiles at surface and 2 mm depths, respectively.
Fig 1: Neutron measurements for a 250-MeV clinical proton beam. a. photograph of experimental set-up and b. measured neutron spectrum. Conclusions: We report a secondary neutron spectrum from a 250-MeV passively scattered proton beam measured by using an extended-range Bonner sphere measurement system that is sensitive to neutron energies over the entire neutron energy range of interest for proton therapy applications. The measurements were carried out using the highest energy available at our facility and for a closed aperture, thus representing the maximum external neutron production. OC-0270 Dosimetric characterization of low energy protons for intra-operative radiation therapy B. Moftah1, F. Alrumayyan2, S. Aldelaijan1, M. Shehadeh1, F. Alzorkani1, M. Alshabanah3, J. Seuntjens4, S. Devic4 1 King Faisal Specialist Hospital & Research Centre, Biomedical Physics, Riyadh, Saudi Arabia 2 King Faisal Specialist Hospital & Research Centre, Cyclotron & Radiopharmaceuticals, Riyadh, Saudi Arabia 3 King Faisal Specialist Hospital & Research Centre, Radiation Oncology, Riyadh, Saudi Arabia 4 McGill University, Medical Physics, Montreal, Canada Purpose/Objective: With advantages of high tumor control to normal tissue complication ratio, high dose rate and conveniently short range, low energy proton beam of typical radiopharmaceutical-producing cyclotrons offer a logical, yet untested, tool for intra-operative radiation therapy (IORT). Our proposal to use a low energy proton beam for IORT relies on the physical configuration of proton beam that can be delivered to a tumor using 'keyhole surgery'. Before embarking on its clinical use, several issues must be addressed: (a) stability of the cyclotron; (b) whether beam properties are suitable to provide adequate penetration and sufficient prescription dose for cancer types to be considered in the future; and (c) if the output of the cyclotron will be able to provide reasonable treatment times. Materials and Methods: At our institution, we possess a CS30 cyclotron which is capable of accelerating protons at 26.5 MeV through seven beam lines. One beam line is connected to a gantry based clinical treatment room and is set to be reconditioned for IOpRT feasibility testing. The dosimetric properties of proton beam are tested on another research beam line running at a 100 nA current with a 2 mm collimator.
Figure 1 a) Percent depth dose in water of 26.5 MeV proton, b) calibration of EBT3 and HDV2 films in proton beam compared to conventional calibration, c) and d) dose profiles measured by HDV2 film at surface and 2 mm depth, respectively. Conclusions: The 26.5 MeV proton beam was characterized and found to have sufficient penetration depth, uniformity, and high dose rate for selected tumor/IORT sites that propel the advancement of this IOpRT project. At such high dose rate, the HDV2 film was shown to have dosimetric characteristics that are suitable for the purpose. OC-0271 Production of high quality 11C beams for radiation therapy and PETCT dose delivery verification M. Lazzeroni1, A. Brahme1 1 Karolinska Institutet, Oncology-Pathology, Stockholm, Sweden Purpose/Objective: This study aims at exploring a method to maximize the generally low production yield of 11C ion beams through in-flight fragmentation of a primary 12C ion beam on a dedicated target. The main steps from the production of the beam and the transport through the beam optics system to the purification of the beam from other potentially contaminating fragments were investigated. Positron emitter light ions have high potential for simultaneously treating and in vivo monitoring the dose delivery with Positron Emission Tomography (PET) or PET-Computed Tomography (CT) imaging. 11C ion beams merge the main distinctive properties of light ion therapy, i.e. highly conformal dose delivery and increased biological effectiveness, with the advantage of a high β+-activity signal mainly produced directly by the beam itself, and therefore not primarily dependent on the stoichiometry of the tissues. Materials and Methods: Monte Carlo simulations with the SHIELD-HIT10+ code were used in combination with analytical models of transport of ions in matter based on the generalized Fermi-Eyges theory. The irradiation geometry of the Monte Carlo simulations consisted of a cylindrical target made of 20 cm liquid hydrogen (ρ≈ 0.071 g/cm3)
ESTRO 33, 2014 followed by a polyethylene (ρ≈0.94 g/cm3) section with variable length. The primary 12C ion beam monoenergetic (400 MeV/u) and monodirectional impinged longitudinally on the cylinder. Particle fluence double differential in energy and angle were scored in 1 cm thick slices. Production yields, as well as energy, velocity and magnetic rigidity of the fragments generated in the target were scored as a function of the depth in the target. Results: A beam line design is proposed, which includes a composite production target made of liquid hydrogen section followed by a variable thickness section consisting of plane parallel slabs of polyethylene. The first section is selected to maximize the 11C ion beam intensity, whereas the second section is used to reduce the beam energy to the desired value, maintaining the high 11C ion yield. To minimize the energy spread of 11C ion beam, and the contamination from other fragments, a variable wedge-shaped degrader and a Time Of Flight (TOF) Radio-Frequency driven velocity filter are included in the beam line. A 11C ion beam intensity of about 4-6% of the primary 12C ion beam intensity with radial spot size confined to 0.5 cm in radius, and an energy and angular spread of about 1% and 1°,respectively, are achievable. The 11C ion beam purity is expected to be about 99%.
S105 Results: For the collimated divergent and uncollimated single pencil beams, GATE results agreed with the analytical model of Safai et al. (PMB 2008) to within 1-2mm, validating the Monte Carlo model. Reducing the SSD of a pencil beam array has a greater effect at lower energies due to the reduction of in-air scattering. Collimation of a monoenergetic pencil beam array reduces the entrance penumbra from 0.4-1.2cm to 0.1-0.2cm, depending on SSD and initial energy. Beams 'pulled back' through a Perspex range shifter suffer penumbral blurring; placing a collimator beyond the range shifter sharpens the penumbra to approximately that of an uncollimated PBS. Collimation of homogeneous volumes is shown in Figure 1.
Figure 1: 2D profiles in a 20cm3 water tank for a (L-R) uncollimated,singly collimated, uncollimated pullback and collimated pullback pencil beam array using a square grid of spots. The latter 2 beams have been pulled back through 10cm Perspex. The beams have been weighted to ensure a homogeneous dose in the spherical volume. Conclusions: Positioning the nozzle of a spot scanned beam at short SSD produces penumbra comparable to that of a double scattered system. For very superficial tumours and for beams which have to be degraded through Perspex, use of a collimator significantly improves the lateral penumbra; this is seen both for single energy layers and for doses to homogeneous volumes. OC-0273 Fast Monte Carlo simulation of proton therapy treatment using an Intel Xeon Phi coprocessor K. Souris1, J. Lee1, E. Sterpin1 1 UCL - IREC, Molecular Imaging Radiotherapy and Oncology (MIRO), Bruxelles, Belgium
Conclusions: The presented system for production of high quality 11C ion beams contributes to the developments of an accurate PET-CT based dose delivery verification. The proposed practical solution allows overcoming the difficulties related to the low quality and production efficiency of light ion positron emitter beams and it is applicable to cyclotron, synchrotron and linac based hospital facilities. OC-0272 Collimation of spot scanned proton therapy beams to sharpen the lateral edge of uniform dose volumes F.C. Charlwood1, A.H. Aitkenhead1, R.I. MacKay1 1 The Christie NHS Foundation Trust, Christie Medical Physics and Engineering, Manchester, United Kingdom Purpose/Objective: In general, the lateral edge (termed penumbra) of a pencil beam scanning (PBS) system is worse than that of a double scattered divergent beam at shallow depths in the patient. This is predominantly due to the in-air scattering associated with the spot scanned beam. Depending on the minimum accelerator energy output, the beam may need to be degraded through Perspex beyond the nozzle, further blurring the penumbra. Here, Monte Carlo simulations have shown that the penumbra is significantly improved by the use of a short source-surface distance (SSD) and/or collimation. To date, there have been few studies of the factors affecting the lateral penumbra of homogeneous dose volumes. Materials and Methods: The GATE (Jan et al., PMB 2011) Monte Carlo software was used to simulate double scattered and pencil beams, with results validated against those of Safai et al. (PMB 2008). Key parameters such as SSD, collimator-surface distance, collimator thickness and diameter, use of range shifter, spot properties and optimisation were separately investigated to assess the conformity of treatment. Additionally the delivery of homogeneous dose volumes using spot scanning was simulated to ensure that the penumbra can be sharpened throughout the whole volume. For spherical volumes, the use of a MLC was simulated in attempt to improve the penumbra.
Purpose/Objective: In proton therapy, range uncertainties jeopardize treatment quality. Monte Carlo (MC) simulations can help reduce them by improving dose calculation accuracy and being integrated in on-line range monitoring techniques, like prompt gamma (PG) imaging. Most current MC methods are however too slow for clinical use. Using graphical processor units (GPUs), computation times of the order of the minute have been reported. However, the highly vectorized architecture of GPUs is not ideal to handle the stochastic nature of MC methods, forcing profound adaption of the inner physics with a loss of generality. As a result, most MC codes based on GPUs are limited to a specific task, namely dose computation with the sole tracking of the protons (no PG emission). In this communication, we present MCsquare (Many-Core Monte Carlo), a new, fast, and accurate MC simulation of protons. MCsquare relies on the new Intel Xeon Phi coprocessor, which does not have the restrictions of GPUs and thus enable more general and realistic simulations. Materials and Methods: The flexible architecture of the Xeon Phi coprocessor provides many independent execution threads that can be assigned to detailed simulations of nuclear reactions and secondary particles without performance loss. This coprocessor is composed of 60 cores, each containing a 512-bit SIMD unit, and is capable of more than 1 teraflops. In MCsquare, nuclear reactions are sampled from the ICRU 63 database, taking into account the atomic composition of tissues. ICRU 63 database provides comprehensive information for PG emission that is incorporated in MCsquare. To illustrate the accuracy and the computation speed, a 200 MeV proton beam has been simulated using MCsquare and compared to Geant4. Two cases are considered 1) a simple box of water; 2) a heterogeneous geometry integrating 3 bone material structures (see figure). The Geant4 simulation was performed with two different nuclear models, Precompound and Binary Cascade. For each experiment, 106 protons were simulated. Integral depth-dose distributions and computation times were then compared. Finally, the capabilities of MCsquare to compute PG emission was compared to Geant4 (Binary Cascade) for a 150 MeV beam in an ICRP soft tissue phantom. Results: MCsquare and Geant4 results are very similar (< 3% differences) for both phantoms. However, we can observe slight differences between
ESTRO 33, 2014 The beam was calibrated according to IAEA TRS398 code of practice using a PTW Markus parallel-plate ionization chamber at 3 mm depth in water. Percentage depth dose (PDD) was measured with the same chamber in a water phantom at a Collimator-to-Surface Distance (CSD) of 100 cm, while a PTW SemiFlex ionization chamber was used to monitor the beam. Calibration curves of HDV2 and EBT3 Gafchromic film models were established at 3mm depth in a Solid WaterTM phantom using the same reference monitor chamber. Dose profiles were acquired at surface and 2 mm depths in Solid Water using HDV2 film. Results: The output at 3 mm depth in water was found to be stable within 5% at 4.8 Gy/sec. Figure 1a shows PDD measurement result with Bragg peak at 7.06 mm which is comparable to theoretical range of 7.08 mm in water according to NIST PSTAR database. Figure 1b shows calibration curves of EBT3 and HDV2 film models in proton beam compared to a typical EBT3 film calibration in 6 MV photon beam. Figures 1c and 1d show relative dose profiles at surface and 2 mm depths, respectively.
Fig 1: Neutron measurements for a 250-MeV clinical proton beam. a. photograph of experimental set-up and b. measured neutron spectrum. Conclusions: We report a secondary neutron spectrum from a 250-MeV passively scattered proton beam measured by using an extended-range Bonner sphere measurement system that is sensitive to neutron energies over the entire neutron energy range of interest for proton therapy applications. The measurements were carried out using the highest energy available at our facility and for a closed aperture, thus representing the maximum external neutron production. OC-0270 Dosimetric characterization of low energy protons for intra-operative radiation therapy B. Moftah1, F. Alrumayyan2, S. Aldelaijan1, M. Shehadeh1, F. Alzorkani1, M. Alshabanah3, J. Seuntjens4, S. Devic4 1 King Faisal Specialist Hospital & Research Centre, Biomedical Physics, Riyadh, Saudi Arabia 2 King Faisal Specialist Hospital & Research Centre, Cyclotron & Radiopharmaceuticals, Riyadh, Saudi Arabia 3 King Faisal Specialist Hospital & Research Centre, Radiation Oncology, Riyadh, Saudi Arabia 4 McGill University, Medical Physics, Montreal, Canada Purpose/Objective: With advantages of high tumor control to normal tissue complication ratio, high dose rate and conveniently short range, low energy proton beam of typical radiopharmaceutical-producing cyclotrons offer a logical, yet untested, tool for intra-operative radiation therapy (IORT). Our proposal to use a low energy proton beam for IORT relies on the physical configuration of proton beam that can be delivered to a tumor using 'keyhole surgery'. Before embarking on its clinical use, several issues must be addressed: (a) stability of the cyclotron; (b) whether beam properties are suitable to provide adequate penetration and sufficient prescription dose for cancer types to be considered in the future; and (c) if the output of the cyclotron will be able to provide reasonable treatment times. Materials and Methods: At our institution, we possess a CS30 cyclotron which is capable of accelerating protons at 26.5 MeV through seven beam lines. One beam line is connected to a gantry based clinical treatment room and is set to be reconditioned for IOpRT feasibility testing. The dosimetric properties of proton beam are tested on another research beam line running at a 100 nA current with a 2 mm collimator.
Figure 1 a) Percent depth dose in water of 26.5 MeV proton, b) calibration of EBT3 and HDV2 films in proton beam compared to conventional calibration, c) and d) dose profiles measured by HDV2 film at surface and 2 mm depth, respectively. Conclusions: The 26.5 MeV proton beam was characterized and found to have sufficient penetration depth, uniformity, and high dose rate for selected tumor/IORT sites that propel the advancement of this IOpRT project. At such high dose rate, the HDV2 film was shown to have dosimetric characteristics that are suitable for the purpose. OC-0271 Production of high quality 11C beams for radiation therapy and PETCT dose delivery verification M. Lazzeroni1, A. Brahme1 1 Karolinska Institutet, Oncology-Pathology, Stockholm, Sweden Purpose/Objective: This study aims at exploring a method to maximize the generally low production yield of 11C ion beams through in-flight fragmentation of a primary 12C ion beam on a dedicated target. The main steps from the production of the beam and the transport through the beam optics system to the purification of the beam from other potentially contaminating fragments were investigated. Positron emitter light ions have high potential for simultaneously treating and in vivo monitoring the dose delivery with Positron Emission Tomography (PET) or PET-Computed Tomography (CT) imaging. 11C ion beams merge the main distinctive properties of light ion therapy, i.e. highly conformal dose delivery and increased biological effectiveness, with the advantage of a high β+-activity signal mainly produced directly by the beam itself, and therefore not primarily dependent on the stoichiometry of the tissues. Materials and Methods: Monte Carlo simulations with the SHIELD-HIT10+ code were used in combination with analytical models of transport of ions in matter based on the generalized Fermi-Eyges theory. The irradiation geometry of the Monte Carlo simulations consisted of a cylindrical target made of 20 cm liquid hydrogen (ρ≈ 0.071 g/cm3)
ESTRO 33, 2014 followed by a polyethylene (ρ≈0.94 g/cm3) section with variable length. The primary 12C ion beam monoenergetic (400 MeV/u) and monodirectional impinged longitudinally on the cylinder. Particle fluence double differential in energy and angle were scored in 1 cm thick slices. Production yields, as well as energy, velocity and magnetic rigidity of the fragments generated in the target were scored as a function of the depth in the target. Results: A beam line design is proposed, which includes a composite production target made of liquid hydrogen section followed by a variable thickness section consisting of plane parallel slabs of polyethylene. The first section is selected to maximize the 11C ion beam intensity, whereas the second section is used to reduce the beam energy to the desired value, maintaining the high 11C ion yield. To minimize the energy spread of 11C ion beam, and the contamination from other fragments, a variable wedge-shaped degrader and a Time Of Flight (TOF) Radio-Frequency driven velocity filter are included in the beam line. A 11C ion beam intensity of about 4-6% of the primary 12C ion beam intensity with radial spot size confined to 0.5 cm in radius, and an energy and angular spread of about 1% and 1°,respectively, are achievable. The 11C ion beam purity is expected to be about 99%.
S105 Results: For the collimated divergent and uncollimated single pencil beams, GATE results agreed with the analytical model of Safai et al. (PMB 2008) to within 1-2mm, validating the Monte Carlo model. Reducing the SSD of a pencil beam array has a greater effect at lower energies due to the reduction of in-air scattering. Collimation of a monoenergetic pencil beam array reduces the entrance penumbra from 0.4-1.2cm to 0.1-0.2cm, depending on SSD and initial energy. Beams 'pulled back' through a Perspex range shifter suffer penumbral blurring; placing a collimator beyond the range shifter sharpens the penumbra to approximately that of an uncollimated PBS. Collimation of homogeneous volumes is shown in Figure 1.
Figure 1: 2D profiles in a 20cm3 water tank for a (L-R) uncollimated,singly collimated, uncollimated pullback and collimated pullback pencil beam array using a square grid of spots. The latter 2 beams have been pulled back through 10cm Perspex. The beams have been weighted to ensure a homogeneous dose in the spherical volume. Conclusions: Positioning the nozzle of a spot scanned beam at short SSD produces penumbra comparable to that of a double scattered system. For very superficial tumours and for beams which have to be degraded through Perspex, use of a collimator significantly improves the lateral penumbra; this is seen both for single energy layers and for doses to homogeneous volumes. OC-0273 Fast Monte Carlo simulation of proton therapy treatment using an Intel Xeon Phi coprocessor K. Souris1, J. Lee1, E. Sterpin1 1 UCL - IREC, Molecular Imaging Radiotherapy and Oncology (MIRO), Bruxelles, Belgium
Conclusions: The presented system for production of high quality 11C ion beams contributes to the developments of an accurate PET-CT based dose delivery verification. The proposed practical solution allows overcoming the difficulties related to the low quality and production efficiency of light ion positron emitter beams and it is applicable to cyclotron, synchrotron and linac based hospital facilities. OC-0272 Collimation of spot scanned proton therapy beams to sharpen the lateral edge of uniform dose volumes F.C. Charlwood1, A.H. Aitkenhead1, R.I. MacKay1 1 The Christie NHS Foundation Trust, Christie Medical Physics and Engineering, Manchester, United Kingdom Purpose/Objective: In general, the lateral edge (termed penumbra) of a pencil beam scanning (PBS) system is worse than that of a double scattered divergent beam at shallow depths in the patient. This is predominantly due to the in-air scattering associated with the spot scanned beam. Depending on the minimum accelerator energy output, the beam may need to be degraded through Perspex beyond the nozzle, further blurring the penumbra. Here, Monte Carlo simulations have shown that the penumbra is significantly improved by the use of a short source-surface distance (SSD) and/or collimation. To date, there have been few studies of the factors affecting the lateral penumbra of homogeneous dose volumes. Materials and Methods: The GATE (Jan et al., PMB 2011) Monte Carlo software was used to simulate double scattered and pencil beams, with results validated against those of Safai et al. (PMB 2008). Key parameters such as SSD, collimator-surface distance, collimator thickness and diameter, use of range shifter, spot properties and optimisation were separately investigated to assess the conformity of treatment. Additionally the delivery of homogeneous dose volumes using spot scanning was simulated to ensure that the penumbra can be sharpened throughout the whole volume. For spherical volumes, the use of a MLC was simulated in attempt to improve the penumbra.
Purpose/Objective: In proton therapy, range uncertainties jeopardize treatment quality. Monte Carlo (MC) simulations can help reduce them by improving dose calculation accuracy and being integrated in on-line range monitoring techniques, like prompt gamma (PG) imaging. Most current MC methods are however too slow for clinical use. Using graphical processor units (GPUs), computation times of the order of the minute have been reported. However, the highly vectorized architecture of GPUs is not ideal to handle the stochastic nature of MC methods, forcing profound adaption of the inner physics with a loss of generality. As a result, most MC codes based on GPUs are limited to a specific task, namely dose computation with the sole tracking of the protons (no PG emission). In this communication, we present MCsquare (Many-Core Monte Carlo), a new, fast, and accurate MC simulation of protons. MCsquare relies on the new Intel Xeon Phi coprocessor, which does not have the restrictions of GPUs and thus enable more general and realistic simulations. Materials and Methods: The flexible architecture of the Xeon Phi coprocessor provides many independent execution threads that can be assigned to detailed simulations of nuclear reactions and secondary particles without performance loss. This coprocessor is composed of 60 cores, each containing a 512-bit SIMD unit, and is capable of more than 1 teraflops. In MCsquare, nuclear reactions are sampled from the ICRU 63 database, taking into account the atomic composition of tissues. ICRU 63 database provides comprehensive information for PG emission that is incorporated in MCsquare. To illustrate the accuracy and the computation speed, a 200 MeV proton beam has been simulated using MCsquare and compared to Geant4. Two cases are considered 1) a simple box of water; 2) a heterogeneous geometry integrating 3 bone material structures (see figure). The Geant4 simulation was performed with two different nuclear models, Precompound and Binary Cascade. For each experiment, 106 protons were simulated. Integral depth-dose distributions and computation times were then compared. Finally, the capabilities of MCsquare to compute PG emission was compared to Geant4 (Binary Cascade) for a 150 MeV beam in an ICRP soft tissue phantom. Results: MCsquare and Geant4 results are very similar (< 3% differences) for both phantoms. However, we can observe slight differences between