- Email: [email protected]
1422 poster IBA PROTON PENCIL BEAM SCANNING : VALIDATION
P ROTON AND ION THERAPY: P HYSICS
process is based on comparing measured to activity distributions with those predicted from the treatment plan. Visual comparison is very time consuming and requires trained observers, so a (semi)automatic evaluation method is desirable. Materials: Deviations in dose delivery appear in most cases in a shift of the ion range. Based upon 81 patient datasets simulations were performed, thereby range modifications of ±6 mm were applied. So there are three classes: without any modification and with range modification of +6 mm in water and -6 mm, respectively.Trained experts visually evaluated the activitydistributions and guessed whether a dataset was modified and tried to identify the kind of modification.A one-dimensional algorithm, comparing two activity profiles along the beam, developed for the comparison of ion ranges was extended to 3D. The results of 3D range comparison algorithm were analyzed statistically. For 6 patients the measured in beam PET images and the associated simulations were evaluated automatically, thereof 12 without any modification, 11 with a positive, 11 with a negative shift.Besides the statistical approach, a tool was developed that provides an assisted visual evaluation of in beam PET measurements. It allows to superimpose relevant data like CT, in-beam PET, dose distribution and the local result of the range comparison algorithm. Results: The highest sensitivity and specificity was obtained by the well trained observers. The one dimensional range comparison algorithm can classify many images correctly but requires previous knowledge of the position of a range deviation.The sensitivity and specificity of the 3D algorithm in combination to the subsequent statistical evaluation is lower than the visual method but higher than the one-dimensional algorithm. The software for assisted visual evaluation shows a good agreement between the calculated range differences and the deviation found by an observer. Conclusions: Automatic evaluation of in beam PET data seems to be feasible, at least as an assistance for the physicist and the clinician. 1422 poster IBA PROTON PENCIL BEAM SCANNING : VALIDATION F. Dessy1 , N. Linthout1 , S. Gillis1 , M. Closset1 1
I ON B EAM A PPLICATIONS (IBA), Louvain la Neuve, Belgium
Purpose: As proton therapy is becoming more and more clinically available and Pencil Beam Scanning (PBS) is being introduced as the newest treatment delivery technique, the validation of the delivery technique as well as the validation of a beam model created for PBS was the objective of this work. Materials: The PBS technique is treating the patient’s target volume in multiple iso-energy layers. Each layer is composed of an array of spots with individual intensities to modulate the fluence within the layer. This results in the delivery of energy and intensity modulated proton beams.The delivery technique accuracy was evaluated in 2D with a complex pattern allowing evaluation of the spot shape, position, in-plane spatial resolution and the fluence accuracy. The delivery technique was evaluated for a subset of possible energies and gantry angles covering the entire range.A beam model has been created in the XiO 4.61®TPS (Elekta AB, Sweden) to allow accurate treatment plan calculation for the PBS technique. Calculated dose distributions were measured using the Zebra (IBA dosimetry GmbH, Germany), a MultiLayer Ionization Chamber (MLIC), for 1D-measurements parallel to the beam axis and the MatriXXEvolution (IBA dosimetry GmbH, Germany) for 2D-measurements perpendicular to the beam axis. The MatriXX evolution was modified to increase the collection efficiency in case of very high dose rates (up to 200Gy/sec). Additionally gafchromic EBT2 (ISP, NJ, USA) film measurements were performed perpendicular to the beam axis to evaluate the lateral penumbra with a higher resolution than achievable with the MatriXX.From the 2D MatriXX measurements, a 3D dose distribution was reconstructed and compared with the one exported from the TPS. This comparison, using gamma analysis, was done using the OmniPro-I’mRT 1.7 software (IBA dosimetry GmbH, Germany). Results: The 1D measurements showed a range accuracy for the different pristine peaks better than ±0.1g/cm and a pull-back accuracy, for small energy changes better than ±0.05g/cmThe complex pattern delivered with PBS showed a 2%/2mm agreement for every beam energy in the range of 100230MeV and at every gantry angle compare to the theoretical fluence. It also indicated an accurate spot delivery and in-plane spatial resolution .The measured 2D dose distributions correspond within a gamma value of 3%/3mm with the calculated distributions extracted from the TPS. Conclusions: This study showed that the IBA PBS, combined with the Xio®TPS, meets the general accepted gamma criteria of 3 % 3mm in a homogenous phantom and is ready for implementation in proton therapy departments. 1423 poster IMAGING CHARACTERIZATION OF PRIMA PROTON IMAGING DEVICE C. Talamonti1 2 3 , S. Pallotta1 2 3 , M. Bruzzi4 2 , M. Bucciolini1 2 3 , P. Cirrone5 , C. Civinini2 , G. Cuttone5 , D. lo presti6 7 , L. Marrazzo8 , N. Randazzo7 , M.
S 529
Scaringella4 2 , C. Stancampiano6 7 U NIVERSITY OF F LORENCE, Clinical Physiopathology Department, Firenze, Italy 2 I STITUTO N AZIONALE DI F ISICA N UCLEARE , INFN SEZIONE DI F IRENZE, Florence, Italy 3 AOUC C AREGGI, Florence, Italy 4 U NIVERSITY OF F LORENCE, Firenze, Italy 5 INFN L ABORATORI N AZIONALI DEL S UD, Catania, Italy 6 U NIVERSITY OF C ATANIA, Catania, Italy 7 I STITUTO N AZIONALE DI F ISICA N UCLEARE , S EZIONE DI C ATANIA, Catania, Italy 8 AOU C AREGGI, Firenze, Italy 1
Purpose: Proton computed tomography (pCT) has several potential advantages in medical applications, as it provides both a direct and precise method for patient positioning using the therapeutic beam and it a technique for an accurate prediction of proton dose distribution. For both these applications the required accuracy is 1-2 mm. Moreover, a successful integration of pCT with proton therapy may lead also to the ultimate form of image-guided 3D conformal radiation therapy.The aim of PRIMA project is to develop a prototype of Computed Tomograph based on the tracking of each single proton traversing the phantom. In this study we describe the results of a test beam in Catania at laboratori nazionali del Sud.Beside testing the full apparatus, checking separately each detector and the data acquisition system, data of phantoms designed to study spatial and contrast resolution have been acquired using a 62 MeV proton beam. Radiography of several phantoms and a nut have been reconstructed. The obtained results will be discussed in this work. Materials: As a first step toward pCT, Prima project developed a proton computed radiography (pCR) prototype capable to carry out a single projection. The pCR apparatus includes a tracker (based on identical tracker modules, each including a silicon microstrip detector) to measure proton trajectory and a calorimeter (made of four YAG:Ce optically separated crystals) to measure residual energy. The tracker modules have been extensively tested and calibrated, to optimize their performance, with b particles and 62 MeV protons at INFN-LNS. YAG:Ce crystals were tested with 62MeV protons at INFN-LNS, and with 200MeV protons at Loma Linda University Medical Center (LLUMC). Results: Beside testing the full apparatus, checking separately each detector and the data acquisition system, data of phantoms designed to study spatial and contrast resolution have been acquired. Radiography of several phantoms and a nut have been reconstructed. The obtained results are encouraging. A tomography experiment has been performed too, projections from 0◦ to 180◦ of a phantom were acquired. These data will be used to test and set up reconstruction algorithms for tomography studies. Conclusions: A beam test of the full pCR prototype was performed last summer. The prototype permits to image phantoms, producing data suitable to develop and validate reconstruction algorithms. A new test beam is foreseen next February, results from these experiments will be presented in this contribution. This work is supported by INFN PRIMA project. 1424 poster IN VIVO DOSIMETRY DURING PROTON TREATMENTS V. La Rosa1 , K. Pepper1 , A. Gibson1 , G. Royle1 , A. Kacperek2 U NIVERSITY C OLLEGE OF L ONDON (UCL), Medical Physics and Biomedical Engineering, London, United Kingdom 2 C LATTERBRIDGE C ENTRE FOR O NCOLOGY, Douglas Cyclotron, Bebington, Merseyside, United Kingdom 1
Purpose: Introduction: Proton therapy offers high conformality and dose reduction to organs at risk. However, these benefits require improved localization of the target and mapping of the dose distribution. Estimating the dose distribution is critical and depends on tissues heterogeneities, organ motion and secondary particle production. Objective: We aim to develop an in-vivo dose measurement technique for proton therapy. Real time evaluation of the dose distribution inside the patient will allow us to protect as much healthy tissue as possible despite uncertainties in the treatment delivery. We propose to use high atomic number seeds implanted within the patient. Heavy metals generate x-ray fluorescence when irradiated with high energy protons ( Particle Induced X-ray Emission). We will measure these fluorescent x-rays outside the patient continuously during the treatment and then relate the fluorescent intensity to the dose received at that point in the patient. Background: We measured x-ray fluorescence over a range of gold nanoparticle concentrations using the SYRMEP beamline at the Elettra synchrotron, Italy [1]. The signal was linear with nanoparticle concentration down to the minimum detectable limit. We are extending this work by measuring the xray fluorescence from proton irradiation of gold to the dose deposited in the vicinity of the gold mass. Alternative metals to gold will also be considered Materials: Metal fiducial markers are often implanted in patients before radiotherapy to improve the target localization and reduce patient setup errors. We simulated emissions from metal seeds in water irradiated by 60 MeV protons with Geant4 Monte Carlo code. The physics model included proton energy loss, multiple Coulomb scattering, nuclear reactions, and radioactive decay. We validated the model by measuring x-ray fluorescence from (a) a gold foil
process is based on comparing measured to activity distributions with those predicted from the treatment plan. Visual comparison is very time consuming and requires trained observers, so a (semi)automatic evaluation method is desirable. Materials: Deviations in dose delivery appear in most cases in a shift of the ion range. Based upon 81 patient datasets simulations were performed, thereby range modifications of ±6 mm were applied. So there are three classes: without any modification and with range modification of +6 mm in water and -6 mm, respectively.Trained experts visually evaluated the activitydistributions and guessed whether a dataset was modified and tried to identify the kind of modification.A one-dimensional algorithm, comparing two activity profiles along the beam, developed for the comparison of ion ranges was extended to 3D. The results of 3D range comparison algorithm were analyzed statistically. For 6 patients the measured in beam PET images and the associated simulations were evaluated automatically, thereof 12 without any modification, 11 with a positive, 11 with a negative shift.Besides the statistical approach, a tool was developed that provides an assisted visual evaluation of in beam PET measurements. It allows to superimpose relevant data like CT, in-beam PET, dose distribution and the local result of the range comparison algorithm. Results: The highest sensitivity and specificity was obtained by the well trained observers. The one dimensional range comparison algorithm can classify many images correctly but requires previous knowledge of the position of a range deviation.The sensitivity and specificity of the 3D algorithm in combination to the subsequent statistical evaluation is lower than the visual method but higher than the one-dimensional algorithm. The software for assisted visual evaluation shows a good agreement between the calculated range differences and the deviation found by an observer. Conclusions: Automatic evaluation of in beam PET data seems to be feasible, at least as an assistance for the physicist and the clinician. 1422 poster IBA PROTON PENCIL BEAM SCANNING : VALIDATION F. Dessy1 , N. Linthout1 , S. Gillis1 , M. Closset1 1
I ON B EAM A PPLICATIONS (IBA), Louvain la Neuve, Belgium
Purpose: As proton therapy is becoming more and more clinically available and Pencil Beam Scanning (PBS) is being introduced as the newest treatment delivery technique, the validation of the delivery technique as well as the validation of a beam model created for PBS was the objective of this work. Materials: The PBS technique is treating the patient’s target volume in multiple iso-energy layers. Each layer is composed of an array of spots with individual intensities to modulate the fluence within the layer. This results in the delivery of energy and intensity modulated proton beams.The delivery technique accuracy was evaluated in 2D with a complex pattern allowing evaluation of the spot shape, position, in-plane spatial resolution and the fluence accuracy. The delivery technique was evaluated for a subset of possible energies and gantry angles covering the entire range.A beam model has been created in the XiO 4.61®TPS (Elekta AB, Sweden) to allow accurate treatment plan calculation for the PBS technique. Calculated dose distributions were measured using the Zebra (IBA dosimetry GmbH, Germany), a MultiLayer Ionization Chamber (MLIC), for 1D-measurements parallel to the beam axis and the MatriXXEvolution (IBA dosimetry GmbH, Germany) for 2D-measurements perpendicular to the beam axis. The MatriXX evolution was modified to increase the collection efficiency in case of very high dose rates (up to 200Gy/sec). Additionally gafchromic EBT2 (ISP, NJ, USA) film measurements were performed perpendicular to the beam axis to evaluate the lateral penumbra with a higher resolution than achievable with the MatriXX.From the 2D MatriXX measurements, a 3D dose distribution was reconstructed and compared with the one exported from the TPS. This comparison, using gamma analysis, was done using the OmniPro-I’mRT 1.7 software (IBA dosimetry GmbH, Germany). Results: The 1D measurements showed a range accuracy for the different pristine peaks better than ±0.1g/cm and a pull-back accuracy, for small energy changes better than ±0.05g/cmThe complex pattern delivered with PBS showed a 2%/2mm agreement for every beam energy in the range of 100230MeV and at every gantry angle compare to the theoretical fluence. It also indicated an accurate spot delivery and in-plane spatial resolution .The measured 2D dose distributions correspond within a gamma value of 3%/3mm with the calculated distributions extracted from the TPS. Conclusions: This study showed that the IBA PBS, combined with the Xio®TPS, meets the general accepted gamma criteria of 3 % 3mm in a homogenous phantom and is ready for implementation in proton therapy departments. 1423 poster IMAGING CHARACTERIZATION OF PRIMA PROTON IMAGING DEVICE C. Talamonti1 2 3 , S. Pallotta1 2 3 , M. Bruzzi4 2 , M. Bucciolini1 2 3 , P. Cirrone5 , C. Civinini2 , G. Cuttone5 , D. lo presti6 7 , L. Marrazzo8 , N. Randazzo7 , M.
S 529
Scaringella4 2 , C. Stancampiano6 7 U NIVERSITY OF F LORENCE, Clinical Physiopathology Department, Firenze, Italy 2 I STITUTO N AZIONALE DI F ISICA N UCLEARE , INFN SEZIONE DI F IRENZE, Florence, Italy 3 AOUC C AREGGI, Florence, Italy 4 U NIVERSITY OF F LORENCE, Firenze, Italy 5 INFN L ABORATORI N AZIONALI DEL S UD, Catania, Italy 6 U NIVERSITY OF C ATANIA, Catania, Italy 7 I STITUTO N AZIONALE DI F ISICA N UCLEARE , S EZIONE DI C ATANIA, Catania, Italy 8 AOU C AREGGI, Firenze, Italy 1
Purpose: Proton computed tomography (pCT) has several potential advantages in medical applications, as it provides both a direct and precise method for patient positioning using the therapeutic beam and it a technique for an accurate prediction of proton dose distribution. For both these applications the required accuracy is 1-2 mm. Moreover, a successful integration of pCT with proton therapy may lead also to the ultimate form of image-guided 3D conformal radiation therapy.The aim of PRIMA project is to develop a prototype of Computed Tomograph based on the tracking of each single proton traversing the phantom. In this study we describe the results of a test beam in Catania at laboratori nazionali del Sud.Beside testing the full apparatus, checking separately each detector and the data acquisition system, data of phantoms designed to study spatial and contrast resolution have been acquired using a 62 MeV proton beam. Radiography of several phantoms and a nut have been reconstructed. The obtained results will be discussed in this work. Materials: As a first step toward pCT, Prima project developed a proton computed radiography (pCR) prototype capable to carry out a single projection. The pCR apparatus includes a tracker (based on identical tracker modules, each including a silicon microstrip detector) to measure proton trajectory and a calorimeter (made of four YAG:Ce optically separated crystals) to measure residual energy. The tracker modules have been extensively tested and calibrated, to optimize their performance, with b particles and 62 MeV protons at INFN-LNS. YAG:Ce crystals were tested with 62MeV protons at INFN-LNS, and with 200MeV protons at Loma Linda University Medical Center (LLUMC). Results: Beside testing the full apparatus, checking separately each detector and the data acquisition system, data of phantoms designed to study spatial and contrast resolution have been acquired. Radiography of several phantoms and a nut have been reconstructed. The obtained results are encouraging. A tomography experiment has been performed too, projections from 0◦ to 180◦ of a phantom were acquired. These data will be used to test and set up reconstruction algorithms for tomography studies. Conclusions: A beam test of the full pCR prototype was performed last summer. The prototype permits to image phantoms, producing data suitable to develop and validate reconstruction algorithms. A new test beam is foreseen next February, results from these experiments will be presented in this contribution. This work is supported by INFN PRIMA project. 1424 poster IN VIVO DOSIMETRY DURING PROTON TREATMENTS V. La Rosa1 , K. Pepper1 , A. Gibson1 , G. Royle1 , A. Kacperek2 U NIVERSITY C OLLEGE OF L ONDON (UCL), Medical Physics and Biomedical Engineering, London, United Kingdom 2 C LATTERBRIDGE C ENTRE FOR O NCOLOGY, Douglas Cyclotron, Bebington, Merseyside, United Kingdom 1
Purpose: Introduction: Proton therapy offers high conformality and dose reduction to organs at risk. However, these benefits require improved localization of the target and mapping of the dose distribution. Estimating the dose distribution is critical and depends on tissues heterogeneities, organ motion and secondary particle production. Objective: We aim to develop an in-vivo dose measurement technique for proton therapy. Real time evaluation of the dose distribution inside the patient will allow us to protect as much healthy tissue as possible despite uncertainties in the treatment delivery. We propose to use high atomic number seeds implanted within the patient. Heavy metals generate x-ray fluorescence when irradiated with high energy protons ( Particle Induced X-ray Emission). We will measure these fluorescent x-rays outside the patient continuously during the treatment and then relate the fluorescent intensity to the dose received at that point in the patient. Background: We measured x-ray fluorescence over a range of gold nanoparticle concentrations using the SYRMEP beamline at the Elettra synchrotron, Italy [1]. The signal was linear with nanoparticle concentration down to the minimum detectable limit. We are extending this work by measuring the xray fluorescence from proton irradiation of gold to the dose deposited in the vicinity of the gold mass. Alternative metals to gold will also be considered Materials: Metal fiducial markers are often implanted in patients before radiotherapy to improve the target localization and reduce patient setup errors. We simulated emissions from metal seeds in water irradiated by 60 MeV protons with Geant4 Monte Carlo code. The physics model included proton energy loss, multiple Coulomb scattering, nuclear reactions, and radioactive decay. We validated the model by measuring x-ray fluorescence from (a) a gold foil