- Email: [email protected]
Increasing precision in particle therapy: In vivo dosimetry and beyond
Abstracts / Physica Medica 30 (2014) e1ee15
concept of lateral buildup ratio (LBR) as an avenue to evaluate electron later scatter equilibrium and compute dose per MU for those fields. Finally, it gives some common clinical examples where electron beam dosimetry are applied. This presentation will try to provide guidance to the audience for better understanding the methods and recommendations in TG-70. In addition, will describe how to link the absolute dose calibration recommendations of TG-51 to the relative dose measurements of TG-71. TOWARDS DAILY ADAPTED PROTON THERAPY Tony Lomax. Centre for Proton Therapy, Paul Scherrer Institute, Switzerland Proton therapy using Pencil Beam Scanning (PBS) is a highly conformal and flexible form of radiotherapy. However, anatomic changes of the patient during the course of therapy are a major challenge due to the potentially major changes in proton ranges that can result. The challenge is even greater given that such changes can occur on a daily basis and current software systems and workflows in radiotherapy are too slow to react to such changes. In order to fully exploit the highly conformal characteristics of PBS proton therapy therefore, methods for the daily adaption of proton therapy need to be developed, a concept we call ‘Daily Adaptive Proton Therapy’ (DAPT). The concept of DAPT is to work towards a flexible and fully automated workflow for PBS proton therapy, with the aim of imaging, planning and delivering a ‘plan-of-the-day’ for patients on a daily basis. In order to achieve this, the time between the imaging of the patient and delivery of the plan has to be reduced to a maximum of 1-2 minutes. With the in-room imaging capabilities of the PSI Gantry 2, and the inherent flexibility of PBS proton therapy, we believe we already have the ideal treatment machine for the implementation of DAPT. However, the challenges are more computational and workflow oriented than technological. In order to move towards a DAPT approach for instance, image registration, planning and optimisation procedures must be made computationally efficient and fully automated. In addition, efficient and informative tools need to be developed that will allow clinical staff to review these ‘plans-ofthe-day’, as well as to allow for fast, but nevertheless safe, quality assurance checks of the plans. For instance, with the introduction of DAPT type approaches, it will be impossible to perform patient or field specific dosimetric verifications, and other, automated methods for checking the fidelity of treatments and treatment control files will need to be developed. Thus, there are many challenges to be met before DAPT will become a reality. However, we firmly believe that moving in this direction is the next major advance in clinical proton therapy, and its introduction could have at least as large an impact on current clinical practice with protons as the introduction of Intensity Modulated Proton Therapy. Indeed, one could argue that PBS proton therapy, with its flexible and automated workflow, is pre-destined for the DAPT concept. FLUORESCENT NUCLEAR TRACK DETECTORS AS A TOOL FOR ION-BEAM THERAPY RESEARCH €kel a,b, c. aGerman Cancer Research Center (DKFZ), Division S. Greilich a, O. Ja of Medical Physics in Radiation Oncology, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany; bHeidelberg University Hospital, Department of Radiation Oncology, Im Neuenheimer Feld 400, 69120 Heidelberg, Germany; cHeidelberg Ion-Beam Therapy Center (HIT), Im Neuenheimer Feld 450, 69120 Heidelberg, Germany Originally designed for optical storage, fluorescent nuclear track detectors (FNTD) based on Al2O3:C,Mg single crystals contain aggregate F2+ 2 (2 Mg) color centers that show permanent radiochromic transformation when bombarded with ionizing radiation. Transformed centers produce high yield fluorescence at 750 nm when stimulated at 620 nm and a short (75±5 ns) lifetime. This enables non-destructive readout using confocal laserscanning microscopes (CLSMs, Akselrod and Sykora, 2011). Since the intensity signal depends on the local energy deposition, 3D particle trajectories through the crystal can be assessed. Together with the excellent sensitivity Al2O3:C,Mg this enables the derivation of information on track location, direction, energy loss, etc. over the entire particle and energy
e3
range found in ion beam therapy. Effects such as projectile fragmentation and secondary electron trajectories can be studied in detail with diffraction-limited resolution (Greilich et al., 2013). Due to their biocompatibility, autoclavability and since post-irradiation chemical processing is not needed, FNTDs can show significant superiority to existing technologies such as plastic nuclear track detectors (PNTDs, e.g. CR-39). Our group studies the FNTD technology for application on three main fields: Fundamental dosimetry quantities (w-value, I-value) in ion beams: FNTDs allow determining particle fluence and range with very high accuracy (Osinga et al., 2013, Klimpki et al., 2013). In-vivo track-based assessment of dose to organs at risk during therapy: FNTDs represent one of a few systems that enable biological dose estimation which is the essential predictor for clinical outcome in ion beam therapy. In addition, FNTD are small, resilient, wireless and biocompatible and can be therefore used within phantoms, animal models or even patients. Radiobiology: our group was the first to use FNTDs as substrate for cell (“Cell-Fit-HD”, Niklas et al., 2013). This enables to correlate microscopic physical parameters and subcellular/cell response both in fixed and living cell and study cellular processes fundamental to ion beam radiotherapy that are hitherto little understood. The talk will present the basic principle of FNTD technology, our group’s technical implementation as well as the latest methodological developments and application results. References 1. Akselrod MS, Sykora GJ: Fluorescent nuclear track detector technology e A new way to do passive solid state dosimetry. Radiat Meas 2011, 46:1671e1679. 2. Greilich S, Osinga J-M, Niklas M, Lauer FM, Klimpki G, Bestvater F, Bartz €kel O: Fluorescent Nuclear Track Detectors as a Tool for JA, Akselrod MS, Ja Ion-Beam Therapy Research. Radiat Meas 2013, 56:267e272. €kel O, Greilich S: Ion 3. Klimpki G, Osinga J-M, Herrmann R, Akselrod MS, Ja Range Measurements using Fluorescent Nuclear Track Detectors. Radiat Meas 2013, 56:342e346. 4. Niklas M, Abdollahi A, Akselrod MS, Debus J, J€ akel O, Greilich S: Subcellular spatial correlation of particle traversal and biological response in clinical ion beams. Int J Radiat Oncol 2013, 87:1141e1147. €kel O, Greilich S: Absorbed 5. Osinga J-M, Brons S, Bartz J a, Akselrod MS, Ja Dose in Ion Beams: Comparison of Ionisation- and Fluence-Based Measurements. Radiat Prot Dosimetry 2014. INCREASING PRECISION IN PARTICLE THERAPY: IN VIVO DOSIMETRY AND BEYOND C. Richter a, b, c, d, G. Pausch a, b, d, J. Seco e, T. Bortfeld e, W. Enghardt a, b, c, d. a OncoRay e National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital C.G. Carus, €t Dresden, Germany; b Department of Radiation Technische Universita Oncology, Faculty of Medicine and University Hospital C.G. Carus, €t Dresden, Germany; c German Cancer Consortium Technische Universita (DKTK), Dresden, & German Cancer Research Center (DKFZ), Heidelberg, d Helmholtz-Zentrum Dresden-Rossendorf, Germany; Germany; e Massachusetts General Hospital and Harvard Medical School, Department of Radiation Oncology, Boston, MA, USA The proton dose distribution including the steep dose gradient at the end of range not only allows a better sparing of normal tissue. It also enforces the need of a precise control of the dose deposition to ensure the correct position of the dose gradient to take full advantage of the superior capabilities of proton therapy. Otherwise, factors like tissue heterogeneities, patient positioning errors and intra-fractional motion can cause high uncertainties in proton distal range resulting in a failing tumor coverage or/ and an unnecessary high dose deposition in healthy tissue due to the use of extended margins. Therefore, an in vivo verification or any other control of proton range and delivered dose distribution is highly desirable. Several in vivo dosimetry approaches will be presented and compared. They rely on either nuclear interactions of the beam with the irradiated matter (In beam-PET and prompt g-ray imaging) or on the visualization of
e4
Abstracts / Physica Medica 30 (2014) e1ee15
biological processes induced by radiation, e.g. with MRI. The most experience exists for in beam-PET. In Dresden, the current research focuses on time-resolved acquisition (4D-PET) and on automated detection of range deviations. In contrast, prompt gamma ray imaging is a relatively new and dynamic field of research. Several prompt g-ray imaging detector systems are under development in various research centers around the world based on active- as well as passively collimated systems. A complementary approach, based on the time spectrum of the g-ray emission, is investigated in Dresden. First promising results will be presented in the talk. However, so far there is no clinical application of prompt g-ray based in vivo dosimetry. In contrast, radiation-induced biological changes have been used in clinical trials at the Massachusetts General Hospital in Boston (MGH) for range verification in both, spine and liver. A recent study, also carried out at MGH, aims at a better understanding of when those treatment related changes in the liver begin to appear. Instead of assuring a safe and precise treatment by measuring the in vivo dose deposition, another approach is to decrease dose deposition uncertainties before beam delivery. This can be done in several ways: One approach tries to increase the robustness of the treatment plan against different types of uncertainties. This can be realized by including the robustness in the optimization and penalizing treatment plans with a dose deposition very prone to expected deviations. A completely different method for increasing dose deposition precision is based on online imaging during treatment: If the exact patient geometry would be known for every time point, the delivered dose deposition could be calculated and even adapted online if necessary. Online imaging could be performed with MRI scanners integrated in the treatment room in analogy to the combined MRI-linac approaches. At the moment this is a field of intense research with quite impressing progress. At this point it is not clear which of the different methods to increase precision in particle therapy will find their way in routine clinical application. Nevertheless, the demand and the potential of these methods are unquestionable. MONTE CARLO MODELING AND IMAGE-GUIDANCE IN PARTICLE THERAPY G. Dedes, K. Parodi. Department of Medical Physics, Ludwig Maximilians University, Munich, Germany The use of protons and heavier ions in external beam therapy offers distinctive advantages with respect to conventional radiotherapy using electromagnetic radiation. The physical selectivity of ions with the characteristic Bragg curve can enable high tumor-dose conformity, resulting in lower irradiation of healthy tissues and critical organs in close vicinity to the target volume. Moreover, the higher relative-biological-effectiveness (RBE), especially in the case of heavier ions, can offer improved control probability for radioresistant tumors. In this context, Monte Carlo (MC) particle transport and interaction methods are increasingly employed in clinical and research institutions as vital tools to support several aspects of beam modeling, treatment planning and quality assurance of high precision ion beam therapy. This talk will review the role of MC methods in selected applications in particle therapy. Drawing on own experience at different European particle therapy facilities, the fine tuning of MC parameters for beam modeling will be presented. In addition, based on ongoing studies and collaborations, we will give an overview on the wide range of MC applications aiming at novel tools for image guidance and treatment planning. These include the support to the development of heavy ion and proton computed tomography, as well as the direct usage of MC-data in the inverse planning process, featuring calculations of both absorbed and biologically weighted dose. Development and validation of new solutions based on clinically established imaging modalities for adaptive strategies in particle therapy will be also addressed, together with research efforts to support unconventional imaging-based techniques detecting secondary radiation for in-vivo confirmation of the actual treatment delivery. Finally, the application of Monte Carlo tools in the emerging research area of laser driven ion acceleration for medical application will be briefly exposed. Parts of this work have been supported by the DFG Cluster of Excellence MAP (Munich-Centre for Advanced Photonics), the DFG Project on Ion
Radiography and Tomography, the FP7 Project ENVISION, and the BMBF Project SPARTA. IMAGE GUIDANCE FOR ADAPTIVE RADIOTHERAPY: IS THERE STILL A NEED FOR SURROGATE SYSTEMS? Torsten Moser. Im Neuenheimer Feld 280, 69120, Heidelberg, Germany In conformal radiation therapy, accurate and reproducible patient setup is required. In this regard, initial setup errors, as well as day-to-day setup variation, still poses a clinically relevant problem. The available anatomic („internal“) information of the patient, however, relies on the images of the planning CT, acquired up to weeks prior to treatment and does not reflect changes during the actual treatment. To correct in the actual situation, the most reliable information is obtained by 3D-imaging techniques like cone beam CT. Adaptive treatment techniques, moreover, adds a further component to the treatment chain, the feed-back. Again by daily image guidance, changes that occur during the treatment can be detected and handled. Meanwhile, most linear accelerators are able to acquire images (eg, kilovoltage/megavoltage setup images or cone beam computed tomography [CT] scans) that allow correlation of the actual patient position with that during treatment planning CT. By the use of such image guided radiation therapy techniques, the potential benefit for the patient has to be weighed against the additional risk associated with the imaging dose. For this reason, non-radiologic techniques to verify the setup position of the patient are of great interest. As such developments, there are various systems available that provide also information of motion and/or position. There are devices available where electromagnetic markers have to be implanted into the patient or technologies where other information’s are used to generate signals that can be used for position or motion correction. One of the latter are optical surface imaging systems. Optical surface imaging systems are able to reconstruct a 3-dimensional (3D) surface model relative to the isocenter position. A setup correction is calculated by registering actual images with reference images stored in the system beforehand. Although the technical accuracy of such systems has been shown to be quite high, their suitability for clinical application depends on additional aspects, in particular on a fixed spatial relation between the surface and target region. To analyze this, setup corrections from a surface imaging system were evaluated in 120 patients. As a measure of reliability, the corrections derived by the optical system were compared with those from 3D radiologic imaging, which is the current gold standard in image guided radiation therapy. We found a dependence on the target region and the used reference image modality. Therefore, additional radiologic imaging may still be necessary on a regular basis (e.g., weekly) or if the corrections of the optical system appear implausibly large. Nevertheless, such a combined application may help to reduce the imaging dose for the patient. SMALL PHOTON FIELD DOSIMETRY: PRESENT STATUS Maria M. Aspradakis. Cantonal Hospital of Lucerne, 6000 Lucerne 16, Switzerland Background: IPEM report 1031 summarised existing knowledge on the physics and challenges in the dosimetry of small MV photon fields, reviewed available detectors for dose measurement, gave recommendations based on existing knowledge and experience, explained the need of commissioning treatment planning systems for small field applications and pointed out directions for future work. This presentation reports on recent developments. Materials and Methods: A megavoltage (MV) photon field is defined as ‘small’ when either the field size is not large enough to provide lateral charged particle equilibrium at the point of dose measurement or the collimating device obstructs part of the focal spot as viewed from that point. The overlapping penubras from opposing jaws result that the full width half maximum of the dose profile (FWHM) no longer matches the collimator setting. Thus, the conventional defintion of field size in terms of FWHM breaks down. The measurement of dosimetric paraments in such non-flat narrow fields becomes a challenge because most detectors are too large to resolve the non flat dose profile or that they perturb fluence in a
concept of lateral buildup ratio (LBR) as an avenue to evaluate electron later scatter equilibrium and compute dose per MU for those fields. Finally, it gives some common clinical examples where electron beam dosimetry are applied. This presentation will try to provide guidance to the audience for better understanding the methods and recommendations in TG-70. In addition, will describe how to link the absolute dose calibration recommendations of TG-51 to the relative dose measurements of TG-71. TOWARDS DAILY ADAPTED PROTON THERAPY Tony Lomax. Centre for Proton Therapy, Paul Scherrer Institute, Switzerland Proton therapy using Pencil Beam Scanning (PBS) is a highly conformal and flexible form of radiotherapy. However, anatomic changes of the patient during the course of therapy are a major challenge due to the potentially major changes in proton ranges that can result. The challenge is even greater given that such changes can occur on a daily basis and current software systems and workflows in radiotherapy are too slow to react to such changes. In order to fully exploit the highly conformal characteristics of PBS proton therapy therefore, methods for the daily adaption of proton therapy need to be developed, a concept we call ‘Daily Adaptive Proton Therapy’ (DAPT). The concept of DAPT is to work towards a flexible and fully automated workflow for PBS proton therapy, with the aim of imaging, planning and delivering a ‘plan-of-the-day’ for patients on a daily basis. In order to achieve this, the time between the imaging of the patient and delivery of the plan has to be reduced to a maximum of 1-2 minutes. With the in-room imaging capabilities of the PSI Gantry 2, and the inherent flexibility of PBS proton therapy, we believe we already have the ideal treatment machine for the implementation of DAPT. However, the challenges are more computational and workflow oriented than technological. In order to move towards a DAPT approach for instance, image registration, planning and optimisation procedures must be made computationally efficient and fully automated. In addition, efficient and informative tools need to be developed that will allow clinical staff to review these ‘plans-ofthe-day’, as well as to allow for fast, but nevertheless safe, quality assurance checks of the plans. For instance, with the introduction of DAPT type approaches, it will be impossible to perform patient or field specific dosimetric verifications, and other, automated methods for checking the fidelity of treatments and treatment control files will need to be developed. Thus, there are many challenges to be met before DAPT will become a reality. However, we firmly believe that moving in this direction is the next major advance in clinical proton therapy, and its introduction could have at least as large an impact on current clinical practice with protons as the introduction of Intensity Modulated Proton Therapy. Indeed, one could argue that PBS proton therapy, with its flexible and automated workflow, is pre-destined for the DAPT concept. FLUORESCENT NUCLEAR TRACK DETECTORS AS A TOOL FOR ION-BEAM THERAPY RESEARCH €kel a,b, c. aGerman Cancer Research Center (DKFZ), Division S. Greilich a, O. Ja of Medical Physics in Radiation Oncology, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany; bHeidelberg University Hospital, Department of Radiation Oncology, Im Neuenheimer Feld 400, 69120 Heidelberg, Germany; cHeidelberg Ion-Beam Therapy Center (HIT), Im Neuenheimer Feld 450, 69120 Heidelberg, Germany Originally designed for optical storage, fluorescent nuclear track detectors (FNTD) based on Al2O3:C,Mg single crystals contain aggregate F2+ 2 (2 Mg) color centers that show permanent radiochromic transformation when bombarded with ionizing radiation. Transformed centers produce high yield fluorescence at 750 nm when stimulated at 620 nm and a short (75±5 ns) lifetime. This enables non-destructive readout using confocal laserscanning microscopes (CLSMs, Akselrod and Sykora, 2011). Since the intensity signal depends on the local energy deposition, 3D particle trajectories through the crystal can be assessed. Together with the excellent sensitivity Al2O3:C,Mg this enables the derivation of information on track location, direction, energy loss, etc. over the entire particle and energy
e3
range found in ion beam therapy. Effects such as projectile fragmentation and secondary electron trajectories can be studied in detail with diffraction-limited resolution (Greilich et al., 2013). Due to their biocompatibility, autoclavability and since post-irradiation chemical processing is not needed, FNTDs can show significant superiority to existing technologies such as plastic nuclear track detectors (PNTDs, e.g. CR-39). Our group studies the FNTD technology for application on three main fields: Fundamental dosimetry quantities (w-value, I-value) in ion beams: FNTDs allow determining particle fluence and range with very high accuracy (Osinga et al., 2013, Klimpki et al., 2013). In-vivo track-based assessment of dose to organs at risk during therapy: FNTDs represent one of a few systems that enable biological dose estimation which is the essential predictor for clinical outcome in ion beam therapy. In addition, FNTD are small, resilient, wireless and biocompatible and can be therefore used within phantoms, animal models or even patients. Radiobiology: our group was the first to use FNTDs as substrate for cell (“Cell-Fit-HD”, Niklas et al., 2013). This enables to correlate microscopic physical parameters and subcellular/cell response both in fixed and living cell and study cellular processes fundamental to ion beam radiotherapy that are hitherto little understood. The talk will present the basic principle of FNTD technology, our group’s technical implementation as well as the latest methodological developments and application results. References 1. Akselrod MS, Sykora GJ: Fluorescent nuclear track detector technology e A new way to do passive solid state dosimetry. Radiat Meas 2011, 46:1671e1679. 2. Greilich S, Osinga J-M, Niklas M, Lauer FM, Klimpki G, Bestvater F, Bartz €kel O: Fluorescent Nuclear Track Detectors as a Tool for JA, Akselrod MS, Ja Ion-Beam Therapy Research. Radiat Meas 2013, 56:267e272. €kel O, Greilich S: Ion 3. Klimpki G, Osinga J-M, Herrmann R, Akselrod MS, Ja Range Measurements using Fluorescent Nuclear Track Detectors. Radiat Meas 2013, 56:342e346. 4. Niklas M, Abdollahi A, Akselrod MS, Debus J, J€ akel O, Greilich S: Subcellular spatial correlation of particle traversal and biological response in clinical ion beams. Int J Radiat Oncol 2013, 87:1141e1147. €kel O, Greilich S: Absorbed 5. Osinga J-M, Brons S, Bartz J a, Akselrod MS, Ja Dose in Ion Beams: Comparison of Ionisation- and Fluence-Based Measurements. Radiat Prot Dosimetry 2014. INCREASING PRECISION IN PARTICLE THERAPY: IN VIVO DOSIMETRY AND BEYOND C. Richter a, b, c, d, G. Pausch a, b, d, J. Seco e, T. Bortfeld e, W. Enghardt a, b, c, d. a OncoRay e National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital C.G. Carus, €t Dresden, Germany; b Department of Radiation Technische Universita Oncology, Faculty of Medicine and University Hospital C.G. Carus, €t Dresden, Germany; c German Cancer Consortium Technische Universita (DKTK), Dresden, & German Cancer Research Center (DKFZ), Heidelberg, d Helmholtz-Zentrum Dresden-Rossendorf, Germany; Germany; e Massachusetts General Hospital and Harvard Medical School, Department of Radiation Oncology, Boston, MA, USA The proton dose distribution including the steep dose gradient at the end of range not only allows a better sparing of normal tissue. It also enforces the need of a precise control of the dose deposition to ensure the correct position of the dose gradient to take full advantage of the superior capabilities of proton therapy. Otherwise, factors like tissue heterogeneities, patient positioning errors and intra-fractional motion can cause high uncertainties in proton distal range resulting in a failing tumor coverage or/ and an unnecessary high dose deposition in healthy tissue due to the use of extended margins. Therefore, an in vivo verification or any other control of proton range and delivered dose distribution is highly desirable. Several in vivo dosimetry approaches will be presented and compared. They rely on either nuclear interactions of the beam with the irradiated matter (In beam-PET and prompt g-ray imaging) or on the visualization of
e4
Abstracts / Physica Medica 30 (2014) e1ee15
biological processes induced by radiation, e.g. with MRI. The most experience exists for in beam-PET. In Dresden, the current research focuses on time-resolved acquisition (4D-PET) and on automated detection of range deviations. In contrast, prompt gamma ray imaging is a relatively new and dynamic field of research. Several prompt g-ray imaging detector systems are under development in various research centers around the world based on active- as well as passively collimated systems. A complementary approach, based on the time spectrum of the g-ray emission, is investigated in Dresden. First promising results will be presented in the talk. However, so far there is no clinical application of prompt g-ray based in vivo dosimetry. In contrast, radiation-induced biological changes have been used in clinical trials at the Massachusetts General Hospital in Boston (MGH) for range verification in both, spine and liver. A recent study, also carried out at MGH, aims at a better understanding of when those treatment related changes in the liver begin to appear. Instead of assuring a safe and precise treatment by measuring the in vivo dose deposition, another approach is to decrease dose deposition uncertainties before beam delivery. This can be done in several ways: One approach tries to increase the robustness of the treatment plan against different types of uncertainties. This can be realized by including the robustness in the optimization and penalizing treatment plans with a dose deposition very prone to expected deviations. A completely different method for increasing dose deposition precision is based on online imaging during treatment: If the exact patient geometry would be known for every time point, the delivered dose deposition could be calculated and even adapted online if necessary. Online imaging could be performed with MRI scanners integrated in the treatment room in analogy to the combined MRI-linac approaches. At the moment this is a field of intense research with quite impressing progress. At this point it is not clear which of the different methods to increase precision in particle therapy will find their way in routine clinical application. Nevertheless, the demand and the potential of these methods are unquestionable. MONTE CARLO MODELING AND IMAGE-GUIDANCE IN PARTICLE THERAPY G. Dedes, K. Parodi. Department of Medical Physics, Ludwig Maximilians University, Munich, Germany The use of protons and heavier ions in external beam therapy offers distinctive advantages with respect to conventional radiotherapy using electromagnetic radiation. The physical selectivity of ions with the characteristic Bragg curve can enable high tumor-dose conformity, resulting in lower irradiation of healthy tissues and critical organs in close vicinity to the target volume. Moreover, the higher relative-biological-effectiveness (RBE), especially in the case of heavier ions, can offer improved control probability for radioresistant tumors. In this context, Monte Carlo (MC) particle transport and interaction methods are increasingly employed in clinical and research institutions as vital tools to support several aspects of beam modeling, treatment planning and quality assurance of high precision ion beam therapy. This talk will review the role of MC methods in selected applications in particle therapy. Drawing on own experience at different European particle therapy facilities, the fine tuning of MC parameters for beam modeling will be presented. In addition, based on ongoing studies and collaborations, we will give an overview on the wide range of MC applications aiming at novel tools for image guidance and treatment planning. These include the support to the development of heavy ion and proton computed tomography, as well as the direct usage of MC-data in the inverse planning process, featuring calculations of both absorbed and biologically weighted dose. Development and validation of new solutions based on clinically established imaging modalities for adaptive strategies in particle therapy will be also addressed, together with research efforts to support unconventional imaging-based techniques detecting secondary radiation for in-vivo confirmation of the actual treatment delivery. Finally, the application of Monte Carlo tools in the emerging research area of laser driven ion acceleration for medical application will be briefly exposed. Parts of this work have been supported by the DFG Cluster of Excellence MAP (Munich-Centre for Advanced Photonics), the DFG Project on Ion
Radiography and Tomography, the FP7 Project ENVISION, and the BMBF Project SPARTA. IMAGE GUIDANCE FOR ADAPTIVE RADIOTHERAPY: IS THERE STILL A NEED FOR SURROGATE SYSTEMS? Torsten Moser. Im Neuenheimer Feld 280, 69120, Heidelberg, Germany In conformal radiation therapy, accurate and reproducible patient setup is required. In this regard, initial setup errors, as well as day-to-day setup variation, still poses a clinically relevant problem. The available anatomic („internal“) information of the patient, however, relies on the images of the planning CT, acquired up to weeks prior to treatment and does not reflect changes during the actual treatment. To correct in the actual situation, the most reliable information is obtained by 3D-imaging techniques like cone beam CT. Adaptive treatment techniques, moreover, adds a further component to the treatment chain, the feed-back. Again by daily image guidance, changes that occur during the treatment can be detected and handled. Meanwhile, most linear accelerators are able to acquire images (eg, kilovoltage/megavoltage setup images or cone beam computed tomography [CT] scans) that allow correlation of the actual patient position with that during treatment planning CT. By the use of such image guided radiation therapy techniques, the potential benefit for the patient has to be weighed against the additional risk associated with the imaging dose. For this reason, non-radiologic techniques to verify the setup position of the patient are of great interest. As such developments, there are various systems available that provide also information of motion and/or position. There are devices available where electromagnetic markers have to be implanted into the patient or technologies where other information’s are used to generate signals that can be used for position or motion correction. One of the latter are optical surface imaging systems. Optical surface imaging systems are able to reconstruct a 3-dimensional (3D) surface model relative to the isocenter position. A setup correction is calculated by registering actual images with reference images stored in the system beforehand. Although the technical accuracy of such systems has been shown to be quite high, their suitability for clinical application depends on additional aspects, in particular on a fixed spatial relation between the surface and target region. To analyze this, setup corrections from a surface imaging system were evaluated in 120 patients. As a measure of reliability, the corrections derived by the optical system were compared with those from 3D radiologic imaging, which is the current gold standard in image guided radiation therapy. We found a dependence on the target region and the used reference image modality. Therefore, additional radiologic imaging may still be necessary on a regular basis (e.g., weekly) or if the corrections of the optical system appear implausibly large. Nevertheless, such a combined application may help to reduce the imaging dose for the patient. SMALL PHOTON FIELD DOSIMETRY: PRESENT STATUS Maria M. Aspradakis. Cantonal Hospital of Lucerne, 6000 Lucerne 16, Switzerland Background: IPEM report 1031 summarised existing knowledge on the physics and challenges in the dosimetry of small MV photon fields, reviewed available detectors for dose measurement, gave recommendations based on existing knowledge and experience, explained the need of commissioning treatment planning systems for small field applications and pointed out directions for future work. This presentation reports on recent developments. Materials and Methods: A megavoltage (MV) photon field is defined as ‘small’ when either the field size is not large enough to provide lateral charged particle equilibrium at the point of dose measurement or the collimating device obstructs part of the focal spot as viewed from that point. The overlapping penubras from opposing jaws result that the full width half maximum of the dose profile (FWHM) no longer matches the collimator setting. Thus, the conventional defintion of field size in terms of FWHM breaks down. The measurement of dosimetric paraments in such non-flat narrow fields becomes a challenge because most detectors are too large to resolve the non flat dose profile or that they perturb fluence in a