- Email: [email protected]
45. Dosimetric comparison of four radiological techniques for percutaneous ablation of hepatic tumors
J.W.H. Wolthaus / Physica Medica 32 (2016) 341–366
Acknowledgement. The authors thank the Région Lorraine and FEDER for financial support. References [1] Langman et al, J Magn Reson Imaging, 2011 [2] Mattei et al, Magn Reson Med, 2015. [3] ASTM F2182-11a, www.astm.org. 2011. http://dx.doi.org/10.1016/j.ejmp.2016.11.096
45. Dosimetric comparison of four radiological techniques for percutaneous ablation of hepatic tumors L. Hadid a, B. Habib Geryes b, J. Le Roy c, C. Costes c, B. Guiu c, J.M. Correas b, O. Seror a a
Hôpital Jean Verdier, Hôpitaux Universitaires, Paris, France b Hôpital Universitaire Necker Enfants Malades, Paris, France c CHU de Montpellier, Montpellier, France Introduction. Radiological interventional procedures are increasingly used to treat tumors. It has already proven its efficiency for hepatic tumor ablation using percutaneous needles. Additionally to echography, useful for tumor tracking and needle guidance during the procedure, other X-ray imaging modalities can be used to control needle positioning according to adjacent critical structures. The aim of this study is to evaluate patient dose across three different university hospitals using four different imaging modalities: cone beam CT (CBCT), Computed tomography using helical mode (CT), Computed tomography using dedicated fluoroscopic mode (CT-fluoro) and finally a combination of CT-fluoro and C-arm (CTfluoro + C-arm). Methods. We included a total of one-hundred and forty-eight (148) procedures. Thirty-four patients were treated with an INNOVA-IGS540 (GEMS) system for CBCT group. One CBCT is performed at the beginning of the procedure to visualize tumors in three dimensions; while a second CBCT is made at the end of the intervention to check the ablation zone. During the procedure, virtual superposition of the target over fluoroscopic images allowed needle positioning. Thirty-four patients were treated with a DISCOVERY-750HD (GEMS) CT without dedicated fluoroscopic mode. Multiple helical acquisitions were made during the procedure: pre-operatively as workup and to locate the tumor; intraoperatively to control needle positioning; and post-operatively to check ablation zones. Forty-nine patients were treated with an optima 660 CT (GEMS) using Smartview fluoroscopic mode (CTfluoro) for intra-operative needle guidance and positioning. Finally, thirty-one patients were treated with the same optima 660 CT, in combination with an OEC 9900 Elite (GEMS) C-arm. This mobile surgical X-ray system was used for hepatic intra-arterial Lipiodol injection for non-visible tumors under echography or watersoluble contrast CT. Beside Lipiodol injection, intra-operative needle positioning was realized under CT-fluoroscopy guidance. Effective doses were estimated from DLP and DAP using conversion factors. Results. The average maximum diameter of treated tumors was 3.7, 2.7, 1.9 and 1.6 cm for CBCT, CT, CT-fluoro, and CT-fluoro + Carm, respectively. The median effective dose for pre-operative, intra-operative per needle, and post-operative phases was respectively estimated to 5, 1 and 6 mSv for CBCT; 3, 4 and 3 mSv for CT; 19, 1 and 12 mSv for CT-fluoro; and 32, 3 and 13 mSv for CTfluoro + C-arm. Conclusions. Compared to CT, CBCT technique delivers lower radiation doses during needle positioning. Regarding global patient
363
dose, CT is still valuable for procedures, especially for those requiring a small number of needles. However, the use of CT-fluoro mode can optimize doses during intra-operative phase. Finally, the use of CT combined with C-arms seems to be the most irradiating modality for patient, but with a possible improvement in tumor visualization. http://dx.doi.org/10.1016/j.ejmp.2016.11.097
Session 8 - MRI for radiotherapy 46. Real-time MR image guided radiotherapy: The time is near! J.W.H. Wolthaus University Medical Center Utrecht, Utrecht, The Netherlands Introduction. Despite the fact that several studies has shown that dose escalation improves treatment outcome, there are currently very limited clinical indications treated with high dose-high precision radiotherapy. Due to the inability to visualize tumor and critical organs sufficiently during delivery, a normal tissue margin around the tumor needs to be included in the target volume, which leads to toxicity and thereby limiting the maximum dose. If high quality (contrast) real-time MRI images of the tumor and surroundings are available during treatment, it is expected that smaller normal tissue margins are necessary (what you see is what you treat), and consequently increasing the possibility for dose escalation. Methods. MR guided radiotherapy is rapidly evolving from research feasibilities towards real clinical treatment machines. Cobalt systems are currently on the market and soon the first clinical MR-linac based on a 7 MV linear accelerator and a 1.5T MRI scanner will become operational. It is a misconception to consider the MR-guided radiotherapy systems as the next generation CBCT-linacs. The combination of a radiotherapy device with an MRI scanner enables high dose-high precision radiotherapy for many complex indications, bringing a new paradigm for radiotherapy. This enables new possibilities of on-line treatment plan adaptation, including gating and tumor tracking. However, the implications on reference dosimetry, machine QA and treatment planning due to the changed dose deposition by the magnetic field must be taken into account. This opens a whole new field of radiotherapy physics. In this talk the different MR radiotherapy solutions currently clinically available or under development will be discussed. Furthermore, a short description of the clinical MR guided workflow is given. The impact of the magnetic field on dose deposition is large due to the Lorentz force on the electrons released in matter. This results in skewed dose distributions and different build-up and exit doses compared to distributions in conventional radiotherapy. Since the trajectories of the electrons are now curved, readings in ionization chambers will also differ. My talk will address these effects on dose based on the Utrecht experience but these implications also apply to the other MR radiotherapy solutions. Conclusions. The use of MRI in radiotherapy is fast growing. To explore the patient benefits of MR guided radiotherapy almost all conventional aspects of current radiotherapy needs an overhaul, from the clinical workflow to dosimetry physics and machine QA. A short overview will be given. http://dx.doi.org/10.1016/j.ejmp.2016.11.098
Acknowledgement. The authors thank the Région Lorraine and FEDER for financial support. References [1] Langman et al, J Magn Reson Imaging, 2011 [2] Mattei et al, Magn Reson Med, 2015. [3] ASTM F2182-11a, www.astm.org. 2011. http://dx.doi.org/10.1016/j.ejmp.2016.11.096
45. Dosimetric comparison of four radiological techniques for percutaneous ablation of hepatic tumors L. Hadid a, B. Habib Geryes b, J. Le Roy c, C. Costes c, B. Guiu c, J.M. Correas b, O. Seror a a
Hôpital Jean Verdier, Hôpitaux Universitaires, Paris, France b Hôpital Universitaire Necker Enfants Malades, Paris, France c CHU de Montpellier, Montpellier, France Introduction. Radiological interventional procedures are increasingly used to treat tumors. It has already proven its efficiency for hepatic tumor ablation using percutaneous needles. Additionally to echography, useful for tumor tracking and needle guidance during the procedure, other X-ray imaging modalities can be used to control needle positioning according to adjacent critical structures. The aim of this study is to evaluate patient dose across three different university hospitals using four different imaging modalities: cone beam CT (CBCT), Computed tomography using helical mode (CT), Computed tomography using dedicated fluoroscopic mode (CT-fluoro) and finally a combination of CT-fluoro and C-arm (CTfluoro + C-arm). Methods. We included a total of one-hundred and forty-eight (148) procedures. Thirty-four patients were treated with an INNOVA-IGS540 (GEMS) system for CBCT group. One CBCT is performed at the beginning of the procedure to visualize tumors in three dimensions; while a second CBCT is made at the end of the intervention to check the ablation zone. During the procedure, virtual superposition of the target over fluoroscopic images allowed needle positioning. Thirty-four patients were treated with a DISCOVERY-750HD (GEMS) CT without dedicated fluoroscopic mode. Multiple helical acquisitions were made during the procedure: pre-operatively as workup and to locate the tumor; intraoperatively to control needle positioning; and post-operatively to check ablation zones. Forty-nine patients were treated with an optima 660 CT (GEMS) using Smartview fluoroscopic mode (CTfluoro) for intra-operative needle guidance and positioning. Finally, thirty-one patients were treated with the same optima 660 CT, in combination with an OEC 9900 Elite (GEMS) C-arm. This mobile surgical X-ray system was used for hepatic intra-arterial Lipiodol injection for non-visible tumors under echography or watersoluble contrast CT. Beside Lipiodol injection, intra-operative needle positioning was realized under CT-fluoroscopy guidance. Effective doses were estimated from DLP and DAP using conversion factors. Results. The average maximum diameter of treated tumors was 3.7, 2.7, 1.9 and 1.6 cm for CBCT, CT, CT-fluoro, and CT-fluoro + Carm, respectively. The median effective dose for pre-operative, intra-operative per needle, and post-operative phases was respectively estimated to 5, 1 and 6 mSv for CBCT; 3, 4 and 3 mSv for CT; 19, 1 and 12 mSv for CT-fluoro; and 32, 3 and 13 mSv for CTfluoro + C-arm. Conclusions. Compared to CT, CBCT technique delivers lower radiation doses during needle positioning. Regarding global patient
363
dose, CT is still valuable for procedures, especially for those requiring a small number of needles. However, the use of CT-fluoro mode can optimize doses during intra-operative phase. Finally, the use of CT combined with C-arms seems to be the most irradiating modality for patient, but with a possible improvement in tumor visualization. http://dx.doi.org/10.1016/j.ejmp.2016.11.097
Session 8 - MRI for radiotherapy 46. Real-time MR image guided radiotherapy: The time is near! J.W.H. Wolthaus University Medical Center Utrecht, Utrecht, The Netherlands Introduction. Despite the fact that several studies has shown that dose escalation improves treatment outcome, there are currently very limited clinical indications treated with high dose-high precision radiotherapy. Due to the inability to visualize tumor and critical organs sufficiently during delivery, a normal tissue margin around the tumor needs to be included in the target volume, which leads to toxicity and thereby limiting the maximum dose. If high quality (contrast) real-time MRI images of the tumor and surroundings are available during treatment, it is expected that smaller normal tissue margins are necessary (what you see is what you treat), and consequently increasing the possibility for dose escalation. Methods. MR guided radiotherapy is rapidly evolving from research feasibilities towards real clinical treatment machines. Cobalt systems are currently on the market and soon the first clinical MR-linac based on a 7 MV linear accelerator and a 1.5T MRI scanner will become operational. It is a misconception to consider the MR-guided radiotherapy systems as the next generation CBCT-linacs. The combination of a radiotherapy device with an MRI scanner enables high dose-high precision radiotherapy for many complex indications, bringing a new paradigm for radiotherapy. This enables new possibilities of on-line treatment plan adaptation, including gating and tumor tracking. However, the implications on reference dosimetry, machine QA and treatment planning due to the changed dose deposition by the magnetic field must be taken into account. This opens a whole new field of radiotherapy physics. In this talk the different MR radiotherapy solutions currently clinically available or under development will be discussed. Furthermore, a short description of the clinical MR guided workflow is given. The impact of the magnetic field on dose deposition is large due to the Lorentz force on the electrons released in matter. This results in skewed dose distributions and different build-up and exit doses compared to distributions in conventional radiotherapy. Since the trajectories of the electrons are now curved, readings in ionization chambers will also differ. My talk will address these effects on dose based on the Utrecht experience but these implications also apply to the other MR radiotherapy solutions. Conclusions. The use of MRI in radiotherapy is fast growing. To explore the patient benefits of MR guided radiotherapy almost all conventional aspects of current radiotherapy needs an overhaul, from the clinical workflow to dosimetry physics and machine QA. A short overview will be given. http://dx.doi.org/10.1016/j.ejmp.2016.11.098