- Email: [email protected]
123 Invited Fiducial markers for MRI-based target volume definition and treatment verification
Symposia
produced, allowing crosses giving multiple specific genetic changes. Such mice can, for example, be used to dissect the genetics of treatment response. This has been done extensively to look at genes affecting chemotherapy response in lymphomas, but could equally well be used to look at the radiation response of solid tumor models. An example of such a study will be presented. Finally, such animal models are potentially amenable for studying factors affecting normal tissue damage after radiotherapy, although to date, little use has been made of such models for this purpose, 121 Invited L i m i t a t i o n s of a n i m a l m o d e l s A.J. van der Kogel
Abstract not received
PATIENT/ORGANM O T I O N 122
Invited
Correction s t r a t e g i e s : a c c u r a t e p o s i t i o n i n g
with minimal imaging workload J.C.J. de Boer, B.J.M. Heijmen Erasmus MC - Daniel den Hoed Cancer Center, Clinical Physics, Rotterdam, The Netherlands Introduction: Systematic set-up errors (occurring each treatment fraction) require substantially larger CTV to PTV margins than random (inter-or intrafraction) set-up variations. Systematic set-up errors can be substantially reduced with off-line correction protocols based on EPID images. We have developed the no-action-level (NAL) off-line protocol and predicted the same systematic error reduction as in the much applied shrinking action level (SAL) protocol, but at less than half of the number of measurements (i.e., fractions to be imaged and analysed). In NAL, a set-up correction is determined at the beginning of treatment from a fixed number of fractions in each patient, and applied in aI{ subsequent fractions. To measure the clinical efficacy of NAL, we have conducted a prospective study, Methods and Materials: In 30 prostate patients, the set-up was corrected using NAL. The correction was determined from 3 initial fractions and applied in following fractions by a treatment couch shift. Proper execution of the correction was verified by imaging the first fraction with correction and subjecting the residue set-up error to a dedicated protocol. For this study, as many fractions as possible were imaged and separately analysed. Concurrently, at the same treatment unit, 55 prostate patients were entered in our standard SAL protocol. The same technologists performed the image analysis and set-up corrections in both patient groups, Results: Before correction, the NAL and SAL groups showed similar standard deviations (SD) of systematic errors (1 SD typically 2 mm). The NAL protocol reduced the SD of systematic set-up errors to 1.1 mm in each direction. With NAL 4.0 measurements per patient were required (3 for the systematic error, one for verification). On average, 23 fractions per patient were imaged, enabling time trend analysis. We found that the effect of trends was minor. The SAL protocol required 9.6 measurements per patient and achieved systematic errors of 1 SD = 1.1 -1.3 mm, dependent on direcrich. Discussion: The NAL protocol yielded a distribution of systematic errors at least as good as SAL, but required only 4 instead of 9.6 measurements per patient. Hence, the threshold for routine application of set-up corrections has been lowered. We currently extend the use of NAL to lung and headand-neck cancer patients. Moreover, we investigate correction of systematic organ displacement with NAL, based on imaging prostate implanted markers, 123
invited
Fiducial markers for MRI-based target v o l u m e d e f i n i t i o n and treatment verification A.G. Visser 1, E.N.J.T. van Lin 1, A. Welmers2, J. Futterer2, J.O. Barentsz2, L.P. van der Vight 1, R.W.M. van derMaazen I 1University Medical Centre Nijmegen, Department of Radiation Oncology, Nijmegen, The Netherlands 2 Uni versity Medical Centre Nijmegen, Department of Radiology, Nijmegen, The Netherlands Introduction Developments in radiology, in particular dynamic contrast enhanced MRI and 1H MR spectroscopic imaging provide new tools for
Thursday, 19 September 2002 S4I
visualizing tumor masses in the prostate. We intend to use MR imaging to select parts of the prostate for dose escalation, given as an integrated boost simultaneous with the standard dose to the whole prostate The purpose of this study is to investigate the feasibility of implanted gold markers in the prostate both for image matching and for EPID-based position corrections. Methods In 25 patients a number of 4 fiducial gotd markers (1 mm diameter, 7 mm length) has been implanted in the prostate under ultrasound guidance. The markers are visible on all imaging modalities (MR, CT, portal imaging). MR-CT matching is done by segmenting the markers and applying translations and rotations. During radiotherapy, daily portal imaging is applied to monitor prostate motion. Initially, the standard off-line set-up corrections have been applied, aligning bony structure contours to the corresponding contours on the reference simulator image. After verifying that single marker displacements are neglegible, off-line corrections are applied not on the bony structures but on the markers. Results and discussion. Registration of MR-based target information (boost volume) to the treatment planning CT appears feasible using the implanted fiducial markers. Migration of individual implanted markers is negligible. Prostate motion is mostly in the ventro-dorsal and cranio-caudal directions. Systematic (0.6-2.4 ram) and random (0.9-1.7 mm) variations (1 SD) of prostate motion relative to bony structures are larger than the bony structure systematic set-up variations after (off-line) corrections (0.9-1.6 ram). So, corrections applied to the prostate position indicated by the markers make more sense than bony stucture set-up corrections. The results on prostate motion will be updated together with a discussion of possible correction strategies, the margins to be chosen and the feasibility of the intended integrated boost treatment. 124 Invited M e t h o d s to r e d u c e t h e e f f e c t s o f r e s p i r a t o r y m o t i o n in radia-
tion treatment J. Wonq William Beaumont Hospital, Royal Oak, Michigan, USA. Modern methods of radiation treatment, such as intensity modulated radiation therapy (tMRT), have greatly enhanced our ability to deliver very high doses that conform tightly to the target, but which also drop steeply to avoid inflicting serious injury to the surrounding critical structures. As expected, the sharp dose gradient invites the use of smaller margin in order to achieve higher dose escalation. To do so, greater attention needs to be focussed on the effect of setup error and organ motion during one (inter-) fraction, and between (intra-) fractions. For tumors in the head and neck, and the pelvic regions, margin reduction is possible with improved patient immobilization, and/or with the judicious use of repeat radiographic and tomographic imaging information. However, margin reduction remains challenging for treatment in the thoracic and upper abdominal regions. There, intra-fraction respiratory motion is significant. Near the diaphragm, it is not uncommon to observe respiration motion with an amplitude of 2 cm, roughly equivalent to a speed of 1 cm per sec. Margin reduction for respiratory motion needs to be minimized proactively. At present, two methods have been proposed by investigators in the cornmunity and are now available commercially. In respiratory gated radiation treatment (RGRT), the beam is only turned on when the medical acceleratot receives an external trigger indicating that the free-breathing patient is at a pre-determined segment of the breathing cycle. In the commercial systerns, the triggering signal is typically acquired using a combination of wallmounted infrared cameras and external reflectors placed on the patient. Typically, the relatively quiescent segment near end-exhalation is chosen to achieve a duty cycle of 25%. In the second active breathing control (ABC) approach, the patient is required to breathe through an ABC apparatus that measured airflow and lung volume. At a pre-determined lung volume, a computer-controlled valve is activated to facilitate breath-hold, thus temporarily immobilizing the patient's respiration motion. The duration of breath-hold is one that can be tolerated repeatedly by the patient and typically applied at moderately deep inspiration, about 75% of the vital capacity. There are pros and cons to both methods. In RGRT, the patient breathes freely thereby preserving comfort as in a normal treatment. On the other hand, the treatment margin must also account for residual respiratory motion during the gating segment. The margin increases with increasing duty cycle. Thus, RGRT is amenable for those patients who might have difficulty coping with lengthy breath-hold, at the expense of increased margin for breathing motion. In the ABC method, immobilization of respiratory motion should result in, theoretically, a smaller margin. In addition, the lung expansion reduces lung mass in the beam while pushes organs away from the beam. However, at present, the ABC is best applied for patients who can maintain their breath-hold comfortably for at least 10 sec. The fundamental question behind all methods to minimize the effects of respiratory motion is "how much margin reduction can be achieved?". Respi-
produced, allowing crosses giving multiple specific genetic changes. Such mice can, for example, be used to dissect the genetics of treatment response. This has been done extensively to look at genes affecting chemotherapy response in lymphomas, but could equally well be used to look at the radiation response of solid tumor models. An example of such a study will be presented. Finally, such animal models are potentially amenable for studying factors affecting normal tissue damage after radiotherapy, although to date, little use has been made of such models for this purpose, 121 Invited L i m i t a t i o n s of a n i m a l m o d e l s A.J. van der Kogel
Abstract not received
PATIENT/ORGANM O T I O N 122
Invited
Correction s t r a t e g i e s : a c c u r a t e p o s i t i o n i n g
with minimal imaging workload J.C.J. de Boer, B.J.M. Heijmen Erasmus MC - Daniel den Hoed Cancer Center, Clinical Physics, Rotterdam, The Netherlands Introduction: Systematic set-up errors (occurring each treatment fraction) require substantially larger CTV to PTV margins than random (inter-or intrafraction) set-up variations. Systematic set-up errors can be substantially reduced with off-line correction protocols based on EPID images. We have developed the no-action-level (NAL) off-line protocol and predicted the same systematic error reduction as in the much applied shrinking action level (SAL) protocol, but at less than half of the number of measurements (i.e., fractions to be imaged and analysed). In NAL, a set-up correction is determined at the beginning of treatment from a fixed number of fractions in each patient, and applied in aI{ subsequent fractions. To measure the clinical efficacy of NAL, we have conducted a prospective study, Methods and Materials: In 30 prostate patients, the set-up was corrected using NAL. The correction was determined from 3 initial fractions and applied in following fractions by a treatment couch shift. Proper execution of the correction was verified by imaging the first fraction with correction and subjecting the residue set-up error to a dedicated protocol. For this study, as many fractions as possible were imaged and separately analysed. Concurrently, at the same treatment unit, 55 prostate patients were entered in our standard SAL protocol. The same technologists performed the image analysis and set-up corrections in both patient groups, Results: Before correction, the NAL and SAL groups showed similar standard deviations (SD) of systematic errors (1 SD typically 2 mm). The NAL protocol reduced the SD of systematic set-up errors to 1.1 mm in each direction. With NAL 4.0 measurements per patient were required (3 for the systematic error, one for verification). On average, 23 fractions per patient were imaged, enabling time trend analysis. We found that the effect of trends was minor. The SAL protocol required 9.6 measurements per patient and achieved systematic errors of 1 SD = 1.1 -1.3 mm, dependent on direcrich. Discussion: The NAL protocol yielded a distribution of systematic errors at least as good as SAL, but required only 4 instead of 9.6 measurements per patient. Hence, the threshold for routine application of set-up corrections has been lowered. We currently extend the use of NAL to lung and headand-neck cancer patients. Moreover, we investigate correction of systematic organ displacement with NAL, based on imaging prostate implanted markers, 123
invited
Fiducial markers for MRI-based target v o l u m e d e f i n i t i o n and treatment verification A.G. Visser 1, E.N.J.T. van Lin 1, A. Welmers2, J. Futterer2, J.O. Barentsz2, L.P. van der Vight 1, R.W.M. van derMaazen I 1University Medical Centre Nijmegen, Department of Radiation Oncology, Nijmegen, The Netherlands 2 Uni versity Medical Centre Nijmegen, Department of Radiology, Nijmegen, The Netherlands Introduction Developments in radiology, in particular dynamic contrast enhanced MRI and 1H MR spectroscopic imaging provide new tools for
Thursday, 19 September 2002 S4I
visualizing tumor masses in the prostate. We intend to use MR imaging to select parts of the prostate for dose escalation, given as an integrated boost simultaneous with the standard dose to the whole prostate The purpose of this study is to investigate the feasibility of implanted gold markers in the prostate both for image matching and for EPID-based position corrections. Methods In 25 patients a number of 4 fiducial gotd markers (1 mm diameter, 7 mm length) has been implanted in the prostate under ultrasound guidance. The markers are visible on all imaging modalities (MR, CT, portal imaging). MR-CT matching is done by segmenting the markers and applying translations and rotations. During radiotherapy, daily portal imaging is applied to monitor prostate motion. Initially, the standard off-line set-up corrections have been applied, aligning bony structure contours to the corresponding contours on the reference simulator image. After verifying that single marker displacements are neglegible, off-line corrections are applied not on the bony structures but on the markers. Results and discussion. Registration of MR-based target information (boost volume) to the treatment planning CT appears feasible using the implanted fiducial markers. Migration of individual implanted markers is negligible. Prostate motion is mostly in the ventro-dorsal and cranio-caudal directions. Systematic (0.6-2.4 ram) and random (0.9-1.7 mm) variations (1 SD) of prostate motion relative to bony structures are larger than the bony structure systematic set-up variations after (off-line) corrections (0.9-1.6 ram). So, corrections applied to the prostate position indicated by the markers make more sense than bony stucture set-up corrections. The results on prostate motion will be updated together with a discussion of possible correction strategies, the margins to be chosen and the feasibility of the intended integrated boost treatment. 124 Invited M e t h o d s to r e d u c e t h e e f f e c t s o f r e s p i r a t o r y m o t i o n in radia-
tion treatment J. Wonq William Beaumont Hospital, Royal Oak, Michigan, USA. Modern methods of radiation treatment, such as intensity modulated radiation therapy (tMRT), have greatly enhanced our ability to deliver very high doses that conform tightly to the target, but which also drop steeply to avoid inflicting serious injury to the surrounding critical structures. As expected, the sharp dose gradient invites the use of smaller margin in order to achieve higher dose escalation. To do so, greater attention needs to be focussed on the effect of setup error and organ motion during one (inter-) fraction, and between (intra-) fractions. For tumors in the head and neck, and the pelvic regions, margin reduction is possible with improved patient immobilization, and/or with the judicious use of repeat radiographic and tomographic imaging information. However, margin reduction remains challenging for treatment in the thoracic and upper abdominal regions. There, intra-fraction respiratory motion is significant. Near the diaphragm, it is not uncommon to observe respiration motion with an amplitude of 2 cm, roughly equivalent to a speed of 1 cm per sec. Margin reduction for respiratory motion needs to be minimized proactively. At present, two methods have been proposed by investigators in the cornmunity and are now available commercially. In respiratory gated radiation treatment (RGRT), the beam is only turned on when the medical acceleratot receives an external trigger indicating that the free-breathing patient is at a pre-determined segment of the breathing cycle. In the commercial systerns, the triggering signal is typically acquired using a combination of wallmounted infrared cameras and external reflectors placed on the patient. Typically, the relatively quiescent segment near end-exhalation is chosen to achieve a duty cycle of 25%. In the second active breathing control (ABC) approach, the patient is required to breathe through an ABC apparatus that measured airflow and lung volume. At a pre-determined lung volume, a computer-controlled valve is activated to facilitate breath-hold, thus temporarily immobilizing the patient's respiration motion. The duration of breath-hold is one that can be tolerated repeatedly by the patient and typically applied at moderately deep inspiration, about 75% of the vital capacity. There are pros and cons to both methods. In RGRT, the patient breathes freely thereby preserving comfort as in a normal treatment. On the other hand, the treatment margin must also account for residual respiratory motion during the gating segment. The margin increases with increasing duty cycle. Thus, RGRT is amenable for those patients who might have difficulty coping with lengthy breath-hold, at the expense of increased margin for breathing motion. In the ABC method, immobilization of respiratory motion should result in, theoretically, a smaller margin. In addition, the lung expansion reduces lung mass in the beam while pushes organs away from the beam. However, at present, the ABC is best applied for patients who can maintain their breath-hold comfortably for at least 10 sec. The fundamental question behind all methods to minimize the effects of respiratory motion is "how much margin reduction can be achieved?". Respi-