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24 Real time tumour tracking radiation therapy
$8 Wednesday, 31 January 2001
Symposia
24
26
Real time tumour tracking radiation therapy H. Shirato 1, S. Shimizu 1, K. Kitamura 1, S. Ogura2, N. Kurauchi 3, N. Shinohara 4, S. Hashimoto 5 1Department of Radiology, 2Medicine, 3Surgery, 4Urology, Hokkaido University School of Medicine, Sapporo, Japan
Real-time verification and feedback for clinically deliverable IMRT plans T. Solbe~ 1, M. Leu2, P. Rosemark 2 N. Agazaryan 1, G. Hugo 1, J. Smathers 1 1UCLA School of Medicine, Radiation Oncology, Los Angeles, USA 2Cedars-Sinai Comprehensive Cancer Center, Radiation Oncology, Los Angeles, USA
oral
Purpose: to reduce set-up margin and internal margin in radiotherapy of lung and liver tumors by means of real-time tumor tracking and gating of a linear accelerator. Methods: the real-time tumor tracking system consists of four sets of diagnostic x-ray television systems (two of which offer an unobstructed view of the patient at any time), an image processor unit, a gating control unit, and an image display unit. The system recognizes the position of a 1.0-2.0 mm gold marker in the human body 30 times per second using two x-ray television systems. The marker is inserted in or near the tumor using imageguided implantation. The linear accelerator is gated to irradiate the tumor only when the marker is within a given tolerance from its planned coordinates relative to the isocenter. The accuracy of the system and the additional dose due to the diagnostic x-ray were examined in a phantom. The geometric performance of the system was evaluated in 4 patients. Results: the phantom experiment demonstrated that the geometric accuracy of the tumor tracking system is better than 1.5 mm for moving targets up to a speed of 40 mm/sec, The dose due to the diganostic x-ray monitoring ranged from 0.2% to 2% of the target dose for a 2.0-Gy irradiation of a chest phantom. In four patients with lung cancer, the range of the coordinates of the tumor marker during irradiation was 2.5 - 5.3 mm which would have been 9,6 - 38.4 mm without tracking. Conclusions: we successfully implemented and applied a tumor tracking and gating system. The system significantly improves the accuracy of irradiation of targets in motion at the expense of an acceptable amount of diagnostic x-ray exposure.
Our real-time verification method was developed and implemented to ensure that radiation is delivered as expected during the delivery of dynamically shaped IMRT. Dynamically shaped clinical IMRT treatments were planned using a pending commercial radiosurgery inverse treatment planning software. The treatments were delivered on a dedicated stereotactic radiotherapy accelerator fitted with a micro-multileaf collimator. The radiation beam was monitored with an pixel amorphous silicon detector array. Radiotherapy images were acquired every 50-80 milliseconds and analyzed while the treatment was delivered. Monitor chamber feedback was digitized and counted using a 16 bit counter; images were time stamped with the delivered cumulative monitor units. Leaf edge positions were found by application of an approximated 2-D Laplacian of gaussian operator and compared to those prescribed in the leaf sequence file. The integral intensity map was calculated based on the leaf sequence file and the LINAC source model. Acquired images were integrated and compared to the expected intensity maps. When treatment delivery errors exceed preset tolerances during the treatment, an interlock can be triggered allowing for further investigation. Results from the studies of the detector properties, dose map verification, leaf position verification and real-time feedback demonstrate that real-time verification is promising with this approach. Additionally, this approach has significant advantages over current methods, particularly in its ability to diagnose dynamic IMRT delivery errors and act upon them before the patient's treatment is completed.
25
27
Treatment verification and quality control for advanced radiation therapy A. Brahme Karolinska Hospital, Stockholm, Sweden Background. During the last 30 years radiation therapy has developed from classical rectangular beams via conformation therapy with largely uniform dose delivery but irregular field shapes to fully intensity-modulated dose delivery where the total dose distribution in the tumor can be fully controlled in three dimensions. This fast step has been developed during the last 15 - 20 years and has opened up the possibilities for truly optimized radiation therapy with multiple intensity-modulated radiation beams. Methods. In order to fully exploit the advantages of intensity-modulated radiation therapy, reliable dosimetdc-, geometric- and ultimately 3D dose delivery- verification methods are fundamental. Results. Radiation therapy is gradually becoming mere and more threedimensional in all its aspects from diagnostic imaging through treatment planning to dose delivery, it is important that also the traditional simulation and portal verification aspects keep up with this development. Equipment capable of this is: CT and MR units with software for generating simulation or portal images, simulators with CT possibilities, treatment units with RCT capabilities and to some extent also treatment units with real time portal verification systems and offset diagnostic X-ray systems for portal verification. The last two groups of equipment are particularly important with the increased flexibility in beam shaping with modern multileaf collimators. For ion therapy with Boron, Carbon, Nitrogen or Oxygen beams the ultimate solution is to use 3D PET imaging of the delivered dose distribution to the patient to verify that the dose really reached the target volumes first delineated by the same PET system. Conclusions. Once accurate genetically and/or cell survival based predictive assays become available, radiation therapy will become an exact science allowing truly individual optimization considering also the panorama of side-effects that the patient is willing to accept. 3D dose delivery verification wilt then be a key to the quality assurance of the whole therapy process.
oral
Some Remarks on IMRT: static vs. dynymie vs. step & shoot.
Where is the realistic f u t u r e in practice? J.M. Jensen, D. Hebbinghaus University of Kiel Medical School, Dept. of Radiooncology, Kiel, Germany In the moment the most individual and advanced application of dose in radiotherapy seems to be the highly sophisticated technique of IMRT. Depending on inverse dose planning the dose distribution within a single treatment field ls modulated by use of a MLC. This technique allows to divide the conventional fields into subsegments of about 1 cm x 1 cm, either moving in discrete steps (step & shoot) or dynamically. Hereby the opportunity is opened to deliver a variable dose to each segment. In total a modulation of dose is the result, according to the individual treatment volume. For example a 10 cm x 10 cm field is equivalent to a number of 100 subsegments of 1 cm x 1 cm and means an increase of beam on time by a factor of 50, taking into consideration a doubling of the dose rate. A slightly time reduction is achieved by classification of the dose segments, by predelivering a basic homogeneous dose, by increasing the beam pixel size (subsegments) or by dynamic moving strip technique. TO reduce the treatment time down to conventional values (5 fields, non-automatic-setup, coplanar, manual discrete wedges, 2 Gy/fraction: ca. 7 rain ) a combination of MLC, compensator and high dose rate is proposed. Compared to automatically delivered step & shoot-IMRT for a reference plan (5-fieldtechnique), a maximum time reduction factor of about 5 can be achieved. The time for preparation of an IMRT session will increase, but there is no treatment unit [cad interference. This clear advantage might be a reason for establishing IMRT in a larger number of radiotherapy centers, and not only in a few single research centers.
Symposia
24
26
Real time tumour tracking radiation therapy H. Shirato 1, S. Shimizu 1, K. Kitamura 1, S. Ogura2, N. Kurauchi 3, N. Shinohara 4, S. Hashimoto 5 1Department of Radiology, 2Medicine, 3Surgery, 4Urology, Hokkaido University School of Medicine, Sapporo, Japan
Real-time verification and feedback for clinically deliverable IMRT plans T. Solbe~ 1, M. Leu2, P. Rosemark 2 N. Agazaryan 1, G. Hugo 1, J. Smathers 1 1UCLA School of Medicine, Radiation Oncology, Los Angeles, USA 2Cedars-Sinai Comprehensive Cancer Center, Radiation Oncology, Los Angeles, USA
oral
Purpose: to reduce set-up margin and internal margin in radiotherapy of lung and liver tumors by means of real-time tumor tracking and gating of a linear accelerator. Methods: the real-time tumor tracking system consists of four sets of diagnostic x-ray television systems (two of which offer an unobstructed view of the patient at any time), an image processor unit, a gating control unit, and an image display unit. The system recognizes the position of a 1.0-2.0 mm gold marker in the human body 30 times per second using two x-ray television systems. The marker is inserted in or near the tumor using imageguided implantation. The linear accelerator is gated to irradiate the tumor only when the marker is within a given tolerance from its planned coordinates relative to the isocenter. The accuracy of the system and the additional dose due to the diagnostic x-ray were examined in a phantom. The geometric performance of the system was evaluated in 4 patients. Results: the phantom experiment demonstrated that the geometric accuracy of the tumor tracking system is better than 1.5 mm for moving targets up to a speed of 40 mm/sec, The dose due to the diganostic x-ray monitoring ranged from 0.2% to 2% of the target dose for a 2.0-Gy irradiation of a chest phantom. In four patients with lung cancer, the range of the coordinates of the tumor marker during irradiation was 2.5 - 5.3 mm which would have been 9,6 - 38.4 mm without tracking. Conclusions: we successfully implemented and applied a tumor tracking and gating system. The system significantly improves the accuracy of irradiation of targets in motion at the expense of an acceptable amount of diagnostic x-ray exposure.
Our real-time verification method was developed and implemented to ensure that radiation is delivered as expected during the delivery of dynamically shaped IMRT. Dynamically shaped clinical IMRT treatments were planned using a pending commercial radiosurgery inverse treatment planning software. The treatments were delivered on a dedicated stereotactic radiotherapy accelerator fitted with a micro-multileaf collimator. The radiation beam was monitored with an pixel amorphous silicon detector array. Radiotherapy images were acquired every 50-80 milliseconds and analyzed while the treatment was delivered. Monitor chamber feedback was digitized and counted using a 16 bit counter; images were time stamped with the delivered cumulative monitor units. Leaf edge positions were found by application of an approximated 2-D Laplacian of gaussian operator and compared to those prescribed in the leaf sequence file. The integral intensity map was calculated based on the leaf sequence file and the LINAC source model. Acquired images were integrated and compared to the expected intensity maps. When treatment delivery errors exceed preset tolerances during the treatment, an interlock can be triggered allowing for further investigation. Results from the studies of the detector properties, dose map verification, leaf position verification and real-time feedback demonstrate that real-time verification is promising with this approach. Additionally, this approach has significant advantages over current methods, particularly in its ability to diagnose dynamic IMRT delivery errors and act upon them before the patient's treatment is completed.
25
27
Treatment verification and quality control for advanced radiation therapy A. Brahme Karolinska Hospital, Stockholm, Sweden Background. During the last 30 years radiation therapy has developed from classical rectangular beams via conformation therapy with largely uniform dose delivery but irregular field shapes to fully intensity-modulated dose delivery where the total dose distribution in the tumor can be fully controlled in three dimensions. This fast step has been developed during the last 15 - 20 years and has opened up the possibilities for truly optimized radiation therapy with multiple intensity-modulated radiation beams. Methods. In order to fully exploit the advantages of intensity-modulated radiation therapy, reliable dosimetdc-, geometric- and ultimately 3D dose delivery- verification methods are fundamental. Results. Radiation therapy is gradually becoming mere and more threedimensional in all its aspects from diagnostic imaging through treatment planning to dose delivery, it is important that also the traditional simulation and portal verification aspects keep up with this development. Equipment capable of this is: CT and MR units with software for generating simulation or portal images, simulators with CT possibilities, treatment units with RCT capabilities and to some extent also treatment units with real time portal verification systems and offset diagnostic X-ray systems for portal verification. The last two groups of equipment are particularly important with the increased flexibility in beam shaping with modern multileaf collimators. For ion therapy with Boron, Carbon, Nitrogen or Oxygen beams the ultimate solution is to use 3D PET imaging of the delivered dose distribution to the patient to verify that the dose really reached the target volumes first delineated by the same PET system. Conclusions. Once accurate genetically and/or cell survival based predictive assays become available, radiation therapy will become an exact science allowing truly individual optimization considering also the panorama of side-effects that the patient is willing to accept. 3D dose delivery verification wilt then be a key to the quality assurance of the whole therapy process.
oral
Some Remarks on IMRT: static vs. dynymie vs. step & shoot.
Where is the realistic f u t u r e in practice? J.M. Jensen, D. Hebbinghaus University of Kiel Medical School, Dept. of Radiooncology, Kiel, Germany In the moment the most individual and advanced application of dose in radiotherapy seems to be the highly sophisticated technique of IMRT. Depending on inverse dose planning the dose distribution within a single treatment field ls modulated by use of a MLC. This technique allows to divide the conventional fields into subsegments of about 1 cm x 1 cm, either moving in discrete steps (step & shoot) or dynamically. Hereby the opportunity is opened to deliver a variable dose to each segment. In total a modulation of dose is the result, according to the individual treatment volume. For example a 10 cm x 10 cm field is equivalent to a number of 100 subsegments of 1 cm x 1 cm and means an increase of beam on time by a factor of 50, taking into consideration a doubling of the dose rate. A slightly time reduction is achieved by classification of the dose segments, by predelivering a basic homogeneous dose, by increasing the beam pixel size (subsegments) or by dynamic moving strip technique. TO reduce the treatment time down to conventional values (5 fields, non-automatic-setup, coplanar, manual discrete wedges, 2 Gy/fraction: ca. 7 rain ) a combination of MLC, compensator and high dose rate is proposed. Compared to automatically delivered step & shoot-IMRT for a reference plan (5-fieldtechnique), a maximum time reduction factor of about 5 can be achieved. The time for preparation of an IMRT session will increase, but there is no treatment unit [cad interference. This clear advantage might be a reason for establishing IMRT in a larger number of radiotherapy centers, and not only in a few single research centers.