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• W2041704071 abstract "Compared with conventional three-dimensional (3D) conformal radiation therapy and intensity-modulated radiation therapy treatments, quality assurance (QA) for motion-adaptive radiation therapy involves various challenges because of the added temporal dimension. Here we discuss those challenges for three specific techniques related to motion-adaptive therapy: namely respiratory gating, breath holding, and four-dimensional computed tomography. Similar to the introduction of any other new technologies in clinical practice, typical QA measures should be taken for these techniques also, including initial testing of equipment and clinical procedures, as well as frequent QA examinations during the early stage of implementation. Here, rather than covering every QA aspect in depth, we focus on some major QA challenges. The biggest QA challenge for gating and breath holding is how to ensure treatment accuracy when internal target position is predicted using external surrogates. Recommended QA measures for each component of treatment, including simulation, planning, patient positioning, and treatment delivery and verification, are discussed. For four-dimensional computed tomography, some major QA challenges have also been discussed. Compared with conventional three-dimensional (3D) conformal radiation therapy and intensity-modulated radiation therapy treatments, quality assurance (QA) for motion-adaptive radiation therapy involves various challenges because of the added temporal dimension. Here we discuss those challenges for three specific techniques related to motion-adaptive therapy: namely respiratory gating, breath holding, and four-dimensional computed tomography. Similar to the introduction of any other new technologies in clinical practice, typical QA measures should be taken for these techniques also, including initial testing of equipment and clinical procedures, as well as frequent QA examinations during the early stage of implementation. Here, rather than covering every QA aspect in depth, we focus on some major QA challenges. The biggest QA challenge for gating and breath holding is how to ensure treatment accuracy when internal target position is predicted using external surrogates. Recommended QA measures for each component of treatment, including simulation, planning, patient positioning, and treatment delivery and verification, are discussed. For four-dimensional computed tomography, some major QA challenges have also been discussed. IntroductionIntrafraction organ motion, mainly caused by patient breathing, can compromise the treatment outcome of radiation therapy for tumors in the thorax and abdomen, either by reducing the tumor control probability with insufficient safety margins or by increasing the normal tissue complication rate with excessively large margins. Various techniques, including breath holding, respiratory gating, and beam tracking, have been developed or are under development to address the organ motion issue during treatment delivery (1Jiang S.B. Radiotherapy of mobile tumors.Semin Radiat Oncol. 2006; 16: 239-248Abstract Full Text Full Text PDF PubMed Scopus (128) Google Scholar). For treatment simulation, four-dimensional computed tomography (4D CT) has been developed and implemented in many cancer centers, to acquire tumor and patient geometry at various breathing phases as well as organ motion information (2Keall P. 4-Dimensional computed tomography imaging and treatment planning.Semin Radiat Oncol. 2004; 14: 81-90Abstract Full Text Full Text PDF PubMed Scopus (402) Google Scholar).As always, when a new technology is being introduced into clinical practice, corresponding quality assurance (QA) measures should be taken. The introduced new hardware and software, along with the existing equipment with which the new device is interfaced, should be properly tested. At the early stage of the implementation, i.e., before the new system becomes a well-integrated part of routine clinical procedure, more frequent QA assessments should be performed, as determined by the physicist.In this article, we do not aim to cover every aspect of QA for motion-adaptive radiation therapy. Instead we will focus on some major QA challenges for respiratory gating, breath holding, and 4D CT.QA Challenges for Respiratory GatingRespiratory gating systems can be categorized, based on the surrogates used to generate gating signals, as internal gating and external gating (3Jiang S.B. Technical aspects of image-guided respiration-gated radiation therapy.Med Dosim. 2006; 31: 141-151Abstract Full Text Full Text PDF PubMed Scopus (113) Google Scholar). Internal gating uses internal tumor motion surrogates such as implanted fiducial markers, whereas external gating uses external respiratory surrogates such as markers placed on the surface of the patient's abdomen. Currently the only internal gating system used in clinical routine is the real-time tumor tracking (RTRT) system developed by Mitsubishi Electronics Co. (Tokyo, Japan) in collaboration with Hokkaido University (4Shirato H. Shimizu S. Shimizu T. et al.Real-time tumour-tracking radiotherapy.Lancet. 1999; 353: 1331-1332Abstract Full Text Full Text PDF PubMed Scopus (235) Google Scholar). Therefore, most of the gated therapy treatments are performed in the form of external gating.In external gating, the tumor position is derived using the external breathing signals. This is a major error source for this new technology, because the relationship between the tumor motion and the surrogate signal may change over time, both inter- and intrafractionally. In our opinion, therefore, maintaining clinically acceptable accuracy under such conditions is the biggest QA challenge for respiratory gating. Here, we use the real-time position management (RPM) respiratory gating system developed by Varian Medical Systems, Inc. (Palo Alto, CA) as an example to facilitate discussion of the QA challenges for gating (3Jiang S.B. Technical aspects of image-guided respiration-gated radiation therapy.Med Dosim. 2006; 31: 141-151Abstract Full Text Full Text PDF PubMed Scopus (113) Google Scholar, 5Mageras G.S. Yorke E. Rosenzweig K. et al.Fluoroscopic evaluation of diaphragmatic motion reduction with a respiratory gated radiotherapy system.J Appl Clin Med Phys. 2001; 2: 191-200Crossref PubMed Google Scholar). The surrogate signal of RPM is the abdominal surface motion.The external gating window corresponds to a segment of the external respiratory signal where we turn on the treatment beam. The tumor position corresponding to the central point of the gating window can be called the tumor home position. For treatment simulation, this position is called the reference home position. To ensure an accurate externally gated treatment, five QA steps should be taken:1.During treatment simulation, the reference home position should be accurately measured, using techniques such as 4D CT.2.During treatment planning, the patient and tumor geometry corresponding to the gating window should be used.3.During patient setup, the tumor home position at this fraction should be matched to the reference home position.4.During the treatment delivery, measures should be taken to maintain a constant tumor home position, i.e., the tumor should always be at the same position when the beam is turned on.5.During the treatment delivery, tumor positions corresponding to the gating window should be measured and compared with the reference tumor home position, either on- or offline.The first two steps are relatively straightforward. The third QA step is critical because the tumor home position, relative to patient skin tattoos or bony structures, can vary significantly from day to day. We suggest that image guidance techniques be applied to measure the tumor home position directly and to match it to the reference home position. This is basically to recalibrate the correlation between the external surrogate signal and the internal target position, to eliminate the inter-fraction variation of the correlation. The daily tumor home position can be measured using an on-board X-ray imaging system, an ultrasound imaging system, or implanted electromagnetic transponders. For patients with liver tumors, implanted fiducial markers can be used to indicate the tumor home position. For lung cancer patients, tumor mass, if visible in the projection X-ray images or the relevant anatomic features such as the diaphragm, can be used for matching (6Tang X. Sharp G. Jiang S. Patient setup based on lung tumor mass for gated radiotherapy.Med Phys. 2006; 33 ([Abstract]): 2244Crossref Scopus (5) Google Scholar). Because of this, the third QA step is much more difficult to implement for lung cancer, and more development work is still required.The fourth QA step is to try to ensure the tumor is always at or near the right position, i.e., the home position, when the beam is turned on. Patient breath coaching can be performed using the RPM system. One coaching technique developed at Massachusetts General Hospital (MGH) is to ensure a stable end-of-exhale (EOE) signal position (7Neicu T. Berbeco R. Wolfgang J. et al.Synchronized moving aperture radiation therapy (SMART): Improvement of breathing pattern reproducibility using respiratory coaching.Phys Med Biol. 2006; 51: 617-636Crossref PubMed Scopus (126) Google Scholar). Two straight lines that contain EOE positions are used to define the amplitude gating window. By looking at his or her own breathing waveform on a pair of video goggles, the patient is asked to put the EOE position in between two lines while breathing out. The procedure should be applied to every step of the treatment, including treatment simulation, patient setup, and treatment delivery, to ensure a stable EOE position.The fifth QA step is to verify the tumor position within the gating window. A technique has been developed at MGH for this purpose for gated three-dimensional conformal radiation therapy using an electronic portal imaging device (EPID) in cine mode (8Berbeco R.I. Neicu T. Rietzel E. et al.A technique for respiratory-gated radiotherapy treatment verification with an EPID in cine mode.Phys Med Biol. 2005; 50: 3669-3679Crossref PubMed Scopus (67) Google Scholar). However, because this technique uses the exit image of a treatment beam, it is difficult to apply to gated IMRT treatment and to large-size patients. Therefore on-board kV X-ray imaging systems are needed for treatment verification. An on-line treatment monitoring technique has been proposed and is under development. Within the external gating window, X-ray images will be taken. The marker or tumor position will be detected and displayed on a computer monitor, along with the reference position and tolerance zone. A warning signal will be given when the detected marker/tumor position is outside of the tolerance zone. When this happens, the therapist can interrupt the treatment and realign the patient.QA Challenges for Breath HoldingBreath-hold methods in different forms have evolved for radiation treatment of lung, liver, and breast cancers (9Wong J.W. Sharpe M.B. Jaffray D.A. et al.The use of active breathing control (ABC) to reduce margin for breathing motion.Int J Radiat Oncol Biol Phys. 1999; 44: 911-919Abstract Full Text Full Text PDF PubMed Scopus (775) Google Scholar, 10Hanley J. Debois M.M. Mah D. et al.Deep inspiration breath-hold technique for lung tumors: The potential value of target immobilization and reduced lung density in dose escalation.Int J Radiat Oncol Biol Phys. 1999; 45: 603-611Abstract Full Text Full Text PDF PubMed Scopus (506) Google Scholar, 11Rosenzweig K.E. Hanley J. Mah D. et al.The deep inspiration breath-hold technique in the treatment of inoperable non-small-cell lung cancer.Int J Radiat Oncol Biol Phys. 2000; 48: 81-87Abstract Full Text Full Text PDF PubMed Scopus (338) Google Scholar, 12Mah D. Hanley J. Rosenzweig K.E. et al.Technical aspects of the deep inspiration breath-hold technique in the treatment of thoracic cancer.Int J Radiat Oncol Biol Phys. 2000; 48 ([In process citation]): 1175-1185Abstract Full Text Full Text PDF PubMed Scopus (264) Google Scholar, 13Stromberg J.S. Sharpe M.B. Kim L.H. et al.Active breathing control (ABC) for Hodgkin's disease: Reduction in normal tissue irradiation with deep inspiration and implications for treatment.Int J Radiat Oncol Biol Phys. 2000; 48: 797-806Abstract Full Text Full Text PDF PubMed Scopus (85) Google Scholar, 14Barnes E.A. Murray B.R. Robinson D.M. et al.Dosimetric evaluation of lung tumor immobilization using breath hold at deep inspiration.Int J Radiat Oncol Biol Phys. 2001; 50: 1091-1098Abstract Full Text Full Text PDF PubMed Scopus (186) Google Scholar, 15Dawson L.A. Brock K.K. Kazanjian S. The reproducibility of organ position using active breathing control (ABC) during liver radiotherapy.Int J Radiat Oncol Biol Phys. 2001; 51: 1410-1421Abstract Full Text Full Text PDF PubMed Scopus (238) Google Scholar, 16Sixel K.E. Aznar M.C. Ung Y.C. Deep inspiration breath hold to reduce irradiated heart volume in breast cancer patients.Int J Radiat Oncol Biol Phys. 2001; 49: 199-204Abstract Full Text Full Text PDF PubMed Scopus (4) Google Scholar, 17Kim D.J. Murray B.R. Halperin R. et al.Held-breath self-gating technique for radiotherapy of non-small-cell lung cancer: A feasibility study.Int J Radiat Oncol Biol Phys. 2001; 49: 43-49Abstract Full Text Full Text PDF PubMed Scopus (99) Google Scholar, 18Remouchamps V.M. Letts N. Yan D. et al.Three-dimensional evaluation of intra- and interfraction immobilization of lung and chest wall using active breathing control: A reproducibility study with breast cancer patients.Int J Radiat Oncol Biol Phys. 2003; 57: 968-978Abstract Full Text Full Text PDF PubMed Scopus (83) Google Scholar, 19Berson A.M. Emery R. Rodriguez L. et al.Clinical experience using respiratory gated radiation therapy: Comparison of free-breathing and breath-hold techniques.Int J Radiat Oncol Biol Phys. 2004; 60: 419-426Abstract Full Text Full Text PDF PubMed Scopus (139) Google Scholar, 20Pedersen A.N. Korreman S. Nystrom H. et al.Breathing adapted radiotherapy of breast cancer: Reduction of cardiac and pulmonary doses using voluntary inspiration breath-hold.Radiother Oncol. 2004; 72: 53-60Abstract Full Text Full Text PDF PubMed Scopus (203) Google Scholar). A common goal of these methods is to exploit the anatomical immobilization to minimize the effects of breathing motion. A further benefit in lung and breast treatments is to move dose-limiting organs away from the target by using a deep or moderately deep breath hold.For radiation therapy, the aim is to achieve the same breath-hold position between fields during a single treatment fraction and between fractions. In practice, reproducibility of breath hold, as well as patient cooperation and comfort need to be considered, particularly for patients with compromised pulmonary status. Most, but not all, methods use some means of monitoring each breath hold. The most commonly used device is a spirometer to measure airflow. Depending on the method, the breath hold can be voluntary or can be assisted by means of an occlusion valve. Transducer-based spirometers are more suitable than classical spirometers for measuring low or null airflow rates during breath hold, and exhibit less signal drift. Another cause of signal drift is air leakage through the patient's mouth or nose. Some clinical applications have used the RPM system to monitor voluntary breath hold (19Berson A.M. Emery R. Rodriguez L. et al.Clinical experience using respiratory gated radiation therapy: Comparison of free-breathing and breath-hold techniques.Int J Radiat Oncol Biol Phys. 2004; 60: 419-426Abstract Full Text Full Text PDF PubMed Scopus (139) Google Scholar, 20Pedersen A.N. Korreman S. Nystrom H. et al.Breathing adapted radiotherapy of breast cancer: Reduction of cardiac and pulmonary doses using voluntary inspiration breath-hold.Radiother Oncol. 2004; 72: 53-60Abstract Full Text Full Text PDF PubMed Scopus (203) Google Scholar).All breath-hold methods involving a monitoring device rely on a physiologic respiratory state as a baseline, from which the inspiration level of the breath hold is determined and its repeatability verified. For most methods, the baseline is at end exhalation, which is usually established by monitoring the respiratory signal over several cycles with the patient breathing normally (9Wong J.W. Sharpe M.B. Jaffray D.A. et al.The use of active breathing control (ABC) to reduce margin for breathing motion.Int J Radiat Oncol Biol Phys. 1999; 44: 911-919Abstract Full Text Full Text PDF PubMed Scopus (775) Google Scholar, 15Dawson L.A. Brock K.K. Kazanjian S. The reproducibility of organ position using active breathing control (ABC) during liver radiotherapy.Int J Radiat Oncol Biol Phys. 2001; 51: 1410-1421Abstract Full Text Full Text PDF PubMed Scopus (238) Google Scholar, 18Remouchamps V.M. Letts N. Yan D. et al.Three-dimensional evaluation of intra- and interfraction immobilization of lung and chest wall using active breathing control: A reproducibility study with breast cancer patients.Int J Radiat Oncol Biol Phys. 2003; 57: 968-978Abstract Full Text Full Text PDF PubMed Scopus (83) Google Scholar, 21Koshani R. Balter J.M. Hayman J.A. et al.Short-term and long-term reproducibility of lung tumor position using active breathing control (ABC).Int J Radiat Oncol Biol Phys. 2006; 65: 1553-1559Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar). For spirometry systems, the respiratory signal is time-integrated air flow; thus, the breath hold is measured in terms of increased lung volume from the baseline position. The RPM system measures abdominal displacement relative to a baseline at end exhalation. One technique, referred to as deep inspiration breath hold (DIBH), uses a modified version of the slow vital capacity maneuver, consisting of a deep inspiration, deep expiration, second deep inspiration and breath hold; thus it uses deep expiration as a baseline (10Hanley J. Debois M.M. Mah D. et al.Deep inspiration breath-hold technique for lung tumors: The potential value of target immobilization and reduced lung density in dose escalation.Int J Radiat Oncol Biol Phys. 1999; 45: 603-611Abstract Full Text Full Text PDF PubMed Scopus (506) Google Scholar). In all of these methods, a reproducible baseline is an essential first step to achieving reproducible breath holds.Similar to respiratory gating, a second key issue is the accuracy of externally placed breath-hold monitors in predicting internal positions of the tumor and nearby organs. The external-to-internal correlation can change, not only by alterations in breathing pattern, but also by changes in the internal anatomy, such as abdominal contents, ascites, and tumor growth or shrinkage with treatment. Thus the external-to-internal constancy requires verification at simulation and throughout the treatment course.Patient training is an important component of a clinical QA program that uses breath hold for treatment (22Keall P.J. Mageras G.S. Balter J.M. et al.The management of respiratory motion in radiation oncology report of AAPM Task Group 76.Med Phys. 2006; 33: 3874-3900Crossref PubMed Scopus (1613) Google Scholar). It allows the patient to become familiar with the equipment and procedure, and provides an evaluation of the patient's ability to perform reproducible breath holds. The training session also establishes the patient's inspiration level for treatment and breath-hold duration. Patient training calls for special staff effort, as therapists must be trained to coach patients in a consistent manner. Some assisted breath hold, or active breathing control, systems use an additional monitor to provide visual feedback; this helps the patient to achieve a steady breathing pattern and to anticipate the onset of the assisted breath hold.The second component of a patient-related QA program is evaluating and monitoring external–internal correlation. Kilovoltage fluoroscopy is commonly used at simulation. More recent methods are fast cine CT and magnetic resonance imaging (23Shimizu S. Shirato H. Aoyama H. et al.High-speed magnetic resonance imaging for four-dimensional treatment planning of conformal radiotherapy of moving body tumors.Int J Radiat Oncol Biol Phys. 2000; 48: 471-474Abstract Full Text Full Text PDF PubMed Scopus (59) Google Scholar). One should verify that the tumor—or nearby surrogates such as diaphragm or chest wall, if the tumor is not visible—is immobilized within each breath hold and that its position is repeatable between breath holds. A program of frequent measurements throughout treatment of the tumor or surrogate organ position at breath hold is essential. Radiographs are the most common means of measurement. An anterior radiograph provides a confirmation that the lung inflation is constant, as measured from the dome of the diaphragm to a fixed anatomical feature. Implanted fiducials near the tumor, in-room CT, or cone-beam CT provide a more direct means of confirming tumor position. Daily verification is recommended for the first few treatments, followed by verification at least weekly thereafter.QA Challenges for 4D CTError in 4D CT can stem from a limited number of sources: (1) irregular patient respiration; (2) CT image reconstruction algorithm; and (3) re-sorting of reconstructed CT images with respiratory signal. Although current 4D CT implementations allow limited control of potential error source (1), measurement of the effectiveness of sources (2) and (3) may be accomplished through the use of a moving phantom capable of reproducing sinusoidal behavior (amplitude and period) similar to that of a typical human subject (2Keall P. 4-Dimensional computed tomography imaging and treatment planning.Semin Radiat Oncol. 2004; 14: 81-90Abstract Full Text Full Text PDF PubMed Scopus (402) Google Scholar, 24Chen G.T. Kung J.H. Beaudette K.P. Artifacts in computed tomography scanning of moving objects.Semin Radiat Oncol. 2004; 14: 19-26Abstract Full Text Full Text PDF PubMed Scopus (178) Google Scholar).The method used to reconstruct static images from the 4D scan occurs commercially in two distinct categories: (1) prospective fixed-interval reconstruction, and (2) respiratory signal—based reconstruction in sinogram space. Prospective reconstruction, such as found in the GE Advantage Workstation (GE Healthcare, Waukesha, WI), requires specification of a time interval for image reconstruction. Since the reconstruction interval is fixed and the patient respiration is highly variable, the amplitude-phase relationship of a given point may not reflect the optimal point for image reconstruction. Therefore it is recommended that the temporal sampling of the respiratory signal be maximized to the software limits of the CT acquisition software. By dense sampling of the respiratory signal, image artifacts from suboptimal temporal image reconstruction can be reduced. Sinogram image reconstruction typically relies on the phase of the respiratory signal for selection of the image reconstruction points. Images reconstructed in sinogram space are subject to suboptimal temporal selection; however, such points may be highly sensitive to amplitude variation of the patient's respiratory signal.Re-sorting of the many reconstructed 4D CT images into defined CT sets occurs by correlating the recorded respiration signal with the timestamps on the individual CT images. The criterion used to sort the CT data is usually by phase, amplitude, or a combination of the two. Phase-based re-sorting relies on an estimation of phase from the recorded respiratory signal. Images from different couch positions along the region of interest with the same respiratory phase value are combined to generate a static CT set reflecting the patient anatomy at a given point in the respiratory cycle. Because phase information is used as the only selection criterion to sort the CT images, there is no guarantee that the 4D CT phases will have correspond to identical values in amplitude space. Thus an inhale CT may consist of several images where the patient took a mixture of very deep and very shallow breaths, yielding poor amplitude control and resulting in a very incoherent 4D CT image.Amplitude sorting of 4D CT data, while preserving the amplitude correspondence between internal organ motion and the external respiration signal, ignores important phase information. In the presence of possible hysteresis, where the internal organ motion path during the inhale–exhale cycle is different from the exhale–inhale cycle, significantly misleading reconstruction error can occur.With respect to the conditions discussed above, care should be taken when examining a clinical implementation of a 4D CT acquisition system. Below are some guidelines for the construction and measurement of a suitable phantom for 4D CT analysis:1.Moving phantom: Measurements should be made using a phantom that can move sinusoidally in a plane perpendicular to the CT scan plane. The period and amplitude of motion should be adjustable parameters centering around normal patient respiration (4-s period, 1.5-cm peak-to-peak amplitude).2.Phantom registration: The phantom should include information that varies along the primary direction of motion. This information can be incorporated in the phantom as an observable change in radiopacity along the cranial–caudal axis or the presence of a long narrow object (cylinder) placed obliquely in the phantom body. Each slice of the object then represents a unique couch position within the phantom. Such information registers the axial slices of the phantom in the reconstructed CT images, allowing observation of sorting and reconstruction errors (discussed above).3.Phantom targets: The phantom should possess an assortment of spheres of varying diameter to allow measurement of the resolution limits of the 4D CT acquisition.4.Measurements: The phantom should be scanned for a range of amplitude and periods reflecting the clinical environment. Amplitude should vary from 0 (static) to 4 cm peak-to-peak motion, and period should vary from 0 (static) to 8 s in intervals of 1 s.5.Analysis: The resulting 4D CT data should be binned by phase into 10 intervals (inhale-inhale) and examined as a function of phase and amplitude for the following:a.Volume of phantom objectsb.Length of phantom objects along direction of phantom motionc.Registration coherence: inspection of 4D CT sets for improper (out-of-sequence) sorting of CT data.Although measurement of points (a) and (b) above may compare well to the static baseline image (0 period, 0 amplitude), it is entirely possible that because of failure of the re-sorting algorithm, CT slices may be out of sequence with one another—an artifact that can only be discovered with an indexed phantom as described above in point (2).ConclusionFor the widely used external gating systems, QA efforts should be focused on the achievement of sufficient tumor localization accuracy using external breathing surrogates. Five major QA steps for external gating should be taken. Breath-hold treatment techniques are beneficial when short-term tumor immobilization is desirable and, in some clinical applications, in moving dose-limiting organs away from the treatment volume. These techniques require the cooperation of patients and the training of both patients and staff for effective clinical application. A program of frequent imaging throughout treatment is important for monitoring of and, if necessary, correcting for interfractional variations. For 4D CT, the largest error source is irregular patient respiration, which causes artifacts in image reconstruction and re-sorting. Therefore QA efforts for 4D CT should be focused on how to maintain a regular and reproducible patient breathing pattern during the scanning process. IntroductionIntrafraction organ motion, mainly caused by patient breathing, can compromise the treatment outcome of radiation therapy for tumors in the thorax and abdomen, either by reducing the tumor control probability with insufficient safety margins or by increasing the normal tissue complication rate with excessively large margins. Various techniques, including breath holding, respiratory gating, and beam tracking, have been developed or are under development to address the organ motion issue during treatment delivery (1Jiang S.B. Radiotherapy of mobile tumors.Semin Radiat Oncol. 2006; 16: 239-248Abstract Full Text Full Text PDF PubMed Scopus (128) Google Scholar). For treatment simulation, four-dimensional computed tomography (4D CT) has been developed and implemented in many cancer centers, to acquire tumor and patient geometry at various breathing phases as well as organ motion information (2Keall P. 4-Dimensional computed tomography imaging and treatment planning.Semin Radiat Oncol. 2004; 14: 81-90Abstract Full Text Full Text PDF PubMed Scopus (402) Google Scholar).As always, when a new technology is being introduced into clinical practice, corresponding quality assurance (QA) measures should be taken. The introduced new hardware and software, along with the existing equipment with which the new device is interfaced, should be properly tested. At the early stage of the implementation, i.e., before the new system becomes a well-integrated part of routine clinical procedure, more frequent QA assessments should be performed, as determined by the physicist.In this article, we do not aim to cover every aspect of QA for motion-adaptive radiation therapy. Instead we will focus on some major QA challenges for respiratory gating, breath holding, and 4D CT." @default.
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• W2041704071 title "Quality Assurance Challenges for Motion-Adaptive Radiation Therapy: Gating, Breath Holding, and Four-Dimensional Computed Tomography" @default.
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