- Dose calculations for external photon beams in radiotherapy
- Browse by Communities & Collections
- Recommended for you
- Multidisciplinary Management of Brain Metastases
- About this product
By design, the system possesses a single isocenter in space that is defined as the interception point of I the C-arm gantry rotational axis; II collimator rotation axis and III the couch rotation axis. With the addition of kV OBI systems to the C-arm gantry, volumetric CBCT can be acquired in addition to the 2D kV planar imaging, both of which possess significantly higher contrast and resolution compared to the conventional MV portal imaging quality. Consequently, the isocenter of beam delivery system must coincide with the isocenter defined from the OBI system Figure 1.
In the context of SBRT implementation, one of the major concerns has always been the integrity of the OBI spatial accuracy and imaging quality in relationship to the radiation beam isocenter. Strict quality assurance checks must therefore be implemented to ensure the isocenter of the imaging system coincide with that of the beam delivery system. Any distortion from one system to another due to mechanical factors such as irregular gantry rotations and hardware sagging etc.
With the introduction and developments of digitally controlled linear accelerator DC-linac such as that implemented in the latest Varian TrueBeam system, concerns on hardware misalignment and miscalibrations are by and large eliminated. New generation of DC-linac systems possess a multi-level feedback and sensor system that allows high definition control of the gantry speed, collimator angles, pulse rate and beam energy switches on the level of every few milliseconds.
With such a level of hardware control, volumetric modulated arc therapy VMAT with a limited number of arcs has become an essential mode for SBRT treatments 25 - For the VMAT mode of delivery, the gantry rotates around the patient in an arc beam with the MLC modulating the field shapes at the same time. In addition, digitally controlled beam pulse rates also vary continuously to deliver different beam outputs at each gantry angle per each MLC-defined segment.
One of the key developments of DC-linacs was the accurate steering of the beam in the so-called flattening-filter-free FFF mode. When operating in the FFF mode, the conventional flattening filter is shifted away on the target carousal leading to multiple folds increase in beam output over that of flattening-filter-attenuated beams. This has significantly shortened the total beam-on time required to deliver a dose of 5 to 20 Gy per fraction as required of SBRT for either single-fractionated or hypofractionated treatments.
For complex cases such as the spine SBRT treatments of 18 to 24 Gy per fraction, rapid beam-delivery not only shortens the treatment time, but also is essential in minimizing the potential for patient shifts during the treatment delivery. Stringent clinical constraints such as 1 degree rotation or 1 mm shift is usually required in order to prevent a high dose from accidentally placed onto the spinal cord leading to disastrous treatment complications 30 , It is in fact not generally feasible for a C-arm S-band linear accelerator to access all the beam angles surrounding a patient, for example, delivering a coronal arc for a supine patient setup etc.
Due to higher X-band microwave power able to accelerate bunched electrons, the X-ray beam generation and transport system was constructed in a significantly more compact size as compare to the conventional S-band linear accelerator. As a result, the entire X-ray generation system Figure 3 can be mounted onto a commercial-grade robotic manipulator that moves like an arm, with full 6 degree-of-freedom similar to the robotic arm adopted for assembling cars and heavy equipment 36 - The X-ray tubes are mounted on the ceiling of the treatment room with two flat panel detectors under the floor Figure 3.
The X-ray tubes are usually synchronized to fire simultaneously to create a pair of near-real time X-ray images that are directly referenced to a library of digitally reconstructed radiographs DDRs that are created from the reference planning CT of the patient.
Dose calculations for external photon beams in radiotherapy
Automatic imaging registration algorithms are implemented for instantaneous target detection for different disease sites. For treatment of bony targets such as spine or pelvis, distinctive landmark features are commonly used for detecting patient movements or setup shifts based on the stereoscopic X-ray imaging.
For soft tissue targets such as the lung or the liver tumors, the system typically relies on metal fiducial markers implanted inside or near the target for online tracking to guide beam deliveries 37 , The kV X-rays frequently fire to track the patient motion and detect the target position, and the detected shifts are used to adjust robotic arm accordingly in near real time Smart determinations of when or how frequently to fire stereoscopic X-rays are primarily influenced by the disease sites as well as patient-specific factors.
For lung SBRT treatments, the real time tracking is achieved through a model based tracking mode called Synchrony TM , where a breathing model is developed before the delivery by correlating the position of the optical markers light-emitting-diodes or LEDs placed on the patient chest to the target position detected by the kV X-ray imaging.
The delivery space is composed of a group of discrete predefined delivery positions nodes, normally — nodes depend on treatment site spherically distributed around the patient. Direct posterior beams are not allowed due to collision to the ground. The dose delivery follows step and shoot fashion. At each node, the planning system typically allows the robotic arm to randomly pick several up to 12 beams beam directions for optimizations.
Browse by Communities & Collections
Given the fix mounting of the in-room kV imaging detector panels, all the treatments rely on a pair of orthogonal images. Compared to the 3D CBCT system of the conventional S-band linear accelerator, the drawback of 2D planar imaging is its lack of volumetric information and soft-tissue contrast information. However, 2D planar imaging has a distinct advantage in its high-speed detection, processing and commanding of the robotic manipulator to move rapidly according to the detected target movements or any other required corrections.
The maximum size for the circular field has been 6. While complicated dosimetric shape can be achieved with fixed or IRIS TM cones, delivery efficiency is not optimal especially for irregular and larger tumors. In addition to treatment time reduction, the initial studies have shown that the MLC enhanced system significantly reduced the total MU required to achieve the same planning quality with cone or IRIS TM -based collimators 42 , Such a result may likely help to reduce distal peripheral dose and alleviate the concern regarding secondary malignancies associated with high-dose SBRT treatments.
Technical and clinical data with this new system have been rapidly accruing since its initial approval by the FDA for the US market in A major innovation of the GKI system is its compact integrated 3D CBCT system mounted on the current GK Perfexion unit, such that any voxel on the acquired scans for the online imaging studies are directly correlated with the stereotactic coordinates of the radiation unit. Due to the functionality of a translation-only couch, any detected rotational shifts via the 3D CBCT are corrected online by computing the resulting dose distributions rather than repositioning the patient.
This is called on-line dose adaption and unique to the GKI-based treatments. As a result, on-line dose adaption or any adjustments via even manual replanning, is an easy and efficient process. Evidently, the new GKI system has successfully taken advantage of simultaneous beam irradiation from wide solid angles to make a hypofractionated delivery more robust against rotational shifts. Such a feature has inherently rendered on-line dose adaption a viable approach for multiple isocentric cross-firing GKI dose distributions.
Recommended for you
The same sequence variant on 9p21 associates with myocardial infarction, abdominal aortic aneurysm and intracranial aneurysm. Bendjilali, N. Genetic variants on 9p Stroke 44 , abstr. TMP30 Emond, M. Exome sequencing of extreme phenotypes identifies DCTN4 as a modifier of chronic Pseudomonas aeruginosa infection in cystic fibrosis. Wright, F. Genome-wide association and linkage identify modifier loci of lung disease severity in cystic fibrosis at 11p13 and 20q Drumm, M.
Genetic modifiers of lung disease in cystic fibrosis. Polymorphisms in genes involved in inflammatory and angiogenic pathways and the risk of hemorrhagic presentation of brain arteriovenous malformations. EPHB4 gene polymorphisms and risk of intracranial hemorrhage in patients with brain arteriovenous malformations. Apoliprotein E epsilon2 is associated with new hemorrhage risk in brain arteriovenous malformation.wellwoomoguwan.tk
Multidisciplinary Management of Brain Metastases
Neurosurgery 58 , —; discussion — Achrol, A. Single nucleotide polymorphisms associated with sporadic brain arteriovenous malformations: where do we stand? Neurosurgery 61 , —; discussion McAllister, T.
Polymorphisms in the brain derived neurotrophic factor BDNF gene influence memory and processing speed one month after brain injury. Neurotrauma 29 , — Qin, L. Siironen, J.
About this product
Westbroek, E. Brain-derived neurotrophic factor Val66Met polymorphism predicts worse functional outcome after surgery patients with unruptured brain arteriovenous malformation. Sato, S. Perinidal dilated capillary networks in cerebral arteriovenous malformations. Neurosurgery 54 , —; discussion — Shankar, J.
- Ethics in Light Of Childhood;
- Leadership for Person-Centered Dementia Care.
- Brain arteriovenous malformations.
Angioarchitecture of brain AVM determines the presentation with seizures: proposed scoring system. AJNR Am. Geibprasert, S. Hydrocephalus in unruptured brain arteriovenous malformations: pathomechanical considerations, therapeutic implications, and clinical course. Lasjaunias, P. Cerebral proliferative angiopathy: clinical and angiographic description of an entity different from cerebral AVMs.
Stroke 39 , — Krings, T. Classification and endovascular management of pediatric cerebral vascular malformations. Bharatha, A. Brain arteriovenous malformation multiplicity predicts the diagnosis of hereditary hemorrhagic telangiectasia: quantitative assessment. Stroke 43 , 72—78 Radiologic assessment of brain arteriovenous malformations: what clinicians need to know. Radiographics 30 , — This article summarizes the imaging features of brain arteriovenous malformations.
Kim, D. Whole-brain perfusion CT patterns of brain arteriovenous malformations: a pilot study in 18 patients. Redekop, G. Arterial aneurysms associated with cerebral arteriovenous malformations: classification, incidence, and risk of hemorrhage.