Diffeent types of radiotherapy

[Terry]

I can't remember who was asking about the difference in radiation therapies. I gave a brief definition in my words but googled some of them and hope this helps. I think from what I understand the biggest difference is what kind of tumor they're dealing with, and how much damage a type does to healthy tissue.

Proton therapy and X-ray therapy both kill cancer cells by preventing them from dividing and growing. The difference between these therapies is that protons can be controlled, depositing the greatest amount of radiation right into the tumor and then stopping, allowing patients to receive higher doses with less damage to nearby healthy tissue.1,2 In contrast, X-ray radiation releases substantial doses of energy quickly after penetrating the skin, damaging healthy tissue and organs on the way to the tumor and continuing to deliver radiation as it leaves the body.

MRT is short for Intensity Modulated Radiation Therapy. The intensity of the radiation in IMRT can be changed during treatment to spare more adjoining normal tissue than is spared during conventional radiation therapy. Because of this an increased dose of radiation can be delivered to the tumor using IMRT. Intensity modulated radiation therapy is a type of conformal radiation, which shapes radiation beams to closely approximate the shape of the tumor.

Local or regional control of a tumor is the ultimate goal of an overall treatment strategy, especially for a patient with cancer. Failure to achieve tumor control can result in a greater likelihood of developing distant metastases, continued tumor growth, severe debilitation or even death of the patient.

Historically, the maximum radiation dose that could be given to a tumor site has been restricted by the tolerance and sensitivity of the surrounding nearby healthy tissues. When a tumor or condition is not eligible for treatment with normal stereotactic radiosurgery, conformal radiation may be used in one or more sessions. Three-dimensional conformal radiation therapy is less than ten years old. It is only available with linear accelerator-based technology. In 2006, there are finally enough linac centers offering image-guided three-dimensional conformal radiation therapy that we soon expect to see more research articles with relevant 5-year followups, upon which patients can rely.


Encyclopedia The CyberKnife is a frameless robotic radiosurgery system used for treating benign tumors, malignant tumors and other medical conditions. The system was invented by John R. Adler, a Stanford University Professor of Neurosurgery and Radiation Oncology, and Peter and Russell Schonberg of Schonberg Research Corporation. The two main elements of the CyberKnife are (1) the radiation produced from a small linear particle accelerator and (2) a robotic arm which allows the energy to be directed at any part of the body from any direction.

The CyberKnife system is a method of delivering radiotherapy, with the intention of targeting treatment more accurately than standard radiotherapy. Over 150 centres, featuring several generations of equipment, offer treatment around the world, particularly centered in North America, East Asia and Europe.

Main features

Several generations of the CyberKnife system have been developed since its initial inception in 1990. There are two essential features of the CyberKnife system that set it apart from other stereotactic therapy methods.
Robotic mounting

The first is that the radiation source is mounted on a general purpose industrial robot. The original CyberKnife used a Japanese Fanuc robot, however the more modern systems use a German KUKA KR 240. Mounted on the Robot is a compact X-band linac that produces 6MV X-ray radiation. The linac is capable of delivering approximately 600 cGy of radiation each minute - a new 800 cGy / minute model was announced at ASTRO 2007. The radiation is collimated using fixed tungsten collimators (also referred to as “cones”) which produce circular radiation fields. At present the radiation field sizes are: 5, 7.5, 10, 12.5, 15, 20, 25, 30, 35, 40, 50 and 60 mm. ASTRO 2007 also saw the launch of the IRIS variable-aperture collimator which uses two offset banks of six prismatic tungsten segments to form a blurred regular dodecagon field of variable size which eliminates the need for changing the fixed collimators. Mounting the radiation source on the robot allows near-complete freedom to position the source within a space about the patient. The robotic mounting allows very fast repositioning of the source, which enables the system to deliver radiation from many different directions without the need to move both the patient and source as required by current gantry configurations.
Image guidance

The image guidance system is the other essential item in the CyberKnife system. X-ray imaging cameras are located on supports around the patient allowing instantaneous X-ray images to be obtained.

Xsight

Additional image guidance methods are available for spinal tumors and for tumors located in the lung. For a tumor located in the spine, a variant of the image guidance called Xsight-Spine is used. The major difference here is that instead of taking images of the skull, images of the spinal processes are used. Whereas the skull is effectively rigid and non-deforming, the spinal vertebrae can move relative to each other, this means that image warping algorithms must be used to correct for the distortion of the X-ray camera images.

A recent enhancement to Xsight is Xsight-Lung which allows tracking of some lung tumors without the need to implant fiduciary markers.
Fiducial

For soft tissue tumors, a method known as fiducial tracking can be utilized. Small metal markers (fiducials) made out of gold for bio-compatibility and high density to give good contrast on X-ray images are surgically implanted in the patient. This is carried out by an interventional radiologist, or neurosurgeon. The placement of the fiducials is a critical step if the fiducial tracking is to be used. If the fiducials are too far from the location of the tumor, or are not sufficiently spread out from each other it will not be possible to accurately deliver the radiation. Once these markers have been placed, they are located on a CT scan and the image guidance system is programmed with their position. When X-ray camera images are taken, the location of the tumor relative to the fiducials is determined, and the radiation can be delivered to any part of the body. Thus the fiducial tracking does not require any bony anatomy to position the radiation. Fiducials are known however to migrate and this can limit the accuracy of the treatment if sufficient time is not allowed between implantation and treatment for the fiducials to stabilize.
Synchrony

The final technology of image guidance that the CyberKnife system can use is called the Synchrony system. The Synchrony system is utilized primarily for tumors that are in motion while being treated, such as lung tumors and pancreatic tumors.

The synchrony system uses a combination of surgically placed internal fiducials, and light emitting optical fibers (markers) mounted on the patient skin. Since the tumor is moving continuously, to continuously image its location using X-ray cameras would require prohibitive amounts of radiation to be delivered to the patients skin. The Synchrony system overcomes this by periodically taking images of the internal fiducials, and predicting their location at a future time using the motion of the markers that are located on the patient's skin. The light from the markers can be tracked continuously using a CCD camera, and are placed so that their motion is correlated with the motion of the tumor.

A computer algorithm creates a correlation model that represents how the internal fiducial markers are moving compared to the external markers. The Synchrony system is therefore continuously predicting the motion of the internal fiducials, and therefore the tumor, based on the motion of the markers. The correlation model can be updated at any time if the patient breathing becomes in any way irregular. The advantage of the Synchrony system is that no assumptions about the regularity or reproducibility of the patient breathing have to be made.

To function properly, the Synchrony system requires that for any given correlation model there is a functional relationship between the markers and the internal fiducials. The external marker placement is also important, and the markers are usually placed on the patient abdomen so that their motion will reflect the internal motion of the diaphragm and the lungs.
RoboCouch

A new robotic six degree of freedom patient treatment couch called RoboCouch has been added to the CyberKnife which provides the capability for significantly improving patient positioning options for treatment.
Frameless

The frameless nature of the CyberKnife also increases the clinical efficiency. In conventional frame-based radiosurgery, the accuracy of treatment delivery is determined solely by connecting a rigid frame to the patient which is anchored to the patient’s skull with invasive aluminum or titanium screws. The CyberKnife is the only radiosurgery device that does not require such a frame for precise targeting. Once the frame is connected, the relative position of the patient anatomy must be determined by making a CT or MRI scan. After the CT or MRI scan has been made, a radiation oncologist must plan the delivery of the radiation using a dedicated computer program, after which the treatment can be delivered, and the frame removed. The use of the frame therefore requires a linear sequence of events that must be carried out sequentially before another patient can be treated. Staged CyberKnife radiosurgery is of particular benefit to patients who have previously received large doses of conventional radiation therapy and patients with gliomas located near critical areas of the brain. Unlike whole brain radiotherapy, which must be administered daily over several weeks, radiosurgery treatment can usually be completed in 1-5 treatment sessions. Radiosurgery can be used alone to treat brain metastases, or in conjunction with surgery or whole brain radiotherapy, depending on the specific clinical circumstances.

By comparison, using a frameless system, a CT scan can be carried out on any day prior to treatment that is convenient. The treatment planning can also be carried out at any time prior to treatment. During the treatment the patient need only be positioned on a treatment table and the predetermined plan delivered. This allows the clinical staff to plan many patients at the same time, devoting as much time as is necessary for complicated cases without slowing down the treatment delivery. While a patient is being treated, another clinician can be considering treatment options and plans, and another can be conducting CT scans.

In addition, very young patients (pediatric cases) or patients with fragile heads because of prior brain surgery cannot be treated using a frame based system. Also, by being frameless the CyberKnife can efficiently re-treat the same patient without repeating the preparation steps that a frame-based system would require.

The delivery of a radiation treatment over several days or even weeks (referred to as fractionation) can also be beneficial from a therapeutic point of view. Tumor cells typically have poor repair mechanisms compared to healthy tissue, so by dividing the radiation dose into fractions the healthy tissue has time to repair itself between treatments. This can allow a larger dose to be delivered to the tumor compared to a single treatment.
Gamma Knife

One of the most widely known stereotactic radiosurgery systems is the Gamma Knife. The Gamma Knife was originally developed by Lars Leksell, remains the gold standard method for delivery of stereotactic radiosurgery to the brain and is manufactured by Elekta. John Adler, the inventor of the CyberKnife system spent time training with Lars Leksell in Stockholm at the Karolinska Institute in 1985.
The GammaKnife system uses 201 Cobalt-60 sources located in a ring around a central treatment point ("isocenter"). The Gamma Knife system is equipped with a series of 4 collimators of 4mm, 8mm, 12mm and 16mm diameter, and is capable of submillimeter accuracies. The Gamma Knife system does however require a head frame to be bolted onto the skull of the patient, and is only capable of treating cranial lesions. As a result of frame placement, treatment with Gamma Knife does not require real time imaging capability as the frame does not allow movement during treatment. This is the reason that the Gamma Knife system is likely to be more accurate than Cyber Knife. The Cyberknife Society and Accuray maintain that there are no peer-reviewed published papers that establish Gamma Knife as being more accurate than CyberKnife.
Novalis

Another popular Stereotactic system is the Novalis produced by Brainlab. The Novalis radiosurgery system utilizes a small computer controlled micro Multi Leaf Collimator mMLC, that can produce many complicated shapes. The maximum radiation field size that the Novalis can produce is 98 mm x 98 mm, and the minimum is 3mm x 3mm allowing a considerable range of tumors to be treated. The Novalis system also has X-ray imaging using amorphous silicon flat panel X-ray detectors. A 2D/3D image fusion of the patient setup X-rays with digitally reconstructed radiographs from a planning CT scan quickly determines a correction vector for the patients position. Infrared fiducial markers attached to the patient then allow precise tracking of the correction vector's application to the patient's position via an infrared camera and a couch that can move in all six dimensions enables the precise positioning of the patient. Patient immobilization can also be performed framelessly using the patients internal anatomy as the frame of reference. An implanted marker based respiratory tracking option known as ExacTrac Gating is also an option. BrainLAB's Novalis has become a leading player in the world of neurosurgery.
Conventional linac

Conventional X-ray therapy linear accelerators can be utilized for radiosurgery, either by the use of additional blocking cones or by a removable or built in micro MLC system.
Examples of removable micro MLC units are the Ergo from 3D line, the mMLC manufactured by Brainlab, and the AccuKnife produced by Direx., or the Novalis TX.

History

The first implementation of tomotherapy was the Corvus system developed by Nomos Corporation.[1] This was the first commercial system for planning and delivering intensity modulated radiation therapy (IMRT). The original system, designed solely for use in the brain, incorporated a rigid skull-based fixation system to prevent patient motion between the delivery of each slice of radiation. But some users[who?] eschewed the fixation system and applied the technique to tumors in many different parts of the body.
Tomotherapy, or Helical Tomotherapy, is a form of computed tomography (CT) guided IMRT or Intensity Modulated Radiation Therapy, which is a relatively new type of radiation therapy delivery system. The system was developed at the University of Wisconsin–Madison by professor Thomas Rockwell Mackie, Ph.D. and Paul Reckwerdt. A small megavoltage x-ray source was mounted in a similar fashion to a CT x-ray source, and the geometry provided the opportunity to provide CT images of the body in the treatment setup position. Although original plans were to include kilovoltage CT imaging, current models use megavoltage energies. With this combination, the unit was one of the first devices capable of providing modern image-guided radiation therapy (IGRT). The first patients were treated in 2002, at the University of Wisconsin under the guidance of Professor Minesh Mehta, M.D., under the auspices of an NIH-funded Program Project Grant.
[edit]General Principles

In general, radiation therapy (or radiotherapy) has developed with a strong reliance on homogeneity of dose throughout the tumor. Tomotherapy embodies the sequential delivery of radiation to different parts of the tumor which raises two important issues. First, this method is known as "field matching" and brings with it the possibility of a less-than-perfect match between two adjacent fields with a resultant hot and/or cold spot within the tumor. The second issue is that if the patient or tumor moves during this sequential delivery, then again, a hot or cold spot will result. The first problem can be overcome, or at least minimized, by careful construction of the beam delivery system. The second requires close attention to the position of the target throughout treatment delivery.
The Corvus tomotherapy system achieved great popularity because it provided a mass market solution to IMRT very early compared to other vendors' systems. Generally speaking, dose homogeneity is less in IMRT than in 3D conformal radiation therapy which may account for the relative lack of concern regarding the field matching issue.
At this time, the Hi-Art system manufactured by TomoTherapy Inc. is the primary tomotherapy device in use although there are still a number of Corvus systems being used. TomoTherapy TomoHD systems are also in use. Other radiation therapy equipment vendors have recently responded to the challenge of short treatment times coupled with a full 360 degree treatment arc by developing methods of delivering IMRT using arcs. The major difference is that these methods are implemented on standard medical linear accelerators, thereby providing for complete volumetric irradiation.


Patient undergoing tomotherapy, face and body covered.
TomoTherapy "beam on" times are comparable to normal radiation therapy treatment times (about 3–5 minutes beam on time for a common prostate treatment) but do add an additional 2–3 minutes for a daily CT. The daily CT is used to precisely place the radiation beam and allows the operator to modify the treatment should the patients anatomy change due to weight loss or tumor shrinkage (adaptive radiotherapy). Lung cancer, head and neck tumors, breast cancer, prostate cancer, stereotactic radiosurgery(SRS) and stereotactic body radiotherapy (SBRT) are some examples of treatments commonly performed using TomoTherapy. While the first clinical use of TomoTherapy was in 2002, at the University of Wisconsin, under the leadership of Dr. Minesh Mehta, M.D., there are now more than 300 sites across Canada, the United States, Europe and Asia.
Due to their internal shielding and small footprint, TomoTherapy Hi-Art and TomoTherapy TomoHD treatment machines are the only radiotherapy treatment machines used in relocatable radiotherapy treatment suites. Two different types of suites are available: TomoMobile developed by TomoTherapy Inc. which is a moveable truck and Pioneer, developed by UK-based Oncology Systems Limited. The latter was developed to meet the requirements of UK and European transport law requirements and is a contained unit that is placed on a concrete pad, delivering radiotherapy treatments in less than five weeks.


RFA is performed to treat tumors in lung,[3][4][5] liver,[6] kidney, bone and (rarely) in other body organs. Once the diagnosis of tumor is confirmed, a needle-like RFA probe is placed inside the tumor. The radiofrequency waves passing through the probe increase the temperature within tumor tissue that results in destruction of the tumor. Generally RFA is used to treat patients with small tumors that started within the organ (primary tumors) or that spread to the organ (metastasis). The suitability of a patient to receive RFA is decided by doctors based on multiple factors. RFA can usually be administered as an out-patient procedure, that may at times require a brief hospital stay. RFA may be combined with locally-delivered chemotherapy to treat hepatocellular carcinoma (primary liver cancer). The low-level heat (hyperthermia) created by the RFA probe causes heat-sensitive liposomes to release concentrated levels of chemotherapy in the margins around the ablated tissue, which is a method commonly used to treat Hepatocellular carcinoma (HCC).[7] Radiofrequency ablation