Radiation Therapy : External beam therapy

Radiation Therapy Portfolios


Soft-Spectrum Filter for External Beam Radiation Therapy

UW–Madison researchers have developed a new soft-spectrum filter called SPECTER that uses beam-filtering material to block the unwanted soft portion of an FFF radiation beam. The high energy ‘hard spectrum’ of the beam can pass unfiltered through a central aperture.

The material and dimensions of the SPECTER may be optimized to control external radiation scatter and loss in high dose rates compared with other system employing FFF beams.

New Radiosurgery Collimator Salvages Scatter, Cuts Treatment Time

UW–Madison researchers have developed an SRS collimator assembly capable of refocusing scattered radiation that would otherwise be lost. The new design features concentric, conical slits oriented along different angles. Radiation striking the top surface of the collimator is redirected along each slit towards a common point, or isocenter.

The slits can be termed ‘Compton slits’ because they are designed to capture and redirect Compton scattered radiation.

Sharper Stereotactic Radiosurgery

UW–Madison researchers have developed a waveguide for use with conical radiosurgery collimators. The waveguide can be installed inside the collimator’s bore hole. Resembling a collection of hypodermic needles, the waveguide is made of concentric spacers and hollow cylinders. Its optimized design cuts down on beam blurring and directs radiation into a target volume with high precision.

More Accurate Method for Generating Proton Therapy Treatment Planning Images

UW–Madison researchers have developed a method of preparing a treatment control sequence for proton radiation therapy involving a program and/or an electronic computer that receives patient data. This method greatly improves the accuracy of converting X-ray photon attenuation to proton stopping power from a conventional X-ray CT image by segmenting tissues into different tissue types and then converting each segment using conversion functions that are unique to each tissue type. The derived proton stopping power data is used to produce the treatment control sequence to accurately target the tumor and preserve healthy tissue.

Controlled Radiation Therapy Delivery for Improved Cancer Cure Rate

UW–Madison researchers have developed a new treatment planning and delivery technique for external beam radiation therapy that minimizes the radiobiological effect on normal tissues while increasing the radiation dose to malignant tissue. The method uses computerized algorithms to determine an optimized sequence for radiation beams directed at the target to maximize the time between beams that also irradiate normal tissue. This temporal separation of radiation beams to normal structures maintains the maximal dose to the tumor target volume while minimizing the radiobiologically effective dose to healthy tissues surrounding the target. In principle, this reduces the normal tissue complication probability and chances of late radiation-related toxicity, and potentially increases the cancer cure rate by permitting higher total radiation doses to be prescribed and administered.

The steps to control radiation dose include obtaining an image of the subject, identifying the planned target region and the normal tissues adjacent to the target, and classifying each identified normal tissue. Then, a spatiotemporal dose-rate distribution is determined using a selected prescribed dose and information about the normal tissue and planned target region. By directing the radiation therapy system to irradiate the target according to the determined spatiotemporal dose-rate distribution, a selected dose-rate to the planned target volume is maintained while a lower effective dose-rate is received by the normal tissues.

Image Reconstruction Method for High Temporal Resolution Image Guided Radiaton Therapy

UW–Madison researchers have developed a medical image reconstruction method designed to increase temporal resolution, while increasing accuracy and reducing the radiation dose to the patient. The method may be applicable to numerous imaging techniques including magnetic resonance imaging (MRI), X-ray computed tomography (CT), positron emission tomography (PET) and single photon emission computed tomography (SPECT).

Acquired data is used to reconstruct a “sparsifying image.” A “correction image” is iteratively determined and subtracted from the sparsifying image to produce a quality image.

The technique also can be applied to current IGRT techniques to increase the accuracy of radiation delivery. Sparsifying images are obtained for a specific phase of the respiratory cycle to more accurately determine the motion characteristics of the target tumor and increase the temporal resolution.

Improved Proton-Based Cancer Radiation Therapy System with Beam Intensity and Energy Modulation

UW-Madison researchers have developed an improved method and system to modulate ion beam intensity and energy for proton-based radiation therapy.  The modulator is mounted on a ring gantry, like a CT scanner, able to rotate around the patient.  In general, the system transforms a pencil beam of ions into a fan beam modulated in intensity and energy through a series of steps. 

The thin pencil beam is first passed through a scattering foil and collimated to form a rectangular area beam.  The area beam then is occluded by a plane of ion-blocking shutters, resembling a series of interlocking fingers, independently actuated by computer to modulate the intensity of the area beam.  The area beam subsequently is collapsed into a fan beam by a pair of quadrupole lenses, which use magnetic fields to longitudinally compress the rectangular area beam.  The intensity of individual beamlets, one from each aperture of the ion-blocking shutters, is averaged by blurring and compression as the ions pass through the lenses.  This achieves parallel time-independent intensity modulation of the proton beamlets. The fan beam then is passed through a plane of opposed, overlapping, ion-attenuating wedges to slow down the protons, thereby modulating the beam energy.  Each pair of synchronized wedges is actuated by computer to provide control of each beamlet’s energy.  Finally, the patient is treated with the resulting energy and intensity modulated fan beam.

This type of beam modulator provides real-time control of proton beams used in radiation therapy and, when multiple modulators are employed in a radiation treatment system, is able to precisely control the dose delivered to complex target tissue areas and also minimize irradiation of healthy cells.  The new device will reform the practice of radiation therapy, improving the patient’s welfare, treatment efficiency and system precision.

Multi-Element Ion Beam Range and Intensity Modulator for Radiation Therapy

UW–Madison researchers have developed a radiation treatment system that uses a shutter modulation device to individually control separate beamlets of an ion fan beam. The fan beam technique combines the benefits of parallel treatment of portions of the tumor such as SOBP with the precise control of small portions of the beam like MSS. With the use of ions the device can control the beam’s range, but when used with photons it can control the beam’s intensity. The device increases both treatment speed and precision.

The shutter system works by using an array of elements containing leaves that lie in the cross section of the fan beam. Each element can be positioned in or out of the beam by the use of individual linear actuators for each element. The purpose of the elements is to decrease the strength of the incoming ion beam fan by allowing attenuation of the beam. The elements can consist of variable thicknesses and be made of any sort of homogenous material. Multiple elements with different weights can be stacked in a row to allow for substantially more control with fewer elements.

Ion Fan Beam Radiation Therapy System with Partial Arc Motion

UW–Madison researchers have developed a radiation therapy system that uses an ion fan beam consisting of separately modulated beamlets that are rotated about the patient in a partial arc during modulation. This technique improves the dose conformity over SOBP while reducing cold spots and treatment time length when compared to MSS. Using the partial arc simplifies the treatment mechanism and the positioning of bulky neutron shields. The partial arc provides dose conformity that is nearly equal to a complete 360 degree arc while removing the dose to the distal side of the patient.

Quadrupole Magnetic Fan Beam Former for Ion Radiation Therapy Systems

UW-Madison researchers have developed a radiation treatment system that uses magnetic deflection to convert a pencil beam into a fan beam made up of individually controllable beamlets.  Both intensity and range can be controlled separately for each beamlet.  This system combines benefits of treating different portions of the tumor at once (SOBP) with the precise control of each individual beamlet (MSS).  The magnetic deflection technique also reduces neutron contamination to the patient compared to other conventional techniques used to form a fan-shaped beam.

The magnet system incorporates one or more quadrupole magnets, which consist of two pairs of magnets that oppose each other on separate magnet axes.  These axes are perpendicular to each other and also perpendicular to the incoming beam axis.  One set has opposed north poles and the other has opposed south poles.  Once the beam is in fan form, its intensity and range of individual sections may be modulated to provide the ability to treat wide areas while maintaining high resolution in the direction normal to the fan beam.

Scanning Aperture Ion Beam Range Compensator and Intensity Modulator for External Radiation Therapy

UW–Madison researchers have developed a technique for external beam ion radiation therapy that modulates an area beam by the use of a shutter system to increase treatment speed while maintaining high precision. The shutters can control beam intensity independently to eliminate the need for a special compensator.

This technique uses an area beam that is occluded with a set of longitudinally opposed and latitudinally adjacent shutter pairs. Each shutter of each pair is controllable and can extend to different longitudinal distances. The shutters can control the range of the beam to conform to complex tumor shapes and can be steered around like a pencil beam while maintaining the proper range for the tumor.

Distal Gradient Tracking (DGT) for Ion Beam Radiation Therapy

UW–Madison researchers have developed an ion radiation treatment system that places the Bragg peak according to a prescribed dose plan to impart non-homogeneous radiation doses to the tumor area. Basically, the Bragg peak is placed at a point where the prescribed dose value falls under a certain level in a dose gradient. Each gradient is specific to the angle that the beam is being applied to, and thus is tailored to the specific tumor.

The system consists of an ion beam source and a range controller. A separate beam controller executes a stored radiation plan in conjunction with a dose plan that defines the region where the dose is to be applied to determine the beam gradients for every angle at which the ion beam is applied. The beam controller sends control signals to the range controller to position the Bragg peaks according to the gradients.

Probabilistic Least Squares Optimization for Radiation Therapy to Remove Patient Motion Effects

UW–Madison researchers have developed a computer-implemented method for optimizing radiation therapy by providing control of independent radiation beams configured to account for the effects of patient motion. The method incorporates a probabilistic linear least squares approach that quantitatively expresses patient motion. This information then is fed into the control of the radiation beams to remove the effects of patient motion.

The total system may include a radiation source that generates multiple rays, a shutter system to control the rays and a computer system to control the shutter system. The computer system is configured to control the radiation source and the shutter system to account for patient motion based on a probability distribution function. A total dose at each specific point in the tumor is determined based on an iterative method to give an intensity map. This intensity map then is used to deliver radiation accordingly.

Multi-Beamlet Resolution Proton Therapy (MBRPT) for Ion Beam Treatment of Tumors

UW–Madison researchers have developed an external radiation therapy system that uses multiple ion beam spot sizes to yield a precise trade-off between tumor treatment speed and accuracy. The system uses larger area beams for large, homogeneous portions of the tumor and then smaller pencil beams for edge delineation and small dose areas. This combination eliminates cold spots altogether.

The system consists of an ion source that produces an ion beam that is steered around the tumor area. The beam’s width and range is determined by a beam controller that executes stored radiation plans for treatment. Different beam widths are applied to different areas to give a flexible trade-off between accuracy and speed. In addition, the ability to control the beam size reduces neutron contamination to the patient. The beam width may be varied by means of quadrupole magnets, scattering foils or a dielectric wall accelerator.

Radiation Therapy Modulation by Virtual Analysis to Improve Cancer Treatment in Moving Tissues

UW–Madison researchers have developed an improved method and system comprising a virtual four-dimensional (4-D) treatment suite for developing and evaluating radiation treatment plans. The virtual 4-D treatment suite includes radiation dose calculation, gating and dose rate adjustment modules. The dose calculation module evaluates the effect of motion by predicting the amount of radiation received by the target tissue and determining the possible variation in dose due to motion of the target tissue. The gating module virtually determines the benefits of employing a gating technique by evaluating a gating window set manually or automatically by a practitioner or computer simulated input. The dose rate adjustment module virtually determines the efficacy of dose rate, also by automated computer simulation or practitioner input. The system also may include a collimator angle adjustment module to direct radiation beams and a database to store information about the patient, treatment plans, breathing information or other treatment data.

The 4-D suite also can recognize large variations in delivered dose and alter particular segments of an IMRT treatment session by lowering dose rates. This process, termed selective dose rate modulation, decreases temporal variations in delivered dose while minimally increasing treatment time. The same can be achieved with gating; however, this process leads to a significant increase in treatment time. Selective dose rate modulation is an advantageous technique because it can be applied to radiation therapy procedures that cannot be gated such as volumetric modulated arc therapy (VMAT) and RapidArc, in which dose rate can be altered as a function of gantry angle.

The 4-D treatment suite improves upon previous techniques of developing and evaluating radiation treatment plans by calculating the expected therapy dose and temporal variation in the expected therapy dose. Utilization of these key parameters reduces treatment time with dose rate modulation and decreases radiation of normal cells with gating and beam angle adjustment modules, making radiation therapy a safer and more effective cancer treatment.

Method and Apparatus for Low Dose Computed Tomography

UW-Madison researchers have developed a CT machine capable of minimizing the radiation dose while providing an image of desirable quality. The contribution of each radiation beamlet to the quality of the resulting tomographic image varies as a complex function of the internal structure of the patient. Although the structure of the patient is generally unknown, in many cases there is sufficient a priori knowledge about the patient to intelligently select beamlets based on how important each beamlet is to the quality of the image. The CT machine of this invention features a controller that uses a stored model of the patient to control the intensity of radiation in each beamlet based on a calculated contribution of the beamlet to image quality.

Low Skin Dose Patient Positioning Device for Radiation Treatment of Prone Breast

UW-Madison researchers have developed a pad that allows radiation to be directed at the breast from many angles without increasing the dose of radiation to the skin. Instead of requiring a specialized table, a foam pad is laid on a standard table. The pad contains one hole for the targeted breast. The area surrounding the hole is made of a transparent bladder that contains either air or helium. Radiation can be directed through the bladder without accumulating build-up because the gasses provide less mass than padding or tissue.

Improved Portal Imaging During Radiation Therapy Using a Modulated Treatment Beam

High-energy treatment beams always include lower energy components, however, and a UW-Madison researcher has now devised a way to modulate the beam, without affecting patient treatment, so that only low-energy X-rays contribute to portal images. The device, which includes multiple filters and bandwidth-narrowed detection, can create quality images at a rate of approximately 10 per second. The filters modulate the low-energy X-rays already present in the treatment beam. The detector then screens out all un-modulated, high-energy beam components to create clear, quality images strictly from low-energy, non-interacting X-rays.