Radiation Therapy : Treatment planning


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.

Automated Radiation Treatment Planning to Improve Consistency

UW–Madison researchers have developed a method for generating high quality radiation treatment plans for every patient. In the new method, planning objectives are automatically determined based on patient data, e.g., target regions and organs at risk (OARs). So-called ‘physical objectives’ take into account the physical constraints and capabilities of the particular therapy system being used.

This approach is contrary to traditional planning schemes based on dose-volume histograms, which fail to convey the same spatial information attainable with the new method.

Image Autosegmentation Improves Treatment Planning

UW–Madison researchers have developed a parameter-free, automatic image segmentation method that overcomes user variations.

To define a target for radiotherapy, for example, the process involves three stages. First, multiple highly discriminate texture feature images are generated. Then, a parameter-free NCRG (non-connected region-growing) is generated to determine the desired segmentation for each image that yields multiple regions of interest. Finally, the tumor region is determined using a synthesis and analysis algorithm.

The new method is called a gradient assisted non-connected automatic region (GANAR) analysis.

Compound to Protect Against Radiation Exposure

A UW–Madison researcher has developed a new family of aminothiol molecules that could prevent tumor formation or DNA damage due to radiation exposure. The well-studied prototype molecule is called PrC-210. It has been demonstrated to suppress CT scan X-ray-induced DNA damage in human blood cells to background. This would likely also suppress cancers resulting from diagnostic radiation to background. Importantly, the new drug lacks both of the severe side effects (nausea/emesis and hypotension/fainting) that preclude the use of amifostine.

The new molecules’ radioprotective properties arise from the combination of a reactive oxygen species (ROS)-scavenging thiol group and a positively charged alkyl-amine backbone that allows the molecule to “hover” around the negatively-charged DNA backbone in cells where the thiol can then capture ROS before they attack DNA.

A decade of research, multiple peer-reviewed publications, both issued and pending patent claims, and more than $2.5 million in research support has gone into PrC-210 development to date.

Tracking Tumors for Real-Time Radiation Therapy by Automatic Segmentation

UW–Madison researchers have developed an extremely fast algorithm-based segmentation technique to guide radiation at a rate commensurate with real-time tissue imaging.

Novel Morphological Processing and Successive Localization (MPSL) can be applied to auto-contour the volume, shape and position of a target. The method utilizes predetermined knowledge of the general location and size range of the tumor and based on similarities within value and positioning data, isolates healthy and diseased regions for radiation. More efficient than manual segmentation and more accurate than existing algorithms, the method enables flexible, medical image-guided radiotherapy.

Easy-to-Assess Image Registration

A UW–Madison researcher and others have developed a program that allows specific correlated points to be clearly displayed on two different medical images. This helps visualize landmarks and flag any errors in the mapping process.

Specifically, a computer is programmed to receive the two different images, register them and display them side-by-side. The user identifies a feature in one of the images. The location of this feature in the second image according to the registration is then determined using the transformation matrix or DVF, and highlighted for the user. Disparities, such as differences in pixel value, also may be displayed. This makes any misalignment visually apparent and provides an efficient method of validating image registration accuracy.

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.

Optimized Intensity Modulated Arc Therapy Treatment Planning System

UW–Madison researchers have developed an optimized system and method for producing an intensity modulated arc therapy treatment plan. The system utilizes two main phases to reach an optimal delivery design. Phase one includes obtaining a small set of linked radiation beam apertures and corresponding beam intensities that optimize the approximation of a collection of real-valued intensity maps that are specified along a treatment arc. Phase two requires re-optimizing the beam intensities using dose distributions corresponding to the apertures generated in phase one.

Correction of Inverse Consistency and Transitivity Errors in Deformable Image Registration

UW–Madison researchers have developed a correction algorithm that forces inverse consistency and transitivity between all deformation vector fields used in dose accumulation. The algorithm provides flexible image deformation that is largely indifferent to the sequence of deforming step and does not require transformation through a particular image. These results are accomplished by ensuring individual deformation maps are inverse consistent, for example, by use of a correlation algorithm or an averaging process. Transitive deformation maps are produced by combining inverse-consistent deformation maps for combinations of different deformation pathways between the same endpoint images. The resulting system allows arbitrary deformation of image-type data among images with consistent results when the deformation endpoints are the same.

IsoPhantom: A Customizable 3-D Phantom for Improved Radiation Dosimetry

A UW–Madison researcher has developed a system and method for utilizing available detector arrays with a highly configurable 3-D phantom to acquire accurate 3-D dosimetry information. This radiation dosimetry quality assurance system is configured to measure actual radiation dose delivered by the radiation delivery system during a planned medical procedure.

The system consists of a 3-D phantom extending along a longitudinal axis to form an exterior surface and an interior volume, a passage that extends the interior volume of the phantom to receive a detector array, an angular-compensation system coupled to the surface of the 3-D phantom to control any angular dependence of the detector array during dose measurement and a detector-angle adjustment system to allow positioning of the detector array with respect to the radiation source (see the figure below for a general schematic of the system). The system: 1) corrects for device-dependent angular dependence, 2) optimizes the measurement plane(s) to any plane rotated about the longitudinal axis to maximize sensitivity specific to each radiation plan, and 3) is capable of serving all 2-D dosimetry arrays. The system can be utilized with flexible analysis software to integrate 2-D array measurements into a 3-D analysis engine and graphical user interface.

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.

Targeted Microwave Hyperthermia Therapy to Eliminate Hot Spots

UW–Madison researchers have developed a method of microwave hyperthermia that prevents hot spots by cycling through different antenna array settings, each having a common treatment zone but providing relative “cold spots” or suppression regions in different locations. Effective hyperthermia treatment schedules can be produced by offsetting potential hotspots in one antenna array setting with cold spots in that location in a different antenna array setting. Cycling through antenna settings over time reduces or eliminates auxiliary hot spots. The treatment planning system may include an electronic computer that executes a stored program to receive data about the tissue of a patient, and then uses the data to model and select a set of power deposition patterns that will control average power deposition to the tissue region outside the intended treatment region.

Tailored Radiopharmaceutical Dosimetry for 4-D Treatment Planning System

UW-Madison researchers have developed a system for precisely tailoring the quantity and timing of the administration of a radiopharmaceutical to a particular patient. To generate time-activity curves, an imaging radioisotope is first administered and the subject is scanned using dynamic PET/CT imaging. From the acquired datasets, the critical organ, which displays toxicity at the lowest injection level, is determined. A fractionation scheme is then developed for tumor control and toxicity avoidance, and precise, patient-specific administration schedules are created based on the effect that varying dose rates have on the critical organs and tumors. This two-step technique can provide sufficient precision to allow the combination of radiopharmaceutical treatment with other radiation treatment such as external-beam radiotherapy.

Treatment Planning Algorithm for Implanting Radioactive Seeds During Brachytherapy

UW–Madison researchers have developed a non-iterative treatment planning algorithm for implant brachytherapy. The algorithm builds off the previous invention to create a faster and more accurate treatment planning algorithm.

The method starts by determining what doses are required for specific locations in the area of interest. An importance function is developed based on the match between the original dose pattern and a hypothetical seed moved through the different locations in the pattern. The locations then are ranked and reserved for a seed in the order of importance. Every time a seed is reserved, the original dose pattern is updated to show the difference between the current dose pattern and the dose provided by seeds at the reserved locations. This difference then is used to update the importance function.  These steps are repeated until a predetermined criterion is met.

Automated Software System for Optimal Beam Setup in Radiation Cancer Therapy Systems

UW-Madison researchers have developed software that uses iterative processes and parallel computing power to select the optimal beam setup to treat tumors while sparing surrounding tissue.  Therapists begin with an estimate of a dosage scheme, and the software computes the average dose that can be applied to each organ that may be at risk of radiation exposure.  Each organ is given an adjustable weight of its importance.  Based on those weights and potential beam configurations, the program uses nested partitioning—an industrial engineering technique that has never been applied to radiation treatment planning before—to evaluate each potential beam setup.

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 Device for Planning Treatment with Implanted Radioactive Seeds

A team of UW-Madison medical physicists has now developed an extremely rapid optimization algorithm for planning the placement of radioactive seeds in prostate tissue. The technique is based on a “greedy” algorithm and an adjoint function for a tissue region-of-interest (ROI). The adjoint function is defined as the sensitivity of the dose in the ROI to the placement of a single seed at any arbitrary position. For each seed position, a ratio is computed that is the sum of the adjoint values for sensitive structures (e.g., urethra) divided by the adjoint value for the target tumor in the ROI. An optimization process then follows in which the greedy algorithm inspects the ratios and ranks the seed positions based on their ability to irradiate the tumor while sparing sensitive tissue. The greedy algorithm then designs the overall seed pattern by choosing the most favorable seed positions.