Varian Medical : Patent Issued for Radiation Therapy Systems and Methods for Delivering Doses to a Target Volume (USPTO 9855445)
The patent's inventor is Mansfield, Stanley (
This patent was filed on
From the background information supplied by the inventors, news correspondents obtained the following quote: "The use of radiation therapy to treat cancer is well known. Radiation therapy (radiotherapy) involves directing a beam of high energy particles such as electrons, protons, or heavy ions into a target volume (e.g., a tumor or lesion) in a patient.
"Before the patient is treated with radiation, a treatment plan specific to that patient is developed. The plan defines various aspects of the radiotherapy using simulations and optimizations based on past experiences. For example, for intensity modulated particle therapy (IMPT), the plan can specify the appropriate beam type and the appropriate beam energy. Other parts of the plan can specify, for example, the angle of the beam relative to the patient/target volume, the beam shape, and the like. In general, the purpose of the treatment plan is to deliver sufficient radiation to the target volume while minimizing the exposure of surrounding healthy tissue to radiation.
"Existing IMPT dose delivery techniques utilize raster scanning that takes advantage of the well-known Bragg peak characteristic of a mono-energetic particle (e.g., proton) beam. By scanning the beam in the X and Y directions, a 'layer' of dose can be 'painted' within the target volume. Subsequent layers are painted in overlapping raster scan patterns using particles with a different energy that would thus stop at a different range (distance). Such scan patterns usually start at the most distal edge of the planning target volume and each subsequent layer is delivered, after a pause to change the beam energy, to a lesser range thus creating a Spread Out
"A fundamental concern during radiation therapy is that the target volume might move during dose delivery (e.g., due to the patient moving, breathing, etc.). Movement during dose delivery can inadvertently place healthy tissue in the path of the radiation intended for the target volume. Although it is theoretically possible for the raster scan pattern to track in-plane motion of the target volume, by superimposing the raster scan pattern with the instantaneous two-dimensional (X-Y) vector corresponding to that motion, any out-of-plane motions (particularly those of normal healthy structures proximal to the target) can introduce motion-related uncertainties that in turn can create dose overlaps ('hot spots') or, even worse, gaps ('cold spots') within the target volume.
"A recent radiobiology study has demonstrated an advantageous effectiveness in sparing normal, healthy tissue from damage by delivering an entire, relatively high therapeutic radiation dose within a single short period of time (e.g., less than one second). However, in conventional raster-scanned IMPT, because dose delivery along each ray passing through the patient occurs successively at different points in time in the scan pattern and is thus spread out over time, the unavoidable dose that is delivered to the normal healthy structures is also spread out over time. Therefore, the radiobiological tissue-sparing effects reported in the aforementioned study are not realized using existing IMPT techniques.
"Furthermore, contemporary radiation therapy delivery systems include dipole electromagnets and scanning magnets. The dipole magnets (often referred to as 'bending magnets') direct (e.g., bend) the particle beam in a direction toward a nozzle, and the scanning magnets steer (deflect or scan) the beam in the X and Y directions. The dipole magnets typically utilize massive ferromagnetic return paths and therefore have a much slower magnetic hysteresis relative to the scanning magnets. That is, it takes much longer to change (increase or decrease) the level of magnetism in the dipole bending magnets than it does to steer the beam using the scanning magnets during IMPT delivery. Also, the relative slowness of varying the magnetic fields of the dipole bending magnets is the primary reason that existing IMPT systems utilize a method of scanning dose one layer at a time. The time spent changing the magnetic strength of the dipole magnets in order to change the incident beam energy constitutes a significant portion of the time required to deliver an IMPT therapy dose. Considering the comfort of the patient, for example, shorter radiotherapy sessions are highly preferred. Thus, the reliance on magnets, particularly the use of the dipole bending magnets, for adjusting particle beams is an obstacle to realizing the benefits of using relatively high therapeutic radiation doses within a very short period of time for dose delivery in radiotherapy."
Supplementing the background information on this patent, VerticalNews reporters also obtained the inventor's summary information for this patent: "In an embodiment according to the present disclosure, a radiation therapy system includes an accelerator and beam transport system and a nozzle that can be aimed toward an object. The nozzle includes at least one scanning magnet that guides (e.g., steers, deflects, or scans) the beam toward various locations within a target volume within the object. The nozzle also includes a beam energy adjuster configured to adjust the beam by, for example, placing different thicknesses of material in the path of the beam to affect the energies of the particles in the beam. The beam energy adjuster may include one or both of a range shifter and a range modulator. In an embodiment, the range shifter is configured to place different thicknesses of material in the path of the beam to affect the distance that the particles penetrate into the object. In an embodiment, the range modulator is configured to place different thicknesses of material in the path of the beam to decrease the energies of at least a portion of the particles by varying the exiting beam particle energy over time, to spread out the Bragg peak.
"Significantly, the range shifter and/or range modulator, placed in the nozzle as described in this disclosure, are 'dynamically variable' (e.g., faster acting than the dipole magnets in the beam transport system). Consequently, a nozzle according to the present disclosure is capable of quickly adjusting the particles in the beam to create a scanned beam (as opposed to a scattered beam) that delivers an entire, relatively high therapeutic radiation dose in the target volume. For example, a dose of four grays can be delivered along a specified beam direction (e.g., a given ray) in less than one second.
"Each ray is a part of a scan pattern and irradiates tissue along a different line segment through the target volume (a 'target line segment'). A high dose that can be delivered in a short period of time along a target line segment may be referred to herein as a 'shot.' In an embodiment, a shot can be adjusted in energy (intensity) or range and delivered to the target volume with a Spread Out
"The intensity of the dose delivered in a shot can be adjusted to match the prescribed dose for a particular target line segment. Shots can be delivered using, for example, a predefined scanning pattern to irradiate different target line segments: a first adjusted beam that delivers a first dose with a SOBP along a first target line segment in a target volume can be created, and a second adjusted beam that delivers a second dose with a second SOBP along a second target line segment in the target volume can be created, where the second target line segment is displaced from the first target line segment. Each shot can be triggered in time and/or aimed in position to coincide with the position of a moving target within a patient based on, for example, a motion tracking system. Subsequent shots can be independently adjusted in intensity, in range, and with a suitable SOBP, and can also be triggered or aimed to coincide with the 4D (three dimensions plus time) position of each target line segment in the scan pattern until the entire target volume has been irradiated to the prescribed dose.
"In an embodiment, a range shifter is in the nozzle, downstream of the scanning magnet(s). In another embodiment, the range shifter is in the nozzle, upstream of the scanning magnet(s). The range shifter provides a rapid means of quickly varying the range of the Bragg peak to match the distal edge of the planning target volume.
"In an embodiment, the nozzle includes both a range modulator and a range shifter. The range modulator is downstream of the scanning magnet(s); the range shifter can be downstream or upstream of the scanning magnet(s). In an embodiment, the range modulator includes a number of arms extending from a hub. In an embodiment, each of the arms has a non-uniform thickness and a non-uniform width (and therefore a non-uniform amount of space between adjacent arms). The range modulator can rotate about the hub, so that the beam will pass through at least one of the arms and also can pass through the space between adjacent arms.
"In an embodiment, the range modulator can be moved in a first direction (e.g., laterally, transverse to the path of the beam) so that it is either completely out of the path of the beam or is in the path of the beam. In an embodiment, the range modulator can also be moved in a second direction different from (e.g., perpendicular to) the first direction and transverse to the path of the beam.
"The range modulator provides a means of quickly varying the energy in a scanned beam to create the desired extent of SOBP in a dynamically variable manner. By adjusting the position of the range modulator and rotating the range modulator, the beam can pass through different parts of at least one of its arms and therefore through different thicknesses of material and also through different amounts of space between adjacent arms, and therefore the extent of spread of the SOBP can be rapidly varied over a useful range.
"The range modulator and/or the range shifter match the SOBP (distally and proximally) to the target volume (the planning target volume). Because the range modulator and the range shifter can achieve these effects quickly, a shot can advantageously be used for dose delivery. Thus, using shots, the entire target volume can be irradiated to the dose prescribed by the treatment plan while exposing healthy tissue to only a single, very short burst of radiation. Also, by delivering the entire dose within a short period of time, movement of the target volume becomes much less of an issue. Likewise, delivering a pattern of shots with varying intensity from a single beam direction quickly results in intensity-modulated radiation therapy delivery. Further, by delivering patterns of shots from multiple beam directions, a more refined intensity modulation can be achieved with lower dose delivered to healthy tissues. Importantly, because no dose is delivered distally to the Bragg peak, the dose delivered in this manner to any healthy tissue, outside the target volume, can thus be limited to a single very short burst of low dose radiation.
"In summary, embodiments according to the present disclosure provide spatially and temporally precise, modulated irradiation of a moving target in a patient and take advantage of the tissue-sparing effects of the study mentioned above. Embodiments according to the present disclosure provide a more direct method for target volume scanning than the use of the conventional raster scanning technique described above. Each shot is aimed directly to coincide with the in-plane motion of the target using the scanning magnet(s), rather than having to distort the raster scan pattern. Aiming subsequent shots thusly avoids creating motion artifacts such as those caused by the interplay between the target motion of sequential raster scan patterns. Likewise, target motion in the distal-to-proximal direction can be compensated for by varying the range shifter accordingly between shots. Quality assurance is also made easier because the tracking and scanning processes are more independent of one another. Significantly, because a SOBP covering the entire length of each target line segment (from the distal edge to the proximal edge of the planning target volume) is delivered in a short burst, motion-induced uncertainties do not create gaps or overlaps (cold spots or hot spots) within the target volume.
"These and other objects and advantages of the various embodiments of the present disclosure will be recognized by those of ordinary skill in the art after reading the following detailed description of the embodiments that are illustrated in the various drawing figures.
"This summary is provided to introduce a selection of concepts in a simplified form that is further described below in the detailed description that follows. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter."
For the URL and additional information on this patent, see: Mansfield, Stanley. Radiation Therapy Systems and Methods for Delivering Doses to a Target Volume.
Keywords for this news article include: Business, Radiotherapy, Therapeutics, Radiation Therapy, Drugs and Therapies, Health and Medicine,
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