BACKGROUND

Radiation therapy is a choreographed procedure that requires an extensive treatment planning phase in order to determine an efficient way to deliver the prescribed radiation dose to the target regions in the patient (e.g., tumor regions) while avoiding radiation-sensitive organs and/or structures (e.g., organs-at-risk or OARs). A treatment planning system integrates patient information (e.g., the size, shape, and location of target regions and OARs) along with radiation treatment system machine parameters (e.g., therapeutic radiation source beam generation capabilities and range of motion relative to the patient, configuration of the beam-shaping components, degrees-of-freedom and motion of the patient platform, etc.) to generate a fluence map that includes a set of beamlets that provide the prescribed dose to the target region. The fluence map is then segmented into a series of machine instructions that are executed by the radiation therapy system, with the assumption that once the set of instructions has been fully executed, the prescribed dose objectives have been met.

In an effort to expedite radiation delivery and shorten the duration of a treatment session, a radiation therapy system may have a continuously-moving patient platform as well as a continuously moving radiation source. For example, in helical tomotherapy, therapeutic radiation is delivered to the patient from a radiation source that rotates around the patient while the patient is continuously moving through the plane of the therapeutic beam. In this fashion, patient target regions can move through the treatment beam without pausing.

However, due to the continuous motion of the patient platform, it can be difficult to apply any radiation doses that are missed due to radiation therapy system failures (e.g., collimator malfunction, random magnetron arcs, etc.) or unexpected patient and/or target region motion, since the patient platform would have moved the target region past the treatment beam plane and the exact location of the target region with respect to the therapeutic radiation source may be difficult to precisely determine. This may cause insufficient dose to be delivered at certain target regions. In addition, target regions where increased dose levels are prescribed may not be able to get the full prescribed dose in the time duration in which that target region is within the treatment beam plane. Accordingly, improved methods of radiation delivery (and corresponding methods of treatment planning) are desirable.

BRIEF SUMMARY

Described herein are methods for beam station delivery of radiation treatment, where the patient platform is moved to a series of discrete patient platform locations and/or orientations that are determined during treatment planning, stopped at each of these locations and/or orientations while the radiation source rotates about the patient delivering radiation to the target regions that intersect the radiation beam plane or path, and then moving to the next location and/or orientation after the prescribed dose of radiation (e.g., in accordance with a calculated fluence map) for that location and/or orientation has been delivered to the patient. These discrete platform orientations and/or locations or steps (e.g., along the IEC-Y axis) where therapeutic radiation is delivered while the platform is stopped (i.e., not moving, static) may be called beam stations, and may be defined by the treatment planning system before the treatment session. Beam stations may be specified by coordinates in IEC-X, -Y, and -Z, and/or may be specified by the orientation of the patient platform (e.g., roll, yaw, and pitch of the patient platform). In some variations, the therapeutic radiation source may be mounted on a rotatable gantry, which may continuously move or rotate the therapeutic radiation source during the treatment session, even when the patient platform is stopped at a beam station. The therapeutic radiation source may rotate around or move about the patient platform one or more times while the platform is stopped at a beam station, e.g., two or more times. The gantry may be rotatable through 360° in a single direction (e.g., clockwise or counterclockwise direction) to deliver radiation from firing positions located 360° in-plane about the patient platform or may sweep about the patient platform in arcs of less than 360° in two directions (e.g., alternating between clockwise and counterclockwise directions to deliver radiation from firing positions located along the arcs). A treatment planning system may generate a desired dose distribution profile that corresponds to a prescribed dose of radiation for each target region, define a series of beam stations based on the geometry and location of the target region(s), generate one or more fluence maps for each of the beam stations using dose optimization methods, and may optionally segment the one or more fluence maps for each beam station into machine instructions (e.g., dynamic multi-leaf collimator or MLC leaf configurations, therapeutic radiation source or linac pulse parameters, etc.) for execution by the radiation therapy system during a treatment session.

Beam station radiation delivery may allow for “digital dose delivery”, since the radiation therapy system fires at predetermined or specified firing positions and/or patient platform positions and orientations. A fast-spinning gantry (e.g., rotating at about 15 RPM or more, about 50 RPM or more, about 60 RPM or more, about 70 RPM or more) may position the therapeutic radiation source at every firing position multiple times while the patient platform is stationary at a beam station. In such manner, radiation fluence or dose may be delivered in discrete dose quanta over multiple gantry revolutions. In addition, since the patient platform is stationary during radiation delivery, the dose can vary greatly from beam station to beam station (i.e., dose is highly modulated). For example, when the patient platform is at a first beam station, the therapeutic radiation source may deliver radiation over a single gantry revolution (e.g., short dwell time and/or deliver radiation during one of multiple revolutions while delivering little or no radiation during the other revolutions) and when moved to a second beam station, the therapeutic radiation source may deliver a much greater amount of radiation over multiple revolutions (e.g., long dwell time and/or deliver radiation during most or all of the multiple revolutions). Radiation therapy systems with fast-spinning gantries (e.g., rotating at about 15 RPM or more, about 50 RPM or more, about 60 RPM or more, about 70 RPM or more) may be able to deliver radiation over multiple gantry revolutions in a relatively short period of time (e.g., without significantly increasing the treatment time). This range of dose modulation is not available in most helical delivery systems that have constant and/or consistent platform motion, because the platform dwell time at any location along the longitudinal axis of the platform (i.e., IEC-Y axis) remains relatively constant. Sudden increases or decreases in platform speed may be jarring to a patient, and cause unnecessary discomfort, which may result in patient position shifts. Beam station delivery may also mitigate any dose delivery variations due to variations in patient platform motion or speed, since the platform is stationary during the dose delivery. This may help relax the specification (i.e., increase the tolerance) for the platform motion system, and remove platform motion as a factor that affects dose delivery. Beam station radiation delivery methods may also help facilitate gated radiation delivery using radiation therapy system comprising fast-spinning gantries (e.g., rotating at about 15 RPM or more, about 60 RPM or more, about 70 RPM or more) and/or gantries with a large rotational inertia in conjunction with an external breathing sensor.

One variation of a radiation therapy system may comprise a circular gantry rotatable about a longitudinal axis, a therapeutic radiation source mounted on the gantry, a patient platform movable to a plurality of beam stations at predetermined locations along the longitudinal axis, and a controller in communication with the gantry, the radiation source, and the patient platform. The controller may be configured to move the patient platform to a first beam station, stop the patient platform at the first beam station, activate the therapeutic radiation source to emit radiation fluence while the patient platform is at the first beam station, and deactivate the therapeutic radiation source while moving the patient platform from the first beam station to a second beam station. The controller may be configured to stop the patient platform at the second beam station, activate the therapeutic radiation source to emit radiation fluence while the patient platform is at the second beam station, and deactivate the therapeutic radiation source while moving the patient platform from the second beam station to a third beam station. The gantry may be configured to rotate at a speed of about 60 RPM. Some variations may further comprise an imaging system in communication with the controller and configured to acquire imaging data. For example, the imaging system may be a PET imaging system comprising one or more PET detectors configured to detect lines-of-response (LORs) data, and/or a CT imaging system comprising one or more kV radiation detectors configured to acquire CT data. The imaging system may be mounted on the gantry. The controller may be configured to calculate the radiation fluence emitted at the first beam station by using imaging data acquired by the imaging system. In some variations, the controller may be configured to continuously monitor the radiation fluence emitted at the first beam station and to compare the emitted radiation fluence with a planned radiation fluence for the first beam station to calculate a remainder fluence. The controller may be configured to segment the remainder fluence into instructions for the therapeutic radiation source and a dynamic multi-leaf collimator (MLC) disposed in a beam path of the therapeutic radiation source, and to activate the therapeutic radiation source to emit the remainder fluence while the patient platform is stopped at the first beam station. Optionally, the controller may be configured to determine whether the remainder fluence is below a predetermined remainder fluence threshold, and if the remainder fluence is below the remainder fluence threshold, the controller may be configured to deactivate the therapeutic radiation source and move the patient platform to the second beam station. In some variations, the predetermined remainder fluence threshold is zero. The controller may be configured to calculate radiation fluence for emission at the second beam station using imaging data acquired before the therapeutic radiation source is moved to the second beam station. The radiation fluence for emission at the second beam station may be calculated using imaging data acquired while the patient platform was located at the first beam station. Alternatively or additionally, the controller may be configured to segment the radiation fluence for emission at the second beam station into instructions for the therapeutic radiation source and a dynamic multi-leaf collimator (MLC) before radiation is emitted by the therapeutic radiation source at the second beam station. The radiation fluence emitted at the second beam station may be compared to the calculated radiation fluence for emission at the second beam station, and if a difference between the emitted radiation fluence and the calculated radiation fluence is below a predetermined threshold, the controller is configured to move the patient platform from the second beam station to the third beam station.

In some variations, the system controller may be configured to sequentially move the patient platform to each of the plurality of beam stations more than once. For example, the controller may be configured to sequentially move the patient platform to each of the plurality of beam stations in a first direction along the longitudinal axis and to sequentially move the patient platform to each of the plurality of beam stations in a second direction that is opposite the first direction. The radiation fluence emitted at each of the plurality of beam stations while moving the patient platform in the first direction may be different from radiation fluence emitted at each of the plurality of beam stations while moving the patient platform in the second direction. In some variations, the radiation therapy system may further comprise a dynamic multi-leaf collimator (MLC) disposed in a beam path of the therapeutic radiation source, where a configuration of the MLC for the second beam station may be determined according to the calculated radiation fluence for emission at the second beam station. Alternatively or additionally, the controller may be configured to detect one or more malfunctions of one or more of the gantry, therapeutic radiation source, and/or the dynamic MLC during radiation fluence emission, calculate a quantity of radiation fluence that is undelivered because of the one or more detected malfunctions, segment the quantity of undelivered radiation fluence into instructions for the therapeutic radiation source and the dynamic MLC for irradiation, and to activate the therapeutic radiation source to emit the remainder fluence while the patient platform is stopped at the first beam station. The gantry may be configured to rotate at least twice around the patient platform while the patient platform is at each the beam station in the plurality of beam stations. In some variations, each gantry rotation is about 360° around the patient platform.

The controller may be configured to stop the patient platform at each beam station of the plurality of beam stations for a predetermined dwell time. For example, the predetermined dwell time may be from about 5 seconds to about 5 minutes. Alternatively or additionally, each beam station in the plurality of beam stations may be separated by a step distance from about 1 mm to about 2 cm (e.g., about 2.1 mm). The step distance between each beam station of the plurality of beam stations may be the same or different.

One method for calculating a fluence map for beam station radiation delivery may comprise determining a plurality of beam stations based on one or more patient target regions, calculating a set of candidate radiation beamlets for each beam station, and generating a fluence map for each beam station by calculating a set of beamlet weights corresponding to the set of candidate radiation beamlets for each beam station such that radiation dose delivered to the one or more target regions over all candidate radiation beamlets meets pre-determined dose constraints and treatment parameters. The plurality of beam stations may be evenly spaced apart from each other, and may have a beam station pitch or step distance between beam stations of about 2 mm. In some variations, the step distance between each of the beam stations may be variable, or the step distance between each of the beam stations and the number of beam stations in the set of beam station may be user-selected. The set of candidate radiation beamlets may comprise a matrix of multi-leaf collimator (MLC) configurations for each radiation firing position about the patient platform that defines a set of radiation beamlets that intersect the one or more patient target regions. Calculating set of beamlet weights may comprise calculating a dose calculation matrix that comprises the contribution of each candidate beamlet to the one or more target regions. Calculating a set of beamlet weights may comprise generating a penalty function that represents treatment plan quality metrics and using iterative optimization methods to calculate the set of beamlet weights that minimizes the penalty function. The method may also comprise quantizing the fluence map for each beam station to generate a quantized fluence map where each beamlet weight is an integer value of dose quanta deliverable by a movable therapeutic radiation source. In some variations, pre-determined dose constraints may comprise user-defined dose constraints, and/or user-defined dose objectives, and/or maximum dose levels, and/or dose coverage metrics. Treatment parameters may comprise treatment time duration and/or beam station dwell time. The fluence map for each beam station may comprise a l×f matrix, where l is a number of leaves in a multi-leaf collimator in a beam path of a therapeutic radiation source, and f is a number of therapeutic radiation source firing positions around the patient platform. The multi-leaf collimator may be a binary multi-leaf collimator having 64 leaves (e.g., l=64). In some variations, there may be 50 firing stations (e.g., f=50) and/or maybe 100 firing positions (e.g., f=100). In some variations, the method may comprise generating a plurality of fluence maps for each beam station. The plurality of beam stations comprises a plurality of discrete patient platform locations along a longitudinal axis of the patient platform (e.g., along IEC-Y).

One variation of a method for beam station radiation delivery may comprise moving a patient platform to a first beam station of a set of beam stations, delivering radiation to the patient target region in accordance with a first fluence map by moving a therapeutic radiation source about the patient platform while the platform is stationary at the first beam station, and comparing the delivered radiation with the first fluence map and calculating a fluence difference. If the fluence difference does not exceed a predetermined threshold, the method may comprise moving the patient platform to the second beam station of the set of beam stations. If the fluence difference meets or exceeds the predetermined threshold, the method may comprise delivering the fluence difference by continuing to move the therapeutic radiation source about the patient platform before moving the patient platform to the second beam station. The therapeutic radiation source may be mounted on a gantry that is continuously rotatable about the patient platform, and the method may further comprise rotating the gantry multiple revolutions about the patient platform while the patient platform is located at the first beam station. In some variations, the number of revolutions per beam station in the set of beam stations may be from about 5 to about 300, and may vary for each beam station in the set of beam stations, or may be constant for each beam station in the set of beam stations. The patient platform may not remain stationary at a beam station where fluence values of a fluence map for the beam station is zero. In some variations, delivering radiation to the patient target region in accordance with the first fluence map comprises segmenting the first fluence map into multi-leaf collimator configurations for each firing position about the patient platform, and adjusting a multi-leaf collimator disposed in a beam path of the therapeutic radiation source to the multi-leaf collimator configurations at each firing position. A method for beam station radiation delivery may further comprise storing in a memory of a controller a multi-leaf collimator configuration and a firing position for which radiation was not delivered, and moving the therapeutic radiation source to the firing position to re-deliver radiation. In some variations, an adjustable-opening jaw may be disposed in the beam path of the therapeutic radiation source, and delivering radiation may comprise adjusting a width of the jaw opening in accordance with the fluence map. The width of the jaw opening may vary for each beam station in the set of beam stations, or may be constant for each beam station in the set of beam stations. In some variations, the patient target region may move while the patient platform is located at the first beam station, and delivering radiation to the patient target region may comprise directing radiation to the patient target region if it is located within a predetermined treatment location and not directing radiation to the patient target region if it is located outside the predetermined treatment location.

Another variation of a method for beam station radiation delivery may comprise moving a patient platform to a first beam station of a set of beam stations, delivering radiation to the patient target region in accordance with predetermined treatment parameters by moving a therapeutic radiation source about the patient platform while the platform is stationary at the first beam station, and determining whether the delivered radiation complies with the predetermined treatment parameters. If the delivered radiation complies with the predetermined treatment parameters, the method may comprise moving the patient platform to a second beam station of the set of beam stations. If the delivered radiation does not comply with the predetermined treatment parameters, the method may comprise continuing to move the therapeutic radiation source about the patient platform before moving the patient platform to the second beam station. In some variations, the predetermined treatment parameters may comprise one or more dose metrics or one or more radiation delivery instructions. Examples of one or more radiation delivery instructions may comprise at least one of beam station dwell time, jaw opening width, number of therapeutic radiation source revolutions about the patient platform, therapeutic radiation pulse parameters, and/or MLC leaf configurations.

