Patent ID: 12251581

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment of the present invention, two subcomponents comprise an electron collimator assembly. The first component, ‘upstream’ of the second component, houses a radiation monitoring device. The second component is a collimation cone, which manually attaches below the monitor component. The design is made such that any of several collimation cones can attach to the monitor component. The range of collimation cones would cover the expected useable radiation field diameters. The collimation cones are circular geometries, similar to x-ray stereotactic cones. Other embodiments can include other non-circular geometries. The cones would be fully enclosed on their sides, allowing for maximum collimation per physical length. In this way, the collimator can be kept short, allowing for the patient to be located closer to the linac gantry head (electron source), thereby taking advantage of higher dose rates available at short source-to-target distances.

The electron collimator design is made such that the entire unit can be manually attached or detached from the linac gantry head. It can be installed when needed for electron FLASH treatments and removed for conventional mode treatments. It is noted that the proposed electron FLASH collimator could be used with conventional electron treatments, possibly offering improved radiation field penumbra and ergonomic advantages of smaller size and lighter weight. The geometric design and material composition allows for minimal radiation leakage outside the intended treatment area, minimal x-ray contamination, and lower weight than conventional electron applicators.

Different types of radiation monitor/dosimetry devices can be implemented. Some examples include: 1) a toroid, 2) a transmission foil, and 3) a capacitive-coupled detector. The toroid, a type of electric transformer, detects the accelerator electron beam passing through its hollow center. The transmission foil, which stretches across the collimator aperture, detects the accelerator electron beam passing through it. The capacitive-coupled detector is a multi-segmented device that senses the proximity of the accelerator beam to the sides of the collimator aperture.

Whereas known electron FLASH applicators in use today are typically not designed to support a beam monitoring device within its assembly, it has been discovered that having an independent, secondary detector is highly advantageous and required. This is because the standard ion chamber present in the linear accelerator may experience high ion recombination, resulting in a non-linear response with respect to dose per pulse. Hence, having the independent, secondary real-time dosimeter to monitor the dose addresses this issue.

In one embodiment, custom ‘cut-outs’ can be manually installed at the distal end of the cone component, to shape the radiation field to the treatment area. For low energy electron FLASH beams, it is possible and advantageous to make the cut-outs out of the same high density plastic used for the cones. The plastic cut-outs reduces x-ray contamination, and also advantageously allows for 3-D printing, additive manufacture, or easy machining of the cut-out.

FIG.1shows a planar view that illustrates an example of an electron applicator100in accordance with the present invention.FIG.2shows a cross-sectional view taken along line2-2ofFIG.1. As described in greater detail below, electron applicator100includes an integrated dosimeter for accurately measuring FLASH radiation levels, and an interchangeable high-density polymer cutout which can be easily, inexpensively, and accurately formed to match the irregular shape of a tumor.

As shown inFIGS.1and2, electron applicator100includes a collimating body110that has a proximate end112and a distal end114. Collimating body110also has an opening116that extends through collimating body110from the proximate end112to the distal end114. Opening116is preferably round, but can alternately be other shapes such as square or hexagonal. Opening116has a diameter D with a range of sizes, such as 1 cm to 10 cm, and a length L.

The minimum size of diameter D is determined by the size of the tumor as the diameter D must preferably be at least as large as the largest feature of the tumor from a particular view. The maximum size of diameter D is determined by the maximum amount of scattering that can be tolerated as wider openings tend to produce more scattering.

Collimating body110is fully enclosed on the sides to allow for maximum collimation per physical length. In this way, collimating body110can be kept short, allowing for a patient to be located closer to the gantry head (electron source) of a linear accelerator, thereby taking advantage of higher dose rates. The thickness of the material surrounding opening116is determined by the level of radiation leakage that is acceptable.

In the present embodiment, collimating body110is fabricated from a high-density polymer, such as polyethylene, but can alternately be fabricated in a conventional manner. Commercial electron applicators are made of metal which provide good radiation shielding, but also generate unwanted x-rays. Scattered electrons in a metal collimator interact with the metal in the collimator and generate unwanted x-rays. Thus, one advantage of a high-density polymer collimator over a conventional metal collimator is that x-ray contamination is substantially reduced.

Another advantage of a high-density polymer collimating body110is that it can be easily, inexpensively, and accurately formed by machining a block of the material. Alternately, molds can be used to form collimating body110. In some embodiments the collimating body may be produced by additive manufacturing or 3D printing.

As further shown inFIGS.1and2, electron applicator100also includes a dosimeter120that is coupled to the proximate end112of collimating body110. Dosimeter120includes a radiation detector122that is coupled to collimating body110, and a processing circuit124that is coupled to radiation detector122to process signals S from radiation detector122and generate a dose reading. In other embodiments, the signal processing circuitry could be remotely located, such as in the gantry. In those embodiments, the electron applicator would provide an interconnect to deliver the signal to the remote processing circuitry.

In the present embodiment, radiation detector122is implemented with a toroidal transformer122T where the central axis of toroidal transformer122T and opening116are aligned. In operation, a radiotherapy linear accelerator outputs a collimated electron beam as shown by arrow A inFIG.2. The collimated electron beam passes through the center area of radiation detector122where the flow of electrons generates an electric signal that is measured by radiation detector122.

Any of the radiation detector devices that would be incorporated into the electron applicator would respond in a stable, consistent, and calibratable manner to changes in the accelerator beam current. A change in the accelerator beam current (arrow A inFIG.2) would result in a corresponding change in the dose per pulse or dose rate (for many pulses). The change in beam current would induce a change in the electrical output signal of the detector. This signal would be processed by the associated circuitry and produce a change in the dose reading, a dose servo response (if servo capability was deployed), and/or assert an interlock if the signal threshold was exceeded. The dosimeter120can be deployed as a dose servo mechanism. The dosimeter120can be deployed as a safety interlock to limit the accelerator beam current to within an acceptable range. Three such embodiments of radiation detector 429122, but not limited to these alone, would deploy either a toroid, a thin transmission foil, or a capacitively-coupled detector. The basic principles of these detectors were explained above. The detectors may be either customized designs or commercially available devices. For example, commercial toroidal-based dosimeters are available.

As additionally shown inFIGS.1and2, electron applicator100may further include a cutout130that is coupled to the distal end114of collimating body110. Cutout130includes an opening132that extends through cutout130, and is shaped to match the irregular shape of a tumor. Cutout130can be coupled to collimating body110in a conventional manner.

Cutout130is interchangeable with other cutouts such that one cutout can be removed and replaced with another cutout. The central axis of radiation detector122, opening116, and opening132are aligned. In operation, after the electron beam has passed through the center of radiation detector122, the beam passes through opening116in collimating body110, and then through opening132in cutout130into a tumor.

In the present embodiment, cutout130is fabricated from a high-density polymer, such as polyethylene, but can alternately be formed from other materials. High-density polymer cutout130has several advantages over the metal openings in conventional electron applicators including the significant reduction in the amount of x-ray contamination.

Further, cutout130and opening132can be easily, inexpensively, and accurately formed by obtaining a layer of high-density polymer, which is thinner than the layer used to form collimating body110, and then machining the layer of high-density polymer to form cutout130and opening132.

One of the advantages of the present invention is that a computer numerical control (CNC) router or similar device can be used to machine opening132in a thin layer of high-density polymer to match the irregular shape of a tumor that is much more accurate than the opening that can be formed with an electron applicator that uses a multi-leaf collimator (MLC).

Further, the fabrication of opening132in a high-density polymer cutout is substantially easier and cheaper than the process for forming openings in a conventional metal electron applicator. Alternately, cutout130can be 3D printed, or formed from molds. The minimum thickness T of cutout130is defined by the minimum thickness required to block the electron beam from passing though the regions surrounding opening132which, in turn, is defined by the energy of the electron beam.

As further shown inFIGS.1and2, in the present embodiment, electron applicator100also includes a housing140that holds collimating body110and radiation detector122. Housing140, which can be implemented in plastic, also facilitates connecting radiation detector122to the gantry head of a radiotherapy linear accelerator, and cutout130to collimating body110.

Collimating body110is interchangeable with other collimating bodies such that housing140can accommodate different collimating bodies. For example, a collimating body110that has a diameter D of 10 cm can be removed from housing140and replaced with a collimating body110that has a diameter D of 4 cm without removing housing140from the linear accelerator. Thus, changing opening116from a first diameter D to a second diameter D is simple.

Similarly, housing140can accommodate different cutouts130. For example, a cutout130that has a first opening that substantially matches the irregular shape of a tumor can be removed from housing140and replaced with a cutout130that has a second opening that substantially matches the irregular shape of the tumor from a different angle.

Another of the advantages of the present invention is that electron applicator100, being largely made from plastic, is substantially lighter than conventional electron applicators. In addition, housing140is fabricated to easily attach to a linear accelerator. As a result, electron applicator100can be installed when needed for electron FLASH treatments, and removed for conventional mode treatments. A further advantage of the present invention is that dosimeter120provides a real-time, accurate measure of the dose.

The length L of opening116in collimating body110is defined by the treatment protocol. For example, conventional radiotherapy utilizes a 100 cm source-to-skin (SSD) measure, while FLASH radiotherapy works better with a shorter 70 cm (or less) SSD. Thus, the applicator-to-skin distance, thickness of cutout130, length L of collimating body110, thickness of radiation detector122, and thickness of housing140have a total thickness of approximately 70 cm or less.

Within the limits of the 70 cm protocol, a longer length L increases the flatness of the beam and also increases the intensity of the beam by reducing scatter and generating a more parallel beam. In addition, as the diameter D increases, the length L increases to provide the same beam quality. Further, reducing the distance between cutout130and the skin reduces the penumbra and provides a sharper falloff of the radiation field.

An alternative embodiment is shown inFIG.4wherein the electron collimator is mounted to the linear accelerator so as to be partially within the treatment head. This is enabled by retracting the linear accelerator's multileaf collimator leaves, and if desired, the primary collimating jaws. This embodiment allows for further reduction of the SSD.

FIG.3shows a block diagram that illustrates an example of a treatment system300in accordance with the present invention. As shown inFIG.3, treatment system300includes a linear accelerator310, an internal ion chamber312, and an internal collimation structure316. The electron applicator100attaches to the output end of the linear accelerator310(the output end is typically referred to as the gantry head). The accelerator310produces the high energy electron beam. After passing through a filter, the beam passes through the ion chamber312where the dose is measured. The beam is shielded and pre-collimated by collimator316. It then enters the electron applicator100per arrow A ofFIG.2. Within the applicator, the beam is monitored with a secondary dosimeter314and final shaping of the radiation field per cutout130

By utilizing the real-time dosimeter incorporated with interchangeable collimator for electron FLASH radiation therapy as described in the various embodiments above, tumors can be treated as follows. First, a high dose of FLASH radiation is generated. This high does FLASH radiation is collimated to form a beam of electrons. This beam of electrons is sent through an electron applicator. Within the electron applicator is a dosimeter that measures the dose in real-time. The electron applicator also shapes the beam to substantially match the shape of the tumor.

Reference has now been made in detail to the various embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. While described in conjunction with the various embodiments, it will be understood that these various embodiments are not intended to limit the present disclosure. On the contrary, the present disclosure is intended to cover alternatives, modifications and equivalents, which may be included within the scope of the present disclosure as construed according to the claims.

Furthermore, in the preceding detailed description of various embodiments of the present disclosure, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be recognized by one of ordinary skill in the art that the present disclosure may be practiced without these specific details or with equivalents thereof. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of various embodiments of the present disclosure.

The drawings showing various embodiments in accordance with the present disclosure are semi-diagrammatic and not to scale and, particularly, some of the dimensions are for the clarity of presentation and are shown exaggerated in the drawing Figures. Similarly, although the views in the drawings for the ease of description generally show similar orientations, this depiction in the Figures is arbitrary for the most part. Generally, the various embodiments in accordance with the present disclosure can be operated in any orientation.

The above embodiments are merely used for illustrating rather than limiting the technical solutions of the present invention. Although the present application is described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that the technical solutions recorded in the foregoing embodiments may still be modified or equivalent replacement may be made on part or all of the technical features therein. These modifications or replacements will not make the essence of the corresponding technical solutions be departed from the scope of the technical solutions in the embodiments of the present invention.