Claims:[0051] CLAIMS

[0052] We claim

1. A radiotherapy apparatus comprising:
a) a primary collimator (101) for delimiting the thus produced electron beam to maximum field size, wherein shielding is provided in all areas outside the maximum field size;
b) a carousal assembly (102) to place the correct flattening filter (201) below the radiation beam wherein the carousal assembly contains plurality of filters that attenuates the beam of same energy based on the field size to be attained for underlying subject;
c) an ion chamber (103) for measuring the dose rate coming out of the flattening filter;
d) a secondary collimator for further reduction of beam that arises from primary collimator;
e) a Multileaf collimator (MLC) collimator to focus the beam coming out of secondary collimator on the underlying subject.
2. The method as claimed in claim 1, wherein said radiotherapy apparatus generates electron in mega volt energy.
3. The method as claimed in claim 1, wherein said primary collimator is made of tungsten.
4. The method as claimed in claim 1, wherein said carousal assembly is placed below the primary collimator such that it can be indexed depending on the filed size to be attained.
5. The method as claimed in claim 1, wherein said flattening filter generates beam with enhanced properties such as flatness, as said filter is specific to the filed size to be attained for underlying subject.
6. The method as claimed in claim 1, wherein said secondary collimator further reduces the maximum allowable field size from the primary collimator to the required rectangular field size.
7. The method as claimed in claim 1, wherein said MLC collimator further reduces the beam size from the secondary collimator to the required irregular shape for the underlying subject.
, Description:[0001] PREAMBLE TO THE DESCRIPTION
[0002] The following specification particularly describes the invention and the manner in which it is performed.
[0003] DESCRIPTION OF THE INVENTION
[0004] Technical field of the invention
[0005] The present invention generally relates to external radiation therapy. More particularly, the invention relates to a radiotherapy apparatus used in medical applications such as diagnosis and treatment of tumors.
[0006] Background of the invention
[0007] Cancer figures among the leading cause of morbidity and mortality worldwide. India is likely to have 17.3 lakh new cases and 8.8 lakh deaths due to cancer by 2020. It is reported that one in eight Indians is likely to develop cancer in their lifetime. The standard treatment for cancer continues to be radiation, surgery and chemotherapy. Toxicity, resistance, hospitalization, cost, pain and patient inconvenience continue to be challenges in effective anticancer therapy.

[0008] Radiation therapy has been an ever-expanding area of scientific endeavor, and has been a critical component of cancer treatment along with surgery and radiation therapy. Where chemotherapy was once accepted only as a means to extend survival time for those patients diagnosed as incurable by surgery and radiation therapy, it is now a recognized modality of treatment in nearly all of the more than two thousand variations of cancer.

[0009] The system used in external radiation therapy generally consists of an electron gun that accelerates electrons to relativistic speeds, an optional target onto which the electron beam is directed in order to produce an X-ray beam, and guidance apparatus to shape and direct the resulting electron or X-ray beam as required.

[0010] The guidance apparatus for a linear accelerator intended for medical use generally comprises a primary collimator, to limit the beam into a generally conical shape, one or more of a range of filters to adjust the distribution of those energies, and various secondary collimators such as block collimators and multi-leaf collimators. The primary collimator and any filters aim to create a uniform generic wide-aperture X-ray or electron beam, which is then shaped as required for a specific treatment by the secondary collimation.

[0011] The filters that are available for use in such apparatuses usually include sections of solid material (such as Nickel) which have an X-ray absorption spectrum corresponding to an energy which needs to be removed from the X-ray beam, flattening filters which have a varying thickness (or other property) across the field of the beam so as to alleviate irregularities in the beam intensity across that field, and (for electron beams) filters having a material and a thickness able to condition the beam and/ or preserve the vacuum within the linear accelerator.
[0012] At present such beam modification filters must be positioned between the primary collimator wheel and the secondary collimator device. They are usually placed in or on a rotating carousel, which is permitted to rotate freely in a manner that does not interfere with the collimator structure. However, a single flattening filter is used irrespective of the field size. Usually this is matched to the maximum field size possible by the product. When the beam is delivered to the lesser field sizes, the beam is passed through the filter whose attenuation is more and thus the dose rate gets degraded because of the additional attenuation.
[0013] The Patent Application No US 8853636 B2 titled “Linear accelerators” discloses a primary collimator for a radiotherapy apparatus that is made up of several layers, each comprising several apertures, and each layer being moveable so as to select a specific aperture to build up the primary collimator shape. In this way, the shape of the primary collimator can be tailored to the beam filters incorporated into the primary collimator assembly. This saves space in the radiation head whilst also allowing filters to be easily interchanged. However, a specific flattening filter depending on the field size is not used which provides beam of higher dose rate and lesser attenuation.
[0014] The Patent Application No US 8890100 B2 titled “Internally mounted collimators for stereotactic radiosurgery and stereotactic radiotherapy” discloses a beam filter positioning device that includes a first and a second axis operable to move a body supporting one or more collimators, one or more photon flattening filters, one or more electron foils, and field light mirror etc. The collimators may be configured to collimate radiation to define a treatment beam suitable for radiosurgery. A controller is programmed to control the servo motor of the first and second axes to accurately position the beam filters. Radiation apparatuses and systems incorporating the beam filter positioning device or assembly are also provided. However, it does not generate beam with a better beam property like flatness as the filters are specifically designed for a field size.
[0015] The Patent Application No US 3678233 A titled “Standardized set of compensating filters for mantle-field radiation therapy” discloses a set of compensating filters that is supported in a filter-holder interposed between the radiation source and the patient and includes a plurality of individual filter elements which are selectively combined to provide the various portions of the mantle-field of the patient with a predetermined, reproducible radiation dosage. However, there is no provision of automated carousal assembly that automatically gets indexed beneath the primary collimator depending on the required field size, so that appropriate flattening filter is employed which in turn provides high dose beam rate.
[0016] Hence looking at the problems that exist in the current state of the art, there is a need for a radiotherapy apparatus which is tailored as per the requirement so that the dose rate of the flattened beam is optimized based on the underlying subject.
[0017] Objective of the invention
[0018] A primary objective of the present invention is the provision of multiple flattening filters to generate radiation of high dose rate.
[0019] It is yet another object of the present invention is to provide a composition that is useful in the treatment of diabetes and weight management.

[0020] It is still another object of the present invention is to provide relative improvements in the dynamic range of the radiotherapy device available at present state of the art.

[0021] Summary of the invention

[0022] The following presents a simplified summary of the disclosure in order to provide a basic understanding to the reader. This summary is not an extensive overview of the disclosure and it does not identify key/critical elements of the invention or delineate the scope of the invention. Its sole purpose is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later.

[0023] The present invention overcomes the drawbacks in the prior art by providing a radiotherapy apparatus consisting of a primary collimator for delimiting the electron beam to maximum field size. Shielding is provided in all areas outside the maximum field size. A carousal assembly is placed beneath the radiation beam that contains multiple flattening filters. These filters assist in the attenuation of the beam of same energy based on the field size to be attained for the underlying subject. The dose rate coming out of the flattening filter is measured in an ion chamber which is placed beneath the carousal assembly. A secondary collimator and a Multileaf collimator are also present for further reduction of the flattened beam and for accurate focus of the beam on the underlying subject.
[0024] The radiotherapy apparatus generates electrons in mega volt energy. The primary collimator is made of tungsten as they can attenuate radiation in a small thickness of material. The carousal assembly is placed below the primary collimator such that it can be indexed depending on the field size to be attained. The flattening filter generates beam with enhanced properties such as flatness, as said filter is specific to the field size to be attained for underlying subject. The secondary collimator further reduces the maximum allowable field size from the primary collimator to the required rectangular field size. The MLC collimator further reduces the beam size from the secondary collimator to the required irregular shape for the underlying subject.
[0025] The present invention provides a radiotherapy apparatus that can generate beam with enhanced properties such as flatness and high dose rate as the flattening filters that are used in the apparatus are specifically designed for different field size as per the requirement.
[0026] Brief description of the drawings
[0027] The foregoing and other features of embodiments will become more apparent from the following detailed description of embodiments when read in conjunction with the accompanying drawings. In the drawings, like reference numerals refer to like elements.

[0028] Figure 1 illustrates the general layout of a typical known form of radiotherapy apparatus in accordance to one or more embodiment of the present invention.

[0029] Figure 2 illustrates a carousal assembly in accordance to one or more embodiment of the present invention.

[0030] Figure 3 illustrates a graph depicting dose rate of the beam for maximum field size in accordance to one or more embodiment of the present invention.

[0031] Figure 4 illustrates a graph depicting dose rate of the beam for a particular field size in accordance to one or more embodiment of the present invention.

[0032] Detailed description of the invention

[0033] Reference will now be made in detail to the description of the present subject matter, one or more examples of which are shown in figures. Each example is provided to explain the subject matter and not a limitation. Various changes and modifications obvious to one skilled in the art to which the invention pertains are deemed to be within the spirit, scope and contemplation of the invention.

[0034] In order to more clearly and concisely describe and point out the subject matter of the claimed invention, the following definitions are provided for specific terms, which are used in the following written description.

[0035] The term "Radiation therapy", means a radiotherapy, often abbreviated RT, RTx, or XRT, is therapy using ionizing radiation, generally as part of cancer treatment to control or kill malignant cells and normally delivered by an electronic gun, as the context requires.

[0036] The term "subject", means a patient lying beneath the radiotherapy device for diagnosis and treatment of tumors that emerges at any part of the body, as the context requires.

[0037] The term "Electron beam", means a stream of electrons in a gas or vacuum, as the context requires.

[0038] The term "Field size", means the size of tumor on which the radiation should fall, as the context requires.

[0039] The term "Attenuate” means a change in a beam of radiation as it passes through matter. The intensity of the electromagnetic radiation decreases as its depth of penetration increases, as the context requires.
[0040] The term "Collimator” means a device that narrows a beam of particles or waves. “To narrow” can mean either to cause the directions of motion to become more aligned in a specific direction (i.e., make collimated light or parallel rays), or to cause the spatial cross section of the beam to become smaller (beam limiting device) as the context requires.
[0041] The term "Dose rate” means the quantity of radiation absorbed per unit time, as the context requires.
[0042] The present invention overcomes the drawbacks of the existing state of the art technologies by providing a combination of flattening filters. As per the required filed size of the subject an appropriate filter is used that delivers radiation of higher dose rate.
[0043] Figure 1 illustrates the general layout of a typical known form of radiotherapy apparatus in accordance with one or more embodiments of the invention. An electron gun is enclosed in a tubular chamber which is used to generate electrons in mega volt energy, which when hit against a heavy metal target produces X-rays. The sharp X-ray beam produced by the electron gun cannot be directly used in all clinical applications, so the X-rays generated from the electron gun will be passed through a primary collimator (101). Primary collimator (101) acts like an aperture which defines the maximum field, the radiotherapy apparatus can deliver. Primary collimator (101) ensures that the shielding is provided in all the areas outside the maximum field size. Primary collimator (101) is usually made of heavy metals such as tungsten to attenuate radiation in a small thickness of material. The radiation exiting out of the primary collimator (101) is now passed on to flattening filter (201), placed in the carousal assembly. The flattening filter (201) will flatten the beam such that it can be used for clinical application depending on the subject. An ion chamber (103) is placed below the flattening filter to measure the dose rate coming out of the flattening filter (201). The flattened beam coming out of the flattening filter (201) will be passed through a secondary collimator where the maximum allowable field size from the primary collimator (101) is reduced to the required rectangular field size. The beam further passes through another collimator called Multileaf collimator (MLC), where the rectangular field is further reduced into irregular shapes to confine the shape of the subject.
[0044] Figure 2 illustrates a carousal assembly in accordance to one or more embodiment of the present invention. Beneath the primary collimator (101), there is a motorized carousel assembly (102) mounted on an axle and includes a plurality of flattening filter (201). The position of carousel assembly (102) is such that it can be indexed depending on the field size so that the flattening filter (201) exactly comes below the center of the beam.
[0045] Figure 3 illustrates a graph depicting dose rate of the beam for maximum field size in accordance to one or more embodiment of the present invention. As clearly seen, in the graph, if a single flattening filter of size 30 x 30 cm square is exposed to electronic beam of energy 6 MeV then irrespective of the field size the highest percentage dose rate that can be achieved is 40 %.
[0046] Figure 4 illustrates a graph depicting dose rate of the beam for a particular field size in accordance to one or more embodiment of the present invention. As clearly seen, in the graph, as the field size increases the flattened dose reduces. As shown in the graph at point A the flattened dose is 40 % of the total dose for a field size of 30 X 30 cm square. At point B the flattened dose is 55 % of the total dose for a field size of 20 X 20 cm square. At point C the flattened dose is 78 % of the total dose for a field size of 10 X 10 cm square
[0047] Having generally described this invention, a further understanding can be obtained by reference to certain specific examples, which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified.
[0048] Example 1: Monte Carlo study

[0049] Two Elekta Precise linear accelerators (Elekta Oncology Systems, Stockholm, Sweden) were modified to deliver flattening filter-free beams, one at St Luke’s Hospital in Dublin, Ireland (SLH) and one at the Medical University of Vienna, Austria (MUW). A 6-mm thick copper plate was inserted into one of the filter carousel ports inside the treatment head. The filter was provided by the linac manufacturer, but it is not necessary the type or thickness of filter that will be used in any possible future release of a flattening filter-free beam from Elekta. As a safety measure, the linac control system for the flattening filter-free beam was run on a separate removable hard drive, preventing it from being used clinically. Both accelerators were equipped with asymmetric jaws and an MLC consisting of 40 leaf pairs producing 1 cm wide fields at isocentre and allowing a maximum field size of 40x40 cm2 at the isocentre plane. In this Monte Carlo study, two photon beam energies, 6 MV and 10 MV, were investigated. The 6 MV beam was from the linac at SLH and the 10 MV beam from MUW. In FFF-mode the incident electron energy was kept the same as for the flattened beams. The 6 MV flattening filter was about 2.5 cm thick at the central axis and made of steel and the 10 MV filter was about 2.3 cm thick and made out of tungsten and aluminium. Depth dose and lateral profiles were measured using a PTW MP3 Water-Tank (PTW Freiburg, Germany) at SLH and an IBA Blue Phantom (IBA dosimetry Schwarzenbruck, Germany) at MUW. Depth dose profiles were measured with ionization chambers (PTW semiflex type 31010 at SLH and IBA CC13 at MUW) and lateral profiles using diodes (PTW type 60008 at SLH and IBA type SFD at MUW) (Kragl et al 2009).

[0050] It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only. Changes may be made in the details, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.