Research On The Minimum Anode Spacing Of Double-anode Target X Ray Tube

Research Background:Since the start of radiation therapy in the last century,it has become one of the most important means of treating tumors.As we all know,there are many inevitable uncertainties in the process of formulating radiotherapy plans and performing radiotherapy.People have realized the impact of these uncertainties on the efficacy of radiotherapy and have made a series of explorations of precise radiotherapy.Radiotherapy has also evolved from traditional 2D radiation therapy to 3D conformal radiation therapy(3D-CRT),intensity-modulated radiation therapy(IMRT),volumetric modulated arc therapy(VMAT)and now emerging image-guided radiation therapy(IGRT).With the advancement of radiotherapy technology,radiotherapy has become more and more precise and effective,and side reactions have become lighter and lighter.Image-guided radiotherapy(IGRT)is a four-dimensional radiotherapy technique.It adds the concept of time sequence on the basis of 3D radiotherapy,and image-guided radiotherapy fully considers the displacement error in inter-fraction(and the movement of anatomical tissues during treatment,the intra-fraction patient position).At present,there are a variety of image guidance methods for implementing IGRT.The most common are skin marking-3D laser light near infrared tracking technology and implanted gold markers’ KV-X ray to achieve positioning or real-time guidance.Each of these devices has certain limitations.The newly proposed radiotherapy tube with dual-target anode generating double cone beam X-ray can solve some of the limitations of the existing IGRT equipment.The minimum target spacing of this double-anode target X-ray tube has not been explored.Research purpose:To investigate the minimum target spacing of this double-anode target X-ray tube and explores it’s viability in performing real-time tracking with pre-implanted gold fiducial markers using an in-house developed custom algorithm.Research method:the Alderson RANDO Pelvic phantom with three implanted fiducial markers is positioned on the in-house made support frame.At first,CBCT imaging of the phantom was carried on linear accelerator to gain the markers’ 3D coordinates as reference.To find the minimum spacing between two anode targets of a double-anode-target X-ray tube,the phantom was manually driven longitudinally to two different positions equidistant from the reference point.An image was acquired at each symmetry position.The distance interval between the two imaging positions were arranged from 2 mm to 12 mm symmetry to position.Images were taken in increments of half-interval from position.After acquiring the KV-X ray’s images of the phantom,overlap each set of two projections and extract the 2D coordinates of the gold markers from superimposed images.Then the algorithm proposed in this paper is used to back-project the 2D coordinates back to the simulated dual target X-ray tube to reconstruct the 3D coordinates.The deviation of each set of coordinate values from the reference coordinates were calculated to estimate the accuracy of the algorithm.Research result:When the phantom is located in a symmetrical position with a spacing of2～12mm,it is equivalent to dual-beam parallel X-ray imaging of a double-target X-ray tube with a target spacing of 2～12mm.At this time,when the position of the phantom is 6mm or less,the 2D coordinates of the gold marker cannot be successfully detected from the superimposed projection image.Therefore,the 3D position of the gold marker cannot be reconstructed.Only when the phantom is at a symmetrical position of 7mm or more,the 2D coordinates of the gold marker can be detected.At this time,the detection accuracy of the 3D coordinates can reach((±0.3711 mm,±0.2666 mm,±0.2942 mm).The time required for the successful reconstruction of the coordinates of a gold marker is no more than 1S,which meets the requirements of real-time tracking in the clinic.Conclusion:a single kV exposure from a double-anode-target X-ray tube with a target spacing of 7mm or more should be able to accurately identify gold markers’ 3D coordinates during treatment.The real-time tracking of the gold marker based on the dual target X-ray tube can be achieved.