Purpose
To perform the final quality assurance of our fluoroscopic‐based markerless tumor tracking for gated carbon‐ion pencil beam scanning (C‐PBS) radiotherapy using a rotating gantry system, we ...evaluated the geometrical accuracy and tumor tracking accuracy using a moving chest phantom with simulated respiration.
Methods
The positions of the dynamic flat panel detector (DFPD) and x‐ray tube are subject to changes due to gantry sag. To compensate for this, we generated a geometrical calibration table (gantry flex map) in 15° gantry angle steps by the bundle adjustment method. We evaluated five metrics: (a) Geometrical calibration was evaluated by calculating chest phantom positional error using 2D/3D registration software for each 5° step of the gantry angle. (b) Moving phantom displacement accuracy was measured (±10 mm in 1‐mm steps) with a laser sensor. (c) Tracking accuracy was evaluated with machine learning (ML) and multi‐template matching (MTM) algorithms, which used fluoroscopic images and digitally reconstructed radiographic (DRR) images as training data. The chest phantom was continuously moved ±10 mm in a sinusoidal path with a moving cycle of 4 s and respiration was simulated with ±5 mm expansion/contraction with a cycle of 2 s. This was performed with the gantry angle set at 0°, 45°, 120°, and 240°. (d) Four types of interlock function were evaluated: tumor velocity, DFPD image brightness variation, tracking anomaly detection, and tracking positional inconsistency in between the two corresponding rays. (e) Gate on/off latency, gating control system latency, and beam irradiation latency were measured using a laser sensor and an oscilloscope.
Results
By applying the gantry flex map, phantom positional accuracy was improved from 1.03 mm/0.33° to <0.45 mm/0.27° for all gantry angles. The moving phantom displacement error was 0.1 mm. Due to long computation time, the tracking accuracy achieved with ML was <0.49 mm (=95% confidence interval CI) for imaging rates of 15 and 7.5 fps; those at 30 fps were decreased to 1.84 mm (95% CI: 1.79 mm–1.92 mm). The tracking positional accuracy with MTM was <0.52 mm (=95% CI) for all gantry angles and imaging frame rates. The tumor velocity interlock signal delay time was 44.7 ms (=1.3 frame). DFPD image brightness interlock latency was 34 ms (=1.0 frame). The tracking positional error was improved from 2.27 ± 2.67 mm to 0.25 ± 0.24 mm by the tracking anomaly detection interlock function. Tracking positional inconsistency interlock signal was output within 5.0 ms. The gate on/off latency was <82.7 ± 7.6 ms. The gating control system latency was <3.1 ± 1.0 ms. The beam irradiation latency was <8.7 ± 1.2 ms.
Conclusions
Our markerless tracking system is now ready for clinical use. We hope to shorten the computation time needed by the ML algorithm at 30 fps in the future.
Positron camera for range verification of heavy-ion radiotherapy Iseki, Yasushi; Mizuno, Hideyuki; Futami, Yasuyuki ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2003, Letnik:
515, Številka:
3
Journal Article
Recenzirano
A positron camera, consisting of a pair of Anger-type scintillation detectors, has been developed to verify ranges by using positron emitter beams. Each detector head is equipped with a NaI(Tl) ...crystal (diameter: 600mm, thickness: 30mm) for high detection efficiency. To get a low counting rate for this application, the electric circuit was designed for flexibility in measurement and analysis by software. The energy and position were calibrated for high measurement accuracy. A spatial resolution of 8.6mm in FWHM within a ±50mm region (field of view) and a linear response of a 0.3mm standard deviation within a ±200mm region were obtained. The camera was designed so as to measure the ranges within an accuracy of 1mm under a dose limitation (about 100mGyE) to reduce the safety margin for the irradiation field, and it met the required characteristics.
It is desirable to reduce range ambiguities in treatment planning for making full use of the major advantage of heavy-ion radiotherapy, that is, good dose localization. A range verification system ...using positron emitting beams has been developed to verify the ranges in patients directly. The performance of the system was evaluated in beam experiments to confirm the designed properties. It was shown that a 10C beam could be used as a probing beam for range verification when measuring beam properties. Parametric measurements indicated the beam size and the momentum acceptance and the target volume did not influence range verification significantly. It was found that the range could be measured within an analysis uncertainty of +/-0.3 mm under the condition of 2.7 x 10(5) particle irradiation, corresponding to a peak dose of 96 mGyE (gray-equivalent dose), in a 150 mm diameter spherical polymethyl methacrylate phantom which simulated a human head.
Washout of 10C and 11C implanted by radioactive beams in brain and thigh muscle of rabbits was studied. The biological washout effect in a living body is important in the range verification system or ...three-dimensional volume imaging in heavy ion therapy. Positron emitter beams were implanted in the rabbit and the annihilation gamma-rays were measured by an in situ positron camera which consisted of a pair of scintillation cameras set on either side of the target. The ROI (region of interest) was set as a two-dimensional position distribution and the time-activity curve of the ROI was measured. Experiments were done under two conditions: live and dead. By comparing the two sets of measurement data, it was deduced that there are at least three components in the washout process. Time-activity curves of both brain and thigh muscle were clearly explained by the three-component model analysis. The three components ratios (and washout half-lives) were 35% (2.0 s), 30% (140 s) and 35% (10 191 s) for brain and 30% (10 s), 19% (195 s) and 52% (3175 s) for thigh muscle. The washout effect must be taken into account for the verification of treatment plans by means of positron camera measurements.
Research and development of an electrodynamic tether propulsion system for space debris removal has been started in the Institute of Space Technology and Aeronautics, Japan Aerospace Exploration ...Agency (JAXA). An experimental investigation of a carbon-nanotube field-emission cathode (FEC), which is suitable as an electron emitter in this propulsion system, was conducted in this study. One of the important issues in the design of a FEC is to suppress an electron flow to a gate electrode to avoid thermal deformation of the electrode and to reduce power loss. For meeting this requirement, we designed an FEC device having a masking plate on a cathode surface. A numerical simulation indicated that presence of the masking plate distorts the electric field adjacent to the cathode surface and a converged electron beam that does not impinge on the gate electrode is formed. Several FEC devices were fabricated based on the simulation results, and they were tested experimentally. Results showed that no electron current flowed to the gate electrode when all the electrodes were assembled and aligned correctly.
The positron camera system has been designed to measure heavy-ion ranges in patients' bodies. The pencil-like beam of positron emitters, such as /sup 11/C, is used to check the range directly and ...precisely by detecting pairs of annihilation gamma-rays emitted from the end point of the beam trajectory. The positron camera consists of a pair of Anger-type scintillation cameras. The efficiency and the spatial resolution are modeled and simulated by a Monte Carlo method and a numerical calculation so that the positron camera has a high position accuracy for a small amount of irradiation dose. The simulation shows that the optimum effective diameter of the camera crystal is 500 mm and its thickness is 30 mm. The crystal diameter is concluded to be 600 mm by taking the outermost photomultiplier mounting into account. The simulation moreover, indicates that the range can be measured within an accuracy of 1 mm under the limitation that the irradiation dose has to be less than a few percent of the therapeutic one.
Interaction of ^11C in(CH)_n Maruyama, Koichi; Kanazawa, Mitsutaka; Kitagawa, Atsushi ...
Meeting Abstracts of the Physical Society of Japan,
2002/08/13
Journal Article
An advantage of heavy - ion therapy is its good dose concentration. A limit for full use of this desirable feature comes from range ambiguities in treatment planning. The treatment planning is based ...on X-ray CT measurements, and the range ambiguities are mainly due to an error in calibration of the CT number. The heavy - ion ranges are related to electron density of the medium while the CT numbers are defined using the X - ray attenuation coefficient. The range verific ation method using positron emitter beams has been developed to reduce the range ambiguities. In this verification, probing beams of positron emitters are implanted into the tumor, and pairs of annihilation gamma rays are detected with a positron camera. This paper demonstrates an application to verify P1treatment planning. P2 Here, the treatment planning was made on a head phantom and the ranges estimated from the CT-number were compared with the ranges measured with the positron camera. As a result, disagreements were detected between the planned ranges and the measured ones; these were 1.6mm at maximum. P3 The disagreements were due to an error of transformation of CT - number to range forP4 the phantom material in the water-column depth - dose measurement. The disagreements could be lowered to 0.4mm by using the calibrated water - equivalent lengths. It was confirmed that the range verification system has a designed measurement accuracy of 1 mm and is useful for verifying irradiation fields on heavy - ion radiotherapy.
