Greetings from the Director
  • Automatic patient position system
    • In radiotherapy, correction is essential for patient position. We developed real time automatic patient position correction system during the radiation therapy. It used two CCD cameras to correct image pattern matching for patient position (Fig. 1) It operate information obtained from between signal from 2D axis (x-y), z-axis CCD cameras and position and correction using its signal. Next, we designed prototype of 3D patient correction system hardware to control and run motion.(Fig. 2) We investigated motion pattern analyzing gating data that result from patient using Varian RPM Respiratory Gating System. To analyze statistical, we collect amplitude, phase and etc. from gating signal of clinical data.
  • Pencil beam dosimetry
    • We need to develop system to verify for radiotherapy dose of the next generation pencil beam technique in proton therapy. For this reason, we developed treatment dose methods for the pencil scanning mode in proton beam using the Cherenkov effect. We develop system of verification for proton dose distribution of high energy pencil beam scanning mode, because of analyzing characteristic of Cherenkov effect of therapeutic proton beam, measuring of pencil beam scanning mode using ionizing chamber, designing prototype to measure dose of 1d double scattering mode. And we investigated dose analysis and verification system for the pencil scanning mode in proton beam using the Monte-Carlo simulation because of simulation modeling using beam data library, analyzing and evaluating for proton pencil beam
  • Secondary neutron dose measurement
    • To compare possible neutron doses produced in scanning and scattering modes, with the latter assessed using a newly built passive-scattering proton beam line. A 40 x 30.5 x 30-cm water phantom was irradiated with 230-MeV proton beams using a gantry angle of 270 deg, a 10-cm-diameter snout, and a brass aperture with a diameter of 7 cm and a thickness of 6.5 cm. The secondary neutron doses during irradiation were measured at various points using CR-39 detectors, and these measurements were cross-checked using a neutron survey meter with a 22-cm range and a 5-cm spread-out Bragg peak. The maximum doses due to secondary neutrons produced by a scattering beam-delivery system were on the order of 0.152mSv/Gy and 1.17mSv/Gy at 50 cm from the beam isocenter in the longitudinal (0 deg) and perpendicular (90 deg) directions, respectively. The neutron dose equivalent to the proton absorbed dose, measured from 10 cm to 100 cm from the isocenter, ranged from 0.071mSv/Gy to 1.96mSv/Gy in the direction of the beam line (i.e., = 0 deg). The largest neutron dose, of 3.88mSv/Gy, was observed at 135 deg and 25 cm from the isocenter.
  • Eye movement tracking system
    • A new motion-based gated proton therapy for the treatment of orbital tumors using real-time eye-tracking system was designed and evaluated. We developed our system by image-pattern matching, using a normalized cross-correlation technique with LabVIEW 8.6 and Vision Assistant 8.6 (National Instruments, Austin, TX). The homemade software for our proton eye-tracking and beam-gating system consists of three components: (1) a calibration component that defines pixel spacing of the real-time images, (2) a reference component that creates a reference image, and (3) a treatment component that executes eye tracking and beam gating. To measure the pixel spacing of an image consistently, four different calibration modes such as the point-detection, the edge-detection, the line-measurement, and the manual measurement mode were suggested and used. After these methods were applied to proton therapy, gating was performed, and radiation dose distributions were evaluated.

      Moving phantom verification measurements resulted in errors of less than 0.1 mm for given ranges of translation. Dosimetric evaluation of the beam-gating system versus non-gated treatment delivery with a moving phantom shows that while there was only 0.83 mm growth in lateral penumbra for gated radiotherapy, there was 4.95 mm growth in lateral penumbra in case of non-gated exposure. The analysis from clinical results suggests that the average of eye movements depends distinctively on each patient by showing 0.44 mm, 0.45 mm, and 0.86 mm for three patients, respectively.
  • Gold Particle Polymer marker (GPPM)
    • To ensure we are hitting target tumor, we need to accurately visualize target. Fiducial markers are a trustworthy tool for tumor position verification. However, we have problems with conventional gold fiducial markers, such as dose distortion and metal artifact generation, in particle radiation therapy. To overcome these problems, we made the gold particle polymer markers(GPPMs) composed of microscopic(2~45m) gold particles and human-compatible polymers. (Fig. 1)

      The gold particles of 2~7.5% concentration with respect to the mass density of the conventional gold marker are mixed with bone cement, and molded so as to be implantable into human body. The GPPMs have good radiographic visibility and produce few CT artifacts in diagnostic X-rays. (Fig. 2) Moreover, our study shows that for the GPPM with the 4.9% normalized gold density, the maximum dose reduction is less than 5%, even when there is parallel alignment of the GPPM and a unidirectional proton beam. (Fig. 3) The GPPMs have excellent potential as fiducial markers for proton therapy of prostate cancer.

  • Applied Proton Range Compensator
    • Multi-Layer Assembled Proton Range Compensator
      To develop and evaluate a reusable proton range compensator which will reduce fabrication cost and time of the patient specific proton range compensator for CSI (Cranio-Spinal Irradiation). As a prototype, we have made a multi-layer assembled proton range compensator (MLAC) with a few tens of layers which are stacked zigzag, layer by layer. In each layer, the shape of the range compensator has been produced by a paired sliding multi leaves. This compensator was designed to fit in the 250 mm snout IBA nozzle and the main target is CSI and huge tumors.
      Each layer was manually configured to the corresponding compensator pattern designed by the proton treatment planning system (TPS).

      To evaluate the validity of the MLAC, we compared the dose distribution of the MLAC with that of the machine-milled patient specific compensator. The coincidence in the dose maps of two compensators (machine-milled patient specific compensator and MLAC) has been evaluated by using the gamma index.
      According to the gamma analysis with the criteria of 3 % dose difference and 3 mm distance to agreement, the percentage of points passing the criteria for the selected patients is above 98 % for various depths. (Fig. 2)
      The feasibility of MLAC has been studied to replace the machine-milled patient specific compensator. The study shows that the MLAC has a few advantages of reducing fabrication cost and time for huge tumors including CSI, as well as good dosimetric agreement with the patient specific compensator.

      Dynamic Proton Range Compensator
      To develop and evaluate a reusable proton range compensator which will be able to form any shape of patient specific compensator automatically in real-time. We are testing several ideas to realize the dynamic proton range compensator.
  • In-vivo gel dosimetry

  • Monte Carlo modeling and simulation of a passive treatment proton beam using GEANT4
    • As the first phase of applying the Monte Carlo technique, specifically using the GEANT4 toolkit, to clinical patient support, we modeled and simulated the beam delivery system of the proton therapy facility installed at the National Cancer Center (NCC), Korea. Thanks to the properly designed architecture of the GEANT4 toolkit to extend its application area, modeling the elements of the beam delivery system and of their dynamic behaviors was efficiently implemented. The simulation was validated over a treatment range of passive scattering mode in a water phantom by estimating the initial beam energy and by applying this information to a simulated therapeutic proton beam (termed the spread-out Bragg peak), resulting in good correlations with the measurement data.

  • Monte Carlo modeling of uniform scanning beam using GEANT4
    • Our proton facility is equipped with uniform scanning (US) mode. The fundamental difference of this technology is using scanning magnets (SM) instead of second scatterer (SS) which was the key component to broaden the beam profile in the double scattering mode. Uniform scanning uses magnets to scan a broad beam across a treatment field. This method has advantages over the double scattering mode in minimizing the material that might shorten the beam range. Therefore, narrow and magnetically steered proton beam allows treatment of a larger tumor at deeper depth, and at the same time, achieve better radiation dose distribution in the patient, reducing unwanted secondary neutron radiation that extend far beyond the treatment field. The Monte Carlo modeling of uniform scanning mode is performed and we compared dose profile with measured data.

  • Proton beam dosimetry using plastic scintillator
    • An interesting issue in proton therapy is how to reduce the time needed for percent depth dose (PDD) measurement and how to prepare a two-dimensional dose measurement tool for a proton scanning beam. Currently, three-dimensional water phantom systems are used for range verification in the scattering beam mode of proton therapy. However, this approach is very slow and is in appropriate for use with a proton scanning beam. We have developed a simple and easy-to-handle range verification system that consists of a plastic scintillation plate, a PMMA (poly methyl methacrylate) phantom, a charge-coupled device camera, and a one-dimensional moving table. In the present study, the linearity of the signal with the dose, the background signal measurement and correction, and the influence of the ionization density on the signal were investigated using our new system. The measured yield depended linearly on the dose, and the dose range measurements had a spatial resolution of about 1 mm.

  • Proton radiography of proton range compensator
    • All patient specific range compensators (RCs) are customized for achieving distal dose conformity of target volume in passively scattered proton therapy. Compensators are milled precisely using a computerized machine. In proton therapy, precision of the compensator is critical and quality assurance (QA) is required to protect normal tissues and organs from radiation damage. This research aims to evaluate the manufacture precision of range compensator using proton radiography method.

  • Proton PBS (Pencil Beam Scanning) technique
    • Pencil Beam scanning is a method in which a proton beam spot is moved by magnetic scanning while the beam intensity is adapted simultaneously yielding finally to the desired dose distribution planned by treatment planning frame by frame (each frame corresponding to one energy selection). This method consists in directing lots of small pencil beam into the target in order to cover the 3D volume. We are installing an innovative pencil beam scanning method. The major advantage of the pencil beam scanning will be the flexibility in dose distribution shapes (figure (a)) in an optimum way, especially in the beam entry region (figure (b)).
      Major advantage of the PBS is that we do not need any patient specific device (aperture and range compensator) to conform the dose distribution to the target volume. Because of the small size of the pencil beam and the thanks to the accurate control of the beam position, those expensive devices are no more necessary. Moreover, inherently to the principle, lowest activation can be achieved since almost all protons end up in the patient.
      Using the PBS method, we are carrying out various innovative researches such as PBS dosimetry, quality assurance protocols, planning studies and IMPT (Intensity-Modulated Proton Therapy).
    Contact for proton therapy experiments
    : Dongho Shin, Ph.D. (, Senior Medical Physicist
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