• Radiation Oncology Journal
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• v.7 no.1
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• pp.101-112
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• 1989

The treatment planning and dosimetry of small fields for stereotactic radiosurgery with 10 MV x-ray isocentrically mounted linear accelerator is presented. Special consideration in this study was given to the variation of absorbed dose with field size, the central axis percent depth doses and the combined moving beam dose distribution. The collimator scatter correction factors of small fields $(1\times1\~3\times3cm^2)$ were measured with ion chamber at a target chamber distance of 300cm where the projected fields were larger than the polystyrene buildup caps and it was calibrated with the tissue equivalent solid state detectors of small size (TLD, PLD, ESR and semiconductors). The central axis percent depth doses for $1\timesl\;and\;3\times3cm^2$ fields could be derived with the same acuracy by interpolating between measured values for larger fields and calculated zero area data, and it was also calibrated with semiconductor detectors. The agreement between experimental and calculated data was found to be under $2\%$ within the fields. The three dimensional dose planning of stereotactic focusing irradiation on small size tumor regions was performed with dose planning computer system (Therac 2300) and was verified with film dosimetry. The more the number of strips and the wider the angle of arc rotation, the larger were the dose delivered on tumor and the less the dose to surrounding the normal tissues. The circular cone, we designed, improves the alignment, minimizes the penumbra of the beam and formats ball shape of treatment area without stellate patterns. These dosimetric techniques can provide adequate physics background for stereotactic radiosurgery with small radiation fields and 10MV x-ray beam.

• Journal of the Korean Applied Science and Technology
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• v.15 no.4
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• pp.11-20
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• 1998

The propagation of light radiation in a turbid medium is an important problem that confronts dosimetry of therapeutic laser delivery and the development of diagnostic spectroscopy. Scattered light is measured as a function of the position(distance r, depth z) between the axis of the incident beam and the detection spot. Turbid sample yields a very forward-directed scattering pattern at short range of position from source to detector, whereas the thicker samples greatly attenuated the on-axis intensity at long range of position. The portions of scattered light reflected from or transmitted throughphantom depend upon internal reflectance and absorption properties of the phantom. Monte Carlo simulation method for modelling light transport in tissue is applied. It uses the photon is moved a distance where it may be scattered, absorbed, propagated, internally reflected, or transmitted out of tissue. The photon is repeatedly moved until it either escape from or is absorbed by the phantom. In order to obtain an optimum therapeutic ratio in phantom material, optimum control the light energy fluence rate is essential. This study is to discuss the physical mechanisms determining the actual light dose in phantom. Permitting a qualitative understanding of the measurements. It may also aid in designing the best model for laser medicine and application of medical engineering.

• Progress in Medical Physics
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• v.10 no.1
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• pp.1-7
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• 1999

In this study, the dose distributions of a $^{32}$ p uniform cylindrical volume source and a surface source, a pure $\beta$emitter, were calculated in order to obtain information relevant to the utilization of a balloon catheter and a radioactive stent. The dose distributions of $^{32}$ p were calculated by means of the EGS4 code system. The sources are considered to be distributed uniformly in the volume and on the surface in the form of a cylinder with a radius of 1.5 mm and length of 20 mm. The energy of $\beta$particles emitted is chosen at random in the $\beta$ energy spectrum evaluated by the solution of the Dirac equation for the Coulomb potential. Liquid water is used to simulate the particle transport in the human body. The dose rates in a target at a 0.5mm radial distance from the surface of cylindrical volume and surface source are 12.133 cGy/s per GBq (0.449 cGy/s per mCi, uncertainty: 1.51%) and 24.732 cGy/s per GBq (0.915 cGy/s per mCi, uncertainty: 1.01%), respectively. The dose rates in the two sources decrease with distance in both radial and axial direction. On the basis of the above results, the determined initial activities were 29.69 mCi and 1.2278 $\mu$Ci for the balloon catheter and the radioactive stent using $^{32}$ P isotope, respectively. The total absorbed dose for optimal therapeutic regimen is considered to be 20 Gy and the treatment time in the case of the balloon catheter is less than 3 min. Absorbed doses in targets placed in a radial direction for the two sources were also calculated when it expressed initial activity in a 1 mCi/ml volume activity density for the cylindrical volume source and a 0.1 mCi/cm$^2$ area activity density for the surface source. The absorbed dose distribution around the $^{32}$ P cylindrical source with different size can be easily calculated using our results when the volume activity density and area activity density for the source are known.

• Journal of radiological science and technology
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• v.40 no.4
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• pp.621-626
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• 2017

In this paper, an optical dosimetric system for radiation dose measurement is developed and characterized for 100 MeV proton beams in KOMAC(Korea Multi-Purpose Accelerator Complex). The system consists of 10 wt% Ultima GoldTM liquid organic scintillator in the ethanol, a camera lens(50 mm / f1.8), and a high sensitivity CMOS(complementary metal-oxide-semiconductor) camera (ASI120MM, ZWO Co.). The FOV(field of view) of the system is designed to be 150 mm at a distance of 2 m. This system showed sufficient linearity in the range of 1~40 Gy for the 100 MeV proton beams in KOMAC. We also successfully got the percentage depth dose and the isodose curves of the 100 MeV proton beams from the captured images. Because the solvent is not a human tissue equivalent material, we can not directly measure the absorbed dose of the human body. Through this study, we have established the optical dosimetric procedure and propose a new volume dose assessment method.

• The Journal of the Korea Contents Association
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• v.14 no.8
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• pp.225-232
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• 2014

Underwent on modified radical mastectomy(MRM) and radiation therapy, it affects increasing rates of chronic morbidity, because of including chest wall and internal mammary nodes(IMNs). It causes the high absorbed dose on heart and ipsilateral lung. Thus in this study, we compared dose distributions through utilizing the intensity modulated radiation therapy(IMRT) and the volumetric modulated arc therapy(VMAT). We selected 10 breast cancer patients at random who took MRM and radiation therapy. Treatment plannings were done by using IMRT and VMAT from each patient ranging supraclavicular lymphnodes(SCL) and IMNs. After that we analysed the planning target volume(PTV)'s conformity and absorbed doses on heart and lungs. As a results, PTV conformities were indicated the same patten(p<0.05) in both plans. In case of Lt breast cancer patients, the dose maximum regions of the heart were more lesser in VMAT technique rather than the IMRT(p<0.05). Also, the maximum dose areas of lungs were lesser in VMAT technique rather than the IMRT(p<0.05). Therefore, it would be safe to say that it is more effective way to adapt the VMAT technique than IMRT in such cases like involve IMNs in breast cancer patients.

• Nuclear Engineering and Technology
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• v.2 no.2
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• pp.85-95
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• 1970

An attempt has been made to do interpretation of the fast neutron dose with two threshold detectors incorporated with the Harwell criticality locket. This method is based on the assumption that the spectral distribution of fission neutrons in criticality accidents may be governed by one spectral parameter. The surface-absorbed dose for a unit fission neutron fluence seems to be insensitive to spectral shifts of the fission neutron spectrum. The average cross-sections for the activation detectors, however, are considerably changed with the neutron spectral shape, which may lead to a large error in calculating the dose from the reaction rate if one uses a fixed value for the average cross sections regardless of the neutron spectral distribution. Besides, the doses calculated from three representative formulae for fission neutron spectra have been compared : these formulae are Watt, Cranberg at al. and Maxwellian forms. The results obtained front the Maxwellian formula show a departure from the Watt and Cranberg's, both being similarly close.

• Journal of the Korean Society of Industry Convergence
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• v.21 no.6
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• pp.337-344
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• 2018

Food irradiation is important not only in ensuring safety but also improving antioxidant activity of peaches. Our objective was to establish the best irradiation treatment for peaches by calculating dose distribution using Monte Carlo simulation. 3-D geometry and component densities of peaches, extracted from CT scan, were entered into MCNP to obtain simulated dose distribution. Radiation energies for electron beam were 1.35 MeV (low energy) and 10 MeV (high energy). Co (1.25 MeV) and the Husman irradiator, containing three sealed Cs source rods in an annular array, were used for gamma irradiation. At 1.35 MeV electron beam simulation, electrons penetrated well beyond the peach skin, enough for surface treatment for microorganisms and allergens. At 10 MeV electron beam simulation, for top-beam only treatment, doses at the core were the highest and for double beam treatment, the electron energy was absorbed by the entire sample. At Co source, the radiation doses were presented on the whole area. At Cs source, the dose uniformity ratios were 2.78 for one source and 1.48 for three ones at 120 degrees interval. Proper control of irradiation treatment is critical to establish confidence in the irradiation process.

• Journal of the Korean Society of Radiology
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• v.18 no.1
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• pp.1-9
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• 2024

Proton therapy is known for its superior treatment method due to Bragg peak. To enhance the therapeutic effects of protons, research has been conducted on distributing gold nanoparticles within tumors to increase the absorbed dose. While previous studies focused on handling gold nanoparticles at micrometer and nonometer scale, this study proposes a method to computationally estimate the effect of gold nanoparticles at the millimeter scale. The Geant4 toolkit was applied to computational modeling. Assuming a uniform distribution of water, similar to the human body, and gold nanoparticles, the concentration of gold nanoparticles was adjusted using density ratios. When the density ratio was 5%, the gain in absorbed energy due to gold nanoparticles was nearly twice that of the pure water phantom at the Bragg peak. As the density ratio increased, the gain in absorbed energy linearly increased. When gold nanoparticles were distributed in only one voxel at the Bragg peak, the energy of the protons affected only the neighboring voxels. However, in cases where gold nanoparticles were distributed over a wide area, the volume showing 95% of the maximum absorbed energy (9.46 keV) for the pure water phantom (9.95 keV) exhibited an improvement in absorbed energy over a region 16 times larger, and this region increased as the density ratio increased. Further research is needed to quantify the relationship between the density ratio of gold nanoparticles and the relative biological effect (RBE) in the millimeter scale.

• Radiation Oncology Journal
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• v.19 no.1
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• pp.66-73
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• 2001

Purpose : For the research of Boron Neutron Capture Therapy (BNCT), fast neutrons generated from the MC-50 cyclotron with maximum energy of 34.4 MeV in Korea Cancer Center Hospital were moderated by 70 cm paraffin and then the dose characteristics were investigated. Using these results, we hope to establish the protocol about dose measurement of epi-thermal neutron, to make a basis of dose characteristic of epi-thermal neutron emitted from nuclear reactor, and to find feasibility about accelerator-based BNCT. Method and Materials : For measuring the absorbed dose and dose distribution of fast neutron beams, we used Unidos 10005 (PTW, Germany) electrometer and IC-17 (Far West, USA), IC-18, ElC-1 ion chambers manufactured by A-150 plastic and used IC-l7M ion chamber manufactured by magnesium for gamma dose. There chambers were flushed with tissue equivalent gas and argon gas and then the flow rate was S co per minute. Using Monte Carlo N-Particle (MCNP) code, transport program in mixed field with neutron, photon, electron, two dimensional dose and energy fluence distribution was calculated and there results were compared with measured results. Results : The absorbed dose of fast neutron beams was $6.47\times10^{-3}$ cGy per 1 MU at the 4 cm depth of the water phantom, which is assumed to be effective depth for BNCT. The magnitude of gamma contamination intermingled with fast neutron beams was $65.2{\pm}0.9\%$ at the same depth. In the dose distribution according to the depth of water, the neutron dose decreased linearly and the gamma dose decreased exponentially as the depth was deepened. The factor expressed energy level, $D_{20}/D_{10}$, of the total dose was 0.718. Conclusion : Through the direct measurement using the two ion chambers, which is made different wall materials, and computer calculation of isodose distribution using MCNP simulation method, we have found the dose characteristics of low fluence fast neutron beams. If the power supply and the target material, which generate high voltage and current, will be developed and gamma contamination was reduced by lead or bismuth, we think, it may be possible to accelerator-based BNCT.

• Progress in Medical Physics
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• v.20 no.2
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• pp.88-96
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• 2009

Radiation treatment for skin cancer has recently increased in tomotherapy. It was reported that required dose could be delivered with homogeneous dose distribution to the target without field matching using electron and photon beam. Therapeutic beam of tomotherapy, however, has several different physical characteristic and irradiation of helical beam is involved in the mechanically dynamic factors. Thus verification of skin dose is requisite using independent tools with additional verification method. Modified phantom for dose measurement was developed and skin dose verification was performed using inserted thermoluminescent dosimeters (TLDs) and GafChromic EBT films. As the homogeneous dose was delivered to the region including surface and 6 mm depth, measured dose using films showed about average 2% lower dose than calculated one in treatment planning system. Region indicating about 14% higher and lower absorbed dose was verified on measured dose distribution. Uniformity of dose distribution on films decreased as compared with that of calculated results. Dose variation affected by inhomogeneous material, Teflon, little showed. In regard to the measured dose and its distribution in tomotherapy, verification of skin dose through measurement is required before the radiation treatment for the target located at the curved surface or superficial depth.