• Radiation Oncology Journal
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• v.20 no.3
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• pp.264-273
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• 2002

Purpose : Three-dimensional radiation dosimetry using magnetic resonance imaging of polymer gel was recently introduced. This dosimetry system is based on radiation induced chain polymerization of acrylic monomers in a muscle equivalent gel and provide accurate 3 dimensional dose distribution. We planned this study to evaluate the clinical value of this 3-dimensional dosimetry. Materials and Methods: The polymer gel poured into a cylindrical glass flask and a spherical glass flask. The cylindrical test tubes were for dose response evaluation and the spherical flasks, which is comparable to the human head, were for isodose curves. T2 maps from MR images were calculated using software, IDL. Dose distributions have been displayed for dosimetry. The same spherical flask of gel and the same irradiation technique was used for film and TLD dosimetry and compared with each other. Results : The R2 of the gel respond linearly with radiation doses in the range of 2 to 15 Gy. The repeated dosimetry of spherical gel showed the same isodose curves. These isodose curves were identical to dose distributions from treatment planning system especially high dose range. In addition, the gel dosimetry system showed comparable or superior results with the film and TLD dosimetry. Conclusion : The 3-dimensional dosimetry for conformal radiation therapy using MRI of polymer gal showed stable and accurate results. Although more studies are needed for convenient clinical application, it appears to be a useful tool for conformal radiation therapy.

• Progress in Medical Physics
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• v.9 no.4
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• pp.247-257
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• 1998

For effective radiotherapy, it should always be considered that calculation of different dose distribution in heterogenous tissue is important particularly on lung which has low density and large volume. To take precise dose distribution of 6MV X-ray in the thoracic cage, the authors had made a tissue equivalent phantom for thorax, measured dose distribution by thermoluminescent dosimeter and mm dosimeter, and derived methmetical equation coincided with provided theoretical formula. In comparision with isodose curve on case of homogeneous soft tissue, dose of heterogeneous lung tissue had been shown increase about 4% per cm depth on one and multiportal field, less than 15% difference on rotation field for esophagus, and around 20% difference on rotation field for lung according to the degree of rotation angle that must be corrected by dose compensation.

• Progress in Medical Physics
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• v.23 no.4
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• pp.269-278
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• 2012

Aquaplast Thermoplastic (AT) is a tissue-equivalent oral compensator that has been developed to improve dose uniformity at the common boundary and around the treated area during radiotherapy in patients with head and neck cancer. In order to assess the usefulness of AT, the degree of improvement in dose distribution and physical properties were compared to those of oral compensators made using paraffin, alginate, and putty, which are materials conventionally used in dental imprinting. To assess the physical properties, strength evaluations (compression and drop evaluations) and natural deformation evaluations (volume change over time) were performed; a Gafchromic EBT2 film and a glass dosimeter inserted into a developed phantom for dose verification were used to measure the common boundary dose and the beam profile to assess the dose delivery. When the natural deformation of the oral compensators was assessed over a two-month period, alginate exhibited a maximum of 80% change in volume from moisture evaporation, while the remaining tissue-equivalent properties, including those of AT, showed a change in volume that was less than 3%. In a free-fall test at a height of 1.5 m (repeated 5 times as a strength evaluation), paraffin was easily damaged by the impact, but AT exhibited no damage from the fall. In compressive strength testing, AT was not destroyed even at 8 times the force needed for paraffin. In dose verification using a glass dosimeter, the results showed that in a single test, the tissue-equivalent (about 80 Hounsfield Units [HU]) AT delivered about 4.9% lower surface dose in terms of delivery of an output coefficient (monitor unit), which was 4% lower than putty and exhibited a value of about 1,000 HU or higher during a dose delivery of the same formulation. In addition, when the incident direction of the beam was used as a reference, the uniformity of the dose, as assessed from the beam profile at the boundary after passing through the oral compensators, was 11.41, 3.98, and 4.30 for air, AT, and putty, respectively. The AT oral compensator had a higher strength and lower probability of material transformation than the oral compensators conventionally used as a tissue-equivalent material, and a uniform dose distribution was successfully formed at the boundary and surrounding area including the mouth. It was also possible to deliver a uniformly formulated dose and reduce the skin dose delivery.

• The Journal of Korean Society for Radiation Therapy
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• v.21 no.1
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• pp.17-23
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• 2009

Purpose: In treating head and neck cancer, it is very important to irradiate uniform dose on the junction of the bilateral irradiation field of the upper head and neck and the anterior irradiation field of the lower neck. In order to improve dose distribution on the junction, this study attempted to correct non uniform dose resulting from under dose and over dose using the field-in-field technique in treating the anterior irradiation field of the lower neck and to apply the technique to the treatment of head and neck cancer through comparison with conventional treatment. Materials and Methods: In order to examine dose difference between the entry point and the exit point where beam diffusion happens in bilateral irradiation on the upper head and neck, we used an anthropomorphic phantom. Computer Tomography was applied to the anthropomorphic phantom, the dose of interest points was compared in radiation treatment planning, and it was corrected by calculating the dose ratio at the junction of the lower neck. Dose distribution on the junction of the irradiated field was determined by placing low-sensitivity film on the junction of the lower neck and measuring dose distribution on the conventional bilateral irradiation of the upper head and neck and on the anterior irradiation of the lower neck. In addition, using the field-in-field technique, which takes into account beam diffusion resulting from the bilateral irradiation of the upper head and neck, we measured difference in dose distribution on the junction in the anterior irradiation of the lower neck. In order to examine the dose at interest points on the junction, we compared and analyzed the change of dose at the interest points on the anthropomorphic phantom using a thermoluminescence dosimeter. Results: In case of dose sum with the bilateral irradiation of the upper head and neck when the field-in-field technique is applied to the junction of the lower neck in radiation treatment planning, The dose of under dose areas increased by 4.7~8.65%. The dose of over dose areas also decreased by 2.75~10.45%. Moreover, in the measurement using low-sensitivity film, the dose of under dose areas increased by 11.3%, and that of over dose areas decreased by 5.3%. In the measurement of interest point dose using a thermoluminescence dosimeter, the application of the field-in-field technique corrected under dose by minimum 7.5% and maximum 17.6%. Thus, with the technique, we could improve non.uniform dose distribution. Conclusion: By applying the field-in-field technique, which takes into account beam divergence in radiation treatment planning, we could reduce cold spots and hot spots through the correction of dose on the junction and, in particular, we could correct under dose at the entry point resulting from beam divergence. This study suggests that the clinical application of the field-in-field technique may reduce the risk of lymph node metastasis caused by under dose on the cervical lymph node.

• Progress in Medical Physics
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• v.15 no.3
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• pp.161-166
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• 2004

A simplistic quality assurance (QA) method was designed for a Linac built-in enhanced dynamic wedge (EDW), which can be utilized to make wedged beam distributions. For the purpose of implementing the EDW symmetry QA, a film dosimetry system, low speedy dosimetry film, film densitometer and 3D RTP system were used, and the films irradiated by means of a 60$^{\circ}$ Reversed wedge pair (REWP) method. The profiles were then analyzed in terms of their symmetries, including partial treatment, which is the case of stopping it abruptly during EDW irradiation, and the measured and calculated values compared using the Cad Plan Golden Segmented Treatment Table (Golden STT). The result of this experiment was in good agreement, within 1 %, of the 'reversed wedge pair counterbalance effect'. For the QA of the effective wedge factor (EWF), the authors measured EWFs in relation to the 10$^{\circ}$, 15$^{\circ}$, 20$^{\circ}$, 25$^{\circ}$, 30$^{\circ}$, 45$^{\circ}$ and 60$^{\circ}$ EDW, which were compared with the calculated values using the correction factor derived from the Golden STT and the log files produced automatically during the process of EDW irradiation. By means of this method it was capable of check up the safety of effective wedge factor without any other dosimetry system. The EDW QA was able to be completed within 1 hour from irradiation to analysis as a consequence of the simplified QA procedure, with maximized effectiveness. Unlike the metal wedge system, the EDW system was heavily dependent on the dose rates and jaw movements; therefore, its features could potentially cause inaccuracy. The frequent simplistic QA for the EDW is essential, and could secure against the flaw of dynamic treatment that uses the EDW.

• Journal of the Korean Society of Radiology
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• v.7 no.1
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• pp.81-84
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• 2013

The use of the dosimetry have been increasingly recognized as high radiation energy and radiation treatment planning(RTP) have rapidly developed in radiotherapy. There are many types of detectors for the dosimetry such as ionization chamber, film, TLD, diode, and etc. Among such detectors, the diode detector uses a photoconductor materials that generate electrical signals by the incident radiation energy. Though many research groups are recently interested in such materials, there is few experimental results except for silicon in the radiation therapy field. In this study, the feasibility of photoconductor materials was verified as a dosimeter through the evaluation of response properties at a high radiation energy. For the fabricated detectors based on $HgI_2$ and $PbI_2$, reproducibility, linearity, and pulse-rate response were analyzed. Such evaluations are essential factors for the use of dosimeter. From results, linearity and reproducibility of the fabricated $HgI_2$ detector indicated about 7% error. The fabricated $PbI_2$ detector showed 1.7% error in linearity, and 12.2% error in reproducibility.

• Progress in Medical Physics
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• v.25 no.4
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• pp.218-224
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• 2014

The small field dosimetry is very important in modern radiotherapy because it has been frequently used to treat the tumor with high dose hypo-fractionated radiotherapy or high dose single fraction stereotactic radiosurgery (SRS) with small size target. But, the dosimetry of a small field (< $3{\times}3cm^2$) has been great challenges in radiotherapy. Small field dosimetry is difficult because of (a) a lack of lateral electronic equilibrium, (b) steep dose gradients, and (c) partial blocking of the source. The objectives of this study were to measure and verify with the various detectors the output factors in a small field (<3 cm) for the 6 MV photon beams. Output factors were measured using the CC13, CC01, EDGE detector, thermoluminescence dosimeters (TLDs), and Gafchromic EBT2 films at the sizes of field such as $0.5{\times}0.5$, $1{\times}1$, $2{\times}2$, $3{\times}3$, $5{\times}5$, and $10{\times}10cm^2$. The differences in the output factors with the various detectors increased with decreasing field size. Our study demonstrates that the dosimetry for a small photon beam (< $3{\times}3cm^2$) should use CC01 or EDGE detectors with a small active volume. And also, Output factors with the EDGE detectors in a small field (< $3{\times}3cm^2$) coincided well with the Gafchromic EBT2 films.

• Progress in Medical Physics
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• v.22 no.1
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• pp.35-41
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• 2011

For overall system test, hidden-target test have been used using film which leads to inherent analysis error. The purpose of our study is to quantify this error and to propose gel dosimeter based verification technique for 3-dimensional target point error. The phantom was made for simulation of human head and this has ability to equip 10 gel-dosimeter. $BANGkit^{TM}$ which we are able to manufacture whenever it is needed as well as to easily change the container with different shapes was used as a gel dosimeter. The 10 targets were divided into two groups based on shapes of areas with a planned 50% isodose line. All treatment and analysis was performed three times using Novalis and $BrainSCAN^{TM}$. The target point error is $0.77{\pm}0.15mm$ for 10 targets and directional target point error in each direction is $0.54{\pm}0.23mm$, $0.37{\pm}0.08mm$, $0.33{\pm}0.10mm$ in AP (anterior-posterior), LAT (lateral), and VERT (vertical) direction, respectively. The result of less than 1 mm shows that the treatment was performed through each precise step in treatment procedure. In conclusion, the 3-dimensional target point verification technique can be one of the techniques for overall system test.

• The Journal of Korean Society for Radiation Therapy
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• v.17 no.1
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• pp.9-17
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• 2005

Purpose : Uniform dose distribution of the target volume is very important in the radiation treatment. We will evaluate the usefulness of Field-in-Field Technique use to get uniform dose distribution of the target volume and try to find Apply possibility out to a whole brain treatment patient of various thickness. Material and method : We compare the dose distribution when we applied Field-in-Field Technique and parallel opposed fields technique. establish the treatment plan to a phantom(acryl 16cm spheral phantom) and do the measurement, assessment use the TLD and Low sensitivity film. Also the assessment did Apply possibility of Field-in-Field Technique to 20 patient object of various thickness. Result : In the case to use the parallel opposed fields at the whole brain treatment $10-12\%$ high dose region appeared but reduce to $3-4\%$ lesses when we used the Field-in-Field technique. We could get similar numerical value the film and TLD measurement result also. The change of the dose distribution appeared to its ${\pm}1{\sim}2\%$ although it applied such Field-in-Field technique to various patient so that we were identical. Conclusion : We can get uniform dose distribution of in the treatment region if we apply the Field-in-Field technique at the whole brain treatment. Also alternate can play the role of the wedge filter and 3D compensator and We are thought by minimizing the obstacle to be happened due to the high dose region when radiation treatment.

• Polymer(Korea)
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• v.36 no.3
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• pp.344-350
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• 2012

New pressure sensitive adhesives (PSAs) for polarizer film were prepared by electron beam (e-beam) radiation to acrylic copolymers, and their adhesive properties were investigated. The acrylic copolymers were synthesized by free radical polymerization of $n$-butylacrylate (BA), 2-hydroxyethyl methacrylate (HEMA), and acrylic acid (AA). The acrylic copolymers were coated on PET release films to a thickness of 25 ${\mu}m$, laminated to polarizer films, and then radiated with e-beam at room temperature. Gel fractions of all the acrylic copolymers after e-beam radiation at 50 kGy were higher than 93%, and their crosslinking densities were increased with increasing the content of HEMA units. PSA prepared by e-beam radiation of acrylic copolymer synthesized with a feed ratio of BA/HEMA/AA = 89.5/10/0.5 (w/w/w) at a dose of 50 kGy exhibited the best adhesion performances in terms of peel strength, creep resistance, durability and reliability, and light leakage. It is expected that the preparation method of PSAs via e-beam irradiation will improve the producibility and workability of polarizer film for liquid crystal display.