• Progress in Medical Physics
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• v.31 no.4
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• pp.163-171
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• 2020

Purpose: In this study, the accuracies of electron Monte Carlo (eMC) calculation algorithms were evaluated to determine whether electron beams were modeled by optional air profiles (APs) designed for each applicator size. Methods: Electron beams with the energies of 6, 9, 12, and 16 MeV for VitalBeam (Varian Medical System, Palo Alto, CA, USA) and 6, 9, 12, 16, and 20 MeV for Clinac iX (Varian Medical System) were used. Optional APs were measured at the source-to-detector distance of 95 cm with jaw openings appropriate for each machine, electron beam energy, and applicator size. The measured optional APs were postprocessed and converted into the w2CAD format. Then, the electron beams were modeled and calculated with and without optional APs. Measured profiles, percentage depth doses, penumbras with respect to each machine, and energy were compared to calculated dose distributions. Results: For VitalBeam, the profile differences between the measurement and calculation were reduced by 0.35%, 0.15%, 0.14%, and 0.38% at 6, 9, 12, and 16 MeV, respectively, when the beams were modeled with APs. For Clinac iX, the differences were decreased by 0.16%, -0.31%, 0.94%, 0.42%, and 0.74%, at 6, 9, 12, 16, and 20 MeV, respectively, with the insertion of APs. Of note, no significant improvements in penumbra and percentage depth dose were observed, although the beam models were configured with APs. Conclusions: The accuracy of the eMC calculation can be improved in profiles when electron beams are modeled with optional APs.

• Radiation Oncology Journal
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• v.9 no.1
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• pp.123-130
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• 1991

A docking intraoperative electron beam applicator system, which is easily docking in the collimator for a linear accelerator after setting a sterilized transparent cone on the tumor bearing area in the operation room, has been designed to optimize dose distribution and to improve the efficiency of radiation treatment method with linear accelerator. This applicator system consisted of collimator holder with shielded metals and docking cone with transparent acrylic cylinder, A number of technical innovations have been used in the design of this system, this dooking cone gives a improving latral dose coverage at therapeutic volume. The position of $90\%$ isodose curve under suface of 8 cm diameter cone was extended $4\sim7$ mm at 12 MeV electron and the isodose measurements beneath the cone wall showed hot spots as great as $106\%$ for acrylic cone. The leakage radiation dose to tissues outside the cone wall was reduced as $3\sim5\%$ of output dose. A comprehensive set of dosimetric characteristics of the intraoperative radiation therapy applicator system is presented.

• The Journal of Korean Society for Radiation Therapy
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• v.27 no.1
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• pp.13-22
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• 2015

Purpose : We investigated the safety of Intrabeam$^{TM}$ system, X-ray unit for Intraoperative Radiotheray (IORT) by measuring surface dose using Optically Stimulated Luminescent Dosimeter(OSLD). Materials and Methods : 30 patients were selected, who were in breast cancer patients and had an operation of breast conserving surgery (BCS). At the inner surface of tumor bed, 20 Gy were described, and 5 Gy at 1cm depth from the inner surface. Along the size of tumor bed which could be decided after resection of tumor, the size of applicator were determined. Usual treatment time were from 18 to 40 minutes. For the measurement of surface doses, OSLD were placed at superior(U1,2), inferior(D1,2), lateral(L1,2) and medial(M1,2) directions from the center of applicator. Each direction, two OSLD were placed at 0.5 cm and 1.5 cm from the center. Mean, maximum, and minimum doses were analyzed to be compared. Results : Mean values were U1 $2.23{\pm}0.80Gy$, U2 $1.54{\pm}0.53Gy$, D1 $1.73{\pm}0.63Gy$, D2 $1.25{\pm}0.45Gy$, L1 $1.95{\pm}0.82Gy$, L2 $1.38{\pm}0.42Gy$, M1 $2.03{\pm}0.70Gy$, and M2 $1.51{\pm}0.58Gy$. Maximum values were 4.34 Gy at U1, and Minimum values were 0.45 Gy at M2. 13.3 % of patient (4pts out of 30) were reported that surface dose were over 4 Gy. Conclusion : The fact that skin dose of all patients were less than 5 Gy based on OSLD measurement showed the safety of Intrabeam$^{TM}$ system. In the relatively small breast volume, the tendency that surface dose was increased had been shown, which was analyzed by the data of patients who irradiated over 4Gy at skin surface. Therefore, for appropriate indication for IORT, it is suggested that breast volume as well as the size and position of tumor should be carfully considered.

• Journal of radiological science and technology
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• v.29 no.2
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• pp.83-92
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• 2006

Based on the data of cervical cancer patients who were treated by the radiotherapy with concurrent chemotherapy at the radiation oncology department of National Cancer Center from January 2002 to February 2003, we have studied the method recommended by ICRU 38 to maximize the prescription dose to the planing target volume (PTV) with minimizing the dose to surrounding normal organs. Clinical stage of the patients are 1 patient for stage IB, 3 patients for IIA, 19 patients for IIB, 3 patients for IIIA, 3 patients for IIIB and 1 patient for IV. All patients took the MRI before treatment and the maximum size of the gross tumor volume were under 4cm for 17 patients and from 4 cm to 6 cm for 12 patients and above 6 cm for 1 patient. The results show that while the irradiated volume can be reduced with optimized dose distribution using PTV treatment planning (p<0.0001) when the remained tumor size is small, the surrounding normal organs will receive unnecessarily large dose when the irradiated tumor volume is relatively large. This is because there is some limitation in controling the intensity of radiation in Fletcher Williamson Applicator. To overcome the limit of applicator and to achieve the optimal dose distribution, we have virtually applied 4 needles with Fletcher Williamson Applicator for 10 patients who have relatively large tumor and studied the change in dose distribution before and after application. The results show that this new virtual treatment plan reduces the volume covered by 100 % isodose (p=0.0608, p=0.0607) and reduces the dose of normal organs (p=0.0162, p=0.008). This evidence suggest that this method is superior than the currently used method such as PTV treatment and ICRU treatment.

• The Journal of Korean Society for Radiation Therapy
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• v.18 no.2
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• pp.119-125
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• 2006

Purpose: To measure the dose for dose optimization at the reference point (A, B) and the critical organ with multi Purpose brachytherapy phantom (MPBP). For this wort the MPBP was custom made, and designed to reconstruct the treatment applicator using multi function applicator (MFA) in the same way as the treatment of patient. Materials and Methods: Dose measurements were made at the reference points (A, B) and the bladder with thermoluminescence dosimeter (TLD) for four patients with tandem and ovoid of uterine cervix cancer using the phantom. In Phantom, Total 20 times of the measurements were made with 5 times a patient. Results: The results of TLD measurements in MPBP phantom showed the relative error ranging from -3.2% to 3.8% at A point, and -1.4% to 4% at B point and 1.3% to 7.15% at the bladder of reference point. Conclusion: The reproducibility of dose measurement under the same condition as the treatment could be achieved using the custom-made MFA in phantom and the dose at the reference point (A, B) and bladder could be analyzed accurately. The measured dose acquired in MPBP can apply for the dose optimization.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• v.11 no.2
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• pp.345-348
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• 2006

• Journal of Biosystems Engineering
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• v.31 no.6 s.119
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• pp.474-481
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• 2006

In this paper, a new type blow head was developed and pneumatic application system was evaluated. The blow head had one operating factor, inserting length of collecting plate, that was directly related to discharge rate and application pattern. To determine Proper blow head arrangement and application height, a blow head set was tested. Three-way ANOVA was conducted to investigate relationships between CV value, the discharge rate and inserting length of collecting plate. The discharge rate and inserting length of collecting plate were statistically significant at p=0.01, affecting uniformity of application pattern. The best CV value among the application tests was 23.3% when the application rate and application height was 23.5 g/sec and 80 cm respectively. The worst CV value was 63.3% in 111.4 g/sec. Therefore, it is necessary to increase number of blow head in a section of the boom in improve application uniformity.

• Progress in Medical Physics
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• v.16 no.1
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• pp.16-23
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• 2005

The objective of this study was to construct multi-element ultrasound applicators for the treatment of gynecologic cancer with high dose rate brachytherapy. For the treatment of uterus, piezo-ceramic crystal transducer (PZT -5A) with outer diameter of 4 mm, wall thickness of 1.3 mm, and length of 24.5 mm was selected. For the treatment of cervix or vagina, it should be possible to insert the applicator into the vagina. Thus, a cylindrical PZT -8 material with outer diameter of 24.5 mm, wall thickness of 1.3 mm, and length of 15.2 mm was selected. The operating frequencies determined by vector impedance measurement were 3.2 MHz for the PZT 5A cylinder (OD=4 mm) and 1.7 MHz for the PZT -8 cylinder (OD: 24.5 mm). The ratios of generated acoustic output power to applied electric power were 33% and 61% for the tandem type crystal and the cylinder type crystal, respectively. The radiated acoustic pressure fields from both transducers were calculated using a Matlab code and measured in water using hydrophone. There was good agreement between measured and calculated acoustic pressure field distribution. For a tandem type transducer, the calculated acoustic pressure field decreased from 0.023 MPa at 10 mm to 0.010 Mpa at 30 mm, the reduction of 57%. For the cylinder type transducer which will be used for the treatment of vagina showed 78% reduction at 15 mm and 66% at 25 mm as compared to values at 5 mm from the surface. Based on the characteristics of the transducers, this study demonstrated the possibility of using the crystals as a heating source. Finally, a 3-element and 4-element prototype applicators were constructed. The 3-element applicator is 75 mm long and 4 mm thick and will be used for the treatment of uterus. The 4-element applicator is 61 mm long and 24.5 mm thick and will be used for the treatment of vagina. Using these applicators, it is possible to generate enough power to increase temperature to therapeutic level.

• The Journal of Korean Society for Radiation Therapy
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• v.15 no.1
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• pp.29-33
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• 2003

I. Purpose Brachytherapy is the main component in treatment of patients with uterine cervical cancer. The reproducibility of applicator position in the same patient at repeated treatments was very important for accurate dose delivery. It was aimed to evaluate the change of applicator location between each high dose rate(HDR) brachytherapy insertion in the patients with uterine cervical cancer. II. Materials and Methods From January 1999 to October 2001, total 52 patients were treated with external beam radiotherapy and HDR brachytherapy (Microselectron, Nucletron). During six to seven times of brachytherapy, all patients had three treatment plans. From the orthogonal radiographs, we measured the following variables; height from upper border of pubic bone to os (HPO), distance from sacral promontory to tip of tandem (DST), distance from coccyx to os (DCO), distance from tip of right ovoid to os (DRO), distance from tip of left ovoid to os (DLO), and distance from center of the first tandem source to ovoid (DTO). To evaluate the reproducibility of applicator position, it was calculated the standard deviation of differences between three insertions for the 7 parameters in each patient. III. Results The ranges of standard deviations of interfractional differences for the variables were as follows. 1)HPO : $0{\sim}0.79cm$ 2)DST : $0{\sim}0.9cm$ 3)DCO : $0.06{\sim}0.76cm$ 4)DRO : $0{\sim}0.53cm$ 5)DLO : $0{\sim}0.45cm$ 6) DTO $0{\sim}0.36cm$ IV. Conclusions There was some change in applicator position on repeated implants in our study. But variation of the interfractional differences was minimal; in all parameters, there were less than 1 cm. We are continued to try for reducing the geometric variation between each procedure.

• The Journal of Korean Society for Radiation Therapy
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• v.31 no.1
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• pp.57-65
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• 2019

Purpose: The purpose is to clarify the effect of additional scattering ratio on the edge of the block according to the increasing block thickness with low melting point lead alloy and pure lead in electron beam therapy. Methods and materials: $10{\times}10cm^2$ Shielding blocks made of low melting point lead alloy and pure lead were fabricated to shield mold frame half of applicator. Block thickness was 3, 5, 10, 15, 20 (mm) for each material. The common irradiation conditions were set at 6 MeV energy, 300 MU / Min dose rate, gantry angle of $0^{\circ}$, and dose of 100 MU. The relative scattering ratio with increasing block thickness was measured with a parallel plate type ion chamber(Exradin P11) and phantom(RW3) by varying the position of the shielding block(cone and on the phantom), the position of the measuring point(surface ans depth of $D_{max}$), and the block material(lead alloy and pure lead). Results : When (depth of measurement / block position / block material) was (surface / applicator / pure lead), the relative value(scattering ratio) was 15.33 nC(+0.33 %), 15.28 nC(0 %), 15.08 nC(-1.31 %), 15.05 nC(-1.51 %), 15.07 nC(-1.37 %) as the block thickness increased in order of 3, 5, 10, 15, 20 (mm) respectively. When it was (surface / applicator / alloy lead), the relative value(scattering ratio) was 15.19 nC(-0.59 %), 15.25 nC(-0.20 %), 15.15 nC(-0.85 %), 14.96 nC(-2.09 %), 15.15 nC(-0.85 %) respectively. When it was (surface / phantom / pure lead), the relative value(scattering ratio) was 15.62 nC(+2.23 %), 15.59 nC(+2.03 %), 15.53 nC(+1.67 %), 15.48 nC(+1.31 %), 15.34 nC(+0.39 %) respectively. When it was (surface / phantom / alloy lead), the relative value(scattering ratio) was 15.56 nC(+1.83 %), 15.55 nC(+1.77 %), 15.51 nC(+1.51 %), 15.42 nC(+0.92 %), 15.39 nC(+0.72 %) respectively. When it was (depth of $D_{max}$ / applicator / pure lead), the relative value(scattering ratio) was 16.70 nC(-10.87 %), 16.84 nC(-10.12 %), 16.72 nC(-10.78 %), 16.88 nC(-9.93 %), 16.90 nC(-9.82 %) respectively. When it was (depth of $D_{max}$ / applicator / alloy lead), the relative value(scattering ratio) was 16.83 nC(-10.19 %), 17.12 nC(-8.64 %), 16.89 nC(-9.87 %), 16.77 nC(-10.51 %), 16.52 nC(-11.85 %) respectively. When it was (depth of $D_{max}$ / phantom / pure lead), the relative value(scattering ratio) was 17.41 nC(-7.10 %), 17.45 nC(-6.88 %), 17.34 nC(-7.47 %), 17.42 nC(-7.04 %), 17.25 nC(-7.95 %) respectively. When it was (depth of $D_{max}$ / phantom / alloy lead), the relative value(scattering ratio) was 17.45 nC(-6.88 %), 17.44 nC(-6.94 %), 17.47 nC(-6.78 %), 17.43 nC(-6.99 %), 17.35 nC(-7.42 %) respectively. Conclusions: When performing electron therapy using a shielding block, the block position should be inserted applicator rather than the patient's body surface. The block thickness should be made to the minimum appropriate shielding thickness of each corresponding using energy. Also it is useful that the treatment should be performed considering the influence of scattering dose varying with distance from the edge of block.