• Progress in Medical Physics
• /
• v.12 no.2
• /
• pp.161-169
• /
• 2001

For the head and neck radiotherapy, the technique of half beam using independent collimator is very useful to avoid overlapping of fields particularly when the lateral neck fields are placed adjacent to anterior supraclavicular field. Also abutting photon field with electron field is frequently used for the irradiation of posterior neck when tolerable dose on spinal cord has been reached. Using 6 MV X-ray and 9 MeV electron beams of Clinac1800(Varian, USA) linear accelerator, we performed film dosimetry by the X-OMAT V film of Kodak in solid water phantom and the dose distribution at beam center of 2 half beams further examined according to depths(0 cm, 1.5 cm, 3 cm, 5 cm) for single anterior half beam and anterior/posterior half beam. The dose distribution to the junction line between photon and electron fields was also measured. For the single anterior half beam, the absorption doses at 0.3 cm, 0.5 cm and 1 cm distances from beam center were 88%, 93% and 95% of open beam, respectively. In the anterior/posterior half beams, the absorption doses at 0.3 cm, 0.5 cm and 1 cm distances from beam center were 92%, 93% and 95% of open beam, respectively At the junction line between photon and electron fields, hot spot was developed on the side of the photon field and a cold spot was developed on that of the electron field. The hot spot in the photon side was developed at depth 1.5 cm with 7 mm width. The maximum dose of hot spot was increased to 6% of reference doses in the photon field. The cold spot in the electron side was developed at all measured depths(0.5 cm-3 cm) with 1-12.5 mm widths. The decreased dose in the cold spot was 4.5-30% of reference dose in the electron field. With above results, we concluded that when using electron beam or independent jaw for head and neck radiotherapy, the hot and cold dose area should be considered as critical point.

• Radiation Oncology Journal
• /
• v.12 no.2
• /
• pp.225-232
• /
• 1994

Purpose : This study was to obtain the basic dosimetric data using the 10 MV X-ray for the total body irradiation. Materials and Methods : A linear accelerator photon beam is planned to be used as a radiation source for total body irradiation (TBI) in Chonnam University Hospital. The planned distance from the target to the midplane of a patient is 360cm and the maximum geometric field size is 144cm x 144cm. Polystyrene phantom sized $30{\times}30{\times}30.2cm^3$ and consisted of several sheets with various thickness, and a parallel plate ionization chamber were used to measure surface dose and percent depth dose (PDD) at 345cm SSD, and dose profiles. To evaluate whether a beam modifier is necessary for TBI, dosimetry in build up region was made first with no modifier and next with an 1cm thick acryl plate 20cm far from the polystyrene phantom surface. For a fixed sourec-chamber distance, output factors were measured for various depth. Results : As any beam modifier was not on the way of radiation of 10MV X-ray, the $d_{max}$ and surface dose was 1.8cm and $61\%$, respectively, for 345cm SSD. When an 1cm thick acryl plate was put 20cm far from polystyrene phantom for the SSD, the $d_{max}$ and surface dose were 0.8cm and $94\%$, respectively. With acryl as a beam spoiler, the PDD at 10cm depth was $78.4\%$ and exit dose was a little higher than expected dose at interface of exit surface. For two-opposing fields for a 30cm phantom thick phantom, the surface dose and maximum dose relative to mid-depth dose in our experiments were $102.5\%$ and $106.3\%$, respectively. The off-axis distance of that point of $95\%$ of beam axis dose were 70cm on principal axis and 80cm on diagonal axis. Conclusion: 1. To increase surface dose for TBI by 10MV X-ray at 360cm SAD, 1cm thick acrylic spoiler was sufficient when distance from phantom surface to spoiler was 20cm. 2. At 345cm SSD, 10MV X-ray beam of full field produced a satisfiable dose uniformity for TBI within $7\%$ in the phantom of 30cm thickness by two-opposing irradiation technique. 3. The uniform dose distribution region was 67cm on principal axis of the beam and 80cm on diagonal axis from beam axis. 4. The output factors at mid-point of various thickness revealed linear relation with depth, and it could be applicable to practical TBI.

• Proceedings of the Korean Society of Medical Physics Conference
• /
• 2002.09a
• /
• pp.407-410
• /
• 2002

Monochromatic x-ray CT has several advantages over conventional CT, which utilizes bremsstrahlung white x-rays from an x-ray tube. There are several methods to produce such monochromatic x-rays. The most popular one is crystal diffraction monochromatization, which has been commonly used because of the fact that the energy spread is very narrow and the energy can be changed continuously. The alternative method is the use of fluorescent x-ray, which has several advantages such as large beam size and fast energy change. We have developed a parallel-beam and a fan-beam monochromatic x-ray CT, and compared some characteristics such as accuracy of CT numbers between those systems. The fan beam monochromatic x-rays were generated by irradiating target materials by incident white x-rays from a bending magnet beam line NE5 in 6.5 GeV Accumulation Ring at Tukuba. The parallel beam monochromatic x-rays were generated by using a silicon double crystal monochromator at the bending magnet beam line BL-20BM in Spring-8. A Cadmium telluride (CdTe) 256 channel array detector with 512mm sensitive width capable of operating at room temperature was used in the photon counting mode. A cylindrical phantom containing eight concentrations of gadolinium was used for the fan beam monochromatic x-ray CT system, while a phantom containing acetone, ethanol, acrylic and water was used for the parallel monochromatic x-ray CT system. The linear attenuation coefficients obtained from CT numbers of those monochromatic x-ray CT images were compared with theoretical values. They showed a good agreement within 3%. It was found that the quantitative measurement can be possible by using the fan beam monochromatic x-ray CT system as well as a parallel beam monochromatic X-ray CT system.

• Radiation Oncology Journal
• /
• v.23 no.4
• /
• pp.230-235
• /
• 2005

Purpose: To evaluate the contralateral breast dose using a virtual wedge compared with that using a Physical wedge and an open beam in a Siemens linear accelerator. Materials and Methods: The contralateral breast dose was measured using diodes placed on a humanoid phantom. Diodes were placed at 5.5 cm (position 1), 9.5 cm (position 2), and 14 cm (position 3) along the medial-lateral line from the medial edge of the treatment field. A 6-MV photon beam was used with tangential irradiation technique at 50 and 230 degrees of gantry angle. Asymmetrically collimated $17{\times}10cm$ field was used. for the first set of experiment, four treatment set-ups were used, which were an open medial beam with a 30-degree wedged lateral beam (physical and virtual wedges, respectively) and a 15-degree wedged medial beam with a 15-degree wedged lateral beam (physical and virtual wedges, respectively). The second set of experiment consists of setting with medial beam without wedge, a 15-degree wedge, and a 50-degree wedge (physical and virtual wedges, respectively). Identical monitor units were delivered. Each set of experiment was repeated for three times. Results: In the first set of experiment, the contralateral breast dose was the highest at the position 1 and decreased in order of the position 2 and 3. The contralateral breast dose was reduced with open beam on the medial side ($2.70{\pm}1.46%$) compared to medial beam with a wedge (both physical and virtual) ($3.25{\pm}1.59%$). The differences were larger with a physical wedge ($0.99{\pm}0.18%$) than a virtual wedge ($0.10{\pm}0.01%$) at all positions. The use of a virtual wedge reduced the contralateral breast dose by 0.12% to 1.20% of the proscribed dose compared to a physical wedge with same technique. In the second experiment, the contralateral breast dose decreased in order of the open beam, the virtual wedge, and the physical wedge at the position 1, and it decreased in order of a physical wedge, an open beam, and a virtual wedge at the position 2 and 3. Conclusion: The virtual wedge equipped in a Siemens linear accelerator was found to be useful in reducing dose to the contralateral breast. Our additional finding was that the surface dose distribution from the Siemens accelerator was different from a Varian accelerator.

• The Journal of Korean Society for Radiation Therapy
• /
• v.29 no.2
• /
• pp.65-73
• /
• 2017

Purpose: Machine Performance Check (MPC) is a self-checking software based on the Electronic Portal Imaging Device (EPID) to measure daily beam outputs without external installation. The purpose of this study is to verify the usefulness of MPC by comparing and correlating daily beam output of QA Beamchecker PLUS. Materials and Methods: Linear accelerator (Truebeam 2.5) was used to measure 10 energies which are composed of photon beams(6, 10, 15 MV and 6, 10 MV-FFF) and electron beams(6, 9, 12, 16 and 20 MeV). A total of 80 cycles of data was obtained by measuring beam output measurement before treatment over five months period. The Pearson correlation coefficient was used to evaluate the consistency of the beam output between the MPC and the QA Beamchecker PLUS. In this study, if the Pearson correlation coefficient is; (1) 0.8 or higher, the correlation is very strong (2) between 0.6 and 0.79, the correlation is strong (3) between 0.4 and 0.59, the correlation is moderate (4) between 0.2 and 0.39, the correlation is weak (5) lower than 0.2, the correlation is very weak. Results: Output variations observed between MPC and QA Beamchecker PLUS were within 2 % for photons and electrons. The beam outputs variations of MPC were $0.29{\pm}0.26%$ and $0.30{\pm}0.26%$ for photon and electron beams, respectively. QA Beamchecker PLUS beam outputs were $0.31{\pm}0.24%$ and $0.33{\pm}0.24%$ for photon and electron beams, respectively. The Pearson correlation coefficient between MPC and QA Beamchecker PLUS indicated that photon beams were very strong at 15 MV, and strong at 6 MV, 10 MV, 6 MV-FFF and 10 MV-FFF. For electron beams, the Pearson correlation coefficient were strong at 16 MeV and 20 MeV, moderate at 9 MeV and 12 MeV, and very weak at 6 MeV. Conclusion: MPC showed significantly strong correlation with QA Beamchecker PLUS when testing with photon beams and high-energy electron beams in the evaluation of daily beam output, but the correlation when testing with low-energy electron beams (6 MeV) appeared to be low. However, MPC and QA Beamchecker PLUS are considered to be suitable for checking daily beam output, as they performed within 2 % of beam output consistency during the observation. MPC which can perform faster than the conventional daily beam output measurement tool, is considered to be an effective method for users.

• Journal of radiological science and technology
• /
• v.41 no.3
• /
• pp.201-207
• /
• 2018

The purpose of this study is to evaluate the performance of a "stealth chamber" as a novel reference chamber for measuring percentage depth dose (PDD) and profile of 6, 8 and 10 MV photon energies. The PDD curves and dose profiles with fields ranging from $3{\times}3$ to $25{\times}25cm^2$ were acquired from measurements by using the stealth chamber and CC 13 chamber as reference chamber. All measurements were performed with Varian VitalBeam linear accelerator. In order to assess the performance of stealth chamber, PDD curves and profiles measured with stealth chamber were compared with measurement data using CC13 chamber. For PPDs measured with both chambers, the dosimetric parameters such as $d_{max}$ (depth of maximum dose), $D_{50}$ (PDD at 50 mm depth), and $D_{100}$ (PDD at 100 mm depth) were analyzed. Moreover, root mean square error (RMSE) values for profiles at $d_{max}$ and 100 mm depth were evaluated. The measured PDDs and profiles between the stealth chamber and CC13 chamber as reference detector had almost comparable. For PDDs, the evaluated dosimetric parameters were observed small difference (<1%) for all energies and field sizes, except for $d_{max}$ less than 2 mm. In addition, the difference of RMSEs for profiles at $d_{max}$ and 100 mm depth was similar for both chambers. This study confirmed that the use of stealth chamber for measuring commission beam data is a feasible as reference chamber for fields ranging from $3{\times}3$ to $20{\times}20cm^2$. Furthermore, it has an advantage with respect to measurement of the small fields (less than $3{\times}3cm^2$ field) although not performed in this study.

• Progress in Medical Physics
• /
• v.20 no.4
• /
• pp.308-316
• /
• 2009

To achieve the accurate evaluation of given absorbed dose from output dose of linear accelerator photon beam through investigate the characteristics of LiF:Mg,Cu,P TLD powder. This experimental TL phosphor is performed with a commercial LiF:Mg,Cu,P powder (Supplied by PTW) and TL reader (LTM, France). The TLD was exposed to 6 MV X rays of linear accelerator photon beam with range 15 to 800 cGy in blind dose at two hospitals. The dose evaluation of TLD was through the experimental algorithms which were dose dependency, dose rate dependency, fading and powder weight dependency. The glow curve has shown the three peaks which are 110, 183 and 232 degrees of heating temperature and the main dosimetric peak showed highest TL response at 232 high temperature. In this experiments, the LiF:Mg,Cu,P phosphor has shown the 2.5 eV of electron trap energy with a second order. This experiments guided the dose evaluation accuracy is within 1% +2.58% of discrepancy. The TLD powder of LiF:Mg,Cu,P was analyzed to dosimetric characterists of electron captured energy and order by glow shape, and dose-TL response curve guided the accuracy within 1.0+2.58% of output dose discrepancy.

• The Journal of Korean Society for Radiation Therapy
• /
• v.19 no.2
• /
• pp.77-82
• /
• 2007

Purpose: This study investigates peripheral dose from physical wedge and dynamic wedge system on a multileaf collimator (MLC) equipment linear accelerator. Materials and Methods: Measurments were performed using a 2D array ion chamber and solid water phantom for a 10$\times$10 cm, source-surface distance (SSD) 90 cm, 6 and 15 MV photon beam at depths of 0.5 cm, 5 cm through dmax. Measurments of peripheral dose at 0.5 cm and 5 cm depths were performed from 1 cm to 5 cm outside of fields for the dynamic wedge and physical wedge 15$^\circ$, 45$^\circ$. Dose profiles normalized to dose at the maximum depth. Results: At 6 MV photon beam, the average peripheral dose of dynamic wedge were lower by 1.4% and 0.1%. At 15 MV photon beam, the peripheral dose of dynamic wedge were lower by maximum 1.6%. Conclusion: This study showed that dynamic wedge can reduce scattered dose of clinical organ close to the field edge and reduced treatment time. The wedge systems produce significantly different peripheral dose that should be considered in properly choosing a wedge system for clinical use.

• The Journal of Korean Society for Radiation Therapy
• /
• v.8 no.1
• /
• pp.41-54
• /
• 1996

The secondary electrons developed by interaction between primary beam and a tray mounted for blocks in Megavoltage irradiation result in excess soft radiation dose to the surface layer. To reduce this electron contamination, electron filters have been used to be attached under a tray. Various filters with Cu and Al plates in six different thickness and Cu/Al combined plates in 3 different thickness were tested to measure the reduction rate of secondary electron contamination to the surface layer. The measurement to find optimal filter was performed on 6MV linear accelerator in $10 cm{\times}10 cm$ field size and fixed 78.5cm source to measurement points distance from surface to maximum build up point in 2mm intervals. The result was analyzed as the ratio of measured doses with using filters, to standard doses of measured open beam. The result of this study was fellowing : 1. The contaminated low energy radiation were mainly produced by blocking tray. 2. The surface absorbed dose was slowly increased by increasing irradiation field size but rapidly increased at field size above $15cm{\times}15cm$. 3. Al plate upto 2.5mm thickness used as a filter was found to be inadequate due to the failure of reduction of the surface absorbed dose below doses of the under surface upto the maximal build up. Cu 0.5mm plate and Cu 0.28mm/A1 1.5mm compound plate were found to be optimal filters. 4. By using these 2 filters, the absorbed dose to the surface were effectively reduced $5.5\%$ in field size $4cm{\times}4cm,\;11.3\%$ in field size $10cm{\times}10cm,\;22.3\%$ in field size $25cm{\times}25cm$. 5. In field size $10cm{\times}10cm$, the absorbed dose to the surface of irradiation was reduced by setting TSD 20cm at least,. but effective and enough dose reduction could be achieved by setting TSD 30cm as 2 optimal filters used. 6. More surface dose absorbed at TSD less than 7.4cm with a tray and filters together indicated that soft radiation was also developed by filters. 7. The variation of PDD by the different size of irradiation field was minimal as 2 optimal filters used. There was also not different in variation of PDD according to using any of two different filters. 8. PDD was not effected either by various TSD or by using the different filter among two.

• Journal of the Korean Society of Radiology
• /
• v.11 no.7
• /
• pp.565-569
• /
• 2017

This research aims at measuring the changes in the dose rate of photoneutron occurring in the process of the investigation into the 10 MV photon beam with a linear accelerator. In addition, the life time of the photoneutron after the end of irradiation was to be analyzed. The photoneutron were measured with a $BF_3$ proportional counter, and the measurement results of the dose rate of the photoneutron were analyzed in 3 parts at intervals of 2 seconds. The measurement results showed that the photoneutron were generated fastest when there was no metal plate inside the radiation field and when there was a lead plate, and that, as for the time that shows the final dose rate at the level of background, the life time was about 1 minute and 40 seconds regardless of the kinds of materials. Therefore, the dose rate according to the time until the photoneutron run out was proved to be different depending on the sorts of the materials and the threshold energy. However, final life time showed similar results regardless of the kinds of the materials, it can be concluded that the kinds of materials don't get involved in the life time of photoneutron.