• Journal of radiological science and technology
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• v.35 no.2
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• pp.157-164
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• 2012

The purpose of this study is to analyze the dose distribution when wedge filter is used in the various tissue electron density materials. The dose distribution was assessed that the enhanced dynamic wedge filter and physical wedge filter were used in the solid water phantom, cork phantom, and air cavity. The film dosimetry was suitable simple to measure 2D dose distribution. Therefore, the radiochromic films (Gafchromic EBT2, ISP, NJ, USA) were selected to measure and to analyze the dose distributions. A linear accelerator using 6 MV photon were irradiated to field size of $10{\times}10cm^2$ with 400 MUs. The dose distributions of EBT2 films were analyzed the in-field area and penumbra regions by using dose analysis program. In the dose distributions of wedge field, the dose from a physical wedge was higher than that from a dynamic wedge at the same electron density materials. A dose distributions of wedge type in the solid water phantom and the cork phantom were in agreements with 2%. However, the dose distribution in air cavity showed the large difference with those in the solid water phantom or cork phantom dose distributions. Dose distribution of wedge field in air cavity was not shown the wedge effect. The penumbra width, out of the field of thick and thin, was observed larger from 1 cm to 2 cm at the thick end. The penumbra of physical wedge filter was much larger average 6% than the dynamic wedge filter. If the physical wedge filter is used, the dose was increased to effect the scatter that interacted with photon and physical wedge. In the case of difference in electron like the soft tissue, lung, and air, the transmission, absorption, and scattering were changed in the medium at high energy photon. Therefore, the treatment at the difference electron density should be inhomogeneity correction in treatment planning system.

• Proceedings of the Materials Research Society of Korea Conference
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• 1993.11a
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• pp.103-103
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• 1993

• Radiation Oncology Journal
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• v.20 no.2
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• pp.172-178
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• 2002

Purpose : X-ray film over responds to low-energy photons in relative photon beam dosimetry because its sensor is based on silver bromide crystals, which are high-Z molecules. This over-response becomes a significant problem in clinical photon beam dosimetry particularly in regions outside the penumbra. In intensity modulated radiation therapy (IMRT), the radiation field is characterized by multiple small fields and their outside-penumbra regions. Therefore, in order to use film dosimetry for IMRT, the nature the source of the over-response in its radiation field need to be known. This study is aimed to verify and possibly improve film dosimetry for IMRT. Materials and Method : Modulated beams were constructed by a combination of five or seven different static radiation fields using 6 MeV X-rays. In order to verify film dosimetry, we used X-ray film and an ion chamber were used to measure the dose profiles at various depths in a phantom. In addition, in order to reduce the over-response, 0.01 inch thick lead filters were placed on both sides of the film. Results : The measured dose profiles showed a film over-response at the outside-penumbra and low dose regions. The error increased with depths and approached 15% at a maximum for the field size of $15{\times}15cm^2$ at 10 cm depth. The use of filters reduced the error to 3%, but caused an under-response of the dose in a perpendicular set-up. Conclusion : This study demonstrated that film dosimetry for IMRT involves sources of error due to its over-response to low-energy Photons. The use of filers can enhance the accuracy in film dosimetry for IMRT. In this regard, the use of optimal filter conditions is recommended.

• Progress in Medical Physics
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• v.17 no.4
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• pp.187-191
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• 2006

The purpose of this study was to measure the dose distribution from the moving phantom for the respiratory motion. The phantom for TLD measurement was designed and built for this study based on the multiple plates for placing TLD and film. The TLDs may be inserted at 3 mm intervals in each TLD plate. For the measurements, TLD plate was inserted into the phantom at 1.5 cm ($d_{max}$) depth, and phantom was allowed to move in SI directions in the range of 1 to 2 cm with 0.5 cm interval for 6 MV X-ray beams. Penumbra and FWHM were measured at both moving state and compared stationary. It was found that penumbra increased 0.71 cm at stationary and 2.10 cm at moving state in 2 cm movement, and that FWHM are 7.52 cm for stationary state and 7.02 cm for moving state (2 cm movement). In this study, film was used to compared with TLD results of measurements and simitar results were observed. Therefore, it is expected that TLD moving phantom may be useful for the treatment of tumors that move due to the respiratory motion.

• The Journal of Korean Society for Radiation Therapy
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• v.6 no.1
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• pp.84-88
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• 1994

Proper evaluation about the penumbra is very important to improve the efficacy of radiation theraphy. There are two kinds of physical penumbra, geometric penumbra and transmission penumbra. In this study, we evaluated the variation of physical penumbra according to the varing enery level, changing the field size and depth. Physical penumbra width was decreased as the source size decreased, and as the SDD increased, but the consideration about the scatter radiation and mechanical stability is an important factor. For the two adjacent beams, upper collimator should be used and especially for Co-60 unit, it is efficient to use the extended collimator.

• Journal of radiological science and technology
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• v.16 no.2
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• pp.81-86
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• 1993

Proper evaluation about the penumbra is very important to improve the efficacy of radiation theraphy. There are two kinds of physical penumbra, geometric penumbra and transmission penumbra. In this study, we evaluated the variation of physical penumbra according to the varing energy level, changing the field size and depth. Physical penumbra width was decreased as the source size decreased, and as the SDD increased, but the consideration about the scatter radiation and mechanical stability is an important factor. For the two adjacent beams, upper collimator should be used and especially for Co-60 unit, it is efficient to use the extended collimator.

• Progress in Medical Physics
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• v.20 no.4
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• pp.191-198
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• 2009

In this study, we evaluated an edge detector for small-beam dosimetry. We measured the dose linearity, dose rate dependence, output factor, beam profiles, and percentage depth dose using an edge detector (Model 1118 Edge) for 6-MV photon beams at different field sizes and depths. The obtained values were compared with those obtained using a standard volume ionization chamber (CC13) and photon diode detector (PFD). The dose linearity results for the three detectors showed good agreement within 1%. The edge detector had the best linearity of ${\pm}0.08%$. The edge detector and PFD showed little dose rate dependency throughout the range of 100~600 MU/min, while CC13 showed a significant discrepancy of approximately -5% at 100 MU/min. The output factors of the three detectors showed good agreement within 1% for the tested field sizes. However, the output factor of CC13 compared to the other two detectors had a maximum difference of 21% for small field sizes (${\sim}4{\times}4\;cm^2$). When analyzing the 20~80% penumbra, the penumbra measured using CC13 was approximately two times wider than that using the edge detector for all field sizes. The width measured using PFD was approximately 30% wider for all field sizes. Compared to the edge detector, the 10~90% penumbras measured using the CC13 and PFD were approximately 55% and 19% wider, respectively. The full width at half maximum (FWHM) of the edge detector was close to the real field size, while the other two detectors measured values that were 8~10% greater for all field sizes. Percentage depth doses measured by the three detectors corresponded to each other for small beams. Based on the results, we consider the edge detector as an appropriate small-beam detector, while CC13 and PFD can lead to some errors when used for small beam fields under $4{\times}4\;cm^2$.

• Progress in Medical Physics
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• v.23 no.3
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• pp.138-144
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• 2012

Dose distribution throughout the clinical organ range of motion was analyzed using a respiratory-motion simulator that was equipped with a polymer gel dosimeter and EBT2 film. The normoxic polymer gel dosimeter was synthesized from gelatin, MAA, HQ, THPC and HPLC. The gel dosimeter and EBT2 film were irradiated with Co-60 gamma rays that were moved along the x-axis and y-axis in ${\pm}1.5cm$ steps at five-second intervals. The field size was $5{\times}5cm^2$. The SSD was 80 cm and set to 10 Gy at a depth of 2 cm. The PDD at a depth of 50 mm was 75.2% in the ion chamber, 82.3% in the static state and 86.1% in the dynamic state in the gel dosimeter. The penumbra for the dynamic state target, which was measured using the gel dosimeter, averaged 10.89 mm, this is a 40.5% increase over the penumbra of the static state target of 7.74 mm. In addition, when measuring with gel dosimetry, the value for the penumbra is 36.6% smaller in the static state and 29.4% smaller in the dynamic state compared to measuring with film. The aim of this study was to investigate the dosimetric properties of a normoxic polymethacrylic acid gel dosimeter in static and dynamic states and to evaluate the potentiality as a relative dosimeter for dynamic therapeutic radiation.

• The Journal of Korean Society for Radiation Therapy
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• v.18 no.2
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• pp.81-87
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• 2006

Purpose: Few researches have been peformed on the dose distribution of the moving organ for radiotherapy so far. In order to simulate the organ motion caused by respiratory function, multipurpose phantom and moving device was used and dosimetric measurements for dose distribution of the moving organs were conducted in this study. The purpose of our study was to evaluate how dose distributions are changed due to respiratory motion. Materials and Methods: A multipurpose phantom and a moving device were developed for the measurement of the dose distribution of the moving organ due to respiratory function. Acryl chosen design of the phantom was considered the most obvious choice for phantom material. For construction of the phantom, we used acryl and cork with density of $1.14g/cm^3,\;0.32g/cm^3$ respectively. Acryl and cork slab in the phantom were used to simulate the normal organ and lung respectively. The moving phantom system was composed of moving device, moving control system, and acryl and cork phantom. Gafchromic film and EDR2 film were used to measure dose ditrbutions. The moving device system may be driven by two directional step motors and able to perform 2 dimensional movements (x, z axis), but only 1 dimensional movement(z axis) was used for this study. Results: Larger penumbra was shown in the cork phantom than in the acryl phantom. The dose profile and isodose curve of Gafchromic EBT film were not uniform since the film has small optical density responding to the dose. As the organ motion was increased, the blurrings in penumbra, flatness, and symmetry were increased. Most of measurements of dose distrbutions, Gafchromic EBT film has poor flatness and symmetry than EDR2 film, but both penumbra distributions were more or less comparable. Conclusion: The Gafchromic EBT film is more useful as it does not need development and more radiation dose could be exposed than EDR2 film without losing film characteristics. But as response of the optical density of Gafchromic EBT film to dose is low, beam profiles have more fluctuation at Gafchromic EBT. If the multipurpose phantom and moving device are used for treatment Q.A, and its corrections are made, treatment quality should be improved for the moving organs.

• The Journal of Korean Society for Radiation Therapy
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• v.20 no.2
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• pp.109-113
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• 2008

Purpose: To evaluate the detector dependency in the various collimator size for Stereotactic Radiosugery (SRS). Materials and Methods: This study was performed with 6 MV photon beam (Varian 21EX, Varian, US) and the measurement detectors are used by ion chamber CC01, CC13 (Wellhofer, Germany) and stereotactic diode detector (SFD, Wellhofer, Germany). SRS collimator size was used by ${\varphi}$5, 10, 20, 30 mm (Brain Lab, Germany). Percentage depth dose (PDD) was measured at SSD 100 cm and field size 10×10 cm from individual detectors. Ouput factor was measured by using same setup of PDD and with maximum dose depth. Data was normalized at field size $10{\times}10\;cm$. Beam profile was measured at SSD 100 cm in SRS collimator ${\varphi}$10, 30 mm and field $10{\times}10\;cm$ and a comparison of FWHM (full width half maximum), penumbra width (20~80%). Results: The CC13 detector was overestimated 16% than other detectors from the PDD in the 5 mm collimator. Output factors were underestimated CC01 28%, CC13 72% in the 5 mm collimator and CC01 9.6%, CC13 25% in the 10 mm collimator than the SFD. Maximum difference was 3% at the FWHM of the dose profile in the 10 mm collimator and difference of the 30 mm collimator was 0% at the FWHM. Penumbra width was increased CC01 122%, CC13 194% in the 10 mm collimator and CC01 68%, CC13 185% in the 30 mm collimator than the SFD. Conclusion: It is very important for accurate dosimetry to select a detector in small field. The SFD was considered with the most accurate dosimeter for small collimator dosimetry in this study.