• 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.

• The Journal of Korean Society for Radiation Therapy
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• v.26 no.2
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• pp.321-327
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• 2014

Purpose : To verify the accuracy of the Ecilpse's dose calculation algorithm(AAA:Analytic anisotropic algorithm) in case of a radiation treatment on Inhomogeneous tissues using FFF beam comparing dose distribution at TPS with actual distribution. Materials and Methods : After acquiring CT images for radiation treatment by the location of tumors and sizes using the solid water phantoms, cork and chest tumor phantom made of paraffin, we established the treatment plan for 6MV photon therapy using our radiation treatment planning system for chest SABR, Ecilpse's AAA(Analytic anisotropic algorithm). According to the completed plan, using our TrueBeam STx(Varian medical system, Palo Alto, CA), we irradiated radiation on the chest tumor phantom on which EBT2 films are inserted and evaluated the dose value of the treatment plan and that of the actual phantom on Inhomogeneous tissue. Results : The difference of the dose value between TPS and measurement at the medial target is 1.28~2.7%, and, at the side of target including inhomogeneous tissues, the difference is 2.02%~7.40% at Ant, 4.46%~14.84% at Post, 0.98%~7.12% at Rt, 1.36%~4.08% at Lt, 2.38%~4.98% at Sup, and 0.94%~3.54% at Inf. Conclusion : In this study, we discovered the possibility of dose calculation's errors caused by FFF beam's characteristics and the inhomogeneous tissues when we do SBRT for inhomogeneous tissues. SBRT which is most popular therapy method needs high accuracy because it irradiates high dose radiation in small fraction. So, it is supposed that ideal treatment is possible if we minimize the errors when planning for treatment through more study about organ's characteristics like Inhomogeneous tissues and FFF beam's characteristics.

• The Journal of Korean Society for Radiation Therapy
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• v.24 no.2
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• pp.107-114
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• 2012

Purpose: Unlike the existing linear accelerator with photon, proton therapy produces a number of second radiation due to the kinds of nuclide including neutron that is produced from the interaction with matter, and more attention must be paid on the exposure level of radiation workers for this reason. Therefore, thermoluminescence dosimeter (TLD) that is being widely used to measure radiation was utilized to analyze the exposure level of the radiation workers and propose a basic data about the radiation exposure level during the proton therapy. Materials and Methods: The subjects were radiation workers who worked at the proton therapy center of National Cancer Center and TLD Badge was used to compare the measured data of exposure level. In order to check the dispersion of exposure dose on body parts from the second radiation coming out surrounding the beam line of proton, TLD (width and length: 3 mm each) was attached to on the body spots (lateral canthi, neck, nipples, umbilicus, back, wrists) and retained them for 8 working hours, and the average data was obtained after measuring them for 80 hours. Moreover, in order to look into the dispersion of spatial exposure in the treatment room, TLD was attached on the snout, PPS (Patient Positioning System), Pendant, block closet, DIPS (Digital Image Positioning System), Console, doors and measured its exposure dose level during the working hours per day. Results: As a result of measuring exposure level of TLD Badge of radiation workers, quarterly average was 0.174 mSv, yearly average was 0.543 mSv, and after measuring the exposure level of body spots, it showed that the highest exposed body spot was neck and the lowest exposed body spot was back (the middle point of a line connecting both scapula superior angles). Investigation into the spatial exposure according to the workers' movement revealed that the exposure level was highest near the snout and as the distance becomes distant, it went lower. Conclusion: Even a small amount of exposure will eventually increase cumulative dose and exposure dose on a specific body part can bring health risks if one works in a same location for a long period. Therefore, radiation workers must thoroughly manage exposure dose and try their best to minimize it according to ALARA (As Low As Reasonably Achievable) as the International Commission on Radiological Protection (ICRP) recommends.

• Progress in Medical Physics
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• v.19 no.1
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• pp.80-88
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• 2008

Recent radiotherapy dose planning system (RTPS) generally adapted the kernel beam using the convolution method for computation of tissue dose. To get a depth and profile dose in a given depth concerened a given photon beam, the energy spectrum was reconstructed from the attenuation dose of transmission of filter through iterative numerical analysis. The experiments were performed with 15 MV X rays (Oncor, Siemens) and ionization chamber (0.125 cc, PTW) for measurements of filter transmitted dose. The energy spectrum of 15MV X-rays was determined from attenuated dose of lead filter transmission from 0.51 cm to 8.04 cm with energy interval 0.25 MeV. In the results, the peak flux revealed at 3.75 MeV and mean energy of 15 MV X rays was 4.639 MeV in this experiments. The results of transmitted dose of lead filter showed within 0.6% in average but maximum 2.5% discrepancy in a 5 cm thickness of lead filter. Since the tissue dose is highly depend on the its energy, the lateral dose are delivered from the lateral spread of energy fluence through flattening filter shape as tangent 0.075 and 0.125 which showed 4.211 MeV and 3.906 MeV. In this experiments, analyzed the energy spectrum has applied to obtain the percent depth dose of RTPS (XiO, Version 4.3.1, CMS). The generated percent depth dose from $6{\times}6cm^2$ of field to $30{\times}30cm^2$ showed very close to that of experimental measurement within 1 % discrepancy in average. The computed dose profile were within 1% discrepancy to measurement in field size $10{\times}10cm$, however, the large field sizes were obtained within 2% uncertainty. The resulting algorithm produced x-ray spectrum that match both quality and quantity with small discrepancy in this experiments.

• Progress in Medical Physics
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• v.20 no.4
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• pp.290-297
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• 2009

In case of radiation treatment using small field high-energy photon beams, an accurate dosimetry is a challenging task because of dosimetrically unfavorable phenomena such as dramatic changes of the dose at the field boundaries, dis-equilibrium of the electrons, and non-uniformity between the detector and the phantom materials. In this study, the absorbed dose in the phantom was measured by using an ion chamber and a diode detector widely used in clinics. $GAFCHROMIC^{(R)}$ EBT films composed of water equivalent materials was also evaluated as a small field detector and compared with ionchamber and diode detectors. The output factors at 10 cm depth of a solid phantom located 100 cm from the 6 MV linear accelerator (Varian, 6 EX) source were measured for 6 field sizes ($5{\times}5\;cm^2$, $2{\times}2\;cm^2$, $1.5{\times}1.5\;cm^2$, $1{\times}1\;cm^2$, $0.7{\times}0.7\;cm^2$ and $0.5{\times}0.5\;cm^2$). As a result, from $5{\times}5\;cm^2$ to $1.5{\times}1.5\;cm^2$ field sizes, absorbed doses from three detectors were accurately identified within 1%. Wheres, the ion chamber underestimated dose compared to other detectors in the field sizes less than $1{\times}1\;cm^2$. In order to correct the observed underestimation, a convolution method was employed to eliminate the volume averaging effect of an ion chamber. Finally, in $1{\times}1\;cm^2$ field the absorbed dose with a diode detector was about 3% higher than that with the EBT film while the dose with the ion chamber after volume correction was 1% lower. For $0.5{\times}0.5\;cm^2$ field, the dose with the diode detector was 1% larger than that with the EBT film while dose with volume corrected ionization chamber was 7% lower. In conclusion, the possibility of $GAFCHROMIC^{(R)}$ EBT film as an small field dosimeter was tested and further investigation will be proceed using Monte Calro simulation.

• Journal of Hospice and Palliative Care
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• v.10 no.1
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• pp.35-42
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• 2007

Purpose: Colorectal ranter is the 4th leading cause of cancer death in Korea and the prevalence is increasing continuously. This study was aimed to figure out the problems through the clinical consideration about terminal colorectal ranter patients who had died in hospice unit. Methods: We retrospectively reviewed the medical records in 78 patients with colorectal ranter who had admitted, received palliative care, and died in a hospice unit between April 2003 and November 2006. Results: The median age of patients was 59.6 years with 45 men (58%) and 24 women (42%). The median survival in hospice and palliative care was 36 days. The median hospitalization was 22 days. The most prevalent reason for admission was pain (38 patients, 49%), and the most common symptom was also pain (70 patients, 90%). Forty eight patients (62%) took analgesics before hospice referral. Twenty seven patients (65%) of 45 patients with intestinal obstruction have been performed palliative procedures. Median survival of patients with palliative procedure was higher than that of no palliative procedure group (47 days vs 19 days, P-value=0.005). Conclusion: The duration of hospice and palliative care was not enough to care the terminal colorectal cancer. Therefore, we suggest that proper education and information should be provided to physician, patients and their family members for effective hospice and palliative care.

• Progress in Medical Physics
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• v.19 no.3
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• pp.191-199
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• 2008

PTV considered for the energy, dose distribution exposed to lung and spinal cord, and the characteristic of DVH(Dose Volume Histogram) were compared and investigated by planning the intensity modulated radiation therapy (IMRT) using the photon energies of 6 MV and 10 MV according to tumor location like as the anterior, middle, and posterior regions of lung, and the mediastinum region in lung cancer patients. Our institution installed the linear accelerator (Varian 21 EX-s, USA) equipped with 120 multileaf collimator for lung cancer patients, which is producing the photon energies of 6 MV and 10 MV, and radiation therapy planning was performed with ECLIPSE system (Varian, SomaVision 6.5, USA), which support inverse treatment planning. The tomographic images of 3 mm slice thickness for lung cancer patients were acquired using planning CT, and acquired tomographic images were sent to the Varis system, and then treatment planning was performed in the ECLIPSE system. The radiation treatment planning of the IMRT was processed from various angles according to the regions of the tumor, and using various beam lines according to the size and location of the tumor. The investigation of the characteristic of dose distributions for the energy of 6 MV and 10 MV according to tumor locations in lung cancer patients resulted that the maximum dose of 10 MV energy was 1.2% less than that of 6 MV energy without depending on the tumor location of lung cancer, and the reduction effects of MU were occurred from 10 to 25 MU. Radiation dose exposed to the lung satisfied the less 30% of V20, however radiation dose in 6 MV energy was from 0.1% to 0.5% less than that in 10 MV energy. Radiation dose exposed to the spinal cord for 6 MV energy was from 0.6% to 2.1% less than that for 6 MV energy.

• Journal of radiological science and technology
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• v.30 no.2
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• pp.139-145
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• 2007

Dose evaluation for small field such as stereotactic radiosurgery was performed using $Gafchromic^{(R)}$ EBT film. Every film which irradiated 6MV photon beam was scanned and obtained the optical density(OD) by flat bed scanner after 24 hours of irradiation. This study compared dose from diode in water and Gafchromic $EBT^{(R)}$ film in acrylic phantom to verify the reliability of the film, and to evaluate the SRS in clinical dose distributions from calculation and measurement in the region of virtual target in humanoid and cylindrical phantoms were compared. The Gafchromic $EBT^{(R)}$ film was found to be linear up to 9Gy. The $D_{max}$ for 6 MV was measured at 1.5 cm from the surface by both of diode and the film. As the depth is deeper, the error was measured within $2{\sim}3%$ at $10{\sim}20\;cm$ depth. Comparing between distribution from calculation and measurement, we found that there is 5% error at 90% isodose line. We found that given dose could be measured accurately by using the phantoms. It was feasible to use the Gafchromic $EBT^{(R)}$ film in quality assurance of SRS.

• Progress in Medical Physics
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• v.14 no.4
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• pp.240-248
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• 2003

The Monte Carlo calculation is the most accurate means of predicting radiation dose, but its accuracy is accompanied by an increase in the amount of time required to produce a statistically meaningful dose distribution. In this study, the effects on calculation time by introducing variance reduction techniques and increasing computing power, respectively, in the Monte Carlo dose calculation for a 6 MV photon beam from the Varian 600 C/D were estimated when maintaining accuracy of the Monte Carlo calculation results. The EGSnrc­based BEAMnrc code was used to simulate the beam and the EGSnrc­based DOSXYZnrc code to calculate dose distributions. Variance reduction techniques in the codes were used to describe reduced­physics, and a computer cluster consisting of ten PCs was built to execute parallel computing. As a result, time was more reduced by the use of variance reduction techniques than that by the increase of computing power. Because the use of the Monte Carlo dose calculation in clinical practice is yet limited by reducing the computational time only through improvements in computing power, introduction of reduced­physics into the Monte Carlo calculation is inevitable at this point. Therefore, a more active investigation of existing or new reduced­physics approaches is required.

• Journal of Biomedical Engineering Research
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• v.25 no.2
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• pp.89-95
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• 2004

Intensity-modulated radiation therapy (IMRT) often uses small beam segments. The heterogeneity effect is well known for relatively large field sizes used in the conventional radiation treatments. However, this effect is not known in small fields such as the beamlets used in IMRT. There are many factors that can cause errors in the small field i.e. electronic disequilibrium and multiple electron scattering. This study prepared geometrically regular heterogeneous phantoms, and compared the measurements with the calculations using the Convolution/Superposition algorithm and Monte Carlo method for small beams. This study used the BEAM00/EGS4 code to simulate the head of a Varian 2300C/D. The commissioning of a 6MV photon beam were performed from two points of view, the beam profiles and depth doses. The calculated voxel size was 1${\times}$1${\times}$2$\textrm{cm}^2$ with field sizes of 1${\times}$1$\textrm{cm}^2$, 2${\times}$2$\textrm{cm}^2$, and 5${\times}$5$\textrm{cm}^2$. The XiOTM TPS (Treatment Planning System) was used for the calculation using the Convolution/Superposition algorithm. The 6MV photon beam was irradiated to homogeneous (water equivalent) and heterogeneous phantoms (water equivalent ＋ air cavity, water equivalent ＋ bone equivalent). The beam profiles were well matched within :t1 mm and the depth doses were within ${\pm}$2%. In conclusion, the dose calculations of the Convolution/Superposition and Monte Carlo simulations showed good agreement with the film measurements in the small field.