• Journal of the Korean Society of Radiology
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• v.15 no.1
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• pp.85-91
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• 2021

The purpose of this study is to derive an equation to verify the accuracy of the dose rate for each component calculated at the measurement point outside the maze door when designing the maze door of 6 MV X-ray beam. Based on the component-specific dose rate calculation formula for the measurement point outside the maze door described in NCRP Report 151 and IAEA Safety Report Series 47, the dose rate calculation formula for each component when applying the values of the drawing-based parameters and the dose rate calculation formula for each component when applying the values of conservative parameters are derived. From the two dose rate calculation formulas for each component, the dose rate verification formula for each component at the measurement point outside the maze door was derived. The resulting dose rate verification formula for each component at the measurement point outside the maze door can be compared and analyzed whether the dose rate for each component at the measurement point outside the maze door calculated by the designer falls within the range of the dose rate obtained from the derived dose rate verification formula for each component. This verification formula is considered to be practically useful in verifying the accuracy of the dose rate for each component calculated by the designer.

• Journal of Radiation Protection and Research
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• v.36 no.2
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• pp.86-92
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• 2011

This study used the optically stimulated luminescence dosimeters (OSLDs), recently, received the revaluation of usefulness in vivo dosimetry, and the diode detecters to measure the skin dose of patient with the rectal cancer. The measurements of dose delivered were compared with the planned dose from the treatment planning system (TPS). We evaluated the clinical application of OSDs in radiotherapy. We measured the calibration factor of OSLDs and used the percent depth dose to verified, also, we created the three point of surface by ten patients of rectal cancer to measured. The calibration factors of OSLD was 1.17 for 6 MV X-ray and 1.28 for 10 MV X-ray, demonstrating the energy dependency of X-ray beams. Comparison of surface dose measurement using the OSLDs and diode detectors with the planned dose from the TPS, The skin dose of patient was increased 1.16 ~ 2.83% for diode detectors, 1.36 ~ 2.17% for OSLDs. Especially, the difference between planned dose and the delivery dose was increased in the perineum, a skin of intense flexure region, and the OSLDs as a result of close spacing of measuring a variate showed a steady dose verification than the diode detecters. Therefore, on behalf of the ionization chamber and diode detecters, OSLDs could be applied clinically in the verification of radiation dose error and in vivo dosimety. The research on the dose verification of the rectal cancer in the around perineal, a surface of intense flexure region, suggest continue to be.

• Journal of the Korean Physical Society
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• v.73 no.10
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• pp.1571-1576
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• 2018

We developed and evaluated an algorithm to calculate the target radiation dose in cancer patients by measuring the transmitted dose during 3D conformal radiation treatment (3D-CRT) treatment. The patient target doses were calculated from the transit dose, which was measured using a glass dosimeter positioned 150 cm from the source. The accuracy of the transit dose algorithm was evaluated using a solid water phantom for five patient treatment plans. We performed transit dose-based patient dose verification during the actual treatment of 34 patients who underwent 3D-CRT. These included 17 patients with breast cancer, 11 with pelvic cancer, and 6 with other cancers. In the solid water phantom study, the difference between the transit dosimetry algorithm with the treatment planning system (TPS) and the measurement was $-0.10{\pm}1.93%$. In the clinical study, this difference was $0.94{\pm}4.13%$ for the patients with 17 breast cancers, $-0.11{\pm}3.50%$ for the eight with rectal cancer, $0.51{\pm}5.10%$ for the four with bone cancer, and $0.91{\pm}3.69%$ for the other five. These results suggest that transit-dosimetry-based in-room patient dose verification is a useful application for 3D-CRT. We expect that this technique will be widely applicable for patient safety in the treatment room through improvements in the transit dosimetry algorithm for complicated treatment techniques (including intensity modulated radiation therapy (IMRT) or volumetric modulated arc therapy (VMAT).

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.248-251
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• 2002

The intensity modulated radiation therapy (IMRT) with a multileaf collimator (MLC) requires the conversion of a radiation fluence map into a leaf sequence file that controls the movement of the MLC during radiation treatment of patients. Patient dose verification is clinically one of the most important parts in the treatment delivery of the radiation therapy. The three dimensional (3D) reconstruction of dose distribution delivered to the target helps to verify patient dose and to determine the physical characteristics of beams used in IMRT. A new method is presented for the pretreatment dosimetric verification of two dimensional distributions of photon intensity by means of Beam Intensity Scanner System (BISS) as a radiation detector with a custom-made software for dose calculation of fluorescence signals from scintillator. The scintillator is used to produce fluorescence from the irradiation of 6MV photons on a Varian Clinac 21EX. The BISS reproduces 3D- relative dose distribution from the digitized fluoroscopic signals obtained by digital video camera-based scintillator(DVCS) device in the IMRT. For the intensity modulated beams (IMBs), the calculations of absorbed dose are performed in absolute beam fluence profiles which are used for calculation of the patient dose distribution. The 3D-dose profiles of the IMBs with the BISS were demonstrated by relative measurements of photon beams and shown good agreement with radiographic film. The mechanical and dosimetric properties of the collimating of dynamic and/or step MLC system alter the generated intensity. This is mostly due to leaf transmission, leaf penumbra and geometry of leaves. The variations of output according to the multileaf opening during the irradiation need to be accounted for as well. These phenomena result in a fluence distribution that can be substantially different from the initial and calculative intensity modulation and therefore, should be taken into account by the treatment planning for accurate dose calculations delivered to the target volume in IMRT.

• Journal of Sensor Science and Technology
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• v.15 no.2
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• pp.102-105
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• 2006

In-vivo dosimetry is an essential tool of quality assurance programs in radiotherapy. The most commonly used techniques to verify dose are thermoluminescence dosimeter (TLD) and diode detectors. Metal oxide semiconductor field-effect transistor (MOSFET) has been recently proposed for using in radiation therapy with many advantages. The reproducibility, linearity, isotropy, dose rate dependence of the MOSFET dosimeter were studied and its availability was verified. Consequently the results can be used to improve therapeutic planning procedure and minimize treatment errors in radiotherapy.

• Journal of Korean Neurosurgical Society
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• v.47 no.2
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• pp.128-133
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• 2010

Objective : The secondary verification of Leksell Gamma Knife treatment planning system (LGP) (which is the primary verification system) is extremely important in order to minimize the risk of treatment errors. Although prior methods have been developed to verify maximum dose and treatment time, none have studied maximum dose coordinates and treatment volume. Methods : We simulated the skull shape as an ellipsoid with its center at the junction between the mammillary bodies and the brain stem. The radiation depths of the beamlets emitted from 201 collimators were calculated based on the relationship between this ellipsoid and a single beamlet expressed as a straight line. A computer program was coded to execute the algorithm. A database system was adopted to log the doses for $31{\times}31{\times}31$ or 29,791 matrix points allowing for future queries to be made of the matrix of interest. Results : When we compared the parameters in seven patients, all parameters showed good correlation. The number of matrix points with a dose higher than 30% of the maximal dose was within ${\pm}\;2%$ of LGP. The 50% dose volume, which is generally the target volume, differs maximally by 4.2%. The difference of the maximal dose ranges from 0.7% to 7%. Conclusion : Based on the results, the variable ellipsoid modeling technique or variable ellipsoid modeling technique (VEMT) can be a useful and independent tool to verify the important parameters of LGP and make up for LGP.

• Progress in Medical Physics
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• v.20 no.2
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• pp.88-96
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• 2009

Radiation treatment for skin cancer has recently increased in tomotherapy. It was reported that required dose could be delivered with homogeneous dose distribution to the target without field matching using electron and photon beam. Therapeutic beam of tomotherapy, however, has several different physical characteristic and irradiation of helical beam is involved in the mechanically dynamic factors. Thus verification of skin dose is requisite using independent tools with additional verification method. Modified phantom for dose measurement was developed and skin dose verification was performed using inserted thermoluminescent dosimeters (TLDs) and GafChromic EBT films. As the homogeneous dose was delivered to the region including surface and 6 mm depth, measured dose using films showed about average 2% lower dose than calculated one in treatment planning system. Region indicating about 14% higher and lower absorbed dose was verified on measured dose distribution. Uniformity of dose distribution on films decreased as compared with that of calculated results. Dose variation affected by inhomogeneous material, Teflon, little showed. In regard to the measured dose and its distribution in tomotherapy, verification of skin dose through measurement is required before the radiation treatment for the target located at the curved surface or superficial depth.

• Journal of the Korean Society of Radiology
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• v.10 no.7
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• pp.521-529
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• 2016

Since Gamma Knife(R) radiosurgery(GKRS) is based on a single-fraction high dose treatment strategy, independent verification for the results of Leksell GammaPlan(R) (LGP) is an important procedure in assuring patient safety and minimizing the risk of treatment errors. Several verification methods have been developed and reported previously. Thus these methods were tested statistically and tried on Leksell Gamma Knife(LGK) target treatments through the embodiment of the previously proposed algorithms(PPA). The purpose of this study was to apply and evaluate the accuracy of verification methods for LGK target treatments using PPA. In the study 10 patients with intracranial lesion treated by GKRS were included. We compared the data from PPA and LGP in terms of maximum dose, arbitrary point dose, and treatment time at the isocenter locations. All data were analyzed by Paired t-test, which is statistical method used to compare two different measurement techniques. No statistical significance in maximal dose at 10 cases was observed between PPA and LGP. Differences in average maximal dose ranged from -0.53 Gy to 3.71 Gy. The arbitrary point dose calculated by PPA and LGP was not statistically significant too. But we found out the statistical difference with p=0.021 between TMR and LGP for treatment time at the isocenter locations. PPA can be incorporated as part of a routine quality assurance(QA) procedure to minimize the chance of a wrong overdose. Statistical analyses demonstrated that PPA was in excellent agreement with LGP when considering the maximal dose and the arbitrary point dose for the best plan of GKRS. Due to the easy applicability we hope PPA can be widely used.

• Progress in Medical Physics
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• v.25 no.1
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• pp.23-30
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• 2014

The purpose of this study is to evaluate the developed dose verification program for in vivo dosimetry based on transit dose in radiotherapy. Five intensity modulated radiotherapy (IMRT) plans of lung cancer patients were used in the irradiation of a homogeneous solid water phantom and anthropomorphic phantom. Transit dose distribution was measured using electronic portal imaging device (EPID) and used for the calculation of in vivo dose in patient. The average passing rate compared with treatment planning system based on a gamma index with a 3% dose and a 3 mm distance-to-dose agreement tolerance limit was 95% for the in vivo dose with the homogeneous phantom, but was reduced to 81.8% for the in vivo dose with the anthropomorphic phantom. This feasibility study suggested that transit dose-based in vivo dosimetry can provide information about the actual dose delivery to patients in the treatment room.

• Progress in Medical Physics
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• v.32 no.4
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• pp.116-121
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• 2021

Purpose: To investigate the effects of dose rate on intensity-modulated radiation therapy (IMRT) quality assurance (QA). Methods: We performed gamma tests using portal dose image prediction and log files of a multileaf collimator. Thirty treatment plans were randomly selected for the IMRT QA plan, and three verification plans for each treatment plan were generated with different dose rates (200, 400, and 600 monitor units [MU]/min). These verification plans were delivered to an electronic portal imager attached to a Varian medical linear accelerator, which recorded and compared with the planned dose. Root-mean-square (RMS) error values of the log files were also compared. Results: With an increase in dose rate, the 2%/2-mm gamma passing rate decreased from 90.9% to 85.5%, indicating that a higher dose rate was associated with lower radiation delivery accuracy. Accordingly, the average RMS error value increased from 0.0170 to 0.0381 cm as dose rate increased. In contrast, the radiation delivery time reduced from 3.83 to 1.49 minutes as the dose rate increased from 200 to 600 MU/min. Conclusions: Our results indicated that radiation delivery accuracy was lower at higher dose rates; however, the accuracy was still clinically acceptable at dose rates of up to 600 MU/min.