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Yoon, Myonggeun,Shin, Dongho,Kwak, Jungwon,Park, Soah,Lim, Young Kyung,Kim, Dongwook,Park, Sung Yong,Lee, Se Byeong,Shin, Kyung Hwan,Kim, Tae Hyun,Cho, Kwan Ho Elsevier 2009 Medical dosimetry Vol.34 No.3
<P><B>Abstract</B></P><P>We compared the main characteristics of movement-induced dose reduction during photon and proton beam treatment, based on an analysis of dose-volume histograms. To simulate target movement, a target contour was delineated in a scanned phantom and displaced by 3 to 20 mm. Although the dose reductions to the target in the 2 treatment systems were similar for transverse (perpendicular to beam direction) target motion, they were completely different for longitudinal (parallel to beam direction) target motion. While both modalities showed a relationship between the degree of target shift and the reduction in dose coverage, dose reduction showed a strong directional dependence in proton beam treatment. Clinical simulation of target movement for a prostate cancer patient showed that, although coverage and conformity indices for a 6-mm lateral movement of the prostate were reduced by 9% and 16%, respectively, for proton beam treatment, they were reduced by only 1% and 7%, respectively, for photon treatment. This difference was greater for a 15-mm target movement in the lateral direction, which lowered the coverage and conformity indices by 34% and 54%, respectively, for proton beam treatment, but changed little during photon treatment. In addition, we found that the equivalent uniform dose (EUD) and homogeneity index show similar characteristics during target movement. These results suggest that movement-induced dose reduction differs significantly between photon and proton beam treatment. Attention should be paid to the target margin in proton beam treatment due to the distinct characteristics of heavy ion beams.</P>
A new homogeneity index based on statistical analysis of the dose–volume histogram
Yoon, Myonggeun,Park, Sung Yong,Shin, Dongho,Lee, Se Byeong,Pyo, Hong Ryull,Kim, Dae Yong,Cho, Kwan Ho unknown 2007 Journal of applied clinical medical physics Vol.8 No.2
<P>The goal of the present study was to develop a new dose–volume histogram (DVH)– based homogeneity index for effectively evaluating the dose homogeneity of intensity‐modulated radiotherapy plans. The new index, called the sigma‐index (“<I>S</I>‐index”) is defined as the standard deviation of the normalized differential DVH curve. In a study of 16 patients with brain tumors at our institution, the <I>S</I>‐index was found to vary from 0.80 to 3.15. Our results showed that the <I>S</I>‐index provides a more reliable and accurate measure of dose homogeneity than that given by conventional methods. A guideline for evaluating the dose homogeneity of treatment plans based on the <I>S</I>‐index and its relation to equivalent uniform dose is discussed.</P><P>PACS numbers: 87.53.Xd, 87.53.Tf</P>
Risk of a second cancer from scattered radiation in acoustic neuroma treatment
Yoon, Myonggeun,Lee, Hyunho,Sung, Jiwon,Shin, Dongoh,Park, Sungho,Chung, Weon Kuu,Jahng, Geon-Ho,Kim, Dong Wook Korean Physical Society 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.12
The present study aimed to compare the risk of a secondary cancer from scattered and leakage doses in patients receiving intensity-modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT), and stereotactic radiosurgery (SRS). Four acoustic neuroma patients were treated with IMRT, VMAT, or SRS. Their excess relative risk (ERR), excess absolute risk (EAR), and lifetime attributable risk (LAR) of a secondary cancer were estimated using the corresponding secondary doses measured at various organs by using radio-photoluminescence glass dosimeters (RPLGD) placed inside a humanoid phantom. When a prescription dose was delivered in the planning target volume of the 4 patients, the average organ equivalent doses (OED) at the thyroid, lung, liver, bowel, bladder, prostate (or ovary), and rectum were 14.6, 1.7, 0.9, 0.8, 0.6, 0.6, and 0.6 cGy, respectively, for IMRT whereas they were 19.1, 1.8, 2.0, 0.6, 0.4, 0.4, and 0.4 cGy, respectively, for VMAT, and 22.8, 4.6, 1.4, 0.7, 0.5, 0.5, and 0.5 cGy, respectively, for SRS. The OED decreased as the distance from the primary beam increased. The thyroid received the highest OED compared to other organs. A lifetime attributable risk evaluation estimated that more than 0.03% of acoustic neuroma (AN) patients would get radiation-induced cancer within 20 years of receiving radiation therapy. The organ with the highest radiation-induced cancer risk after radiation treatment for AN was the thyroid. We found that the LAR could be increased by the transmitted dose from the primary beam. No modality-specific difference in radiation-induced cancer risk was observed in our study.
Yoon, Myonggeun,Kim, Jin-Sung,Shin, Dongho,Park, Sung Yong,Lee, Se Byeong,Kim, Dae Yong,Kim, Taehyun,Shin, Kyung Hwan,Cho, Kwan Ho Wiley (John WileySons) 2008 Medical physics Vol.35 No.8
<P>The authors have developed an automatic quality assurance method based on computerized tomography (CT) data for physically manufactured proton range compensators. Eight range compensators used for proton therapy at their institution were scanned using CT and their depth distributions were compared with data provided by a proton treatment planning system (TPS). The depth difference (DD), distance to agreement (DTA), and a composite analysis (CA) indicating regions that passed either of the tests were used for depth verification. When the tolerance limits were set at 3 mm for DD and 1 mm for DTA, the average percentages of points exceeding the acceptance criteria for DD, DTA, and CA for the eight compensators were 9.0%, 5.3% and 3.2%, respectively. In general, the percentages of points exceeding the acceptance criteria were much higher in DD than in DTA analysis and mismatch of depth was greater in regions with high depth gradients. This is considered to arise mainly because of systematic errors such as the physical size of the drill, slight bending or slipping of the drill bit near high gradient regions, the limit of CT resolution, and the uncertainty in CT number. When the tolerance limit of DTA was increased from 1 to 2 mm, the average percentage of points exceeding the acceptance criteria for DTA was reduced from 5.3% to 0.9%. Their results show that depth comparison of proton range compensators based on CT images can provide more systematic data than does the current method, in which a representative group of drill points is measured manually.</P>
Effect of radiation scattering on dose uniformity in open and closed cell culture vessels
Yoon, Myonggeun,Park, Sung Yong,Shin, Jungwook,Kwak, Jungwon,Park, Junghun,Shin, Dongho,Park, Soah,Lee, Se Byeong,Lee, Doo Hyun,Shin, Kyung Hwan,Pyo, Hong Ryull,Kim, Joo-Young,Cho, Kwan Ho Informa Healthcare 2007 International Journal of Radiation Biology Vol.83 No.8
<P> Purpose: Dose uniformity in cell culture vessels such as Petri dishes and anoxic irradiation chambers is very important in radiobiological work as dose uniformity affects cell survival probabilities. In this study, we investigated X-ray dose inhomogeneity, caused by scattering, in typical culture vessels. Materials and methods: Three different cubic cell culture vessels, with side lengths of 10 cm, 15 cm and 20 cm, were designed and irradiated by X-rays of 6 MV and 15 MV at a source-to-surface distance (SSD) of 100 cm using a Varian 2100CD linear accelerator. Results: The relative X-ray dose distribution in a cell culture vessel depended strongly on whether the vessel had a lid. The percentage of the cell culture surface with the dose differing by more than 10% from the mean value of the dose was 43.4% in lidless vessels and 9.7% in lidded vessels. Conclusions: In radiobiological work, X-ray dose inhomogeneity within a cell culture vessel is not negligible and the placement of cells in the vessel should be carefully considered.</P>
Increased Eciency of Range Verification in Routine QA for Pencil-Beam Scanning Proton Therapy
Seonghoon Jeong,Myonggeun Yoon,Jaeman Son,Kwangzoo Chung 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.7
Quality assurance (QA) is required when performing pencil-beam scanning proton therapy, but the eciency of QA is degraded in proportion to the energy of the protons. We developed a method to assess the preferred energy range and distal fall-off by combining multiple Bragg peaks to increase the eciency of QA. Beams of 70, 110, 150, 190, and 230 MeV for exposure were planned using a treatment planning system. The Bragg curves for therapeutic proton beams were modeled using three different fitting function models, allowing the feasibility of a simple modeling of the Bragg curve to be investigated. The planned beams were exposed and measured using a multi-layered ionization chamber. Software developed using a Python tool could detect five Bragg peaks from the integrated curves that were fitted based on polynomial, cubic spline and Landau distributions. This software could calculate the range and distal fall-off of the five fitted peaks. For the verification of the accuracy of this method, the calculated results were compared with the range and distal fall- off obtained by exposing and analyzing five single-energy beams individually. Comparisons of the Bragg peaks for the five energies exposed individually with the results obtained by exposing them all at once showed that the ranges of the energy beams when using the polynomial fitting and the cubic spline modes were 0.16 mm and 0.10 mm longer, respectively, while the distal fall-offs were 0.14 mm and 0.06 mm shorter, respectively. When using the Landau distribution fitting, the range was 0.06 mm longer and the distal fall-off was 0.04 mm shorter. Analyses of the ranges and distal fall-offs of the five energy beams exposed at once with single-beam loading by using the method developed in this study showed no significant differences from the results obtained by exposing the energy beams individually. Thus, range verification QA by using the proposed method is not only suitable for single-proton beams with multiple energies but also reduces the measurement time.
Seonghoon Jeong,Myonggeun Yoon,Kwangzoo Chung 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.8
This study describes the development of a simple method to assess inter-fractional deviations of delivered proton beams in treatment rooms. To monitor the treatment beam, we measured the field-by-field beam fluences by attaching the EBT3 film to the snout, followed by a simple constancy check based on comparisons between the reference beam fluences (acquired during the pre-treatment quality assurance process) and the test beam fluences (acquired during treatment). The feasibility of the proposed treatment beam-monitoring system was confirmed by evaluating 12 treatment fields for each of six patients (brain, liver, prostate, lung, cranial and spinal area, and head and neck). The constancy of the treatment beams was verified by using a gamma index analysis to compare three measurements per field with the reference beam fluence. On the basis of the 3%/3 mm criterion, the average gamma-index passing rates for all measurements were over 99.6%. These results suggest that the constancy of fractional proton beams delivered to patients in treatment rooms can be verified with EBT3 film-based proton-beam monitoring system that can be easily attached to the treatment nozzle and is cost effective.
Chung, Kwangzoo,Yoon, Myonggeun,Son, Jaeman,Yong Park, Sung,Lee, Kiho,Shin, Dongho,Kyung Lim, Young,Byeong Lee, Se The American Association of Physicists in Medicine 2013 Medical physics Vol.40 No.2
<P>To evaluate the transit dose based patient specific quality assurance (QA) of intensity modulated radiation therapy (IMRT) for verification of the accuracy of dose delivered to the patient.</P>