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  • Original Article 2014-09-30 2014-09-30 \ 0 \ 283 \ 136

    Determination of TRS-398 Quality Factors for Cs-137 Gamma Rays in Reference Dosimetry

    Sang Koo Kang, Dong Joo Rhee, Yeong Rok Kang, Jeung Kee Kim, Dong Hyeok Jeong

    Abstract
    The Cs-137 irradiator is widely used to irradiate biological samples for radiobiological research. To obtain the accurate outcomes, correct measurements of the delivered absorbed dose to a sample is important. The IAEA protocols such as TRS-277 and TRS-398 were recommended for the Cs-137 reference dosimetry. However in TRS-398 protocol, currently known as the most practical dosimetry protocol, the quality factor (????) for Cs-137 gamma rays is not suggested. Therefore, the use of TRS-398 protocol is currently unavailable for the Cs-137 dosimetry directly. The calculation method previously introduced for high energy photon beams in radiotherapy was used for deriving the Cs-137 beam qualities (????) for the 15 commercially available farmer type ionization chambers in this study. In conclusion, ???? values were ranged from 0.998 to 1.002 for Cs-137 gamma rays. These results can be used as the reference and dosimeter calibrations for Cs-137 gamma rays in the future radiobiological researches.
  • Original Article 2014-09-30 2014-09-30 \ 0 \ 144 \ 78

    Verification of Gated Radiation Therapy: Dosimetric Impact of Residual Motion

    Inhwan Yeo, Jae Won Jung

    Abstract
    In gated radiation therapy (gRT), due to residual motion, beam delivery is intended to irradiate not only the true extent of disease, but also neighboring normal tissues. It is desired that the delivery covers the true extent (i.e. clinical target volume or CTV) as a minimum, although target moves under dose delivery. The objectives of our study are to validate if the intended dose is surely delivered to the true target in gRT and to quantitatively understand the trend of dose delivery on it and neighboring normal tissues when gating window (GW), motion amplitude (MA), and CTV size changes. To fulfill the objectives, experimental and computational studies have been designed and performed. A custom-made phantom with rectangle- and pyramid-shaped targets (CTVs) on a moving platform was scanned for four-dimensional imaging. Various GWs were selected and image integration was performed to generate targets (internal target volume or ITV) for planning that included the CTVs and internal margins (IM). The planning was done conventionally for the rectangle target and IMRT optimization was done for the pyramid target. Dose evaluation was then performed on a diode array aligned perpendicularly to the gated beams through measurements and computational modeling of dose delivery under motion. This study has quantitatively demonstrated and analytically interpreted the impact of residual motion including penumbral broadening for both targets, perturbed but secured dose coverage on the CTV, and significant doses delivered in the neighboring normal tissues. Dose volume histogram analyses also demonstrated and interpreted the trend of dose coverage: for ITV, it increased as GW or MA decreased or CTV size increased; for IM, it increased as GW or MA decreased; for the neighboring normal tissue, opposite trend to that of IM was observed. This study has provided a clear understanding on the impact of the residual motion and proved that if breathing is reproducible gRT is secure despite discontinuous delivery and target motion. The procedures and computational model can be used for commissioning, routine quality assurance, and patient-specific validation of gRT. More work needs to be done for patient-specific dose reconstruction on CT images.
  • Original Article 2014-09-30 2014-09-30 \ 0 \ 124 \ 65

    Clinical Application of Dose Reconstruction Based on Full-Scope Monte Carlo Calculations: Composite Dose Reconstruction on a Deformed Phantom

    Inhwan Yeo*, Qianyi Xu, Yan Chen, Jae Won Jung, Jong Oh Kim

    Abstract
    The purpose of this study was to develop a system of clinical application of reconstructed dose that includes dose reconstruction, reconstructed dose registration between fractions of treatment, and dose-volume-histogram generation and to demonstrate the system on a deformable prostate phantom. To achieve this purpose, a deformable prostate phantom was embedded into a 20 cm-deep and 40 cm-wide water phantom. The phantom was CT scanned and the anatomical models of prostate, seminal vesicles, and rectum were contoured. A coplanar 4-field intensity modulated radiation therapy (IMRT) plan was used for this study. Organ deformation was simulated by inserting a “transrectal” balloon containing 20 ml of water. A new CT scan was obtained and the deformed structures were contoured. Dose responses in phantoms and electronic portal imaging device (EPID) were calculated by using the XVMC Monte Carlo code. The IMRT plan was delivered to the two phantoms and integrated EPID images were respectively acquired. Dose reconstruction was performed on these images using the calculated responses. The deformed phantom was registered to the original phantom using an in-house developed software based on the Demons algorithm. The transfer matrix for each voxel was obtained and used to correlate the two sets of the reconstructed dose to generate a cumulative reconstructed dose on the original phantom. Forwardly calculated planning dose in the original phantom was compared to the cumulative reconstructed dose from EPID in the original phantom. The prescribed 200 cGy isodose lines showed little difference with respect to the “prostate” and “seminal vesicles”, but appreciable difference (3%) was observed at the dose level greater than 210 cGy. In the rectum, the reconstructed dose showed lower volume coverage by a few percent than the plan dose in the dose range of 150 to 200 cGy. Through this study, the system of clinical application of reconstructed dose was successfully developed and demonstrated. The organ deformation simulated in this study resulted in small but observable dose changes in the target and critical structure.
  • Original Article 2014-09-30 2014-09-30 \ 0 \ 269 \ 166

    An Experimental Method for the Scatter Correction of MV Images Using Scatter to Primary Ratios (SPRs)

    Hosang Jeon*, Dahl Park, Jayeong Lee*, Jiho Nam*, Wontaek Kim, Yongkan Ki, Donghyun Kim, Ju Hye Lee, Dongwon Kim

    Abstract
    In general radiotherapy, mega-voltage (MV) x-ray images are widely used as the unique method to verify radio-therapeutic fields. But, the image quality of MV images is much lower than that of kilo-voltage x-ray images due to scatter interactions. Since 1990s, studies for the scatter correction have performed with digital-based MV imaging systems. In this study, a novel method for the scatter correction is suggested using scatter to primary ratio (SPR), instead of conventional methods such as digital image processing or scatter kernel calculations.We measured two MV images with and without a solid water phantom describing a patient body with given imaging conditions, and calculated un-attenuated ratios. Then, we obtained SPR distributions for the scatter correction. For experimental validation, a line-pair (LP) phantom using several Al bars and a clinical pelvis MV image was used. As the result, scatter signals of the LP phantom image were successfully reduced so that original density distribution of the phantom was restored. Moreover, image contrast values increased after SPR correction at all ROIs of the clinical image. The mean value of increases was 48%. The SPR correction method suggested in this study has high reliability because it is based on actually measured data. Also, this method can be easily adopted in clinics without additional cost. We expected that the SPR correction can be an effective method to improve the quality of MV image guided radiotherapy.
  • Original Article 2014-09-30 2014-09-30 \ 0 \ 242 \ 84

    Preliminary Study for Imaging of Therapy Region from Boron Neutron Capture Therapy

    Joo-Young Jung*, Do-Kun Yoon*, Seong-Min Han, HongSeok Jang, Tae Suk Suh*

    Abstract
    The purpose of this study was to confirm the feasibility of imaging of therapy region from the boron neutron capture therapy (BNCT) using the measurement of the prompt gamma ray depending on the neutron flux. Through the Monte Carlo simulation, we performed the verification of physical phenomena from the BNCT; (1) the effects of neutron according to the existence of boron uptake region (BUR), (2) the internal and external measurement of prompt gamma ray dose, (3) the energy spectrum by the prompt gamma ray. All simulation results were deducted using the Monte Carlo n-particle extended (MCNPX, Ver.2.6.0, Los Alamos National Laboratory, Los Alamos, NM, USA) simulation tool. The virtual water phantom, thermal neutron source, and BURs were simulated using the MCNPX. The energy of the thermal neutron source was defined as below 1 eV with 2,000,000 n/sec flux. The prompt gamma ray was measured with the direction of beam path in the water phantom. The detector material was defined as the lutetium-yttrium oxyorthosilicate (Lu0,6Y1,4Si0,5:Ce; LYSO) scintillator with lead shielding for the collimation. The BUR's height was 5 cm with the 28 frames (bin: 0.18 cm) for the dose calculation. The neutron flux was decreased dramatically at the shallow region of BUR. In addition, the dose of prompt gamma ray was confirmed at the 9 cm depth from water surface, which is the start point of the BUR. In the energy spectrum, the prompt gamma ray peak of the 478 keV was appeared clearly with full width at half maximum (FWHM) of the 41 keV (energy resolution: 8.5%). In conclusion, the therapy region can be monitored by the gamma camera and single photon emission computed tomography (SPECT) using the measurement of the prompt gamma ray during the BNCT.
  • Original Article 2014-09-30 2014-09-30 \ 0 \ 194 \ 57

    Effect of ATP on Calcium Channel Modulation in Rat Adrenal Chromaffin Cells

    Kyung Ah Kim*, Yong Sook Goo

    Abstract
    ATP in quantity co-stored with neurotransmitters in the secretory vesicles of neurons, by being co-released with the neurotransmitters, takes an important role to modulate the stimulus-secretion response of neurotransmitters. Here, in this study, the modulatory effect of ATP was studied in Ca2+ channels of cultured rat adrenal chromaffin cells to investigate the physiological role of ATP in neurons. The Ca2+ channel current was recorded in a whole-cell patch clamp configuration, which was modulated by ATP. In 10 mM Ba2+ bath solution, ATP treatment (0.1 mM) decreased the Ba2+ current by an average of 36±6% (n=8), showing a dose-dependency within the range of 10−4∼10−1 mM. The current was recovered by ATP washout, demonstrating its reversible pattern. This current blockade effect of ATP was disinhibited by a large prepulse up to +80 mV, since the Ba2+ current increment was larger when treated with ATP (37±5%, n=11) compared to the control (25±3%, n=12, without ATP). The Ba2+ current was recorded with GTPγS, the non-hydrolyzable GTP analogue, to determine if the blocking effect of ATP was mediated by G-protein. The Ba2+ current decreased down to 45% of control with GTPγS. With a large prepulse (+80 mV), the current increment was 34±4% (n=19), which 25±3% (n=12) under control condition (without GTPγS). The Ba2+ current waveform was well fitted to a single-exponential curve for the control, while a double-exponential curve best fitted the current signal with ATP or GTPγS. In other words, a slow activation component appeared with ATP or GTPγS, which suggested that both ATP and GTPγS caused slower activation of Ca2+ channels via the same mechanism. The results suggest that ATP may block the Ca2+ channels by G-protein and this Ca2+ channel blocking effect of ATP is important in autocrine (or paracrine) inhibition of adrenaline secretion in chromaffin cell.
  • Original Article 2014-09-30 2014-09-30 \ 0 \ 214 \ 142

    Evaluation of Dose Change by Using the Deformable Image Registration (DIR) on the Intensity Modulated Radiation Therapy (IMRT) with Glottis Cancer

    Woo Chul Kim*, Chul Kee Min*, Suk Lee, Sang Hyoun Choi, Kwang Hwan Cho*, Jae Hong Jung*, Eun Seog Kim*, Seung-Gu Yeo*, Soo-Il Kwon, Kil-Dong Lee

    Abstract
    The purpose of this study is to evaluate the variation of the dose which is delivered to the patients with glottis cancer under IMRT (intensity modulated radiation therapy) by using the 3D registration with CBCT (cone beam CT) images and the DIR (deformable image registration) techniques. The CBCT images which were obtained at a one-week interval were reconstructed by using B-spline algorithm in DIR system, and doses were recalculated based on the newly obtained CBCT images. The dose distributions to the tumor and the critical organs were compared with reference. For the change of volume depending on weight at 3 to 5 weeks, there was increased of 1.38∼2.04 kg on average. For the body surface depending on weight, there was decreased of 2.1 mm. The dose with transmitted to the carotid since three weeks was increased compared be more than 8.76% planned, and the thyroid gland was decreased to 26.4%. For the physical evaluation factors of the tumor, PITV, TCI, rDHI, mDHI, and CN were decreased to 4.32%, 5.78%, 44.54%, 12.32%, and 7.11%, respectively. Moreover, Dmax, Dmean, V67.50, and D95 for PTV were increased or decreased to 2.99%, 1.52%, 5.78%, and 11.94%, respectively. Although there was no change of volume depending on weight, the change of body types occurred, and IMRT with the narrow composure margin sensitively responded to such a changing. For the glottis IMRT, the patient’s weight changes should be observed and recorded to evaluate the actual dose distribution by using the DIR techniques, and more the adaptive treatment planning during the treatment course is needed to deliver the accurate dose to the patients.
  • Original Article 2014-09-30 2014-09-30 \ 0 \ 250 \ 107

    Comparison of Dose Distribution in Spine Radiosurgery Plans: Simultaneously Integrated Boost and RTOG 0631 Protocol

    Su Yeon Park, Dongryul Oh, Hee Chul Park, Jin Sung Kim, Jong Sik Kim, Eun Hyuk Shin, Hye Young Kim, Sang Hoon Jung, Youngyih Han

    Abstract
    In this study, we compareddose distributions from simultaneously integrated boost (SIB) method versus the RTOG 0631 protocol for spine radiosurgery. Spine radiosurgery plans wereperformed in five patients with localized spinal metastases from hepatocellular carcinoma. The computed tomography (CT) and T1- and T2-weighted magnetic resonance imaging (MRI) were fused for delineating of GTV and spinal cord. In SIB plan, the clinical target volume (CTV1) was included the whole compartments of the involved spine, while RTOG 0631 protocol defines the CTV2 as the involved vertebral body and both left and right pedicles. The CTV2 includes transverse process and posterior element according to the extent of GTV. The doses were prescribed 18 Gy to GTV and 10 Gy to CTV1 in SIB plan, while the prescription of RTOG 0631 protocol was applied 18 Gy to CTV2. The results of dose-volume histogram (DVH) showed that there were competitive in target coverage, while the doses of spinal cord andother normal organs were lower in SIB method than in RTOG 0631 protocol. The 85% irradiated volume of VB in RTOG 0631 protocol was similar to that in the SIB plan. However, the dose to normal organs in RTOG 0631 had a tendency to higher than that in SIB plan. The SIB plan might be an alternative method in case of predictive serious complications of surrounded normal organs. In conclusion, although both approaches of SIB or RTOG 0631 showed competitive planning results, tumor control probability (TCP) and normal tissue complication probability (NTCP) through diverse clinical researches should be analyzed in the future.
  • Original Article 2014-09-30 2014-09-30 \ 0 \ 123 \ 63

    Analysis of Output Constancy Checks Using Process Control Techniques in Linear Accelerators

    Se An Oh*, Ji Woon Yea*, Sang Won Kim*, Rena Lee, Sung Kyu Kim*

    Abstract
    The purpose of this study is to evaluate the results for the quality assurance through a statistical analysis on the output characteristics of linear accelerators belonging to Yeungnam University Medical Center by using the Shewhart-type chart, Exponentially weighted moving average chart (EWMA) chart, and process capability indices Cp and Cpk. To achieve this, we used the output values measured using respective treatment devices (21EX, 21EX-S, and Novalis Tx) by medical physicists every month from September, 2012 to April, 2014. The output characteristics of treatment devices followed the IAEA TRS-398 guidelines, and the measurements included photon beams of 6 MV, 10 MV, and 15 MV and electron beams of 4 MeV, 6 MeV, 9 MeV, 12 MeV, 16MeV, and 20 MeV. The statistical analysis was done for the output characteristics measured, and was corrected every month. The width of control limit of weighting factors and measurement values were calculated as ?= 0.10 and L=2.703, respectively; and the process capability indices Cp and Cpk were greater than or equal to 1 for all energies of the linear accelerators (21EX, 21EX-S, and Novalis Tx). Measured values of output doses with drastic and minor changes were found through the Shewhart-type chart and EWMA chart, respectively. The process capability indices Cp and Cpk of the treatment devices in our institution were, respectively, 2.384 and 2.136 for 21EX, 1.917 and 1.682 for 21EX-S, and 2.895 and 2.473 for Novalis Tx, proving that Novalis Tx has the most stable and accurate output characteristics.
Korean Society of Medical Physics

Vol.35 No.2
2014-09-30

pISSN 2508-4445
eISSN 2508-4453
Formerly ISSN 1226-5829

Frequency: Quarterly

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