• Progress in Medical Physics
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• v.26 no.4
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• pp.208-214
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• 2015

The aim of this study is to investigate the effect of low magnetic field on dose distribution in the partial-breast irradiation (PBI). Eleven patients with an invasive early-stage breast carcinoma were treated prospectively with PBI using 38.5 Gy delivered in 10 fractions using the $ViewRay^{(R)}$ system. For each of the treatment plans, dose distribution was calculated with magnetic field and without magnetic field, and the difference between dose and volume for each organ were evaluated. For planning target volume (PTV), the analysis included the point minimum ($D_{min}$), maximum, mean dose ($D_{mean}$) and volume receiving at least 90% ($V_{90%}$), 95% ($V_{95%}$) and 107% ($V_{107%}$) of the prescribed dose, respectively. For organs at risk (OARs), the ipsilateral lung was analyzed with $D_{mean}$ and the volume receiving 20 Gy ($V_{20\;Gy}$), and the contralateral lung was analyzed with only $D_{mean}$. The heart was analyzed with $D_{mean}$, $D_{max}$, and $V_{20\;Gy}$, and both inner and outer shells were analyzed with the point $D_{min}$, $D_{max}$ and $D_{mean}$, respectively. For PTV, the effect of low magnetic field on dose distribution showed a difference of up to 2% for volume change and 4 Gy for dose. In OARs analysis, the significant effect of the magnetic field was not observed. Despite small deviation values, the average difference of mean dose values showed significant difference (p<0.001), but there was no difference of point minimum dose values in both sehll structures. The largest deviation for the average difference of $D_{max}$ in the outer shell structure was $5.0{\pm}10.5Gy$ (p=0.148). The effect of low magnetic field of 0.35 T on dose deposition by a Co-60 beam was not significantly observed within the body for PBI IMRT plans. The dose deposition was only appreciable outside the body, where a dose build-up due to contaminated electrons generated in the treatment head and scattered electrons formed near the body surface.

• The Journal of Korean Society for Radiation Therapy
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• v.19 no.2
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• pp.107-112
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• 2007

Purpose: The pelvic phantom was fabricated in the following purposes: (1) Dose verification of IMRT plan using Eclipse planning computer, (2) to study the interface effect at the interface between rectal wall and air. The TLD can be inserted in the pelvic phantom to confirm the dose distribution as well as uncertainty at the interface. Materials and Methods: A pelvic phantom with the dimension of 30 cm diameter, 20 cm height and 20 cm thickness was fabricated to investigate the dose at the rectal wall. The phantom was filled with water and has many features like bladder, rectum, and prostate and seminal vesicle (SV). The rectum is made of 3 cm-dimater plastic pipe, and it cab be blocked by using a plug, and film can be inserted around the rectal wall. The phantom was scanned with Philips Brillance scanner and various organs such as prostate, SV, and rectal wall, and bladder wall were delineated. The treatment parameters used in this study are the same as those used in the protocols in the SNUH. TLD chips are inserted to the phantom to evaluate the dose distribution to the rectal wall (to simulate high dose gradient region), bladder wall and SV (to simulate the high dose region) and 2 spots in anterior surface (to simulate the low dose region). The TLD readings are compared with those of the planning computer (ECLIPSE, Varian, USA). Results: The target TLD doses represented as the prostate and SV show excellent agreements with the doses from the RTP within +/-3%. The rectal wall doses measured at the rectal wall are different from the those of the RTP by -11%. This is in literatures called as an interface effect. The underdosages at the rectal wall is independent of 3 heterogeneity correction algorithm in the Eclipse RTP. Also the low dose regions s represented as surface in this study were within +/-1%. Conclusion: The RTP estimate the dosage very accurately withihn +/-3% in the high dose (SV, or prostate) and low dose region (surface). However, the dosage at the rectal wall differed by as much as 11% (In literatures, the underdosage of 9$\sim$15% were reported). This range of errors occurs at the interface, for example, at the interface between lung and chest wall, or vocal cord. This interface effect is very important in clinical situations, for example, to estimate the NTCP (normal tissue complication probability) and to estimate the limitations of the current RTP system. Monte-carlo-based RTP will handle this issue correctly.

• The Journal of Korean Society for Radiation Therapy
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• v.25 no.1
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• pp.57-67
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• 2013

Purpose: Replacing the film which used to be used for checking the set-up of the patient and dosimetry during radiation therapy, more and more EPID equipped devices are in use at present. Accordingly, this article tried to evaluated the accuracy of the position check-up and the usefulness of dosimetry during the use of an electronic portal imaging device. Materials and Methods: On 50 materials acquired with the search of Korea Society Radiotherapeutic Technology, The Korean Society for Radiation Oncology, and Pubmed using "EPID", "Portal dosimetry", "Portal image", "Dose verification", "Quality control", "Cine mode", "Quality - assurance", and "In vivo dosimetry" as indexes, the usefulness of EPID was analyzed by classifying them as history of EPID and dosimetry, set-up verification and characteristics of EPID. Results: EPID is developed from the first generation of Liquid-filled ionization chamber, through the second generation of Camera-based fluoroscopy, and to the third generation of Amorphous-silicon EPID imaging modes can be divided into EPID mode, Cine mode and Integrated mode. When evaluating absolute dose accuracy of films and EPID, it was found that EPID showed within 1% and EDR2 film showed within 3% errors. It was confirmed that EPID is better in error measurement accuracy than film. When gamma analyzing the dose distribution of the base exposure plane which was calculated from therapy planning system, and planes calculated by EDR2 film and EPID, both film and EPID showed less than 2% of pixels which exceeded 1 at gamma values (r%>1) with in the thresholds such as 3%/3 mm and 2%/2 mm respectively. For the time needed for full course QA in IMRT to compare loads, EDR2 film recorded approximately 110 minutes, and EPID recorded approximately 55 minutes. Conclusion: EPID could easily replace conventional complicated and troublesome film and ionization chamber which used to be used for dosimetry and set-up verification, and it was proved to be very efficient and accurate dosimetry device in quality assurance of IMRT (intensity modulated radiation therapy). As cine mode imaging using EPID allows locating tumors in real-time without additional dose in lung and liver which are mobile according to movements of diaphragm and in rectal cancer patients who have unstable position, it may help to implement the most optimal radiotherapy for patients.

• Progress in Medical Physics
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• v.25 no.1
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• pp.15-22
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• 2014

The IMRT is proper implement to get high dose deliver to tumor as its shape and selective approach in radiation therapy. Since the IMRT is performed as modulated the radiation fluence by the MLC created the open shapes and its irradiation time, the dose of segment of radiation field effects on the cumulated portal dose. The accurate output factor of small and step shape of segment is important to improve the determination of deliver tumor dose as it is directly proportional to dose. This experiment performed with the 6 MV photon beam of Clinac Ex(Varian) from $3{\times}3cm^2$ to $0.5{\times}0.5cm^2$ small field size for collimator jaw in MLC free and/or for MLC open field in fixed collimator jaw $10{\times}10cm^2$ using the CC01 ion chamber, SFD diode, diamond detector and X-Omat film dosimetry. As results of normalized to the reference field of $10{\times}10cm^2$ of MLC, the output factor of $3{\times}3cm^2$ showed $0.899{\pm}0.0106$, $0.855{\pm}0.0106$ for $2{\times}2cm^2$, $0.764{\pm}0.0082$ for $1{\times}1cm^2$ and $0.602{\pm}0.0399$ for $0.5{\times}0.5cm^2$. The output factor of MLC open field has shown a maximum 3.8% higher than that of the collimator jaw open field.

• Korean Journal of Head & Neck Oncology
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• v.19 no.1
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• pp.9-15
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• 2003

Purpose: To introduce our early experience with intensity-modulated radiotherapy (IMRT) in the treatment of nasopharyngeal carcinoma. Methods and Materials: Eight patients who underwent IMRT for no disseminated nasopharyngeal carcinoma at the Asan Medical Center between September 2001 and November 2002 were evaluate by prospective analysis. According to the 1997 American Joint Committee on Cancer staging classification, 5 had Stage III, and 3 had Stage IVB disease. The IMRT plans were designed to be delivered as a 'Simultaneous Modulated Accelerated Radiation Therapy' (SMART) using the 'step and shoot' technique with a MLC (multileaf collimator). Daily fractions of 2.2-2.5Gy and 1.9-2Gy were prescribed and delivered to the GTV and CTV and clinically negative neck node, respectively. The prescribed dose was 70A-79.0Gy to the gross tumor volume (GTV), 60Gy to the clinical target volume (CTV) and metastatic nodal station, and 46Gy to the clinically negative neck. All patients also received weekly cisplatin during radiotherapy. Acute and late normal tissue effects were graded according to the Radiation Therapy Oncology Group (RTOG) radiation morbidity scoring criteria. Results: Follow-up period was ranging from 5 to 18 months. All patients showed complete response and loco-regional control rate was 100% but one patient died of malnutrition due to treatment related toxicity. There were no Grade 3 or 4 xerostomia and all patients had experienced improvement of salivary gland function. Conclusion: 'Simultaneous Modulated Accelerated Radiation Therapy' (SMART) boost intensity-modulated radiotherapy technique allows parotid sparing as evidenced both clinically and by dosimetry. Initial tumor response and loco-regional control was promising. It is clinically feasible. A larger population of patients and a long-term follow-up are needed to evaluate ultimate tumor control and late toxicity.

• Progress in Medical Physics
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• v.18 no.3
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• pp.126-133
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• 2007

A head-and-neck phantom was designed in order to evaluate remotely the quality of the delivery dose of intensity modulated radiation therapy (IMRT) in each institution. The phantom is homogeneous or inhomogeneous by interchanging the phantom material with the substructure like an air or bone plug. Monte Carlo simulations were executed for one beam and three beams to the phantom and compared with ion chamber and thermoluminescent dosimeter (TLD) measurements of which readings were from two independent institutions. For single beam, the ion chamber results and the MC simulations agreed to within about 2% TLDs agreed with the MC results to within 2% or 7% according to which institution read the TLDs. For three beams, the ion chamber results showed -5% maximum discrepancy and those of TLDs were $+2{\sim}+3%$. The accuracy of the TLD leadings should be increased for the remote dose monitoring. MC simulations are a valuable tool to acquire the reliability of the measurements in developing a new phantom.

• Progress in Medical Physics
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• v.26 no.2
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• pp.79-86
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• 2015

The purpose of this study is to evaluate efficacy and feasibility of adaptive radiotherapy according to tumor volume change (TVC) in early stage non-small cell lung cancer (NSCLC) using stereotactic body radiotherapy (SBRT). Twenty-two lesions previously treated with SBRT were selected. SBRT was usually performed with a total dose of 48 Gy or 60 Gy in four fractions with an interval of three to four days between treatments. For evaluation of TVC, gross tumor volume (GTV) was contoured on each cone-beam computed tomography (CBCT) image used for image guidance. Intensity modulated radiotherapy (IMRT) planning was performed in the first CBCT (CBCT1) using a baseline plan. For ART planning (ART), re-optimization was performed at $2^{nd}$, $3^{rd}$, and $4^{th}$ CBCTs (CBCT2, CBCT3, and CBCT4) using the same angle and constraint used for the baseline plan. The ART plan was compared with the non-ART plan, which generated copying of the baseline plan to other CBCTs. Average GTV volume was 10.7 cc. Average TVC was -1.5%, 7.3%, and -25.1% in CBCT2, CBCT3, and CBCT4 and the TVC after CBCT3 was significant (p<0.05). However, the nine lesions were increased GTV in CBCT2. In the ART plan, $V_{20\;Gy}$, $D_{1500\;cc}$, and $D_{1000\;cc}$ of lung were significantly decreased (p<0.05), and $V_{30\;Gy}$ and $V_{32\;Gy}$ of the chest wall were also decreased (p<0.05). While D min of planning target volume (PTV) decreased by 8.3% in the non-ART plan of CBCT2 compared with the baseline plan in lesions with increased tumor size (p=0.021), PTV coverage was not compromised in the ART plan. Based on this result, use of the ART plan may improve target coverage and OAR saving. Thus ART using CBCT should be considered in early stage NSCLC with SBRT.

• Radiation Oncology Journal
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• v.24 no.1
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• pp.11-20
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• 2006

Puroose: In order to find out whether stereotactic radiation therapy (RT) using CyberKnife (CK) could improve survival rate and lower acute toxicity compared to conventional RT. Materials and Methods: From April 2003 through April 2004, 19 patients with Eastern Cooperative Oncology Group (ECOG) performance status ${\leq}3$ and locally advanced pancreas cancer without distant metastasis, evaluated by CT or PET/CT, were included. We administered stereotactic RT consisting of either 33 Gy, 36 Gy or 39 Gy in 3 fractions to 6, 4 and 9 patients, respectively, in an effort to increase the radiation dose step by step, and analyzed the survival rate and gastrointestinal toxicities by the acute radiation morbidity criteria of Radiation Therapeutic Oncology Group (RTOG). Prognostic factors of age, sex, ECOG performance score, chemotherapy, bypass surgery, radiation dose, CA 19-9, planning target volume (PTV), and adjacent organ and vessel invasion on CT scan were evaluated by Log Rank test. Results: The median survival time was 11 months with 1-year survival rate of 36.8%. During follow-up period (range $3{\sim}20$ months, median 10 months), no significant gastrointestinal acute toxicity (RTOG grade 3) was observed. In univariate analysis, age, sex, ECOG performance score, chemotherapy, bypass surgery, radiation dose, CA 19-9 level, and adjacent organ and vessel invasion did not show any significant changes of survival rate, however, patients with PTV (80 cc showed more favorable survival rate than those with PTV>80 cc (p-value<0.05). In multivariate analysis, age younger than 65 years and PTV>80 cc showed better survival rate. Conclusion: In terms of survival, the efficacy of stereotactic radiation therapy using CK was found to be superior or similar to other recent studies achieved with conventional RT with intensive chemotherapy, high dose conformal RT, intraoperative RT (IORT), or intensity modulated RT (IMRT). Furthermore, severe toxicity was not observed. Short treatment time in relation to the short life expectancy gave patients more convenience and, finally, quality of life would be increased. Consequently, this could be regarded as an effective novel treatment modality for locally advanced, unresectable pancreas cancer. PTV would be a helpful prognostic factor for CK.

• Progress in Medical Physics
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• v.26 no.4
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• pp.193-200
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• 2015

The aim of this study is to present commissioning results of the ViewRay system. We verified safety functions of the ViewRay system. For imaging system, we acquired signal to noise ratio (SNR) and image uniformity. In addition, we checked spatial integrity of the image. Couch movement accuracy and coincidence of isocenters (radiation therapy system, imaging system and virtual isocneter) was verified. Accuracy of MLC positioing was checked. We performed reference dosimetry according to American Association of Physicists in Medicine (AAPM) Task Group 51 (TG-51) in water phantom for head 1 and 3. The deviations between measurements and calculation of percent depth dose (PDD) and output factor were evaluated. Finally, we performed gamma evaluations with a total of 8 IMRT plans as an end-to-end (E2E) test of the system. Every safety system of ViewRay operated properly. The values of SNR and Uniformity met the tolerance level. Every point within 10 cm and 17.5 cm radii about the isocenter showed deviations less than 1 mm and 2 mm, respectively. The average couch movement errors in transverse (x), longitudinal (y) and vertical (z) directions were 0.2 mm, 0.1 mm and 0.2 mm, respectively. The deviations between radiation isocenter and virtual isocenter in x, y and z directions were 0 mm, 0 mm and 0.3 mm, respectively. Those between virtual isocenter and imaging isocenter were 0.6 mm, 0.5 mm and 0.2 mm, respectively. The average MLC positioning errors were less than 0.6 mm. The deviations of output, PDDs between mesured vs. BJR supplement 25, PDDs between measured and calculated and output factors of each head were less than 0.5%, 1%, 1% and 2%, respectively. For E2E test, average gamma passing rate with 3%/3 mm criterion was $99.9%{\pm}0.1%$.

• The Journal of Korean Society for Radiation Therapy
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• v.20 no.1
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• pp.45-53
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• 2008

Purpose: We are trying to analyze 130 patients' conditions by using our Helical Tomotherapy, which was installed in our center in Oct. 2007. We will be statistically approach this examination and analyze so that we will be able to figure out adaptive plans according to the change in place of the tumor, GTV (gross tumor volume), total amount of time it took, vector (${\upsilon}=\surd$x2+y2+z2) and the change in size of the tumor. Materials and Methods: Objectives were the patients who were medicated with Tomotherapy in our medical center since Oct. 2007 August 2008. The Average age of the patients were 53 years old (Minimum 25 years old, Maximum 83 years old). The parts of the body we operated were could be categorized as Head&neck (n=22), Chest (n=47), Abdomen (n=25), Pelvis (n=11), Bone (n=25). MVCT had acted on 2702 times, and also had acted on our adaptive plan toward patients who showed big difference in the size of tumor. Also, after equalizing our gained MVCT and kv-CT we checked up on the range of possible mistake, using x, y, z, roll and vector. We've also investigated on Set-up, MVCT, average time of operation and target volume. Results: Mean time on table was 22.8 minutes. Mean treatment time was 13.26 minutes. Mean correction (mm) was X=-0.7, Y=-1.4, Z=5.77, roll=0.29, vector=8.66 Head&neck patients had 2.96 mm less vector value in movement than patients of Chest, Abdomen, Bone. In increasing order, Head&neck, Bone, Abdomen, Chest, Pelvis showed the vector value in movement. Also, there were 27 patients for adaptive plan, 39 patients, who had long or multiple tumor. We could know that When medical treatment is one cure plan, it takes 32 minutes, and when medical treatment is two cure plan, it takes 40 minutes that one medical treatment takes 21 minutes, and the other medical treatment takes 19 minutes. Conclusion:With our basic tools, we could bring more accurate IMRT with MVCT. Also, through our daily image, we checked up on the change in tumor so that adaptive plan could work. It was made it possible to take the cure of long or multiple tumor, the cure in a nearby OAR, and the complicated cure that should make changes of gradient dose distribution.