• The Journal of Korean Society for Radiation Therapy
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• v.25 no.1
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• pp.1-8
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• 2013

Purpose: A selection of proper energy in treatment planning is very important because of having different dose distribution in body as photon energy. In generally, the low energy photon has been used in intensity-modulated radiation therapy (IMRT) for head and neck (H&N) cancer. The aim of this study was to evaluate the effect of partially used high energy photon at posterior oblique fields on IMRT plan for H&N cancer. Materials and Methods: The study was carried out on 10 patients (nasopharyngeal cancer 5, tonsilar cancer 5) treated with IMRT in Seoul National University Bundang Hospital. CT images were acquired 3 mm of thickness in the same condition and the treatment plan was performed by Eclipse (Ver.7.1, Varian, Palo Alto, USA). Two plans were generated under same planing objectives, dose volume constraints, and eight fields setting: (1) The low energy plan (LEP) created using 6 MV beam alone, (2) the partially used high energy plan (PHEP) created partially using 15 MV beam at two posterior oblique fields with deeper penetration depths, while 6 MV beam was used at the rest of fields. The plans for LEP and PHEP were compared in terms of coverage, conformity index (CI) and homogeneity index (HI) for planning target volume (PTV). For organs at risk (OARs), $D_{mean}$ and $D_{50%}$ were analyzed on both parotid glands and $D_{max}$, $D_{1%}$ for spinal cord were analyzed. Integral dose (ID) and total monitor unit (MU) were compared as addition parameters. For the comparing dose to normal tissue of posterior neck, the posterior-normal tissue volume (P-NTV) was set on the patients respectively. The $D_{mean}$, $V_{20Gy}$ and $V_{25Gy}$ for P-NTV were evaluated by using dose volume histogram (DVH). Results: The dose distributions were similar with regard to coverage, CI and HI for PTV between the LEP and PHEP. No evident difference was observed in the spinal cord. However, the $D_{mean}$, $D_{50%}$ for both parotid gland were slightly reduced by 0.6%, 0.7% in PHEP. The ID was reduced by 1.1% in PHEP, and total MU for PHEP was 1.8% lower than that for LEP. In the P-NTV, the $D_{mean}$, $V_{20Gy}$ and $V_{25Gy}$ of the PHEP were 1.6%, 1.8% and 2.9% lower than those of LEP. Conclusion: Dose to some OARs and a normal tissue, total monitor unit were reduced in IMRT plan with partially used high energy photon. Although these reduction are unclear how have a clinical benefit to patient, application of the partially used high energy photon could improve the overall plan quality of IMRT for head and neck cancer.

• Progress in Medical Physics
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• v.26 no.3
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• pp.127-136
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• 2015

The purpose of this study is to perform a dosimetric evaluation of amplitude-based respiratory gating for the delivery of volumetric modulated arc therapy (VMAT). We selected two types of breathing patterns, subjectively among patients with respiratory-gated treatment log files. For patients that showed consistent breathing patterns (CBP) relative to the 4D CT respiration patterns, the variability of the breath-holding position during treatment was observed within the thresholds. However, patients with inconsistent breathing patterns (IBP) show differences relative to those with CBP. The relative isodose distribution was evaluated using an EBT3 film by comparing gated delivery to static delivery, and an absolute dose measurement was performed with a $0.6cm^3$ Farmer-type ion chamber. The passing rate percentages under the 3%/3 mm gamma analysis for Patients 1, 2 and 3 were respectively 93.18%, 91.16%, and 95.46% for CBP, and 66.77%, 48.79%, and 40.36% for IBP. Under the more stringent criteria of 2%/2 mm, passing rates for Patients 1, 2 and 3 were respectively 73.05%, 67.14%, and 86.85% for CBP, and 46.53%, 32.73%, and 36.51% for IBP. The ion chamber measurements were within 3.5%, on average, of those calculated by the TPS and within 2.0%, on average, when compared to the static-point dose measurements for all cases of CBP. Inconsistent breathing patterns between 4D CT simulation and treatment may cause considerable dosimetric differences. Therefore, patient training is important to maintain consistent breathing amplitude during CT scan acquisition and treatment delivery.

• Progress in Medical Physics
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• v.22 no.4
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• pp.216-223
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• 2011

Recently PTW developed a MicroLion liquid ionization chamber which is water_equivalent and has a small sensitive volume of $0.002cm^3$. The aim of this work is to investigate such dosimetric characteristics as dose linearity, dose rate dependency, spatial resolution, and output factors of the chamber for the external radiotherapy photon beam. The results were compared to those of Semiflex chamber, Pinpoint chamber and Diode chamber with the sensitive volumes of $0.125cm^3$, $0.03cm^3$ and $0.0025cm^3$, respectively and evaluated to be suitable for small fields. This study was performed in the 6MV photon energy from a Varian 2300 C/D linac accelerator and the MP3 water phantom (PTW, Freiburg) was used. Penumbras in the varios field sizes ranged from $0.5{\times}0.5cm^2$ to $10{\times}10cm^2$ were used to evaluate the spatial resolution. Output factors were measured in the field sizes of $0.5{\times}0.5$ to $40{\times}40cm^2$. Readings of the chamber was linearly proportional to dose. Dose rate dependency was measured from 100 MU/min to 600 MU/min, showed a maximum difference of 5.0%, and outputs decreased with dose rates. The spatial resolutions determined with comparing profiles for the field sizes of $0.5{\times}0.5cm^2$ to $10{\times}10cm^2$ agreed between every detector except the Semiflex chamber to within 2%. Outputs of detectors were compared to that of Semiflex chamber and showed good agreements within 2% for every chamber. This study shows that MicroLion chamber characterized by a high signal-to-noise ratio and water equivalence could be suitable for the small field dosimetry.

• Radiation Oncology Journal
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• v.1 no.1
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• pp.37-40
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• 1983

Whole brain irradiation is one mode in the treatment of brain cancer and brain metastasis, but it might cause brain injury such as brain necrosis. It has been studied whether the dose distribution could be a cause of brain injury. The dose distribution in whole brain irradiated by Co-60 beam has been measured by means of calibrated TLD chips inserted in the brain of Humanoid phantom. The following results were obtained. 1. Dose distribution on each transverse section of the brain was uniform. 2. On the midsagital plane of the brain, the dose was highest in upper portion and lowest in lower portion, varying 8 from 104% to 90%. 3. When the radiation field includes free space of 2cm or more width out of the head, the dose distribution in the whole brain is almost independent of the field width. 4. It is important to determine adequate shielding area and to set shielding block exactly in repetition of treatment.

• Journal of Radiation Protection and Research
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• v.9 no.1
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• pp.19-25
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• 1984

There is not yet an universal method of electron dosimetry. The Authors measured dose distributions of the electron beams from Clinac-18 by means of silicon detector connected to X-Y recorder, and compared them in water phantom with dose distributions measured by film and ion chamber, both inserted in polystyrene phantom. The results are as followings, 1. Dose in build-up region increased with the field size for all energy, and depth dose profiles of $6{\sim}12MeV$ beam under the depth of maximum dose were independent of field size, but those of 15 and 18 MeV beam were dependent on the field size. 2. The widths of penumbra by semiconductor detector were narrower than those by film for same energy beam. 3. Depth dose profiles by three different dosimeter did not coincide each other. In the build-up region, dose by semiconductor detector was lower than that by any other dosimeter.

• Radiation Oncology Journal
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• v.2 no.1
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• pp.129-137
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• 1984

In brachytherapy, it is important to determine the positions of the radiation sources which are inserted into a patient and to estimate the dose resulting from the treatment. Calculation of the dose distribution throughout an implant is so laborious that it is rarely done by manual methods except for model cases. It is possible to calculate isodose distributions and tumor doses for individual patients by the use of a microcomputer. In this program, the dose rate and dose distributions are calculated by numerical integration of point source and the localization of radiation sources are obtained from two radiographs at right angles taken by a simulator developed for the treatment planning. By using microcomputer for brachytherapy, we obtained the result as following 1. Dose calculation and irradiation time for tumor could be calculated under one or five seconds after input data. 2. It was same value under$\pm2\%$ error between dose calculation by computer program and measurement dose. 3. It took about five minutes to reconstruct completely dose distribution for intracavitary irradiation. 4. Calculating by computer made remarkly reduction of dose errors compared with Quimby's calculation in interstitial radiation implantation. 5. It could calculate the biological isoffect dose for high and low dose rate activities.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.315-315
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• 2010

양성자 빔을 이용하여 두경부 암 치료를 South Africa의 iTHEMBA에서 시행하고 있다. 200 MeV의 양성자 빔라인으로부터 진공에서 대기로 인출하여 노즐을 통과하여 종양세포에 조사된다. 치료계획에 적합하게 빔에너지와 모양을 변환하고, 빔을 모니터링하는 기계적 장치들이 노즐에 구성된다. 빔라인에는 이온챔버, Steering Magnet, Multi-wire 이온챔버, Range trimmer plates, lead scattering plate, Double-wedge energy degrader, Multi-layer Faraday cup, Range modulator, Range monitor, occluding ring, Shielding collimators, Quadrant and monitor ionization chamber, Treatment collimator, 그리고 Wellhofer dosimetry tank로 구성되어 있다. 총길이는 6.6m이며 노즐 끝에서 환자의 isocenter 까지는 30cm 정도 아래에 위치한다. 상기의 배치를 갖는 시스템의 양성자 scattering system의 성능을 MCNPX v2.5.0 Monte Carlo simulation을 실시하였다. 또한 정확한 선량을 실시간으로 측정하는 방법인 투과형 검출기를 개발하여 치료와 빔 특성을 동시에 수행하는 기술개발연구가 보고되고 있다. 본 연구에서는 Multileaf Faraday Cup (MLPC) 검출기 설계구조와 데이터 측정방법에 관한 연구를 수행하고자 한다. 빔의 전송 방향으로 3개층의 $4{\times}4$ 배열의 구조로 48 channel의 전류값을 측정하여 입자빔의 분포를 실시간으로 관측하고, 측정된 전류는 ADC를 거쳐 치료계획에 의해 선택된 영역의 SOBP를 유지하도록 range modulation propeller를 조절하는 feed-back system을 갖춘 방사선치료빔 실시간 측정장치 개발에 관한 결과를 보고하고자 한다.

• Radiation Oncology Journal
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• v.10 no.2
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• pp.219-225
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• 1992

Fifty patients with carcinoma of the uterine cervix received curative radiotherapy by external irradiation of the whole pelvis and intracavitary radiation at the Department of Therapeutic Radiology, Kangnam St. Mary's Hospital from September, 1983 to October, 1986. External beam whole pelvic irradiation was done first up to 4500-5940 cGy in 5 weeks to 6.5 weeks, followed by an intracavitary radiation. Total dose of radiation to point A varied from 6500 cGy to 11344 cGy (average 6764 cGy). Of the 50 patients, one patient was lost to follow up and follow up period of the remaining 49 patients ranged from 3 months to 93 months (median 32 months). According to FIGO classification, 6 ($12.2\%$) were in stage Ib, 6 ($12.2\%$) in stage IIa, 25 ($51\%$) in stage IIb, 7 ($14\%$) in stage III, and 5 ($10.2\%$) in stage IV. Age of the patients ranged from 33 to 76 years (median 60 years). Pathologically, fourty six ($94\%$) patients had squamous cell carcinoma, 2 ($4\%$) had adenocarcinoma, and 1 ($2\%$) had adenosquamous cell carcinoma. Overall response rate was $84\%$. 5-year survival rate was $49\%$ for entire group ($75\%$ for stage Ib, $83\%$ for Stage IIa, $42.5\%$ for stage IIb, $25\%$ for stage III, $40\%$ for stage IV). Complications were observed in 11 ($22.4\%$) patients, who revealed rectal complications with most common frequency. Others were self limiting trifle ones such as wet desquamation, fatigue, mild leukopenia, etc. The correlation of the survival rate with various factors (age, dose, Hb level, pelvic lymph node status, performance status, local recurrence) was evaluated but showed no statistical significance except the age and local recurrence in this series; survival of patients less than 50 years of age was worse than that of the older, and the presence of local recurrence had worse prognosis (p<0.05).

• Radiation Oncology Journal
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• v.21 no.1
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• pp.94-99
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• 2003

Purpose : To explore a 3D conformal radiotherapy technique for a posterior fossa boost, and the potential advantages of a prone position for such radiotherapy. Materials and Methods :A CT simulator and 3D conformal radiotherapy Planning system was used for the posterior fossa boost treatment on a 13-year-old medulloblastoma patient. He was placed In the prone position and Immobilized with an aquaplast mask and immobilization mold. CT scans were obtained of the brain from the top of the skull to the lower neck, with IV contrast enhancement. The target volume and normal structures were delineated on each slice, with treatment planning peformed using non-coplanar conformal beams. Results : The CT scans, and treatment In the prone position, were peformed successfully. In the prone position, the definition of the target volume was made easier due to the well enhanced tentorium, In audition, the posterior fossa was located anteriorly, and with the greater choice of beam arrangements, more accurate treatment planning was possible as the primary beams were not obstructed by the treatment table. Conclusion : .A posterior fossa boost, in the prone position, Is feasible in cooperating patients, but further evaluation is needed to define the optimal and most comfortable treatment positions.

• Radiation Oncology Journal
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• v.22 no.2
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• pp.98-105
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• 2004

Purpose : To evaluate whether positron omission tomography (PET) with 2-[F-18]fluoro-2-deoxy-D-giucose(FDG) can be used to predict of early response to definitive aim radlotherapy (RT) in squamous cell carcinoma of the head and neck using response rate and locoreglonal control as study endpoints. Materials and Methods : Twenty-two patients with head and neck cancer underwent a FDG-PET study before RT, after a flrst dose of 45 Gy, and after a second dose on more 4han 70 Gy. Standard uptake value (SUV) was calculated for primary tumor (n=22) and neck lymph node (n:10). Attenuation corrected PET scans acquired 60 min after tracer injection were used for evaluation of FDG uptake In tumors. A quantitative FDG uptake index was expressed as Suvlean (corrected for iean body mass). The follow-up time was at least 5 months (range S-1 S months). Results : A total of 22 primary tumors and 10 metastatic lymph nodes were analyzed In FDG-PET. In the first PET study the mean SUVlean the primary tumors and nodes were 5.4 (SD, 2.5) and 4.6 (SD, 2.3), respectively. In the second PET, study peformed after 46 Gy RT the mean SUV in primary tumor and node decreased to 2.9 (SD, 1.9, p<0.001) and 1.7 (SD, 1.3) respectively. in the third PET study peformed at the full dose (more than 70 Gy), RT the mean SUV In the primary tumors and nodes decreased to 2.3 (SD, 1.5, p<0.001) and 1.5 (SD, 1 .1) respectively. Conclusions: FDG uptake In tumors showed a significant decrease after the 45 Gy and more than 70 Gy of RT for squamous cell carcinoma of the head and neck. Reduction of metabolic activity after 46 Gy of radiotherapy Is closely correlated with radiation response.