• Progress in Medical Physics
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• v.13 no.1
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• pp.32-36
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• 2002

For Intensity Modulated Radiation Therapy(IMRT), the spatial resolution of intensity map(IM) is limited by the width of multi-leaf collimator, which would make an effect on the conformity of the target, as well as organs at risk. Several Methods are suggested to increase the spatial resolution, which can be categorized by the hardware-dependent technique and the software-based technique. However the best solution might be to make the width of MLC finer. it has several obstacles in the respects of technical difficulty and cost. This preliminary study is designed to investigate the clinical effectiveness of the virtual-micro IMRT(VMIMRT) technique, one of the software-based technique. A particular intensity map was created, which has 42$\times$54 pixel dimension ,0.5cm pixel size and 15 intensity levels. Using this intensity map, segment fields of IMRT were generated with 1$\times$lcm, 0.5$\times$1cm, 0.5$\times$0.5cm(VMIM) beamlet size, respectively As results, we found that there was no evidence of improvement for VMIMRT, compared with the 0.5$\times$lcm beamlet size which can be delivered by 1cm width MLC. The reason seems to be due to the constraint of VMIMRT. Further study is required to prove the benefit of the VIMRT in clinical case like head and neck cancer, where is expected that higher resolution than 1cm is necessary.

• Progress in Medical Physics
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• v.14 no.2
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• pp.90-98
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• 2003

Purpose : A new virtual simulation technique for craniospinal irradiation (CSI) that uses a CT-simulator was developed to improve the accuracy of field and shielding placement as well as patient positioning. Materials and Methods : A CT simulator (CT-SIM) and a 3-D conformal radiation treatment planning system (3D-CRT) were used to develop CSI. The head and neck were immobilized with a thermoplastic mask while the rest of the body was immobilized with a Vac-Loc. A volumetric image was then obtained with the CT simulator. In order to improve the reproducibility of the setup, datum lines and points were marked on the head and body. Virtual fluoroscopy was performed with the removal of visual obstacles, such as the treatment table or immobilization devices. After virtual simulation, the treatment isocenters of each field were marked on the body and on the immobilization devices at the conventional simulation room. Each treatment fields was confirmed by comparing the fluoroscopy images with the digitally reconstructed radiography (DRR) and digitally composited radiography (DCR) images from virtual simulation. Port verification films from the first treatment were also compared with the DRR/DCR images for geometric verification. Results : We successfully performed virtual simulations on 11 CSI patients by CT-SIM. It took less than 20 minutes to affix the immobilization devices and to obtain the volumetric images of the entire body. In the absence of the patient, virtual simulation of all fields took 20 min. The DRRs were in agreement with simulation films to within 5 mm. This not only reducee inconveniences to the patients, but also eliminated position-shift variables attendant during the long conventional simulation process. In addition, by obtaining CT volumetric image, critical organs, such as the eyes and the spinal cord, were better defined, and the accuracy of the port designs and shielding was improved. Differences between the DRRs and the portal films were less than 3 m in the vertebral contour. Conclusion : Our analysis showed that CT simulation of craniospinal fields was accurate. In addition, CT simulation reduced the duration of the patient's immobility. During the planning process. This technique can improve accuracy in field placement and shielding by using three-dimensional CT-aided localization of critical and target structures. Overall, it has improved staff efficiency and resource utilization by standard protocol for craniospinal irradiation.

• Korean Journal of Head & Neck Oncology
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• v.19 no.1
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• pp.34-40
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• 2003

Objective: To analyze the treatment-related parameters after the radiotherapy of T1N0 squamous cell carcinoma of the glottic larynx. Materials and Methods: Between October 1989 and August 2000, 54 patients with histologically proven T1N0 squamous cell carcinoma of the glottic larynx who received definitive radiation therapy in Department of Radiation Oncology, Asan Medical Center were analyzed. They were all males with age ranged from 31 to 80 years (median 61 years). 1997 AJCC stages were 31 T1a, 23 T1b. Patients were treated with 4-MV X-rays with a parallel-opposed two-field technique. Ten patients received 66.0-68.4Gy at 1.2Gy per fraction twice daily, 21 patients received 64.8-66.6Gy at 1.8Gy per fraction once daily, and 23 patients received 66.0Gy at 2.0Gy per fraction once daily. Follow-up period was 16-119 months (median 56 months). Results: 5-year overall survival and local control rates for patients with T1 lesions were 87.0% and 88.5%, respectively. 5-year local control with larynx preservation rate was 90.5%. Host and tumor-related prognostic factors including age, stage, anterior commissure involvement and tumor bulk proved not to be significant. Only shorter overall treatment time among treatment-related factors had correlation with imporved local control. Conclusion: Comparable high local control rate with organ preservation was achieved with primary radiation therapy and salvage surgery. Shortening of overall treatment time is related to improved local control rate. To determine the optimal fractionation scheme, randomized trial is mandatory.

• Korean Journal of Head & Neck Oncology
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• v.40 no.1
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• pp.7-13
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• 2024

The current standard of treatment for differentiated thyroid cancer is surgical resection followed by radioactive iodine therapy according to the recurrence risk. However, external beam radiotherapy may be recommended in limited cases where surgical resection is impossible or residual gross lesion remains or the aforementioned standard therapy is deemed insufficient in achieving local control. We report a case of 59 year old patient who presented with advanced papillary thyroid carcinoma of right neck but was unable to receive surgical resection due to underlying Eisenmenger syndrome. He received radiation therapy of 67.5 Gy in 30 fractions with palliative aim with no further treatment and has been maintaining long-term stable disease state for 38 months. Herein, we report a rare case of palliative aim radiation therapy alone for advanced papillary thyroid carcinoma with literature review.

• The Journal of Korean Society for Radiation Therapy
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• v.34
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• pp.7-12
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• 2022

Purpose: When it is difficult to secure the skin dose when treating Irregularly Shaped Skin Surface such as the nose where it is difficult to apply a bolus, increase the skin dose with a treatment plan that combines the IMRT (Intensity Modulated Radiation Therapy) delivery technique and FFF (Flattening Filter Free), It was tried to find out whether or not through the phantom experiment. Materials & Methods: Based on the 6MV-FF (Flattening Filter) and VMAT (Volumetric-Modulated Arc Therapy) treatment plans, which are the most commonly used treatment plans for head and neck cancer, A comparison group was created by combining VMAT and IMRT, FF and FFF, and the presence or absence of 5 mm bolus application. A virtual target was created on the Rando Phantom's nose, and a virtual bolus of 5 mm was applied assuming full contact on the Rando Phantom's nose. Five measurement points were determined based on the phantom's nose, and the absorbed dose was measured by irradiating each treatment plan 3 times per treatment plan according to the treatment technique and whether or not the bolus was applied. Result: The difference in skin dose in FF vs FFF increased in the case of FFF in VMAT bolus off, and there was no difference in case of IMRT bolus off. In VMAT bolus 5 mm and IMRT bolus 5 mm, it was confirmed that the skin dose was rather decreased in FFF. The difference in skin dose between VMAT and IMRT increased only in the case of FFF bolus off, and there was no statistical difference in the rest. For the difference in skin dose between bolus off vs bolus 5 mm, it was confirmed that the skin dose increased at bolus 5 mm, except for the case of using IMRT FFF. The treatment plan combining IMRT and FFF did not find any statistically significant difference as a result of analyzing the measured values of the treatment plan skin dose applied with a 5 mm bolus using the commonly used VMAT and FF. Therefore, it is thought that by using IMRT_FFF, it is possible to deliver a skin dose similar to that of applying a 5 mm bolus to VMAT_FF, which can be useful for patients who need a high skin dose but have difficulty applying a bolus. Conclusion: For patients who find it difficult to apply bolus, an increase in skin dose can be expected with a treatment plan that properly combines IMRT and FFF compared to VMAT and FF.

• The Journal of Korean Society for Radiation Therapy
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• v.27 no.2
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• pp.167-174
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• 2015

Purpose : The pre-treatment QA using Portal dosimetry for Volumetric Arc Therapy To analyze whether maintaining the reproducibility depending on various factors. Materials and Methods : Test was used for TrueBeam STx$^{TM}$ (Ver.1.5, Varian, USA). Varian Eclipse Treatment planning system(TPS) was used for planning with total of seven patients include head and neck cancer, lung cancer, prostate cancer, and cervical cancer was established for a Portal dosimetry QA plan. In order to measure these plans, Portal Dosimetry application (Ver.10) (Varian) and Portal Vision aS1000 Imager was used. Each Points of QA was determined by dividing, before and after morning treatment, and the after afternoon treatment ended (after 4 hours). Calibration of EPID(Dark field correction, Flood field correction, Dose normalization) was implemented before Every QA measure points. MLC initialize was implemented after each QA points and QA was retried. Also before QA measurements, Beam Ouput at the each of QA points was measured using the Water Phantom and Ionization chamber(IBA dosimetry, Germany). Results : The mean values of the Gamma pass rate(GPR, 3%, 3mm) for every patients between morning, afternoon and evening was 97.3%, 96.1%, 95.4% and the patient's showing maximum difference was 95.7%, 94.2% 93.7%. The mean value of GPR before and after EPID calibration were 95.94%, 96.01%. The mean value of Beam Output were 100.45%, 100.46%, 100.59% at each QA points. The mean value of GPR before and after MLC initialization were 95.83%, 96.40%. Conclusion : Maintain the reproducibility of the Portal Dosimetry as a VMAT QA tool required management of the various factors that can affect the dosimetry.

• Korean Journal of Head & Neck Oncology
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• v.18 no.1
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• pp.30-35
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• 2002

Objective: To determine the effectiveness and toxicity of chemoradiation therapy in nasopharyngeal carcinoma by comparing with radiation therapy alone. Materials and Methods: Between October 1989 and July 2000, One hundred eleven patients with newly diagnosed and histologically proven nasopharyngeal carcinoma treated in Department of Radiation Oncology, Asan Medical Center were retrospectively reviewed. Forty-five patients were treated with radiation therapy alone (Group I) and 66 patients were treated with radiation therapy and concurrent cisplatin (Group II). Cisplatin was administered once a week, on the first day of each successive week of treatment, starting on day 1 of radiation therapy and given as a intravenous bolus at a dose of $20mg/m^2$ of body-surface area. Radiation therapy was given in doses of 1.8Gy, once a day, 5 days per week with 4MV or 6 MV photons. Initial field was received a total of 60Gy and a primary tumor and enlarged lymph nodes were boosted with an high dose intracavitory brachytherapy and 3D conformal therapy. Results: The complete response rate was 86.7% in Group I, and was 90.9% in Group II. The 5 year overall survival rate for Group I was 60% and for Group II was 45% (p=0.2520). The 5 year disease free survival rate was 52% versus 45%, respectively (p=0.7507). The median follow up was 44 months versus 34 months, respectively. Conclusion: Analysis of the III patients showed no significant difference in disease free survival and overall survival in two treatment group. This retrospective analysis did not demonstrate benefit with concurrent chemoradiation using cisplatin at a dose of $20mg/m^2$ of body-surface area in treatment result than radiation alone.

• Progress in Medical Physics
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• v.23 no.4
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• pp.269-278
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• 2012

Aquaplast Thermoplastic (AT) is a tissue-equivalent oral compensator that has been developed to improve dose uniformity at the common boundary and around the treated area during radiotherapy in patients with head and neck cancer. In order to assess the usefulness of AT, the degree of improvement in dose distribution and physical properties were compared to those of oral compensators made using paraffin, alginate, and putty, which are materials conventionally used in dental imprinting. To assess the physical properties, strength evaluations (compression and drop evaluations) and natural deformation evaluations (volume change over time) were performed; a Gafchromic EBT2 film and a glass dosimeter inserted into a developed phantom for dose verification were used to measure the common boundary dose and the beam profile to assess the dose delivery. When the natural deformation of the oral compensators was assessed over a two-month period, alginate exhibited a maximum of 80% change in volume from moisture evaporation, while the remaining tissue-equivalent properties, including those of AT, showed a change in volume that was less than 3%. In a free-fall test at a height of 1.5 m (repeated 5 times as a strength evaluation), paraffin was easily damaged by the impact, but AT exhibited no damage from the fall. In compressive strength testing, AT was not destroyed even at 8 times the force needed for paraffin. In dose verification using a glass dosimeter, the results showed that in a single test, the tissue-equivalent (about 80 Hounsfield Units [HU]) AT delivered about 4.9% lower surface dose in terms of delivery of an output coefficient (monitor unit), which was 4% lower than putty and exhibited a value of about 1,000 HU or higher during a dose delivery of the same formulation. In addition, when the incident direction of the beam was used as a reference, the uniformity of the dose, as assessed from the beam profile at the boundary after passing through the oral compensators, was 11.41, 3.98, and 4.30 for air, AT, and putty, respectively. The AT oral compensator had a higher strength and lower probability of material transformation than the oral compensators conventionally used as a tissue-equivalent material, and a uniform dose distribution was successfully formed at the boundary and surrounding area including the mouth. It was also possible to deliver a uniformly formulated dose and reduce the skin dose delivery.

• Korean Journal of Head & Neck Oncology
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• v.13 no.2
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• pp.200-205
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• 1997

Background: There is considerable controversy concerning the most appropriate surgical treatment of patients with DTC. Objectives: In order to selection of the appropriate surgical treatment for DTC, we have analyzed the outcome of the different types of surgical treatment in low and high risk groups of DTC. Materials and Methods: From January 1968 through december 1980, a total of 71 patients with DTC were treated surgically at our institution. According to Cady and Rossi's scoring system, the patients were divided into low risk and high risk groups. Results: Seventy percent of patients were defined as low risk group with a 4% death rate whereas 30% of patients at high risk with a death caused by thyroid cancer in 38%(p<0.05). There was no difference in mortality between ipsilateral lobectomy and total thyroidectomy in both low and high risk groups(p>0.1). Conclusion: In our study, total thyroidectomy was not benefit in high risk group. These results suggested that total thyroidectomy must be selected carefully and based on clear evidence of major improvement in outcome or absence of other suitable surgical approaches. However, follow up study of more cases will be needed for accurate determination of the efficacy of total thyroidectomy in high risk group.

• Radiation Oncology Journal
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• v.25 no.1
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• pp.43-53
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• 2007

[ $\underline{Purpose}$ ]: To evaluate the relationship between the expression of EGFR, p53, Cox-2, Bcl-2 and the clinical parameters of NPC (nasopharyngeal carcinoma) patients treated with radiotherapy with/without chemotherapy, and to determine if these could be used as a biologic marker. $\underline{Materials\;and\;Methods}$: This study retrospectively examined 75 NPC patients who were pathologically diagnosed at St. Mary's Hospital and Kangnam St Mary's Hospital from March 1988 to August 2002 and treated with radiotherapy with/without chemotherapy. The levels of EGFR, p53, Cox-2, and Bcl-2 expression were determined immunohistochemically. The relationship between the levels of EGFR, p53, Cox-2 and Bcl-2 expression and the H- E staining findings including the WHO classification, TNM stage, tumor response to chemotherapy and radiotherapy, disease free survival (DFS), and overall survival (OS) was analyzed. $\underline{Results}$: At a median follow up of 50.8 months (range: $5.5{\sim}201$ months), the 3 years OS rate and PFS rate were 68.7% and 68.2%, respectively. The five year OS rate and PFS rate were 53.5% and 51.1%, respectively. The median OS duration and PFS duration were 85.5 months and 61.1 months, respectively. The WHO classification correlated with the complete response rate, lymph node metastasis and distant metastasis. The expression of p53 was associated with increased mitosis and poor overall survival. The expression of Bcl-2 correlated with the DFS and WHO classification. The expression of Cox-2 correlated with a poor overall survival and response rate in the lymph node. However, EGFR was not correlated with any factors. $\underline{Conclusion}$: These results suggest that the expression of p53, Cox-2, Bcl-2 plays role in predicting prognostic factors for NPC treated with radiotherapy with/without chemotherapy. However, further study on a larger number of patients will be needed to identify more useful biomarkers of NPC.