Do Hoon Oh

Dosimetric characteristics of linear accelerator photon beams with small monitor unit settings

Several studies on the effect of tumor cell killing by dose rate variation have implied that the use of a shorter treatment time is more favorable for intensity modulated radiation therapy (IMRT). Aiming at step-and-shoot IMRT with higher dose rates, the stabilities of beam output and profiles with small monitor unit (MU) settings were investigated for various dose rates. With the use of a Varian 21EX (Varian Medical Systems Inc., Palo Alto, CA), static and step-and-shoot IMRT beam output along with profiles were measured by use of an ion chamber and a two-dimensional diode array detector as a function of monitor units and dose rates. For a static case, as the MU approached 1, the beam output increased up to 2% for 300 MU/min and 4.5% for 600 MU/min, showing a larger overdose as the dose rate increased. Deterioration of the beam symmetry and flatness were also observed as the MU decreased to 1 monitor unit. For the step-and-shoot IMRT case, a large dosimetric error of more than 10% was also detected with the use of a small MU segment. However, no definite correlation with the dose rate was observed due to the combined beam start-up effects by the grid pulse and finite communication time between the machine console and multileaf collimator (MLC) controller. For step-and-shoot IMRT with higher dose rates, beam output and beam profile stability with small MU needs to be checked, and adequate MU limitation where segments are not allowed need to be reflected in the step-and-shoot IMRT planning.

Human Leukocyte Antigen Class II Association with Spontaneous Recovery from Hepatitis B Virus Infection in Koreans: Analysis at the Haplotype Level

It has been speculated that human leukocyte antigen (HLA) alleles are associated with the outcome of hepatitis B virus (HBV) infection although the data obtained from various populations have shown some inconsistencies. A total of 464 HBV-infected Korean individuals (80 spontaneously recovered [SR] and 384 chronically infected [CI]) were selected to investigate the association of HLA class II alleles with the viral clearance and persistence. Our results showed that: 1) multiple HLA class II alleles and haplotypes were associated with viral clearance (DRB1*1302, DRB1*1502, DQB1*0302, DQB1*0609, and related-haplotypes) and persistence (DRB1*0701, DQB1*0301, and related-haplotypes); 2) DRB1*1302 and DQB1* 0609 were more strongly associated with viral clearance. And the association of DQB1*0609 (pc=0.0084; OR, 7.24) with vial clearance was much stronger than previously recognized, DRB1*1302 (pc=0.0038; OR, 4.34); and 3) linkage to a specific DPB1 allele in a haplotype strengthened the association with viral clearance, although DPB1 itself was not associated with the outcome. These results indicate the existence of multiple factors controlling viral clearance in the HLA class II gene region. Further extended investigation on the genetic factors related to the outcome of HBV infection will provide valuable insights into the understanding of the mechanisms involved.

Electron arc planning on the commercial radiation treatment planning system

A commercial radiation treatment planning system, Pinnacle3, has been prepared for the electron arc treatment with a Varian machine. For this purpose, a new physics machine was commissioned for the exclusive electron arc therapy. The electron arc plan was made with multiple static beams with fixed interval. The phantom measurements were executed with a MOSFET and EBT films. The resulting plan shows an impressive dose distribution, however, in-vivo dosimetry for a few representative points should be proceeded before treatment to be sure of the calculation accuracy.

Patterns of Radiation Therapy Practice in Nonmetastatic Non—Small-Cell Lung Cancer: Results of Web-Based Patterns of Care Study in Korea

Abstract Background A Patterns-of-Care Study (PCS) was conducted to determine the patterns of evaluation and treatment for nonmetastatic non— small-cell lung cancer (NSCLC) in Korea. Patients and Methods A Web-based data system for Korean PCS was developed, and a national survey was conducted. Patients who received thoracic radiation therapy (RT) for clinical or pathologic stage I-III NSCLC without other malignancy in 1998 and 1999 were eligible and randomly selected by power allocation method. Results The records of 446 selected patients from 19 institutions were reviewed, and 10 patients were excluded because of incomplete clinical information. Accordingly, 436 patients were the subjects of this study, with a median age of 62.2 years (range, 33.1–88 years) and male-to-female ratio of 86:14. The histologies were squamous cell carcinoma in 61.2%, adenocarcinoma in 28.4%, large-cell carcinoma in 2.3%, and NSCLC not otherwise specified in 8% of patients, respectively. Bone scan, abdominal ultrasonography or computed tomography (CT), brain CT or magnetic resonsance imaging, and positron emission tomography were examined in 92.5%, 81.5%, 44.8%, and 26.6% of patients, respectively. The clinical stage was I in 8.9%, II in 12.2%, IIIA in 37.4%, and IIIB in 41.5%, respectively. Regarding treatment modalities, RT was used alone in 38.1%; RT combined with operation in 22.9%; RT combined with chemotherapy in 27.1%; and trimodalities including RT, operation, and chemotherapy in 11.9%. The median total dose was 59.4 Gy with daily median fraction size of 1.8 Gy, and the percent delivered dose > 90% was achieved in 87.6%. Most of patients received RT in supine position (99.3%) with beam direction of anterior-posterior/posterior-anterior (95.6%) as their first RT plan and with photon energy of 6 MV (42%) followed by 10 MV (41.7%). The chemotherapy-based planning was used in 2.3 % and 32.6% for their first and second RT plan, respectively. The 3-or-more RT planning was performed in 13.5% of patients. Elective nodal irradiation was used in 87.8% of patients, and the N2 nodal station (48.6%) was most frequently included. The 8% of patients received thoracic RT based on prospective protocol. Conclusion This study is the first PCS for NSCLC conducted in Korea. We confirmed that various types of RT planning were used according to each institution, but beam delivery techniques were not much different between 1998 and 1999. Another PCS is planned to evaluate changing trends in national practice.