Biomedical subjects

Géza Varjas

Publications and source records attributed to Géza Varjas.

3 recordsLinked to original sources

PubMed2005

[Dosimetric assessment of external treatment plans for breast cancer: the significance of dose prescription selection].

PURPOSE: To analyze the treatment plans of breast irradiation performed with two tangential beams, to discuss the importance of dose prescription, and to estimate the differences in delivered dose due to various dose prescription methods. MATERIAL AND METHODS: A survey was performed between the Hungarian radiotherapy centers in order to compare the dose prescription methods. Then, treatment plans of 125 breast cancer patients treated in our department were evaluated. The irradiations were performed with cobalt unit, and with 6 and 9 MV photon beams of linear accelerators. The dose distributions were normalized to izocenter, then dose values in five points in central plane; local medial, lateral and central maximums (D(med), D(lat) and D(cent)); volumetric maximum and its location were determined. To characterize the dose to lung and to heart at left-sided tumors the central lung distance (CLD) and maximum heart distance (MHD) were used. Based on the results, estimation was made to assess the differences between delivered dose due to various dose prescriptions applied at the institutions. RESULTS: Four types of dose prescription are currently used in our country, and most frequently the isocenter is selected as a reference point. In the central plane the calculated dose in all but one points differed only a little from the dose to isocenter. The mean D(med), D(lat) and D(cent) were 107%, 107% and 101%, respectively. The volumetric maximum was on average 13% higher than the dose to isocenter. Regarding the beam qualities, this value was 16%, 13% and 11% for cobalt unit, 6 MV and 9 MV photon beams, respectively. The mean CLD and MHD were 1.9 and 0.8 cm, respectively. The difference between delivered doses at the institutions was 6% on average, but in extreme cases it can be as high as 20%. CONCLUSIONS: Three-dimensional treatment planning and plan evaluation are recommended at breast irradiation, especially for large breasts. Since the various dose prescriptions may result in significant differences in the delivered doses, use of a standard dose prescription protocol is recommended.

Adult↗

PubMed2005

[Computerized radiotherapy planning: retrospective analysis and current methods].

PURPOSE: To present the development of treatment planning methods at the National Institute of Oncology (NIO) from 1969 till 2005. METHODS: The methods and devices of treatment planning is described chronologically. RESULTS: First we did the treatment planning with in-house made devices: body contour drawing instrument, simplified anatomical cross sections, treatment planning table for the cross section projection, archives of isodose curves adjusted to body contours, etc. It was a significant improvement when the graphical addition of isodose curves was followed by computerized dose calculation. In 1978 the work of the Computerized National Treatment Planning Network was started. The Network was organized by IAEA, Ministry of Health Hungary and NIO. The modern treatment planning started at NIO in 1981. From this year, the treatment planning was based on CT, using the CT apparatus of the Medical Postgraduate University. In 1991 a Siemens MEVAPLAN treatment planning system was installed at NIO. The CT data were transferred to the system via floppy disk. The 3D treatment planning program (Pinnacle software of ADAC) started in 2000. The CT, the treatment planning system and newer linear accelerators are connected through the computerized radiotherapy network. Patient positioning, fixing and control devices (mask, EPID etc.) increased the efficacy of the treatment. In-house made devices help this aim too: mirrors at the linear accelerators, special skin marks for CT, block verification unit, multileaf collimator for x-ray treatment simulator. In this year the intensity-modulated radiotherapy (IMRT) will be started at NIO. CONCLUSIONS: The treatment planning at NIO developed to high degree during the investigated time, and it had a considerable effect on the efficacy of radiotherapy.

Humans↗

PubMed2002

[The possibility of the use of MRI images in the three-dimensional external radiotherapy treatment planning].

PURPOSE: To review the application of MRI images in the radiation treatment planning,to discuss the advantages and disadvantages of MR imaging with respect to treatment planning, and to investigate the geometric distortion. METHODS: Humanoid therapy phantom was used for MRI and CT scanning, and distances between markers inside and on the surface of the phantom were measured in order to quantify the geometric distortion. The procedure of MRI/CT image fusion, which makes it possible to use the data of both imaging modalities for treatment planning, was described. RESULTS: At small volumes (head phantom) the geometric distortion was negligible (<2 mm), but at large volumes (eg. pelvis) remarkable geometric inaccuracies were observed. For example, the width of the pelvis measured in the MRI images was 7 mm less than the real distance, which corresponds to 2% inaccuracy. Geometric distortion was observed not only in the axial, but also in the sagittal and coronal planes. We have found that the geometric error increases with the distance measured from the magnetic isocenter. When the geometric distortion is not significant, the MRI/CT image fusion can be carried out reliably with the use of surface markers. CONCLUSIONS: At small volumes the MRI images can be used for treatment planning after their fusion with CT images. At larger volumes the geometric distortion without any correction may preclude the MRI images from using them in the treatment planning. A detailed assessment of geometric distortion must be carried out before the introduction of MRI images into the radiation treatment planning.

Computer Simulation↗