Dosimetry of Irregular Field Using Thermoluminescence Dosimetry / 대한치료방사선과학회지

In clinical radiotherapy, the use of wide and irregular field techniques frequently results in considerable tumor dose inhomogeneity because of, the variation in physical characteristics of irradiated volumes. This report describes an analysis of the dosimetry of the irregular fields such as radiation fields for Hodgkin's disease(mantle filed), esophageal cancer, and lung cancer when a 6 MV and a 15 MV linear accelerators are utilized. Doses were measured in an Rando phantom using methods of thermoluminescence dosimetry(TDL), and were calculated by radiotherapy planning computer system with the Clarkson's method for calculation of a irregular field. A dose variation of 5-22%, 6-9%, 6-14% were found in the mantle field, esophageal cancer field, lung cancer field respectively. Higher doses occurred in the superior portion of the irregular field. The sites of maximum dose variation were the supraclavicular and the upper spinal cord region. To adjust for these substantial differences, a compensator or a shrinking filed technique should be adopted.

Verification of Dose Distribution for Stereotactic Radiosurgery with a Linear Accelerator / 대한치료방사선과학회지

The calculation of dose distribution in multiple arc stereotactic radiotherapy is a three-dimensional problem and, therefore, the three-dimensional dose calculation algorithm is important and the algorithm's accuracy and reliability should be confirmed experimentally. The aim of this study is to verify the dose distribution of stereotactic radiosurgery experimentally and to investigate the effect of the beam quality, the number of arcs of radiation, and the tertiary collimation on the resulting dose distribution. Film dosimetry with phantom measurements was done to get the three-dimensional orthogonal isodose distribution. All experiments were carried out with a 6 MV X-ray, except for the study of the effects of beam energy on dose distribution, which was done for X-ray energies of 6 and 15 MV. The irradiation technique was from 4 to 11 arcs at intervals of from 15 to 45 degrees between each arc with various field sizes with additional circular collimator. The dose distributions of square field with linear accelerator collimator compared with the dose distributions obtained using circular field with tertiary collimator. The parameters used for comparing the results were the shape of the isodose curve, dose fall-offs from 90% to 50 % and from 90% to 20% isodose line for the steepest and shallowest profile, and A= (90% idsose area) /( 50% isodose area - 90% isodose area (modified from Chierego)). This ratio may be considered as being proportional to the sparing of normal tissue around the target volume. The effect of beam energy in 6 and 15 MV X-ray indicated that the shapes of isodose cuties were the same. The value of ratio A and the steepest and shallowest dose fall-offs for 6 MV X-ray was minimally better than that for 15 MV X-ray. These data illustrated that an increase in the dimensions of the field from 10 to 28 mm in diameter did not significantly change the isodose distribution. There was no significant difference in dose gradient and the shape of isodose cutie regardless of the number of arcs for field sizes of 10, 21, and 32 mm in diameter The shape of isodose cuties was more circular in circular field and square in square field. And the dose gradient for the circular field was slightly better than that for the square field.

The dosimetric Properties of Electron Beam Using Lyon Intraoperative Device for Intraoperative Radiation Therapy / 대한치료방사선과학회지

We have studied the dosimetric properties of electron beam using Lyon intraoperative device for intraoperative radiation therapy. The dosimetry data had compiled in such a way that a quick and correct decision regarding the cone shape, energy, and accurate calculations could be made. Using 3 dimensional water phantom, we have got the following data: cone output ratios, surface dose, dmax, dgo, flatness, symmetry, beam profiles, isodose curve, and SSD correction factors. The cone output ratios were measured with straight and bevelled cone, respectively. As the cone size and the energy were reduced, the cone output ratios decreased rapidly. With the flattening filter, the surface dose increased by electron beam to 85.3%, 89.2%, and 93.4%, for 6MeV, 9MeV, and 12MeV, respectively. It is important to increase the surface dose to 90% or more. Inspite of diminishing dose rate and beam penetration, this flattening filter increases the treatment volume significantly. With the combination of the three levels collimation and the flattening filter, we achieved good homogeneity of the beam and better flatness and the diameter of the 90% isodose curve was increased. It is important to increase the area that is included in the 90% isodose level. The value of measured and calculated SSD correction factors did not agree over the clinically important range from 100cm to 110cm .

Characteristics of 15 MV Photon Beam from a Varian Clinac 1800 Dual Energy Linear Accelerator / 대한치료방사선과학회지

A comprehensive set of dosimetric measurements has been made on the Varian Clinac 1800 15 MV photon beam. Beam quality percentage depth dose, dose in the build up region, output, symmetry and flatness, transmission through lead (Cerrobend), tray attenuation, isodose curves for the open and wedged fields were measured using 3 dimensional water phantom dosimetry system (including film densitometer system) and polystryrence phantoms. These dosimetric measurements sufficiently characterized the beam to permit clinical use. The depth dose characteristics of photon beam is dmax of 3.0 cm and percentage depth dose of 76.8% at 10 cm, 100 cm source-surface distance, field size of 10 x 10 cm2 for 15 MV X-ray beam. The Output factors ranged 0.927 for 4 X 4 cm2 field to 1.087 for 35 X 35 cm2 field. The build-up level of maximum dose was at 3.0 cm and surface dose was approximately 15.5% for a field size 10 x 10 cm2 . The stability of output is within+/-1% and flatness and symmetry are within+/-3%. The half value thickness (HVL) of lead is 13 mm, which corresponds to an attenuation coefficient of 0.053 mm-1. These figures compare favorably with the manufacturer's specifications.

Thermal Distribution in a Phantom Using 8MHz RF Capacitive Type Hyperthermia / 대한치료방사선과학회지

To evaluate the temperature distribution according to the size of the electrode and the thickness of the phantom using 8MHz radiofrequency capacitive heating device, various sized electrodes and phantoms were used in combination. The radii of the electrodes are 10, 15, 20, 25, 30 and 35cm. When the thickness of the phantom was 25cm or 30cm, homogenous heating was achieved by using the electrode which diameter was equal to or greater than the thickness of the phantom. When the thickness of the phantom was 20cm or less. Homogenous heating was not achieved by the larger diameter of the electorode. When the sizes of paired electrodes were not equal, the smaller electrode side was preferentially heated.