In recent years there has been a growing interest in all forms of rotational therapy, and many different types of therapy machines designed for this kind of treatment have become available. To the medical radiation physicist, the dosimetry of rotation therapy has presented a number of interesting problems, and much useful work has been published on the basic date of dose distribution and dosage calculation. The setting dose for ARC therapy were obtained by computer calculation and measurement with cylindrical phantom. Authors compared computer calculation with measured value. And in ARC therapy, the region of maximum dose in shifted from the tumor center. The extent of shift was analyzed by isodose distribution for ARC therapy techniques.
Particle Accelerators*

The beam characteristics and dosimetric measurements of the 10 MV X-ray beam from a Mevatron KD linear accelerator are examined. The Percent Depth Dose (PDD) table and the Tissue Maximum Ratio (TMR) table are taken from measurement as a function of the field size and the depth. The calculated TMR table from PDD table is compared with those from measurement. Other beam characteristics such as output factor, beam profile (including flatness, symmetry and penumbra), wedge, and the variation of Dmax are presented.
Particle Accelerators*

Recent radiotherapy dose planning system (RTPS) generally adapted the kernel beam using the convolution method for computation of tissue dose. To get a depth and profile dose in a given depth concerened a given photon beam, the energy spectrum was reconstructed from the attenuation dose of transmission of filter through iterative numerical analysis. The experiments were performed with 15 MV X rays (Oncor, Siemens) and ionization chamber (0.125 cc, PTW) for measurements of filter transmitted dose. The energy spectrum of 15 MV X-rays was determined from attenuated dose of lead filter transmission from 0.51 cm to 8.04 cm with energy interval 0.25 MeV. In the results, the peak flux revealed at 3.75 MeV and mean energy of 15 MV X rays was 4.639 MeV in this experiments. The results of transmitted dose of lead filter showed within 0.6% in average but maximum 2.5% discrepancy in a 5 cm thickness of lead filter. Since the tissue dose is highly depend on the its energy, the lateral dose are delivered from the lateral spread of energy fluence through flattening filter shape as tangent 0.075 and 0.125 which showed 4.211 MeV and 3.906 MeV. In this experiments, analyzed the energy spectrum has applied to obtain the percent depth dose of RTPS (XiO, Version 4.3.1, CMS). The generated percent depth dose from 6x6 cm2 of field to 30x30 cm2 showed very close to that of experimental measurement within 1% discrepancy in average. The computed dose profile were within 1% discrepancy to measurement in field size 10x10 cm, however, the large field sizes were obtained within 2% uncertainty. The resulting algorithm produced x-ray spectrum that match both quality and quantity with small discrepancy in this experiments.
Particle Accelerators ; Uncertainty

PURPOSE: For the purpose of quality assurance of self-developed stereotactic radiosurgery system, a multi-purpose phantom was fabricated, and accuracy of radiation dose distribution during radiosurgery was measured using this phantom. MATERIALS AND METHODS: A farmer chamber, a 0.125 cc ion chamber and a diode detector were used for the dosimetry. Six MV x-ray from a linear accelerator (CL2100C, Varian) with stereotactic radiosurgery technique (Green Knife) was used, and multi-purpose phantom was attached to a stereotactic frame (Fisher type). Dosimetry was done by combinations of locations of the detectors in the phantom, fixed or arc beams, gantry angles (20 ~100 ), and size of the circular tertiary collimators (inner diameters of 10 degrees~40 degrees mm). RESULTS: The measurement error was less than 0.5% by Farmer chamber, 0.5% for 0.125 cc ion chamber, and less than 2% for diode detector for the fixed beam, single arc beam, and 5-arc beam setup. CONCLUSION: We confirmed the accuracy of dose distribution with the radiosurgery system developed in our institute and the data from this study would be able to be effectively used for the improvement of quality assurance of stereotactic radiosurgery or fractionated stereotactic radiotherapy system.
Particle Accelerators ; Radiosurgery* ; Radiotherapy

The technical advances that have been achieved over the last decade in the area of 3-dimensional radiotherapy treatment planning capabilities and new and more flexible hardware capabilities, such as computer-controlled treatments, multileaf collimators, and real-time portal imaging devices, have brought about 3-dimensional conformal radiation therapy. For the purpose of highly conformal radiation therapy, a variety of radiation treatment techniques and treatment machines such as stereotactic radiosurgery(SRS) using gamma-knife, stereotactic radiotherapy(SRT) using linear accelerator, and stereotactic whole body radiotherapy have been invented. Intensity-modulated radiation therapy(IMRT) is a new and evolving technological advance in high-precision radiation therapy. It is an extension of 3-dimensional conformal radiotherapy(3-DCRT) that allows the delivery of highly complex isodose profiles to the target, while minimizing radiation exposure to surrounding normal tissues. Image-guided adaptive radiotherapy(IGRT) combines scanning and radiation equipment, to provide images of the patient's organs in the treatment position, at the time of the treatment, optimizing the accuracy and precision of the radiotherapy. Respiratory-gated radiotherapy was developed to overcome the motion of organs. Most high precision radiation therapy approaches increase the time and efforts required by physicians and physicists, because optimization systems are not yet robust enough to provide automated solutions for all disease sites, and routine QA testing is still quite time-consuming. Preliminary clinical experiences of high precision radiation therapy have been encouraging by high rates of local control and decrease of toxicity. This article provides an overview of high precision radiotherapy such as 3-DCRT, SRS, SRT, Cyberknife, IMRT, and IGRT.
Particle Accelerators ; Radiosurgery ; Radiotherapy*

A method to get a size of the radiation isocenter of linear accelerators using star-shot images was presented and a computer program was developed to automate the method. Accuracy of the method was verified. The developed program was used to measure sizes of the radiation isocenters for a Clinac 21EX (Varian, USA) using data of quality assurance (QA) performed from June 2008 to December 2010. To calculated the size of radiation isocenter, positions of two points on each central ray of the star-shot image were found and the equation of the central ray was determined using the positions of two points. Using the equations of central rays the radius of the minimum circle intersecting all the central rays, which is one half of the size of radiation isocenter, was calculated. The program measured X-intercepts and y-intercepts of the central rays within errors of 0.084 mm and sizes of radiation isocenters within 0.053 mm. All the errors were less than the spatial resolution of star-shot images 0.085 mm. The radiation isocenter sizes of Clinac 21EX were 0.33+/-0.27 mm, 0.71+/-0.36 mm, 0.50+/-0.16 mm for collimator, gantry and couch respectively. During the measurement period all the measured sizes were less than 2.0 mm and within tolerance. The developed program could calculate the size of radiation isocenters and it would be helpful to routine QA.
Particle Accelerators ; Radius ; Software

Experimental measurements of dose characteristics with pentagonal applicator at nominal energy of 4, 6, 9, 12 and 15 MeV electron beam were performed for intraoperative radiotherapy (IORT) in ML-15MDX linear accelerator. This paper presents the percent depth dose, surface dose, beam flatness and output factors of using the IORT applicator in different electron beam energy. The output factor showed as a 24 percent higher in IORT applicator than that of reference 10x10 cm? applicator. The surface dose of using the IORT applicator showed 7.7 and 2.7 percent higher than that of reference field in 4 and 15 MeV electron beam, respectively. In our experiments, the variation of percent depth dose was very small but the output factor and flatness at 0.5 cm depth have showed a large value in IORT applicator.
Particle Accelerators ; Radiotherapy

An important problem in radiosurgery is the utilization of the proper beam parameters, to which dose shape is sensitive. Streotactic radiosurgery techniques for a linear accelerator typically, use circular radiation fields with multiple arcs to produce an spherical radiation distribution. Target volumes are irregular in shape for a certain case, and spherical distributions can irradiate normal tissues to high dose as well as the target region. The current improvement to dose distribution utilizes treating multiple isocenters or weighting various arcs to change treatment volume shape. In this paper another premising study relies upon dynamically shaping the treatment beam to fit the beam's eye view of the target. This conformal irradiation technique was evaluated by means of visual three dimensional dose distribution, dose volume histograms to the target volume and surrounding normal brain. It is shown that using even less arcs than multiple isocenter irradiation technique, the conformal therapy yields comparable dose gradients and superior homogeneity of dose within the target volume.
Brain ; Particle Accelerators ; Radiosurgery*

PURPOSE: To evaluate the contralateral breast dose using a virtual wedge compared with that using a physical wedge and an open beam in a Siemens linear accelerator. MATERIALS AND METHODS: The contralateral breast dose was measured using diodes placed on a humanoid phantom. Diodes were placed at 5.5 cm (position 1), 9.5 cm (position 2), and 14 cm (position 3) along the medial-lateral line from the medial edge of the treatment field. A 6-MV photon beam was used with tangential irradiation technique at 50 and 230 degrees of gantry angle. Asymmetrically collimated 17 x 10 cm field was used. For the first set of experiment, four treatment set-ups were used, which were an open medial beam with a 30-degree wedged lateral beam (physical and virtual wedges, respectively) and a 15-degree wedged medial beam with a 15-degree wedged lateral beam (physical and virtual wedges, respectively). The second set of experiment consists of setting with medial beam without wedge, a 15-degree wedge, and a 60-degree wedge (physical and virtual wedges, respectively). Identical monitor units were delivered. Each set of experiment was repeated for three times. RESULTS: In the first set of experiment, the contralateral breast dose was the highest at the position 1 and decreased in order of the position 2 and 3. The contralateral breast dose was reduced with open beam on the medial side (2.70+/-1.46%) compared to medial beam with a wedge (both physical and virtual) (3.25+/-1.59%). The differences were larger with a physical wedge (0.99+/-0.18%) than a virtual wedge (0.10+/-0.01%) at all positions. The use of a virtual wedge reduced the contralateral breast dose by 0.12% to 1.20% of the prescribed dose compared to a physical wedge with same technique. In the second experiment, the contralateral breast dose decreased in order of the open beam, the virtual wedge, and the physical wedge at the position 1, and it decreased in order of a physical wedge, an open beam, and a virtual wedge at the position 2 and 3. CONCLUSION: The virtual wedge equipped in a Siemens linear accelerator was found to be useful in reducing dose to the contralateral breast. Our additional finding was that the surface dose distribution from the Siemens accelerator was different from a Varian accelerator.
Breast* ; Particle Accelerators

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.
Particle Accelerators* ; Water