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*

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*

In case of radiation treatment using small field high-energy photon beams, an accurate dosimetry is a challenging task because of dosimetrically unfavorable phenomena such as dramatic changes of the dose at the field boundaries, dis-equilibrium of the electrons, and non-uniformity between the detector and the phantom materials. In this study, the absorbed dose in the phantom was measured by using an ion chamber and a diode detector widely used in clinics. GAFCHROMIC(R) EBT films composed of water equivalent materials was also evaluated as a small field detector and compared with ionchamber and diode detectors. The output factors at 10 cm depth of a solid phantom located 100 cm from the 6 MV linear accelerator (Varian, 6 EX) source were measured for 6 field sizes (5x5 cm2, 2x2 cm2, 1.5x1.5 cm2, 1x1 cm2, 0.7x0.7 cm2 and 0.5x0.5 cm2). As a result, from 5x5 cm2 to 1.5x1.5 cm2 field sizes, absorbed doses from three detectors were accurately identified within 1%. Wheres, the ion chamber underestimated dose compared to other detectors in the field sizes less than 1x1 cm2. In order to correct the observed underestimation, a convolution method was employed to eliminate the volume averaging effect of an ion chamber. Finally, in 1x1 cm2 field the absorbed dose with a diode detector was about 3% higher than that with the EBT film while the dose with the ion chamber after volume correction was 1% lower. For 0.5x0.5 cm2 field, the dose with the diode detector was 1% larger than that with the EBT film while dose with volume corrected ionization chamber was 7% lower. In conclusion, the possiblity of GAFCHROMIC(R) EBT film as an small field dosimeter was tested and further investigation will be proceed using Monte Calro simulation.
Electrons ; Particle Accelerators ; Water

In this study, Geant4 based Monte Carlo simulations were carried out for medical linear accelerator. Modified Medical Linac2 toolkit was used for calculation. The energy spectrum, most probable energy and the photon mean energy compared with the published results using the EGS4 code. The results well agreed with published results. The calculated results of photon fluence, energy fluence and mean energy according to the radius from the centre of the beam were analyzed. Monte Carlo simulation using Medical Linac2 code is considered to be useful for analysis of medical linear accelerator. Because the calculated results varies depending on Physics List model for same head structure. It it important to choose the right model for research purpose. Monte Carlo simulation using GEANT4 Medical Linac2 is a valuable for any novice to adopt this code to the study related to 6 MV photon fluence from medical linear accelerator.
Head ; Particle Accelerators ; Radius

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*

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

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

The stereotactic radiosurgery (SRS) describes a method of delivering a high dose of radiation to a small target volume in the brain, generally in a single fraction, while the dose delivered to the surrounding normal tissue should be minimized. To perform automatic plan of the SRS, a new method of multi-isocenter/shot linear accelerator (linac) and gamma knife (GK) radiosurgery treatment plan was developed, based on a physical lattice structure in target. The optimal radiosurgical plan had been constructed by many beam parameters in a linear accelerator or gamma knife-based radiation therapy. In this work, an isocenter/shot was modeled as a sphere, which is equal to the circular collimator/helmet hole size because the dimension of the 50% isodose level in the dose profile is similar to its size. In a computer-aided system, it accomplished first an automatic arrangement of multi-isocenter/shot considering two parameters such as positions and collimator/helmet sizes for each isocenter/shot. Simultaneously, an irregularly shaped target was approximated by cubic structures through computation of voxel units. The treatment planning method by the technique was evaluated as a dose distribution by dose volume histograms, dose conformity, and dose homogeneity to targets. For irregularly shaped targets, the new method performed optimal multi-isocenter packing, and it only took a few seconds in a computer-aided system. The targets were included in a more than 50% isodose curve. The dose conformity was ordinarily acceptable levels and the dose homogeneity was always less than 2.0, satisfying for various targets referred to Radiation Therapy Oncology Group (RTOG) SRS criteria. In conclusion, this approach by physical lattice structure could be a useful radiosurgical plan without restrictions in the various tumor shapes and the different modality techniques such as linac and GK for SRS.
Brain ; Particle Accelerators ; Radiosurgery*

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

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