The peak scatter factor (PSF) for a photon beam is defined as the ratio of the total dose and the primary dose at the depth of dose maximum. The values of the PSF for photon beams ranging from 60Co to 24 MV are calculated using the EGS4 Monte Carlo technique, to avoid measurement difficulties. The calculation shows that the effect of SSD on PSF for high energy photon beams is not significant fo...

Introduction: Craniospinal radiotherapy is a therapeutic technique for central nervous system (CNS) tumors, which requires meticulous attention to technique and dosimetry.Treatment planning system (TPS) is one of the main equipment in radiotherapy; therefore, the evaluation of its accuracy is essential for dose calculation. The present study evaluates the validity of Isogray TPS in craniospinal...

Background: The electron contamination may reduce or even diminish the skin sparing property of the megavoltage beam. The detailed characteristics of contaminant electrons are presented for different field sizes and cases. Materials and Methods: The Monte Carlo code, MCNPX, has been used to simulate 18 MV photon beam from a Varian Linac-2300 accelerator. All dose measurements were car...

introduction the first medical intervention for many breast cancer patients is breast conserving surgery (bcs) and/or modified radical mastectomy (mrm). most of these patients undergo radiation therapy, following surgery. the most common side-effect of breast radiotherapy is skin damage. in the present study, the severity of acute skin changes and the underlying causes were investigated in pati...

background: in conventional radiation therapy, regarding normal tissue tolerance, the treatment of bulk tumors is one of the remaining challenges. grid radiation therapy (grt) is a technique to deliver high doses, approximately 15 – 20 gy per fraction, to several small volumes located in a large radiation field. this can be performed using a grid block. the current work has concentrated on the ...

Strongly enhanced and spatially confined near-fields in the vicinity of plasmonic nanostructures open up exciting new capabilities for photon-driven processes and particularly also for optical spectroscopy. Surface enhanced Raman signatures of single molecules can provide us with important information about the optical near-field. We discuss one- and two-photon excited surface enhanced Raman sc...

By solving Maxwell’s equations, we observed photon localization and strong electromagnetic field enhancement in laser-irradiated, one-dimensional random multilayer and twodimensional random media, with particle size around the laser wavelength. Higher refractive index contrast and degree of randomness result in stronger localization. The probability density and the location of enhanced fields a...

The temperatures of interstellar dust grains are analyzed using stochastic simulations, taking into account the grain composition and size and the discreteness of the photon flux. Grains of radii smaller than about 0.02 μm are found to exhibit large temperature fluctuations with narrow spikes following the absorption of UV photons. The temperatures of such grains may rise by a few × 10 K for ve...

Introduction: Breast cancer is one of the most common known cancers in women all around the world. It is the most common cause of death in women after lung cancer. Radiotherapy is a method for therapy of cancer in which certain dose of high energy radiations is used to destruct cancer cells. Radiotherapy is designed so that radiation of eartain does to the target area in body i...

PURPOSE With the advent of state-of-the-art treatment technologies, the use of small fields has increased, and dosimetry in small fields is highly challenging. In this study, the potential use of Varian electronic portal imaging device (EPID) for small field measurements was explored for 6 and 15 MV photon beams. MATERIALS AND METHODS The output factors and profiles were measured for a range ...