Dosimetric characteristics of 6 MV modified beams by physical wedges of a siemens linear accelerator

Physical wedges still can be used as missing tissue compensators or filters to alter the shape of isodose curves in a target volume to reach an optimal radiotherapy plan without creating a hotspot. The aim of this study was to investigate the dosimetric properties of physical wedges filters such as off-axis photon fluence, photon spectrum, output factor and half value layer. The photon beam quality of a 6 MV Primus Siemens modified by 150 and 450 physical wedges was studied with BEAMnrc Monte Carlo (MC) code. The calculated present depth dose and dose profile curves for open and wedged photon beam were in good agreement with the measurements. Increase of wedge angle increased the beam hardening and this effect was more pronounced at the heal region. Using such an accurate MC model to determine of wedge factors and implementation of it as a calculation algorithm in the future treatment planning systems is recommended

Quality control of acuity-varian radiotherapy simulator system

One of the main and primarily phase to success of radiotherapy is accurately localization of the target volume and health peripheral tissues by radiotherapy simulator. The aim of this study is to investigate the some specific quality control tests necessary to provide adequate confidence of radiotherapy simulator performance Various essential parameters for quality control of Acuity- Varian radiotherapy simulator such as matching of mechanical measurements and electrical readouts, isocenter check, Congruence between optical field and radiation field, laser positioning system, kVp accuracy of X-ray beam, flat panel performance (resolution and low contrast sensitivity), etc were checked by quality control test tools. All investigated tests for matching of mechanical measurements and electrical readouts of field size, rotation and movement of table, gantry and flat panel detector were within the tolerance limits. The accuracy and reproducibility of KV passed the acceptable values. All the lasers were aligned with isocenter. However resolution of flat panel was within tolerance limit but low contrast sensitivity was not passed. The various quality control tests carried out on Acuity-Varian radiotherapy simulator were within recommended limits except the low contrast sensitivity that is in borderline of tolerance

Dose perturbation due to the magnetic port of tissue breast expander in patient undergoing the postmastectomy radiation therapy

There is a concern about dose perturbation due to high-Z metallic port of temporary tissue expander (TTE) for patients with breast reconstruction undergoing to the postmastectomy radiation therapy (PMRT). The aim of this study is exactly determination the value of dose perturbation due to the presence of metallic port of TTE. The BEAMnrc code was used to simulate of a 6 MV-Primus Siemens Linac and to calculate the dose due to emerge of magnetic port (McGhan Style 133 model) at different depths in water phantom. The present depth dose and profile curves were calculated. A dose enhancement about 15 at front of the port and a dose reduction of about 10 at 5 cm distance from the backward direction of the port were resulted. The dose reduction at the shadow region of the magnetic port of TTE is significant and must be considered to calculate of accurate dose distribution