This study assesses the feasibility of using stereotactic field diode (SFD) as an alternate to gaf chromic films for field output factor (FF) measurement and further evaluating three new detectors for small field dosimetry. Varian 21EX linear accelerator was used to generate 6 and 10 MV beams of nominal square fields ranging from 0.5 × 0.5 cm2 to 10 × 10 cm2. One passive (EBT3 films) and five active detectors including IBA RAZOR diode(RD), SFD, RAZOR nanochamber (RNC), pinpoint chamber (PTW31023), and semiflex chamber (PTW31010) were employed. FFs were measured using films and SFD while beam profiles and percentage depth dose (PDD) distribution were acquired with active detectors. Polarity (kpol) and recombination (ks) effects of ion chambers were determined and corrected for output ratio measurement. Correction factors (CF) of RD, RNC, and PTW31023 in axial and radial orientation were also measured. Stereotactic field diode measured FFs have shown good agreement with films (with difference of <1%). RD and RNC measured beam profiles were within 3% deviation from the SFD values. Variation in kpol with field size for RNC and PTW31023 was up to 4% and 0.4% (for fields ≥ 1 × 1 cm2), respectively, while variation in ks of PTW31023 was <0.2 %. The maximum values of CF have been calculated to be 5.2%, 2.0%, 13.6%, and 25.5% for RD, RNC, PTW31023‐axial, and PTW31023‐radial respectively. This study concludes that SFD with appropriate CFs as given in TRS 483 may be used for measuring FFs as an alternate to EBT3 films. Whereas RD and RNC may be used for beam profile and PDD measurement in small fields. Considering the limit of usability of 2%, RNC may be used without CF for FF measurement in the smallfields investigated in this study.
This study is aimed at the evaluation of the absorbed dose to the thyroid gland from scattered/primary radiations in patients who have undergone radiotherapy. In this study, the skin entrance dose (SED) on the anterior neck at the level of the thyroid gland was measured using thermoluminescent dosimeters for 57 patients during radiotherapy with (60)Co teletherapy unit. Phantom dosimetry was also performed to find the correlation between the SED and the dose at the depth of the thyroid. SED of patients treated for breast cancer was 6.77±3.49 Gy and that of those with Hodgkin's disease and Ca. lung irradiation were 21.29±13.52 Gy and 28.80±14.94 Gy, respectively. SED at the level of the thyroid gland was found to be highest for patients whose thyroid gland was within the radiation field, while lowest for patients with skull irradiation. Thyroid gland is recommended to be shielded or excluded from the field whenever possible.
Abstract. Flexible eyepiece telescope has been designed and verified. The rotating eyepiece of telescope will facilitate viewing of objects in a remote or out of sight target. Eyepiece arm of telescope can be rotated upto 360 o keeping objective and reticule unchanged and ensuring zero deviation in reticule inclination. Main application of this scope is off axis viewing of objects. Image inversion has been carried out by using pair of mirrors and length of telescope is controlled by using relay lenses. The optical design, simulation and image analysis has been carried out by using ZEMAX ® . Magnification of telescope is between 10~12 times with FOV of 6 0 . Experiment has been carried out using uncoated Edmund Optics and optical tool box of Micro Series Kit, NEWPORT.
IntroductionA periscope is an optical instrument that facilitates viewing of objects which are beyond line of sight [1]. It is an optical instrument that facilitates visual imagery through bent geometries and can be described as a telescope having a bent optical path and a limited field of view [2]. The requirement of brightness, proper image orientation, field of view and maneuverability has led the periscope optics to consist of several image forming, image rotating and image scanning elements.Periscope is an important tool of submarines. It is a necessity in searching and identifying the targets before attack. Due to the powerful and vital threat, submarine technologies such as periscope design, sonar sensors, engines, communications, and weaponry are confidential by designers. A complete periscope design includes the head piece, the relay optics in the mast, and the observation eyepiece.An endoscope is a miniature periscope used to examine the inside of a cavity through a small orifice; they are widely used in medical applications. The size of the optics in a medical endoscope is on the order of 2 or 3mm in diameter. In an endoscope or periscope, the number of relay stages is determined by the length of the instrument. The relay lenses are typically made as cemented doublets, with the flint (negative) element made thick enough to fill the space. The outer surface of the flint is made convex so that it functions as the field lens. This is often referred to as a rod-lens endoscope. The reduction in the number of relay components both reduces the cost of the endoscope and improves the image quality (especially by reducing the secondary spectrum and the Petzval field curvature) [3].Design presented can also be utilized in these applications when realized at miniature scale. Further CCD cameras can also be used directly to view image on mounts.
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