According to International Atomic Energy Agency (IAEA) recommendations, the calibration of Ionization chambers used for radiotherapy dosimetry follows the substitution method which demands the use of a reference Ionization chamber. This work introduces the Design and fabrication of cylindrical Ionization chamber for dosimetry to be used by standard dosimetry laboratories. The result of the quality control tests in Secondary Standard Dosimetry Laboratory (SSDL) of the Atomic Energy Organization Which was carried out in accordance with the standards and limits set by the International Atomic Energy Agency, are evidence of the accuracy of the claim that this chamber can be used as a reference dosimeter in standard dosimetric laboratories. The low polarity effect and leakage current, high ion collection efficiency and stability, linear response of the detector to the dose and the rate of dosing are some of this instrument characteristic through optimum design of guard ring and collecting electrode and also the proper choice of materials in fabrication.

Background and Objective: Cylindrical Ionization chamber is used for measurements of patient dose in radiation therapy. By determination the effective point of measurement we can determine the dose distribution and the parameters of treatment. Therefore in this research we introduce an analytical approach for determination this point in CC13 cylindrical Ionization chamber that used for dosimetry of linear accelerator.Subjects and Methods: In this study a CC13 Ionization chamber was used for dose measurement of 6 and 18 photon beams of Variant accelerator in different field sizes, 5*5 cm2 up to 35*35cm2. Measurements were performed in blue phantom, up to 5cm depth and data fit software was used for evaluation of experimental data.Results: with our formalism the Pdis quantity in 6MV for 5x5 thought 35x35cm2 were measured 3.088 to 2.88 mm and in 18 MV are measured 4.62 to 4.20 mm.Conclusion: The first critical point of each curve is caused by changing environment from air to water during measuring of Ionization. In fact it can be considered critical point as effective point of measurement of Ionization chamber. Investigation shows that any increasing in field size, decrease and increasing of energy increase the depth of this critical point.

Introduction: Recently, modern radiotherapy techniques have been extensively developed to deliver doses only to therapeutic volume. The objective of the present study was to empirically evaluate the performance capability of the Ionization chamber in comparison to the edge detector. Material and Methods: Firstly, the performance of the Ionization chamber, compared to that of the edge diode detector, was validated at a 10×10 cm2 field size. Then, the percentage depth dose (PDD), percentage surface dose, and transverse profile doses at the 2×2, 3×3, and 4×4 cm2 field sizes were evaluated for both dosimeters. The empirical and statistical results in a water phantom were compared to those reported for the edge diode detector as the reference field dosimeter using the 6 MV Elekta linear accelerator. Results: The empirical and statistical results of the transverse profiles of the Ionization chamber and edge detector are in agreement for the reference field of 10×10 cm2. However, a small difference between the two dosimeters could be observed in small fields. A discrepancy of less than 1% was observed between the results of PDDs for two dosimeters in small fields. Conclusion: The dosimetric characteristics of the Ionization chamber and edge detector illustrated some differences, especially in terms of transverse profiles at the small-field size. This discrepancy could be related to the volume effect of the chamber which affects the penumbra. Due to the importance of sensitive organs, it is recommended to utilize the Ionization chamber for small radiotherapy fields.

Introduction: Well type Ionization chamber is a measuring device which is used to determine the activity of brachytherapy sources. The chamber has a cylindrical volume in which a cylindrical tube is mounted in the middle of the chamber. For the measurements, the brachytherapy sources are transferred to the middle of the tube.Materials and Methods: For designing the wen type chamber, the measurement principals of wen type chambers were considered and MCNP-4C code as a calculation tool was used. The designed chamber was simulated and the response of the chamber was evaluated. In this investigation, the chamber operational parameters such as operating voltage, leakage current, reproducibility, reference measuring point, recombination and polarization factors as well as response stability for 137Cs, 57CO and 241Am sources were studied.Results: The chamber leakage currents at the operating voltage in comparison to the chamber response for the measurement of the above mentioned sources were negligible. The responses of the fabricated chamber for these sources are reproducible and its reference measurement position for these sources was obtained at 6 cm from the bottom of the chamber. The recombination factor for the well type chamber was negligible and the polarization factor is close to 1. Therefore, these two factors were not considered in the measurements. The reproducibility of the measurements in different intervals shows the stability of the chamber response for each source. Also the results of the chamber current measurement in term of source strength were compared to the response of the simulated chamber for different source positions and energy ranges of the used sources.Discussion and Conclusion: The results show that the measurement of the reference positions for each source in the simulated and fabricated chamber is quite in a good agreement. Regarding the reliable operational properties of the fabricated chamber, this chamber can be used to determine the activities of brachytherapy sources in which the energy ranges are greater than 50 KeV.

Free-air well-type Ionization chambers are used in brachytherapy medical centers for measurement of brachytherapy source strengths. In this investigation, the HDR-33004 free-air well-type Ionization chamber has been simulated using MCNP-4C computer code for several aluminum alloys as chamber wall material. The relative response (electric current) behavior of the simulated chamber for various source positions along the chamber central axis has been calculated and shows good agreement with measured values. We have also observed that the calculated and measured reference points are situated at the same positions. The results showed that the calculated electric current for unit source strength of 137Cs does not depend on the chamber wall aluminum alloy type, but for 57CO and 241 Am sources, a strong dependency on the type of aluminum alloy as chamber wall material is observed. The presence of high atomic number elements such as zinc in some aluminum alloys resulted in higher response of the chamber. It is also found that for similar Al-7091 alloys the calculated and measured responses for 137Cs, 57CO and 241A msources are in good agreement, showing that the alloy type of the chamber wall material would likely be an alloy similar to Al-7091. The results of this investigation can be applied for design of free-air well-type Ionization chambers for low energy gamma sources.

Introduction: Computed Tomography scans are a very important tool for diagnosis and assessment of response to treatment in the practice of medicine. Ionizing radiation in medical imaging is undoubtedly one of the most powerful diagnostic tools in medicine. Yet, as with all medical interventions, there are potential risks in addition to the clear potential benefits.Materials and Methods: Two reference dose quantities have been defined in order to promote the use of good technique in CT. These are weighted CT dose index (CTDIw) in (mGy) for a single slice in serial scanning or per rotation in helical scanning, and dose–length product (DLP) per complete examination (mGy.cm), All measurements were performed using a pencil shaped Ionization chamber introduced into polymethyl methacrylate cylindrical brain and body phantoms. This survey was performed on 7 CT scanners in Khorasan Province-Iran.Results: DLP for brain, chest, abdomen and pelvic examinations had a range of 255 - 1026, 76-1277, 48-737, 69-854 mGy.cm, respectively.Conclusion: The results obtained in this study show that the DLP values obtained in this province are lower than European Commission reference dose levels (EC RDL), in other words performance of all the scanners were satisfactory.

Background: Absolute dosimetry of external beam radiotherapy is carried out by the use of Ionization chambers. These chambers must be calibrated at a standard dosimetry laboratory before any use in clinical dosimetry. The secondary standard dosimetry laboratory of Iran (SSDL) has the duty of calibrating the Ionization chambers used in radiotherapy centers in Iran.Materials and Methods: The present work has described traceability of SSDL radiation measurement standards to relevant international standards, and calibration of therapy level Ionization chambers in terms of air kerma and absorbed dose to water against 60Co gamma radiation, as well as uncertainty evaluation of calibration coefficients.Results: The expanded uncertainties in the determination of air kerma and absorbed dose to water are estimated to be 2% and 2.3% at approximately 95% confidence level, respectively.Conclusion: In order to maintain the requirement of ±5% accuracy in the dose delivery, the combined standard uncertainty of the other factors in the dose delivery; i.e., dose measurement set-up, dose calculations, treatment planning, patient set-up, etc, should be less than 2.3%.

Introduction: Studies carried out with synchrotron radiation have shown that micro-beam radiation therapy (MRT) has unique advantages in the treatment of cancerous tumors. In this method, the determination of dose distribution and calculation of peak to valley dose ratio (PVDR) are considered as the most important steps in treatment planning. The PVDR is a criterion to evaluate the destruction of cancer cells and protection of normal cells in the tissues surrounding a tumor. Materials and Methods: Using a multi-slit collimator, planar sliced beams were generated in an X-ray generator in order to determine dose distribution in a multilayer phantom made of plexiglass. An Ionization chamber was used to measure absorbed dose. Given the large size of the sensitive area of the chamber in comparison with the narrow beams, a mono-slit collimator made of tungsten with a slit of 0. 3×7. 5 mm2 in its center was placed in front of the Ionization chamber. Furthermore, by using Geant4 computer code, a model, including X-ray source, multi-slit collimator, phantom, mono-slit collimator, and detector, was designed to compare experimental and simulation results. Findings: The investigation of dose distribution in the phantom with both methods indicated the presence of peaks and valleys. Given the low intensity of Xray beam generated by the X-ray generator, and limited exposure time, the experimental errors were considerable. When using 1 mm (Air)+0. 5 mm (W) collimator, PVDRs were obtained as 8. 7 and 10. 5 for Ionization chamber and simulation, respectively, in the depth of 8 mm of the phantom. On the other hand, with a 1 mm (Air)+1 mm (W) collimator, the values obtained for this parameter were 11. 1 and 13. 3 for Ionization chamber and simulation, respectively. Conclusions: Based on the results, a multislit collimator made of tungsten could produce multi-slice X-ray. The estimated dose distribution using the Geant4 code was more accurate than the one obtained through Ionization chamber, which can be due to the possibility of using a detector in much smaller dimensions in the Geant4 code.

Background: Modern radia on therapy such as intensity modulated radia on therapy (IMRT) and volumetric modulated arc therapy (VMAT) has resulted in using small therapeu c photon beams. The scope of this work is to inves gate the varia on in efficiency of different ioniza on chambers and semiconductor diodes in small mul-leaf collimator (MLC) defined fields of ARTISTE linear accelerator. Materials and Methods: Dose distribu ons measurements was done in field sizes ranging from 0. 5×0. 5 to 10×10 cm2 combining with Monte Carlo (MC) simula on. The treatment head of linac and the detectors were simulated by means of BEAMnrc/DOSXYZnrc of EGSnrc MC. The parameters such as output ra o (OR), penumbral width, dosimetric field size and the percentage surface dose in small radia on fields was evaluated using ioniza on chambers and semiconductor dosimeters. Results: ORs and beam profiles resul ng from various measurements showed significant difference between ioniza on chambers and diodes in small fields. Deriva on of less than 2% was observed between EDGE and Diode P. ORs vary by more than 30% for 1×1 cm2 field size but, in larger field sizes differences was less than 1%. Penumbra underes ma on was seen in Semiflex rela ve to pinpoint ioniza on chamber. No difference was seen in the pa? ern of surface dose among the applied detectors. Conclusion: Dosimetric characteris cs of different detectors showed significant differences in small photon beams. Profiles and ORs analysis with different dosimeters showed that not only water equivalency of detectors, but also dosimeter ac ve volume is important factors for determina on of dosimetric behavior in small photon beams.