introduction for dose measurement in megavoltage (mv) photon beams with ion chambers, the effect of volume occupied by the air cavity is not negligible. therefore, the result of measurement should be corrected with a displacement perturbation correction factor (pdis) or using an effective point of measurement (epom). the aim of this study is to calculate the epom for cylindrical ion chamber and...

background: in order to deliver the precise dose to the target in radiotherapy, absorbed dose to water at the reference point should be assessed. when the calibration procedure is performed for a reference dosimeter in the 60co beam of a secondary standard dosimetry laboratory (ssdl), the total uncertainty in absorbed dose to water (dw) is estimated to be approximately 1.5%. this study attempts...

Background: In order to deliver the precise dose to the target in radiotherapy, absorbed dose to water at the reference point should be assessed. When the calibration procedure is performed for a reference dosimeter in the 60Co beam of a Secondary Standard Dosimetry Laboratory (SSDL), the total uncertainty in absorbed dose to water (Dw) is estimated to be approximately 1.5%. This study attempts...

The work presented focuses on the measurement of Ja e plots and determination of ion recombination factors for plane parallel ionisation chambers used in pulsed electron beams. The ability to measure the Ja e plots accurately is useful when commisioning a new chamber and the ion recombination correction factor needs to be known when the chamber is calibrated in a beam quality di erent from the ...

The flattening filter free (FFF) X-rays can provide much higher dose rate at the treatment target compared to the conventional flattened X-rays. However, the substantial increase of dose rate for FFF beams may affect the ion recombination correction factor, which is required for accurate measurements using ionization chambers in clinical dosimetry. The purpose of this work is to investigate the...

Recent dosimetry protocols for clinical high-energy electron beams recommend measurements of absorbed dose-to-water with a plane-parallel or cylindrical ionization chamber. For well-guarded plane-parallel ionization chambers, the ionization chamber perturbation factor in water, p(Q), has a recommended value of unity in all protocols. This assumption was investigated in detail in this study for ...

PURPOSE To provide a comprehensive investigation of electron beam reference dosimetry using Monte Carlo simulations of the response of 10 plane-parallel and 18 cylindrical ion chamber types. Specific emphasis is placed on the determination of the optimal shift of the chambers' effective point of measurement (EPOM) and beam quality conversion factors. METHODS The EGSnrc system is used for calc...