The saturation loss for plane parallel ionization chambers at high dose per pulse values

Area of Science:

• Medical Physics
• Radiation Dosimetry

Background:

• Plane parallel ionization chambers can overestimate ion recombination factors (k) in high dose per pulse electron beams, leading to dose uncertainties up to 20% with conventional protocols.
• Accurate dosimetry is crucial for radiotherapy, especially with advanced electron beam techniques.

Purpose of the Study:

• To calibrate plane parallel ionization chambers using radiochromic films as a reference dosimeter for high dose per pulse electron beams.
• To determine accurate ion recombination factors (ksat(V0)) for plane parallel chambers to reduce dose uncertainties.

Main Methods:

• MD-55-2 radiochromic films were used as reference dosimeters to measure dose to water per pulse (DGAF(w)) for 5.8 MeV electron beams.
• Three plane parallel ionization chambers were calibrated using the film-derived doses.
• The general formula for k determination was tested, and consistent ksat(V0) values were estimated based on Boag theory.

Main Results:

• Radiochromic films provided reliable calibration doses to water per pulse (DGAF(w)) for Novac7 electron beams.
• Consistent ion recombination factors (ksat(V0)) were determined for the tested chambers, aligning with Boag theory.
• The study demonstrated that specific ksat(V0) determination is necessary for each ionization chamber.

Conclusions:

• Accurate calibration of plane parallel ionization chambers using reference dosimeters like radiochromic films is essential for precise dose delivery in high dose per pulse electron beam radiotherapy.
• The established method allows for accurate determination of dose to water per pulse, applicable to various electron beam qualities and configurations.
• This approach enhances the reliability of periodic quality control procedures in radiation oncology.