Output factor measurement in high dose-per-pulse IORT electron beams

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Intraoperative radiotherapy (IORT) utilizes high dose-per-pulse electron beams.
• Accurate measurement of relative output factors (OF) is crucial for precise dose delivery in IORT.
• Alanine dosimeters serve as a dose-rate independent reference standard for OF measurements.

Purpose of the Study:

• To evaluate the performance of various detectors in measuring OF at high dose per pulse.
• To compare detector capabilities against alanine dosimeters, a reliable reference standard.
• To determine the accuracy of different detector types under specific irradiation conditions.

Main Methods:

• Measurements were conducted using 7 and 9 MeV electron beams from a Novac7 accelerator.
• Various applicator sizes (4-10 cm diameter) were employed, resulting in dose per pulse up to 70 μGy.
• Detectors included five ionization chambers, two silicon diodes, and one microDiamond. Ion recombination corrections were applied to ionization chambers.

Main Results:

• Alanine dosimeters provided reference OF values with 0.8% uncertainty.
• Most detectors showed deviations within 1.5% of reference OFs, falling within alanine's confidence interval.
• Minor deviations up to 2% were observed in some cases, consistent with detector reproducibility.

Conclusions:

• All tested detectors (ionization chambers, diodes, microDiamond) are suitable for measuring OF in high dose-per-pulse electron beams.
• An accuracy better than 2% can be achieved with these detectors.
• Ionization chambers require appropriate corrections for ion recombination effects to ensure accuracy.