Evaluation of detectors for acquisition of pristine depth‐dose curves in pencil beam scanning

Abstract

Acquisition of quasi‐monoenergetic ("pristine") depth‐dose curves is an essential task in the frame of commissioning and quality assurance of a proton therapy treatment head. For pencil beam scanning delivery modes this is often accomplished by measuring the integral ionization in a plane perpendicular to the axis of an unscanned beam. We focus on the evaluation of three integral detectors: two of them are plane‐parallel ionization chambers with an effective radius of 4.1 cm and 6.0 cm, respectively, mounted in a scanning water phantom. The third integral detector is a 6.0 cm radius multilayer ionization chamber. The experimental results are compared with the corresponding measurements under broad field conditions, which are performed with a small radius plane‐parallel chamber and a small radius multilayer ionization chamber. We study how a measured depth‐dose curve of a pristine proton field depends on the detection device, by evaluating the shape of the depth‐dose curve, the relative charge collection efficiency, and intercomparing measured ranges. Our results show that increasing the radius of an integral chamber from 4.1 cm to 6.0 cm increases the collection efficiency by 0%–3.5% depending on beam energy and depth. Ranges can be determined by the large electrode multilayer ionization chamber with a typical uncertainty of 0.4 mm on a routine basis. The large electrode multilayer ionization chamber exhibits a small distortion in the Bragg Peak region. This prohibits its use for acquisition of base data, but is tolerable for quality assurance. The good range accuracy and the peak distortion are characteristics of the multilayer ionization chamber design, as shown by the direct comparison with the small electrode counterpart.PACS number: 87.55.Qr

Implementation of dosimetry equipment and phantoms at the MedAustron light ion beam therapy facility

“…Table summarizes the expected uncertainties on range measurements with MP3 systems as a function of measured range. Our uncertainty budget is consistent with other studies …”

“…It permits acquiring a complete integral depth‐dose profile in a few seconds with a specified accuracy of ± 0.5 mm using curve fitting algorithms based on Ref. MLIC detectors are often used for Quality Control (QC) in LIBT facilities to reduce the acquisition time . The Giraffe has also been tested in the context of proton radiography experiments .…”

Dose detectors, sensors, and their applications

“…The more recent Stingray chambers (IBA Dosimetry) mitigates this effect thanks to the larger radius (6.0 cm) as compared with the Bragg peak chamber (4.08 cm), therefore it reduces the need of MC correction. The Stingray chamber can also be moved remotely and with 0.1 mm steps when mounted on the Blue Phantom2 system (IBA Dosimetry).…”

Toward a novel dosimetry system using acrylic disk radiation sensor for proton pencil beam scanning

“…The MLIC has been used for IDD measurements of the PBS beam via an array of Bragg ionization chambers with radius of 4.1 and 6.0 cm . In Ref.…”

“…In addition, the system is much more expensive than conventional quality assurance equipment used in radiation therapy. Furthermore, as the diameter of the Bragg chamber in an MLIC is less than 10 cm, the measured signal has a slightly smaller value than the calculated dose . Thus, a detector with large sensor volume could provide more accuracy, but the related cost will considerably increase.…”