Initial testing of a pixelated silicon detector prototype in proton therapy

Abstract

As technology continues to develop, external beam radiation therapy is being employed, with increased conformity, to treat smaller targets. As this occurs, the dosimetry methods and tools employed to quantify these fields for treatment also have to evolve to provide increased spatial resolution. The team at the University of Wollongong has developed a pixelated silicon detector prototype known as the dose magnifying glass (DMG) for real‐time small‐field metrology. This device has been tested in photon fields and IMRT. The purpose of this work was to conduct the initial performance tests with proton radiation, using beam energies and modulations typically associated with proton radiosurgery. Depth dose and lateral beam profiles were measured and compared with those collected using a PTW parallel‐plate ionization chamber, a PTW proton‐specific dosimetry diode, EBT3 Gafchromic film, and Monte Carlo simulations. Measurements of the depth dose profile yielded good agreement when compared with Monte Carlo, diode and ionization chamber. Bragg peak location was measured accurately by the DMG by scanning along the depth dose profile, and the relative response of the DMG at the center of modulation was within 2.5% of that for the PTW dosimetry diode for all energy and modulation combinations tested. Real‐time beam profile measurements of a 5 mm 127 MeV proton beam also yielded FWHM and FW90 within ±1 channel (0.1 mm) of the Monte Carlo and EBT3 film data across all depths tested. The DMG tested here proved to be a useful device at measuring depth dose profiles in proton therapy with a stable response across the entire proton spread‐out Bragg peak. In addition, the linear array of small sensitive volumes allowed for accurate point and high spatial resolution one‐dimensional profile measurements of small radiation fields in real time to be completed with minimal impact from partial volume averaging.

Semiconductor dosimetry in modern external-beam radiation therapy

“…A Dose Magnifying Glass, this time with diodes spaced by 0.1 mm, measured full-width half-maximum (FWHM) and full-with 90%-maximum (FW90) of small proton beams, of energy 127 MeV and 157 MeV, in agreement to within 0.1 mm with Monte Carlo calculations and film measurements. Furthermore, measurements of a SOBP suggested that the sensitivity of the Dose Magnifying Glass had no significant dependence on LET, for proton energies used in proton therapy (Wroe et al 2017). The Dose Magnifying Glass was also used for range verification in proton (Merchant et al 2017) and heavy-ion therapy (Debrot et al 2018), and the depth of the Bragg peak measured in silicon was in agreement to within 0.2 mm with Monte Carlo simulations 15 .…”

Monte Carlo evaluation of high-gradient magnetically focused planar proton minibeams in a passive nozzle

“…Monoenergetic unmodulated protons and secondary particles were tracked through a model of the Gantry 1 clinical passive treatment nozzle at the James M Slater, MD, Proton Treatment and Research Center at Loma Linda University Medical Center. Several Monte Carlo and experimental studies using this nozzle have been previously reported, including studies employing Halbach cylinders to focused protons (Wroe et al 2013, McAuley et al 2015a, Wroe et al 2017. This nozzle is used clinically for proton therapy (including radiosurgery) and, when configured for radiosurgery, has several advantages for this study: (1) it allows the creation of pencil beams that match the diameters of the Halbach cylinders (10-15 mm diameter).…”