Microdosimetric measurements of a clinical proton beam with micrometer‐sized solid‐state detector

Abstract

Purpose: Microdosimetry is a vital tool for assessing the microscopic patterns of energy deposition by radiation, which ultimately govern biological effect. Solid-state, silicon-on-insulator microdosimeters offer an approach for making microdosimetric measurements with high spatial resolution (on the order of tens of micrometers). These high-resolution, solid-state microdosimeters may therefore play a useful role in characterizing proton radiotherapy fields, particularly for making highly resolved measurements within the Bragg peak region. In this work, we obtain microdosimetric measurements with a solid-state microdosimeter (MicroPlus probe) in a clinical, spot-scanning proton beam of small spot size. Methods: The MicroPlus probe had a 3D single sensitive volume on top of silicon oxide. The sensitive volume had an active cross-sectional area of 250 lm 9 10 lm and thickness of 10 lm. The proton facility was a synchrotron-based, spot-scanning system with small spot size (r % 2 mm). We performed measurements with the clinical beam current (%1 nA) and had no detected pulse pile-up. Measurements were made in a water-equivalent phantom in water-equivalent depth (WED) increments of 0.25 mm or 1.0 mm along pristine Bragg peaks of energies 71.3 MeV and 159.9 MeV, respectively. For each depth, we measured lineal energy distributions and then calculated the dose-weighted mean lineal energy, y D . The measurements were repeated for two field sizes: 4 9 4 cm 2 and 20 9 20 cm Conclusions: We performed microdosimetric measurements with a novel solid-state, silicon-oninsulator microdosimeter in a clinical spot-scanning proton beam of small spot size and unmodified beam current. For all of the proton field sizes and energies considered, the measurements of y D were in agreement with expected trends. Furthermore, we obtained measurements with a spatial resolution of 10 lm in the beam direction. This spatial resolution greatly exceeded that possible with a conventional gaseous tissue-equivalent proportional counter and allowed us to perform a high-resolution investigation within the Bragg peak region. The MicroPlus probe is therefore suitable for applications in proton radiotherapy.

scCVD Diamond Membrane based Microdosimeter for Hadron Therapy

“…Although not calibrated with the energy and therefore not directly comparable to related microdosimeters responses, a general trend can be observed in which there is an increase in pulse‐height (lineal energy) at higher energies (distal part) for the Bragg peak. However, this similar behavior of the scCVD diamond membrane based microdosimeters can be also observed for known measurements obtained from TEPC and silicon dosimeters, which demonstrates the microdosimeter's ability to measure microdosimetric quantities in clinical ion beams.…”

Implementation of planar proton minibeam radiation therapy using a pencil beam scanning system: A proof of concept study

“…Modeling the LET distributions of collimated pMBRT beams, particularly by taking secondaries into account, may therefore be useful for interpretation of radiobiological experiments, as a LET‐RBE (Relative Biological Effectiveness) relationship has often been described . An accurate quantification of these physical quantities should be the subject of a future study, especially since the measurement of lineal energy distributions with new solid‐state (silicon or diamond) microdosimeters now appears to be accessible . Lastly, EUD corrections could also be recommended when evaluating and comparing uniform with spatially fractionated irradiation geometries …”

“…51 An accurate quantification of these physical quantities should be the subject of a future study, especially since the measurement of lineal energy distributions with new solid-state (silicon or diamond) microdosimeters now appears to be accessible. 52 Lastly, EUD corrections could also be recommended when evaluating and comparing uniform with spatially fractionated irradiation geometries. 53 A particularly interesting potential clinical application of pMBRT irradiations with pencil beam scanning would be management of intra-fraction motion during treatment delivery, as hypofractionation is typically a key objective of pMBRT (a few tens of grays per fraction, 5,6 ).…”

Using the Proton Energy Spectrum and Microdosimetry to Model Proton Relative Biological Effectiveness

“…are reported in the Supplementary Data. Recently, a series of microdosimetric measurements were conducted by Anderson et al[29] where they measured ‫ݕ‬ at various depths along a 71.3 MeV and 159.9 MeV proton beam and compared those measurements to calculations of LET D . They found a similar, linear relationship between LET D and ‫ݕ‬ , and our values of ‫ݕ‬ at similar LET D are similar to theirs.…”