Microdosimetric measurements of a monoenergetic and modulated Bragg Peaks of 62 MeV therapeutic proton beam with a synthetic single crystal diamond microdosimeter

Abstract

Purpose The purpose of this study was to investigate for the first time the performance of a synthetic single crystal diamond detector for the microdosimetric characterization of clinical 62 MeV ocular therapy proton beams. Methods A novel diamond microdosimeter with a well‐defined sensitive volume was fabricated and tested with a monoenergetic and spread‐out Bragg peak (SOBP) of the CATANA therapeutic proton beam in Catania, Italy. The whole sensitive volume of the detector has an active planar‐sectional area of 100 µm × 100 µm and a thickness of approximately 6.3 um. Microdosimetric measurements were performed at several water equivalent depths, corresponding to positions of clinical relevance. From the measured spectra, microdosimetric quantities such as the frequency mean lineal energy (y¯F), dose mean lineal energy (y¯D) as well as microdosimetric relative biological effectiveness (RBEµ) values were derived for each depth along both a pristine Bragg curve and SOBP. Finally, Geant4 Monte Carlo simulations were performed modeling the detector geometry and CATANA beamline in order to calculate the average linear energy transfer (LET) values in the diamond active layer and water. Results The microdosimetric spectra acquired by the diamond microdosimeter show different shapes as a function of the water equivalent depths. No spectral distortion, due to pile‐up events and polarization effects, was observed. The experimental spectra have a very low detection threshold due to the electronic noise during the irradiation of about 1 keV/μm. The y¯F and y¯D values were in agreement with expected trends, showing a sharp increase in mean lineal energy at the distal edge of the Bragg peak. In addition, a good agreement between the mean lineal energy values and the calculated average LET ones was also observed. Finally, the RBE values evaluated with the diamond microdosimeter were in excellent agreement with those obtained with a mini tissue equivalent proportional counter as well as with radiobiological measurements in the same proton beam field. Conclusions The microdosimetric performance of the tested synthetic single crystal diamond microdosimeter clearly indicates its suitability for quality assurance in clinical proton therapy beam.

A systematic review on the usage of averaged LET in radiation biology for particle therapy

“…• Only the primary protons [5,[117][118][119][120][121][122][123][124][125][126][127][128] • Primary and secondary protons 3 [14, • any particle with z = 1 (meaning also deuterons and tritons) [152] as described in [24] • all secondary particles (most noteworthy also He-3 and He-4) [27,[153][154][155][156], also covered by [24].…”

Multi-arrays of 3D cylindrical microdetectors for beam characterization and microdosimetry in proton therapy

“…New mini-TEPCs have improved performance over the last few years [9], but they are still pointlike and suffer pile-up effects under therapeutic fluence rates. Other alternatives are based on diamond detectors since they are close to tissue equivalent and exhibit radiation hardness [10,11]. Finally, silicon-based radiation detectors have demonstrated their reliability over the last years by overcoming some of the aforementioned disadvantages.…”

First experimental measurements of 2D microdosimetry maps in proton therapy

“…However, there is still room for improving several solid‐state microdosimeter features; for example, the CCE, the spatial resolution along the transverse plane, the data acquisition for further adaptation in clinical conditions to make it practical for daily quality assurance (QA) measurements of y . Alternative solid‐state microdosimeters are based on diamond as they are close to tissue equivalent and have a high radiation hardness 27,28 . To improve the performance of silicon‐based microdosimeters and overcome some of those limitations, in 2013–2015, we proposed and created a new 3D‐cylindrical architecture 29,30 .…”

“…Alternative solid-state microdosimeters are based on diamond as they are close to tissue equivalent and have a high radiation hardness. 27,28 To improve the performance of silicon-based microdosimeters and overcome some of those limitations, in 2013-2015, we proposed and created a new 3D-cylindrical architecture. 29,30 The sensors have already shown a good performance in microdosimetry in both carbon therapy 31 and low-energy proton 32 facilities.…”