Development of a synthetic single crystal diamond dosimeter for dose measurement of clinical proton beams

Abstract

The scope of this work was to develop a synthetic single crystal diamond dosimeter (SCDD-Pro) for accurate relative dose measurements of clinical proton beams in water. Monte Carlo simulations were carried out based on the MCNPX code in order to investigate and reduce the dose curve perturbation caused by the SCDD-Pro. In particular, various diamond thicknesses were simulated to evaluate the influence of the active volume thickness (e ) as well as the influence of the addition of a front silver resin (250 µm in thickness in front of the diamond crystal) on depth-dose curves. The simulations indicated that the diamond crystal alone, with a small e of just 5 µm, already affects the dose at Bragg peak position (Bragg peak dose) by more than 2% with respect to the Bragg peak dose deposited in water. The optimal design that resulted from the Monte Carlo simulations consists of a diamond crystal of 1 mm in width and 150 µm in thickness with the front silver resin, enclosed by a water-equivalent packaging. This design leads to a deviation between the Bragg peak dose from the full detector modeling and the Bragg peak dose deposited in water of less than 1.2%. Based on those optimizations, an SCDD-Pro prototype was built and evaluated in broad passive scattering proton beams. The experimental evaluation led to probed SCDD-Pro repeatability, dose rate dependence and linearity, that were better than 0.2%, 0.4% (in the 1.0-5.5 Gy min range) and 0.4% (for dose higher than 0.05 Gy), respectively. The depth-dose curves in the 90-160 MeV energy range, measured with the SCDD-Pro without applying any correction, were in good agreement with those measured using a commercial IBA PPC05 plane-parallel ionization chamber, differing by less than 1.6%. The experimental results confirmed that this SCDD-Pro is suitable for measurements with standard electrometers and that the depth-dose curve perturbation is negligible, with no energy dependence and no significant dose rate dependence.

Investigating the lateral dose response functions of point detectors in proton beams

“…In other words, the volume effect of diode-type detectors can be solely attributed to averaging over sensitive volume of the detector. This agrees with findings by Moignier et al (2017), who studied diamond detector design and performed Monte Carlo simulations mimicking the measurement process of a 100 MeV proton pencil beam profile. They used a water voxel, diamond voxels of various size (widths between 0.25 mm and 4 mm) and a complete detector geometry.…”

“…For general PBS with gaussian shaped pencil beams, previous studies indicate that the volume effect of detectors, which comprises the volume-averaging and density effects, does not or only slightly influence the measurement process (Brodbek et al, 2020;Furukawa et al, 2013;Moignier et al, 2017;Sahoo et al, 2010;Schwaab et al, 2011). In contrast, insight into the performance of point detectors in proton beams with reduced penumbrae is scarce.…”

Comprehensive investigation of lateral dose profile and output factor measurements in small proton fields from different delivery techniques

“…For some detectors in PBS fields,similar findings were presented in the past. 13,15,17,29,45,46 Schwaab et al, 16 Sahoo et al 15 and Sawakuchi et al 45 measured proton and/or carbon ion pencil beam profiles with ionization chambers and concluded that the effect of detector size can be neglected for the Gussian like lateral profiles in scanned fields. 15,16,29,45 Furukawa et al and Brodbek et al 13 showed that the volume effect of ionization chambers of 2D arrays only has a minor or even negligible impact on the plan verification process of the intensity modulated carbon ion or proton therapy fields studied.…”

The Many Facets of Diamond Crystals

“…Diamond is known to be an ideal material for solid-state detectors of ionizing radiation and high-energy particles. Indeed, in this particular niche, diamond has found diverse applications in biomedical sciences [57,58] and high-energy physics [59]. It is sufficient to mention the ATLAS and CMS experiments at the Large Hadron Collider (LHC), both of which include diamond detectors and have been involved, for example, in the search, discovery, and exploration of the elusive Higgs boson.…”