Design, realization, and characterization of a novel diamond detector prototype for FLASH radiotherapy dosimetry

Abstract

Purpose FLASH radiotherapy (RT) is an emerging technique in which beams with ultra‐high dose rates (UH‐DR) and dose per pulse (UH‐DPP) are used. Commercially available active real‐time dosimeters have been shown to be unsuitable in such conditions, due to severe response nonlinearities. In the present study, a novel diamond‐based Schottky diode detector was specifically designed and realized to match the stringent requirements of FLASH‐RT. Methods A systematic investigation of the main features affecting the diamond response in UH‐DPP conditions was carried out. Several diamond Schottky diode detector prototypes with different layouts were produced at Rome Tor Vergata University in cooperation with PTW‐Freiburg. Such devices were tested under electron UH‐DPP beams. The linearity of the prototypes was investigated up to DPPs of about 26 Gy/pulse and dose rates of approximately 1 kGy/s. In addition, percentage depth dose (PDD) measurements were performed in different irradiation conditions. Radiochromic films were used for reference dosimetry. Results The response linearity of the diamond prototypes was shown to be strongly affected by the size of their active volume as well as by their series resistance. By properly tuning the design layout, the detector response was found to be linear up to at least 20 Gy/pulse, well into the UH‐DPP range conditions. PDD measurements were performed by three different linac applicators, characterized by DPP values at the point of maximum dose of 3.5, 17.2, and 20.6 Gy/pulse, respectively. The very good superimposition of three curves confirmed the diamond response linearity. It is worth mentioning that UH‐DPP irradiation conditions may lead to instantaneous detector currents as high as several mA, thus possibly exceeding the electrometer specifications. This issue was properly addressed in the case of the PTW UNIDOS electrometers. Conclusions The results of the present study clearly demonstrate the feasibility of a diamond detector for FLASH‐RT applications.

Application of a novel diamond detector for commissioning of FLASH radiotherapy electron beams

“…The linearity tests, whose results are reported in Figure 1, demonstrate that the fD response is linear at least up to the maximum DPP of 11.9 Gy available in this study, well in the UH‐DPP range. This confirms the results previously reported for fDs by the authors 33 . Two experimental data shown in Figure 1a and obtained by using the 30 and 35 mm applicators, that is, the ones at the highest DPPs in the plot, deserve a specific comment.…”

“…In this study, an fD prototype was investigated, whose physical properties were recently reported by Marinelli et al 33 . It consists of a diamond Schottky diode, based on the same working principle of the commercially available PTW microDiamond (mD) (PTW‐Freiburg, Germany) 35,36 .…”

“…They were calibrated and analyzed by the FilmQA Pro software (Ashland Inc., Covington, KY, USA), according to the protocol suggested by the manufacturer and the measurement procedure reported by the authors in Ref. [33]. PTW electrometers were used for the measurements performed by active real‐time detectors.…”

“…Novel detector prototypes are being designed and characterized by several research groups, 30–32 whose properties are expected to overcome these limitations. In particular, a diamond Schottky diode detector prototype was recently proposed, 33 the so‐called flashDiamond (fD), specifically designed for UH‐DPP and UH‐DR applications. A thorough characterization was performed in terms of detector response linearity, which has been proven for DPPs up to at least 20 Gy, average DRs of the order of 1 kGy/s, and instantaneous DRs of about 5 MGy/s.…”

Development of an ultra‐thin parallel plate ionization chamber for dosimetry in FLASH radiotherapy

“…Maximum dose rate achievable with applicator 10 cm is beyond 1000 Gy/s, with a dose per pulse above tition rate. A PMMA phantom was built for the insertion of the UTIC and a specially modified diamond detector (flash-diamond) for UHDR 22 which was used as a reference dosimeter (Figure 3). Flash-diamond was placed at 30 mm transversal distance from UTIC axis at the same depth of material.…”