Jean-Marc Galvan

PCB-based integration of electrochemiluminescence detection for microfluidic systems.

This communication presents an instrumental development based on the printed circuit board (PCB) technology to integrate electrochemiluminescence (ECL) analysis in microfluidic systems. PCB gold macro- (10 mm2) and micro- (0.09 mm2) electrodes and two ECL microfluidic devices are designed, fabricated and tested via luminol ECL detection. Potential modulation is performed between 0.7 and 0 V vs. Ag/AgCl for luminol oxidation, thus giving rise to on/off ECL responses in the presence of hydrogen peroxide. Synchronous detection is adopted to allow weak ECL signal recovery at a very low signal-to-noise ratio (SNR). The detection limit obtained with the two ECL microfluidic devices is 50 nM and 100 nM H2O2 for macroelectrodes and microelectrodes, respectively.

Design and testing of a phantom and instrumented gynecological applicator based on GaN dosimeter for use in high dose rate brachytherapy quality assurance

PURPOSE High dose rate brachytherapy (HDR-BT) is widely used to treat gynecologic, anal, prostate, head, neck, and breast cancers. These treatments are typically administered in large dose per fraction (>5 Gy) and with high-gradient-dose-distributions, with serious consequences in case of a treatment delivery error (e.g., on dwell position and dwell time). Thus, quality assurance (QA) or quality control (QC) should be systematically and independently implemented. This paper describes the design and testing of a phantom and an instrumented gynecological applicator for pretreatment QA and in vivo QC, respectively. METHODS The authors have designed a HDR-BT phantom equipped with four GaN-based dosimeters. The authors have also instrumented a commercial multichannel HDR-BT gynecological applicator by rigid incorporation of four GaN-based dosimeters in four channels. Specific methods based on the four GaN dosimeter responses are proposed for accurate determination of dwell time and dwell position inside phantom or applicator. The phantom and the applicator have been tested for HDR-BT QA in routine over two different periods: 29 and 15 days, respectively. Measurements in dwell position and time are compared to the treatment plan. A modified position-time gamma index is used to monitor the quality of treatment delivery. RESULTS The HDR-BT phantom and the instrumented applicator have been used to determine more than 900 dwell positions over the different testing periods. The errors between the planned and measured dwell positions are 0.11 ± 0.70 mm (1σ) and 0.01 ± 0.42 mm (1σ), with the phantom and the applicator, respectively. The dwell time errors for these positions do not exhibit significant bias, with a standard deviation of less than 100 ms for both systems. The modified position-time gamma index sets a threshold, determining whether the treatment run passes or fails. The error detectability of their systems has been evaluated through tests on intentionally introduced error protocols. With a detection threshold of 0.7 mm, the error detection rate on dwell position is 22% at 0.5 mm, 96% at 1 mm, and 100% at and beyond 1.5 mm. On dwell time with a dwell time threshold of 0.1 s, it is 90% at 0.2 s and 100% at and beyond 0.3 s. CONCLUSIONS The proposed HDR-BT phantom and instrumented applicator have been tested and their main characteristics have been evaluated. These systems perform unsupervised measurements and analysis without prior treatment plan information. They allow independent verification of dwell position and time with accuracy of measurements comparable with other similar systems reported in the literature.

Failure Detection Method for GaN-Based Dosimetric Systems

We propose a failure detection method for GaN-based dosimetric systems, which basically consist of a GaN-incorporated optical fiber probe coupled to a photodetection module. The method consists in introducing UV excitation with a 285nm LED, and detecting the photoluminescence (PL) of the GaN transducer centered at 380nm. Spectral analysis of the detected signal allows verification of normal operation and identification of failure cases, due to problems of GaN-fiber coupling and poor fiber connection between probe and photodetection module. The proposed method is implemented and experimentally tested, including the use of a 660nm LED to illuminate the probe to verify the transmission ratio between probe and photodetection module. The validity of this method has been verified.

Bi-Crystal Compensation Method for the Over-Response of Solid-State Dosimetry

Solid-state dosimetry employs highly sensitive semiconductors such as Gallium Nitride (GaN) and Silicon (Si), but they have a common drawback of over response compared to tissues for low-energy scattered photons, which induces inacceptable errors for radiotherapy application. To tackle this issue, we propose a compensation method consisting in using two different materials of dosimetric interest with different atomic numbers. Their responses are denoted as SC1 and SC2. The response ratio SC1/water as a function of the ratio SC1/SC2 exhibits a monotonic curve that can serve as reference to compensate the over-response of SC1. To validate this method, we have studied the dosimetric response of GaN (0.1 mm3) and Si crystals (2.5 mm3) by simulations, using a validated model based on the general cavity theory in a homogeneous water phantom. The dosimetric response of GaN and Si calculated using the model has errors within 2.5% compared to measured data. The local fluence spectra have been obtained by convolution of pencil beam kernel built by Monte Carlo simulations for different clinical irradiation conditions with field size (from 5×5 cm2 up to 20×20 cm2) at depth in the phantom (from 2 cm to 25 cm). The obtained results confirm a monotone relationship between GaN/water dose ratio and GaN/Si dose ratio. The reference curve is independent of irradiation conditions (field size, dosimeter position...), and allows determination of compensation value by identification.

Implantable in vivo Dosimetric Probe Based on GaN Radioluminescence

This paper presents an implantable in-vivo dosimetric probe using a small-volume GaN bulk as scintillator. The high light yield of GaN under irradiation in radiotherapy conditions is observed. Heavily-doped n-type GaN is chosen because of enhanced and dominant UV emission. The fabrication process of the probe is described. It is tested using 6 and 18MV photon beams. Measured results show reproducibility errors of less than 2% for a delivered dose of 50cGy. The linearity of the measure and its independence of the dose rate are also verified. The probe’s output light has both GaN and fiber contributions. The fiber contribution may vary with the beam incidence angle (due to dominant Cerenkov effect), while the GaN does not have such dependence.

Combining microfluidics and electrochemical detection

This paper describes two configurations that integrate electrochemical detection into microfluidic devices. The first configuration is a low-cost approach based on the use of PCB technology. This device was applied to electrochemiluminescence detection. The second configuration was used to carry out amperometric quantification of electroactive species using a serial dilution microfluidic system.

Implementation of Electrochemiluminescence Microanalysis in PCB Technology

We present an instrumental development to implement electrochemiluminescence (ECL) microanalysis using printed circuit board (PCB) technology. PCB gold macro- (10 mm2) and micro- (0.09 mm2) electrodes and two ECL microfluidic devices are designed, fabricated and tested via luminol ECL detection. Potential modulation is performed between 0.7 and 0 V vs. Ag/AgCl for luminol oxidation, thus giving rise to on/off ECL responses in the presence of hydrogen peroxide. Synchronous detection is adopted to allow weak ECL signal recovery at a very low signal-to-noise ratio (SNR). The detection limit obtained with the two ECL microfluidic devices is 50 nM and 100 nM H2O2 for macroelectrodes and microelectrodes, respectively.