Characterization of a cable-free system based on p-type MOSFET detectors for “in vivo” entrance skin dose measurements in interventional radiology

• Published in: Medical physics (Lancaster) 2012-08, Vol.39 (8), p.4866-4874
• Main Authors: Falco, Maria Daniela, D’Andrea, Marco, Strigari, Lidia, D’Alessio, Daniela, Quagliani, Francesco, Santoni, Riccardo, Bosco, Alessia Lo
• Format: Article
• Language: English
• Subjects: 60 APPLIED LIFE SCIENCES; Algorithms; Calibrating of instruments or apparatus; CALIBRATION; Dose-Response Relationship, Radiation; DOSIMETRY; Dosimetry/exposure assessment; Electric measurements; Electromagnetic radiation detectors; energy calibration; entrance skin dose; Equipment Design; Field effect devices; Gafchromic® films; HEALTH HAZARDS; Humans; Image guided radiation therapy; in vivo dosimetry; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; IRRADIATION; KEV RANGE; Linear Models; MEV RANGE; Models, Statistical; Models, Theoretical; MOSFET; MOSFETs; OneDoseTM System; PATIENTS; Photons; POLYNOMIALS; Radiation detectors; RADIATION DOSES; RADIATION PROTECTION AND DOSIMETRY; Radiation therapy; RADIOLOGY; Radiology, Interventional - instrumentation; Radiology, Interventional - methods; Radiometry - instrumentation; Radiometry - methods; Radiotherapy Dosage; Reproducibility of Results; Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having at least one potential‐jump barrier or surface barrier; Capacitors or resistors with at least one potential‐jump barrier or surface barrier, e.g. pn‐junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof; SIDE EFFECTS; SKIN; Skin - radiation effects; Testing or calibrating of apparatus or arrangements provided for in groups G01D1/00 to G01D15/00; Time Factors; Transistors, Electronic
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.4736806

Purpose: During radiological interventional procedures (RIP) the skin of a patient under examination may undergo a prolonged x-ray exposure, receiving a dose as high as 5 Gy in a single session. This paper describes the use of the OneDoseTM cable-free system based on p-type MOSFET detectors to determine the entrance skin dose (ESD) at selected points during RIP. Methods: At first, some dosimetric characteristics of the detector, such as reproducibility, linearity, and fading, have been investigated using a C-arc as a source of radiation. The reference setting (RS) was: 80 kV energy, 40 cm × 40 cm field of view (FOV), current-time product of 50 mAs and source to skin distance (SSD) of 50 cm. A calibrated PMX III solid state detector was used as the reference detector and Gafchromic® films have been used as an independent dosimetric system to test the entire procedure. A calibration factor for the RS and correction factors as functions of tube voltage and FOV size have been determined. Results: Reproducibility ranged from 4% at low doses (around 10 cGy as measured by the reference detector) to about 1% for high doses (around 2 Gy). The system response was found to be linear with respect to both dose measured with the PMX III and tube voltage. The fading test has shown that the maximum deviation from the optimal reading conditions (3 min after a single irradiation) was 9.1% corresponding to four irradiations in one hour read 3 min after the last exposure. The calibration factor in the RS has shown that the system response at the kV energy range is about four times larger than in the MV energy range. A fifth order and fourth order polynomial functions were found to provide correction factors for tube voltage and FOV size, respectively, in measurement settings different than the RS. ESDs measured with the system after applying the proper correction factors agreed within one standard deviation (SD) with the corresponding ESDs measured with the reference detector. The ESDs measured with Gafchromic® films were in agreement within one SD compared to the ESDs measured using the OneDoseTM system, as well. The global uncertainty associated to the OneDoseTM system established in our experiments, ranged from 7% to 10%, depending on the duration of the RIP due to fading. These values are much lower than the uncertainty commonly accepted for general diagnostic practices (20%) and of about the same size of the uncertainty recommended for practices with high risk of determi