Calibration and validation of a bleeding detector for beveled PMMA applicators in electron intraoperative radiotherapy

• Published in: Measurement science & technology Vol. 35; no. 8; p. 85115
• Main Authors: Garcia-Gil, Rafael, Casans, Silvia, Navarro-Antón, A Edith, Martos, Julio, Giompliaki, Malamati, Pérez-Calatayud, Ignacio, Sanchis, Enrique, Pérez-Calatayud, José, Sanchis-Sánchez, Enrique
• Format: Journal Article
• Language: English
• Published: 01.08.2024
• ISSN: 0957-0233; 1361-6501
• DOI: 10.1088/1361-6501/ad48a6

Abstract This study aimed to calibrate and validate a capacitive-sensor bleeding detector, originally designed for flat applicators, with beveled applicators (bPMMA), which are among the most commonly used applicators in intraoperative radiotherapy with electron mobile linacs. The detector will help prevent dose misadministration during irradiation in the event of fluid accumulation in the applicator, thus allowing for appropriate intervention. The handicap with employing this detector for bPMMA stems from the fact that the level of accumulated fluid depends on both the tilting angle and orientation of the applicator. Furthermore, the fluid remains accumulated at the bottom corner of the applicator, reducing the sensitivity of the sensor. A 5-strip capacitive sensor has been used, attached to a 4 cm diameter 30° beveled applicator with a tilting angle range from 0° to 30°. The sensor is read out using dedicated electronics, including a Wheatstone bridge circuit, amplifier, filter stages, and microcontroller. To calculate the sensitivity of the sensor, a prior calibration of the circuit has been carried out in order to obtain the relationship between the output voltage of the conditioning circuit and the height of the fluid present in the applicator for different inclinations. Using the average sensitivity over the inclination range of interest can provide accurate measurements of the estimated fluid height up to 12 mm, with a maximum deviation of approximately 2.0 mm and less than 1.0 mm for the 5 mm clinic threshold. The use of the mean sensitivity is a practical approach for detecting bleeding in beveled applicators because it simplifies the measurement process by avoiding the need to obtain detector sensitivity for each inclination and orientation of the applicator, which would be complex if not impractical in clinical use.