Surface applicator of a miniature X‐ray tube for superficial electronic brachytherapy of skin cancer

Abstract

Purpose: We designed and fabricated a surface applicator of a novel carbon nanotube (CNT)-based miniature X-ray tube for the use in superficial electronic brachytherapy of skin cancer. To investigate the effectiveness of the surface applicator, the performance of the applicator was numerically and experimentally analyzed. Methods: The surface applicator consists of a graphite flattening filter and an X-ray shield. A Monte Carlo radiation transport code, MCNP6, was used to optimize the geometries of both the flattening filter and the shield so that X-rays are generated uniformly over the desired region. The performance of the graphite filter was compared with that of conventional aluminum (Al) filters of different geometries using the numerical simulations. After fabricating a surface applicator, the X-ray spatial distribution was measured to evaluate the performance of the applicator.Results: The graphite filter shows better spatial dose uniformity and less dose distortion than Al filters. Moreover, graphite allows easy fabrication of the flattening filter due to its low X-ray attenuation property, which is particularly important for low-energy electronic brachytherapy. The applicator also shows that no further X-ray shielding is required for the application because unwanted X-rays are completely protected. As a result, highly uniform X-ray dose distribution was achieved from the miniature X-ray tube mounted with the surface applicators. The measured values of both flatness and symmetry were less than 5% and the measured penumbra values were less than 1 mm. All these values satisfy the currently accepted tolerance criteria for radiation therapy. Conclusions: The surface applicator exhibits sufficient performance capability for their application in electronic brachytherapy of skin cancers.

Three‐dimensional‐printed vaginal applicators for electronic brachytherapy of endometrial cancers

“…The spatial dose distribution around the cylindrical applicator was measured using a radiochromic film (Gafchromic EBT3 films, International Specialty Products, Wayne, NJ, USA). The EBT3 films were calibrated according to AAPM TG‐55 and the detailed description is included in previous research …”

“…The EBT3 films were calibrated according to AAPM TG-55 and the detailed description is included in previous research. 21,22 The film was cut to encompass the applicator via waterjet cutting method in order to minimize structural damage to the film. The miniature x-ray tube was operated for 10 min at each dwell position to obtain a comprehensive spatial dose distribution in the film prior to dwell time optimization.…”

Measured low-energy x-ray spectra of interest in diagnostic radiology and mammography

“…Low-energy x-rays are widely used for diagnostic radiology, mammography, and brachytherapy. For instance, the low energy x-ray emitters 103 Pd and 125 I (Massillon-JL et al 2011) as well as miniature x-ray tubes (Kim et al 2018, Ramachandran et al 2019 are used for brachytherapy treatments. To calculate the absorbed dose to water in these fields, the AAPM TG-61 recommends averaging the monoenergetic mass energy absorption coefficients over the photon energy fluence spectrum at the point of interest to obtain the ratio for water-to-air of the mean mass energy-absorption coefficient (Ma et al 2001).…”