SU‐GG‐T‐549: Dosimetry of An X‐Ray Endocavitary Proctoscope Adapted for Use with the Axxent® Electronic Brachytherapy System

Abstract

Purpose: To analyze the dose rate and uniformity at the aperture of an Electro‐Surgical Instrument (ESI). Proctoscope when used with an Axxent® Model S700 X‐ray Source. Method and Materials: The ESI proctoscope was originally designed for use with a Philips RT‐50 x‐ray contact therapy unit. Because these units are no longer supported, an alternative x‐ray source is being sought which allows for duplication of the Papillon technique for treating anal‐rectal lesions. A source holder was fabricated to position the Axxent model S700 X‐ray Source collinearly on axis within a lead‐lined proctoscope possessing a 24 mm inner diameter aperture. This mechanism allows the distance from the proctoscope aperture to the source to be adjusted from 1 to 10 cm and allows a filter to be placed at the distal end of the source to harden the beam and/or flatten the dose distribution. The dose rate was measured at the proctoscope aperture using a PTW 34013 Soft X‐ray Chamber set into the surface of a Gammex RMI 457 solid water phantom. GAFChromic EBT radiochromic film was used for profile measurements. Results: For operation at 50 kVp and 0.30 mA beam current with a 0.5 mm thick Al filter and source‐to‐aperture distance of 3.4 cm, the dose rate was 1.1 Gy per minute. Profile evaluation indicated a dose uniformity of 5%, 8% and 15% across 80%, 93% and 98% of the aperture diameter, respectively, without use of a flattening filter. Conclusion: Measurements of dose rate and uniformity at the aperture of a 24 mm diameter ESI proctoscope indicate that the Axxent S700 x‐ray source may be a suitable alternative to the Philips RT‐50 Endocavitary Unit for treatment of anal‐rectal lesions. Conflict of interest: Research sponsored by Xoft, Inc.