SU‐E‐T‐373: Treatment Plan Validation of the XPS (Interstitial) Applicator for Use with the Xoft Axxent 50kVp X‐Ray Source

Abstract

Purpose: To determine the dosimetric properties of a new interstitial applicator designed for the Xoft 50 kVp X‐ray Electronic Brachytherapy (eBx) system. Methods: A 0.64 cm diameter polymer sheath applicator interfaces with the Xoft 50kVp x‐ray source to provide radiation treatment to interstitial and other small target areas using eBx. Measurements of the dose profiles in a plane parallel to the applicator axis were determined. The absolute dose delivered to a prescription point at 90° off the central axis 1 cm from the source center, was determined using GafChromic EBT‐2 radiochromic film. The dose distribution measured in this parallel plane is compared to the distribution determined by the treatment planning software (Varian Brachyvision V8). Three x‐ray sources were paired with three interstitial applicators for the tests. Results: Using a single position treatment plan, the absolute dose at the defined prescription point was determined from calibrated film images. The measured dose agreed with the dose predicted by the treatment plan to within ±5%, with the actual range from −4.6% to +3.1% for the three samples. The measured isodose contours, including the 1 cm prescription point contour, agreed with the contours predicted by the treatment plan to within 5% (1 sigma) and the applicator does not perturb the water‐based dose distribution. The absolute dose determined from each of these contours agreed with the predicted dose to within +1/−6%. Conclusions: The XPS applicator can be used to treat small cavities using eBx with the Xoft X‐ray source. The applicator delivers dose profiles in good agreement with those predicted from the treatment planning software. It can be used for treatment in lightly shielded rooms due to the low energies employed. There are also intriguing possibilities for this applicator to be used intra‐operatively.Research supported by Xoft, Inc. — an iCAD Company