Article Abstract

Dosimetric characteristics of INTRABEAM® flat and surface applicators

Authors: Simon C. P. Lam, Yang Xu, Gregory Ingram, Lanceford Chong

Abstract

Purpose: Spherical applicators INTRABEAM® system has been successfully used for post-lumpectomy Intra-Operative Radiation Therapy (IORT). Recently Zeiss Meditec AG obtained USA FDA approval of their Flat and Surface applicators for gastrointestinal and or skin tumors. We investigated the dosimetric characteristics of these applicators and considered their feasible clinical applications.
Investigation design: Investigation was performed using the Gafchromic EBT 2 QD+ (GEBT) film in solid water phantom, ionization chamber and solid state detector in scanning water phantom.
Results: Conventional and unconventional dosimetry findings revealed uniqueness of these applicators. It is found to have good potential for clinical application for skin cancer treatment and intra-abdomen and intrapelvis IORT.
Conclusions: From the study, it is clear that the two types of applicator may be interchangeable. It is however important to appreciate the different characteristics of the applicators and take advantage of its special features. Generally, the surface applicators have a higher dose rate with less uniform dose at depth. They provide uniform dosimetry at the surface without any hot spots at the perimeter of the field. This feature is good for uniform dose treatment for the first 2-3 millimeters. For treatment with larger field sizes and deeper depth, one needs to allow larger margin for treament volume to compensate for the dose tappering at the edge of the field.
The flat applicators has high penetration and uniform dose at depth. They provide uniform dosimetry at 5 millimeter depth. This feature is good for treatments desiring uniform dose across the field at 5 to 8 millimeter depth. For larger field sizes one needs to watch for the a higher dose ring at 2-3 millimeter depth near the perimeter of the field. Extra margin for treatment volume is not as critical, beacuse of the uniform dose at depth.

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