Intraoperative Radiation Therapy: Characterization and Application

摘要

The goal of this project was to define and perform the dosimetry measurements required to characterize a set of 18 applicators for use in Intraoperative Radiation Therapy (IORT). IORT is one of the newest tools in the fight against cancer. In IORT, malignant tumors are exposed directly to high-energy electrons delivered through a specially designed applicator mounted on a linear accelerator. The medical physicist must provide an adequate description of the dose delivery characteristics for every combination of IORT applicator and electron-beam energy. Briefly, the characteristics of interest include: isodose charts, output factors, effective Source-to-Source-Distances (SSDs), offset factors, and Central-Axis (CAX) profiles. Each characteristic is important in the IORT treatment planning process. Isodose charts are used to help select the right combination of IORT applicator and electron-beam energy. Output factors and the offset factors are used to scale the prescribed dose to the appropriate number of monitor units (MUs). CAX profiles are used to find surface dose factors, output factors, and x-ray dose factors. Radiographic film is used to obtain the isodose charts and CAX profiles. Effective SSDs are measured using a parallel-plate ionization chamber. In general the results are comparable to those found by personnel at the Mayo Clinic for their IORT system. The only difference is the observation that effective SSDs are dependent upon the diameter of the IORT applicator and the electron-beam energy. Keywords: Military theses; Radiology; Nuclear medicine. (kt)