Nuclear Physics Comparison of Measured and Monte Carlo Calculated Dose Distributions for the Novac7® Linear Accelerator

Percentage depth doses (PDDs) and transverse dose profiles (TDPs) were calculated by a Monte Carlo simulation of electron beams of different energies (3, 5, 7 and 9 MeV) produced by a NOVAC7® accelerator. The NOVAC7® is a linear accelerator designed for Intraoperative Radiation Therapy (IORT). The PDDs and TDPs were also experimentally determined. Both calculations and measurements were done on the central axis of the beam for the PDDs and at 1 mm depth in water for TPDs. The electron beams obtained with and without IORT applicators (open beams) have been modeled by the code BEAMnrc, a general purpose Monte Carlo code for simulating radiotherapy beams from linear accelerators or 60Co units. The realistic electron beams were stored in phase-space files which have been used as input into DOSXYZnrc code to calculate the dose distributions. The agreement between calculations and measurements was generally better than ±2% with and without IORT cylindrical applicator. This shows that the values adopted in this work for the energy and spatial distribution of the initial electron beam as well as the modeling parameters are realistic. The accelerator modeling considered in this work gives accurate phase-space data files that can be used for determining in full the characteristics for all of the clinical beams produced by the NOVAC7®.