AbstractID: 6787 Title: FFT of PTVs
Purpose: The purpose of this work is to evaluate the spatial resolution required to treat a range of different
clinical PTVs, with an emphasis on the resolution requirements for Intensity Modulated Radiation Therapy
(IMRT).
Methods: The 3-D PTV is defined by a 2-D area, with unity inside the volume and zero outside. In the case
of clinical shapes, the 2-D area is taken as the BEV manually selected by the planner. 2-D discrete Fast
Fourier Transforms of the 2-D area are obtained using MatlabTM. The 2-D Fourier Transforms are
displayed using a logarithmic scale for semi-quantitative analysis. The 2-D Fourier Transforms are
quantified by evaluating the spread of the central (zero frequency) peak. The highest frequency at 10% of
the peak value is used.
Results: We apply the method to an investigation of a series of shapes: circles, complex geometrical shapes
and clinical PTVs of prostate, head/neck (NPC), and central nervous system (AVMs). Specifically, we
present a series of histograms representing the highest frequencies contained in 2-D sections of the shapes
and clinical PTVs studied.
Discussion: The spatial resolution inherent in the delivery system must be greater than the spatial
frequencies inherent in the PTV, and this study provides a methodology for quantitative assessment of
PTVs. We suggest rules-of-thumb for manual treatment planning. Further, we will discuss implications
for treatment planning and treatment delivery systems used for IMRT.
This work was supported by Varian Medical Systems.
’’FFT of PTVs’’ Abstract Submission Number 6787-50498