deletions | additions       diff --git a/Introduction.tex b/Introduction.tex  index c04139a..c1c2c0e 100644  --- a/Introduction.tex  +++ b/Introduction.tex 
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\section{Introduction}  \subsection{Restatement of the Problem}  An optimal treatment plan for the gamma knife must be formulated as a sphere-packing problem. This plan must based upon various constraints and requirements detailed below.  \subsection{Background}  \subsubsection{Gamma Ray Knife}  Stereotactic radiosurgery delivers a single high dose of ionizing radiation to a small intracranial 3D brain tumor without delivering any significant fraction of the prescribed dose to the healthy brain tissue surrounding the tumor. The gamma knife delivers a single high dose of ionizing radiation emanating from 201 cobalt-60 unit sources through a helmet. Each irradiation is known as a "shot", which resembles a circle. Multiple shots can be used if individual shots do not cover the target. Helmets have beam channel diameters of 4, 8, 14 \& 18 mm.\cite{aoyama2006stereotactic}