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Review of Radiation Therapy Physics: A syllabus for teachers ... - IRSN

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Chapter 11. Computerized Treatment Planning Systems <strong>for</strong> External Beam radiotherapyTraditional “<strong>for</strong>ward-based” treatment planning which is based on a trial and error approachby experienced pr<strong>of</strong>essionals is giving way to “inverse planning” which make use <strong>of</strong> doseoptimization techniques to satisfy user specified criteria <strong>for</strong> the dose to the target and criticalstructures. Dose optimization is possible by making use <strong>of</strong> Dose-Volume Histograms (DVH)based on CT, MR or other digital imaging techniques. These optimized plans make use <strong>of</strong>Intensity Modulated <strong>Radiation</strong> <strong>Therapy</strong> (IMRT) to deliver a required dose to a target organwhile respecting dose constraint criteria <strong>for</strong> critical organs.Computerized treatment planning is a rapidly evolving modality, relying heavily on bothhardware and s<strong>of</strong>tware. As such it is necessary <strong>for</strong> related pr<strong>of</strong>essionals to develop aworkable Quality Assurance (QA) programme that reflects the use <strong>of</strong> the TP system in theclinic, and is sufficiently broad in scope to ensure proper treatment delivery.11.2. SYSTEM HARDWARE11.2.1. TP system hardwareThe principal hardware components <strong>of</strong> a TP system include: CPU, graphics display, memory,digitizing devices, output devices, archiving and network communication devices. Ashardware capabilities tend to change quickly, the general approach is to acquire equipmenthaving the highest current specifications while allowing <strong>for</strong> future upgrades.• The Central Processing Unit (CPU) must have sufficient memory and processorspeed as required by the operating system, and the treatment planning s<strong>of</strong>tware. Inparticular the specifications <strong>for</strong> the system speed, Random Access Memory(RAM) and free memory, as well as networking capabilities must be considered.• The graphics display is normally sufficient <strong>for</strong> accommodating the patienttransverse anatomy on a 1:1 scale, typically 17 to 21 inches (43 to 53 cm) orlarger. The resolution is sub-millimeter or better so as not to distort the input.Graphics speed can be enhanced with video cards and hardware drivers.• Memory and archiving functions are carried out either through removable mediaor networking. Removable media may include floppy disks, re-writable harddisks,optical disks, or DVDs. Mass archiving may also be accomplished withslower DAT tape, however, these devices have been reported to suffer from longterm instability. Archiving may be carried out over a network on a remotecomputer or server, and these archiving operations may be carried outautomatically during low use periods <strong>of</strong> the day. Archiving operations can includebeam data and parameters, patient related data such as CT-scans and dosedistributions, and data used <strong>for</strong> setting up the patient <strong>for</strong> treatment on the linacwith record-and-verify systems.• Digitizing devices are used to acquire manually entered patient data such astransverse contours and beams-eye-views <strong>of</strong> irregular field shapes. These aretypically backlit tablets with either a magnetic or acoustic stylus <strong>for</strong> manuallytracing shapes. Scanners, either flatbed or upright, can be used to digitize imagesfrom hardcopy such as paper or radiographic film. Video frame grabbers may alsobe used to digitize images.318

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