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Target volumes – PTV
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ICRU 62 suggested 2 components to the PTV:
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Internal Margin IM – for eg organ movement
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Setup Margin SM – for set-up inaccuracies
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CTV + “Internal Margin” (IM) = Internal Target Volume (ITV)
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ITV + “Set-up Margin” (SM) = PTV
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Inadequate PTV margins:
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risk increased treatment failure
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Excessive PTV margins risk:
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increased treatment toxicity