P. Kneschaurek, J. Traub Dose Escalation with Photons - Emerging Technologies: a Physicist´s Point of View Eighth International Meeting on Progress in Radio-Oncology, May 16-19, 2007, Salzburg, Austria (bib)
	To further reduce the possibility of local recurrences it is in many clinical cases necessary to increase the dose to the PTV. This is in general only achievable if the volume of the PTV can be reduced. A reduction in the volume of the PTV and assuming an appropriately conforming dose distribution leads to a reduction of the treated volume and reduces the amount of healthy tissue within the PTV. These two factors may lead to a reduction of side effects and may make dose escalation possible. According to ICRU reports 50 and 62 [1,2] the PTV encloses the ITV, the CTV, and the GTV. New imaging techniques allow a more accurate definition of the GTV. This may lead to an increase or decrease of the volume of the GTV. The exact definition of the CTV remains a “guesswork” which depends very much on the experience of the radiation oncologist. This paper describes methods which allow a reduction of the margins between the CTV and the ITV and the ITV and the PTV.
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