Friday, 24 June 2016

PTV (planning target volume)

It includes the gross tumor volume (GTV), the clinical target volume (CTV), and a margin to account for setup error, movement, and any possible geometric variations. The volume that includes the CTV with any internal target volume (ITV), if present, as well as a setup margin to account for patient movement and daily setup uncertainties [1]. When the patient moves or internal organs change in size and shape during a fraction of treatment or between fractions (intra- or inter-fractionally), the position of the CTV may also move. Therefore, to ensure a homogeneous dose to the CTV throughout a fractionated course of irradiation, margins must be added around the CTV. These allow for physiological organ motion (internal margin) and variations in patient positioning and alignment of treatment beams (set-up margin), creating a geometric planning target volume [2]. PTV is the ultimate target volume, the primary focus of the treatment planning and delivery. Adequate dose delivered to PTV at each treatment session, presumably, assures adequate treatment of the entire disease-bearing volume, the CTV [3].
Bibliographic references:
[1] Fisher, B.,  Daugherty, L, Reiff J. E. (2013). P. In: L. Brady and T. Yaeger, ed., Encyclopedia of Radiation Oncology, 1st ed. Springer-Verlag Berlin Heidelberg, pp.585-693.
[2] Barrett, A., Dobbs, J., Morris, S. and Roques, T. ed., (2009). 2 Principles of radiotherapy planning. In: Practical Radiotherapy Planning, 4th ed. London: Hodder Arnold, an Hachette UK Company, pp.9-31.
[3] Khan, F. (2007). Chapter 1 - Introduction: Process, Equipment, and Personnel. In: F. Khan, ed., Treatment Planning in Radiation Oncology, 2nd ed. Lippincott Williams & Wilkins.

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