ABSTRACT
Background : Adequate dose to Clinical Target Volume is needed to control tumour and to deliver adequate dose without missing the target, this Clinical Target Volume must be encompassed by two margins for uncertainties; first, Internal margin uncertainties and second, set up margin uncertainty will form Planning Target Volume. Three mm setup error of couch location resulted in 38% decrease of minimum target radiation dose and 42 % increase of minimal Spinal Cord and Parotid Gland radiation dose. Aims and Objectives : Objectives of this retrospective study are, before implementation of high precession radiotherapy technique for Head and Neck Malignancy, we want determine optimal 3-dimensional Clinical Target Volume to planning target volume margin and to assess our setup accuracy in our institute, NRS Medical College & Hospital, Kolkata. Material and Methods : We analyzed retrospectively set up error from 691 set Cone Beam CT images of 94 patients. According to Standard Guidelines Target Volume delineated and for creation Clinical Target Volume to Planning target volume margin, we have used 5-7 mm margin around Clinical Target Volume. Results : In 99% patients’ setup deviation were within 0.5 cm. The population systematic error (?) in in Super Inferior; mediolateral; and anterior posterior direction were 0.13 cm, 0.12 cm and 0.14 cm respectively. The population random error in Super Inferior; mediolateral; and anterior posterior direction were 0.021 cm, 0.022 cm and 0.173 cm respectively. Using van Herk formula Clinical Target Volume to Planning Target Volume margin in Super Inferior; mediolateral; and anterior posterior direction were 0.34, 0.47 and 0.32 cm respectively. Corresponding values with Stroom formula 0.28, 0.40 and 0.26 cm respectively. Conclusions : In our study Set up margin of 5mm all around the CTV to create PTV is found to be safe and adequete