| dc.description.abstract | The aim of this study was calculating geometric uncertainties in the treatment and estimated the sufficiency of the margins employed for PTV generation in the treatment of patients undergoing head and neck cancer radiotherapy with two different techniques 3D CRT and IMRT
Materials and methods
We obtained weekly portal images for forty patients with 3D CRT technique and daily portal images for forty patients with IMRT technique of setup fields in anterior-posterior and lateral directions. These images were match with the reference image (DRR). The displacement of portal image from the reference image was record in X (SI), Y (LR) and Z (AP). The population systematic and random errors were calculated. Moreover, the values for the clinical to planning target volume (CTV-PTV) margins were calculated using van Herk’s formula and ICRU Report 62 recommendations, also Stroom formula.
Results
EPID images obtained in Anterior-posterior and lateral for any patients. The patients offset calculated by MOSAIQ software before beginning of the treat.
Systematic and Random errors separately calculated by two different techniques. In 3D CRT technique, Systematic error was 1.5, 1.8and 2.0 mm in SI, LR and AP direction. also, Random error was 2.6, 2.9 and 2.9 mm in SI, LR and AP direction respectively. As well as for IMRT technique, Systematic error in SI, LR and AP direction was 1.0, 0.95 and 1.2 mm and for Random error calculated 1.8, 1.8 and 1.9 mm in SI, LR and AP direction respectively. Obtained margin from Van Herk formula for 3D CRT in tree direction SI, LR and AP respectively was 5.8, 6.7 and 7.2 mm, and for IMRT was 4.0, 3.6 and 4.5mm in SI, LR and AP direction. | en_US |
