The planning target volume margins detected by cone-beam CT in head and neck cancer patients treated by image-guided intensity modulated radiotherapy / 中华放射肿瘤学杂志

ABSTRACT

Objective To determine the planning target volume margins of head and neck cancers treated by image guided radiotherapy (IGRT).Methods 464 sets cone beam computed tomography (CBCT) images before setup correction and 126 sets CBCT images after correction were obtained from 51 head and neck cancer patients treated by IGRT in our department.The systematic and random errors were evaluated by either online or offline correction through registering the CBCT images to the planning CT.The data was divided into 3 groups according to the online correction times.Results The isocenter shift were 0.37 mm±2.37 mm, -0.43 mm±2.30 mm and 0.47 mm±2.65 mm in right-left (RL), anterior-posterior (AP) and superior-inferior (SI) directions respectively before correction, and it reduced to 0.08 mm±0.68 mm, -0.03 mm±0.74 mm and 0.03 mm±0.80 mm when evaluated by 126 sets corrected CBCT images.The planning target volume (PTV) margin from clinical target volume (CTV) before correction were:6.41 mm,6.15 mm and 7.10 mm based on two parameter model, and it reduced to 1.78 mm,1.80 mm and 1.97 mm after correction.The PTV margins were 3.8 mm,3.8 mm,4.0 mm;4.0 mm,4.0 mm,5.0 mm and 5.4 mm,5.2 mm,6.1 mm in RL, AP and SI respectively when online-correction times were more than 15 times, 11-15 times,5-10 times.Conclusions CBCT-based on online correction reduce the PTV margin for head and neck cancers treated by IGRT and ensure more precise dose delivery and less normal tissue complications.