Comparison of Dose Distributions for Stereotactic Radiotherapy of Lung Cancer Using Two Dynamic Techniques: IMRT and VMAT

Abstract

The aim of this study was to compare dose distributions for stereotactic radiotherapy of lung cancer using two dynamic techniques: intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT). The study group consisted of five patients with tumors located in the right lung, with tumor diameters on computed tomography images not exceeding 5 cm. During patient preparation for radiotherapy, four-dimensional computed tomography (4DCT) was performed. The prescribed dose to the planning target volume (PTV) was 50 Gy delivered in 5 fractions, using 6 MV flattening filter-free (FFF) photon beams. Dosimetric verification was performed for each treatment plan using the OCTAVIUS 4D dosimetric phantom and the OCTAVIUS 1600 SRS detector array (PTW, Freiburg, Germany). The plans were compared using local gamma analysis with the following criteria: dose difference (DD) of 2%, distance to agreement (DTA) of 2 mm, a low-dose threshold of 5% of the maximum dose, and an acceptable gamma passing rate of >95%. For the PTV, the following parameters were analyzed: doses delivered to 98% and 2% of the PTV volume, as well as doses received by organs at risk (OARs). The doses to the OARs were within the tolerance limits specified in the QUANTEC (Quantitative Analyses of Normal Tissue Effects in the Clinic) report. The results showed that with the IMRT technique, organs at risk received slightly higher doses; however, these did not exceed the tolerance limits. Due to the greater number of treatment beams used in IMRT, the treatment delivery time was considerably longer than with the VMAT technique.