Dosimetric Evaluation of Adaptive Therapy in Non-Small Cell Lung Cancer Patients Undergoing Palliative Thoracic Radiotherapy

Abstract

This study aimed to describe changes in gross tumour volume (GTV) that occurred during the course of radiotherapy (RT) in patients who underwent palliative thoracic radiotherapy (PTR), and to describe the role of adaptive treatment for protection of normal tissue. Twenty patients with non-small cell lung cancer (NSCLC) referred for PTR were treated using a total of 10 fractions and a dose of 300 cGy/day in accordance with the initial GTV, clinical target volume (CTV), and planning target volume (PTV). Computed tomography simulation (CTS) images were retaken for each patient at the end of the fifth fraction, and the second plan was created. The fractional volume reduction (FVR) of the GTV and the PTV were then calculated. The changes in normal tissue dose-volume histogram (DVH) parameters between the two plans were compared. Mean GTV and PTV values were 223.9 cc and 1113.3 cc for the first plan and 196.2 cc and 1029.7 cc for the second plan , respectively. After five fractionated treatments, the FVR was 15.9% of the GTV (p < 0.001) and 8% of the PTV (p< 0.001). The daily regression for GTV was 3.1 percent. A statistically non-significant decrease occurred for the normal tissue doses. The geometric changes in GTV and PTV positively influenced the DVH parameters, but were not statistically significant. The clinical implications of this approach to CTS plan assessment should be examined using prospective studies with adequate number of patients.