Investigation of lung normal tissue doses in lung tumors radiation therapy using both gated and conventional radiotherapy

Introduction: In radiation therapy of lung tumors, respiratory motion causes target moving, so a larger margin is needed to cover the clinical target volume (CTV). With the margin increasing, a larger volume of normal tissue will be exposed to high-dose.  In this study, dosimetric parameters of normal lung tissue were compared between gated and conventional radiotherapy (RT), using the NCAT digital phantom.   Materials and Methods: Different series of CT images of sample patients were created, using the NCAT digital phantom and MATLAB software. Lesions with diameters of 3, 4 and 5cm were located in different positions of lung (left upper and lower lobes, right upper and lower lobes) in the CT images. Appropriate margins were applied to the CTVs depending on the radiation therapy technique and respiratory cycles. To evaluate the effect of diaphragm extension on the margins to CTV, different diaphragm motions were considered from 2 to 3.5 cm with 0.5 cm intervals. PCRT treatment planning system with Superposition computational algorithm was used to deliver a dose of 60Gy in 30 fractions to the PTVs. Totally, 36 treatment plans were evaluated for each RT technique and Mean lung dos (MLD) and V20 were calculated for both conventional and gated RT techniques. Results: A significant impact on MLD and V20 reduction was seen in lung normal tissue in gated RT up to 5Gy and 37%, respectively. Conclusion: In all cases, gated RT has a superior advantage compared to conventional RT, especially for the lesions that are near to the diaphragm.