Dosimetric Comparison between Coplanar and Non-Coplanar Fields in Irradiation of Middle and Lower Lobes Lung Tumors

Abstract

Purpose: To compare between the coplanar and non-coplanar fields regarding planning target volume (PTV) coverage, conformity index and preservation of organs at risk (heart-lungs-esophagus and spinal cord). Materials and Methods: 10 patients presented with stage IIIA or IIIB NSCLC with a tumor located in the middle or lower lobes. Because of this location, the heart is one of the main organs at risk. Two plans, coplanar and non-coplanar 3 dimensional conformal radiotherapy plans are performed for each patient. All treatment plans are created using Xio-Computerized medical system treatment planning system. The prescribed dose is 64 Gy in 32 fractions. Results: For both plans, the maximum dose to the PTV doesn't exceed 110% of the prescribed dose; the 95% isodose (60.8 Gy) covers at least 95% of the PTV volume and the mean conformity index values are also very similar 0.59 vs 0.61 for coplanar and non-coplanar plans respectively without statistically significant difference (P = 0.1711). Regarding organs at risk, large advantage for adding a non-coplanar field in the preservation of the heart is observed. The mean V30 values for noncoplanar plan are 17.3 Gy versus 28.9 Gy for the coplanar plan with statistically significant difference (P = 0.0060). Also, the mean V40 and V50 values for the non coplanar compared to coplanar plan are 12.6 Gy and 7.9 Gy versus 23.1 Gy and 14.9 Gy respectively, and these differences are statistically significant (P = 0.0162) (P = 0.0084). No statistically significant differences are found between coplanar and non-coplanar plans for lungs, esophagus or the spinal cord. Conclusion: Using non-coplanar beams in the irradiation of middle and lower lung tumors significantly reduces the radiation dose to the heart with the same target volume coverage and conformity index.