SU‐E‐T‐626: Three‐Beam Technique for Intensity Modulated Radiation Therapy in Oesophagus: Dosimetric Differences in Organs at Risk

Abstract

Purpose: To compare planning results of intensity modulated radiotherapy (IMRT) with conformal external radiotherapy (3DCRT) for oesophagus cancer treatment. Methods: IMRT and 3DCRT options were planned for 6 patients of oesophagus cancer and dose‐volume histograms were evaluated for the main organs at risk: lungs, heart and spinal cord. The prescription dose was 54Gy in all cases and the treatment planning system used was Eclipse (10.0 version with Anisotropic Analytical Algorithm 10.0.28 version). A conventional field arrangement was applied for 3DCRT with antero‐posterior and lateral opposed fields and a 3 field technique (antero‐posterior and 2 oblique posterior entrances) for IMRT. Results: Similar PTV coverage was found and spinal cord maximal dose was under recommendations in both cases. Main difference was in lung and heart dose. A significant reduction on heart dose was obtained with IMRT: mean values of V30, V40, V45 and V50 (volume irradiated with 30, 40, 45 and 50Gy) were reduced by 13.2, 9.9, 2.7 and 2.3Gy respectively. For lungs, mean dose and V5 were quite similar between IMRT and 3DCRT (less than 1Gy of difference); a mean reduction of 2.8Gy and a mean increase of 5.6Gy were found for V10 and V20 respectively. Compared with other IMRT options reported in the literature, such as 5 or more field entrances, a reduction on lung volume irradiated at low dose (V5) was observed. Rest of parameters were close to shown values in this work. Conclusion: This study shows the dosimetric advantages of using a three‐field IMRT technique for heart and lung dose values, keeping the rest of parameters within tolerances. Special attention was put in low lung dose parameters.