P20.06 Dosimetric Comparison of the Real and Virtual Plans in Non-Small Cell Lung Cancer Patients Treated With Respiratory Motion Management

Abstract

We conducted a prospective study to increase tumor control, reducing side effects and dosimetric comparison of the real and virtual plans by using motion management in 40 patients with locally advanced non-small cell lung cancer. The study was approved by the ethics (2018-7/7) and scientific committee (OUAP (T) 2019/2) as scientific research project in our university. Simulation images were obtained using free breathing in the treatment position using axial cine mode 16-slice 4D-CT scanner and RPM in 10 respiratory phases. In the MIP phase, PTV with a 5 mm border in each direction was created for the ITV including the tumor and involved nodes. A volumetric arc treatment plan was established by taking the 98% of prescription dose to 95% of PTV and also taking into account the risky organ doses. Patients were treated with CBCT imaging on LINAC device every other day. For virtual plan, GTV for tumor and involved nodes and CTV according to ICRU83 were created in the free respiratory phase. PTV was created with a 5 mm margin to CTV and virtual treatment plan was created with the same prescribed dose. 10 patients were treated till December 2019. The median age was 59 years (49-72) and the M/F ratio was 8/2. Histopathological diagnosis were SCC (4), adenocarcinoma (5), LCNEC (1). AJCC18 staging were listed as IA2 (1), IIIA (2), IIIB (4), IIIC (2) and IVB (1). The median RT dose was 6300 cGy (5940-6400) with 32 fractions (30-35). In the third month, 2 complete, 3 partial responses and 1 locoregonal progression were detected by PET/CT. ITVtm was 46.98 and GTVtm was 31.27 cc (p = 0.66), while PTV volumes were 173.53 and 494.50 cc (p = 0.008) in treatment and virtual plans, respectively. The tumor volume was higher but PTV volume was lower in the treatment plans. D95 for ITVtm and GTVtm were found 6311 and 6326 cGy (p = 0.72) whereas D95 for PTV 6297 and 6051 cGy (p = 0.13), respectively. The mean lung dose, V5, V20 and V30 were 15.14 vs 16.07 Gy (p = 0.077), 55.95% vs 63.8% (p = 0.087), 26.44% vs 31.55% (p = 0.23) and 17.44% vs 20.64 (p = 0.085), median heart dose was 6.03 and 10.36 Gy (p = 0.043), heart V50 was 8.2% vs 33.9% (p = 0.007), median esophageal dose was 18.94 vs 21.43 Gy (p = 0.35) and esophagus V50 11.39% vs 18% (p = 0.69), the median and maximum spinal cord dose was 8.11 vs 8.22 Gy (p = 0.61) and 33.15 vs 37.39 Gy, respectively (p = 0.22), in treatment and virtual plans. It was observed that all risky organ doses were less in treatment plans than virtual plans with statistical significance in heart doses. In this study, it was shown that the target volume did not increase, the target was covered with 95% accuracy and the risky organ doses were lower in 10 patients who were treated with 4D-CT planning and respiratory motion management.