Comparison of dosimetric parameters and delivery accuracy between conformal radiotherapy-intensity modulated radiotherapy-combined and intensity-modulated radiotherapy planning for central lung cancer patients receiving stereotactic body radiotherapy

Background: With the development of technology, stereotactic body radiotherapy (SBRT) has been increasingly applied in the treatment of patients with central lung cancer. Three-dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT) are common SBRT techniques for lung cancer. Although 3DCRT plans have low complexity, the quality of such plans is highly dependent on the experience of the planner. IMRT plans can provide better organ-at-risk (OAR) sparing, but they are associated with a high degree of modulation. Therefore, an SBRT planning strategy that combines the advantages of 3DCRT and IMRT has been developed. The purpose of this study was to investigate the differences in dosimetric parameters and delivery accuracy between CRT-IMRT-combined (Co-CRIM) and IMRT plans for central lung cancer patients treated with SBRT.

Methods: Twenty patients were retrospectively included in this study. Four plans were designed for each patient. Co-CRIM-E and IMRT-E plans were designed based on Co-CRIM and IMRT, and delivered with Varian Edge. Co-CRIM-T and IMRT-T plans were designed based on Co-CRIM and IMRT, and delivered with Varian TrueBeam. Dosimetric parameters were compared between Co-CRIM-E and IMRT-E plans, as well as between Co-CRIM-T and IMRT-T plans. Monitor unit (MU), modulation factor (MF) and gamma (γ) passing rate were calculated for each plan. Paired-samples t-test was used to check the differences between datasets and P<0.05 was considered statistically significant.

Results: Conformity index (CI), ratio of 50% prescription isodose volume to the planning target volume (PTV) volume (R50) and maximum dose (in % of dose prescribed) at 2 cm from PTV in any direction (D2cm) were significantly higher in Co-CRIM-E plans than those in IMRT-E plans. The CI, D2cm in Co-CRIM-T plans were also significantly higher than those in IMRT-T plans. Mean lung dose (MLD), percentage of the total lung volume receiving more than 10 Gy (V10), 12.5 Gy (V12.5), 13.5 Gy (V13.5) and 20 Gy (V20) were significantly higher in Co-CRIM-E plans than those in IMRT-E plans. MLD, V10, V12.5, V13.5 and V20 of total lung in Co-CRIM-T plans were also significantly higher than those in IMRT-T plans. MU and MF were significantly lower in Co-CRIM-E and Co-CRIM-T plans than those in IMRT-E and IMRT-T plans and γ passing rate was significantly higher than that in IMRT-E and IMRT-T plan.

Conclusions: For central lung cancer patients treated with SBRT, the Co-CRIM approach was able to achieve plans that met clinical constraints. Compared with IMRT, Co-CRIM significantly reduced plan complexity and improved delivery accuracy with slightly reduced target conformability.