Room: Exhibit Hall
Purpose: Radiotherapy (RT)-induced lymphopenia has been known to affect treatment outcome. Recently, it has been reported that higher effective dose to the immune cells (EDIC) in circulating blood, which is a function of mean lung doses (MLD), mean heart doses (MHD), integral dose (IND), and the RT-fraction number, is correlated with poorer survival in patients with locally advanced non-small cell lung cancer (NSCLC). This study aimed to evaluate the feasibility of reducing EDIC in lung stereotactic body radiation therapy (SBRT) patients through optimized replanning.
Methods: Twenty consecutive NSCLC patients previously treated with SBRT were included. The original treatment plans used either non-coplanar 3D-conformal radiotherapy (3D-CRT) (14 cases) or intensity-modulated radiation therapy (IMRT) (6 cases). The new plans were optimized using non-coplanar IMRT with re-arrangement of beam directions. All plans were normalized with planning target volume (PTV) coverage of 95% prescription. Dose-volume histogram (DVH) for the corresponding structures and EDIC were calculated and compared.
Results: All new plans have met with the clinical constraints according to RTOG-0915 protocol. Compared to the original plans, the new plans had better dose conformality, with the mean conformality index improved from 1.10 to 1.05 (p < 0.05). MLD was reduced by 1.12 Gy (4.18 Gy vs. 5.30 Gy, p < 0.01), MHD was reduced by 0.60 Gy (1.86 Gy vs. 2.46 Gy, p < 0.01) and IND was reduced by 0.33 Gy (1.45 Gy vs. 1.78 Gy, p < 0.01). The mean EDIC was reduced by 22% (0.65 Gy vs. 0.83 Gy, p < 0.01).
Conclusion: The clinical radiotherapy treatment plans can be improved by using optimal beam arrangement and specific constrains in IMRT to reduce the mean EDIC by 22%, without compromising PTV coverage. This reduction of EDIC may translate into a benefit of tumor control and survival.