SU‐E‐T‐572: Normal Lung Tissue Sparing in Radiation Therapy for Locally Advanced Non‐Small Cell Lung Cancer

Purpose: To compare normal lung‐sparing capabilities of three advanced radiation therapy techniques for locally advanced non‐small cell lung cancer (LA‐NSCLC). Methods: Four‐dimensional computed tomography (4DCT) was performed in 10 patients with stage IIIb LA‐NSCLC. The internal target volume (ITV); planning target volume (PTV); and organs at risks (OARs) such as spinal cord, total normal lung, heart, and esophagus were delineated for each CT data set. Intensity‐modulated radiation therapy (IMRT), Tomohelical‐IMRT (TH‐IMRT), and TomoDirect‐IMRT (TD‐IMRT) plans were generated (total prescribed dose, 66 Gy in 33 fractions to the PTV) for each patient. To reduce the normal lung dose, complete and directional block function was applied outside the normal lung far from the target for both TH‐IMRT and TD‐IMRT, while pseudo‐ OAR was set in the same region for IMRT. Dosimetric characteristics of the three plans were compared in terms of target coverage, the sparing capability for the OAR, and the normal tissue complication probability (NTCP). Beam delivery efficiency was also compared. Results: TH‐IMRT and TD‐IMRT provided better target coverage than IMRT plans. Lung volume receiving ≥–30 Gy, mean dose, and NTCP were significant with TH‐IMRT than with IMRT (p=0.006), and volume receiving ≥20–30 Gy was lower in TD‐IMRT than in IMRT (p<0.05). Compared with IMRT, TH‐IMRT had better sparing effect on the spinal cord (Dmax, NTCP) and heart (V45) (p<0.05). NTCP for the spinal cord, V45 and V60 for the heart, and Dmax for the esophagus were significantly lower in TD‐IMRT than in IMRT. The monitor units per fraction were clearly smaller for IMRT than for TH‐IMRT and TD‐IMRT (p=0.006). Conclusion: In LA‐NSCLC, TH‐IMRT gave superior PTV coverage and OAR sparing compared to IMRT. TH‐IMRT provided better control of the lung volume receiving ≥5–30 Gy. The delivery time and monitor units were lower in TD‐IMRT than in TH‐IMRT.