Evaluation of Auto-Contouring and Dose Distributions for Online Adaptive Radiation Therapy of Patients With Locally Advanced Lung Cancers.

PURPOSE

Retrospective studies were performed to evaluate the accuracy of automatically mapped structures and dosimetric consequences of daily online adaptive radiation therapy (ART) for lung cancer treatments.

METHODS AND MATERIALS

Ten patients with locally advanced lung cancer (prescription = 2 Gy × 30) with 297 fractions of treatment were selected for this retrospective study on a research emulator (Ethos, Varian Medical Systems). All adaptive treatments were simulated twice: automatic-ART (A-ART), automatic contours were used without modification, and supervised-ART (S-ART), automatic contours were modified manually by physicians and physicists. Dosimetric results were analyzed by relating supervised scheduled (S-SCH) dose (initial baseline reference plan delivered on daily anatomy and supervised contour correction without any adaptation), A-ART and S-ART to the initial baseline reference dose.

RESULTS

Two hundred ninety (of 297) fractions were analyzed. Comparing target volumes between A-ART and S-ART, dice similarity coefficient was 0.93 ± 0.05, mean contour distance was 1.5 ± 1.2 mm, and Hausdorff distance was 4.0 ± 2.3 mm. Analysis of daily results over 290 fractions of treatment showed that average target coverage improved from 0.96 ± 0.04 (S-SCH) to 1.00 ± 0.02 (A-ART) and 1.02 ± 0.04 (S-ART); average upper dose constraint was reduced from 1.01 ± 0.11 (S-SCH) to 0.94 ± 0.10 (A-ART) and 0.93 ± 0.12 (S-ART). A-ART and S-ART improved planning target volume minimum doses by 4.85 ± 3.03 Gy (P = .049) and 4.46 ± 8.99 Gy (P = .058), respectively. Statistical analysis shows that A-ART and S-ART significantly improved cumulative target dose by 0.033 ± 0.087 (P = .002) and 0.032 ± 0.086 (P = .003) and reduced upper constraints by 0.033 ± 0.072 (P < .001) and 0.032 ± 0.072 (P < .001) relative to S-SCH dose results, respectively.

CONCLUSIONS

Accuracy of Ethos automatic contouring for lung cancer is considered clinically acceptable. The online adaptive radiation therapy improves target coverage and spares organs-at-risk significantly.