Encouraging the Dose Homogeneity in Lung SBRT by Reweighted Total-Variation (TV) Minimization
H Kim1*, R Li1, R Lee2, L Xing1, (1) Department of Radiation Oncology, Stanford University, Stanford, CA, (2) Department of Radiation Oncology, Ewha Womans University, SeoulMO-F-108-3 Monday 4:30PM - 6:00PM Room: 108
Purpose: To meet stronger dose constraints required in lung SBRT, the high dose inhomogeneity inside the PTV has been considered potentially beneficial; yet it may cause clinically unwanted damage. This work, therefore, proposes to lower the dose inhomogeneity by using reweighted total-variation(TV) minimization(min.) in lung SBRT, while achieving the safe plan quality that the inhomogeneous plan can do.
Methods: RTOG 0915 protocol regulating lung SBRT planning prescribes far stronger dose constraints around and outside PTV by high/intermediate dose spillage (HDS/IDS), where the tissue around the target is protected from high dose (lower HDS) and steep dose fall-off gradient outside the PTV is required by IDS constraint. Inside the PTV, however, the high dose inhomogeneity has been encouraged to lower the HDS when dose fall-off gradient is sufficiently steep. It could, however, irradiate too high dose to the marginal side of PTV or healthy tissues in actual treatment. Thus, this study employed reweighted TV min. to lower dose inhomogeneity in lung SBRT by simplifying the fluence-map complexity, while preserving HDS/IDS constraints that inhomogeneous plan can perform. To validate it, the pre-treated lung SBRT data was applied with three cases: homogeneous/inhomogeneous plans by TV min. and homogeneous plan by reweighted TV min (proposed).
Results: Reweighted TV min. with homogeneous plan successfully yields as low HDS around the PTV as the inhomogeneous plan can do, while maintaining the same steep fall-off gradient outside the target. Even compared with the homogeneous plan with TV min., the proposed method can further enhance the dose homogeneity inside the PTV mainly due to the decrease in the fluence-map complexity by reweighting process.
Conclusion: Reweighted TV min. can improve such plan safety as protecting healthy tissue with steep fall-off gradient required in lung SBRT without the necessity of increasing the dose inhomogeneity inside the PTV.