Effect of deformable registration uncertainty on lung SBRT dose accumulation

Abstract

Purpose: Deformable image registration (DIR) plays an important role in dose accumulation, such as incorporating breathing motion into the accumulation of the delivered dose based on daily 4DCBCT images. However, it is not yet well understood how the uncertainties associated with DIR methods affect the dose calculations and resulting clinical metrics. The purpose of this study is to evaluate the impact of DIR uncertainty on the clinical metrics derived from its use in dose accumulation. Methods: A biomechanical model based DIR method and a biomechanical-intensity-based hybrid method, which reduced the average registration error by 1.6 mm, were applied to ten lung cancer patients. A clinically relevant dose parameter [minimum dose to 0.5 cm 3 (Dmin)] was calculated for three dose scenarios using both algorithms. Dose scenarios included static (no breathing motion), predicted (breathing motion at the time of planning), and total accumulated (interfraction breathing motion). The relationship between the dose parameter and a combination of DIR uncertainty metrics, tumor volume, and dose heterogeneity of the plan was investigated. Results: Depending on the dose heterogeneity, tumor volume, and DIR uncertainty, in over 50% of the patients, differences greater than 1.0 Gy were observed in the Dmin of the tumor in the static dose calculation on exhale phase of the 4DCT. Such differences were due to the errors in propagating the tumor contours from the reference planning 4DCT phase onto a subsequent 4DCT phase using each DIR algorithm and calculating the dose on that phase. The differences in predicted dose were more subtle when breathing motion was modeled explicitly at the time of planning with only one patient exhibiting a greater than 1.0 Gy difference in Dmin. Dmin differences of up to 2.5 Gy were found in the total accumulated delivered dose due to difference in quantifying the interfraction variations. Such dose uncertainties could potentially be clinically significant. Conclusions: Reductions in average uncertainty in DIR algorithms by 1.6 mm may have a clinically significant impact on the decision-making metrics used in dose planning and dose accumulation assessment. C

A novel concept to include uncertainties in the evaluation of stereotactic body radiation therapy after 4D dose accumulation using deformable image registration

“…The overall accuracy of good registration in lung nodules per spatial direction should be comparable to the voxel size in that direction . The effect of the uncertainties associated with DIR in its application to treatment planning in SBRT is still largely unknown . Another relevant study is that of Samavati et al who looked at the role of DIR in lung SBRT dose accumulation and the impact of geometrical uncertainties in several dose metrics for tumor and lung used in clinical practice.…”

“…The effect of the uncertainties associated with DIR in its application to treatment planning in SBRT is still largely unknown . Another relevant study is that of Samavati et al who looked at the role of DIR in lung SBRT dose accumulation and the impact of geometrical uncertainties in several dose metrics for tumor and lung used in clinical practice. They showed how the combination of the quantitative measurement of DIR uncertainty with patient‐specific properties such as tumor volume and planning heterogeneity have an important effect on the dosimetric uncertainty, concluding that a 1.6 mm average reduction in DIR uncertainty may have clinical impact.…”

“Patient‐specific validation of deformable image registration in radiation therapy: Overview and caveats”

“…Indeed, despite similar results in terms of geometrical matching, different DIR techniques resulted in dose differences up 2% of the prescribed dose. 55,124 Comparative studies also highlighted that regions of higher dose gradient and poorer image contrast are more prone to larger variability in warped doses 55,125 and that dose deformation accuracy computed with dose-based metrics (similar to those presented in Section 4.A) are not correlated with DIR geometric accuracy. 120,126 Although these approaches allow to estimate dose uncertainties due to DIR as well as to provide tolerances for a clinical workflow, 123,125 they are not suitable for a patientspecific application.…”

Planning 4D intensity-modulated arc therapy for tumor tracking with a multileaf collimator

“…However, for these cases, it is not easy to exclude the errors of delineation and 4D CT, so as to conclude the performance of SAM. Several attempts to quantify the uncertainty of deformable registration have been reported (Samavati et al 2016). Here, an analysis was conducted for the dose error caused by the deformable registration in the environment of our 4D dose accumulation (using MIMvista system).…”