AUTHOR=Sun Xingru , Dai Zhitao , Xu Meiling , Guo Xueling , Su Huanfan , Li Yang 

TITLE=Quantifying 6D tumor motion and calculating PTV margins during liver stereotactic radiotherapy with fiducial tracking

JOURNAL=Frontiers in Oncology

VOLUME=Volume 12 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2022.1021119

DOI=10.3389/fonc.2022.1021119

ISSN=2234-943X

ABSTRACT=Objective Our study aimed to estimating intra-fraction 6D tumor motion with rotational correction
and the related correlations between motions of different dimension, as well as to quantify
adequate anisotropic clinical target volume (CTV)-to-planning target volume (PTV) margins
during stereotactic liver radiotherapy based on fiducial tracking.
Methods A cohort of 12 patients who were implanted with 3 or 4 golden markers were included
in this study, and 495 orthogonal kilovoltage (KV) pairs of image acquired during the first fraction
were used to extract the spacial position of each gold marker.Translational and rotational motions
of tumor were calculated based on the marker coordinates by using an iterative closest point (ICP)
algorithm. Moreover, the Pearson product-moment correlation coefficients (r) were applied to
quantify the correlations between motions with different degree of freedom (DoF).The population
mean displacement (MP ), systematic error (Σ) amd random error (σ) were obtained to calculate
 the intrafractional PTV margins based on Published recipes.
Results The mean translational variability of tumors were 0.56, 1.24 and 3.38 mm in the left-right
(X), anterior-posterior (Y),and superior-inferior (Z) directions, respectively. The average rotational
 angles θX, θY and θZ around the three coordinate axes were 0.88, 1.24 and 1.12◦, respectively.
|r| > 0.4) were obtainted between Y -Z, Y -θZ, Z-θZ and θX-θY . The PTV margins calculated
based on 13 published recipes in X, Y and Z directions were 1.08, 2.26 and 5.42 mm , and the
95% confidence interval of them were (0.88,1.28), (1.99,2.53) and (4.78,6.05), respectively.
Conclusions The maximum translational motion was in SI direction, and the largest correlation
coefficient of Y -Z was obtained. We recommend margins of 2, 3 and 7 mm in left-right, anterior-
posterior, and superior-inferior directions, respectively.