Comprehensive target geometric errors and margin assessment in stereotactic partial breast irradiation

Abstract

BackgroundRecently developed stereotactic partial breast irradiation (S-PBI) allows delivery of a high biologically potent dose to the target while sparing adjacent critical organs and normal tissue. With S-PBI tumoricidal doses, accurate and precise dose delivery is critical to achieve high treatment quality. This study is to investigate both rigid and non-rigid components of target geometric error and their corresponding margins in S-PBI and identify correlated clinical factors.MethodsForty-three early-stage breast cancer patients with implanted gold fiducial markers were enrolled in the study. Fiducial positions recorded on the orthogonal kV images on a Cyberknife system during treatment were used to estimate intra-fraction errors and composite errors (including intra-fraction errors and residual errors after patient setup). Both rigid and non-rigid components of intra-fraction and composite errors were analyzed and used to estimate rigid and non-rigid margins, respectively. Univariate and multivariate linear regressions were conducted to evaluate correlations between clinical factors and errors.ResultsFor the study group, the intra-fraction rigid and non-rigid errors are 2.0 ± 0.6 mm and 0.3 ± 0.2 mm, respectively. The composite rigid and non-rigid errors are 2.3 ± 0.5 mm and 1.3 ± 0.8 mm, respectively. The rigid margins in the left-right, anterior-posterior, and superior-inferior directions are estimated as 2.1, 2.4, and 2.3 mm, respectively. The estimated non-rigid margin, assumed to be isotropic, is 1.7 mm. The outer breast quadrants are more susceptible to composite errors occurrence than the inner breast quadrants. The target to chest wall distance is the clinical factor correlated with target geometric errors.ConclusionsThis is the first comprehensive analysis of breast target geometric rigid and non-rigid errors in S-PBI. Upon the estimation, the non-rigid margin is comparable to rigid margin, and therefore should be included in planning target volume as it cannot be accounted for by the Cyberknife system. Treatment margins selection also need to consider the impact of relevant clinical factor.Electronic supplementary materialThe online version of this article (10.1186/s13014-017-0889-6) contains supplementary material, which is available to authorized users.

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“…A very limited number of phase I or II prospective study have been published with CK-SAPBI [30][31][32][33][34][35][36]. One of the earliest studies published by Vermuelen et al in 2011 reported 46 patients treated with CK-SAPBI [31].…”

“…Stereotactic treatment approaches are emerging and are widely accepted in early stage lung cancer, prostate cancer, or bone and brain metastasis patients [26][27][28][29]. However, to date, only a few phase I/II studies were published with CyberKnife-based stereotactic APBI (CK-SAPBI) [30][31][32][33][34][35][36].…”

Multicatheter interstitial brachytherapy versus stereotactic radiotherapy with CyberKnife for accelerated partial breast irradiation: a comparative treatment planning study with respect to dosimetry of organs at risk

“…With frequent intra-fraction imaging and correction by the robotic arm, the 2 mm margin seems to be enough to account for the nonrigid components of composite errors. 41 For evaluation purpose, PTV_EVAL was created from PTV with the subtraction of the 5 mm skin layer. The prescribed dose was 25 Gy with fractionation of 4 x 6.25 Gy, exactly the same as in MIBT.…”

Robotic Stereotactic Boost in Early Breast Cancer, a Phase 2 Trial

“…Finally, specific radiologist training for fiducial placement is warranted, and larger setup margins may be necessary in conditions that do not allow optimal rotation tracking. 27,28…”