Inter- and intrafractional setup errors and baseline shifts of fiducial markers in patients with liver tumors receiving free-breathing postoperative radiation analyzed by cone-beam computed tomography.

Tao Zhang,Shulian Wang,Weihu Wang,Yongwen Song,Jing Jin,Yexiong Li,Yueping Liu

doi:10.1120/jacmp.v15i6.4914

Abstract

This study was to evaluate the interfractional and intrafractional setup errors and baseline shifts of golden fiducial markers in patients receiving postoperative radiotherapy (RT) using cone‐beam computed tomography (CBCT) in order to calculate PTV margins for patients with liver cancer. Twelve patients with liver tumors underwent postoperative RT. CBCT images were acquired before and after the treatment. Off‐line vertebral body match and fiducial marker match were used, respectively. The results of vertebral body match represented the setup errors of the patients, while the results of fiducial marker match represented the absolute position errors of the target volume. Baseline shifts of the target volume were calculated as the absolute target position errors minus setup errors. A total of 12 patients with 214 acquisitions of CBCTs were analyzed. Both Σ and σ of setup errors and baseline shifts in left–right (L/R), superior–inferior (S/I), and anterior–posterior(A/P) directions were calculated, including interfractional and intrafractional uncertainties. Planning target volume (PTV) margins were calculated according to margin=2.5Σ+0.7σ. Margins of 1.8 mm, 3.8 mm, and 1.4 mm in L/R, S/I, and A/P directions are needed to compensate intrafractional errors when daily online CBCT correction is used. When CBCT correction with no action level (NAL) protocol is used, PTV margin should be 2.6 mm, 5.9 mm, and 2.6 mm in L/R, S/I, and A/P directions. Margins of 5.5 mm, 14.6 mm, and 7.2 mm were needed to compensate the baseline shifts when electronic portal imaging devices (EPID) or CBCT with bone match is used for online correction of setup error.PACS number: 87.55.‐x

Highlights

139 Zhang et al.: Setup errors and baseline shifts in patients with liver tumorsRT delivered to patients with unresectable liver tumors, while sparing the adjacent organs and normal liver
Radiotherapy plays an important role in the treatment of unresectable or inoperable Hepatocellular carcinoma (HCC).[3,4] Combined with transcatheter arterial chemoembolization (TACE), which is the first choice for patients with unresectable HCC, radiotherapy can improve the survival of the unresectable HCC patients.[5,6,7] intensity-modulated radiotherapy (IMRT) and 3D CRT can provide conformal dose distribution, while geometrical uncertainties in treatments influence the delivered dose distribution
Using cone-beam computed tomography (CBCT), we acquired the data of absolute errors, setup errors, and baselines shifts in patients with liver tumors

Summary

Introduction

139 Zhang et al.: Setup errors and baseline shifts in patients with liver tumorsRT delivered to patients with unresectable liver tumors, while sparing the adjacent organs and normal liver. 139 Zhang et al.: Setup errors and baseline shifts in patients with liver tumors. Geometrical uncertainties in radiation to the liver tumors include breathing motion, changes in the amplitude of breathing motion, changes in the overall patient position (setup error), changes in the liver tumor position relative to the patient position, and deformation of target volume. Online correction using CBCT with tumor matching can correct interfractional setup error and baseline shifts, while planning target volume (PTV) margin is still needed due to the presence of intrafractional errors. PTV margins compensating the baseline shifts are needed in such a situation because bone match can only correct the setup errors. The data of random errors and intrafractional errors are needed when calculating the PTV margin for NAL protocol. PTV margins compensating both baseline shifts and setup errors are needed in such institutions

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