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Title: SU-F-J-30: Application of Intra-Fractional Imaging for Pretreatment CBCT of Breath-Hold Lung SBRT

Abstract

Purpose: Clinical implementation of gated lung SBRT requires tools to verify the accuracy of the target positioning on a daily basis. This is a particular challenge on Elekta linacs where the XVI imaging system does not interface directly to any commercial gating solution. In this study, we used the Elekta’s intra-fractional imaging functionality to perform the pretreatment CBCT verifications and evaluated both the image quality and gating accuracy. Methods: To use intrafraction imaging tools for pretreatment verifications, we planned a 360-degree arc with 1mmx5mm MLC opening. This beam was designed to drive the gantry during the gated CBCT data collection. A Catphan phantom was used to evaluate the image quality for the intra-fractional CBCT. A CIRS lung phantom with a 3cm sphereinsert and a moving chest plate were programmed with a simulated breathhold breathing pattern was used to check the gating accuracy. A C-Rad CatalystHD surface mapping system was used to provide the gating signal. Results: The total delivery time of the arc was 90 seconds. The uniformity and low contrast resolution for the intra-fractional CBCT was 1.5% and 3.6%, respectively. The values for the regular CBCT were 1.7% and 2.5%, respectively. The spatial resolution was 7 line-pairs/cm and themore » 3D spatial integrity was less than 1mm for the intra-fractional CBCT. The gated CBCT clearly demonstrated the accuracy of the gating image acquisition. Conclusion: The intra-fraction CBCT capabilities on an Elekta linac can be used to acquire pre-treatment gated images to verify the accuracy patient positioning. This imaging capability should provide for accurate patient alignments for the delivery of lung SBRT. This research was partially supported by Elekta.« less

Authors:
; ; ;  [1]
  1. Swedish Cancer Institute, Seattle, WA (United States)
Publication Date:
OSTI Identifier:
22632165
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; 61 RADIATION PROTECTION AND DOSIMETRY; ACCURACY; BIOMEDICAL RADIOGRAPHY; CHEST; COMPUTERIZED TOMOGRAPHY; IMAGES; LINEAR ACCELERATORS; LUNGS; PATIENTS; PHANTOMS; POSITIONING; SPATIAL RESOLUTION; VERIFICATION

Citation Formats

Cao, D, Jermoumi, M, Mehta, V, and Shepard, D. SU-F-J-30: Application of Intra-Fractional Imaging for Pretreatment CBCT of Breath-Hold Lung SBRT. United States: N. p., 2016. Web. doi:10.1118/1.4955938.
Cao, D, Jermoumi, M, Mehta, V, & Shepard, D. SU-F-J-30: Application of Intra-Fractional Imaging for Pretreatment CBCT of Breath-Hold Lung SBRT. United States. doi:10.1118/1.4955938.
Cao, D, Jermoumi, M, Mehta, V, and Shepard, D. 2016. "SU-F-J-30: Application of Intra-Fractional Imaging for Pretreatment CBCT of Breath-Hold Lung SBRT". United States. doi:10.1118/1.4955938.
@article{osti_22632165,
title = {SU-F-J-30: Application of Intra-Fractional Imaging for Pretreatment CBCT of Breath-Hold Lung SBRT},
author = {Cao, D and Jermoumi, M and Mehta, V and Shepard, D},
abstractNote = {Purpose: Clinical implementation of gated lung SBRT requires tools to verify the accuracy of the target positioning on a daily basis. This is a particular challenge on Elekta linacs where the XVI imaging system does not interface directly to any commercial gating solution. In this study, we used the Elekta’s intra-fractional imaging functionality to perform the pretreatment CBCT verifications and evaluated both the image quality and gating accuracy. Methods: To use intrafraction imaging tools for pretreatment verifications, we planned a 360-degree arc with 1mmx5mm MLC opening. This beam was designed to drive the gantry during the gated CBCT data collection. A Catphan phantom was used to evaluate the image quality for the intra-fractional CBCT. A CIRS lung phantom with a 3cm sphereinsert and a moving chest plate were programmed with a simulated breathhold breathing pattern was used to check the gating accuracy. A C-Rad CatalystHD surface mapping system was used to provide the gating signal. Results: The total delivery time of the arc was 90 seconds. The uniformity and low contrast resolution for the intra-fractional CBCT was 1.5% and 3.6%, respectively. The values for the regular CBCT were 1.7% and 2.5%, respectively. The spatial resolution was 7 line-pairs/cm and the 3D spatial integrity was less than 1mm for the intra-fractional CBCT. The gated CBCT clearly demonstrated the accuracy of the gating image acquisition. Conclusion: The intra-fraction CBCT capabilities on an Elekta linac can be used to acquire pre-treatment gated images to verify the accuracy patient positioning. This imaging capability should provide for accurate patient alignments for the delivery of lung SBRT. This research was partially supported by Elekta.},
doi = {10.1118/1.4955938},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = 2016,
month = 6
}
  • Purpose: Tumor motion in lung SBRT is typically managed by creating an internal target volume (ITV) based on 4D-CT information. Another option, which may reduce lung dose and imaging artifact, is to use a breath hold (BH) during simulation and delivery. Here we evaluate the reproducibility of tumor position at repeated BH using a newly released spirometry system. Methods: Three patients underwent multiple BH CT’s at simulation. All patients underwent a BH cone beam CT (CBCT) prior to each treatment. All image sets were registered to a patient’s first simulation CT based on local bony anatomy. The gross tumor volumemore » (GTV), and the diaphragm or the apex of the lung were contoured on the first image set and expanded in 1 mm increments until the GTVs and diaphragms on all image sets were included inside an expanded structure. The GTV and diaphragm margins necessary to encompass the structures were recorded. Results: The first patient underwent 2 BH CT’s and fluoroscopy at simulation, the remaining patients underwent 3 BH CT’s at simulation. In all cases the GTV’s remained within 1 mm expansions and the diaphragms remained within 2 mm expansions on repeat scans. Each patient underwent 3 daily BH CBCT’s. In all cases the GTV’s remained within a 2 mm expansions, and the diaphragms (or lung apex in one case) remained within 2 mm expansions at daily BH imaging. Conclusions: These case studies demonstrate spirometry as an effective tool for limiting tumor motion (and imaging artifact) and facilitating reproducible tumor positioning over multiple set-ups and BH’s. This work was partially supported by Qfix.« less
  • Purpose: Lung stereo-tactic body radiotherapy(SBRT) treatment requires high accuracy of lung tumor positioning during treatment, which is usually accomplished by free breathing Cone-Beam computerized tomography (CBCT) scan. However, respiratory motion induced image artifacts in free breathing CBCT may degrade such positioning accuracy. The purpose of this study is to investigate the feasibility of gated CBCT imaging for lung SBRT treatment. Methods: Six Lung SBRT patients were selected for this study. The respiratory motion of the tumors ranged from 1.2cm to 3.5cm, and the gating windows for all patients were set between 35% and 65% of the respiratory phases. Each Lungmore » SBRT patient underwent free-breathing CBCT scan using half-fan scan technique. The acquired projection images were transferred out for off-line analyses. An In-house semi-automatic algorithm was developed to trace the diaphragm movement from those projection images to acquire a patient's specific respiratory motion curve, which was used to correlate respiratory phases with each projection image. Afterwards, a filtered back-projection algorithm was utilized to reconstruct the gated CBCT images based on the projection images only within the gating window. Results: Target volumes determined by free breathing CBCT images were 71.9%±72% bigger than the volume shown in gated CBCT image. On the contrary, the target volume differences between gated CBCT and planning CT images at exhale stage were 5.8%±2.4%. The center to center distance of the targets shown in free breathing CBCT and gated CBCT images were 9.2±8.1mm. For one particular case, the superior boundary of the target was shifted 15mm between free breathing CBCT and gated CBCT. Conclusion: Gated CBCT imaging provides better representation of the moving lung tumor with less motion artifacts, and has the potential to improve the positioning accuracy in lung SBRT treatment.« less
  • Purpose: To evaluate correlation between the reproducibility of tumor position under feedback guided voluntary deep inspiration breath hold gating at simulation and at treatment. Methods: All patients treated with breath hold (BH) have 3-6 BH CTs taken at simulation (sim). In addition, if the relationship between the tumor and nearby bony anatomy on treatment BH CT(or CBCT) is found to be greater than 5 mm different at treatment than it was at sim, a repeat BH CT is taken before treatment. We retrospectively analyzed the sim CTs for 19 patients who received BH SBRT lung treatments and had repeat BHmore » CT on treatment. We evaluated the reproducibility of the tumor position during the simulation CTs and compared this to the reproducibility of the tumor position on the repeat treatment CT with our in-house CT alignment software (CT-Assisted Targeting for Radiotherapy). Results: Comparing the tumor position for multiple simulation BH CTs, we calculated: maximum difference (max) = 0.69cm; average difference (x) = 0.28cm; standard deviation (σ) = 0.18cm. Comparing the repeat BH CBCTs on treatment days we calculated: max = 0.44cm; x = 0.16cm; σ = 0.22cm. We also found that for 95% of our BH cases, the absolute variation in tumor position within the same imaging day was within 5mm of the range at the time of simulation and treatment. We found that 75% of the BH cases had less residual tumor motion on treatment days than at simulation. Conclusion: This suggests that a GTV contour based upon the residual tumor motion in multiple BH datasets plus 2 mm margin should be sufficient to cover the full range of residual tumor motion on treatment days.« less
  • Purpose: To analysis delivered dose on target using gafchromic films for evaluating accuracy of target margin size obtained from cone beam computed tomography (CBCT) during lung stereotactic body radiation therapy (SBRT) Methods: The phantom consists of measurement part and driving part. The motor of Quasar motion phantom (Modus Medical Devices Inc, London, ON, Canada) was used for driving part and we developed measurement part which consist of cork cylindrical body and acrylic target with radiochromic film inserted into central and both ends of acrylic target. In this study lung SBRT cases through both four dimensional computed tomography (4DCT) and CBCTmore » were selected. Target contouring including margin based on 4DCT is defined with a 1 cm margin around gross tumor volume (GTV) in all directions except for inferior direction. The moving range in inferior direction was larger than other directions thus, including 2 cm margin. In case of CBCT, the margin means blurring of target on CBCT images. This study was compared margin size determined through 4DCT and that of based on CBCT and we also evaluated dose profile and the length of margin in superior-inferior direction on CBCT compared with 4DCT. Results: The length of target including margin was 2.48 cm (based on CBCT) and 2.66 cm (based on 4DCT), respectively in superior-inferior direction. The difference of delivered dose on target between two margins was only within 1%. Conclusions: This study has shown the feasibility of determining target margin using CBCT for delivering more accurate prescription dose to lung cancer.« less
  • Purpose: Quantification of volume changes on CBCT during SBRT for NSCLC may provide a useful radiological marker for radiation response and adaptive treatment planning, but the reproducibility of CBCT volume delineation is a concern. This study is to quantify inter-scan/inter-observer variability in tumor volume delineation on CBCT. Methods: Twenty earlystage (stage I and II) NSCLC patients were included in this analysis. All patients were treated with SBRT with a median dose of 54 Gy in 3 to 5 fractions. Two physicians independently manually contoured the primary gross tumor volume on CBCTs taken immediately before SBRT treatment (Pre) and after themore » same SBRT treatment (Post). Absolute volume differences (AVD) were calculated between the Pre and Post CBCTs for a given treatment to quantify inter-scan variability, and then between the two observers for a given CBCT to quantify inter-observer variability. AVD was also normalized with respect to average volume to obtain relative volume differences (RVD). Bland-Altman approach was used to evaluate variability. All statistics were calculated with SAS version 9.4. Results: The 95% limit of agreement (mean ± 2SD) on AVD and RVD measurements between Pre and Post scans were −0.32cc to 0.32cc and −0.5% to 0.5% versus −1.9 cc to 1.8 cc and −15.9% to 15.3% for the two observers respectively. The 95% limit of agreement of AVD and RVD between the two observers were −3.3 cc to 2.3 cc and −42.4% to 28.2% respectively. The greatest variability in inter-scan RVD was observed with very small tumors (< 5 cc). Conclusion: Inter-scan variability in RVD is greatest with small tumors. Inter-observer variability was larger than inter-scan variability. The 95% limit of agreement for inter-observer and inter-scan variability (∼15–30%) helps define a threshold for clinically meaningful change in tumor volume to assess SBRT response, with larger thresholds needed for very small tumors. Part of the work was funded by a Kaye award; Disclosure/Conflict of interest: Raymond H. Mak: Stock ownership: Celgene, Inc. Consulting: Boehringer-Ingelheim, Inc.« less