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Title: SU-F-J-32: Do We Need KV Imaging During CBCT Based Patient Set-Up for Lung Radiation Therapy?

Abstract

Purpose: To evaluate the role of 2D kilovoltage (kV) imaging to complement cone beam CT (CBCT) imaging in a shift threshold based image guided radiation therapy (IGRT) strategy for conventional lung radiotherapy. Methods: A retrospective study was conducted by analyzing IGRT couch shift trends for 15 patients that received lung radiation therapy to evaluate the benefit of performing orthogonal kV imaging prior to CBCT imaging. Herein, a shift threshold based IGRT protocol was applied, which would mandate additional CBCT verification if the applied patient shifts exceeded 3 mm to avoid intraobserver variability in CBCT registration and to confirm table shifts. For each patient, two IGRT strategies: kV + CBCT and CBCT alone, were compared and the recorded patient shifts were categorized into whether additional CBCT acquisition would have been mandated or not. The effectiveness of either strategy was gauged by the likelihood of needing additional CBCT imaging for accurate patient set-up. Results: The use of CBCT alone was 6 times more likely to require an additional CBCT than KV+CBCT, for a 3 mm shift threshold (88% vs 14%). The likelihood of additional CBCT verification generally increased with lower shift thresholds, and was significantly lower when kV+CBCT was used (7% withmore » 5 mm shift threshold, 36% with 2 mm threshold), than with CBCT alone (61% with 5 mm shift threshold, 97% with 2 mm threshold). With CBCT alone, treatment time increased by 2.2 min and dose increased by 1.9 cGy per fraction on average due to additional CBCT with a 3mm shift threshold. Conclusion: The benefit of kV imaging to screen for gross misalignments led to more accurate CBCT based patient localization compared with using CBCT alone. The subsequently reduced need for additional CBCT verification will minimize treatment time and result in less overall patient imaging dose.« less

Authors:
; ; ; ;  [1]
  1. University of Maryland School of Medicine, Baltimore, MD (United States)
Publication Date:
OSTI Identifier:
22632166
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; BIOMEDICAL RADIOGRAPHY; COMPUTERIZED TOMOGRAPHY; IMAGES; LUNGS; PATIENTS; RADIATION DOSES; RADIOTHERAPY; VERIFICATION

Citation Formats

Gopal, A, Zhou, J, Prado, K, D’souza, W, and Yi, B. SU-F-J-32: Do We Need KV Imaging During CBCT Based Patient Set-Up for Lung Radiation Therapy?. United States: N. p., 2016. Web. doi:10.1118/1.4955940.
Gopal, A, Zhou, J, Prado, K, D’souza, W, & Yi, B. SU-F-J-32: Do We Need KV Imaging During CBCT Based Patient Set-Up for Lung Radiation Therapy?. United States. doi:10.1118/1.4955940.
Gopal, A, Zhou, J, Prado, K, D’souza, W, and Yi, B. 2016. "SU-F-J-32: Do We Need KV Imaging During CBCT Based Patient Set-Up for Lung Radiation Therapy?". United States. doi:10.1118/1.4955940.
@article{osti_22632166,
title = {SU-F-J-32: Do We Need KV Imaging During CBCT Based Patient Set-Up for Lung Radiation Therapy?},
author = {Gopal, A and Zhou, J and Prado, K and D’souza, W and Yi, B},
abstractNote = {Purpose: To evaluate the role of 2D kilovoltage (kV) imaging to complement cone beam CT (CBCT) imaging in a shift threshold based image guided radiation therapy (IGRT) strategy for conventional lung radiotherapy. Methods: A retrospective study was conducted by analyzing IGRT couch shift trends for 15 patients that received lung radiation therapy to evaluate the benefit of performing orthogonal kV imaging prior to CBCT imaging. Herein, a shift threshold based IGRT protocol was applied, which would mandate additional CBCT verification if the applied patient shifts exceeded 3 mm to avoid intraobserver variability in CBCT registration and to confirm table shifts. For each patient, two IGRT strategies: kV + CBCT and CBCT alone, were compared and the recorded patient shifts were categorized into whether additional CBCT acquisition would have been mandated or not. The effectiveness of either strategy was gauged by the likelihood of needing additional CBCT imaging for accurate patient set-up. Results: The use of CBCT alone was 6 times more likely to require an additional CBCT than KV+CBCT, for a 3 mm shift threshold (88% vs 14%). The likelihood of additional CBCT verification generally increased with lower shift thresholds, and was significantly lower when kV+CBCT was used (7% with 5 mm shift threshold, 36% with 2 mm threshold), than with CBCT alone (61% with 5 mm shift threshold, 97% with 2 mm threshold). With CBCT alone, treatment time increased by 2.2 min and dose increased by 1.9 cGy per fraction on average due to additional CBCT with a 3mm shift threshold. Conclusion: The benefit of kV imaging to screen for gross misalignments led to more accurate CBCT based patient localization compared with using CBCT alone. The subsequently reduced need for additional CBCT verification will minimize treatment time and result in less overall patient imaging dose.},
doi = {10.1118/1.4955940},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = 2016,
month = 6
}
  • Purpose: To develop a CBCT HU correction method using a patient specific HU to mass density conversion curve based on a novel image registration and organ mapping method for head-and-neck radiation therapy. Methods: There are three steps to generate a patient specific CBCT HU to mass density conversion curve. First, we developed a novel robust image registration method based on sparseness analysis to register the planning CT (PCT) and the CBCT. Second, a novel organ mapping method was developed to transfer the organs at risk (OAR) contours from the PCT to the CBCT and corresponding mean HU values of eachmore » OAR were measured in both the PCT and CBCT volumes. Third, a set of PCT and CBCT HU to mass density conversion curves were created based on the mean HU values of OARs and the corresponding mass density of the OAR in the PCT. Then, we compared our proposed conversion curve with the traditional Catphan phantom based CBCT HU to mass density calibration curve. Both curves were input into the treatment planning system (TPS) for dose calculation. Last, the PTV and OAR doses, DVH and dose distributions of CBCT plans are compared to the original treatment plan. Results: One head-and-neck cases which contained a pair of PCT and CBCT was used. The dose differences between the PCT and CBCT plans using the proposed method are −1.33% for the mean PTV, 0.06% for PTV D95%, and −0.56% for the left neck. The dose differences between plans of PCT and CBCT corrected using the CATPhan based method are −4.39% for mean PTV, 4.07% for PTV D95%, and −2.01% for the left neck. Conclusion: The proposed CBCT HU correction method achieves better agreement with the original treatment plan compared to the traditional CATPhan based calibration method.« less
  • Purpose: Four-dimensional-computed-tomography(4D-CT) imaging for target-volume delineation and cone-beam-tomography(CBCT) for treatment localization are widely utilized in lung-SABR.Aim of this study was to perform a quantitative-assessment and inter-comparison of Internal-targetvolumes( ITV) drawn on various phases of breathing-cycle 4D-CT-scans, Maximum-intensity-projection(MIP), average-intensity-projection(AIP)and static CT-scans of lung-motion-phantom to simulate lung-SABR patient geometry. We also analyzed and compared the ITVs drawn on freebreathing- CBCT. Materials and Methods: 4D-CT-scans were acquired on Philips big-bore 16slice CT and Bellows-respiratory monitoring-system using retrospective phase-binning method. Each respiratory cycle divided into 10-phases. Quasar-Phantom with lung-inserts and 3cm-diameter nylonball to simulate tumor and was placed on respiratory-motion-platform for 4D-CT and CBCT-acquisition.more » Amplitudes of motions: 0.5,1.0,2.0,3.0cm in superior-inferior direction with breathing-cycle time of 6,5,4,6sec, respectively used.4D-CTs with 10-phases(0%to90%)for each excursion-set and 3D-CT for static-phantom exported to iPlan treatment-planningsystem( TPS).Tumor-volumes delineated in all phases of 4D-CT, MIP,AIP,CBCT scans using fixed-HU-threshold(−500to1000)values automatically.For each 4D-dataset ITV obtained by unifying the tumorcontours on all phases.CBCT-ITV-volumes were drawn in Eclipse-TPS. Results: Mean volume of tumor contours for all phases compared with static 3D-CT were 0.62±0.08%, 1.67±0.26%, 4.77±0.54% and 9.27±1.23% for 0.5cm,1cm,2cm,3cm excursions respectively. Differences of mean Union-ITV with MIP-ITV were close(≤2.4%).Mean Union-ITV from expected-theoretical values differed from −4.9% to 3.8%.Union-ITV and MIP-ITV were closer within 2.3%. AIP-ITVs were underestimated from 14 to 32% compared to union-ITV for all motion datasets. Differences of −5.9% to −44% and −5% to 6.7% for CBCT-ITV from MIP-ITV and AIP-ITV respectively.Motion excursions and centroid positions were within 2mm for 4D-CT and CBCT-ITVs to that of expected values. Conclusion: 4D-CT MIP-ITV and Union-ITV showed very good agreement that validates that ITV can be fast contoured on MIP.Contouring ITV in AIP must be avoided as it significantly underestimates the volume with all excursions. Free breathing CBCT-ITV showed good agreement with AIP-ITV but underestimated the MIP-ITV. Estimation of excursions and centroid values for 4D-CT and CBCT were in good agreement with expected values.« less
  • Purpose: Ensuring reproducibility of target localization is critical to accurate stereotactic body radiation treatment (SBRT) for lung and soft tissue metastatic lesions. To characterize interfraction variability in set-up and evaluate PTV margins utilized for SBRT, daily CBCTs were used to calculate delivered target and OAR doses compared to those expected from planning. Methods: CBCT images obtained prior to each fraction of SBRT for a lung and thyroid metastatic lesion were evaluated. The target CTV/ITV and OARs on each of 8 CBCT data sets were contoured. Using MIM fusion software and Pinnacle{sup 3} RTP system, delivered dose distribution was reconstructed onmore » each CBCT, utilizing translational shifts performed prior to treatment. Actual delivered vs. expected doses received by target CTV/ITV and adjacent critical structures were compared to characterize accuracy of pre-treatment translational shifts and PTV margins. Results: The planned CTV/ITV D95% and V100% were 4595cGy and 91.47% for the lung lesion, and 3010cGy and 96.34% for the thyroid lesion. Based on CBCT analysis, actual mean D95% and V100% for lung ITV were 4542±344.4cGy and 91.54±3.45%; actual mean D95% and V100% for thyroid metastasis CTV were 3005±25.98cGy and 95.20±2.522%. For the lung lesion, ipsilateral lung V20, heart V32 (cc) and spinal cord (.03 cc) max were 110.15cc, 3.33cc, and 1680cGy vs. 110.27±14.79cc, 6.74±3.76cc, and 1711±46.56cGy for planned vs. delivered doses, respectively. For the thyroid metastatic lesion, esophagus V18, trachea (.03 cc) max, and spinal cord (.03 cc) max were 0.35cc, 2555cGy, and 850cGy vs. 0.16±0.13cc, 2147±367cGy, and 838±45cGy for planned vs. delivered treatments, respectively. Conclusion: Minimal variability in SBRT target lesion dose delivered based on pre-treatment CBCT-based translational shifts suggests tighter PTV margins may be considered to further decrease dose to surrounding critical structures. Guidelines for optimal target alignment during CBCT-guidance for lung and soft tissue metastatic lesions treated with SBRT are being established.« 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
  • Purpose: The Iterative Subtraction Algorithm (ISA) method generates retrospectively a pre-selected motion phase cone-beam CT image from the full motion cone-beam CT acquired at standard rotation speed. This work evaluates ISA method with real lung patient data. Methods: The goal of the ISA algorithm is to extract motion and no- motion components form the full reconstruction CBCT. The workflow consists of subtracting from the full CBCT all of the undesired motion phases and obtain a motion de-blurred single-phase CBCT image, followed by iteration of this subtraction process. ISA is realized as follows: 1) The projections are sorted to various phases,more » and from all phases, a full reconstruction is performed to generate an image CTM. 2) Generate forward projections of CTM at the desired phase projection angles, the subtraction of projection and the forward projection will reconstruct a CTSub1, which diminishes the desired phase component. 3) By adding back the CTSub1 to CTm, no motion CBCT, CTS1, can be computed. 4) CTS1 still contains residual motion component. 5) This residual motion component can be further reduced by iteration.The ISA 4DCBCT technique was implemented using Varian Trilogy accelerator OBI system. To evaluate the method, a lung patient CBCT dataset was used. The reconstruction algorithm is FDK. Results: The single phase CBCT reconstruction generated via ISA successfully isolates the desired motion phase from the full motion CBCT, effectively reducing motion blur. It also shows improved image quality, with reduced streak artifacts with respect to the reconstructions from unprocessed phase-sorted projections only. Conclusion: A CBCT motion de-blurring algorithm, ISA, has been developed and evaluated with lung patient data. The algorithm allows improved visualization of a single phase motion extracted from a standard CBCT dataset. This study has been supported by National Institute of Health through R01CA133539.« less