Fast, Low-Dose Megavoltage-Topogram Localization on TomoTherapy: Initial Clinical Experience With Mesothelioma Patients

Our plain-English summary of Fast, Low-Dose Megavoltage-Topogram Localization on TomoTherapy: Initial Clinical Experience With Mesothelioma Patients, by X.S. Qi, L. Yang, P. Lee, et al (Practical Radiation Oncology, 2019).

The study

• Authors: X.S. Qi, L. Yang, P. Lee, D. O'Connell, F.I. Chu, M.L. Steinberg, D.A. Low
• Journal: Practical Radiation Oncology
• Published: 2019;9(5):373-380
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Purpose: This study aimed to evaluate the potential of megavoltage-topogram (MV-topogram)-based alignment as an alternative to megavoltage computed tomography (MVCT) in reducing setup time and imaging dose for patients with malignant pleural mesothelioma who are receiving TomoTherapy.

Methods And Materials: Twelve patients were enrolled in an ongoing institutional review board approved clinical trial at our institute. Patients were set up with a clinical protocol using red lasers. Anteroposterior (AP) and lateral (LAT) MV-topograms were acquired using gantry angles of 0°/90° with a 1 mm collimator opening, all multileaf collimator leaves open, a couch speed of 4 cm/s, and a 12.5-second scanning time. Routine MVCT scans were performed immediately afterward. The MV-topograms were reconstructed and enhanced using contrast-limited adaptive histogram equalization. Anteroposterior and LAT kilovoltage digital reconstructed topogram images were reconstructed based on TomoTherapy geometry from computed tomography simulation scans. Registrations between MV-topograms and kilovoltage-digital reconstructed topogram images were performed manually, and patients' daily shifts were recorded. Results were compared against the corresponding daily MVCT shifts. MV-topogram and MVCT doses were measured and recorded using an ion chamber on a cheese phantom with depths between 1 and 14 cm, as well as the times required to acquire the 2 image modalities.

Results: The mean and standard deviation of shift discrepancies between MV-topogram and MVCT were 0.74 ± 2.08, -0.09 ± 4.46, and 0.45 ± 3.57 mm in the LAT, longitudinal, and vertical directions, respectively. The MVCT imaging doses measured were 14.74 to 26.92 times higher than the MV-topogram doses, depending on depth. On average, MV-topograms with a mean scan length of 50 cm achieved a 5-fold image acquisition time savings over MVCT, with a mean scan length of 38 cm.

Conclusions: MV-topograms has the potential to provide alignment performance equivalent to that of MVCT for patients with mesothelioma, with a significant reduction in imaging dose and acquisition time.

Copyright © 2019 American Society for Radiation Oncology. Published by Elsevier Inc. All rights reserved.

In plain English

This study did not examine asbestos exposure. It tested an imaging technique for positioning patients with malignant pleural mesothelioma before TomoTherapy radiation treatment. At the University of California, Los Angeles, 12 trial patients had weekly two-dimensional scans called MV-topograms in addition to the standard positioning scan (MVCT). One patient dropped out early because of back pain. Across 53 paired scans, the authors compared how far each method said a patient needed to be shifted. Average differences were under 1 mm in each direction, for example 0.74 mm (standard deviation 2.08 mm) side to side. An equivalence test using 2 mm limits found the methods equivalent in all three directions, although a few patients had differences over 8 mm. In measurements on a test object (phantom), MVCT doses were 14.74 to 26.92 times higher than MV-topogram doses. MV-topograms took 25 seconds, against an average of 213.4 seconds for MVCT. The authors concluded that MV-topograms have the potential to match MVCT alignment with much lower dose and time. They noted that yaw and pitch rotations went uncorrected with both methods, that roll was corrected only for MVCT, and that breathing motion affected the images.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Pilot study within a prospective clinical trial approved by an institutional review board, comparing two imaging methods for patient positioning in the same patients, plus imaging-dose measurements on a phantom
• Who was studied: 12 patients with malignant pleural mesothelioma treated with TomoTherapy at the Department of Radiation Oncology, University of California, Los Angeles. The tumor target was on the right side in 7 patients and the left side in 5. One patient dropped out after the first fraction because of back pain in the treatment position. Enrollment dates were not given.
• Exposure: No asbestos exposure was studied. The comparison was between weekly MV-topogram scans (front-to-back and side views, 12.5-second scans covering 50 cm) and standard MVCT scans taken immediately afterward. Each patient had 5 or 6 weekly MV-topogram sets.
• Main results:
  • 53 pairs of weekly MV-topograms and matching MVCT scans were compared. The mean (standard deviation) differences in patient shifts between the two methods were 0.74 (2.08) mm in the lateral direction, -0.09 (4.46) mm in the longitudinal direction and 0.45 (3.57) mm in the vertical direction.
  • Using an equivalence test with bounds of -2 mm and 2 mm, the shifts determined by MVCT and MV-topogram were found equivalent in the lateral, longitudinal and vertical directions (P less than .001 for both upper and lower bounds in each).
  • Large discrepancies (greater than 8 mm) in the longitudinal and vertical directions were found for a few patients. The authors suggested these were possibly due to setup markers not being visible and to breathing-related motion artifacts on the side-view MV-topograms.
  • The regression slopes comparing the two methods were 0.91 lateral, 0.45 longitudinal and 0.81 vertical.
  • On a phantom, MVCT imaging doses were 14.74 to 26.92 times higher than MV-topogram doses at depths of 1 to 14 cm (ratio 15.16 at 1 cm, 14.74 at 2 cm, 18.89 at 5 cm, 19.18 at 10 cm, 26.92 at 14 cm).
  • The average MVCT scan time was 213.4 seconds (standard deviation 40.8), covering an average target length of 35.2 cm. The MV-topogram acquisition time was 25 seconds for a 50 cm extent.
• The authors' conclusion: The authors concluded that MV-topograms have the potential to provide alignment performance equivalent to MVCT for patients with mesothelioma, with a significant reduction in dose and acquisition time on TomoTherapy.
• Limitations the authors state:
  • Patient roll was corrected for MVCT by slightly rotating the gantry, but roll corrections were not accounted for in the MV-topograms.
  • Yaw and pitch rotational discrepancies were not corrected; for MVCT they were reset to zero as standard practice. Patients with larger uncorrected rotations had larger discrepancies between the methods.
  • Breathing caused about 5 mm of longitudinal movement of the carina in a few randomly selected patients.
  • Registrations varied between observers.
  • MV-topogram processing was done off-line. The current workflow added 2 to 3 minutes of operational time.
  • MV-topograms have not yet been used alone for patient alignment because their performance is still under investigation.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma, Pleural Mesothelioma, Clinical Trial.

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