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Development and Evaluation of a Fast Patient Alignment Tool Using Megavoltage-Topogram On Helical TomoTherapy: A Pooled Analysis

X Qi*, F Chu, D Low, UCLA, Los Angeles, CA


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To develop and systemically evaluate megavoltage (MV)-topogram as an alternative fast patient localization tool on helical TomoTherapy for three anatomical sites.

Methods: We enrolled 19 head-and-neck, 12 thorax, and 18 pelvis cancer patients for the MV-topogram image acquisition under an IRB-approved clinical trial. Prior to the standard MVCT imaging and treatment procedure, each patient underwent weekly MV-topogram scans in AP/LAT views for 6-8 weeks. Each pair of the MV-topogram acquisition time ranged from 20 or 25 seconds at the couch speed of 4 cm/second. An in-house software was developed to reconstruct the MV-topograms offline. The relations between the shifts determined from MVCT and MV-topogram imaging techniques were assessed via linear mixed-effects model with site as random effect to account for within-site correlation. Two one-sided t-tests (TOST) equivalence procedure with paired design was used to analyze the patient shifts (R version.3.6.0). The discrepancy was defined as the numerical distance between MV-topogram and MVCT. Two techniques were considered to be equivalent if the discrepancy were within ?2 mm with significance level <0.05.

Results: 285 pairs of MV-topograms were reconstructed and compared to their corresponding MVCTs. The shifts, as the mean measure obtained from each subject, determined by MVCT and MV-topograms were found to be equivalent consistently in lateral (X), longitudinal (Y), and vertical (Z) directions across three anatomical sites and entire cohort (TOST p_values<0.02). With MV-topogram shift being independent variable and MVCT being response variable, the coefficients (and the standard errors) were 1.00 (0.04), 0.75 (0.07), and 0.77 (0.05) in the X, Y and Z directions, respectively.

Conclusion: MV-topograms showed equivalent clinical performance to the standard MVCT with significantly less acquisition time for the three anatomical sites. The MV-topogram can be utilized as an alternative or complimentary tool for bony landmark-based patient alignment on TomoTherapy.

Funding Support, Disclosures, and Conflict of Interest: This work is partially supported by a research grant from Accuray Inc (Sunnyvale, CA).


Not Applicable / None Entered.


IM/TH- RT X-Ray Imaging: combined KV/MV imaging

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