# Comparative analysis of kVCT- and MVCT-guided helical tomotherapy for total body irradiation: evaluation of process times and residual setup errors

## TL;DR

This study compares kilovoltage and megavoltage CT for guiding total body irradiation, showing that kilovoltage CT reduces setup times while maintaining accuracy.

## Contribution

Demonstrates that whole-body kVCT improves workflow efficiency in tomotherapy-based TBI without compromising setup accuracy.

## Key findings

- kVCT reduced setup cycle times for upper and lower body segments by nearly 6 minutes each.
- Total fraction time decreased by 15 minutes with kVCT while maintaining sub-2 mm residual setup errors.
- kVCT halved the additional time needed for second correction cycles when errors exceeded 5 mm.

## Abstract

Helical tomotherapy-based total body irradiation (TBI) traditionally employs megavoltage computed tomography (MVCT) for image-guided setup; however, its 390 mm field of view (FOV) and long acquisition times constrain workflow efficiency and whole-body alignment. This study evaluated whether a newly implemented whole-body fan-beam kilovoltage CT (kVCT; 500 mm FOV) can streamline this process. In a retrospective study involving 14 patients treated with a Radixact X9 system (September 2021–September 2023), we timed the patient setup, imaging, registration, re-setup, and beam delivery for each upper-body (UB) and lower-body (LB) segment. Residual setup errors were measured along the lateral, longitudinal, and vertical axes. The kVCT shortened the initial setup cycle (setup + imaging + registration) from 25.4 ± 4.6 to 15.9 ± 3.3 min for UB and from 14.5 ± 3.8 to 9.4 ± 2.4 min for LB (P < 0.001 for both). The total fraction time, including delivery time, decreased from 71.8 ± 7.5 to 56.7 ± 5.3 min. When residual errors exceeded 5 mm, the additional time required for a second cycle was nearly halved with kVCT (7.3 vs. 14.3 min for UB; 4.8 vs. 8.2 min for LB). The kVCT maintained mean absolute residual errors below 2 mm in all axes, and every 95th-percentile value remained within the 5 mm tolerance recommended for tomotherapy-based TBI. These time savings are expected to reduce intrafraction motion and staff workload. Overall, whole-body kVCT enables faster, comprehensive image guidance while preserving accuracy, thereby streamlining tomotherapy-based TBI and reducing the burden on patients and clinical staff.