Utilizing the TrueBeam Advanced Imaging Package to monitor intrafraction motion with periodic kV imaging and automatic marker detection during VMAT prostate treatments

Abstract

Background Fiducial markers are frequently used before treatment for image‐guided patient setup in radiation therapy (RT), but can also be used during treatment for image‐guided intrafraction motion detection. This report describes our implementation of automatic marker detection with periodic kV imaging (TrueBeam v2.5) to monitor and correct intrafraction motion during prostate RT. Methods We evaluated the reproducibility and accuracy of software fiducial detection using a phantom with 3 implanted fiducial markers. Clinical implementation for patients with intraprostatic fiducials receiving volumetric modulated arc therapy (VMAT) utilized periodic on‐board kV imaging with 10 s intervals during treatment delivery. For each image, the software automatically identified fiducial locations and determined whether their distance relative to planned locations were within a 3 mm tolerance. Motion was corrected if either ≥2 fiducials in a single image or ≥1 fiducial in sequential images were out of tolerance. Results Phantom studies demonstrated poorer performance of linear fiducials compared to collapsible fiducials, and wide variability to accurately detect fiducials across eight software settings. For any given setting, results were relatively reproducible and precise to ~0.5 mm. Across 17 patients treated with a median of 20 fractions, the software recommended a shift in 44% of fractions, and a shift was actually implemented after visual confirmation of movement greater than the 3 mm threshold in 20% of fractions. Adjustment of our approach led to improved accuracy for the latter (n = 7) patient subset. On average, table repositioning added 3.0 ± 0.3 min to patient time on table. Periodic kV imaging increased skin dose by an estimated 1 cGy per treatment arc. Conclusions Periodic kV imaging with automatic detection of motion during VMAT prostate treatments is commercially available, and can be successfully implemented to mitigate effects of intrafraction motion with careful attention to software settings.

Triggered kV Imaging During Spine SBRT for Intrafraction Motion Management

“…If the marker is outside of a pre-set tolerance threshold distance, indicator color changes and an operator can choose to stop treatment to adjust or, if the auto beam hold (ABH) function is active, the treatment beam can be automatically paused. In various studies, intrafraction motion was detected in a surprisingly large percentage of fractions with this marker tracking technique despite standard patient immobilization (eg, shift recommended in 44% of fractions for prostate treatment, 9 second localization with CBCT was required in 11.6% of liver SBRT patients. 18 ) Thus, intrafraction motion tracking can help detect clinically meaningful patient motion that happens rather frequently and reduce radiotherapy related morbidity.…”

“…Those techniques often require specialized equipment and/or invasive implants (e.g., electromagnetic tracking or ultrasound-guidance), or use surrogates rather than direct tracking of patient anatomy (e.g., surface guidance) and most are not applicable to spine SBRT. [5][6][7][8][9][10][11] In this work we describe a cost effective, highly accessible and non-invasive intrafraction motion monitoring approach with more readily available equipment that directly tracks patient anatomy.…”

A prospective trial of stereotactic body radiation therapy for unresectable pancreatic cancer testing ablative doses

“…The use of a standard expansion on normal tissues may help to address variation in position that may have affected dose to these structures, and a planning organ at risk volume (PRV) margin on the duodenum is now employed in our clinic. The use of intrafraction monitoring with triggered kV images (27) or other means of accounting for setup variation [e.g., MR linac with adaptive real time planning (28,29)] may justify tigher PTV margins. An optimistic view would be that continued improvements in targeting and motion management, and prolonged treatment over 5 fractions or more, will improve the therapeutic ratio of RT in the ablative dose range.…”

Interpretation of intrafraction motion review data and method for verification

“…While IMR has been shown to be useful by investigators, 1 , 2 , 3 , 4 , 5 , 6 the current version of IMR (TrueBeam® v2.7 MR3) is not without its limitations. The tolerance information received by the clinical user during treatment is displayed qualitatively as green, red, or orange corresponding to whether the location for each fiducial is detected within the set tolerance, outside of the tolerance, or not found, respectively, as shown in Figure 1 .…”