Intrafractional accuracy and efficiency of a surface imaging system for deep inspiration breath hold during ablative gastrointestinal cancer treatment

Abstract

Purpose Beam gating with deep inspiration breath hold (DIBH) usually depends on some external surrogate to infer internal target movement, and the exact internal movement is unknown. In this study, we tracked internal targets and characterized residual motion during DIBH treatment, guided by a surface imaging system, for gastrointestinal cancer. We also report statistics on treatment time. Methods and materials We included 14 gastrointestinal cancer patients treated with surface imaging‐guided DIBH volumetrically modulated arc therapy, each with at least one radiopaque marker implanted near or within the target. They were treated in 25, 15, or 10 fractions. Thirteen patients received treatment for pancreatic cancer, and one underwent separate treatments for two liver metastases. The surface imaging system monitored a three‐dimensional surface with ± 3 mm translation and ± 3° rotation threshold. During delivery, a kilovolt image was automatically taken every 20° or 40° gantry rotation, and the internal marker was identified from the image. The displacement and residual motion of the markers were calculated. To analyze the treatment efficiency, the treatment time of each fraction was obtained from the imaging and treatment timestamps in the record and verify system. Results Although the external surface was monitored and limited to ± 3 mm and ± 3°, significant residual internal target movement was observed in some patients. The range of residual motion was 3–21 mm. The average displacement for this cohort was 0–3 mm. In 19% of the analyzed images, the magnitude of the instantaneous displacement was > 5 mm. The mean treatment time was 17 min with a standard deviation of 4 min. Conclusions Precaution is needed when applying surface image guidance for gastrointestinal cancer treatment. Using it as a solo DIBH technique is discouraged when the correlation between internal anatomy and patient surface is limited. Real‐time radiographic verification is critical for safe treatments.

Surface guidance compared with ultrasound-based monitoring and diaphragm position in cone-beam computed tomography during abdominal stereotactic radiotherapy in breath-hold

“…Some studies suggested that SGRT can be used as surrogate for internal motion during 4D-CT/CBCT or BH for individual patients [34] , [35] , [36] . Zeng et al recently discouraged using SGRT as solo monitoring method and Wang et al recommended patient-based assessment of internal/external correlation as correlation differed by a high degree for various patients [37] , [38] . The AAPM task group states that SGRT may not track the internal target with sufficient accuracy and therefore recommends a synergistic approach in combination with internal imaging [53] .…”

“…SGRT-systems have been implemented for breast radiotherapy [33] and during abdominal/thoracic SBRT [18] , [19] , [20] . However, their accuracy as surrogate for internal motion during abdominal DIBH-SBRT is still controversial and previous literature lacks comparison with internal monitoring, e.g., an US-system [18] , [23] , [34] , [35] , [36] , [37] , [38] .…”