Evaluation of setup and intrafraction motion for surface guided whole‐breast cancer radiotherapy

Abstract

Surface Guided Radiotherapy (SGRT) is a relatively new technique for positioning patients and for monitoring patient movement during treatment. SGRT is completely non‐invasive since it uses visible light for determining the position of the patient surface. A reduction in daily imaging for patient setup is possible if the accuracy of SGRT is comparable to imaging. It allows for monitoring of intrafraction motion and the radiation beam can be held beyond a certain threshold resulting in a more accurate irradiation. The purpose of this study was to investigate setup uncertainty and the intrafraction motion in non‐gated whole breast cancer radiotherapy treatment using an integrated implementation of AlignRT (OSMS) system as SGRT. In initial setup, SGRT was compared to three‐point setup using tattoos on the patient and orthogonal kV imaging. For the investigation of intrafraction motion, OSMS monitored the patient with six degrees of freedom during treatment. Using three‐point setup resulted in a setup root‐mean‐square error from the isocenter of 5.4 mm. This was improved to 4.2 mm using OSMS. For the translational directions, OSMS showed improvements in the lateral direction (P = 0.0009, Wilcoxon rank‐sum), but for the longitudinal direction and rotation it was not possible to show improvements (P = 0.96 and P = 0.46, respectively). The vertical direction proved more accurate for three‐point setup than OSMS (P = 0.000004). Intrafraction motion was very limited with a translational median of 1.1 mm from the isocenter. While OSMS showed marked improvements over laser and tattoo setup, the system did not prove accurate enough to replace the daily orthogonal kV images aligned to bony anatomy.

Recent advances in Surface Guided Radiation Therapy

“…There is a broad agreement on the supremacy of SGRT over 3-point laser-based patient setup, when the surface serves as a surrogate for the target positioning, i.e. breast and other skin-near targets [13,16,[21][22][23][24][25][26][27][28][29][30]. For deeper situated targets, surface imaging should be used with caution [13,22,31,32].…”

“…Regarding setup of breast cancer patients, studies comparing laser alignment with surface imaging report a reduction of positioning errors for skin and clip alignment [ 23 – 26 ] by around 40% on average, with absolute errors (1SD) for all studies being smaller than 4 mm, verified with kV orthogonal imaging [ 29 , 30 , 33 , 34 ], portal imaging [ 16 , 27 , 30 ], or cone-beam computed tomography (CBCT) [ 13 ]. In addition to accurate isocenter positioning, the surface imaging provides guidance for correcting patient posture, i.e.…”

Feasibility of Optical Surface-Guidance for Position Verification and Monitoring of Stereotactic Body Radiotherapy in Deep-Inspiration Breath-Hold

“…We observed highest interfractional variability in cranio-caudal direction and lowest in left-right direction, underpinning the idea that respiratory motion, which is mostly performed by the diaphragm, impacts most on target localization. Indeed, using SGRT for positioning of breast cancer patients in free-breathing showed least errors for lateral set-up compared to imaging ( 28 ). Our data further suggest a higher correlation of thoracic DIBH surface to intrathoracic targets than to abdominal targets, despite the fact that we chose to set the ROI for DIBH monitoring to the lower thorax for both thoracic and abdominal targets.…”

Comparison of surface guidance and target matching for image‐guided accelerated partial breast irradiation (APBI)

“…Three‐dimensional (3D) surface guidance has been previously introduced for localization, tracking, and monitoring during radiation therapy, with the advantage that it does not deliver ionizing radiation dose to the patient . It has been investigated in both conventional free breathing and deep inspiration breath hold (DIBH) breast radiation therapy . It has also been investigated via planar MV portal imaging for potential to improve the reproducibility and stability of relatively smaller targets associated with APBI …”