Session Item

In radiotherapy, the positioning of the patient is a pivotal part of the treatment. This study aims to evaluate the patient positioned with tattoos and surface guidance for pre-imaging setup considering two IGRT workflows:  paired-orthogonal MV-kV images and kV-CBCT guidance.

The workflow was performed in a TrueBeam SVC unit with a six-dimensional IGRT couch and the optical surface guidance imaging system, i.e., AlignRT surface-guidance system (Version 6.3, Vision RT, London, UK) as follows:
For the current study, we have divided the patient into two groups.
In the first group, we included thirty patients divided into two arms, each having fifteen patients. So, in one arm patient surface was matched to the simulation position with the aid of Vision RT postural video land a region of interest (ROI shown in fig1). On the other arm, patients were positioned using reference tattoos to the room lasers; pre-treatment imaging was taken using a daily 3D cone-beam CT online correction strategy. Finally, automatic image registration was done by selecting a suitable ROI around the PTV structure.
In the second group, we included twenty patients divided into two arms, each having ten patients. Similar to above setup an orthogonal MV-kV paired imaging was taken for all patients and registration was done to bony structures. 

The average shifts due to translations and rotation obtained from CBCT registration are lateral (0.02±0.205), longitudinal (0.001±0.31), vertical (0.31±0.180) and Pitch (0.52±0.92), Yaw (0.14±0.77), Roll (0.08 ±0.70) for surface setup, lateral (0.06±0.320), longitudinal (0.043±0.17), vertical (0.004±0.254) and pitch (0.09±0.87), Yaw (0.03±0.53) and roll (0.50 ±0.63) with tattoo-based setup. It has been observed that the shift of the SGRT-based setup is smaller than the tattoo-based setup, except for the vertical shift, which is not statistically significant(p=0.06). In addition roll of  SGRT-based setup is smaller and statistically significant(p=0.0044).

The average shifts due to translations and rotation obtained from MV-kV registration are lateral (0.09±0.213), longitudinal (0.014±0.22), vertical (0.216±0.190) and Pitch (0.36±1.58), Yaw (0.40±0.66), Roll (0.04 ±0.10) for surface setup, lateral (0.12±0.150), longitudinal (0.075±0.19), vertical (0.124±0.28) and pitch (0.55±0.89), Yaw (0.56±0.62) and roll (0.05 ±0.12) with tattoo-based setup. Similarly, with SGRT based setup, all shifts are smaller than the tattoo-based setup, except for the vertical shift, which is statistically significant(p=0.034).In addition rotation with SGRT based setup is smaller and statistically significant(p=0.0038).

In current study both IGRT workflows showed excellent improvement in pelvic patient positioning using SGRT compared to the tattoos-based setup. In addition, patient roll and yaw have been improved using the SGRT setup. So, pelvic patients can undergo daily SGRT-based setup for accurate and reproducible patient positioning without additional imaging dose.