Prepositioning evaluation of breast/chest wall patient: surface guided versus lasers and skin marks
Constance Nicolet,
France
PO-1175
Abstract
Prepositioning evaluation of breast/chest wall patient: surface guided versus lasers and skin marks
Authors: Constance Nicolet1, Laurent Delcoudert2, Leone Aubignac2, Karine Peignaux1, Mathieu Gonod2
1Centre Georges François Leclerc, Radiotherapy department, Dijon, France; 2Centre Georges François Leclerc, Medical physics department, Dijon, France
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Purpose or Objective
Evaluation of the efficiency of a 3D surface imaging compared to “lasers and skin marks” modality for prepositioning, in term of accuracy and time required, concerning patients treated by adjuvant Volumetric Modulated Arc Therapy (VMAT) radiotherapy for a breast cancer.
Material and Methods
40 patients, retrospectively included, were prepositioned with “laser and skin marks” method and were compared to 51 patients, prospectively included, and prepositioned with AlignRT (Vision RT, London, UK). A daily Cone Beam Computed Tomography (CBCT) has been acquired to reposition each patient at each fraction.
Regarding the accuracy, shifts values were analyzed for the six degrees of freedom, with absolute values for the first session and normalized values for all sessions. Indeed, shifts values analyzed were the residual set-up errors after the acquisition of the CBCT.
To evaluate the time needed to position, prepositioning time (defined as the time between the plan opening on the linac and the acquisition of the first CBCT) and positioning time (defined as the time between the plan opening on the linac and the beginning of the first treatment beam) were analyzed.
Results
Through all sessions, pitch, longitudinal and lateral shifts were significantly lower while yaw and vertical shifts were significantly higher with the AlignRT system compared to “lasers and skin marks”. There was no significant difference between the two cohorts for roll shifts. Every residual set-up error was < 0.5cm or < 1° for both cohorts.
At the first session, prepositioning time and positioning time were longer with AlignRT compared to “lasers and skin marks”, but there was no significant difference for positioning time and prepositioning time regarding all sessions. There would even be a significant lower positioning time with AlignRT if only unilateral locations are considered.
Conclusion
AlignRT and “lasers and skin marks» methods are consistent towards translation and rotation shifts. However, AlignRT present a lower positioning time than “lasers and skin marks” for unilateral location. In addition, AlignRT offers the advantage of automatic monitoring based on the quantification of intra fraction movement. To conclude, AlignRT is an efficient system for the initial set up of VMAT breast or chest wall involving lymph nodes radiotherapy.