ESTRO 2024 - Abstract Book

S5626

RTT - Patient care, preparation, immobilisation and IGRT verification protocols

ESTRO 2024

2996

Digital Poster

Performance of large longitudinal shifts on treatment couches with automatic couch compensation

Tze Yee Lim, Xin Wang

University of Texas MD Anderson Cancer Center, Radiation Physics, Houston, USA

Purpose/Objective:

To determine whether couch longitudinal shifts should be performed in float mode or using the toggle (on the pendant or couch side panel) for multi-isocenter treatments involving large longitudinal shifts on Varian TrueBeam couches with automatic couch compensation. This is especially pertinent for craniospinal irradiation treatments and with the increasing use of volumetric arc therapy for total body/marrow irradiation.

Material/Methods:

A ruler was taped to a phantom with the ruler markings aligned vertically. The phantom was then set at the head of the couch at isocenter and aligned with lasers. The initial in-room vertical location, as indicated by the horizontal laser on the ruler, was recorded. Using the float mode, couch longitudinal shifts of 10 cm, 20 cm, 30 cm, 40 cm, 50 cm, 60 cm, 70 cm, and 80 cm were performed. At each increment, the phantom was moved back to isocenter, then the ruler indicated vertical location and the couch vertical coordinate as displayed on the computer monitor were recorded. Next, a stack of solid water amounting to approximately 30 kg was added to the head of the couch. Using the float mode, couch longitudinal shifts of 50 cm, 60 cm, 70 cm, and 80 cm were performed. Similarly, at each increment, the ruler-indicated vertical location at isocenter as well as the displayed couch vertical coordinate were recorded. The experiments described above, with and without the added weight, were then repeated using the toggle on the pendant to perform the couch shifts instead of using the float mode.

Results:

The ruler-indicated vertical location went down to -0.07 cm when the couch shifts were performed in the float mode, but went up to +0.46 cm when the couch shifts were performed with the toggle. The difference in displayed couch vertical coordinate were up to 0.51 cm when the couch shifts were performed in float mode, while it stayed the same when couch shifts were performed with the toggle. Therefore, when shifting the couch longitudinally in float mode, while the displayed couch vertical coordinate is different, the actual location difference is minimal at isocenter. Conversely, when shifting the couch longitudinally with the toggle, the impact on vertical alignment is ≥0.1 cm with >20 cm longitudinal shifts and ≥0.2 cm with >50 cm longitudinal shifts. With the added weight, the results were similar (ruler-indicated vertical location down to -0.05 cm with float mode but up to +0.50 cm with the toggle; displayed couch vertical coordinate up to 0.51 cm with float mode but same value with toggle).