Setup error assessment based on "Sphere-Mask" Optical Positioning System: Results from a multicenter study

Abstract

Background: The setup accuracy plays an extremely important role in the local control of tumors. The purpose of this study is to verify the feasibility of "Sphere-Mask" Optical Positioning System (S-M_OPS) for fast and accurate setup.

Methods: From 2016 to 2021, we used S-M_OPS to supervise 15441 fractions in 1981patients (with the cancer in intracalvarium, nasopharynx, esophagus, lung, liver, abdomen or cervix) undergoing intensity-modulated radiation therapy (IMRT), and recorded the data such as registration time and mask deformation. Then, we used S-M_OPS, laser line and cone beam computed tomography (CBCT) for co-setup in 277 fractions, and recorded laser line-guided setup errors and S-M_OPS-guided setup errors with CBCT-guided setup result as the standard.

Results: S-M_OPS supervision results: The average time for laser line-guided setup was 31.75s. 12.8% of the reference points had an average deviation of more than 2 mm and 5.2% of the reference points had an average deviation of more than 3 mm. Co-setup results: The average time for S-M_OPS-guided setup was 7.47s, and average time for CBCT-guided setup was 228.84s (including time for CBCT scan and manual verification). In the LAT (left/right), VRT (superior/inferior) and LNG (anterior/posterior) directions, laser line-guided setup errors (mean±SD) were -0.21±3.13mm, 1.02±2.76mm and 2.22±4.26mm respectively; the 95% confidence intervals (95% CIs) of laser line-guided setup errors were -6.35 to 5.93mm, -4.39 to 6.43mm and -6.14 to 10.58mm respectively; S-M_OPS-guided setup errors were 0.12±1.91mm, 1.02±1.81mm and -0.10±2.25mm respectively; the 95% CIs of S-M_OPS-guided setup errors were -3.86 to 3.62mm, -2.53 to 4.57mm and -4.51 to 4.31mm respectively.

Conclusion: S-M_OPS can greatly improve setup accuracy and stability compared with laser line-guided setup. Furthermore, S-M_OPS can provide comparable setup accuracy to CBCT in less setup time.

Keywords: CBCT; S-M_OPS; laser line; radiotherapy; setup.

Figure 1

The workflow of S-M_OPS.

Figure 2

Reference positions of the positioning spheres in different parts (Upper left: top view; Upper right: skeletal diagram; Lower left: left view; Lower right: right view).

Figure 3

The workflow of clinical co-setup experiment.

Figure 4

Schematic diagram of CBCT tumor center, laser line tumor center, S-M_OPS tumor center, D_Laser and D_{S-M_OPS} .

Figure 5

(A) Histogram of setup time of laser line; (B) Histogram of mask deformation; (C) Histogram of setup error in the LAT direction; (D) Histogram of setup error in the VRT direction; (E) Histogram of setup error in the LNG direction.

Figure 6

Distributions of D_Laser and D_{S-M_OPS} in the LAT (left/right), VRT (superior/inferior) and LNG (anterior/posterior) and D ( $\text{D=}\sqrt{{\text{LAT}}^2+{\text{LNG}}^2+{\text{VRT}}^2}$ ) directions. (A) D_Laser -LAT; (B) D_{S-M_OPS} -LAT; (C) D_Laser -VRT; (D) D_{S-M_OPS} -VRT ; (E) D_Laser -LNG; (F) D_{S-M_OPS} -LNG; (G) D_Laser -D; (H) D_{S-M_OPS} -D.

Figure 7

95% Confidence intervals of D_Laser and D_{S-M_OPS} in different parts in the LAT, VRT, LNG and D directions. (A) Intracalvarium; (B) Nasopharynx; (C) Esophagus; (D) Lung; (E) Liver (F) Abdomen; (G) Cervix.

Figure 8

Comparison between laser line-guide setup consistency and S-M_OPS-guide setup consistency in different parts in the LAT, VRT, and LNG directions (A) Intracalvarium; (B) Nasopharynx; (C) Esophagus; (D) Lung; (E) Liver (F) Abdomen; (G) Cervix.