Abstract Book

S1291

ESTRO 37

Results All positioning errors were small, we found smaller errors for the Encompass/Hexapod combination after set-up correction and after treatment. Intra fraction movement was smaller for the BrainLab system. Overall rotations errors are smaller because of the use of the Hexapod couch (due to the 6D corrections). Results are shown in the Table. After Setup (AS) correction; After Radiation (AR); Intrafraction Movement (IM)

For 35 patients, treated from 2016 and onwards, the Encompass mask system was used (Qfix positioning), combined with the PreciseBite mouth piece (Civco medical solutions) (figure 1B). Patients were treated on different tumour sites with 5-30 fractions (median 15 fractions). During each fraction, 3 ConeBeam CTs (CBCTs) were made: before and after set-up correction, and after treatment. Corrections were performed using the 6D Hexapod couch (Elekta). We compared the data with the data reported in 2008 [1].

Translation s AS [mm]

Rotation s AS [º]

Translation s AR [mm]

Rotation s AR [º]

Translation s IM[mm]

Rotation s IM [º]

X

Y

Z

X

Y

Z

X

Y

Z

X

Y

Z

X

Y

Z

X

Y

Z

Brainlab -mask with Exactra c

- 0.0 3 0.0 6 0.2 1

- 0.0 2 0.1 5 0.1 5

- 0.0 1 0.2 5 0.3 5

- 0.0 2 0.1 7 0.2 9

- 0.0 4 0.3 8 0.5 2

- 0.0 3 0.4 6 0.4 2

0.0 6

0.0 4

0.0 2

0.0 5

0.0 7

0.1 3

Mean of means

-0.02

0.01

-0.39

0.02

-0.45

-0.11

0.1 7 0.2 7

0.1 3 0.3 0

0.4 9 0.4 6

0.2 2 0.4 2

0.4 7 0.4 3

0.5 2 0.3 9

Stdev of mean Mean of stdev Qfx- mask with Hexapo d

0.11

0.16

0.40

0.25

0.49

0.10

0.14

0.29

0.35

0.44

0.39

0.30

- 0.0 3 0.2 2 0.1 7

- 0.0 3 0.3 3 0.3 2

- 0.1 3 0.1 3 0.1 9

- 0.0 8 0.1 6 0.1 8

- 0.0 1 0.1 7 0.2 1

- 0.0 4 0.0 8 0.1 5

- 0.1 0 0.2 0 0.1 3

0.0 0

0.0 1

0.1 0

0.0 1

0.0 2

Mean of means

-0.10

-0.04

0.05

0.10

0.01

-0.02

0.0 6 0.1 3

0.2 3 0.3 2

0.2 6 0.3 0

0.1 2 0.1 8

0.2 0 0.3 1

Stdev of mean Mean of stdev

0.09

0.12

0.19

0.14

0.17

0.09

0.15

0.13

0.27

0.17

0.24

0.17

Conclusion Both systems demonstrated sub millimetre accuracy. Differences are small and not clinically relevant. The newly adopted procedure is safe. 1. Int. J. Radiation Oncology Biol. Phys., 2008; 72;1:261– 267