ESTRO meets Asia 2024 - Abstract Book

S335

Physics – Motion management and adaptive radiotherapy

ESTRO meets Asia 2024

Totally 101 CBCTs (101 treatment fractions) were analyzed after excluding the artifacts. The GTV motions were exceeding >5mm, >7mm and >10 mm in 58%, 26% and 6% of total treatment fractions.

Table 1: GTV motion and its variations

LR direction

SI direction

AP direction

Maximal GTV motion

1.07 cm

1.5 cm

1.03 cm

0.30 cm (0.15 to 0.75 cm) ( p<0.001 )

0.28 cm (0.16 to 0.51 cm) ( p<0.047 )

0.29 cm (0.16 to 0.48 cm) ( p<0.001 )

GTV variation (median)

Extent of GTV motion (mean)

0.42 ± 0.41 cm

0.58 ± 0.57 cm

0.43 ± 0.39 cm

Table 2: variations of GTV motion with chest expansion

Chest

expansion

LR

SI

AP

DSC

(cm)

0.30 cm (r= -.560)

0.27 cm (r= -.386)

0.78

<2 cm (7 patients)

0.32 cm (r= .386)

≥2 cm (3 patients)

0.15 cm (r=-.866)

0.47 cm (r=.000)

0.28 cm (r= -.866)

0.76

Overall

chest

0.30 cm (r= -.341) (p=0.01)

0.29 cm (r= -.866)

0.28 cm (r= .075)

0.75 (p<0.001)

expansion

Table 3: Variation of GTV motion with the tumour location in the mediastinum

Extent of GTV motion

Supra-mediastinum

Infra-mediastinum

P value

LR

0.37 ± 0.36 cm

0.46 ± 0.41 cm

p=0.954

SI

0.69 ± 0.66 cm

0.48 ± 0.47 cm

p<0.001

AP

0.47 ± 0.46 cm

0.38 ± 0.31 cm

p=0.04

Conclusion:

From this first pilot study, we are concluding that

• High chest expansion associated with better control of GTV motion • Tumour location in the mediastinum plays the main role in the direction of the GTV motion • Additional ITV margin required for mediastinal tumour in addition to the 5 mm PTV margin (the extent of GTV motion is more than 4 mm and the GTV motion exceeded the 5 mm PTV margin in 58 % of total treatment fractions)