ESTRO 2020 Abstract book

S412 ESTRO 2020

With more extensive imaging in diagnosis and follow-up of malignancies, adrenal metastases are more frequently identified. Studies show that patients with isolated adrenal metastases may benefit of local therapy. To improve local control precise dose delivery without increasing toxicity is vital. Decreasing the Clinical Target Volume (CTV) – Planning Target Volume (PTV) margins by reducing breathing movement could achieve this. In literature data concerning the effect of breath-hold (BH) in the radiotherapeutic treatment of adrenal metastases are scarce. This study investigates the potential of Active Breathing Control (ABC) to limit adrenal breathing movement and reduce CTV-PTV margins. Material and Methods We compared adrenal gland movement in free breathing (FB), making use of 4D-CT scans, and a BH technique (ABC). Data were used from a cohort of patients with liver metastases treated with Stereotactic Body Radiotherapy (SBRT) in BH of which at least one adrenal gland was visible on both scans. The coordinates of the adrenal glands on the ten phases of a 4D-CT (peak-to-peak amplitude) and on several repeat ABC CT-scans (standard deviation) were measured. Separate coordinates, the random margin component and margin vector norm were computed and compared between both techniques. Normality tests were executed and if needed a log transformation was performed. Depending on the data a paired or unpaired T-test was used (SPSS version 22). Results We compared both techniques in 11 patients (21 adrenal glands) and found the largest movement in the Z-direction, with values of 8.7±4.2 mm for FB and 2.4±1.5 mm for ABC. No large differences in the random margin component were found between both techniques, see the Table.

Table 1 shows the subject demographics. The lateral, longitudinal and vertical mean shift (mm) and ρ values were 0.8±0.6, 1.4±0.9, 0.6±0.75 and -0.14(p=0.67), 0.36(p=0.3), 0.36(p=0.31) respectively. The mean 3D vector was 0.7±0.63 with a ρ of 0.53(p=0.114).The mean rotation correction and ρ values were 0.91°±1.19, 0.03°±1.1, 0.43°±2.0 and 0.47(p=0.18), -0.25(p=-0.49), - 0.56(p=0.09) for pitch, roll and yaw respectively. The distribution of translational and rotational corrections is shown in Figure 1. The average DSC was 0.95±0.03 with ρ=0.26(p=0.46).

Random component [margin in mm]

4D-CT [x,y,z]

4D-CT vectornorm

ABC [x,y,z]

ABC vectornorm

[0.5, 1.1, 1.9] [0.2, 0.8, 0.8]

[0.6, 1.3, 1.7] [0.3, 0.9, 1.1]

Mean

2.3

2.3

0.9

1.3

SD

Conclusion In this preliminary study, the bra gives a promising reproducibility with a mean translational and rotational displacement of only about 1mm and 1° for all directions. All DSC values were above 0.9. It seems more deviation was found on larger breast size, especially in lateral and longitudinal direction, however no statistical difference was found. A future study on comparison between the reproducibility with and without bra with larger sample size on patients are needed to give a more concrete evaluation. PD-0677 Breath-hold versus free breathing in SBRT of adrenal metastases M. Mast 1 , M. De Kuijer 1 , J. Van Egmond 1 , E. Kouwenhoven 1 , D. Krist 1 , H. Ceha 1 1 Haaglanden Medical Centre, Radiation Therapy, Leidschendam, The Netherlands Purpose or Objective Although cancer treatment is improving, distant metastases occur. This is mostly related to a poor prognosis. However, this does not apply to patients with oligometastases, i.e. fewer than five distant metastases.

In 71% of the cases ABC resulted in a non-significant smaller margin component to FB (p≥0.4). There was a considerable variation of breathing motion among the patients. In some cases large amplitudes were found, being responsible for the major contribution to the margin. Also, our study showed that adrenal glands were more clearly visible on the ABC scans, see the sagittal view in the Figure.

Conclusion Movement of the adrenal gland is largest in the Z- direction. The mean difference in the margin vector norm between both techniques was small with large variations