ESTRO 2024 - Abstract Book

S895

Clinical - CNS

ESTRO 2024

Material/Methods:

Eighteen radiation oncologists participated in a virtual contouring laboratory as part of a nationwide multistep prospective study, regarding the management of postoperative SRT of brain metastases. The referral expert for each participant center received five cases, with relative imaging (pre and post-surgery T1 post gadolinium MRI), and CT simulation without contrast. Clinical cases were selected in order to evaluate various scenarios in relation to size, location and local extent of brain metastases pre-surgery. Specifically, case 1 concerned a supratentorial lesion <4 cm with dural/venous sinus contact from triple negative breast cancer. Case 2 involved an infratentorial lesion >4 cm with dural/venous sinus contact from NSCLC. Case 3 was a supratentorial lesion <4 cm with no contact from HER2+ breast cancer. Case 4 was an infratentorial lesion <4 cm with no contact from NSCLC; finally, the case 5 consisted in a supratentorial lesion >4 cm with dural contact from triple negative breast cancer. For each case, all radiation oncologists were required to delineate the clinical tumor volume (CTV), independently.

Results:

A total of 79 CTV was received. Results of IOV are showed in Table 1. For case 3, one CTV had a volume of 3.4 cc and a mean Dice of 0.3 (0.23-0.39, SD 0.05), strongly deviating from the others (Figure 1). Therefore, it was excluded from the calculation of the global mean Dice. Similarly, for case 5 one volume had a major deviation (Figure 2) with a volume of 67.9 cc and a mean Dice of 0.57 (0.45-0.69, SD 0.07). In general, CTV of case 3 showed the higher agreement as demonstrated by a mean Dice of 0.78, with minimum value of 0.72.

Dice similarity coefficient

Volume (cc) Mean (smallest-larger)

CT

Mean (95% CI)

Case 1

20.9 (15.2-35.5)

0.70 (95% CI, 0.62-0.77)

Case 2

45.3 (28.7-61.3)

0.72 (95% CI, 0.61-0.76)

Case 3

18.4 (3.4-25.4)

0.78 (95% CI, 0.72-0.82)

Case 4

8.1 (3.4-14.7)

0.70 (95% CI, 0.58-0.76)

Case 5

30.6 (19.5-67.9)

0.74 (95% CI, 0.7-0.78)