ESTRO 2024 - Abstract Book

S1686

Clinical - Lung

ESTRO 2024

Ultra-central tumors were defined as planning target volume (PTV) overlapping the trachea, proximal bronchial tree (PBT) or esophagus. An internal target volume (ITV) was generated from 4D-CT simulation scans and an isotropic margin of 5mm expanded from the ITV to form the PTV.

Lesions abutting PBT or trachea were further stratified based on proximity of GTV to the mainstem bronchus – Group A (tumors ≤ 1 cm from the main bronchi and trachea) or group B (all other tumors).

For all cases, the prescription isodose was kept between 80-90% and the maximum point doses (Dmax) received by the trachea, PBT and esophagus were limited to less than 105% of the prescription dose.

Clinical outcomes including local failure free survival, distant failure free survival and overall survival were calculated using the Kaplan-Meier method. Toxicity was graded by CTCAE v5.0. Fisher’s Exact Test was performed to determine if there were statistical differences in toxicity outcomes between Group A and B tumours

Results:

A total of 66 patients were analysed. 23 lesions were primary lung tumours and 43 were lung metastases. Median follow up was 54 months.

57 patients (86%) received 50Gy in 5 fractions, while 7 (10.6%) received 60Gy in 8 fractions and 2 (4%) received 35Gy in 5 fractions. The median prescription isodose was 85.55%.

Tumour PTV overlapped with the PBT or trachea in 61 lesions and oesophagus in 10 lesions.

1 year and 2 year local failure-free survival were 98% and 88% respectively. Median distant failure free survival was 28 months. Median overall survival was 59 months.

For lesions abutting PBT/trachea, for group A lesions, the incidence of G2 or above atelectasis or upper airway bleeding was 38% (4 cases of atelectasis and 4 cases of airway bleeding) while for Group B lesions it was 17.5% (6 cases of atelectasis, 1 case of bleeding).

Fisher’s exact test showed a statistically significant association between Group A lesions and incidence of G2 or above airway bleeding (p < 0.05).

For the 10 lesions overlapping with the esophagus, the incidence of G2 or above esophageal toxicity was 40% (one G5 esophageal ulcer bleeding, one G3 esophageal stricture and two cases of G2 dysphagia).

For the overall population G5 toxicity rate was 6% (one esophageal ulcer bleeding, one obstructive pneumonia, two cases of airway bleeding).

Conclusion:

In this cohort of 66 Chinese patients undergoing SBRT for ultra central lung lesions, high rates of local control were achieved with manageable toxicity. Slightly higher rates of symptomatic esophageal toxicity were observed for lesions overlapping the esophagus. Group A lesions were associated with higher incidence of symptomatic airway