A dosimetric comparison of different radiotherapy modalities for Non-Resected oligometastatic liver Disease

The role of radiotherapy in the context of limited liver metastases is emerging rapidly with a variety of available technical approaches. Here, we provide a dosimetric comparison of three different radiotherapy modalities for non-resected liver metastases.

This multicentric study included 30 patients previously treated for solitary liver metastases. Interstitial high dose-rate brachytherapy (HDR), stereotactic body radiation therapy (SBRT), and kilovoltage electronic brachytherapy (eBT) with a single dwelling point, as an in this context novel modality, were planned with a 25-Gy single fraction and dosimetrically compared. The primary endpoint was difference in healthy liver tissue exposure. Secondary endpoints included target volume coverage, dose to the surrounding organs at risk (OARs), and radiation treatment time.

The median (range) lesion volume was 9.3 (2.5 - 29.7) cm³. Electronic BT yielded a significantly better OAR dose sparing compared to SBRT. Radiation exposure to the healthy liver was significantly lower with eBT (V9.1 Gy 13.8 [3.4-41.6] cm³) and HDR (49.2 [12.7-116.8] cm³) when compared with SBRT (98.8 [54.3-303.7] cm³; p < 0.001 for both). Mean treatment time was shortest for SBRT (6.1 min vs. 7.8 min for HDR [p = 0.003] vs. 16.1 min for eBT [p < 0.001]). Equally, CTV D90% and D95% were superior for SBRT (p < 0.001 vs. HDR and eBT).

Minimally invasive single-catheter eBT provides a new potential approach in the context of unresectable liver metastases, with optimal OAR dose sparing, yet suboptimal target volume coverage. Combining the advantages of both modalities, a multi-dwelling eBT approach as in HDR might ease applicability in clinical routine with optimized target coverage while maintaining excellent OAR doses. Future prospective investigations are required to further define its role within well-established liver-directed therapies.