Inter- and intrafraction dose variations in robotic stereotactic body radiation therapy (SBRT) for perihilar cholangiocarcinoma in the prospective phase I STRONG trial

Chiara Paronetto; Wilhelm den Toom; Maaike T W Milder; Yvette van Norden; Rogier Baak; Ben J M Heijmen; Alejandra Méndez Romero

doi:10.3389/fonc.2023.1114737

Inter- and intrafraction dose variations in robotic stereotactic body radiation therapy (SBRT) for perihilar cholangiocarcinoma in the prospective phase I STRONG trial

Front Oncol. 2023 Mar 8:13:1114737. doi: 10.3389/fonc.2023.1114737. eCollection 2023.

Authors

Chiara Paronetto^{1

2}, Wilhelm den Toom¹, Maaike T W Milder¹, Yvette van Norden¹, Rogier Baak¹, Ben J M Heijmen¹, Alejandra Méndez Romero¹

Affiliations

¹ Department of Radiotherapy, Erasmus MC Cancer Institute, University Medical Center Rotterdam, Rotterdam, Netherlands.
² Department of Radiotherapy, Istituto Oncologico Veneto (IOV), Padova, Italy.

Abstract

Using fiducial-marker-based robotic respiratory tumor tracking, we treated perihilar cholangiocarcinoma patients in the STRONG trial with 15 daily fractions of 4 Gy. For each of the included patients, in-room diagnostic-quality repeat CTs (rCT) were acquired pre- and post-dose delivery in 6 treatment fractions to analyze inter- and intrafraction dose variations. Planning CTs (pCTs) and rCTs were acquired in expiration breath-hold. Analogous to treatment, spine and fiducials were used to register rCTs with pCTs. In each rCT, all OARs were contoured, and the target was rigidly copied from the pCT based on grey values. The rCTs acquired were used to calculate the doses to be delivered through the treatment-unit settings. On average, target doses in rCTs and pCTs were similar. However, due to target displacements relative to the fiducials in rCTs, 10% of the rCTs showed PTV coverage losses of >10%. Although target coverages had been planned below desired values in order to protect OARs, many pre-rCTs contained OAR constraint violations: 44.4% for the 6 major constraints. Most OAR dose differences between pre- and post-rCTs were not statistically significant. The dose deviations observed in repeat CTs represent opportunities for more advanced adaptive approaches to enhancing SBRT treatment quality.

Keywords: Inter- and intrafraction dose variations; adaptive radiotherapy (ART); perihilar cholangiocarcinoma; robotic tumor tracking; stereotactic body radiation therapy (SBRT).