ESTRO 2022

Session Item

Saturday

May 07

09:00 - 10:00

Poster Station 2

02: Palliation, mixed sites

Chair: , The Netherlands

Session Code: 1190

Session Type: Poster Discussion

Track: Clinical

Benefit of replanning in MR-guided online adaptive radiation therapy in liver metastasis treatment

Michael Mayinger, Switzerland

Presentation Number: PD-0083

Abstract

Abstract Title:

Benefit of replanning in MR-guided online adaptive radiation therapy in liver metastasis treatment

Authors:

Michael Mayinger¹, Roman Ludwig¹, Sebastian Christ¹, Riccardo Dal Bello¹, Alex Ryu¹, Nienke Weitkamp¹, Matea Pavic¹, Helena Garcia Schüler¹, Lotte Wilke¹, Matthias Guckenberger¹, Jan Unkelbach¹, Stephanie Tanadini-Lang¹, Nicolaus Andratschke¹

¹University Hospital of Zurich, University of Zurich, Radiation Oncology, Zurich, Switzerland

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Purpose or Objective

To assess the effects of daily adaptive MR-guided replanning in stereotactic body radiation therapy (SBRT) of liver metastases based on a patient individual longitudinal dosimetric analysis.

Material and Methods

Fifteen patients assigned to SBRT for oligometastatic liver metastases underwent daily MR-guided target localization and on-table treatment plan re-optimization. A Monte Carlo algorithm based, intensity-modulated RT (IMRT) step and shoot treatment plan, referred to as “baseline plan (BP)” was calculated, using a grid spacing of 0.2 cm (Figure 1 A). Gross tumor volume (GTV) and organs at risk (OARs) were adapted to the anatomy-of-the-day. A rigidly shifted baseline plan (sBP; Figure 1 B) without re-optimization a reoptimized plan (RP; Figure 1 C) were generated for each fraction. After extraction of DVH parameters for GTV, planning target volume (PTV), and OARs (stomach, duodenum, bowel, liver, heart) plans were compared on a per-patient basis.

Figure 1:

Illustration of the benefit of reoptimization for patient A: (TOP) DVH comparison of baseline, rigidly shifted, and reoptimized plan; A Dose distribution of the baseline plan overlayed on the pre-treatment MR; B rigidly shifted plan overlayed on the MR of the first treatment fraction; C reoptimized plan for the first treatment fraction. Doses exceeding 45 Gy are shown. The contours displayed are the PTV (red) and the heart (rose).

Results

Median pre-treatment GTV and PTV were 14.9 cc (interquartile range (IQR): 7.7-32.9) and 62.7 cc (IQR: 42.4-105.5) respectively. SBRT with RP improved PTV coverage (V100%) for 47/75 of the fractions and reduced doses to the most proximal OARs (D1cc, Dmean) in 33/75 fractions compared to sBP. RP significantly improved PTV coverage (V100%) for metastases within close proximity to an OAR by 4.0% (≤ 0.2 cm distance from the edge of the PTV to the edge of the OAR; n = 7; p = 0.01; Figure 2), but only by 0.2% for metastases farther away from OAR (> 2 cm distance; n = 7; p = 0.37). No acute grade 3 treatment-related toxicities were observed.

Figure 2:
A Benefit of reoptimization, measured as improvement in ∆V100% as a function of the distance to the closest OAR.
B Location of metastasis in liver. Patients with a benefit of adaptation of ∆V100% > 1% are highlighted in cyan.

Conclusion

MR-guided online replanning SBRT improved target coverage and OAR sparing for liver metastases with a distance from the edge of the PTV to the nearest luminal OAR < 2 cm. Only marginal improvements in target coverage were observed for target distant to critical OARs, indicating that these patients do not benefit from daily adaptive replanning.