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Characterization of Recombination Effects in a Liquid Ionization Chamber Used for the Dosimetry of a Radiosurgical Accelerator

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Adaptive fractionation at the MR-linac.

Y Pérez Haas¹, R Ludwig¹, R Dal Bello¹

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

Physics in Medicine and Biology

|January 3, 2023

Summary

This summary is machine-generated.

Adaptive fractionation (AF) adjusts radiation doses daily to maximize tumor dose, but typically offers only small benefits. However, AF shows significant potential for patients with large variations in tumor and organ geometry during treatment.

Keywords:

MR-guided radiotherapy Mr-linac adaptive fractionation adaptive radiotherapy inter-fraction motion

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Area of Science:

Radiation Oncology
Medical Physics
Image-Guided Therapy

Background:

Fractionated radiotherapy usually delivers a consistent dose per fraction.
Adaptive fractionation (AF) aims to optimize dose delivery by adjusting for daily variations in tumor and organ at risk (OAR) positions.

Purpose of the Study:

To develop and evaluate an AF algorithm for abdominal tumors treated with MR-linac.
To assess the potential of AF to increase tumor biologically effective dose (BED) while respecting OAR constraints.

Main Methods:

An AF algorithm was developed using dynamic programming to maximize expected tumor BED10 under OAR BED3 constraints.
The algorithm estimated daily sparing factors (OAR-to-tumor dose ratio) and used patient-specific data to predict future variations.
The algorithm was evaluated on 16 MR-linac patients with abdominal tumors previously treated in 5 fractions.

Main Results:

AF increased tumor BED10 in 14 of 16 patients compared to standard fractionation.
The average BED10 increase was modest (below 1 Gy in 11 patients).
Two patients with significant sparing factor variation experienced BED10 increases exceeding 10 Gy; one patient had a BED10 decrease due to unfavorable sparing factor sequence.

Conclusions:

Adaptive fractionation offers a modest average increase in tumor BED for abdominal tumors.
AF may provide substantial therapeutic gains for individual patients exhibiting large inter-fractional geometric variations.
Further investigation is warranted to optimize AF strategies for diverse patient anatomies and treatment scenarios.