Four-dimensional treatment planning strategies for dynamic tumor tracking

Emilie E Carpentier; Ronan L McDermott; Marie-Laure A Camborde; Tania Karan; Alanah M Bergman; Ante Mestrovic

doi:10.1002/acm2.14269

Four-dimensional treatment planning strategies for dynamic tumor tracking

J Appl Clin Med Phys. 2024 Jan 18:e14269. doi: 10.1002/acm2.14269. Online ahead of print.

Authors

Emilie E Carpentier^{1

2}, Ronan L McDermott³, Marie-Laure A Camborde², Tania Karan², Alanah M Bergman², Ante Mestrovic²

Affiliations

¹ Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada.
² Department of Medical Physics, BC Cancer - Vancouver, Vancouver, British Columbia, Canada.
³ Radiation Oncology, BC Cancer Vancouver, Vancouver, British Columbia, Canada.

PMID: 38235952
DOI: 10.1002/acm2.14269

Abstract

Introduction: Dynamic tumor tracking (DTT) is a motion management technique where the radiation beam follows a moving tumor in real time. Not modelling DTT beam motion in the treatment planning system leaves an organ at risk (OAR) vulnerable to exceeding its dose limit. This work investigates two planning strategies for DTT plans, the "Boolean OAR Method" and the "Aperture Sorting Method," to determine if they can successfully spare an OAR while maintaining sufficient target coverage.

Materials and methods: A step-and-shoot intensity modulated radiation therapy (sIMRT) treatment plan was re-optimized for 10 previously treated liver stereotactic ablative radiotherapy patients who each had one OAR very close to the target. Two planning strategies were investigated to determine which is more effective at sparing an OAR while maintaining target coverage: (1) the "Boolean OAR Method" created a union of an OAR's contours from two breathing phases (exhale and inhale) on the exhale phase (the planning CT) and protected this combined OAR during plan optimization, (2) the "Aperture Sorting Method" assigned apertures to the breathing phase where they contributed the least to an OAR's maximum dose.

Results: All 10 OARs exceeded their dose constraints on the original plan four-dimensional (4D) dose distributions and average target coverage was V_100% = 91.3% ± 2.9% (ranging from 85.1% to 94.8%). The "Boolean OAR Method" spared 7/10 OARs, and mean target coverage decreased to V_100% = 87.1% ± 3.8% (ranging from 80.7% to 93.7%). The "Aperture Sorting Method" spared 9/10 OARs and the mean target coverage remained high at V_100% = 91.7% ± 2.8% (ranging from 84.9% to 94.5%).

Conclusions: 4D planning strategies are simple to implement and can improve OAR sparing during DTT treatments. The "Boolean OAR Method" improved sparing of OARs but target coverage was reduced. The "Aperture Sorting Method" further improved sparing of OARs and maintained target coverage.

Keywords: 4D dose calculation; 4D treatment planning; dynamic tumor tracking; gimballed linac system.