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The influence of breathing motion and a variable relative biological effectiveness in proton therapy of left-sided breast cancer
Stockholm University, Faculty of Science, Department of Physics. RaySearch Laboratories, Sweden.
Stockholm University, Faculty of Science, Department of Physics. Karolinska Institutet, Sweden.ORCID iD: 0000-0002-7101-240X
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2017 (English)In: Acta Oncologica, ISSN 0284-186X, E-ISSN 1651-226X, Vol. 56, no 11, p. 1428-1436Article in journal (Refereed) Published
Abstract [en]

Background: Proton breast radiotherapy has been suggested to improve target coverage as well as reduce cardiopulmonary and integral dose compared with photon therapy. This study aims to assess this potential when accounting for breathing motion and a variable relative biological effectiveness (RBE).

Methods: Photon and robustly optimized proton plans were generated to deliver 50 Gy (RBE) in 25 fractions (RBE=1.1) to the CTV (whole left breast) for 12 patients. The plan evaluation was performed using the constant RBE and a variable RBE model. Robustness against breathing motion, setup, range and RBE uncertainties was analyzed using CT data obtained at free-breathing, breath-hold-at-inhalation and breath-hold-at-exhalation.

Results: All photon and proton plans (RBE=1.1) met the clinical goals. The variable RBE model predicted an average RBE of 1.18 for the CTVs (range 1.14–1.21) and even higher RBEs in organs at risk (OARs). However, the dosimetric impact of this latter aspect was minor due to low OAR doses. The normal tissue complication probability (NTCP) for the lungs was low for all patients (<1%), and similar for photons and protons. The proton plans were generally considered robust for all patients. However, in the most extreme scenarios, the lowest dose received by 98% of the CTV dropped from 96 to 99% of the prescribed dose to around 92–94% for both protons and photons. Including RBE uncertainties in the robustness analysis resulted in substantially higher worst-case OAR doses.

Conclusions: Breathing motion seems to have a minor effect on the plan quality for breast cancer. The variable RBE might impact the potential benefit of protons, but could probably be neglected in most cases where the physical OAR doses are low. However, to be able to identify outlier cases at risk for high OAR doses, the biological evaluation of proton plans taking into account the variable RBE is recommended.

Place, publisher, year, edition, pages
2017. Vol. 56, no 11, p. 1428-1436
National Category
Cancer and Oncology
Identifiers
URN: urn:nbn:se:su:diva-146097DOI: 10.1080/0284186X.2017.1348625ISI: 000423464400013OAI: oai:DiVA.org:su-146097DiVA, id: diva2:1135169
Available from: 2017-08-22 Created: 2017-08-22 Last updated: 2018-03-05Bibliographically approved
In thesis
1. Proton plan evaluation: a framework accounting for treatment uncertainties and variable relative biological effectiveness
Open this publication in new window or tab >>Proton plan evaluation: a framework accounting for treatment uncertainties and variable relative biological effectiveness
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2017. p. 47
Keywords
Proton therapy, Relative biological effectiveness, Robustness evaluation, Plan selection
National Category
Other Physics Topics
Research subject
Medical Radiation Physics
Identifiers
urn:nbn:se:su:diva-146256 (URN)
Presentation
2017-09-19, CCK Lecture Hall (R8), Karolinska University Hospital, Stockholm, 10:00 (English)
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Supervisors
Available from: 2017-08-29 Created: 2017-08-28 Last updated: 2017-09-15Bibliographically approved

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