Dosimetric effect of respiratory motion on planned dose in whole-breast volumetric modulated arc therapy using moderate and ultra-hypofractionation

Mikko Mankinen; Tuomas Virén; Jan Seppälä; Heikki Hakkarainen; Tuomas Koivumäki

doi:10.1186/s13014-022-02014-5

Dosimetric effect of respiratory motion on planned dose in whole-breast volumetric modulated arc therapy using moderate and ultra-hypofractionation

Radiat Oncol. 2022 Mar 5;17(1):46. doi: 10.1186/s13014-022-02014-5.

Authors

Mikko Mankinen^{1

2}, Tuomas Virén³, Jan Seppälä³, Heikki Hakkarainen⁴, Tuomas Koivumäki^{5

4}

Affiliations

¹ Department of Physics, University of Jyväskylä (JYU), P.O. Box 35, FI-40014, Jyväskylä, Finland. mikko.mankinen@ksshp.fi.
² Department of Medical Physics, Central Finland Health Care District, Hoitajantie 3, FI-40620, Jyväskylä, Finland. mikko.mankinen@ksshp.fi.
³ Center of Oncology, Kuopio University Hospital (KUH), Kuopio, Finland.
⁴ Department of Medical Physics, Central Finland Health Care District, Hoitajantie 3, FI-40620, Jyväskylä, Finland.
⁵ Department of Physics, University of Jyväskylä (JYU), P.O. Box 35, FI-40014, Jyväskylä, Finland.

Abstract

Background and purpose: The interplay effect of respiratory motion on the planned dose in free-breathing right-sided whole-breast irradiation (WBI) were studied by simulating hypofractionated VMAT treatment courses.

Materials and methods: Ten patients with phase-triggered 4D-CT images were included in the study. VMAT plans targeting the right breast were created retrospectively with moderately hypofractionated (40.05 Gy in 15 fractions of 2.67 Gy) and ultra-hypofractionated (26 Gy 5 fractions of 5.2 Gy) schemes. 3D-CRT plans were generated as a reference. All plans were divided into respiratory phase-specific plans and calculated in the corresponding phase images. Fraction-specific dose was formed by deforming and summing the phase-specific doses in the planning image for each fraction. The fraction-specific dose distributions were deformed and superimposed onto the planning image, forming the course-specific respiratory motion perturbed dose distribution. Planned and respiratory motion perturbed doses were compared and changes due to respiratory motion and choice of fractionation were evaluated.

Results: The respiratory motion perturbed PTV coverage (V95%) decreased by 1.7% and the homogeneity index increased by 0.02 for VMAT techniques, compared to the planned values. Highest decrease in CTV coverage was 0.7%. The largest dose differences were located in the areas of steep dose gradients parallel to respiratory motion. The largest difference in DVH parameters between fractionation schemes was 0.4% of the prescribed dose. Clinically relevant changes to the doses of organs at risk were not observed. One patient was excluded from the analysis due to large respiratory amplitude.

Conclusion: Respiratory motion of less than 5 mm in magnitude did not result in clinically significant changes in the planned free-breathing WBI dose. The 5 mm margins were sufficient to account for the respiratory motion in terms of CTV dose homogeneity and coverage for VMAT techniques. Steep dose gradients near the PTV edges might decrease the CTV coverage. No clinical significance was found due to the choice of fractionation.

Keywords: Breast cancer; Respiratory motion; Ultra-hypofractionation; Volumetric modulated arc therapy; Whole-breast irradiation.

MeSH terms

Humans
Lung Neoplasms / radiotherapy*
Radiation Dose Hypofractionation*
Radiometry
Radiotherapy Dosage
Radiotherapy, Intensity-Modulated / methods*
Retrospective Studies