Breathing-motion induced interplay effects for stereotactic body radiotherapy of liver tumours using flattening-filter free volumetric modulated arc therapy

Research output: Contribution to journalArticle

Abstract

The purpose of this study was to investigate breathing-motion induced interplay effects for stereotactic body radiotherapy (SBRT) of liver tumours treated with flattening-filter free (FFF) volumetric modulated arc therapy (VMAT). Ten patients previously treated with liver SBRT were included in this study. All patients had four-dimensional computed tomography (4DCT) scans acquired prior to treatment. The 4DCT was sorted into 8-10 phases covering an equal time interval. A FFF VMAT plan was created for one fraction in the mid-ventilation phase for each patient. To generate dose distributions including both interplay effects and dose blurring, a sub-plan was calculated for each phase. The total dose distributions were accumulated to the mid-ventilation phase using the deformed vector fields (DVF) from deformable image registration between the corresponding CT and the mid-ventilation phase CT. A blurred dose distribution, not including interplay effects, was also obtained by distributing the delivery of the whole plan uniformly on all phases, and was similarly accumulated to the mid-ventilation phase. To isolate interplay effects, this blurred dose distribution was subtracted from the total dose distribution with interplay effects. The near minimum dose (D 98%), mean dose (D mean), heterogeneity index (HI), and the near minimum dose difference (ΔD 98%) between the accumulated dose distributions with and without interplay effects were calculated within the gross tumour volume (GTV) for each patient. Comparing the accumulated dose distributions with and without interplay effects, the D 98% decreased for nine of the ten patients and the HI increased for all patients. The median and minimum differences in D 98% were  -2.1% and  -5.0% (p  =  0.006), respectively, and the median HI significantly increased from 6.2% to 12.2% (p  =  0.002). The median ΔD 98% was  -4.0% (range  -7% to  -1.5%). In conclusion, statistically significant breathing-induced interplay effects were observed for a single fraction of FFF VMAT liver SBRT, resulting in heterogeneous dose distributions within the GTV.

Details

Authors
Organisations
External organisations
  • Skåne University Hospital
  • Karolinska University Hospital
  • University of Gothenburg
  • Sahlgrenska University Hospital
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Cancer and Oncology
  • Radiology, Nuclear Medicine and Medical Imaging
Original languageEnglish
Article number025006
JournalPhysics in Medicine and Biology
Volume64
Issue number2
Publication statusPublished - 2019 Jan 8
Publication categoryResearch
Peer-reviewedYes