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

Edvardsson, A. LU ; Scherman, J.; Nilsson, M. P. LU ; Wennberg, B.; Nordström, F.; Ceberg, C. LU and Ceberg, S. LU (2019) In Physics in Medicine and Biology 64(2).
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... (More)

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.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Physics in Medicine and Biology
volume
64
issue
2
publisher
IOP Publishing
external identifiers
  • scopus:85059927493
ISSN
1361-6560
DOI
10.1088/1361-6560/aaf5d9
language
English
LU publication?
yes
id
99336ee2-4b3d-490a-805b-6f097dc639a7
date added to LUP
2019-01-23 13:09:35
date last changed
2019-09-17 04:47:33
@article{99336ee2-4b3d-490a-805b-6f097dc639a7,
  abstract     = {<p>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.</p>},
  articleno    = {025006},
  author       = {Edvardsson, A. and Scherman, J. and Nilsson, M. P. and Wennberg, B. and Nordström, F. and Ceberg, C. and Ceberg, S.},
  issn         = {1361-6560},
  language     = {eng},
  month        = {01},
  number       = {2},
  publisher    = {IOP Publishing},
  series       = {Physics in Medicine and Biology},
  title        = {Breathing-motion induced interplay effects for stereotactic body radiotherapy of liver tumours using flattening-filter free volumetric modulated arc therapy},
  url          = {http://dx.doi.org/10.1088/1361-6560/aaf5d9},
  volume       = {64},
  year         = {2019},
}