Two‐dimensional <i>in vivo</i> dose verification using portal imaging and correlation ratios

Peca, Stefano; Brown, Derek

doi:10.1120/jacmp.v15i4.4752

Cited by 15 publications

(9 citation statements)

References 37 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The CAX EPID signal range over 18 weeks was very stable: the SD of the 10 readings was 0.9% of the mean signal. F and f correlation ratios were in agreement with previous reports 16 , 24 (eg, F for 6 MV in Figure 8 ).…”

Section: Resultssupporting

confidence: 93%

“…In our previous work, we proposed an empirical method to correct for this, based on the shape of F profiles for various field sizes and absorber thicknesses. 24 Although results were good along the central in-plane and cross-plane profiles, this solution was inadequate in the corners of larger (>10 × 10 cm 2 ) fields.…”

Section: Methodsmentioning

confidence: 99%

“…Previously, we presented preliminary results in anthropomorphic phantoms for a simple method for 2-D dose calculation using correlation ratios and an empirical off-axis correction. 24 In this article, we describe details of our improved model and test its ability to accurately calculate the dose. The purpose of this article is to allow other centers to adopt this method of EPID IVD.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

A Simple Method for 2-D In Vivo Dosimetry by Portal Imaging

Peca

Brown

Smith

2017

Technol Cancer Res Treat

Self Cite

View full text Add to dashboard Cite

Purpose:To improve patient safety and treatment quality, verification of dose delivery in radiotherapy is desirable. We present a simple, easy-to-implement, open-source method for in vivo planar dosimetry of conformal radiotherapy by electronic portal imaging device (EPID).Methods:Correlation ratios, which relate dose in the mid-depth of slab phantoms to transit EPID signal, were determined for multiple phantom thicknesses and field sizes. Off-axis dose is corrected for by means of model-based convolution. We tested efficacy of dose reconstruction through measurements with off-reference values of attenuator thickness, field size, and monitor units. We quantified the dose calculation error in the presence of thickness changes to simulate anatomical or setup variations. An example of dose calculation on patient data is provided.Results:With varying phantom thickness, field size, and monitor units, dose reconstruction was almost always within 3% of planned dose. In the presence of thickness changes from planning CT, the dose discrepancy is exaggerated by up to approximately 1.5% for 1 cm changes upstream of the isocenter plane and 4% for 1 cm changes downstream.Conclusion:Our novel electronic portal imaging device in vivo dosimetry allows clinically accurate 2-dimensional reconstruction of dose inside a phantom/patient at isocenter depth. Due to its simplicity, commissioning can be performed in a few hours per energy and may be modified to the user’s needs. It may provide useful dose delivery information to detect harmful errors, guide adaptive radiotherapy, and assure quality of treatment.

show abstract

Section: Resultssupporting

confidence: 93%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A Simple Method for 2-D In Vivo Dosimetry by Portal Imaging

Peca

Brown

Smith

2017

Technol Cancer Res Treat

Self Cite

View full text Add to dashboard Cite

show abstract

“…Early work involved using the central pixels of the EPID to measure the transmitted signal to determine the dose to the isocenter (9) . More recent work has enabled the photon fluence exiting the patient to be imaged and, from this, the dose inside the patient can be reconstructed (10,11) . In vivo portal dosimetry is of particular interest, as this can be used to calculate the 3D dose distribution within the patient based on images acquired during the treatment (12) .…”

Section: Introductionmentioning

confidence: 99%

Feasibility of portal dosimetry for flattening filter‐free radiotherapy

Chuter

Rixham

Weston

et al. 2016

J Applied Clin Med Phys

View full text Add to dashboard Cite

The feasibility of using portal dosimetry (PD) to verify 6 MV flattening filter‐free (FFF) IMRT treatments was investigated. An Elekta Synergy linear accelerator with an Agility collimator capable of delivering FFF beams and a standard iViewGT amorphous silicon (aSi) EPID panel (RID 1640 AL5P) at a fixed SSD of 160 cm were used. Dose rates for FFF beams are up to four times higher than for conventional flattened beams, meaning images taken at maximum FFF dose rate can saturate the EPID. A dose rate of 800 MU/min was found not to saturate the EPID for open fields. This dose rate was subsequently used to characterize the EPID for FFF portal dosimetry. A range of open and phantom fields were measured with both an ion chamber and the EPID, to allow comparison between the two. The measured data were then used to create a model within The Nederlands Kanker Instituut's (NKI's) portal dosimetry software. The model was verified using simple square fields with a range of field sizes and phantom thicknesses. These were compared to calculations performed with the Monaco treatment planning system (TPS) and isocentric ion chamber measurements. It was found that the results for the FFF verification were similar to those for flattened beams with testing on square fields, indicating a difference in dose between the TPS and portal dosimetry of approximately 1%. Two FFF IMRT plans (prostate and lung SABR) were delivered to a homogeneous phantom and showed an overall dose difference at isocenter of ∼0.5% and good agreement between the TPS and PD dose distributions. The feasibility of using the NKI software without any modifications for high‐dose‐rate FFF beams and using a standard EPID detector has been investigated and some initial limitations highlighted.PACS number: 87.55.Qr

show abstract

“…Also, most field incidences can be directly measured. The properties and adaptation requirements for the use of EPID as dosimeters have been evaluated in the literature 13 , 14 , 15 , 16 , 17 , 18 …”

Section: Introductionmentioning

confidence: 99%

EPID based in vivo dosimetry system: clinical experience and results

Celi

Costa

Wessels

et al. 2016

J Applied Clin Med Phys

View full text Add to dashboard Cite

Mandatory in several countries, in vivo dosimetry has been recognized as one of the next milestones in radiation oncology. Our department has implemented clinically an EPID based in vivo dosimetry system, EPIgray, by DOSISOFT S.A., since 2006. An analysis of the measurements per linac and energy over a two‐year period was performed, which included a more detailed examination per technique and treatment site over a six‐month period. A comparison of the treatment planning system doses and the doses estimated by EPIgray shows a mean of the differences of 1.9% (±5.2%) for the two‐year period. The 3D conformal treatment plans had a mean dose difference of 2.0% (±4.9%), while for intensity‐modulated radiotherapy and volumetric‐modulated arc therapy treatments the mean dose difference was −3.0 (±5.3%) and −2.5 (±5.2%), respectively. In addition, root cause analyses were conducted on the in vivo dosimetry measurements of two breast cancer treatment techniques, as well as prostate treatments with intensity‐modulated radiotherapy and volumetric‐modulated arc therapy. During the breast study, the dose differences of breast treatments in supine position were correlated to patient setup and EPID positioning errors. Based on these observations, an automatic image shift correction algorithm is developed by DOSIsoft S.A. The prostate study revealed that beams and arcs with out‐of‐tolerance in vivo dosimetry results tend to have more complex modulation and a lower exposure of the points of interest. The statistical studies indicate that in vivo dosimetry with EPIgray has been successfully implemented for classical and complex techniques in clinical routine at our institution. The additional breast and prostate studies exhibit the prospects of EPIgray as an easy supplementary quality assurance tool. The validation, the automatization, and the reduction of false‐positive results represent an important step toward adaptive radiotherapy with EPIgray.PACS number(s): 87.53.Bn, 87.55.Qr, 87.56.Fc, 87.57.uq

show abstract

Two‐dimensional in vivo dose verification using portal imaging and correlation ratios

Cited by 15 publications

References 37 publications

A Simple Method for 2-D In Vivo Dosimetry by Portal Imaging

A Simple Method for 2-D In Vivo Dosimetry by Portal Imaging

Feasibility of portal dosimetry for flattening filter‐free radiotherapy

EPID based in vivo dosimetry system: clinical experience and results

Contact Info

Product

Resources

About