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Isodoses—a set theory-based patient-specific QA measure to compare planned and delivered isodose distributions in photon radiotherapy

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Abstract

Background

The gamma index and dose–volume histogram (DVH)-based patient-specific quality assurance (QA) measures commonly applied in radiotherapy planning are unable to simultaneously deliver detailed locations and magnitudes of discrepancy between isodoses of planned and delivered dose distributions. By exploiting statistical classification performance measures such as sensitivity or specificity, compliance between a planned and delivered isodose may be evaluated locally, both for organs-at-risk (OAR) and the planning target volume (PTV), at any specified isodose level. Thus, a patient-specific QA tool may be developed to supplement those presently available in clinical radiotherapy.

Materials and methods

A method was developed to locally establish and report dose delivery errors in three-dimensional (3D) isodoses of planned (reference) and delivered (evaluated) dose distributions simultaneously as a function the dose level and of spatial location. At any given isodose level, the total volume of delivered dose containing the reference and the evaluated isodoses is locally decomposed into four subregions: true positive—subregions within both reference and evaluated isodoses, true negative—outside of both of these isodoses, false positive—inside the evaluated isodose but not the reference isodose, and false negatives—inside the reference isodose but not the evaluated isodose. Such subregions may be established over the whole volume of delivered dose. This decomposition allows the construction of a confusion matrix and calculation of various indices to quantify the discrepancies between the selected planned and delivered isodose distributions, over the complete range of values of dose delivered. The 3D projection and visualization of the spatial distribution of these discrepancies facilitates the application of the developed method in clinical practice.

Results

Several clinical photon radiotherapy plans were analyzed using the developed method. In some plans at certain isodose levels, dose delivery errors were found at anatomically significant locations. These errors were not otherwise highlighted—neither by gamma analysis nor by DVH-based QA measures. A specially developed 3D projection tool to visualize the spatial distribution of such errors against anatomical features of the patient aids in the proposed analysis of therapy plans.

Conclusions

The proposed method is able to spatially locate delivery errors at selected isodose levels and may supplement the presently applied gamma analysis and DVH-based QA measures in patient-specific radiotherapy planning.

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Abbreviations

DTA:

distance to agreement

DVH:

dose–volume histogram

FN:

false negative

FP:

false positive

MC:

Monte Carlo

TN:

true negative

TP:

true positive

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Funding

Kinga Jeleń acknowledges the support of InterDokMed project No. POWR.03.02.00-00-I013/16. This work was supported by the POIR.04.04.00-00-15E5/18 project. The POIR.04.04.00-00-15E5/18 project is carried out within the “TEAM-NET” program of the Foundation for Polish Science co-financed by the European Union under the European Regional Development Fund.

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Authors and Affiliations

  1. AGH University of Science and Technology, Al. Mickiewicza 30, 30-059, Krakow, Poland

    Mateusz Baran, Zbisław Tabor, Krzysztof Rzecki, Bohdan Forostianyi, Konrad Bałabuszek & Robert Koziarski

  2. Maria Skłodowska-Curie National Research Institute of Oncology Krakow Branch, Garncarska 11, 31-115, Krakow, Poland

    Damian Kabat & Monika Tulik

  3. Faculty of Materials Science and Physics, Cracow University of Technology, Podchorążych 1, 30-084, Krakow, Poland

    Mateusz Baran, Zbisław Tabor, Krzysztof Rzecki & Michael P. R. Waligórski

  4. Institute of Nuclear Physics Polish Academy of Sciences, Radzikowskiego 152, 31-342, Kraków, Poland

    Kinga Jeleń & Michael P. R. Waligórski

Authors
  1. Mateusz Baran
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  2. Zbisław Tabor
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  3. Damian Kabat
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  4. Monika Tulik
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  5. Kinga Jeleń
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  6. Krzysztof Rzecki
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  7. Bohdan Forostianyi
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  8. Konrad Bałabuszek
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  9. Robert Koziarski
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  10. Michael P. R. Waligórski
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Contributions

MB conceived the work, conducted the simulations, wrote the manuscript and revised it. ZT conceived the work, performed the subsequent analyses, wrote the manuscript and revised it. DK, MT, KJ, and KR conducted the measurements, wrote the manuscript and revised it. MB, BF, KB and RK developed the graphic representation of the isodose analysis and illustrated the clinical examples. MW wrote, edited and revised the manuscript.

Corresponding author

Correspondence to Zbisław Tabor.

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Conflict of interest

M. Baran, Z. Tabor, D. Kabat, M. Tulik, K. Jeleń, K. Rzecki, B. Forostianyi, K. Bałabuszek, R. Koziarski and M.P. R. Waligórski declare that they have no competing interests.

Supplementary Information

Table S.1.

Summary of 23 plans selected from the Head–Neck Cetuximab. Region of interest (ROI) names according to the DICOM RTStruct files are used. The isodose was selected as the planned dose for planning target volume (PTV) regions and, for organs-at-risk (OAR) regions, by taking the isodose for which the volume of the hot region is the largest. For OAR regions, if for any isodose of the hot region the volume of 0.03 cm3 was not exceeded, N/A was written instead, to indicate that our isodose analysis did not detect any notable hot regions. In the table ∆D5% and ∆D95% are differences between simulated and planned doses to, respectively, 5% and 95% of ROI volume and GPR is gamma passing rate.

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Baran, M., Tabor, Z., Kabat, D. et al. Isodoses—a set theory-based patient-specific QA measure to compare planned and delivered isodose distributions in photon radiotherapy. Strahlenther Onkol 198, 849–861 (2022). https://doi.org/10.1007/s00066-022-01964-9

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