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Table 2 Application of failure mode and effects analysis for the treatment planning stage in proton beam radiotherapy

From: Application of failure mode and effects analysis to treatment planning in scanned proton beam radiotherapy

Sub-process N Potential failure mode Potential causes of failure Potential effects of failure O S D RPN
(I) Selection of the reference CT scan for planning 1 Error in selecting the CT scan (e.g. incorrect patient set up, outdated representation of the anatomy) in case of multiple CT scans Human error, failure in the communication between operators Wrong dose distribution/wrong dose delivery 3 8 4 96
2 Outdated representation of the anatomy (single CT scan) Anatomical changes (related to time delay) Wrong dose distribution/wrong dose delivery 3 8 8 192
(III) Manual correction of external contour 3 Incorrect external contour definition (body or patient mask countour underestimation, i.e. not fully included in the external contour) Human error Wrong dose distribution / wrong dose delivery 4 5 4 80
  4 Failure of object/region identification Human error Wrong dose distribution 3 8 4 96
5 Inaccurate delineation Human error Wrong dose distribution 4 6 6 144
(IV) Delineation of CT artefacts, altered structures, metal implants and manual assignment of specific HU numbers
6 Incorrect HU number manual assignment Human error or lack of documentation from the referring clinicians (e.g. surgeons) Wrong dose distribution 4 7 7 196
  7 Lack of couch origin of coordinates definition Human error Unintended normal tissue irradiated and CTV missing 3 10 3 90
(IX) Couch origin of coordinates identification for absolute positioning 8 Wrong definition of couch origin of coordinates (large amount) Human error Unintended normal tissue irradiated and CTV missing 3 10 3 90
9 Wrong definition of couch origin of coordinates (small amount, in terms of 2–3 mm) Human error Unintended normal tissue irradiated and CTV missing 4 5 6 120
(XI) Target selection and dose prescription for each target (dose prescription type - point or volume, mean, median, minimum-, total dose, fractionation scheme) 10 Wrong setting of dose prescription type Human error Wrong dose delivery 3 8 4 96
11 Wrong dose fractionation setting Human error and lack of verbal-written communication (patient chart) Wrong dose delivery 2 10 4 80
  12 Improper selection of gantry angle/couch rotation: beam passing through OARs, when otherwise avoidable Inadequate operator skill Sub-optimal treatment quality: increased treatment toxicity 4 6 4 96
(XV - XVI) Selection of field direction (gantry angle and couch rotation) 13 Improper selection of gantry angle/couch rotation: beam stopping against OARs, when otherwise avoidable Inadequate operator skill Low plan robustness (range uncertainty) 4 8 4 128
14 Improper selection of gantry angle/couch rotation: beam passing through unstable tissues (such as bowel), when otherwise avoidable Inadequate operator skill Low plan robustness (range uncertainty) 3 8 5 120
(XVII) Setting of pencil beam parameters: 15 Improper selection of beam parameters: FWHM, scanning or energy step too large in relationship to PTV volume Inadequate operator skill Sub-optimal treatment quality: increased treatment toxicity or reduced TCP 4 5 4 80
- FWHM
- scanning step in the transversal plane
- energy step
- passive elements
(XIX) Definition of dose calculation parameters: 16 Improper selection of physical beam model and/or calculation grid Human error due to time pressure or inadequate skills Wrong dose distribution 4 7 5 140
- physical beam model 17 Improper selection of properties of the particles per spot matrix Human error Sub-optimal treatment quality 4 4 5 80
- dose calculation grid
- properties of the particles per spot matrix
- dose calculation algorithm, nuclear correction, spot decomposition
(XX) Setting of the optimization modality (SFUD, IMPT) 18 Improper selection of IMPT modality Inadequate operator skill Low plan robustness: increased treatment toxicity or reduced TCP 4 5 4 80
(XXII) Initial/iterative definition of target/OAR constraints and weights for dose optimization 19 Wrong or incomplete definition of one or more dose constraints Inadequate operator skill or inattention Sub-optimal treatment quality 4 8 3 96
(XXV) Plan evaluation 20 Improper acceptance of results Time pressure or inadequate operator skill Sub-optimal treatment quality 5 4 4 80
(XXVI) Production of competing plan 21 Lack of producing enough competing plans Time pressure or inadequate operator skill Sub-optimal treatment quality 5 4 4 80
(XXVIII) Creation of set-up fields and calculation of DRRs 22 Wrong definition of field isocenter (small amount 2 mm) Human error Wrong dose delivery 3 5 8 120
(XXX) Plan approval 23 Approval of wrong plan Human error, failure in the communication between operators Wrong delivery 3 8 5 120
  1. Failure modes having an assigned RPN ≥80 are reported.