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Table 1 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 Potential failure mode
(III) Manual correction of external contour Lack of removal of metallic skin markers
(V) Localization of the origin of coordinates identified by lasers Incorrect localization of the origin of coordinates identified by lasers (small amount, 1–2 mm)
Incorrect localization of the origin of coordinates identified by lasers (large amount)
(VIII) Transfer of definitive isocenter coordinates to movable lasers if different from the origin of coordinates Lack of information transfer (no virtual simulation)
Wrong data transfer
Overwrite of file data
(XI) Target selection and dose prescription setting for each target (dose prescription type - point or volume, mean, median, minimum, - total dose, - fractionation scheme) Incomplete target selection
Wrong target selection
Wrong target dose prescription
(XIII) Assignment of targets to the field Incomplete or wrong target assignment
(XIV) Field isocenter position setting Incorrect isocenter definition
(XV - XVI) Selection of field direction (gantry angle and couch rotation) Improper selection of gantry angle/couch rotation: tissue interfaces lying parallel to beam direction, when otherwise avoidable (i.e. when more robust alternative geometry would be feasible)
Improper selection of gantry angle/couch rotation: not reachable position (potential collision or movement limitations)
(XVII) Setting of pencil beam parameters:  
- Full Width Half Maximum (FWHM) Improper selection of beam parameters: FWHM, scanning or energy step too low in relationship to the PTV volume
- scanning step in the transversal plane
- energy step
- passive elements (range shifter and ripple filter)
(XVIII) Selection of the physical and biological database for dose calculation Selection of unapproved (i.e. not validated for clinical practice, for experimental use only) database.
(XX) Setting of the optimization modality (SFUD, IMPT) Improper setting of the cost function parameters
Improper selection of optimization modality rather than IMPT
(XXVII) Evaluation of the best plan Improper selection of the best plan among the competing calculated onces in terms of optimal trade-off between plan quality (PTV dose coverage versus OAR sparing) and robustness
(XXVIII) Creation of set-up fields and calculation of DRRs Wrong definition of field isocenter (large amount)
Improper selection of parameters for DRR calculation
(XXXI) Selection of the phantom for the verification plan Improper phantom selection
  1. Failure modes having an assigned RPN value lower than 80 are listed.