Evaluation and improvement the safety of total marrow irradiation with helical tomotherapy using repeat failure mode and effects analysis

Table 2 Discription of 10-point scales used to derive values of probability, severity, and detectability for each failure mode

Rank	Occurence(O)	Severity(S)	Detectability(D)
1	Very low; less than 2%	No effect	Very easy to detect; alomost never miss
2	Very low; less than 2%	Inconvenience; discomfort or distress	Very easy to detect; alomost never miss
3	Low; approximately 5%	Inconvenience; discomfort or distress	Easy to detect, double check should be performed
4	Low; approximately 5%	Minor dosimetric error; approximately 5%	Easy to detect, double check should be performed
5	Moderate	Limited toxicity or underdose; 10% dose difference with insufficient accutacy	Moderate, a “lucky catch”
6	Medium; occasional failure		Very difficult to detect a subtle error in mechanical position or highly unusual situation, e.g., treatment table auto setup error
7	Medium; occasional failure	Serious toxicity or underdose; 20% dose difference, wrong site irradiation
8	High; repeated failures
9	High; repeated failures	Very serious toxicity; patient injury or death	Almost impossible to detect
10	Inevitable	Very serious toxicity; patient injury or death	Almost impossible to detect