[Statistical Process Control (SPC) can help prevent treatment errors without increasing costs in radiotherapy].
OBJECTIVE
Statistical Process Control (SPC) was applied to monitor patient set-up in radiotherapy and, when the measured set-up error values indicated a loss of process stability, its root cause was identified and eliminated to prevent set-up errors.


METHODS
Set up errors were measured for medial-lateral (ml), cranial-caudal (cc) and anterior-posterior (ap) dimensions and then the upper control limits were calculated. Once the control limits were known and the range variability was acceptable, treatment set-up errors were monitored using sub-groups of 3 patients, three times each shift. These values were plotted on a control chart in real time.


RESULTS
Control limit values showed that the existing variation was acceptable. Set-up errors, measured and plotted on a X chart, helped monitor the set-up process stability and, if and when the stability was lost, treatment was interrupted, the particular cause responsible for the non-random pattern was identified and corrective action was taken before proceeding with the treatment.


CONCLUSIONS
SPC protocol focuses on controlling the variability due to assignable cause instead of focusing on patient-to-patient variability which normally does not exist. Compared to weekly sampling of set-up error in each and every patient, which may only ensure that just those sampled sessions were set-up correctly, the SPC method enables set-up error prevention in all treatment sessions for all patients and, at the same time, reduces the control costs.
Govindarajan
R
R
Departamento de Operaciones e Innovación, ESADE, Barcelona, España. rajaram@certificadoiso9001.com
Llueguera
E
E
Melero
A
A
Molero
J
J
Soler
N
N
Rueda
C
C
Paradinas
C
C
D003365:Costs and Cost Analysis; D003663:Decision Trees; D006801:Humans; D019300:Medical Errors / Q000517:prevention & control*; D056888:Patient Positioning / Q000592:standards*; D011878:Radiotherapy / Q000191:economics / Q000592:standards*