[Risk analysis study for patients care in radiotherapy: Learning curve and methodological evolution]

PURPOSE

To describe the evaluation of our risk mapping methodology over the past two years.

MATERIALS AND METHODS

Based on the FMEA (failure mode effects analysis) method, some aspects have been adapted, e.g. the concept of risk control and effort scale, some others have been introduced, e.g. the concept of residual risk management. A weekly meeting is scheduled by a multidisciplinary team in order to support the different projects.

RESULTS

Experiments and practice have led us to upgrade our scales of gravity and detectability, identify critical points and introduce the residual risk management concept. Some difficulties with regards to the multiplicity of scenarios still prevail.

CONCLUSION

Risk mapping is an essential tool in the implementation of risk quality management, specifically when the methodology is progressive and takes into consideration all the members of a pluridisciplinary team.

[Interobserver variability study for daily cone beam computed tomography registration of prostate volumetric modulated arc therapy]

PURPOSE

This work evaluated the interobserver variability in cone beam computed tomography (CBCT) registration for prostate cancers treated with intensity-modulated radiotherapy.

MATERIAL AND METHODS

Twelve technologists realized 286 CBCT/CT registrations (bone registration followed by prostate to prostate registration). The registration results were compared to those obtained by two radiation oncologists (reference). Each technologist reported the shifts calculated by the software in all three axes. A statistical analysis allowed us to calculate the minimum threshold under which 95% of the observers found similar values. A variance analysis followed by the post hoc test were used to find differences in interobserver registration variability and determine whether any individual users performed registrations which differed significantly from those of the other users.

RESULTS

The registration differences compared to the reference in the three directions in terms of 95th percentile are: 2.1mm left-right, 3.5mm target-gun, 7.3mm anterior-posterior. In the posterior direction, 4% of the observers have found differences superior to 8mm, margin used in routine without the use of a daily CBCT. The variance test revealed a P-value <0.05 only for target-gun and for all observers there was no significant difference compared to the reference.

CONCLUSION

This study confirmed the interest of a 3D tissue registration for prostate treatments. The registration study showed a good interobserver reproducibility. This showed the importance of a daily CBCT/CT registration in prostate treatment with the possibility of a planning target volume margin reduction in the three directions. An evaluation of a partial delegation of registration to technologists should be done by the radiation oncologists.