Medical Physics Seminar – Friday, May 18, 2012
Improving Patient-Specific Pre-Treatment Quality Assurance
Heming Zhen (student of Dr. Wolfgang Tome)
Research Assistant, Department of Medical Physics, UW-School of Medicine & Public Health, Madison, WI - USA -
The rapid development of technology has brought us many advanced treatment techniques, as well as increasing sources of errors that sometimes makes the radiotherapy treatment more fragile. As a result, the role of pre-treatment patient-specific QA has become more important than ever before. This work presents the effort to improve the method and metric of pre-treatment patient-specific dose QA. Conventionally, patient-specific QA is performed by comparing the planned and measured phantom dose, and action levels are based on the Gamma passing rate that is generated from this comparison. However, through a correlation study, we found only weak to moderate correlation between the planar QA passing rate and patient DVH errors. Then we went on to perform similar study on 3D Gamma passing rate, both in phantom and in patient, and determined the conventional QA paradigm lacks predictive power to clinically important patient dose error. We then moved on to evaluated a commercially available QA system that is capable of predicting the delivered patient dose from phantom measurement. Upon the success of the validation, we demonstrated the use of radiobiological models (∆TCP and ∆NTCP) as QA metric, as well as its potential use in evaluating the robustness of a treatment plan under perturbation.