Monthly Archives: September 2013

New Publication: Interplay of Target Motion and Dynamic VMAT Delivery for SBRT

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Together with Moffitt Cancer Center (Tampa, FL) and the team of Vladimir Feygelman, Ph.D., we continue our ongoing scientific studies with a new publication called “Experimentally studied dynamic dose interplay does not meaningfully affect target dose in VMAT SBRT lung treatments,” just published in Medical Physics 40(9). We are proud to say this paper was selected as one of the “Editor’s Picks” for this issue (which, among other things, means anybody can download the PDF of the article for free – a really nice feature offered by the Medical Physics journal).

Prior to this work, we had been building up our knowledge and toolset for analyzed 4D doses, specifically for volume-modulated arc therapy (VMAT). We applied to clinical SBRT plans (hypo-fractionated with 10 Gy/fraction, 5 total fractions), and at first we were surprised by our results. Then, as we set about understanding the interplay phenomenon for hypo-fractionated VMAT, it started to make more and more intuitive sense why we didn’t see interplay effects. First, the high dose per fraction ultimately allows for many cycles of breathing motion during each daily delivery, which tends to average out the interplay effect. Second, the VMAT segments tend to be less complex at any given time than dynamic IMRT segments (which we know are susceptible to interplay, at least per fraction), also working to drive down interplay. And finally, a strategy of optimization of our VMAT plans was to pump up the dose at the PTV periphery, i.e. purposely induce dose heterogeneity, and the benefits of this for a moving target are evidence in this paper....

New Publication: Bio-Models to Assess Plan Robustness / Dose QA

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It has my pleasure to work with my colleagues Wolfgang Tomé and Heming Zhen on a multi-phased study on the methods and metrics of patient-specific Dose QA.

Recently, we published our third paper on this topic called “On the use of biomathematical models in patient-specific IMRT dose QA,” which was published in Medical Physics 40(7). This paper looked at how to use biological model-based DVH reduction methods to analyze dose changes observed during per-patient dose QA, but more importantly raised the idea of using bio-models to assess the “robustness” of highly conformal plans (IMRT and VMAT). That is, wouldn’t it be useful to quantify how susceptible these plans are (or would be) to TPS or delivery errors? Moreover, wouldn’t this make sense to do as part of optimizing the plan vs. after? It’s a common sense approach to quality....