A machine learning tool for re-planning and adaptive RT: A multicenter cohort investigation.

PURPOSE: To predict patients who would benefit from adaptive radiotherapy (ART) and re-planning intervention based on machine learning from anatomical and dosimetric variations in a retrospective dataset. MATERIALS AND METHODS: 90 patients (pts) treated for head-neck cancer (H&N) formed a multicenter data-set. 41 H&N pts (45.6%) were considered for learning; 49 pts (54.4%) were used to test the tool. A homemade machine-learning classifier was developed to analyze volume and dose variations of parotid glands (PG). Using deformable image registration (DIR) and GPU, patients' conditions were analyzed automatically. Support Vector Machines (SVM) was used for time-series evaluation. "Inadequate" class identified patients that might benefit from replanning. Double-blind evaluation by two radiation oncologists (ROs) was carried out to validate day/week selected for re-planning by the classifier. RESULTS: The cohort was affected by PG mean reduction of 23.7±8.8%. During the first 3weeks, 86.7% cases show PG deformation aligned with predefined tolerance, thus not requiring re-planning. From 4th week, an increased number of pts would potentially benefit from re-planning: a mean of 58% of cases, with an inter-center variability of 8.3%, showed "inadequate" conditions. 11% of cases showed "bias" due to DIR and script failure; 6% showed "warning" output due to potential positioning issues. Comparing re-planning suggested by tool with recommended by ROs, the 4th week seems the most favorable time in 70% cases. CONCLUSIONS: SVM and decision-making tool was applied to overcome ART challenges. Pts would benefit from ART and ideal time for re-planning intervention was identified in this retrospective analysis.

Measurement of in vivo myocardial microcirculatory function with electron beam CT.

PURPOSE: The purpose of this work was to examine the capability of electron beam CT (EBCT) to characterize responses of recruitable (capillaries and small arterioles) compared with nonrecruitable (small to large arterioles) myocardial microvessels to vasoactive substances. METHOD: Myocardial perfusion (F) and total intramyocardial blood volume (BV) of the anterior cardiac wall were quantitated in 36 pigs, using EBCT and intravenous contrast agent injections, before and after intracoronary administration of either NG-monomethyl-L-arginine (L-NMMA), nitroglycerin, adenosine, or saline. Plotting the relationship of BV and F provided values for the recruitable and nonrecruitable microvascular transit times and BV allotment. RESULTS: Nitroglycerin increased nonrecruitable BV by 84.5+/-7.4%, whereas adenosine increased both recruitable and nonrecruitable microvascular BV (47.1+/-18.9 and 66.0+/-10.9%, respectively). L-NMMA led to a 25.1% decrease only in the recruitable BV. In the control group, no changes were observed. CONCLUSION: Characteristic responses of different-size myocardial microvessels may be inferred with EBCT, which provides a unique opportunity to portray intramyocardial microcirculatory function noninvasively.