Human-computer interaction in radiotherapy target volume delineation: A prospective, multi-institutional comparison of user input devices

The purpose of this study was the prospective comparison of objective and subjective effects of target volume region of interest (ROI) delineation using mouse- keyboard and pen-tablet user input devices (UIDs). The study was designed as a prospective test/retest sequence, with Wilcoxon signed rank test for matchedpair comparison. Twenty-one physician-observers contoured target volume ROIs on four standardized cases (representative of brain, prostate, lung, and head and neck malignancies) twice: once using QWERTY keyboard/ scroll-wheel mouse UID and once with pen-tablet UID (DTX2100, Wacom Technology Corporation, Vancouver, WA, USA). Active task time, ROI manipulation task data, and subjective survey data were collected. One hundred twenty-nine target volume ROI sets were collected, with 62 paired pen-tablet/mouse-keyboard sessions. Active contouring time was reduced using the pen-tablet UID, with mean ± SD active contouring time of 26±23 min, compared with 32±25 with the mouse (p=0.01). Subjective estimation of time spent was also reduced from 31±26 with mouse to 27±22 min with the pen (p=0.02). Task analysis showed ROI correction task reduction (p=0.045) and decreased panning and scrolling tasks (p<0.01) with the pen-tablet; drawing, window/ level changes, and zoom commands were unchanged (p= n.s.) Volumetric analysis demonstrated no detectable differences in ROI volume nor intra- or inter-observer volumetric coverage. Fifty-two of 62 (84%) users preferred the tablet for each contouring task; 5 of 62 (8%) denoted no preference, and 5 of 62 (8%) chose the mouse interface. The pen-tablet UID reduced active contouring time and reduced correction of ROIs, without substantially altering ROI volume/coverage.