# A Large Area Pixelated Silicon Array Detector for Independent Transit In Vivo Dosimetry
## 3 Results
### IMRT Transit Dosimetry Study  
The pass rates for the gamma analysis of the IMRT treatment between the MP987 and TPS is presented in Table 1. With the criteria of 5%/5 mm, the segment with the closest agreement was segment 3, with a pass rate of 97.4% and the worst agreement was in segment 1, with a pass rate of 94.2%. When the criteria are restricted to 3%/3 mm, a good pass rate is still maintained with values from 89.3% to 93.9% for the four segments.  
Figure 9: Transit dose measured with the MP987 compared to TPS predicted response with 7 mm of SW buildup. Error bars represent 1 SD of the measured value for MP987 and error of TPS considered as the deviation in response for \(\pm\)0.5 mm in buildup.  
Figure 10 displays the dose maps for segment 3 for the MP987 with and without the deliberate target shift, the TPS dose map and the associated gamma maps. In the gamma maps presented in Figure 10d,e the greyscale represents how closely the dose at the position agrees between the two maps, with white showing complete agreement. When the specified criteria fails at a point the pixel is displayed as red. This red does not show how far from agreement the point was. For the standard delivery, the gamma map Figure 10d shows that the dose in the centre of the field is within the agreement of the TPS value. Most fail points are all located in the penumbras or tail of the field. This may be in part attributed to the interpolation of the MP987 data to match the required 1 mm grid size, which may not reconstruct the shape of the penumbra accurately.  
The 5 mm alignment error results in little difference in pass rates at the 5%/5 mm criteria (less than 1% reduction compared to the regular delivery) but is more prominent with the 3%/3 mm criteria. With the more stringent criteria, the reduction in the pass rate from the correctly delivered plan is reduced by 3.7%, on average for the four segments.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Delivery** & \multicolumn{2}{c}{**Pass Rate (\%)**} \\ \hline  & **3\%/3 mm** & **5\%/5 mm** \\ \hline Segment 1 & 89.3 & 94.2 \\ Segment 1-5 mm shift & 84.3 & 93.7 \\ Segment 2 & 93.0 & 96.6 \\ Segment 2-5 mm shift & 90.2 & 96.5 \\ Segment 3 & 93.9 & 97.4 \\ Segment 3-5 mm shift & 92.3 & 97.3 \\ Segment 4 & 90.9 & 95.4 \\ Segment 4-5 mm shift & 85.5 & 94.5 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Gamma analysis pass rate for MP987 measured map, compared to TPS calculation for each segment of the IMRT delivery. Both the standard delivery and the introduction of the deliberate 5 mm misalignment were presented.  
Figure 10: Transit dose maps measured/calculated at the dual detector level for segment 3 of the IMRT treatment (**a**) MP987; (**b**) TPS; (**c**) MP987 with 5 mm misalignment error introduced. Additionally, the gamma maps (red represents fail points) for (**d**) MP987 compared to TPS; (**e**) MP987 with error compared to TPS.  
It can be observed in the dose map in Figure 10c that the target has moved, but only the shift of the high-density gold fiducial results in additional fail points Figure 10e, when using a 5%/5 mm criteria. The misalignment of the target therefore creates a measurable difference in dose at the level of the MP987, but may not necessarily fail a gamma analysis. This highlights the advantage of having a dual detector system, where imaging performed with the EPID can quantify any shift in a target, as previously demonstrated [14].