Patient 1
Integral Error (%) Solid Water Phantom Timber Phantom Sup-Inf Med-Lat Combined Sup-Inf Med-Lat Combined
No Tracking 5272 796 6068 4914 3619 8532
Passive 637 771 1408 476 905 1381
Predictive 497 797 1294 372 912 1283
Patient 2
Integral Error (%) Solid Water Phantom Timber Phantom Sup-Inf Med-Lat Combined Sup-Inf Med-Lat Combined
No Tracking 3219 2340 5559 2739 2166 4906
Passive 1447 1278 2726 1401 1432 2833
Predictive 704 812 1517 854 1563 2417
Table 4.7: Integral error values (%) for both patient motion traces using the 3DCRT delivery. The integral is obtained by summing percentage error values along each dimension of the detector
The integral error for each patient is tabulated for the 3DCRT delivery in table 4.7 and for the IMRT delivery in table 4.8. The integral error is calculated in each direction and then summed to give the ’combined’ integral error for the overall treatment.
Improvement of the treatment using tracking is quantified with the percentage im- provement metric. The percentage improvement for both patients using the 3DCRT delivery is listed in table 4.9 and for the IMRT delivery in table 4.10. The percent- age improvement is calculated for each direction (sup-inf and med-lat) separately to highlight the tracking performance for each direction independently. It is also calculated from the combined integral error to give an overall improvement when tracking is used, taking the contribution from each direction into account.
Patient 1
Integral Error (%) Solid Water Phantom Timber Phantom Sup-Inf Med-Lat Combined Sup-Inf Med-Lat Combined
No Tracking 4927 1053 5980 5085 1167 6252
Passive 642 1787 2429 1014 1573 2587
Predictive 637 1765 2402 633 1819 2452
Patient 2
Integral Error (%) Solid Water Phantom Timber Phantom Sup-Inf Med-Lat Combined Sup-Inf Med-Lat Combined
No Tracking 2429 656 3086 2180 714 2894
Passive 1213 1482 2696 1832 1299 3131
Predictive 797 1527 2324 999 1457 2456
Table 4.8: Integral error values (%) for both patient motion traces using the IMRT delivery. The integral is obtained by summing percentage error values along each dimension of the detector
Patient 1
Percentage Improvement (%) Solid Water Phantom Timber Phantom Sup-Inf Med-Lat Combined Sup-Inf Med-Lat Combined
Passive 87.9 3.1 76.8 90.3 75.0 83.8
Predictive 90.6 -0.1 78.7 92.4 74.8 85.0
Patient 2
Percentage Improvement (%) Solid Water Phantom Timber Phantom Sup-Inf Med-Lat Combined Sup-Inf Med-Lat Combined
Passive 55.0 45.4 51.0 48.8 33.9 42.2
Predictive 78.1 65.3 72.7 68.8 27.9 50.7
Table 4.9: Percentage improvement (%) for both patient motion traces using the 3DCRT delivery. Percentage improvement is the calculated as the percentage difference of the integral error values between each tracking modality and the no tracking modality.
Patient 1
Percentage Improvement (%) Solid Water Phantom Timber Phantom Sup-Inf Med-Lat Combined Sup-Inf Med-Lat Combined
Passive 87.0 -69.8 59.4 80.1 -34.8 58.6
Predictive 87.1 -67.7 59.8 87.6 -55.9 60.8
Patient 2
Percentage Improvement (%) Solid Water Phantom Timber Phantom Sup-Inf Med-Lat Combined Sup-Inf Med-Lat Combined
Passive 50.0 -125.8 12.6 16.0 -82.0 -8.2
Predictive 67.2 -132.7 24.7 54.2 -104.2 15.1
Table 4.10: Percentage improvement (%) for both patient motion traces using the IMRT delivery. Percentage improvement is the calculated as the percentage difference of the integral error values between each tracking modality and the no tracking modality.
There could be a case where tracking performs extremely well in the sup-inf direction but poorly in the med-lat direction. The overall percentage improvement may be good, however it would be important to consider the organs at risk close by in each direction. In lung for example, if there is poor tracking performance in the med-lat direction then the heart could be getting excess dose. If only the overall tracking performance was considered then this may not be immediately apparent.
For the 3DCRT delivery (table 4.9) there is relatively large improvement in the sup-inf direction; the lowest and highest percentage improvement values were 48.8% and 92%, respectively. Patient 1 had better tracking performance in the sup-inf direction and overall than patient 2. In the med-lat direction in solid water for patient 1, it appears the tracking performed poorly, considering the improvement values of 3.1% and -0.1% for passive and predictive tracking, respectively. This is due to the minimal impact motion had in this direction in solid water; the profiles for all motion modalities are very similar. In fact the integral error from each (table 4.7) is essentially the same. This highlights the complex nature of MLC tracking and the need to evaluate tracking performance using multiple metrics (eg a combination of profiles, percentage improvement and gamma analysis).
Tracking performance is better in the sup-inf direction than med-lat direction, this agrees with the profiles in figures 4.24 and 4.25. The reason for this trend is dis- cussed below. Overall, tracking was beneficial for both patients with the 3DCRT delivery; minimum overall improvement was 50.7% and maximum was 85%. Overall performance in each phantom was dependent on the patient motion, there was no clear better performer.
The tracking performance with the IMRT delivery (table 4.10) in the sup-inf di- rection is comparable to the 3DCRT delivery. Both patients saw a benefit using tracking; the minimum improvement was 16% and maximum 87%. Tracking perfor- mance in this direction was better in solid water than in timber. However, tracking performance in the med-lat direction was worse than using no tracking. Tracking introduced a larger dose error than the uncorrected motion for both patients. Track- ing performance ranges from 35% to 133% worse than no tracking. However, despite this, the overall percentage improvement is favourable in solid water for both pa- tients and in timber for patient 1. For patient 2 in timber only the predictive tracking was favourable. This again highlights the need to evaluate the performance in each direction independently, in addition to considering the overall performance. Organs at risk sitting laterally to the target in this case would have gotten a much larger dose than predicted in the TPS.