We plotted dose-volume histograms and dose-color-wash displays (Figure 2-3 to Figure 2-8) for head and neck sites to compare the dose obtained from BIS and no-sampling (NS) methods. The first step in the process optimized the dose to target structures. To compare the doses to target structures, we computed D95 of each of the target structures using the treatment plan obtained from BIS and NS.
The D95 obtained from BIS was almost the same as that obtained from NS. Out of seven head and neck treatment plans, one treatment plan had lower, one had equal, and five treatment plans
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had higher D95 from BIS than from NS. The D95 obtained from BIS was 0.29% lower than that obtained from the NS for one treatment plan. Similarly, on average, the D95 obtained from BIS was 0.36% higher than that obtained from the NS for the five treatment plans. The results show that the target coverage from the sampling is comparable with that of NS.
The second step of hierarchical optimization minimized the mean dose of the hottest 1% (MOHx) of the brainstem voxels. The dose to the brainstem obtained from BIS was comparable to that obtained from the NS. On average, the MoHx obtained from BIS was 0.6% higher than that obtained from the NS for the two treatment plans. The results show that the dose to the brainstem obtained from BIS was equivalent to that of NS.
The third step of hierarchical optimization minimized the mean dose to normal structures. There were a number of normal structures in the optimization and we chose the spinal cord as a representative structure to show the dose to the normal structure. The dose to the spinal cord obtained from BIS was comparable to that obtained from NS. On average, the mean dose to spinal cord obtained from BIS was 5.19% less than that obtained from NS. The result indicates that BIS minimized radiation exposure to the normal structures.
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b)
Figure 2-2 a) Dose color wash and b) dose-volume histogram produced in the boundary and interior sampling (BIS) and no-sampling methods for head and neck treatment plan 1. The BIS and no-sampling methods produced almost the same dose distribution. Therefore, the dose-volume histogram of BIS and no-sampling almost overlap and the dose color wash produced in BIS and no-sampling have similar colors.
a)
Boundary and Interior Sampling (BIS) No-sampling 0 72.7 Spinal cord Brainstem PTV
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b)
Figure 2-3 a) Dose color wash and b) dose-volume histogram produced in the boundary and interior sampling (BIS) and no-sampling methods for head and neck treatment plan 2. The BIS and no-sampling methods produced almost the same dose distribution. Therefore, the dose-volume histogram of BIS and
a)
Boundary and Interior Sampling (BIS) No-sampling 0 73.2 Spinal cord PTV Brainstem
30
no-sampling almost overlap and the dose color wash produced in BIS and no-sampling have similar colors.
b)
Figure 2-4 a) Dose color wash and b) dose-volume histogram produced in the boundary and interior sampling (BIS) and no-sampling methods for head and neck treatment plan 3. The BIS and no-sampling methods produced almost the same dose distribution. Therefore, the dose-volume histogram of BIS and
a)
Boundary and Interior Sampling (BIS) No-sampling 0 72.7 Spinal cord Brainstem PTV
31
no-sampling almost overlap and the dose color wash produced in BIS and no-sampling have similar colors.
b)
Figure 2-5 a) Dose color wash and b) dose-volume histogram produced in the boundary and interior sampling (BIS) and no-sampling methods for head and neck treatment plan 4. The BIS and no-sampling methods produced almost the same dose distribution. Therefore, the dose-volume histogram of BIS and
a)
Boundary and Interior Sampling (BIS) No-sampling 0 73.1 Spinal cord Brainstem PTV
32
no-sampling almost overlap and the dose color wash produced in BIS and no-sampling have similar colors.
b)
Figure 2-6 a) Dose color wash and b) dose-volume histogram produced in the boundary and interior sampling (BIS) and no-sampling methods for head and neck treatment plan 5. The BIS and no-sampling
a)
Boundary and Interior Sampling (BIS) No-sampling 0 71.3 Spinal cord Brainstem PTV
33
methods produced almost the same dose distribution. Therefore, the dose-volume histogram of BIS and no-sampling almost overlap and the dose color wash produced in BIS and no-sampling have similar colors.
a)
Boundary and Interior Sampling (BIS)
No-sampling 72.1
0
b)
Figure 2-7 a) Dose color wash and b) dose-volume histogram produced in the boundary and interior sampling (BIS) and no-sampling methods for head and neck treatment plan 6. The BIS and no-sampling methods produced almost the same dose distribution. Therefore, the dose-volume histogram of BIS and
Spinal cord
Brainstem
34
no-sampling almost overlap and the dose color wash produced in BIS and no-sampling have similar colors.
Figure 2-8 a) Dose color wash and b) dose-volume histogram produced in the boundary and interior sampling (BIS) and no-sampling methods for head and neck treatment plan 7. The BIS and no-sampling methods produced almost the same dose distribution. Therefore, the dose-
a)
Boundary and Interior Sampling (BIS) No-sampling 74.1 0 Spinal cord Brainstem PTV b)
35
volume histogram of BIS and no-sampling almost overlap and the dose color wash produced in BIS and no-sampling have similar colors.