TABLE 3.
Effect of Distortion on Target Coverage and SRS Plan
| Inadequacy of true target coverage with plans using uncorrected (distorted) target | ||||
|---|---|---|---|---|
| Distortion with patient in original† position | ||||
| Criterion for inadequate plan |
No. of cases (n=28) |
Median* |
Maximum * |
|
| (A ) |
>2% of target received <100% Rx dose | 20 | 12.3% | 98.2% |
| (B ) |
>10% of target received <90% Rx dose | 4 | 43.0% | 74.7% |
| (C ) |
>125mm3 of target received <90% Rx dose |
4 | 258 mm3 |
427 mm3 |
| Geometric miss by criteria (B) or (C) | 8 | - | - | |
| Distortion with patient in alternate†† position | ||||
| Criterion for inadequate plan |
No. of cases (n=28) |
Median* |
Maximum * |
|
| (A ) |
>2% of target received <100% Rx dose | 25 | 17.8% | 100.0% |
| (B ) |
>10% of target received <90% Rx dose | 10 | 21.6% | 92.4% |
| (C ) |
>125mm3 of target received <90% Rx dose |
10 | 359 mm3 |
1966 mm3 |
| Geometric miss by criteria (B) or (C) | 13 | - | - | |
*
The median and maximum values (across patients) for each criterion are shown
†
Original position=refers to the actual MR images with the patient in whatever position he or she was scanned in
††
Alternate position=refers to images modified to reflect a hypothetical, small change in the patient’s positioning in the MRI system
‖
Geometric miss=a plan is considered a geometric miss if it fails by either criterion (B) or (C)