TABLE 2.
SPR comparison based on SECT and commercial SPR image sets of the CIRS Electron Density Phantom. The values are compared to the average measured values for each tissue surrogate plug. The SPR for the Dense Bone plug could not be measured due to the size of the surrogate material relative to the size of the proton beam
| Material | Vendor specified physical density (g cm3) | MLIC Measured rSPR | SECT‐based Assigned rSPR | rSPR from DirectSPR scan | SECT difference from measurement (%) | DirectSPR difference from measurement (%) |
|---|---|---|---|---|---|---|
| Lung inhale | 0.20 | 0.2181 | 0.1945 | 0.2193 | −10.8 | 0.5 |
| Adipose | 0.96 | 0.9843 | 0.9791 | 0.9833 | −0.5 | −0.1 |
| Muscle | 1.06 | 1.0404 | 1.0557 | 1.0436 | 1.5 | 0.3 |
| Trabecular Bone | 1.16 | 1.1211 | 1.1369 | 1.1200 | 1.4 | −0.1 |
| Breast | 0.99 | 1.0048 | 0.9943 | 1.0051 | −1.0 | 0.0 |
| Liver | 1.07 | 1.0452 | 1.0481 | 1.0490 | 0.3 | 0.4 |
| Lung exhale | 0.50 | 0.5349 | 0.5341 | 0.5379 | −0.1 | 0.6 |
| Solid water | 1.01 | 1.0542 | 1.0388 | 1.0538 | −1.5 | 0.0 |
| Dense bone | 1.53 | NA | 1.4438 | 1.3912 | NA | NA |