Table 3.
Dosimetric parameters for the 4 beam arrangements optimized to the 5-cm rectal diameter and iterated across rectal diameter sizes including plan CT
| Dosimetric parameter | Beam arrangement |
||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 beam (PA) |
3 beam (PA, opposed lateral) |
||||||||||||
| 5 cm | 4 cm | 3 cm | 2 cm | 1 cm | Plan CT | 5 cm | 4 cm | 3 cm | 2 cm | 1 cm | Plan CT | ||
| CTV45 | V100% (%) | 99.9 | 98.1 | 94.2⁎ | 89.0⁎ | 84.1⁎ | 81.5⁎ | 100.0 | 99.7 | 97.9 | 90.1⁎ | 79.0⁎ | 72.5⁎ |
| CTV50 | V100% (%) | 97.6 | 94.7⁎ | 87.5⁎ | 77.1⁎ | 67.0⁎ | 63.4⁎ | 99.8 | 98.2 | 84.8⁎ | 61.2⁎ | 41.4⁎ | 34.7⁎ |
| CTV50 | Dmax (%) | 55.6⁎ | 56.5⁎ | 58.9⁎ | 60.9⁎ | 58.9⁎ | 56.6⁎ | 53.9 | 53.8 | 54.4 | 55.5⁎ | 56.6⁎ | 54.7 |
| Small bowel | V40Gy (%) | 68.6 | 64.7 | 62.6 | 61.9 | 61.9 | 61.8 | 77.2⁎ | 75.5⁎ | 73.8⁎ | 72.9⁎ | 72.6⁎ | 72.4⁎ |
| V35Gy (%) | 85.9 | 81.4 | 78.6 | 77.5 | 77.2 | 77.1 | 100.3 | 98.1 | 96.4 | 95.3 | 94.7 | 94.6 | |
| V30Gy (%) | 102.0 | 96.4 | 93.0 | 91.7 | 91.5 | 91.3 | 119.5 | 117.1 | 115.1 | 114.1 | 113.6 | 113.6 | |
| Dmax (Gy) | 50.6 | 50.4 | 51.0 | 50.6 | 50.7 | 50.3 | 48.1 | 48.0 | 48.1 | 48.1 | 48.1 | 48.1 | |
| Bladder | V40Gy (%) | 24.0 | 8.4 | 2.4 | 1.8 | 1.8 | 1.8 | 26.0 | 19.9 | 14.4 | 7.9 | 6.6 | 6.6 |
| V30Gy (%) | 36.0 | 17.0 | 6.5 | 4.7 | 4.7 | 4.7 | 36.0 | 31.3 | 27.5 | 25.6 | 25.0 | 25.0 | |
| Internal genitalia | V30Gy (%) | 23.6 | 23.3 | 20.0 | 13.0 | 5.7 | 2.1 | 17.8 | 17.7 | 17.5 | 16.4 | 14.6 | 12.6 |
| V20Gy (%) | 33.2 | 32.7 | 29.6 | 21.8 | 13.1 | 6.3 | 26.4 | 26.3 | 26.1 | 23.7 | 21.8 | 20.3 | |
| 2 beam (RPO, LPO) | 5 beam (PA, RPO, LPO, opposed lateral) | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| CTV45 | V100% (%) | 99.9 | 99.9 | 99.0 | 94.8⁎ | 87.7⁎ | 82.0⁎ | 99.9 | 99.7 | 97.9 | 91.6⁎ | 81.8⁎ | 74.4⁎ |
| CTV50 | V100% (%) | 99.9 | 99.8 | 94.2⁎ | 81.3⁎ | 67.2⁎ | 58.5⁎ | 99.6 | 99.0 | 85.7⁎ | 61.6⁎ | 40.9⁎ | 33.1⁎ |
| Dmax (%) | 54.9 | 54.3 | 55.0⁎ | 55.0⁎ | 55.1⁎ | 55.5⁎ | 53.4 | 53.6 | 54.4 | 55.6⁎ | 56.0⁎ | 54.8 | |
| Small bowel | V40Gy (%) | 68.9 | 67.9 | 67.5 | 67.3 | 67.0 | 67.0 | 77.1⁎ | 74.9⁎ | 72.5⁎ | 70.7⁎ | 70.0⁎ | 69.8 |
| V35Gy (%) | 85.4 | 84.1 | 83.3 | 83.2 | 83.0 | 82.9 | 99.6 | 96.7 | 94.0 | 91.9 | 91.2 | 91.2 | |
| V30Gy (%) | 99.1 | 98.1 | 97.4 | 96.9 | 96.9 | 97.0 | 118.9 | 115.4 | 112.5 | 110.6 | 109.4 | 109.4 | |
| Dmax (Gy) | 49.2 | 48.7 | 48.7 | 48.7 | 48.8 | 48.6 | 47.7 | 47.6 | 47.5 | 47.6 | 47.5 | 47.4 | |
| Bladder | V40Gy (%) | 21.3 | 20.4 | 19.9 | 19.5 | 19.4 | 19.5 | 26.9 | 19.3 | 11.0 | 3.7 | 2.3 | 1.9 |
| V30Gy (%) | 26.3 | 25.1 | 24.6 | 24.5 | 24.4 | 24.4 | 37.8 | 30.1 | 24.2 | 19.5 | 16.9 | 16.5 | |
| Internal genitalia | V30Gy (%) | 15.2 | 15.1 | 14.4 | 11.8 | 10.4 | 10.1 | 19.8 | 19.6 | 18.6 | 15.8 | 13.0 | 9.7 |
| V20Gy (%) | 21.9 | 21.9 | 21.3 | 19.6 | 18.9 | 18.8 | 29.1 | 20.1 | 27.3 | 23.9 | 21.4 | 18.4 | |
Abbreviations: CT = computed tomography; CTV45 = clinical target volume prescribed 45 GyE; CTV50 = clinical target volume prescribed 50 GyE; Dmax = maximum dose to 0.03 cubic centimeters; LPO = left posterior oblique; PA = posteroanterior; RPO = right posterior oblique; V100% = volume receiving 100% of the prescribed dose; V40Gy = percentage of volume receiving 40 Gy.
⁎
Values did not meet institutional dose constraints.