Dosimetric Comparisons of Volumetric Modulated Arc Therapy and Tomotherapy for Early T-Stage Nasopharyngeal Carcinoma
Table 3
Dosimetric comparisons of OARs between RapidArc and HT plans.
OAR
Dose Parameter
RapidArc
HT
P-value
Average (SD)
Average (SD)
Spinal Cord
Dmax (cGy)
3603
(368)
3412
(149)
NS
D1cc (cGy)
3331
(400)
3240
(131)
NS
D0.1cc (cGy)
3429
(408)
3347
(132)
NS
Brain Stem
Dmax (cGy)
4965
(130)
4912
(103)
NS
D1cc (cGy)
4524
(146)
4304
(179)
0.012
D0.1cc (cGy)
4767
(149)
4684
(151)
NS
Optic Chiasm
Dmax (cGy)
3282
(1436)
4829
(735)
<0.001
D2 (cGy)
3003
(1220)
4763
(736)
<0.001
Optic Nerve I
Dmax (cGy)
2745
(1728)
4906
(1025)
<0.001
D2 (cGy)
2352
(1578)
4822
(989)
<0.001
Optic Nerve C
Dmax (cGy)
3040
(1595)
4921
(763)
<0.001
D2 (cGy)
2621
(1419)
4807
(731)
<0.001
Temporal Lobe I
Dmax (cGy)
6643
(350)
6447
(285)
0.015
V60Gy (%)
1.7
(1.3)
2.1
(1.6)
NS
Temporal Lobe C
Dmax (cGy)
6512
(101)
6283
(162)
0.001
V60Gy (%)
1
(0.5)
1.1
(0.6)
NS
Lens I
Dmax (cGy)
524
(98)
427
(119)
0.009
D2 (cGy)
505
(93)
400
(94)
0.002
Dmean (cGy)
431
(97)
299
(46)
<0.001
Lens C
Dmax (cGy)
509
(87)
425
(135)
0.047
D2 (cGy)
492
(86)
391
(100)
0.005
Dmean (cGy)
418
(92)
291
(47)
<0.001
Parotid I
Dmean (cGy)
4114
(493)
3636
(514)
0.002
Dmedian (cGy)
3791
(618)
3437
(809)
NS
V30Gy (%)
70.4
(13.9)
54.8
(9.8)
0.009
Parotid C
Dmean (cGy)
3909
(431)
3336
(449)
<0.001
Dmedian (cGy)
3585
(525)
3033
(658)
0.018
V30Gy (%)
67.3
(12.7)
48.2
(9.6)
0.005
Pituitary
Dmax (cGy)
5548
(1023)
5786
(521)
NS
Body
V15 Gy (%)
32.1
(5.2)
40
(15.1)
NS
V20 Gy (%)
27.9
(4.9)
34.5
(13.7)
NS
V30 Gy (%)
19.9
(4.3)
23.1
(11)
NS
V40 Gy (%)
12.5
(2.9)
14.2
(6.7)
NS
OAR: organ at risk; SD: standard deviation; Dmax: maximum point dose; D1cc: maximum dose encompassing 1cc of the structure; D0.1cc: maximum dose encompassing 0.1cc of the structure; D2: maximum dose encompassing 2% of the structure; Dmean: mean dose of the structure; Dmedian: median dose of the structure; V15,20,30,40,60 Gy: the relative volume of the structure receiving over 15,20,30,40,60Gy.
