Journal List > Prog Med Phys > v.27(4) > 1098560

Kim, Jung, Cho, Ryu, Moon, Bae, Ahn, and Jung: Comparison of Two Different Immobilization Devices for Pelvic Region Radiotherapy in Tomotherapy

Abstract

The purpose of this study was to compare the patient setup errors of two different immobilization devices (Feet Fix: FF and Leg Fix: LF) for pelvic region radiotherapy in Tomotherapy. Thirty six-patients previously treated with IMRT technique were selected, and divided into two groups based on applied immobilization devices (FF versus LF). We performed a retrospective clinical analysis including the mean, systematic, random variation, 3D-error, and calculated the planning target volume (PTV) margin. In addition, a rotational error (angles, o) for each patient was analyzed using the automatic image registration. The 3D-errors for the FF and the LF groups were 3.70 mm and 4.26 mm, respectively; the LF group value was 15.1% higher than in the FF group. The treatment margin in the ML, SI, and AP directions were 5.23 mm (6.08 mm), 4.64 mm (6.29 mm), 5.83 mm (8.69 mm) in the FF group (and the LF group), respectively, that the FF group was lower than in the LF group. The percentage in treatment fractions for the FF group (ant the LF group) in greater than 5 mm at ML, SI, and AP direction was 1.7% (3.6%), 3.3% (10.7%), and 5.0% (16.1%), respectively. Two different immobilization devices were affected the patient setup errors due to different fixed location in low extremity. The radiotherapy for the pelvic region by Tomotherapy should be considering variation for the rotational angles including Yaw and Pitch direction that incorrect setup error during the treatment. In addition the choice of an appropriate immobilization device is important because an unalterable rotation angle affects the setup error.

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Fig. 1.
Patient positioning with supine by using the Feet Fix (a) or Leg Fix (b) for the immobilization of the leg area.
pmp-27-250f1.tif
Fig. 2.
Percentage of distribution in the treatment fractions of the patient setup variations, the FF group (a) and the LF group (b), in overall patients that the ML, SI, AP directions, and Roll rotational angles.
pmp-27-250f2.tif
Table 1.
Patient characteristics of each group (FF group and LF group) in this study.
Parameter Value (range or number)
FF LF
Age (year) 56 (31∼76) 59 (33∼76)
Site    
Bladder 1 4
Cervix 7 4
Endometrium 1 2
Prostate 1 6
Rectum 5 1
Other 3 1
Total dose (cGy) 4,930 (4,000∼5,400) 4,891 (4,000∼6,600)
Fraction dose (cGy) 182 (180∼200) 192 (154∼230)
Number of fractions (number) 27 (20∼30) 26 (20∼33)
Treatment time (sec) 203 (125∼323) 237 (156∼354)

FF: Feet Fix device, LF: Leg Fix device.

Table 2.
Patients’ setup uncertainty compared with the Feet Fix (FF) and Leg Fix (LF) devices.
Immobilization device
Direction FF LF   FF LF FF LF FF LF p-value
  Mean (M)   Systematic (Σ) Random (σ) Margin
ML (mm) −0.51 −0.88 1.61 1.71 1.73 2.57 5.23 6.08 0.358
SI (mm) −0.82 0.22 1.37 2.06 1.72 1.61 4.64 6.29 0.019
AP (mm) 1.13 0.15 1.73 2.83 2.16 2.32 5.83 8.69 0.099
Roll (o) 0.25 0.54 0.31 0.70 0.35 0.71 N/A N/A 0.03
3D-error (mm) 3.70  4.26      2.73  3.90  3.26  3.82  N/A N/A 0.081

Significant of these differences (p<0.05).

Table 3.
Correlation analysis of directional setup displacement in the Feet Fix immobili(FF).
Direction
Direction ML SI AP Pitch Roll Yaw
ML 1          
SI 0.276 1        
AP −0.198 −0.087 1      
Pitch 0.291 0.178 0.048 1    
Roll −0.145 0.063 0.037 0.097 1  
Yaw 0.141 −0.262 −0.237 −0.120 −0.096 1

Significant of these differences (p<0.05).

Table 4.
Correlation analysis of directional setup displacement in the Leg Fix immobilization device (LF).
Direction
Direction ML SI AP Pitch Roll Yaw
ML 1          
SI −0.177 1        
AP −0.464∗∗ 0.122 1      
Pitch 0.82 0.183 −0.55 1    
Roll −0.222 0.212 0.095 0.024 1  
Yaw 0.109 −0.315 −0.145 0.420∗∗ −0.188 1

Significant of these differences (p<0.05)

∗∗ Significant differences (p<0.01).

Table 5.
Patients’ setup uncertainty compared with the Feet Fix (FF) and Leg Fix (LF) in automatic image registration.
Immobilization device
Direction FF LF FF LF p-value
M SD
ML (mm) −0.41 −0.91 2.07 2.95 0.296
SI (mm) −0.61 0.03 1.85 2.60 0.136
AP (mm) 1.32 −0.04 2.62 3.21 0.014
Pitch (o) 0.12 0.33 0.66 1.08 0.197
Roll (o) 0.35 0.55 0.41 0.72 0.07
Yaw (o) 0.00 0.16 0.68 0.89 0.268

Significant of these differences (p<0.05), M: value of mean, and SD: standard deviation.

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