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Year : 2016  |  Volume : 12  |  Issue : 1  |  Page : 43-46

The clinical application of in-house double lower limb auxiliary device in treating pelvic tumors

1 Department of Radiation Oncology, The Central Hospital of Cangzhou, Hebei, Cangzhou 061000, China
2 Department of Radiation Oncology, Third Hospital of Hebei Medical University, Shijiazhuang 050051, China
3 Procure Proton Therapy Center, Oklahoma City, 73142, USA

Date of Web Publication13-Apr-2016

Correspondence Address:
Prof. Zhai Fu-Shan
Department of Radiation Oncology, Third Hospital of Hebei Medical University, Shijiazhuang 050051
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0973-1482.151942

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 > Abstract 

Objective: Patient positioning accuracy is critical in radiotherapy. To improve the patient positioning accuracy, a double lower limb auxiliary device has been developed to fix pelvis patients to treatment couch. A clinical study for comparing new device to conventional devices has been performed.
Materials and Methods: Thirty patients with pelvic tumor were randomly divided into conventional thermoplastic membrane fixation group (conventional fixing group) and conventional thermoplastic membrane plus lower limb auxiliary fixture group (auxiliary fixing group). The setup error was acquired by simulator position alignment with center field digital radiograph reconstruction (DRR) image from treatment planning system, The correlations between the conventional fixing group and the auxiliary fixing group were analyzed using Pearson's Chi-squared test.
Results: Set-up errors in conventional fixing group and auxiliary fixing group were respectively 3.8 ± 1.5 mm and 1.4 ± 0.9 mm (P< 0.02), 5.4 ± 2.5 mm and 1.2 ± 1.2mm (P < 0.001), 2.2 ± 1.3 mm and 1.9 ± 1.0 mm (P < 0.05) in the bilateral, superior-inferior and anterior-posterior direction.
Conclusion: The double lower limbs auxiliary device can reduce pelvic patient positioning errors. It is very helpful in improving the daily clinical setup accuracy.

Keywords: Lower limbs auxiliary device, pelvic tumors, set-up error

How to cite this article:
Xing-De L, Jin Z, Fu-Shan Z, Li-Jie H, Yue Z, Jun-Fang G. The clinical application of in-house double lower limb auxiliary device in treating pelvic tumors. J Can Res Ther 2016;12:43-6

How to cite this URL:
Xing-De L, Jin Z, Fu-Shan Z, Li-Jie H, Yue Z, Jun-Fang G. The clinical application of in-house double lower limb auxiliary device in treating pelvic tumors. J Can Res Ther [serial online] 2016 [cited 2021 Jan 23];12:43-6. Available from: https://www.cancerjournal.net/text.asp?2016/12/1/43/151942

 > Introduction Top

The set-up error during the radiotherapy is one of the key factors to affect the irradiation accuracy. Many scholars tried to reduce the set-up error and improve the radiotherapy accuracy by means of improving the patients' fixing methods.[1],[2] During the treatment of pelvis of the patient in radiotherapy, the flabby skin, fatty abdominal, rotated lower limb and the separated leg angle all will change marker position and increase the set-up error.[3] Therefore, some reliable and stable devices are really in the need of the pelvic tumor radiotherapy for better positioning. One in-house Double Lower Limbs Auxiliary Fixing Device (Patent No.: ZL 2013 20222024.2) has been developed and used in our daily clinic. This manuscript will present structure detail and fixing method of the in-house device. A systemic set-up error reduction analysis by using the new device is reported first time. This device is also recommended to be used in new technologies such as volumetric-modulated radiation therapy (VMAT) and proton therapy.

 > Materials and Methods Top

Auxiliary fixing devices and equipments

The Double Lower Limbs Auxiliary Fixing Device is mainly composed of the foot plates, lower limbs containing grooves, vacuum pads, foot connecting rods, fixed body frame (MEDTEC Company, USA), thermoplastic film (MEDTEC Company, USA), and the electrode pastes (I type, Hangzhou Tianyi Medical Instrument Co., Ltd.). Electrode pastes (which are used in EKG procedure) are only to fasten the film to the patient's body, and not for any electrical connection. The treatment planning system of Varian Eclipse 10.0 is used during the planning.

Fixing methods

The conventional fixing group: The patient lies on his back on carbon fiber table and settles his head into the spoon-shaped pillow, with hands folded his elbow on the forehead, and then fixed by the thermoplastic body film [Figure 1];
Figure 1: Fixed lower limbs

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The auxiliary fixing group: Fixing the lower limbs: We keep the patient's body position the same as the conventional group, adjust the patient's position with the laser, use the Double Lower Limbs Auxiliary Fixing Device to fix his lower limbs, adjust the patient's position to make him feel comfortable and easy to repeat the positioning, and use the foot connecting rods to fix the space between the two lower limbs, then use the vacuum pump to remove the air from the inside of the vacuum pad to shape it, at last, tie up the fixing bands for the lower limbs. For making the body film: We take the thermoplastic film out of the thermostatic water tank, remove the adherent water, spread out the thermoplastic film evenly on the patient's body and immobilize it on the carbon fiber table, take the cooled and shaped body film away from the patient, drill 4 holes (the hole size is as big as the electrode paste metal head size, about 5 mm in diameter) in the thighs of lower limbs where close to the skin and the bilateral anterior superior spine, put the body film back into the patient to mark the positions of the 4 holes and paste the electrode pastes there (no skin allergy phenomenon); use the electrode pastes to mark the relative position of the body film and the patient to avoid the beam center frame rotating electrode level [Figure 2]. During each treatment, the therapist aims the body film holes at the electrode paste metal head, then locks the body film naturally, but not be hard forced to lock.
Figure 2: Auxiliary fixation combination

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The research objects and grouping

Pelvic cancer patients were selected from 30 patients who underwent intensity modulated radiation therapy (IMRT) at the center hospital of Cangzhou city from March 2013 to October 2013. They were 6 males and 24 females with the age ranging from 38 to 78 years. The average age was 52.6 years. There were 22 cases of cervical cancer and 8 cases of colorectal cancer. Thirty patients with pelvic tumors were randomly divided into conventional thermoplastic membrane fixation group (conventional group) and conventional thermoplastic membrane plus lower limbs auxiliary fixture group (auxiliary fixation group). There were 15 cases in each group.

The measuring method of the set-up errors

After we scanned all patients by 64-sliced CT scanner, we transferred all patient images to the treatment planning system to create the treatment plan. The central field DRR image was rebuilt as a reference image. The two groups of patient were localized by using the simulated locator and compared with fully digital X-ray simulated locator to shoot anterior and lateral portal field on central position, and then let the patient get out of bed and rest for a moment, reset the position 3 times to collect 180 pieces of portal images. We compare the patient's portal images with the reconstructed central field (anterior field, lateral field) DRR image of the treatment planning system. One osseous mark (such as sacral promontory, the sacral coccygeal vertebra, pubic symphysis, obturator foramen, etc.) was selected as a comparison reference point. The distance between the reference point and the edge of the irradiation field was measured by the tool, which is carried by the simulated locator. Then the measured value of the simulated locator portal images was subtracted from the measured value of the treatment planning system. We measured and calculated the lateral, superior-inferior and anterior-posterior set-up errors. The superior-inferior set-up errors took the average value of the measurement of the anterior field from lateral field images. The determination of the osseous reference point and the measurement of distance were completed by the same doctor. When the shift in X, Y, Z axis was less than ± 3 mm, it means that the result confines to the treatment center. Otherwise, it means out of tolerance, we need to reset the patient. The set-up error rate is defined as the percentage of each group reset times out of all patients' set-up times.

Statistical method

Statistical analyses were implemented by using SPSS 11.0 Statistical software. The results were presented as the X– ± s. The correlations between the conventional group and secondary fixation group were analyzed using Pearson's Chi-squared test. This is the standard way to perform the correlation analysis.

 > Results Top

Test results were considered significant at P < 0.05. Two groups of patients' anterior-posterior set-up errors are similar. But the superior-inferior and lateral direction set-up errors of the auxiliary fixing group are much lower than that of the conventional fixing group, especially the discrepancy in superior-inferior direction (P < 0.001), which is shown in [Table 1]. The error rates in three-dimensional direction of two groups are shown in [Table 2].
Table 1: Two different immobilization techniques set - up error conditions (x- ±s) mm

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Table 2: The percentage of each group reset times of all patients' set - up times (%)

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 > Discussion Top

The IMRT technology has become the mainstream of the Pelvic Tumor Radiotherapy technology, which uses the Multi-Leaf Collimator (MLC) technology to realize the adjustment of ray beam intensity and shape, which makes the high dose area shape consistent with the gross tumor volume in three-dimensional direction and the conformity index of dose distribution higher. The shape increase and decrease of the dose gradient in the high dose area makes the complex irregular clinical target volume irradiated and the adjacent normal tissues free from irradiation, which increases the gain ratio of treatment.[4] Because IMRT needs high target accuracy, people should be careful when they use it, or they may miss the target because of the patient's position change, the movement of the internal organs and tumor shrinkage. Therefore, it is significant to discuss the patients with pelvic tumors' posture fixation, placement accuracy and set-up errors during the radiation therapy.

The posture fixation is very important in the process of designing and practicing the treatment plan.[5] And a good posture fixation is the key link to reduce the set-up errors and increase the radiotherapy accuracy. Therefore, people should try to choose a treatment position, which makes the patient feel comfortable, easy to be fixed and repeats well, and explain it to the patient to make him cooperate actively. In this study, the author used the in-house Double Lower Limbs Auxiliary Fixing Device and the thermoplastic body film to immobilize the patients with pelvic tumor. Even though the positioning takes a little bit more time, it significantly reduces the set-up errors to ensure the radiotherapy accuracy. The study results show that the lateral and superior-inferior set-up errors are 1.4 ± 0.9 mm, 1.2 ± 1.2 mm only, and they are lower than the conventional fixing group (P < 0.05). The reasons might be that the patient's double lower limbs' long axis rotation causes the hip muscles to change, which displaces marks on the skin and causes the set-up errors. The usage of the Double Lower Limbs Auxiliary Fixing Device decreases the double lower limbs rotation and displacement, so the set-up errors are reduced. Moreover, drilling 4 holes in device close to the skin and the bilateral anterior-superior spine of the body film and pasting the electrode pastes on the same positions of the patient's skin did not only keep away from the abdominal fat and high mobility, but also follow the proximity principle of choosing the position markers. Four electrode pastes make the patient's body and the body film fit together, and reduce the displacement when positioning repeats, and then decrease the set-up errors, especially the errors of the direction of superior-inferior (P < 0.001).

 > Conclusion Top

In conclusion, with simple usage and low price, the Double Lower Limbs Auxiliary Fixing Device improved the stability and repeatability of pelvic tumor patient positioning. It can reduce the set-up errors. It not only can offer auxiliary function to the various fixed body frames, but can also be used alone to the lower limbs tumor radiotherapy fixing. It is a very valuable device in our routine clinic. Double Lower Limbs Auxiliary Fixing Device was originally developed for the IMRT delivery at the authors' hospital. More recently, advanced treatment techniques such as VMAT and proton therapy are available for the treatment of cancers in the pelvic region.[6],[7],[8],[9] Future studies may include the application of this device in VMAT and proton treatments.

 > References Top

Hui H, Chen HL, Wang Q, Geng C, Chi ZF, Du AN. The use of thermoplastic body immobilization membrane technology to improve research. Chin J Radiat Oncol 2013;22:45-6.  Back to cited text no. 1
De LX, Zhao J, Zhang MY, Zhai FS, Zhao Y, Zhu ZC. Positioning accuracy analysis of two breast cancer radiotherapy membrane fixation methods. Chin J Radiat Oncol 2013;22:397-9.  Back to cited text no. 2
Bel A, Vos PH, Rodrigus PT, Creutzberg CL, Visser AG, Stroom JC, et al. High-precision prostate cancer irradiation by clinical application of an offine patient set up verification procedure by using portal imaging. Int J Radiat Oncol Biol Phys 1996;35:321-32.  Back to cited text no. 3
Li DP, Sheng XG. Intensity modulated radiation therapy in gynecologic malignancies. Foreign Med Oncol Branch 2004;3:233-6.  Back to cited text no. 4
Hu YM. Treatment of position and fixed technology. In: Yin WB, Yu ZH, Xu GZ, Hu YM, Wang LH, Liu XF, editors. Radiaation Oncology [M]. Version 1.4. Beijing: China Union Medical University Press; 2008. p. 85.  Back to cited text no. 5
Rana S, Cheng C, Zheng Y, Hsi W, Zeidan O, Schreuder N, et al. Dosimetric study of uniform scanning proton therapy planning for prostate cancer patients with a metal hip prosthesis, and comparison with volumetric-modulated arc therapy. J Appl Clin Med Phys 2014;15:4611.  Back to cited text no. 6
Pokharel S. Dosimetric impact of mixed-energy volumetric modulated arc therapy plans for high- risk prostate cancer. Int J Cancer Ther Oncol 2013;1:01011.  Back to cited text no. 7
Rana S, Cheng C, Zheng Y, Risalvato D, Cersonsky N, Ramirez E, et al. Proton therapy vs. VMAT for prostate cancer: A treatment planning study. Int J Particle Therapy 2014;1:22-33.  Back to cited text no. 8
Rout BK, Muralidhar KR, Ali M, Shekar MC, Kumar A. Dosimetric study of RapidArc plans with flattened beam (FB) and flattening filter-free (FFF) beam for localized prostate cancer based on physical indices. Int J Cancer Ther Oncol 2014;2:02046.  Back to cited text no. 9


  [Figure 1], [Figure 2]

  [Table 1], [Table 2]


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