Home About us Editorial board Ahead of print Current issue Search Archives Submit article Instructions Subscribe Contacts Login 


 
 Table of Contents  
ORIGINAL ARTICLE
Year : 2014  |  Volume : 10  |  Issue : 4  |  Page : 937-941

A comparative study of set up variations and bowel volumes in supine versus prone positions of patients treated with external beam radiation for carcinoma rectum


1 Department of Radiation Oncology, Regional Cancer Centre, Trivandrum, India
2 Department of Radiation Oncology, AIMS, Kochi, India
3 Department of Radiation Physics, AIMS, Kochi, Kerala, India

Date of Web Publication9-Jan-2015

Correspondence Address:
K R Rajeev
Department of Radiation Oncology, Regional Cancer Centre, Medical College Campus, Trivandrum, Kerala
India
Login to access the Email id

Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0973-1482.138021

Rights and Permissions
 > Abstract 

Purpose: A prospective study was undertaken to evaluate the influence of patient positioning on the set up variations to determine the planning target volume (PTV) margins and to evaluate the clinical relevance volume assessment of the small bowel (SB) within the irradiated volume.
Materials and Methods: During the period of months from December 2011 to April 2012, a computed tomography (CT) scan was done either in supine position or in prone position using a belly board (BB) for 20 consecutive patients. All the patients had histologically proven rectal cancer and received either post- or pre-operative pelvic irradiation. Using a three-dimensional planning system, the dose-volume histogram for SB was defined in each axial CT slice. Total dose was 46-50 Gy (2 Gy/fraction), delivered using the 4-field box technique. The set up variation of the study group was assessed from the data received from the electronic portal imaging device in the linear accelerator. The shift along X, Y, and Z directions were noted. Both systematic and random errors were calculated and using both these values the PTV margin was calculated.
Results: The systematic errors of patients treated in the supine position were 0.87 (X-mm), 0.66 (Y-mm), 1.6 (Z-mm) and in the prone position were 1.3 (X-mm), 0.59 (Y-mm), 1.17 (Z-mm). The random errors of patients treated in the supine positions were 1.81 (X-mm), 1.73 (Y-mm), 1.83 (Z-mm) and in prone position were 2.02 (X-mm), 1.21 (Y-mm), 3.05 (Z-mm). The calculated PTV margins in the supine position were 3.45 (X-mm), 2.87 (Y-mm), 5.31 (Z-mm) and in the prone position were 4.91 (X-mm), 2.32 (Y-mm), 5.08 (Z-mm). The mean volume of the peritoneal cavity was 648.65 cm 3 in the prone position and 1197.37 cm 3 in the supine position.
Conclusion: The prone position using BB device was more effective in reducing irradiated SB volume in rectal cancer patients. There were no significant variations in the daily set up for patients treated in both supine and prone positions.

 > Abstract in Chinese 

直肠癌外粒子束放疗仰卧位与俯卧位计划变动与直肠受量的比较研究

摘要

目的:前瞻性研究评估病人体位对于计划靶体积(PTV)边缘确立的变化的影响,以及探讨照射体积内临床相关的小肠体积。

材料与方法:从2011年12月到2012年4月期间, 20例连续的病人用腹板(BB)进行了CT扫描,体位为仰卧或俯卧。所有患者均病理证实为直肠癌,接受术前或术后的盆腔放疗。使用三维计划系统,精确地画出每层轴向CT片上的小肠剂量体积直方图。总剂量为46-50戈瑞(2 Gy /次),使用4野技术实施。研究组的计划变动是由直线加速器电子门户成像装置接收到的数据进行评估的。沿X、Y和Z方向的移动也被记录下。系统和随机误差都被计算,用于确定PTV边界。

结果:在仰卧位患者的系统误差为0.87(X毫米),0.66(Y毫米),1.6(Z毫米),俯卧位1.3(X毫米),0.59(Y毫米),1.17(Z毫米)。在仰卧位的患者随机误差为1.81(X毫米),1.73(Y毫米),1.83(Z毫米),俯卧位2.02(X毫米),1.21(Y毫米),3.05(Z毫米)。计算出的PTV边缘,仰卧位3.45(X毫米),2.87(Y毫米),5.31(Z毫米),俯卧位4.91(X毫米),2.32(Y毫米),5.08(Z毫米)。腹膜腔的平均体积为:俯卧位648.65 cm3,仰卧位1197.37cm3

结论:在直肠癌患者中,俯卧位使用腹板装置可以更有效地减少小肠照射体积。而在日常设置中,仰卧位和俯卧位治疗的患者没有显著差异。

关键词:腹板,俯卧,直肠


Keywords: Belly board, prone, rectum


How to cite this article:
Rajeev K R, Menon SS, Beena K, Holla R, Kumar R R, Dinesh M. A comparative study of set up variations and bowel volumes in supine versus prone positions of patients treated with external beam radiation for carcinoma rectum. J Can Res Ther 2014;10:937-41

How to cite this URL:
Rajeev K R, Menon SS, Beena K, Holla R, Kumar R R, Dinesh M. A comparative study of set up variations and bowel volumes in supine versus prone positions of patients treated with external beam radiation for carcinoma rectum. J Can Res Ther [serial online] 2014 [cited 2019 Nov 14];10:937-41. Available from: http://www.cancerjournal.net/text.asp?2014/10/4/937/138021


 > Introduction Top


Pre-or post-operative radiotherapy alone or in combination with chemotherapy plays a significant role in the treatment of rectal cancer. For pelvic irradiation, the small bowel (SB) is the most important dose-limiting structure. The overall incidence of acute and chronic SB complications after pelvic irradiation up to a dose of 50 Gy is in the order of 2-9%. [1],[2]

Reducing gastrointestinal toxicity is not the only aim of SB sparing. Improved SB sparing also permits dose escalation for pelvic irradiation. The irradiated small bowel volume (SBV) can be minimized by different surgical techniques such as clip placement in high risk areas, pelvic reconstruction, reperitonealization of the pelvic floor, placement of an omental sling, retroversion of the uterus or by placing a synthetic prosthesis under the SB (a removable pelvic spacer). [3],[4] The irradiated SBV can also be minimized by nonsurgical radiotherapeutical means, including three-dimensional (3D) conformal radiotherapy, intensity modulated radiotherapy, adaptive radiotherapy, customized shielding, a shrinking field technique, bladder distension, and optimal irradiation positions such as supine, prone or by using a belly board (BB). [5] The theory behind the BB device is that, by creating a space cephalic to the radiation fields due to a negative pressure effect, the SB loops in the pelvis are expected to be pulled cephalad into the space.

The position of the opening of the BB in relation to patient anatomy has not been defined in most studies. The position of the BB opening influences the volume of SB within the pelvis. If the lower border of the opening is near the lumbosacral junction, the volume of SB irradiated is the lowest. [6] Uncertainties in the daily set up of the patients during treatment can give rise to complications or influence the results of the treatment. Those uncertainties can be reduced by the repositioning of the patient according to the set up verification. [7]

A prospective study was undertaken to evaluate the influence of patient positioning (supine vs. prone using a BB) on the set up variations to determine the planning target volume (PTV) margins and to evaluate the clinical relevance of contouring and volume assessment of the SB within the irradiated volume.


 > Materials and methods Top


Patients

Twenty consecutive patients (7 female and 13 male), with histologically confirmed rectal cancer, scheduled to receive pelvic irradiation were evaluated prospectively from December 2011 to April 2012. Twelve patients had undergone pelvis surgery previously (low anterior resection [LAR]: 10 and abdominoperineal resection [APR]: 2) and in eight patients surgical procedures had been carried out after preoperative chemo radiation. The median age of the patients was 55 years (range 20-80 years). The median body weight of the patients was 65 kg (range 40-120 kg) [Table 1]a and b.
Table 1:

Click here to view


Patients who were unlikely to comply with the treatment, patients who were having a colostomy bag, short-stature patients who could not position themselves in prone BB were excluded from the study. All the patients underwent complete physical examination prior to the treatment. The patients were randomized into two groups:

ARM 1: Patients treated in supine position, receiving either pre-or post-operative radiation treatment

ARM 2: Patients treated in prone position, receiving either pre-or post-operative radiation treatment.

Types of surgery carried out for the primary tumor were either LAR or APR. The type of surgery was decided by the operating surgeon, depending on the location and extent of primary lesion and involvement of the regional lymph nodes.

Imaging

After informed consent was obtained from all patients, they were made to undergo computed tomography (CT) simulation and were positioned exactly in the same condition in which the treatment will be delivered in the linear accelerator. Patients in the supine position were immobilized by using either wing board or head rest, with knee and ankle fixed in the supine position, while patients in the prone position were immobilized by using BB [Figure 1]a-c. No instructions for bladder or rectum filling were given. Intravenous or oral contrast media was not used obligatorily. The position and alignment of the fiducials were verified by taking a CT slice through the fiducials. The CT scan was performed and slices were obtained from L2 to mid-thigh with a slice thickness of 5 mm.
Figure 1: (a) Prone belly board device (b) Foot support-belly board (c) Arm support-belly board

Click here to view


Treatment planning

Planning was done by a 3D planning system. The volumes of interest were defined in each axial CT slice. In the treatment planning system, the beam was placed according to patient coordinates. A suitable beam angle (gantry angle) was chosen in such a way to cover the target volume. Based on the prescription depth, the energy of the beam was chosen. The fields were shaped according to the anatomy of the target volume and normal structures by means of asymmetric jaws and multi-leaf collimators. The dose prescription was done according to ICRU 50. Whole pelvis was treated using the 3-field or the 4-field technique. The tumor bed was irradiated with a dose of 45-50 Gy in 23-25 fractions, 1.8-2 Gy per fraction. Postoperative radiotherapy started as soon as the wound was healed, preferably in 8 weeks. The volume of bowel in relation to the PTV is shown in [Figure 2]a and b.
Figure 2: (a) Three-dimensional conformal radiation therapy plan-prone: Image showing small bowel pushed away from the radiation field (b) Three-dimensional conformal radiation therapy plan-supine: More amount of small bowel receiving 100% and 98% of the prescription dose

Click here to view


Treatment set up

The set up variation of the study group was assessed from the data received from electronic portal imaging device (EPID). In the eye view using template matching, the port film was matched with digitally reconstructed radiographs. The shift along X (lateral shift), Y (in-out shift) and Z (up-down shift) was noted. For each patient, approximately six port films were taken. The variations along X, Y, and Z directions were noted.

The set up variation was calculated as follows:

For each patient, x1, x2, x3,…, x6 were the variations along X direction, y1, y2, y3,…, y6 the variations along Y direction and z1, z2, z3,…, z6 the variations along Z direction. The average value along each direction was calculated, i.e., X = x1 + x2 + x3+… + x, Y = y1 + y2 + y3+…+ y, Z = z1 + z2 + z3+… + z. For all 20 patients, the average values X1, X2, X3,…, X20 were taken. The standard deviation of x1, x2, x3,…, x6, the variation along X direction, y1, y2, y3,…, y6, the variation along Y direction and z1, z2, z3,…, z6, the variation along Z direction were calculated using "nonbiased" or "n - 1" method. Twenty such average and standard deviation values were determined separately along X, Y, and Z directions. With the help of these mean and standard deviation values the systematic and random errors were calculated.

Systematic errors were calculated by taking the standard deviation of the average values along X, Y, and Z directions for prone and supine positions while random errors were calculated by taking the root mean square values of the standard radiation values along X, Y, and Z directions. Using both these values the PTV margin was calculated using the formula,

Planning target volume margin = 2.5 ∑ +0.7 σ,

Where ∑ is the quadratic sum of standard deviation of all preparation (systematic) errors and σ is the quadratic sum of standard deviation of all execution (random) errors.


 > Results Top


When contoured the bowel as loops, the mean bowel volume within the PTV was 204.66 cm 3 in prone position and 480.918 cm 3 in supine position [Figure 3]a and b. When contoured the peritoneal cavity, the mean volume of the peritoneal cavity was 648.65 cm 3 in prone position and 1197.37 cm 3 in supine position [Figure 4]a and b.
Figure 3: (a) Bowel contour as loops-prone (b) Bowel contour as loops- supine

Click here to view
Figure 4: (a) Peritoneal cavity-prone (b) Peritoneal cavity-supine

Click here to view


A total of 120 ports (six ports/patient) were taken, including 10 patients in prone and 10 patients in supine position. The mean variations in X, Y, and Z directions for each patient treated in both supine and prone positions are given in [Table 2] and [Table 3].
Table 2: Mean variation-supine

Click here to view
Table 3: Mean variation-prone

Click here to view


Mean variation

The systematic errors of patients [Table 4] treated in supine positions were 0.87 (X-mm), 0.66 (Y-mm), 1.6 (Z-mm) and of those treated in prone positions were 1.3 (X-mm), 0.59 (Y-mm), 1.17 (Z-mm). The random errors of patients [Table 5] treated in supine positions were 1.81 (X-mm), 1.73 (Y-mm), 1.83 (Z-mm) and of those treated in prone positions were 2.02 (X-mm), 1.21 (Y-mm), 3.05 (Z-mm).
Table 4: Systematic error

Click here to view
Table 5: Random error

Click here to view


The calculated PTV margin values [Table 6] in supine positions were 3.45 (X-mm), 2.87 (Y-mm), 5.31 (Z-mm) and those in prone positions were 4.91 (X-mm), 2.32 (Y-mm), 5.08 (Z-mm).
Table 6: The calculated PTV margins in prone and supine

Click here to view


There were no significant variations in the set up for patients treated in both supine and prone positions. The calculated PTV margins were around 0.5 cm in both the treatment groups (P < 0.001).


 > Discussion Top


A combined modality approach with surgery and chemo radiation or preoperative chemo radiation followed by surgery is the standard of care for rectal cancer treatment. [8],[9] In radiotherapy of rectal carcinoma the dose-limiting normal tissue is first and foremost the SB, but organs or structures such as the urinary bladder, ureters, rectum, femoral head, skin, and nerves are at risk of adverse effects. [2] The reduction of toxicity is a major challenge for clinicians even in the era of sophisticated surgical and radiation treatment modalities. There have been various improvements in the surgical and radiation treatment modalities with the availability of newer techniques. These help to reduce the side-effects of radiation treatment. The use of prone BB device helps to reduce the SBV in the irradiation field. [10],[11],[12] However, the reproducibility of such newer techniques remains unverified, especially in the Indian scenario. The major challenges in treating the patient in the prone position are probable daily set up variations, patient compliance and suspected technical issues in female patients due to difficulties in achieving pubic locking and breast positioning on the BB device . [12] The authors report that this procedure takes about 1 h, meaning high personal costs and therefore low practicability for routine simulation. [13]

There have been many trials evaluating the benefits of prone BB reducing the SBV in the radiation treatment field . [5],[12] In the present study, volume of bowel was less in patients treated in the prone position using prone BB. Even though, the bowel contouring was not standardized, the data showed that the volume of bowel was minimal either we contour the entire peritoneal cavity or single bowel loops. Although, this study demonstrated that the use of a BB was beneficial in reducing the irradiated SBV, it was a comparative study between two treatment positions and plans, but not real treatments. Thus, clinical outcomes such as bowel toxicity could not be studied. However, the reduced volume of the SB irradiated may be beneficial to patients with rectal cancer who receive treatment in the prone BB device.

The concern remains regarding the set up variation and reproducibility with prone BB either with 3D conformal radiation therapy (CRT) or intensity modulated radiation therapy (IMRT) techniques. Adli et al. have reported that even though there may be more set up uncertainties in prone positioning than in supine positioning, they have generally not observed a greater rate of field corrections or a greater rate of tumor/nodal failure in patients treated in the prone position compared with those treated in the supine position. [14] In the present study, all our patients received radiation treatment with 3D CRT except one patient who received adjuvant IMRT. Keys et al. have reported more systematic and random errors in treating patients with the prone BB device. [15] However, the methods used for the verification were conventional X-ray simulation film systems instead of EPIDs. The trial has reported problems in accommodating patients in the prone BB position. Thus, the extent of benefits from the use of prone BB cannot be assessed from the available data. There are not many studies available in this scenario, addressing the Indian population. The present study was carried out to evaluate the feasibility of using prone BB in patients receiving external radiation therapy for rectal cancer.

Of the 20 patients, seven were females of which three were treated with prone BB device. There was no significant mean variation in the daily set up for any of these three female patients. Both the systematic and random errors were not higher in the one patient who received IMRT. The body weight found to be a factor that shows a trend toward more daily patient set up variations in the prone position. The variations in each direction (X, Y and Z) were more in the two patients with bodyweight >100 kg.

In the present study, we compared both the systematic and random errors in both supine and prone positions. None of the values was significantly higher in either arm. Thus, the PTV margin calculated was the same, i.e., 0.5 cm in both the treatment groups. There was no major variation in daily patient set up. Patient compliance was good with adequate reproducibility


 > Limitations of the study Top


This study was performed on 20 patients divided into two groups of 10 each in prone and supine positions. Determination of systematic and random errors on a group of 10 patients gives a reasonable, but not definite estimate of the errors. Larger studies are required to improve the statistical power of the analyzed variations. The study does, however, give a good estimate of the order of magnitude and especially the heterogeneity of systematic and random errors for shape variation, especially in Indian patients. There were technical problems in strictly not following bladder filling protocol as in some patients this found difficult, especially for patients in prone position. There were other issues in getting the patient data from the supine and prone position for the same patient. The impact of bowel volume variations between different surgical modalities may have an influence which cannot be analyzed in the present study.


 > Conclusion Top


The present study found that the use of BB was more effective in reducing irradiated SBV in rectal cancer patients. These dosimetric findings may result in a reduction in SB complications in patients receiving external beam radiation for rectal cancer. Both prone and supine positions are acceptable for pelvic radiotherapy in patients with rectal cancer as no significant variation was observed in daily patient set up either in the prone or supine position. Factors like weight of the patient, patient comfort, and technical expertise are important when deciding the treatment position for pelvic radiation.

 
 > References Top

1.
Kavanagh BD, Pan CC, Dawson LA, Das SK, Li XA, Ten Haken RK, et al. Radiation dose-volume effects in the stomach and small bowel. Int J Radiat Oncol Biol Phys 2010;76:S101-7.  Back to cited text no. 1
    
2.
Emami B, Lyman J, Brown A, Coia L, Goitein M, Munzenrider JE, et al. Tolerance of normal tissue to therapeutic irradiation. Int J Radiat Oncol Biol Phys 1991;21:109-22.  Back to cited text no. 2
    
3.
Rudat V, Flentje M, Engenhart R, Metzger M, Wannenmacher M. The belly-board technic for the sparing of the small intestine. Studies on positioning accuracy taking into consideration conformational irradiation technics. Strahlenther Onkol 1995;171:437-43.  Back to cited text no. 3
    
4.
Shank B, LoSasso T, Brewster L, Burman C, Cheng E, Chu JC, et al. Three-dimensional treatment planning for postoperative treatment of rectal carcinoma. Int J Radiat Oncol Biol Phys 1991;21:253-65.  Back to cited text no. 4
    
5.
Koelbl O, Richter S, Flentje M. Influence of patient positioning on dose-volume histogram and normal tissue complication probability for small bowel and bladder in patients receiving pelvic irradiation: A prospective study using a 3D planning system and a radiobiological model. Int J Radiat Oncol Biol Phys 1999;45:1193-8.  Back to cited text no. 5
    
6.
Koelbl O, Vordermark D, Flentje M. The relationship between belly board position and patient anatomy and its influence on dose-volume histogram of small bowel for postoperative radiotherapy of rectal cancer. Radiother Oncol 2003;67:345-9.  Back to cited text no. 6
    
7.
Cazzaniga LF, Frigerio M. Errors in positioning the patient during transcutaneous radiotherapy of the pelvis. Radiol Med 1997;94:664-70.  Back to cited text no. 7
    
8.
NIH consensus conference. Adjuvant therapy for patients with colon and rectal cancer. JAMA 1990;264:1444-50.  Back to cited text no. 8
    
9.
Skibber JM, Hoff PM, Minsky BD, Cancer of the rectum. In: Devita VT, Hellman S, Rosenberg SA, editors. Cancer: principles and Practice of Oncology. Philadelphia: Lippincott Williams and Wilkins; 2001. p. 1271-318.  Back to cited text no. 9
    
10.
Fu YT, Lam JC, Tze JM. Measurement of irradiated small bowel volume in pelvic irradiation and the effect of a bellyboard. Clin Oncol (R Coll Radiol) 1995;7:188-92.  Back to cited text no. 10
    
11.
Shanahan TG, Mehta MP, Bertelrud KL, Buchler DA, Frank LE, Gehring MA, et al. Minimization of small bowel volume within treatment fields utilizing customized "belly boards". Int J Radiat Oncol Biol Phys 1990;19:469-76.  Back to cited text no. 11
    
12.
Das IJ, Lanciano RM, Movsas B, Kagawa K, Barnes SJ. Efficacy of a belly board device with CT-simulation in reducing small bowel volume within pelvic irradiation fields. Int J Radiat Oncol Biol Phys 1997;39:67-76.  Back to cited text no. 12
    
13.
Huh SJ, Lim DH, Ahn YC, Kim DY, Kim MK, Wu HG, et al. Effect of customized small bowel displacement system in pelvic irradiation. Int J Radiat Oncol Biol Phys 1998;40:623-7.  Back to cited text no. 13
    
14.
Adli M, Mayr NA, Kaiser HS, Skwarchuk MW, Meeks SL, Mardirossian G, et al. Does prone positioning reduce small bowel dose in pelvic radiation with intensity-modulated radiotherapy for gynecologic cancer? Int J Radiat Oncol Biol Phys 2003;57:230-8.  Back to cited text no. 14
    
15.
Keys HM, Bundy BN, Stehman FB, Muderspach LI, Chafe WE, Suggs CL 3 rd , et al. Cisplatin, radiation, and adjuvant hysterectomy compared with radiation and adjuvant hysterectomy for bulky stage IB cervical carcinoma. N Engl J Med 1999;340:1154-61.  Back to cited text no. 15
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]



 

Top
 
 
  Search
 
Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
Access Statistics
Email Alert *
Add to My List *
* Registration required (free)

  >Abstract>Introduction>Materials and me...>Results>Discussion>Limitations of t...>Conclusion>Article Figures>Article Tables
  In this article
>References

 Article Access Statistics
    Viewed2303    
    Printed68    
    Emailed3    
    PDF Downloaded113    
    Comments [Add]    

Recommend this journal


[TAG2]
[TAG3]
[TAG4]