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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

Correspondence Address:
K R Rajeev
Department of Radiation Oncology, Regional Cancer Centre, Medical College Campus, Trivandrum, Kerala
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0973-1482.138021

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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

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