Differences in abdominal organ movement between supine and prone positions measured using four-dimensional computed tomography

Background and purposeTo analyze the differences in intrafractional organ movement throughout the breathing cycles between the supine and prone positions using four-dimensional computed tomography (4D CT).Materials and methodsWe performed 4D CT on nine volunteers in the supine and prone positions, with each examinee asked to breathe normally during scanning. The movement of abdominal organs in the cranio–caudal (CC), anterior–posterior (AP) and right–left (RL) directions was quantified by contouring on each phase between inspiration and expiration.ResultsThe mean intrafractional motions of the hepatic dome, lower tip, pancreatic head and tail, both kidneys, spleen, and celiac axis in the supine/prone position were 17.3/13.0, 14.4/11.0, 12.8/8.9, 13.0/10.0, 14.3/12.1, 12.3/12.6, 11.7/12.6 and 2.2/1.8 mm, respectively. Intrafractional movements of the liver dome and pancreatic head were reduced significantly in the prone position. The CC directional excursions were major determinants of the 3D displacements of the abdominal organs. Alteration from the supine to the prone position did not change the amount of intrafractional movements of kidneys, spleen, and celiac axis.ConclusionThere was a significant reduction in the movements of the liver and pancreas during the prone position, especially in the CC direction, suggesting possible advantage of radiotherapy to these organs in this position.     

Radiation therapy of the pelvic and paraaortic lymph nodes in cervical carcinoma: a prospective three-dimensional analysis of patient positioning and treatment technique.

PURPOSE: Pelvic box fields in prone position are the standard treatment for patients with cervical carcinomas. The issue investigated in this report is whether this technique should also be used when extending the planning target volume to the paraaortic region. MATERIALS AND METHODS: In a prospective study of eight consecutive patients with cervical carcinomas, two patient positions (prone and supine) and three radiation techniques (A, anteroposterior/posteroanterior opposed fields; B, four-field box; and C, three-field technique) were examined concerning the dose to critical organs. The analysis was based on three-dimensional planning, dose-volume histograms and normal tissue complication probabilities (NTCP). RESULTS: Compared to the prone position, the supine position led to improved organ sparing in four of seven organs (liver, both kidneys, spinal canal). In two of seven organs (rectum and bladder) no difference between prone and supine position was observed. The best sparing of small bowel was achieved in prone position. Technique B followed by technique C in the supine position resulted in the best overall sparing of critical organs concerning the volumes receiving the respective TD(5/5) doses or more. Mean NTCP values for liver, rectum and bladder were below 1.0%. The highest values of up to 12% were found for both kidneys in prone position with C and for the spinal canal with A in the prone and supine position. CONCLUSION: According to this analysis, for the treatment of the pelvic and paraaortic lymph node regions together, supine position and technique B (alternatively C) should be preferred despite the advantages of prone position on belly boards for pelvic irradiation alone.     

A comparison of ventilatory prostate movement in four treatment positions

PURPOSE: To ensure target coverage during radiotherapy, all sources of geometric uncertainty in target position must be considered. Movement of the prostate due to breathing has not traditionally been considered in prostate radiotherapy. The purpose of this study is to report the influence of patient orientation and immobilization on prostate movement due to breathing. METHODS AND MATERIALS: Four patients had radiopaque markers implanted in the prostate. Fluoroscopy was performed in four different positions: prone in alpha cradle, prone with an aquaplast mold, supine on a flat table, and supine with a false table under the buttocks. Fluoroscopic movies were videotaped and digitized. Frames were analyzed using 2D-alignment software to determine the extent of movement of the prostate markers and the skeleton for each position during normal and deep breathing. RESULTS: During normal breathing, maximal movement of the prostate markers was seen in the prone position (cranial-caudal [CC] range: 0.9-5.1 mm; anterior-posterior [AP] range: up to 3.5 mm). In the supine position, prostate movement during normal breathing was less than 1 mm in all directions. Deep breathing resulted in CC movements of 3.8-10.5 mm in the prone position (with and without an aquaplast mold). This range was reduced to 2.0-7.3 mm in the supine position and 0.5-2.1 mm with the use of the false table top. Deep breathing resulted in AP skeletal movements of 2.7-13.1 mm in the prone position, whereas AP skeletal movements in the supine position were negligible. CONCLUSION: Ventilatory movement of the prostate is substantial in the prone position and is reduced in the supine position. The potential for breathing to influence prostate movement, and thus the dose delivered to the prostate and normal tissues, should be considered when positioning and planning patients for conformal irradiation.     

Patient positioning in prostate radiotherapy: is prone better than supine?

PURPOSE: To assess potential dose reductions to the rectum and to the bladder with three-dimensional conformal radiotherapy (3D-CRT) to the prostate in the prone as compared with the supine position; and to retrospectively evaluate treatment position reproducibility without immobilization devices. METHODS AND MATERIALS: Eighteen patients with localized prostate cancer underwent pelvic CT scans and 3D treatment planning in prone and supine positions. Dose-volume histograms (DVHs) were constructed for the clinical target volume, the rectum and the bladder for every patient in both treatment positions. "Comparative DVHs" (cDVHs) were defined for the rectum and for the bladder: cDVH was obtained by subtracting the organ volume receiving a given dose increment in the prone position from the corresponding value in the supine position. These values were then integrated over the entire dose range. The prescribed dose to the planning target volume (PTV) was 74 Gy using a 6-field technique. To evaluate reproducibility, portal films were subsequently reviewed in 12 patients treated prone and 10 contemporary patients treated supine (controls). No immobilization devices were used. Deviations in the anterio-posterior (X) and cranio-caudal (Y) axes were measured. Mean treatment position variation, total setup variation, systematic setup variation, and random setup variation were obtained. RESULTS: Prone position was associated with a higher dose to the rectum or to the bladder in 6 (33%) and 7 (39%) patients, respectively. A simultaneously higher dose to rectum and bladder was noted in 2 (11%) patients in prone and in 7 (39%) patients in supine. Rectal and bladder volumes were frequently larger in prone than in supine: mean prone/supine volume ratios were 1.21 (SD, 0.68) and 1.03 (SD, 1.32), respectively. In these cases cDVH analysis more often favored the prone position. Mean treatment position variation and total setup variation were similar for both prone and supine plans. A higher systematic setup variation was observed in prone positioning: 2.7 mm vs. 1.9 mm (X axis) and 4.1 mm vs. 2.2 mm (Y axis). The random variation was similar for both prone and supine: 4. 0 mm vs. 3.6 mm (X axis) and 3.7 mm vs. 3.6 mm (Y axis). CONCLUSIONS: Prone position 3D-CRT is frequently, but not always, associated with an apparent dose reduction to the rectum and/or to the bladder for prostate cancer patients. As suggested by the increased mean prone/supine rectal volume ratio, the advantage of prone positioning for the rectum may be artifactual, at least partly reflecting a position-dependent rectal air volume, which may significantly vary from treatment to treatment. In the absence of immobilization devices, daily setup reproducibility appears less accurate for the prone position, primarily due to systematic setup variations.     

直肠癌辅助放疗中患者腹围在不同体位下与肠道剂量体积的相关性分析

目的:通过对比分析直肠癌辅助放疗患者的不同腹围在俯卧位联合Belly-board和仰卧位两种治疗体位下与肠道剂量体积的相关性,为不同腹围大小患者选择合适的治疗模式提供临床证据。方法:通过单因素线性回归分析初步评估与各剂量水平的肠道剂量体积（肠道 V10、V20、V30、V40、V50）相关的临床因素和体型指标（身高、体重、脐部腹围、BMI）;多因素线性回归分析评估各个体型指标对肠道剂量体积的独立作用,筛选可以预测肠道剂量体积的体型指标。应用配对t检验在中大和小腹围两组患者间进行仰卧位和俯卧位的肠道剂量体积均数比较。结果:多因素线性回归分析显示,无论何种体位,脐部腹围与各肠道剂量体积均有显著的负的线性关系;配对t检验显示,在中大腹围患者中,V30、V40、V50在俯卧位时显著低于仰卧位,V10在俯卧位时显著高于仰卧位,而在小腹围患者中,V20、V30、V40、V50在俯卧位和仰卧位间均无显著差异,V10在俯卧位时仍显著高于仰卧位,而且均值差显著大于中大腹围患者。结论:对于中大腹围的患者,俯卧位垫Belly-board较仰卧位有中高剂量的肠道剂量学优势;在小腹围患者中,仰卧位在肠道低剂量体积（V10）更有优势,而其他肠道剂量体积与俯卧位并无差异。     

体质量指数对宫颈癌调强放疗摆位误差影响

目的:探讨宫颈癌患者体质量指数(BMI)对调强放疗摆位误差的影响,以及在不考虑旋转误差、靶区及邻近器官变化的情况下不同BMI宫颈癌患者放疗的最佳体位。方法:将90例宫颈癌患者根据BMI分为过轻组(BMI≤18.4 kg/m 2)、正常组(18.5 kg/m 2≤BMI≤23.9 kg/m ...     

A randomized trial of supine vs. prone positioning in patients undergoing escalated dose conformal radiotherapy for prostate cancer.

BACKGROUND AND PURPOSE: The optimal treatment position for patients receiving radical radiation therapy for prostate cancer has been a source of controversy. To resolve this issue, we conducted a randomized trial to evaluate the effects of supine and prone positioning on organ motion, positioning errors, and dose to critical organs during escalated dose conformal irradiation for localized prostate cancer and patient and therapist satisfaction with setup technique. PATIENTS AND METHODS: Twenty eight patients were randomized to commence treatment immobilized in the supine or prone position and were subsequently changed to the alternate positioning for the latter half of their treatment. Patients underwent CT simulation and conformal radiotherapy planning and treatment in both positions. The clinical target volume encompassed the prostate gland. Alternate day lateral port films were compared to corresponding simulator radiographs to measure the isocentre positioning errors (IPE). Prostate motion (PM) and total positioning error (TPE) were measured from the same films by the displacements of three implanted fiducial markers. Dose volume histograms (DVHs) for the two treatment positions were compared at the 95, 80 and 50% dose (D%) levels. The patients and radiation therapists completed weekly questionnaires regarding patient comfort and ease of setup. RESULTS: Seven patients, who started in the supine position, subsequently refused prone position and received their whole treatment supine. Small bowel in the treatment volume, not present in the supine position, prevented one patient from being treated prone. PM in anterior posterior direction was statistically significantly less in the supine position (P<0.05). There was no significant difference in superior inferior PM for the two treatment positions. No statistically significant difference between supine and prone positioning was observed in isocentre positioning error (IPE) or total positioning error (TPE) due to a policy of daily pre-treatment correction. However, more pre-treatment corrections were required for patients in the prone position. The DVH analysis demonstrated larger volumes of the bladder wall, rectal wall and small bowel within the D95, D80 and D50% when comparing the planning target volumes (PTVs) actually treated for prone positioning. When the prone PTV was expanded to account for the greater PM encountered in that position, a statistically significant difference (P<0.007) was observed in favour of the supine position at all dose levels. In the prone position, four patients had small bowel within the 60 Gray (Gy) isodose and in the supine position, no patients had small bowel in the 60 or 38Gy volumes. Supine position was significantly more comfortable for the patients and setup was significantly easier for the radiation therapists. The median patient comfort score was 0.79 (Standard deviation (SD) 0.03) supine and 0.45 (SD 0.05) prone (P<0.001) The therapist convenience of setup was 0.80 (SD 0.016) supine and 0.54 (SD 0.025) prone (P<0.005). No statistically significant difference was seen for the other parameters studied. CONCLUSIONS: We demonstrated significantly less PM in the supine treatment position. There was no difference for either treatment position in IPE or TPE, however, more pre-treatment corrections were required in the prone position. Prone position required a larger PTV with resulting increased dose to critical organs. There were statistically significant improvements at all dose levels for small bowel, rectal wall and bladder wall doses in the supine position once corrections were made for differences in organ motion. Linear analogue scores of patient comfort and radiation therapist convenience demonstrated statistically significant improvement in favour of the supine position. Supine positioning has been adopted as the standard for conformal prostatic irradiation at our centre.     

Internal organ motion in prostate cancer patients treated in prone and supine treatment position.

BACKGROUND AND PURPOSE: To compare supine and prone treatment positions for prostate cancer patients with respect to internal prostate motion and the required treatment planning margins. MATERIALS AND METHODS: Fifteen patients were treated in supine and fifteen in prone position. For each patient, a planning computed tomography (CT) scan was used for treatment planning. Three repeat CT scans were made in weeks 2, 4, and 6 of the radiotherapy treatment. Only for the planning CT scan, laxation was used to minimise the rectal content. For all patients, the clinical target volume (CTV) consisted of prostate and seminal vesicles. Variations in the position of the CTV relative to the bony anatomy in the four CT scans of each patient were assessed using 3D chamfer matching. The overall variations were separated into variations in the mean CTV position per patient (i.e. the systematic component) and the average 'day-to-day' variation (i.e. the random component). Required planning margins to account for the systematic and random variations in internal organ position and patient set-up were estimated retrospectively using coverage probability matrices. RESULTS: The observed overall variation in the internal CTV position was larger for the patients treated in supine position. For the supine and prone treatment positions, the random components of the variation along the anterior-posterior axis (i.e. towards the rectum) were 2.4 and 1.5 mm (I standard deviation (1 SD)), respectively; the random rotations around the left-right axis were 3.0 and 2.9 degrees (1 SD). The systematic components of these motions (1 SD) were larger: 2.6 and 3.3 mm, and 3.7 and 5.6 degrees, respectively. The set-up variations were similar for both treatment positions. Despite the smaller overall variations in CTV position for the patients in prone position, the required planning margin is equal for both groups (about 1 cm except for 0.5 cm in lateral direction) due to the larger impact of the systematic variations. However, significant time trends cause a systematic ventral-superior shift of the CTV in supine position only. CONCLUSIONS: For internal prostate movement, it is important to distinguish systematic from random variations. Compared to patients in supine position, patients in prone position had smaller random but somewhat larger systematic variations in the most important coordinates of the internal CTV position. The estimated planning margins to account for the geometrical uncertainties were therefore similar for the two treatment positions.     

A phase II trial for the optimisation of treatment position in the radiation therapy of prostate cancer

BACKGROUND: Patient immobilisation and position are important contributors to the reproducibility and accuracy of radiation therapy. In addition the choice of position can alter the external contour of the treated area and has the potential to alter the spatial relationship between internal organs. The published literature demonstrates variation in the use of the prone and supine position for prostate cancer radiation therapy. Previous investigators using different protocols for patient preparation, imaging and target volume definition have demonstrated changes in the calculated therapeutic ratio comparing the two positions. We did not use rigid immobilisation, laxatives, rectal catheters or bladder voiding and assessed if in the prone position would cause a reduction of the dose to the rectum. We performed a prospective comparison of the two positions in 26 patients to determine if the differences in the spatial relation between the rectum and the planning target volume (PTV) would impact on dose-volume histograms to organs at risk (OAR). We also determined if any such improvement might permit dose escalation. MATERIALS AND METHODS: Twenty-six patients with clinically localized prostate cancer consented to participate in this study. All patients underwent a planning CT scan in both the prone and supine treatment positions. The PTV and OAR were drawn on each set of scans by one of the investigators. The PTV included the prostate and seminal vesicles with a 1cm margin except posteriorly where this margin was reduced to 5mm. The outer circumference of the bladder, rectal wall, small bowel (when present) was drawn along with femoral heads. 3D conformal treatment plans were computed using Helax TMS version 6.1B. A 3-field treatment technique was employed with energy of 10/15 MV. The prescribed dose was 70 Gy and the PTV was encompassed by the 95% isodose and the maximum dose was always less than 107%. Cumulative dose-volume histograms were calculated for the PTV, rectum, bladder, femoral heads and small bowel (when present). These non-uniform histograms for both the prone and supine treatment positions were transformed into uniform ones using the effective volume method [Kutcher J, Burman C. Calculation of probability factors for non-uniform normal tissue irradiation: the effective volume method. Med Phys 1987;14:487]. RESULTS: Twenty-one of the 26 (80%) patients had a lower effective volume of rectum irradiated if the prone instead of the supine treatment position was used. The median value of the effective volume in the supine treatment position was 31.74 Gy while the median value in the prone position was 22.48 Gy. The dose escalation was applied to the patients in the prone treatment position until the effective volume for the rectum was the same as that in the supine position. The range of dose escalation possible for these patients was 0.1-7.9 Gy. These patients could potentially have the dose escalated from the prescribed dose of 70 Gy for the supine position without any increase in side effects. For the five patients where no potential benefit was found when changing treatment position, only two patients displayed a significant (>1 Gy) advantage for the supine treatment position. Twenty-one of the 26 patients also showed an advantage for the prone treatment position in relation to bladder dose. CONCLUSION: The use of the prone position reduced the dose to the unprepared rectum and unvoided bladder in the majority of cases. It should be considered particularly in cases where large posterior seminal vesicles cause significant overlap between the planning target volume and the rectum.     

乳腺癌保乳术后俯卧位与仰卧位放疗危及器官剂量比较的Meta分析

目的 探讨乳腺癌保乳术后采用俯卧位与仰卧位放疗危及器官的剂量差异,为临床实践提供证据。方法 制定严格的纳入和排除标准,全面检索PubMed、FMJS、CHKD和万方全文数据库。纳入乳腺癌保乳术后俯卧位与仰卧位危及器官剂量对比的相关研究。统计学处理采用Cochrane协作网提供的RevMan5.2统计软件计算标准化均差及其95%可信区间。结果 共检索到267篇文献,经评价后最终16个研究442例乳腺癌患者符合本系统评价的纳入标准。Meta分析结果显示：乳腺癌保乳术后患者采用俯卧位放疗患侧肺（SMD=-4.36,95%CI：-5.41~-3.31,P<0.001）和心脏（SMD=-0.24,95%CI：-0.4~-0.09,P<0.05）受照剂量明显低于仰卧位;对侧乳腺受照剂量在两种体位间差异无统计学意义（SMD=0.19,95%CI：-0.02~0.40,P>0.05）。结论 与仰卧位相比,乳腺癌保乳术后俯卧位放疗可明显降低心脏和患侧肺的受照剂量。     

An evaluation of intrafraction motion of the prostate in the prone and supine positions using electromagnetic tracking

Purpose

To evaluate differences in target motion during prostate irradiation in the prone versus supine position using electromagnetic tracking to measure prostate mobility.

Materials/methods

Twenty patients received prostate radiotherapy in the supine position utilizing the Calypso Localization System® for prostate positioning and monitoring. For each patient, 10 treatment fractions were followed by a session in which the patient was repositioned prone, and prostate mobility was tracked. The fraction of time that the prostate was displaced by >3, 5, 7, and 10 mm was calculated for each patient, for both positions (400 tracking sessions).

Results

Clear patterns of respiratory motion were seen in the prone tracks due to the influence of increased abdominal motion. Averaged over all patients, the prostate was displaced >3 and 5 mm for 37.8% and 10.1% of the total tracking time in the prone position, respectively. In the supine position, the prostate was displaced >3 and 5 mm for 12.6% and 2.9%, respectively. With both patient setups, inferior and posterior drifts of the prostate position were observed. Averaged over all prone tracking sessions, the prostate was displaced >3 mm in the posterior and inferior directions for 11.7% and 9.5% of the total time, respectively.

Conclusions

With real-time tracking of the prostate, it is possible to study the effects of different setup positions on the prostate mobility. The percentage of time the prostate moved >3 and 5 mm was increased by a factor of three in the prone versus supine position. For larger displacements (>7 mm) no difference in prostate mobility was observed between prone and supine positions. To reduce rectal toxicity, radiotherapy in the prone position may be a suitable alternative provided respiratory motion is accounted for during treatment. Acute and late toxicity results remain to be evaluated for both patient positions.     

The impact of imaging modality (CT vs MRI) and patient position (supine vs prone) on tangential whole breast radiation therapy planning

Purpose

The purpose of this study was to evaluate the impact of magnetic resonance imaging (MRI) versus computed tomography (CT)-derived planning target volumes (PTVs), in both supine and prone positions, for whole breast (WB) radiation therapy.

Real-time tumor-tracking radiotherapy for adrenal tumors.

PURPOSE: To investigate the three-dimensional movement of internal fiducial markers near the adrenal tumors using a real-time tumor-tracking radiotherapy (RTRT) system and to examine the feasibility of high-dose hypofractionated radiotherapy for the adrenal tumors. MATERIALS AND METHODS: The subjects considered in this study were 10 markers of the 9 patients treated with RTRT. A total of 72 days in the prone position and 61 treatment days in the supine position for nine of the 10 markers were analyzed. All but one patient were prescribed 48 Gy in eight fractions at the isocenter. RESULTS: The average absolute amplitude of the marker movement in the prone position was 6.1+/-4.4 mm (range 2.3-14.4), 11.1+/-7.1 mm (3.5-25.2), and 7.0+/-3.5 mm (3.9-12.5) in the left-right (LR), craniocaudal (CC), and anterior-posterior (AP) directions, respectively. The average absolute amplitude in the supine position was 3.4+/-2.9 mm (0.6-9.1), 9.9+/-9.8 mm (1.1-27.1), and 5.4+/-5.2 mm (1.7-26.6) in the LR, CC, and AP directions, respectively. Of the eight markers, which were examined in both the prone and supine positions, there was no significant difference in the average absolute amplitude between the two positions. No symptomatic adverse effects were observed within the median follow-up period of 16 months (range 5-21 months). The actuarial freedom-from-local-progression rate was 100% at 12 months. CONCLUSIONS: Three-dimensional motion of a fiducial marker near the adrenal tumors was detected. Hypofractionated RTRT for adrenal tumors was feasible for patients with metastatic tumors.     

Three-dimensional photon dosimetry: a comparison of treatment of the intact breast in the supine and prone position

PURPOSE: To compare the adequacy of target coverage, dose homogeneity, and volume of normal tissue irradiated in treatment of the intact breast in the supine and prone position. METHODS AND MATERIALS: Fifteen patients with early breast cancer who presented for treatment to the intact breast after excisional biopsy were studied. A specially designed device was used for the prone setup to displace the contralateral breast away from the tangential field borders. Treatment planning computed tomography was performed for each patient in both the supine and prone positions. Dosimetric data were obtained in both positions and isodose distributions were calculated for each patient in both positions. RESULTS: The volume of breast receiving greater than 5% of the prescribed dose was significantly less in the prone position. Medial wedges were either not used or their angles were reduced for all patients in the prone position compared with the supine position. The average volume of lung receiving >10 Gy and >20 Gy was significantly less in the prone positions. The volume of heart irradiated at critical dose levels did not vary consistently in the prone and supine positions. The integral dose delivered to the contralateral breast was not significantly different. CONCLUSION: Treatment of the intact breast in the prone position may result in improved dose homogeneity within the target volume as well as sparing of normal lung compared with treatment in the conventional supine position.     

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

Purpose: A prospective study was undertaken to evaluate the influence of patient positioning (prone position using a belly board vs. supine position) on the dose-volume histograms (DVHs) of organs of risk, and to analyze its possible clinical relevance using radiobiological models.

Methods and Materials: From November 1996 to August 1997 a computed tomography (CT) scan was done in the prone position using a belly board and in supine position in 20 consecutive patients receiving postoperative pelvic irradiation because of rectal cancer. Using a three-dimensional (3D) planning system (Helax, TMS®) the DVH for small bowel, bladder, a standard planning target volume (PTV) of postoperative irradiation of rectal cancer, the intersection of volume of PTV and small bowel (PTV ∩ V_SB), respectively, of PTV and bladder (PTV ∩ V_B) were defined in each axial CT slice. The normal tissue complication probability (NTCP) was determined by the radiobiological model of Lyman and Kutcher using the tolerance data of Emami. For evaluation of late toxicity /β ratio was 2.5; for evaluation of acute toxicity, it was 10. Total dose was 50.4 Gy (1.8 Gy/fraction) (ICRU 50).

Results: Using the prone position compared to the supine position, the median volume of PTV ∩ V_B was reduced by 18.5 cm³ (62%). Median dose (related to the reference dose) to the bladder was 44.5% (22.4 Gy) in prone and 66.05% (33.3 Gy) in supine position (p < 0.001). Median V_B within the 90% (45.4 Gy), 80% (40.3 Gy), 60% (30.2 Gy), and 40% (20.2 Gy) isodose was significantly lower in the prone position when compared to the supine position. Using the radiobiological models, however, there was no difference of NTCP between prone position or supine position. In the prone position, median volume of PTV ∩ V_SB was reduced by 32.5 cm³ (54%). The median dose to small bowel was 30.85% (15.4 Gy) in the prone position and 47.35% (23.9Gy) in the supine position (p < 0.001). Significant differences between prone and supine position were found for median V_SB within the 90% (45.4 Gy), 80% (40.3 Gy), 60% (30.2 Gy), and 40% (20.2 Gy) isodose. According to the method of Lyman, median NTCP of small bowel was significant lower in prone than in supine position.

Conclusion: The prone position with a standard belly board should be the standard positioning technique for patients receiving adjuvant postoperative radiation therapy following surgery of rectal cancer. Both irradiated volume and total dose to the organs of risk can be reduced significantly. As a consequence of this, radiation induced toxicity will be minimized.     

直肠癌术后放疗体位对小肠和膀胱照射剂量及体积影响观察

目的：探讨腹腔镜直肠癌根治术后应用仰卧臀高腹低与俯卧垫有孔泡沫板2种放疗体位对小肠及膀胱照射体积及剂量的影响。方法：选取201006—01—2012—12—31我科收治腹腔镜下直肠癌根治术患者37例，分别在2种不同体位下进行CT模拟定位，勾画治疗靶区和正常器官，进行3野适形计划的设计，比较2种体位下小肠及膀胱的平均剂量，以及在20、30、40和45Gy等剂量水平小肠和膀胱受照体积V20、V30、V40及V45。结果：采用仰卧臀高腹低位和俯卧位垫有孔泡沫板住时，小肠在20 Gy剂量水平受照体积分别为76．22和156．27cm3，t=-3．352；30Gy处分别为31．26和56．35cm3，t=-3．412；40Gy处分别为21．22和45．35cm3，t=-4．072；45Gy处分别为21．22和45．35cm3，t=-3．768；均仰卧高于俯卧位，P值均〈0．05。膀胱在40Gy剂量水平受照体积分别为132．46和202．57cm3，显著低于俯卧位垫有孔泡沫板位的57．52和100．35cm3，t值分别为-4．072和-3．768，P值均〈0．05。但在20和30Gy剂量水平两组患者间差异无统计学意义，t值分别为-1．739和0．218，P值均〉O．05。结论：直肠癌术后放疗，应用仰卧臀高腹低体位能减少小肠的受照体积及剂量，也能减少高剂量区膀胱的受照体积。     

Three-dimensional intrafractional movement of prostate measured during real-time tumor-tracking radiotherapy in supine and prone treatment positions

To quantify three-dimensional (3D) movement of the prostate gland with the patient in the supine and prone positions and to analyze the movement frequency for each treatment position.

The real-time tumor-tracking radiotherapy (RTRT) system was developed to identify the 3D position of a 2-mm gold marker implanted in the prostate 30 times/s using two sets of fluoroscopic images. The linear accelerator was triggered to irradiate the tumor only when the gold marker was located within the region of the planned coordinates relative to the isocenter. Ten patients with prostate cancer treated with RTRT were the subjects of this study. The coordinates of the gold marker were recorded every 0.033 s during RTRT in the supine treatment position for 2 min. The patient was then moved to the prone position, and the marker was tracked for 2 min to acquire data regarding movement in this position. Measurements were taken 5 times for each patient (once a week); a total of 50 sets for the 10 patients was analyzed. The raw data from the RTRT system were filtered to reduce system noise, and the amplitude of movement was then calculated. The discrete Fourier transform of the unfiltered data was performed for the frequency analysis of prostate movement.

No apparent difference in movement was found among individuals. The amplitude of 3D movement was 0.1–2.7 mm in the supine and 0.4–24 mm in the prone positions. The amplitude in the supine position was statistically smaller in all directions than that in the prone position (p < 0.0001). The amplitude in the craniocaudal and AP directions was larger than in the left-right direction in the prone position (p < 0.0001). No characteristic movement frequency was detected in the supine position. The respiratory frequency was detected for all patients regarding movement in the craniocaudal and AP directions in the prone position. The results of the frequency analysis suggest that prostate movement is affected by the respiratory cycle and is influenced by bowel movement in the prone position.

The results of this study have confirmed that internal organ motion is less frequent in the supine position than in the prone position in the treatment of prostate cancer. RTRT would be useful in reducing uncertainty due to the effects of the respiratory cycle, especially in the prone position.     

Dose-volume histogram evaluation of prone and supine patient position in external beam radiotherapy for cervical and endometrial cancer.

BACKGROUND AND PURPOSE: To evaluate the influence of patient positioning on dose-volume histograms of organs at risk in external beam radiotherapy for cervical and endometrial cancer. MATERIALS AND METHODS: In 20 patients scheduled for definitive (7) or postoperative (13) external beam radiotherapy of the pelvis treatment planning CT scans were performed in supine and prone (belly board) positions. After volume definition of target and organs at risk treatment plans were calculated applying the four-field box technique. The dose-volume histograms of organs at risk were compared. RESULTS: Radiotherapy in prone position causes a reduction of the bladder portion (mean 15%, p<0.001) and an increase of the rectum portion (mean 11%, p<0.001) within the 90% isodose. A reduction of the bowel portion could only be observed in postoperatively treated patients (mean 13%, p<0.001). In definitive radiotherapy the target volume increases in supine position (mean 7%, p=0.02) due to an anterior tumour/uterus movement, so that bowel portions within the 90% isodose are similar. The bladder filling correlates with a reduction of bladder and bowel (postoperatively treated patients) dose. CONCLUSIONS: External beam radiotherapy of the pelvis should be performed in prone position in postoperative patients because of best bowel protection. Considering the additional HDR brachytherapy rectum protection takes the highest priority in definitive treatment-the requirements are best met in supine position. An adequate bladder filling is important to reduce the irradiated bladder and bowel volumes.     

宫颈癌放疗仰、俯卧位固定下的摆位误差及剂量学差异探讨

目的:对比研究宫颈癌调强放疗中行仰卧位与俯卧位的两种固定方式时的摆位误差及剂量学差异。方法:随机选取64例宫颈癌患者分成两组,每组32例,分别选取仰卧位和俯卧位方式固定。两组患者均行首次摆位、摆位误差纠正及治疗期间的CBCT扫描,将CBCT扫描图像与治疗计划CT图像自动匹配配准,分别得到X轴（左右方向）、Y轴（头脚方向）、Z轴（腹背方向）的摆位误差数据;同时通过TPS计算两组病例靶区的D95、Dmean、CI、HI以及危及器官小肠、膀胱、直肠、结肠、股骨头、盆骨、脊髓、乙状结肠分别在等剂量线包含的体积百分比下的剂量值大小。结果:仰卧位患者与俯卧位患者在X、Y、Z轴方向平均误差分别为［（2.55±1.21） mm,（2.13±1.12） mm］、［（4.01±1.16） mm,（2.44±1.57） mm］、［（3.46±1.43） mm,（2.89±1.21） mm］。俯卧位固定组X、Y、Z轴方向平均误差均小于仰卧位固定组,且均具有统计学差异（P<0.05）;在靶区的D95、Dmean、CI、HI均不具有统计学差异（P>0.05）,除股骨头、盆骨、脊髓、乙状结肠外,俯卧位固定组的危及器官小肠、膀胱、直肠、结肠在等剂量线包含的体积百分比下的剂量值明显小于仰卧位固定组,且均具有统计学差异（P<0.05）。结论:在宫颈癌调强放疗中,与仰卧位固定相比,俯卧位固定可明显减少其摆位误差,以及在靶区受量归一一致的情况下,更好地保护了危及器官。