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At least 109 records · Page 6Linked to original sources
PubMed2006

Adverse effect of a distended rectum in intensity-modulated radiotherapy (IMRT) treatment planning of prostate cancer.

BACKGROUND AND PURPOSE: The retrospective planning study for intensity-modulated radiotherapy (IMRT) of prostate cancer evaluated whether proximal rectum and supra-anal rectum/anal canal should be delineated as separated organs-at-risk (OARs) to achieve optimal dose distributions to the anorectal region. PATIENTS AND METHODS: For 10 patients with localized prostate cancer IMRT plans were generated with the rectum and anal canal as separated OARs (Rec-sep) and as one single OAR (Rec-tot). Two different treatment planning systems (TPS) were utilized. Influence on dose distributions to target and OARs was analyzed. RESULTS: Results from both TPS showed significantly increased doses to the distal rectum/anal canal for plans Rec-tot compared with Rec-sep in case of a distended rectum in the planning CT study: doses were increased by up to mean 31% (P = 0.02) and 18% (P = 0.03), respectively, in both TPS. For the patient with the largest rectum, the maximum dose increase was 61%. No significant differences in doses to target, bladder, femoral head and proximal rectum were seen. CONCLUSIONS: For patients with a distended rectum in the planning CT, delineation of separated OARs for proximal rectum and distal rectum/anal canal resulted in superior dose distributions to the anorectal region and therefore, we recommend this as standard procedure for IMRT planning of prostate cancer.

Algorithms↗
PubMed1997

An analysis of the effect of ovoid shields in a selectron-LDR cervical applicator on dose distributions in rectum and bladder.

PURPOSE: A disadvantage of ovoid shields in a Fletcher-type applicator is that these shields cause artifacts on postimplant CT images. CT images, however, make it possible to calculate the dose distribution in the rectum and the bladder. To be able to estimate the possible advantage of having CT information over the use of ovoid shields without having CT information, we investigated the influence of shielding segments in a Fletcher-type Selectron-LDR applicator on the dose distribution in rectum and bladder. METHODS AND MATERIALS: Contours of rectum and bladder were delineated on transaxial CT slices of 15 unshielded applications. Of the volumes contained within these structures dose-volume histograms (DVHs) were calculated. In a similar way, DVHs of simulated shielded applications were calculated. The reduction, due to shielding, of the dose to the 2 cm3 (D2) and 5 cm3 (D5) volume of the cumulative DVHs of rectum and bladder, were determined. An isodose pattern in the sagittal plane through the center of each applicator was plotted to compare the location of the shielded area with the location of maximum dose in rectum and bladder in the unshielded situation. In two cases local dose reductions to the rectal wall were determined by calculating the dose in points at 10-mm intervals on the rectal contours. RESULTS: For the rectum, the reduction of D2 ranged from 0 to 11.1%, with an average of 5.0%; the reduction of D5 ranged from 2.3 to 12.1%, with an average of 6.4%. The reduction of D2 and D5 for the bladder ranged from 0 to 11.9% and from 0 to 11.6%, with average values of 2.2 and 2.6%, respectively. In 8 out of 15 cases the rectal maximum dose was located inferior to the shielded area. In all cases except one the bladder maximum dose was located superior to the shielded area. Local dose reductions on the rectal wall can be as high as 30% or more in an optimally shielded area. CONCLUSIONS: Reductions of D2 and D5 to rectum and bladder due to shielding are rather small, because the shielded area does usually not coincide with the high dose region and even if it does, the shielded area is too small to result in large reductions of these values. Because local dose reductions vary largely, one should proceed with caution when calculating the dose in just one rectal or bladder reference point. Because large overall dose reductions cannot be achieved with shielding, it is safe to use an unshielded applicator when post implant CT images are used to realize optimized dose distributions.

Artifacts↗
PubMed1998

Extrafascial excision of the rectum for rectal cancer.

BACKGROUND: The fascia propria of the rectum is an upward capsular projection from the superior fascia of the pelvic floor which surrounds the rectum and its mesorectum posteriorly and the fat, blood vessels, nerves and lymphatics in front and laterally. It is postulated that if rectal cancer is contained within the fascia propria and extrafascial excision of the rectum is performed then it would be exceptional for the cancer to recur locally. METHODS: A total of 122 consecutive patients with rectal cancer underwent extrafascial excision of the rectum. The operation involved mobilizing the rectum outside its fascia propria and removing not only the rectum and its mesorectum posteriorly but also the fat, blood vessels, nerves and lymphatics in front and laterally. Resection was considered curative unless there were distant metastases or the tumour had involved the resection margins. RESULTS: There was one postoperative death. The cumulative cancer-free survival rate at 5 years was 68 per cent. In 100 patients in whom the operation was considered to be curative, the cumulative cancer-free survival rate was 81 per cent. Eighty-four of these patients were available for a minimum follow-up of 24 (median 73, range 24-193) months. Three (4 per cent) developed local recurrence. In two patients this was at the anastomosis. CONCLUSION: If the cancer is contained within the fascial tube surrounding the rectum and complete extrafascial excision has been performed, local recurrence will be minimal.

Adult↗
PubMed2006

[Dosimetric consequences of the application of a rectum hull-planning volume for treatment planning of intensity modulated radiotherapy of prostate cancer].

The present study evaluated a hull-volume definition strategy for the planning organ at risk volume (PRV) for the rectum in the planning of radiotherapy of prostate cancer. The bounding volumes of rectum contours of 1 to 5 CT scans were compared on the basis of the rectum coverage probabilities for 5 patients. In addition, IMRT treatment plans were optimized using the rectum hull PRV5 of 5 CTs and each of the conventional rectum contours PRV1. The plans were compared on the basis of the organ doses caused by the individual organ motion. PRV5 allowed to cover the rectum with a probability of nearly 90% (PRV1 67%). Rectal wall dose showed a great variability for PRV1, while planned and treatment dose agreed well for PRV5 due to the improved geometric information which resulted in a better rectal sparing. In conclusion, the rectum hull-volume PRV5 is a well suited PRV for planning of IMRT dose distributions allowing dose escalation as well as rectal sparing.

Humans↗
PubMed1988

Urinary diversion to the augmented and valved rectum. An experimental study in dogs.

A new model for diverting urine to the rectum was tried in dogs. An intussusception valve was constructed at the junction of the sigmoid colon and the rectum allowing passage only in aboral direction. The rectum was augmented by patching it with an opened and folded ileal segment. The ureters were implanted into the rectum by a new anti-reflux method. All three dogs survived the operation. The volume of the augmented rectum increased from 80-150 ml at operation to a maximum of 750 ml six months after the operation. The pressure in the rectum did not exceed 18 cm of water during maximal filling. No reflux to the bowel proximal to the intussusception valve or to the ureters could be observed even during maximal filling of the augmented rectum. No signs of obstruction of the fecal stream by the intussusception valve were seen. In three out of five implanted renal units strictures developed at the implantation sites and resulted in impaired renal function. In the two renal units without strictures, no impairment of kidney function was found. Involuntary leak from the anus was not observed and no masceration was found around the anus. These experiments are regarded as very encouraging an a clinical trial is now under way.

Animals↗
PubMed2004

The diameter of the rectum on ultrasonography as a diagnostic tool for constipation in children with dysfunctional voiding.

PURPOSE: We proved the accuracy of the transverse diameter of the rectum on ultrasonography as an additional parameter for diagnosing constipation in children with lower urinary tract dysfunction. MATERIALS AND METHODS: The diameter of the rectum on bladder ultrasonography in a constipated group of patients with dysfunctional voiding was compared to this diameter in a control group of patients with a normal defecation pattern. A total of 49 children were included. Group 1 consisted of 23 patients with a positive history of dysfunctional voiding and, according to pediatric gastroenterological practice, constipation. Control group 2 consisted of 26 patients without lower urinary tract dysfunction and a normal defecation pattern. In each group a defecation questionnaire was administered and physical examination of the abdomen was done. In all patients a 7.5 MHz probe was used to measure the transverse diameter of the rectum behind the bladder on ultrasonography. The probe was applied on the abdominal skin approximately 2 cm above the symphysis. Measurement was performed with a filled bladder at an angle of about 15 degrees downward from the transverse plane. RESULTS: In constipated group 1 the mean diameter of the rectum was 4.9 cm (95% CI 4.4 to 5.3). In the control group the mean diameter of the rectum was 2.1 cm (95% CI 1.8 to 2.4). In group 1 the diameter of the rectum was significantly larger than in group 2 (p < 0.001). None of the patients had a sensation to defecate during the investigation. There was no significant difference in age between the 2 groups (p = 0.20) and no significant difference between them in the period between the last time that stool was passed prior to the time of rectal measurement (p = 0.16). CONCLUSIONS: The transverse diameter of the rectum measured by lower abdominal ultrasound provides an additional accurate parameter with which to diagnose constipation in patients with nonneurogenic bladder-sphincter dyssynergia.

Adolescent↗
PubMed2003

[Anatomic observation of the prostate for clinical application of local drug injection through the rectum for chronic prostatitis].

OBJECTIVE: To provide anatomic evidences for local drug injection through the rectum for treating chronic prostatitis and observe the therapeutic effect of this treatment. METHODS: Anatomic observation of the median sagittal plane of 16 male pelvic specimens was conducted, with special attention to the structures between the prostate and the rectum. The distance from the posterior wall of the prostate to the anterior wall of the rectum, the scope that allowed the entry of the puncture needle, the appropriate puncture depth, and the distance from the anus to the safe were carefully measured. Analysis of the clinical record was performed in 51 chronic prostatitis cases treated with local injection of prednisolone, antibiotic and lidocaine through the rectum. RESULTS: Only some fat tissues and venous plexus were found between the prostate and the anterior wall of the rectum, and the distance from posterior wall of the prostate to the anterior wall of the rectum averaged 5.773+/-0.710 mm. The scope for possible puncture was 15.408 8+/-1.438 2 mm with a depth of 15.703 1+/-0.944 1 mm. The maximum and minimum distances from the anus to the puncture were 47.594+/-2.432 mm and 35.781+/-1.850 mm, respectively. Among the 51 cases investigated, the total cure rate was 84.31%, and improvement was achieved in 13.73% of the case, with only one case (2%) failed to respond to the treatment. CONCLUSION: Local drug injection through the rectum can be ideal for the treatment of prostatitis for its safety and effectiveness.

Adolescent↗
PubMed2006

[An anatomical study on lateral ligaments of rectum].

OBJECTIVE: To identify the location and contents of the rectal lateral ligaments and its relationship with the middle rectal artery and pelvic plexus. METHODS: Twenty-nine pelvics of human cadavers were sagittally sectioned into 58 hemipelvic specimens. All of hemipelvics were dissected with sharp technique under direct vision by one surgeon. The lateral ligaments were identified and the distances from the center of its pelvic attachment to sacral promontory and coccyx were measured. Then, the lateral ligaments were transected for histologic examination. RESULTS: Lateral ligaments of rectum were found in all 58 hemipelvics. The lateral ligaments connected the posterolateral aspect of the middle 1/3 of the rectum and mesorectum to the lateral aspect of the bodies of the second, third and fourth sacral vertebrae. The distance from the lateral ligament to sacral promontory was (8.3 +/- 1.6) cm on the right side and (8.4 +/- 1.4) cm on left side. The width of lateral ligaments was (3.2 +/- 0.4) cm on the right side and (3.1 +/- 0.4) cm on the left side. The distances from lateral ligament to the coccyx on the right and left sides were (5.2 +/- 1.4) cm and (5.0 +/- 1.3) cm respectively. The content of the lateral ligaments consisted of loose connective tissue with clusters of small nerves and blood vessels. Middle rectal artery was found in 83% (48/58) of hemipelvics and 47% (27/58) of the middle rectal artery went through the lateral ligaments. The inferior hypogastric nerve plexuses were formed inside the lateral ligament, and separated the ligament into two parts. The lateral segment of the lateral ligament contained the tributaries of internal iliac artery, and the medial segment contained nerve fibers or branches to the rectum, together with the middle rectal artery. CONCLUSION: The lateral ligaments of rectum are located on the posterolateral side of the rectum, much closer to the coccyx than to the sacral promontory, consisting of connective tissue containing multiple small nerves and middle rectal artery. The lateral ligament is a pathway of blood vessels and nerve fibers toward the rectum and lymphatic vessels from the lower rectum toward the iliac lymph nodes.

Adult↗
PubMed1984

A critical evaluation of dissection of the perineum in synchronous combined abdominoperineal excision of the rectum.

Two methods of perineal dissection were studied in a prospective clinical trial of 62 consecutive patients undergoing synchronous combined abdominoperineal resection of the rectum for carcinoma. Of the 62 patients, 39 were included in method 1 and 23, in method 2. The technical difference and the merits between the two methods have been evaluated. The results showed that the operative injury to the anterior wall of the rectum occurred in three patients in the method 1 group and in eight patients in the method 2 group; but in the latter, the urethral injury occurred in one of 15 male patients. Apart from the operative injuries to the rectum or urethra, the factors influencing the bladder dysfunction after excision of the rectum have been reviewed. There was no evidence of bladder dysfunction in 62 patients. This was due to the fact that the plane of dissection in both methods was kept close to the rectum to avoid damage of the neural plexus supplying the external sphincter urethrae and the membranous urethra, which are vulnerable to injury in perineal dissection. It is questionable whether or not the bladder dysfunction is the consequence of the perineal dissection. Results of this study, therefore, suggest that the risk of injury to the rectum or urethra and the problems of bladder dysfunction are both avoidable if method 1 is used for abdominoperineal excision of the rectum.

Aged↗
PubMed2006

Endoscopic posterior mesorectal resection after transanal local excision of T1 carcinomas of the lower third of the rectum.

PURPOSE: The rectum-sparing transanal local excision is a well-established treatment of T1 carcinomas of the lower third of the rectum. A potentially increased locoregional recurrence rate by this procedure is tolerated because of the high morbidity and mortality risk of transabdominal rectal resection. Dorsoposterior extraperitoneal pelviscopy makes it possible to remove the relevant lymphatic drainage of the lower third of the rectum minimally invasively, in the sense of a rectum-sparing endoscopic posterior mesorectal resection. It has to be considered whether endoscopic posterior mesorectal resection in combination with transanal local excision allows for local radicality and an adequate tumor staging in T1 carcinomas of the lower third of the rectum, in terms of better-directed therapy planning compared with transanal local excision alone. METHODS: We operated on 11 consecutive patients with T1 carcinomas of the lower third of the rectum by transanal local excision in combination with endoscopic posterior mesorectal resection as a two-stage procedure in the period from 1998 to 2005. RESULTS: It was possible to perform a complete excision of the primary and to resect the posterior part of the mesorectum in all cases. Postoperative morbidity consisted of two transient neurologic complications and a pulmonary embolism. There was no mortality. Histologic analysis revealed a median of eight (range, 4-20) lymph nodes. Two patients diagnosed with lymph-node metastases received adjuvant radiochemotherapy. After a median follow-up of 48 (range, 4-60) months, there was no evidence for locoregional recurrence. In one patient liver metastasis was detected eight months postoperatively. CONCLUSIONS: Radical excision of the primary tumor and an adequate tumor staging in T1 carcinomas of the lower third of the rectum seems to be achievable by means of transanal local excision and endoscopic posterior mesorectal resection.

Adult↗
PubMed1976

Diagnosis and prognosis of early cancer of the colon and rectum.

Diagnostic methods for the cancer of the colon and rectum were compared in two groups of patients, i.e., patients of stage A malignancy in the Dukes classification, and those with the so-called "early cancer of the colon and rectum", and the best way to find cancer of the colon and rectum in its early stage was investigated. At the same time, the prognosis of early cancer of the colon and rectum was studied by the use of the relative survival rate. The following results were obtained. 1) The so-called "early cancer of the colon and rectum", of which invasion was limited to the mucosa and submucosa, can be correctly diagnosed by the combined application of both biopsy and exfoliative cytology under direct vision even before surgery and/or polypectomy. 2) Cancer of the colon and rectum is considered to be a curable disease, if discovered and resected at or before the stage A in the Dukes classification, in which the cancerous proliferation is limited to the wall of the colon and rectum without any metastasis.

Adult↗
PubMed2000

[Transcription regulation of intercellular adhesion molecule (ICAM-1) on lymphatic endothelial cells of rectum adenocarcinoma of human].

This study inquired into the mechanism of cancer lymphatic metastasis. The immunohistochemistry method and DNA hybridization in situ were employed in examining the peritumoral rectum tissues and metastatic lymph nodes from 8 rectum carcinoma patients and the rectum tissues and lymph nodes from 5 normal subjects. The results showed that the proteins of ICAM-1 and nuclear factor kappa B (NF kappa Bp65) were expressed on the lymphatic endothelial cells of the rectum adenocarcinoma patients, and there was a NF kappa B binding consensus sequences on ICAM-1 promoter in lymphatic endothelial cells of rectum adenocarcinoma patients. When DIG-AKP labeled 38 bp oligonucleotide probe was used, there was no the expression of ICAM-1 and NF kappa Bp65 on the lymphatic endothelial cells of the normal human lymph node and rectum tissues. It is suggested that the activation of ICAM-1 promoter may critically depend on NF kappa Bp65 homodimers or heterodimers binding to a variant kappa B site on the lymphatic endothelial cells of the rectum adencarcinoma of human. These observations may indicate the potential roles of NF kappa B in cancer metastasis, thus giving clues to facilitate the development of a novel anti-metastasis strategy, that is obstruction the NF kappa B-activation pathways.

Adenocarcinoma↗
PubMed1999

The surgical anatomy of the fasciae and the fascial spaces related to the rectum.

The perirectal fasciae and their vascular and neural relationships were studied based on the dissection of 46 fresh cadavers. The rectal fascia is a tubular sleeve, areolar in nature, which houses the superior rectal vessels and lymphatics. The nerves which supply fibres to the pelvic plexus run close to the rectum, contained in the urogenital and presacral fasciae. The rectum is attached to these two fasciae by the rectal stalks, which take a spiral course round the rectum, being posterolateral in the upper rectum, lateral in the mid-rectum and anterolateral in the lower rectum. During rectal resection the pelvic nn. may be preserved if the rectal dissection proceeds close to the rectal fascia. After cutting the rectal insertion of the presacral fascia, the lower rectal stalks (paraproctium) come into direct view and can be divided close to the rectal wall with no risk of damage to the pelvic plexus.

Fascia↗
PubMed1994

Factors affecting the risk of rectal cancer following rectum-preserving surgery in patients with familial adenomatous polyposis.

PURPOSE: Rectum-preserving surgery is one of the most common surgeries for familial adenomatous polyposis (FAP). It is appropriate to analyze factors influencing risk of rectal cancer after rectum-preserving surgery in FAP patients. METHODS: Three hundred twenty-two patients with FAP (169 males, 153 females) who had undergone rectum-preserving surgery and were part of 1050 FAP patients registered at our FAP registry were included in the study. Postoperative survival was investigated and cause of death was elucidated from the death certificate or by inquiry to the hospitals that registered the patients. For risk analysis, log-rank tests were used. RESULTS: Forty-four cases developed invasive cancer within a mean interval of 119 months after surgery. Cumulative risk of rectal cancer was 24.2 +/- 7 percent (mean +/- limit of 95 percent confidence interval) at 15 years. Influencing risk factors for rectal cancer were a postoperative period over ten years or age over 44 years, a rectum longer than 7 cm, and dense polyposis. Other factors such as sex and cancer in the colon at initial surgery were not correlated with risk. CONCLUSION: The rectum may be reasonably preserved in patients with FAP when polyps in the rectum are sparse, ileorectal anastomosis is made on or below the peritoneal reflection, and patients continue having rectal examinations for life.

Adenomatous Polyposis Coli↗
PubMed1999

Comparison between the biofragmentable anastomosis ring and stapled anastomoses in the extraperitoneal rectum: a prospective, randomized study.

Serious complications can be carried by intestinal anastomoses, particularly in the distal and proximal part of the gastrointestinal tract. The biofragmentable anastomosis ring (BAR) has been shown to be a safe anastomotic technique, but its clinical applicability in the extraperitoneal rectum has not yet been completely established. This study compared BAR anastomoses and stapled anastomoses in the middle rectum. Thirty-six consecutive patients initially suitable for elective colorectal anastomosis in the middle rectum were enrolled into this study. All patients had intraperitoneal rectum carcinoma, and 31 underwent a colorectal anastomosis in the middle extraperitoneal rectum. They were randomly allocated to a stapled technique or BAR anastomosis. Intraoperative findings and technical drawbacks, tumor behavior, and postoperative course were recorded. All patients were followed up, and late stenosis rate was investigated by endoscopy. The procedure was carried out in each of the 15 patients randomized to receiving a BAR anastomosis. No major difficulties were encountered, and the time needed was even less than that required for a stapled anastomosis. One patient in the stapled group had an early bleeding that required a further laparotomy. No significant differences in postoperative complications were noted between the two groups, although one patient with stapled anastomosis experienced a clinical leakage that needed loop colostomy. Biofragmentability was regular; buttons were eliminated in 3 weeks without any bowel disturbance. BAR ring insertion in the deep pelvis did not produce a shorter colonic resection. The late stenosis rate was similar between the groups. This study shows that in extraperitoneal middle rectum BAR anastomosis is as feasible and safe as the stapled method. The latter is more expensive, and manual suture is more difficult. Therefore the BAR is now the method of choice for this anastomosis in the authors' unit.

Absorbable Implants↗
PubMed2005

Magnetic resonance imaging of the rectum during distension.

PURPOSE: A knowledge of the relationships between the rectum and its surrounding structures during distention may improve our understanding of the results of studies assessing rectal sensory-motor responses to distention. This magnetic resonance imaging study was designed to assess the shape of the rectum and the degree of distention at which the surrounding structures are compressed. METHODS: Nine healthy patients underwent magnetic resonance imaging of the rectum under resting conditions and after the inflation of a plastic bag to volumes of 50, 100, 150, 200, and 250 ml. The thickness of the rectovesical space was assessed as a measure of the compression of the perirectal structures, and the perception of sensations were recorded. RESULTS: The shape of the rectum changed from being quasicylindrical at distention volumes of <100 ml to bean-shaped at larger volumes. The thickness of the rectovesical space at a distention volume of 50 ml was the same as when the bag was not inflated, but it progressively decreased until the difference became statistically significant at distention volumes of > or = 200 ml, corresponding to a mean +/- standard deviation rectal radius of 2.66 +/- 0.37 cm. Statistically significant compression of the rectovesical space was recorded when the sensations of gas, desire to defecate, and urgency were perceived. CONCLUSIONS: The shape of the rectum changes during distention; it significantly compresses the extrarectal structures in the tested range of distention that induces non-painful sensations. Magnetic resonance imaging is a useful means of assessing the morphologic changes in the rectum during distention.

Adult↗
PubMed2002

Risk of lymph node metastasis in T1 carcinoma of the colon and rectum.

PURPOSE: Several recent reports of high local recurrence and lymph node metastasis in T1 carcinoma of the rectum prompted us to study the risk factors for lymph node metastasis in these lesions. METHODS: We reviewed the clinical records of 7,543 patients who underwent operative treatment for carcinoma of the colon and rectum from 1979 to 1995. Only patients with sessile T1 lesions who underwent colorectal resection were included in the study, yielding an analysis cohort of 353 patients. The following carcinoma-related variables were assessed: size, mucinous subtype, carcinomatous component, grade, site in colon and rectum, lymphovascular invasion, and depth of submucosal invasion. For the depth, the submucosa was divided into upper third (sm1), middle third (sm2), and lower third (sm3). Chi-squared tests and logistic regression were used to evaluate the variables as potential risk factors for lymph node metastasis. RESULTS: The incidence of T1 lesions was 8.6 percent. In the analysis cohort, the lymph node metastasis rate was 13 percent. Significant predictors of lymph node metastasis both univariately and multivariately were sm3 (P = 0.001), lymphovascular invasion (P = 0.005), and lesions in the lower third of the rectum (P = 0.007). Poorly differentiated carcinoma was significant univariately (P = 0.001) but not in the multivariate model. No other parameter was associated with a significant risk. CONCLUSIONS: T1 colorectal carcinomas with lymphovascular invasion, sm3 depth of invasion, and location in the lower third of the rectum have a high risk of lymph node metastasis. These lesions should have an oncologic resection. In a case of the lesion in the lower third of the rectum, local excision plus adjuvant chemoradiation may be an alternative.

Adenocarcinoma↗
PubMed2004

Impact of knee support and shape of tabletop on rectum and prostate position.

PURPOSE: To evaluate the impact of different tabletops with or without a knee support on the position of the rectum, prostate, and bulb of the penis; and to evaluate the effect of these patient-positioning devices on treatment planning. METHODS AND MATERIALS: For 10 male volunteers, five MRI scans were made in four different positions: on a flat tabletop with knee support, on a flat tabletop without knee support, on a rounded tabletop with knee support, and on a rounded tabletop without knee support. The fifth scan was in the same position as the first. With image registration, the position differences of the rectum, prostate, and bulb of the penis were measured at several points in a sagittal plane through the central axis of the prostate. A planning target volume was generated from the delineated prostates with a margin of 10 mm in three dimensions. A three-field treatment plan with a prescribed dose of 78 Gy to the International Commission on Radiation Units and Measurements point was automatically generated from each planning target volume. Dose-volume histograms were calculated for all rectal walls. RESULTS: The shape of the tabletop did not affect the rectum and prostate position. Addition of a knee support shifted the anterior and posterior rectal walls dorsally. For the anterior rectal wall, the maximum dorsal shift was 9.9 mm (standard error of the mean [SEM] 1.7 mm) at the top of the prostate. For the posterior rectal wall, the maximum dorsal shift was 10.2 mm (SEM 1.5 mm) at the middle of the prostate. Therefore, the rectal filling was pushed caudally when a knee support was added. The knee support caused a rotation of the prostate around the left-right axis at the apex (i.e., a dorsal rotation) by 5.6 degrees (SEM 0.8 degrees ) and shifts in the caudal and dorsal directions of 2.6 mm (SEM 0.4 cm) and 1.4 mm (SEM 0.6 mm), respectively. The position of the bulb of the penis was not influenced by the use of a knee support or rounded tabletop. The volume of the rectal wall receiving the same dose range (e.g., 40-75 Gy) was reduced by 3.5% (SEM 0.9%) when a knee support was added. No significant differences were observed between the first and fifth scan (flat tabletop with knee support) for all measured points, thereby excluding time trends. CONCLUSIONS: The rectum and prostate were significantly shifted dorsally by the use of a knee support. The rectum shifted more than the prostate, resulting in a dose benefit compared with irradiation without knee support. The shape of the tabletop did not influence the rectum or prostate position.

Equipment Design↗