Prostate Displacement Research Articles

Real-time Image-guided Adaptive-predictive Prostate Radiotherapy using Rectal Diameter as a Predictor of Motion

AimsTo investigate a relationship between maximum rectal diameter (MRD) on pre-treatment cone beam computed tomography (CBCT) and intra-fraction prostate motion, in the context of an adaptive image-guided radiotherapy (IGRT) method. Materials and methodsThe MRD was measured on 2125 CBCTs from 55 retrospective patient datasets and related to prostate displacement from intra-fraction imaging. A linear regression model was developed to determine a threshold MRD associated with a high probability of small prostate displacement. Standard and reduced adaptive margin plans were created to compare rectum and bladder normal tissue complication probability (NTCP) with each method. ResultsA per-protocol analysis carried out on 1910 fractions from 51 patients showed with 90% confidence that for a MRD≤3 cm, prostate displacement will be ≤5 mm and that for a MRD≤3.5 cm, prostate displacement will be ≤5.5 mm. In the first scenario, if adaptive therapy was used instead of standard therapy, median reductions in NTCP for rectum and bladder were 0.5% (from 9.5% to 9%) and 1.3% (from 6.6% to 5.3%), respectively. In the second scenario, the NTCP for rectum and bladder would have median reductions of 1.1% and 2.6%, respectively. ConclusionsWe have identified a potential method for adaptive prostate IGRT based upon predicting small prostate intra-fraction motion by measuring MRD on pre-treatment CBCT.

SU‐F‐J‐131: Reproducibility of Positioning Error Due to Temporarily Indwelled Urethral Catheter for Urethra‐Sparing Prostate IMRT

Purpose:The purpose of this study was to prospectively assess the reproducibility of positioning errors due to temporarily indwelled catheter in urethra‐sparing image‐guided (IG) IMRT.Methods:Ten patients received urethra‐sparing prostate IG‐IMRT with implanted fiducials. After the first CT scan was performed in supine position, 6‐Fr catheter was indwelled into urethra, and the second CT images were taken for planning. While the PTV received 80 Gy, 5% dose reduction was applied for the urethral PRV along the catheter. Additional CT scans were also performed at 5th and 30th fraction. Positions of interests (POIs) were set on posterior edge of prostate at beam isocenter level (POI1) and cranial and caudal edge of prostatic urethra on the post‐indwelled CT images. POIs were copied into the pre‐indwelled, 5th and 30th fraction's CT images after fiducial matching on these CT images. The deviation of each POI between pre‐ and post‐indwelled CT and the reproducibility of prostate displacement due to catheter were evaluated.Results:The deviation of POI1 caused by the indwelled catheter to the directions of RL/AP/SI (mm) was 0.20±0.27/−0.64±2.43/1.02±2.31, respectively, and the absolute distances (mm) were 3.15±1.41. The deviation tends to be larger if closer to the caudal edge of prostate. Compared with the pre‐indwelled CT scan, a median displacement of all POIs (mm) were 0.3±0.2/2.2±1.1/2.0±2.6 in the post‐indwelled, 0.4±0.4/3.4±2.1/2.3±2.6 in 5th, and 0.5±0.5/1.7±2.2/1.9±3.1 in 30th fraction's CT scan with a similar data distribution. There were 6 patients with 5‐mm‐over displacement in AP and/or CC directions.Conclusion:Reproducibility of positioning errors due to temporarily indwelling catheter was observed. Especially in case of patients with unusually large shifts by indwelling catheter at the planning process, treatment planning should be performed by using the pre‐indwelled CT images with transferred contour of the urethra identified by post‐indwelled CT images.

Real-Time 3D Image Guidance Using a Standard LINAC: Measured Motion, Accuracy, and Precision of the First Prospective Clinical Trial of Kilovoltage Intrafraction Monitoring–Guided Gating for Prostate Cancer Radiation Therapy

Kilovoltage intrafraction monitoring (KIM) is a new real-time 3-dimensional image guidance method. Unlike previous real-time image guidance methods, KIM uses a standard linear accelerator without any additional equipment needed. The first prospective clinical trial of KIM is underway for prostate cancer radiation therapy. In this paper we report on the measured motion accuracy and precision using real-time KIM-guided gating. Imaging and motion information from the first 200 fractions from 6 patient prostate cancer radiation therapy volumetric modulated arc therapy treatments were analyzed. A 3-mm/5-second action threshold was used to trigger a gating event where the beam is paused and the couch position adjusted to realign the prostate to the treatment isocenter. To quantify the in vivo accuracy and precision, KIM was compared with simultaneously acquired kV/MV triangulation for 187 fractions. KIM was successfully used in 197 of 200 fractions. Gating events occurred in 29 fractions (14.5%). In these 29 fractions, the percentage of beam-on time, the prostate displacement was >3 mm from the isocenter position, reduced from 73% without KIM to 24% with KIM-guided gating. Displacements >5 mm were reduced from 16% without KIM to 0% with KIM. The KIM accuracy was measured at <0.3 mm in all 3 dimensions. The KIM precision was <0.6 mm in all 3 dimensions. Clinical implementation of real-time KIM image guidance combined with gating for prostate cancer eliminates large prostate displacements during treatment delivery. Both in vivo KIM accuracy and precision are well below 1 mm.

Impact of hydrogel spacer injections on interfraction prostate motion during prostate cancer radiotherapy

Background The dosimetric advantage of prostate-rectum spacers to displace the anterior rectal wall outside of the high-dose radiation regions has been clearly established in prostate cancer radiotherapy (RT). The aim of this study was to assess the impact of hydrogel spacer (HS) in the interfraction prostate motion in patients undergoing RT for prostate cancer.Material and methods Twenty prostate cancer patients implanted with three fiducial markers (FM) with (n = 10) or without (n = 10) HS were analyzed. Displacements between the prostate isocenter based on the FM’s position and the bony anatomy were quantified in the left-right (LR), anterior-posterior (AP), superior-inferior (SI) axes by offline analyses of 122 cone beam computed tomography scans. Group systematic (M), systematic (Σ) and random (σ) setup errors were determined.Results In patients with or without HS, the overall mean interfraction prostate displacements were 0.4 versus −0.4 mm (p = 0.0001), 0.6 versus 0.6 mm (p = 0.85), and −0.6 mm versus −0.3 mm (p = 0.48) for the LR, AP, and SI axes, respectively. Prostate displacements >5 mm in the AP and SI directions were similar for both groups. No differences in M, Σ and σ setup errors were observed in the three axes between HS + or HS- patients.Conclusions HS implantation does not significantly influence the interfraction prostate motion in patients treated with RT for prostate cancer. The major expected benefit of HS is a reduction of the high-dose levels to the rectal wall without influence in prostate immobilization.

Effect of ProSpare (PS), a rectal obturator, on inter- and intrafraction prostate motion and anorectal doses in prostate radiotherapy (RT).

e633 Background: PS is a single use, self-insertable endorectal device designed as a daily image-guidance tool for prostate cancer RT. Rectal filling is a significant factor in prostate motion. We investigated the effect of PS on inter- and intrafraction prostate motion and its effect on anorectal dosimetry. Methods: 19 patients with localized prostate cancer were randomized to receive prostate RT with PS either in the 1st or 2nd half of treatment. For each patient two planning CT scans were acquired, without and with PS. Contours were delineated by one physician and planned with a forward multi-segment technique to a dose of 74Gy/37F. Dose surface histograms were created (VODCA). In all patients, 3 electromagnetic transponders (EM) were implanted into the prostate and daily online image-guided RT was performed using either cone-beam CT (Elekta) or Calypso–based localization with tracking. Interfraction systematic (Σ) and random (σ) errors were estimated for bone matching without and with PS using EM position as reference. CTV-PTV margins were generated using the Van Herk formula. In-house code was used to analyse intrafraction motion recorded by Calypso of the EM centroid in the RL, SI and AP planes for individual fractions. A 2-way ANOVA test (SPSS v22) was used to determine if PS had an effect on maximal intrafraction prostate displacement. Results: See Table. Conclusions: PS affects the dosimetric pattern to the anal canal and rectum and this may impact GI toxicity. Also, PS stabilizes the prostate, which could enable reduced planning margins. PS will now be assessed in post-prostatectomy RT within a randomized controlled trial, POPS. Clinical trial information: 11814. [Table: see text] [Table: see text] [Table: see text]

Prostate displacement during transabdominal ultrasound image-guided radiotherapy assessed by real-time four-dimensional transperineal monitoring

ABSTRACTBackground. Transabdominal ultrasound (TAUS) imaging is currently available for localizing the prostate in daily image-guided radiotherapy (IGRT). The aim of this study was to determine the induced prostate displacement during such TAUS imaging. The prostate displacement was monitored using a novel transperineal four-dimensional (4D) US (TPUS) system.Material and methods. Ten prostate cancer patients, with a mean age of 68 years (58/76), were US scanned in the computed tomography (CT) room utilizing the Clarity 4D TPUS monitoring system. The patients were asked to comply with a moderate bladder filling protocol. After US-CT fusion, the prostate volume was delineated and used as a reference for weekly US imaging in the treatment room. Immediately after treatment delivery the TPUS monitoring system was set up. During real-time monitoring of the prostate, a conventional 2D probe was applied to simulate a TAUS scan. The time dependent prostate displacements induced by the 2D probe pressure were recorded for the three orthogonal directions. In total 42 monitoring curves with applied 2D probe were recorded.Results. Data analysis of 42 US scans resulted in pressure induced prostate displacements with mean values (± 1 SD) (mm); inferior (+)-superior (I/S): (−0.1 ± 0.8); left (+)-right (L/R): (0.2 ± 0.7); and anterior (+)-posterior (A/P): (−0.1 ± 1.0). The majority of the displacements were within 1–2 mm. Only two scans (5%) (A/P direction) and 16% of Euclidean distances were larger than 2.0 mm. The largest displacement was 2.6 mm in the anterior direction.Conclusion. The novel 4D TPUS system was capable of tracking and recording the prostate positional displacements. The study demonstrated that the prostate induced displacements due to applied TAUS IGRT are small, and in most cases clinically irrelevant to prostate radiotherapy.

MO‐DE‐210‐04: Repositioning and Monitoring of Prostate Cancer Radiotherapy with a New 4D Ultrasound Intra‐Modality IGRT Device

Purpose:We report our clinical experience using a non‐invasive transperineal (TP) ultrasound (US) probe dedicated to pre‐positioning and monitoring of prostate cancer patients. The accuracy of pre‐treatment positioning was compared to CBCT for prostate and post‐prostatectomy patients. Intrafraction motions were recorded for both localizations. The dosimetric impact of these displacements was finally investigated on prostate patients.Methods:Differences between CBCT/CT and TP‐US/TP‐US registrations were analyzed on 427 and 453 sessions for 13 prostate and 14 post‐prostatectomy patients, respectively. Ten prostate patients’ dosimetries were retrospectively planned using 2 different protocols: 80Gy in 40 fractions and 36.25Gy in 5 fractions with a 5mm CTV‐ to‐ PTV margin. The delivery time was measured in order to analyze ranges of intrafraction motions related to each protocol. Mean prostate displacements were calculated for each patient and applied to the treatment isocenter coordinates to evaluate the dosimetric impact of these motions.Results:CBCT and TP‐US shifts agreements at ±5mm were 76.6%, 95.1%, 96.3% and 90.3%, 85.0%, 97.6% in anterior‐ posterior, superior‐ inferior and left‐right directions, for prostate and post‐prostatectomy patients, respectively. Intrafraction motions were analyzed considering delivery times of 140 and 290s with an additional time of 120s for patient installation for doses of 2 and 7.25Gy, respectively. Intrafraction motions were patient‐dependent and were larger as the irradiation time increased. Larger displacements were observed for prostate compared to post‐prostatectomy localizations. Shifts above 3mm were observed on 17.6% and 4.5% of the 2Gy sessions against 30.6% and 7.3% of the 7.25Gy sessions in the anterior‐posterior direction for prostate and post‐prostatectomy localizations, respectively. Preliminary dosimetric results showed that intrafraction motions mainly impact the PTV coverage.Conclusion:4D TP‐US modality is a promising alternative to irradiating and/or invasive IGRT modalities for both inter and intrafraction motions management. Preliminary dosimetric results show that intrafraction monitoring is mandatory especially for hypofractionated treatments.M Fargier‐Voiron was supported by a PhD grant from Elekta

Design and experimental study of joint torque balance mechanism of seed implantation articulated robot

This article discusses several new mechanisms that may be used in prostate cancer seed implant robotics. We have developed relatively simple but effective mathematical models of multi-needle puncture prostate using nonlinear spring–damper model; based on Automatic Dynamic Analysis of Mechanical Systems or dynamics module, displacement simulation for prostate is performed, and simulation results indicate that the multi-needle puncture mechanism could reduce prostate displacement in the y- or z-direction. Then aiming at the limitation of human body structure space and seed implant needle insertion path, a revolute-revolute-translational-type prostate seed implantation robot with three-dimensional transrectal ultrasound navigation is designed. It is noteworthy that drive torque fluctuation is caused by the center of gravity change of revolute-revolute tandem cantilever structure; an elastic balance mechanism is designed to realize the complete balance of cantilever weight. Based on Automatic Dynamic Analysis of Mechanical Systems or dynamics module, static drive torque simulation of 2-revolute tandem cantilever structure is performed. Finally, we manufacture the robot prototype and make verification experiment to the cantilever balancing device, and the experiment results provide evidence that elastic balance mechanism can realize the complete balance of cantilever weight, improve the fluctuation in the amplitude value of driving torque, and increase its operation stationary of seed implantation robot system.

Clinical evaluation of an endorectal immobilization system for use in prostate hypofractionated Stereotactic Ablative Body Radiotherapy (SABR)

BackgroundThe objective of this study was to evaluate a novel prostate endorectal immobilization system (EIS) for improving the delivery of hypofractionated Stereotactic Ablative Body Radiotherapy (SABR) for prostate cancer.MethodsTwenty patients (n = 20) with low- or intermediate-risk prostate cancer (T1-T2b, Gleason Score < 7, PSA ≤ 20 ng/mL), were treated with an EIS in place using Volumetric Modulated Arc Therapy (VMAT), to a prescription dose of 26 Gy delivered in 2 fractions once per week; the intent of the institutional clinical trial was an attempt to replicate brachytherapy-like dosimetry using SABR. EBT3 radiochromic film embedded within the EIS was used as a quality assurance measure of the delivered dose; additionally, prostate intrafraction motion captured using pre- and post-treatment conebeam computed tomography (CBCT) scans was evaluated. Treatment plans were generated for patients with- and without the EIS to evaluate its effects on target and rectal dosimetry.ResultsNone of the observed 3-dimensional prostate displacements were ≥ 3 mm over the elapsed treatment time. A Gamma passing rate of 95.64 ± 4.28 % was observed between planned and delivered dose profiles on EBT3 film analysis in the low-dose region. No statistically significant differences between treatment plans with- and without-EIS were observed for rectal, bladder, clinical target volume (CTV), and PTV contours (p = 0.477, 0.484, 0.487, and 0.487, respectively). A mean rectal V80% of 1.07 cc was achieved for plans using the EIS.ConclusionsThe EIS enables the safe delivery of brachytherapy-like SABR plans to the prostate while having minimal impact on treatment planning and rectal dosimetry. Consistent and reproducible immobilization of the prostate is possible throughout the duration of these treatments using such a device.

Sparing Healthy Tissue and Increasing Tumor Dose Using Bayesian Modeling of Geometric Uncertainties for Planning Target Volume Personalization

To develop a mathematical tool that can update a patient's planning target volume (PTV) partway through a course of radiation therapy to more precisely target the tumor for the remainder of treatment and reduce dose to surrounding healthy tissue. Daily on-board imaging was used to collect large datasets of displacements for patients undergoing external beam radiation therapy for solid tumors. Bayesian statistical modeling of these geometric uncertainties was used to optimally trade off between displacement data collected from previously treated patients and the progressively accumulating data from a patient currently partway through treatment, to optimally predict future displacements for that patient. These predictions were used to update the PTV position and margin width for the remainder of treatment, such that the clinical target volume (CTV) was more precisely targeted. Software simulation of dose to CTV and normal tissue for 2 real prostate displacement datasets consisting of 146 and 290 patients treated with a minimum of 30 fractions each showed that re-evaluating the PTV position and margin width after 8 treatment fractions reduced healthy tissue dose by 19% and 17%, respectively, while maintaining CTV dose. Incorporating patient-specific displacement patterns from early in a course of treatment allows PTV adaptation for the remainder of treatment. This substantially reduces the dose to healthy tissues and thus can reduce radiation therapy-induced toxicities, improving patient outcomes.

Perineal repair of pelvic fracture urethral injury: in pursuit of a successful outcome

To determine perioperative factors that may optimize the outcome after delayed perineal repair of a pelvic fracture urethral injury (PFUI). In all, 86 consecutive patients who underwent perineal repair of a PFUI between 2004 and 2011 were prospectively enrolled in this study. The mean (range) patient age was 23 (5-50) years. The mean (range) follow-up was 5.5 (2-8) years. We examined seven perioperative variables that might influence the outcome including: prior failed treatment, condition of the bulbar urethra, displacement of the prostate, excision of scarred tissues, fixation of the mucosae of the two urethral ends, and the number and size of sutures used for urethral anastomosis. Univariate and multivariate analyses were used to identify factors that influence postoperative outcome. Of the patients, 76 (88%) had successful outcomes and 10 (12%) were considered treatment failures. On univariate analysis, four variables were significant factors influencing the outcome: excision of scarred tissues, prostatic displacement, condition of the bulbar urethra and fixation of the mucosae. On multivariate analysis only two remained strong and independent factors namely complete excision of scarred tissues and prostatic displacement in a lateral direction. Meticulous and complete excision of scar tissue is critically important to optimise the outcome after perineal urethroplasty. This is particularly emphasised in cases associated with lateral prostatic displacement. Six sutures of 3/0 or 4/0 polyglactin 910 are usually sufficient to create a sound urethral anastomosis. Prior treatment and scarring of the anterior urethra do not affect the outcome.

Role of MR urethrography in assessment of urethral lesions

Aim of the workTo evaluate the utility of magnetic resonance (MR) urethrogram in the diagnosis and characterization of different urethral lesions in comparison with conventional urethrography. Material and methodsThis prospective study included 18 male patients diagnosed to have urethral lesions. All of these patients were evaluated by using conventional urethrography prior to MR imaging. MR urethrography technique included: thick slab fast spin echo T2 (TSFSE) and fast recovery fast spin echo (FRFSE). ResultsThe causes of urethral lesions were: trauma in 13 patients (affecting the anterior urethra in 5 patients, the posterior urethra in 7 patients, the anterior and posterior urethra in one patient).Congenital abnormality in 3 patients at the anterior urethra and infection at the anterior urethra in 2 patients.Conventional urethrography and MRI diagnosed the presence of urethral pathology in all examined patients, However MR urethrography was superior in better delineation and characterization of the urethral pathology in four cases (22.2%) diagnosing prostatic displacement as well as periurethral fibrosis. Conventional urethrography was superior to MR urethrogram in diagnosing a case of diffuse pseudodiverticulosis. ConclusionMR urethrography is a suitable technique for the evaluation of urethral and periurethral abnormalities.

Observation of intrafraction prostate displacement through the course of conventionally fractionated radiotherapy for prostate cancer

Intrafraction prostate displacement (IFPD) through the course of conventionally fractionated radiotherapy was observed by real-time tracking. IFPD was observed by using a CyberKnife real-time tracking system over 39 serial fractions in two patients. Stereoscopic X-ray images tracking the implanted fiducial markers were obtained with mean intervals of 58 s. In preparation for treatment, urination was performed routinely 1 h before treatment and rectal gas was evacuated if necessary. Patients were immobilized by a thermoplastic body shell. The maximal absolute values of IFPD in all 78 fractions were 7.9, 2.1, and 11.5 mm in cranio-caudal (CC), left-right (LR), and antero-posterior (AP) direction, respectively. Only in 5 % of fractions (4/78 fractions), the maximal absolute values of IFPD were 5.0 mm or larger. In these fractions, large IFPD was temporary or persistent. IFPD of ≥3 mm was detected in only ~2-3 % of all obtained tracking images. Daily maximal IFPD changed day by day. Although maximal IFPD was more than 10 mm, IFPD of ≥3 mm was observed in a comparatively small proportion of treatment time. Through the course of conventionally fractionated radiotherapy, fractions with IFPD of ≥5 mm were infrequent.

Continuous Monitoring and Intrafraction Target Position Correction During Treatment Improves Target Coverage for Patients Undergoing SBRT Prostate Therapy

To compare the potential benefits of continuous monitoring of prostate position and intervention (CMI) using 2-mm displacement thresholds during stereotactic body radiation therapy (SBRT) treatment to those of a conventional image-guided procedure involving single localization prior to treatment. Eighty-nine patients accrued to a prostate SBRT dose escalation protocol were implanted with radiofrequency transponder beacons. The planning target volume (PTV) margin was 5 mm in all directions, except for 3 mm in the posterior direction. The prostate was kept within 2 mm of its planned position by the therapists halting dose delivery and, if necessary, correcting the couch position. We computed the number, type, and time required for interventions and where the prostate would have been during dose delivery had there been, instead, a single image-guided setup procedure prior to each treatment. Distributions of prostate displacements were computed as a function of time. After the initial setup, 1.7 interventions per fraction were required, with a concomitant increase in time for dose delivery of approximately 65 seconds. Small systematic drifts in prostate position in the posterior and inferior directions were observed in the study patients. Without CMI, intrafractional motion would have resulted in approximately 10% of patients having a delivered dose that did not meet our clinical coverage requirement, that is, a PTV D95 of >90%. The posterior PTV margin required for 95% of the dose to be delivered with the target positioned within the PTV was computed as a function of time. The margin necessary was found to increase by 2 mm every 5 minutes, starting from the time of the imaging procedure. CMI using a tight 2-mm displacement threshold was not only feasible but was found to deliver superior PTV coverage compared with the conventional image-guided procedure in the SBRT setting.

Effect of intrafractional prostate motion on simultaneous boost intensity-modulated radiotherapy to the prostate: A simulation study based on intrafractional motion in the prone position

Although the prostate displacement of patients in the prone position is affected by respiration-induced motion, the effect of intrafractional prostate motion in the prone position during “simultaneous integrated boost intensity-modulated radiotherapy” (SIB-IMRT) is unclear. The purpose of this study was to evaluate the dosimetric effects of intrafractional motion on SIB-IMRT to a dominant intraprostatic lesion (IPL) using measured motion data of patients in a prone position, fixed with a thermoplastic shell. We obtained 2 orthogonal x-ray fluoroscopic images at the same moment every 0.2 seconds for 30 seconds before and after treatment, once weekly, from 7 patients with localized prostate cancer with detectable prostatic calcification. Prostate displacements in the left-right (LR), anteroposterior (AP), and superoinferior (SI) directions were calculated using the prostatic calcification as a fiducial marker. We defined the displacement between pretreatment and posttreatment as baseline drift (BD). An SIB-IMRT plan was generated in which each IPL + 3mm received a dose of 94.5Gy, whereas the remainder of the prostate + 7mm received a dose of 75.6Gy in 9 fields. A simulated plan of dose blurring was generated by the convolution of isocenter-shifted plans using measured motion data in 30 seconds and motion in 30 seconds + distance between pretreatment and posttreatment position (BD) for each of the 7 patients. The motion in 30 seconds mainly reflected respiration-induced motion. The mean displacements of BD were 1.4mm (− 3.1 to 8.2mm), − 2.2mm (− 9.1 to 1.5mm), and − 0.3mm (− 5.0 to 1.8mm) in the AP, SI, and LR directions, respectively. The differences in the target coverage with V90% of the IPL and V100% of the prostate between the simulated plan and original plan were − 3.9% to − 0.3% and − 0.6% to 1.1% for respiration-induced motion and 3.1% to − 67.8% and 3.6% to − 13.3% for BD with respiration-induced motion, respectively. The large motion of BD resulted in an inadequate coverage by the prescribed dose of the SIB-IMRT to the IPL. A 7-mm margin is recommended when real-time tracking techniques are not applied. The effect of respiration-induced motion was small, so long as a 3-mm margin was added.

Prostatic displacement during extreme hypofractionated radiotherapy using volumetric modulated arc therapy (VMAT).

BackgroundTo determine prostate displacement during extreme hypofractionated volume modulated arc radiotherapy (VMAT) using pre- and post-treatment orthogonal images with three implanted gold seed fiducial markers.MethodsA total of 150 image pairs were obtained from 30 patients who underwent extreme hypofractionated radiotherapy to a dose of 40 Gy in five fractions on standard linear accelerators. Position verification was obtained with orthogonal x-rays before and after treatment and were used to determine intra-fraction prostate displacement.ResultsThe mean prostate displacements were 0.03 ± 1.23 mm (1SD), 0.18 ± 1.55 mm, and 0.37 ± 1.95 mm in the left-right, superior-inferior, and anterior-posterior directions, respectively. The mean 3D displacement was 2.32 ± 1.55 mm. Only 6 (4%) fractions had a 3D displacement of >5 mm. The average time of treatment delivery for a given fraction was 195 ± 59 seconds.ConclusionsThe mean intra-fraction prostate displacement during a course of extreme hypofractionated radiotherapy delivered via VMAT, continues to be small. Clinical margins typically used in a similar fixed-angle IMRT treatment are adequate. The use of VMAT in further extreme hypofractionation may limit prostatic motion uncertainties that would be otherwise be associated with longer treatment times.

Effect of rectal enema on intrafraction prostate movement during image-guided radiotherapy.

Rectal volume and movement are major factors that influence prostate location. The aim of this study was to assess the effect of a rectal enema on intrafraction prostate motion. The data from 12 patients with localised prostate cancer were analysed. Each patient underwent image-guided radiotherapy (RT), receiving a total dose of 70 Gy in 28 fractions. Rectal enemas were administered to all of the patients before each RT fraction. The location of the prostate was determined by implanting three fiducial markers under the guidance of transrectal ultrasound. Each patient underwent preparation for IGRT twice before an RT fraction and in the middle of the fraction. The intrafraction displacement of the prostate was calculated by comparing fiducial marker locations before and in the middle of an RT fraction. The rectal enemas were well tolerated by patients. The mean intrafraction prostate movement in 336 RT fractions was 1.11 ± 0.77 mm (range 0.08-7.20 mm). Intrafraction motions of 1, 2 and 3 mm were observed in 56.0%, 89.0% and 97.6% of all RT fractions, respectively. The intrafraction movements on supero-inferior and anteroposterior axes were larger than on the right-to-left axes (P < 0.05). The CTV-to-PTV margin necessary to allow for movement, calculated using the van Herk formula (2.5Σ + 0.7σ), was 1.50 mm. A daily rectal enema before each RT fraction was tolerable and yielded little intrafraction prostate displacement. We think the use of rectal enemas is a feasible method to reduce prostate movement during RT.

Seminal vesicle intrafraction motion analysed with cinematic magnetic resonance imaging.

PurposeThis study analyses seminal vesicle displacement relative to the prostate and in relation to treatment time.MethodA group of eleven patients undergoing prostate cancer radiotherapy were imaged with a continuous 3 T cine-MRI in the standard treatment setup position. Four images were recorded every 4 seconds for 15 minutes in the sagittal plane and every 6.5 seconds for 12 minutes in the coronal plane. The prostate gland and seminal vesicles were contoured on each MRI image. The coordinates of the centroid of the prostate and seminal vesicles on each image was analysed for displacement against time. Displacements between the 2.5 percentile and 97.5 percentile (i.e. the 2.5% trimmed range) for prostate and seminal vesicle centroid displacements were measured for 3, 5, 10 and 15 minutes time intervals in the anterior-posterior (AP), left-right (LR) and superior-inferior (SI) directions. Real time prostate and seminal vesicle displacement was compared for individual patients.ResultsThe 2.5% trimmed range for 3, 5, 10 and 15 minutes for the seminal vesicle centroids in the SI direction measured 4.7 mm; 5.8 mm; 6.5 mm and 7.2 mm respectively. In the AP direction, it was 4.0 mm, 4.5 mm, 6.5 mm, and 7.0 mm. In the LR direction for 3, 5 and 10 minutes; for the left seminal vesicle, it was 2.7 mm, 2.8 mm, 3.4 mm and for the right seminal vesicle, it was 3.4 mm, 3.3 mm, and 3.4 mm. The correlation between the real-time prostate and seminal vesicle displacement varied substantially between patients indicating that the relationship between prostate displacement and seminal vesicles displacement is patient specific with the majority of the patients not having a strong relationship.ConclusionOur study shows that seminal vesicle motion increases with treatment time, and that the prostate and seminal vesicle centroids do not move in unison in real time, and that an additional margin is required for independent seminal vesicle motion if treatment localisation is to the prostate.

SU‐E‐J‐20: Adaptive Aperture Morphing for Online Correction for Prostate Cancer Radiotherapy

Purpose:Online adaptive aperture morphing is desirable over translational couch shifts to accommodate not only the target position variation but also anatomic changes (rotation, deformation, and relation of target to organ‐atrisks). We proposed quick and reliable method for adapting segment aperture leaves for IMRT treatment of prostate.Methods:The proposed method consists of following steps: (1) delineate the contours of prostate, SV, bladder and rectum on kV‐CBCT; (2) determine prostate displacement from the rigid body registration of the contoured prostate manifested on the reference CT and the CBCT; (3) adapt the MLC segment apertures obtained from the pre‐treatment IMRT planning to accommodate the shifts as well as anatomic changes. The MLC aperture adaptive algorithm involves two steps; first move the whole aperture according to prostate translational/rotational shifts, and secondly fine‐tune the aperture shape to maintain the spatial relationship between the planning target contour and the MLC aperture to the daily target contour. Feasibility of this method was evaluated retrospectively on a seven‐field IMRT treatment of prostate cancer patient by comparing dose volume histograms of the original plan and the aperture‐adjusted plan, with/without additional segments weight optimization (SWO), on two daily treatment CBCTs selected with relative large motion and rotation.Results:For first daily treatment, the prostate rotation was significant (12degree around lateral‐axis). With apertureadjusted plan, the D95 to the target was improved 25% and rectum dose (D30, D40) was reduced 20% relative to original plan on daily volumes. For second treatment‐fraction, (lateral shift = 6.7mm), after adjustment target D95 improved by 3% and bladder dose (D30, maximum dose) was reduced by 1%. For both cases, extra SWO did not provide significant improvement.Conclusion:The proposed method of adapting segment apertures is promising in treatment position correction, including target translational displacement, rotation and deformation. Additional SWO could improve ROIs dose distribution.

MP9-12 PREDICTING RISK OF ERECTILE DYSFUNCTION FOLLOWING PELVIC FRACTURE URETHRAL INJURY DURING CHILHOOD

You have accessJournal of UrologyTrauma/Reconstruction: Trauma & Reconstructive Surgery III1 Apr 2014MP9-12 PREDICTING RISK OF ERECTILE DYSFUNCTION FOLLOWING PELVIC FRACTURE URETHRAL INJURY DURING CHILHOOD Mamdouh Koraitim Mamdouh KoraitimMamdouh Koraitim More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2014.02.500AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES It has been reported that erectile dysfunction (ED) is a common complication after pelvic fracture urethral injury (PFUI). However, almost all studies have been concerned with adult patients at the time of injury. We thought to study the incidence of postpubertal ED following PFUI during childhood, as well as to identify the related risk factors. METHODS All patients who had undergone repair of a PFUI from 1980 to 2010, and aged <15 years at the time of injury and aged >18 years at the time of assessment, were identified from our database. Patients were invited by mail to participate in the study. Responding patients were asked to answer a brief questionnaire consisting of 6 questions that were designed to assess erectile experience within the past 4 weeks. This questionnaire is the erectile function (EF) domain of the International Index of Erectile Function (IIEF). Based on the total score of 30 of the EF domain, the score was calculated for every patient. Medical records and imaging studies were reviewed with a focus on 4 variables: pattern of pelvic fracture, presence of pubic diastasis, displacement of the prostate, and length of urethral gap. RESULTS Overall, 51 patients participated in the study. The mean age of patients at the time of pelvic trauma was 10 years (range 3 to <15). Of the patients, 24 (47%) exhibited ED at puberty with the majority (21 patients, 88%) reporting severe ED (score 6 -10). Single ramus fracture was found in 18 patients and ipsilateral ischiopubic rami fracture in 21, of whom 3 (17%) and 9 (43%) exhibited ED, respectively. Bilateral 2 or more rami fracture and ipsilateral rami fracture associated with disruption of sacroiliac joint (Malgaigne’s fracture) was found in 6 patients each, all 12 (100%) exhibited ED. Of 12 patients with pubic diastasis 9 (75%) developed ED, and of 39 patients with intact symphysis pubis 15 (38%) developed ED. Of 21 patients having prostatic displacement in superior and lateral directions 18 (86%) exhibited ED, while of 30 patients having superior prostatic displacement 6 (20%) had ED. The mean length of urethral gap of patients with normal EF was 1.8 cm (range 1 – 2.5), while that of impotent patients was 3.9 cm (range 2.5 – 6). CONCLUSIONS The prognosis to the parents of a child who sustains a PFUI must remain guarded until the patient attains a postpubertal status. About half of the patients exhibit ED at puberty. The risk of ED is increased in the presence of a long urethral gap, bilateral pubic rami fracture, Malgaigne’s fracture, pubic diastasis, and lateral prostatic displacement. © 2014FiguresReferencesRelatedDetails Volume 191Issue 4SApril 2014Page: e126 Advertisement Copyright & Permissions© 2014MetricsAuthor Information Mamdouh Koraitim More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...