Prostate Displacement Research Articles

Investigation of pelvic floor influence on prostate displacement in image-guided radiotherapy.

The uncertainty of target location during prostate cancer radiotherapy plays an important role in accurate dose delivery and radiation toxicity in adjacent organs. This study analyzed displacement correlations between the prostate and pelvic floor. We retrospectively analyzed registration results from 467 daily cone-beam computed tomography (CT) in 12 patients with prostate cancer who received radiation therapy. We analyzed prostate displacement and the pelvic floor relative to the pelvic bone's anatomy in the translational and rotational directions and identified statistical correlations. The systematic (Σ) and random (σ) displacements of the prostate in the three translational directions, anterior-posterior (AP), superior-inferior (SI), and right-left (RL), were 1.49 ± 1.45, 2.10 ± 1.40, and 0.24 ± 0.53 mm, respectively, and in the rotational directions of the pitch, roll, and yaw were 2.10 ± 2.02°, 0.42 ± 0.74°, and 0.42 ± 0.64°, respectively. The pelvic floor displacements were 2.37 ± 1.96, 2.71 ± 2.28, and 0.47 ± 0.84 mm in the AP, SI, and RL directions, respectively, and 0.93 ± 1.49°, 0.98 ± 1.28 °, and 0.87 ± 0.94° in the pitch, roll, and yaw directions, respectively. Additionally, there were statistically significant correlations between the displacement of the prostate and pelvic floor in the AP and SI directions, with correlation coefficients (r) of 0.74 (p < 0.001) and 0.69 (p < 0.001), respectively. The movement of the pelvic floor may be an important factor that causes prostate displacement, affecting the accuracy of radiotherapy. Therefore, it is necessary to take appropriate measures to ensure that the pelvic floor muscle tension is as consistent as possible in the treatment' CT scan and daily treatment.

Computed tomographic features of canine prostatic carcinoma.

Canine prostatic carcinoma (PC) has incompletely defined CT features. The purpose of this multicenter retrospective case series was to assess prostatic, regional, and distant findings of PC. Thirty dogs were enrolled. Consistent prostatic features included postcontrast heterogeneity with hypoattenuating, nonenhancing areas (30/30), capsular distortion (29/30), prostatic urethral effacement, displacement, or invasion (28/30), precontrast heterogeneity (27/30), and mineralization (24/30) which was always within or at the margin of the hypoattenuating areas. Consistent extraprostatic features included medial iliac lymph node enlargement (20/30), internal iliac lymph node enlargement (15/30), and periprostatic fat streaking or fluid (15/29). In a minority of dogs, there was lymph node mineralization, bladder trigone invasion, ureteral dilation, ductus deferens invasion, and bony changes consistent with hypertrophic osteopathy. Strongly suspected and potential bony metastases were noted infrequently (8/26), all in vertebrae regional to the prostate. In conclusion, these findings provide guidance on the expected CT features of canine PC.

Towards Personalization of Planning Target Volume Margins Fitted to the Abdominal Adiposity in Localized Prostate Cancer Patients Receiving Definitive or Adjuvant/Salvage Radiotherapy: Suggestive Data from an ExacTrac vs. CBCT Comparison.

This study aimed to assess whether the patient's abdominal adiposity affects the performance of the Exactrac imaging system compared to the cone beam computed tomography (CBCT)-based setup, which was used as the reference positioning for the image-guided radiotherapy (IGRT) delivery to patients with localized prostate cancer. The daily positionings of patients with localized prostate cancer undergoing definitive or adjuvant/salvage radiotherapy (RT) were analyzed. The abdominal fat areas and pelvic incidence angle were determined on the CT simulation for each patient. A couple of ExacTrac images and a CBCT were acquired daily to verify the patient setup. We recorded every daily set of the three residual translational errors detected on the CBCT after the ExacTrac-based setup. These sets were clustered within three different thresholds (0.1 mm, 0.2 mm, and 0.3 mm), for each of which the influence of adipose tissues on Exactrac accuracy was assessed as the percentage of sub-threshold displacements as the fat parameters varied. A full bladder and empty rectum preparation protocol was adopted as much as possible. From the assessment of 1,770 daily positionings in 55 patients (38 definitive RT, 17 adjuvant/salvage RT), a good agreement between ExacTrac and CBCT could be inferred, which was quite robust against slight variations in the bladder and rectal filling, and the presence or not of the prostate. The percentages of above-threshold corrections increased with increasing abdominal fat, which therefore seemed to reduce the ExacTrac accuracy. This might be influenced by any intrafraction prostate displacement, likely induced by abdominal respiratory movements, and are more pronounced among overweight men. Our results promote the CBCT use over ExacTrac for IGRT of overweight patients with localized prostate cancer, while calling for attention to the probable need for personalization of planning target volume margins depending on the patient's body habitus.

Factors Affecting Prostate Displacement During Volumetric Modulated Arc Therapy in Prone Position After High-Dose-Rate Brachytherapy for Prostate Cancer

In irradiating the prostate and pelvic lymph node regions, registration based on bony structures matches the pelvic lymph node regions but not necessarily the prostate position, and it is important to identify factors that influence prostate displacement. Therefore, we investigated factors influencing prostate displacement during volumetric modulated arc therapy after single-fraction high-dose-rate brachytherapy (HDR-BT) for prostate cancer and the trends in displacement for each fraction. Seventy patients who underwent pelvic volumetric modulated arc therapy of 46 Gy in the prone position 15 days after 13 Gy HDR-BT were included. Prostate displacement relative to bony structures was calculated using cone beam computed tomography. Systematic error (SE) and random error (RE) were evaluated in the right-left (RL), craniocaudal (CC), and anteroposterior (AP) directions. The association with clinical and anatomic factors on the planning computed tomography or magneticresonanceimaging was analyzed. Prostate volume change (PVC) was defined as the volume change at 2 days after HDR-BT. Displacement trends were individually examined from the first to 23rd fractions. The mean SE in the RL, CC, and AP directions was -0.01 mm, -2.34 mm, and -0.47 mm, respectively. The root mean square of the RE in the RL, CC, and AP directions was 0.44 mm, 1.14 mm, and 1.10 mm, respectively. SE in the CC direction was independently associated with bladder volume (P=.021, t statistic=2.352) and PVC (P < .001, t statistic=-8.526). SE in the AP direction was independently associated with bladder volume (P=.013, t statistic=-2.553), PVC (P < .001, t statistic=5.477), and rectal mean area (P=.008, t statistic=2.743). RE in the CC direction was independently associated with smoking (P=.035). RE in the AP direction was associated with PVC (P=.043). Gradual displacement caudally and posteriorly occurred during the irradiation period. Anatomic characteristics of the bladder, rectum, and prostate predict SE. Smoking and PVC predict RE. In particular, whether PVC is ≥140% affects setting internal margins.

Transperineal ultrasound is a good alternative for intra-fraction motion monitoring for prostate stereotactic body radiotherapy.

To report our experience in a prospective study of implementing a transperineal ultrasound system to monitor intra-fractional prostate motion for prostate stereotactic body radiotherapy (SBRT). This IRB-approved prospective study included 23 prostate SBRT patients treated between 04/2016 and 11/2019 at our institution. The prescription doses were 36.25Gy to the Low-Dose planning target volume (LD-PTV) and 40Gy to the High-Dose PTV (HD-PTV) in five fractions with 3mm planning margins. The transperineal ultrasound system was successfully used in 110 of the 115 fractions. For intra-fraction prostate motion, the real-time prostate displacements measured by ultrasound were exported for analysis. The percentage of time prostate movement exceeded a 2mm threshold was calculated for each fraction of all patients. T-test was used for all statistical comparisons. Ultrasound image quality was adequate for prostate delineation and prostate motion tracking. The setup time for each fraction under ultrasound-guided prostate SBRT was 15.0±4.9 min and the total treatment time per fraction was 31.8±10.5 min. The presence of an ultrasound probe did not compromise the contouring of targets or critical structures. For intra-fraction motion, prostate movement exceeded 2mm tolerance in 23 of 110 fractions for 11 of 23 patients. For all fractions, the mean percentage of time when the prostate moved more than 2mm in any direction during each fraction was 7%, ranging from 0% to 62% of a fraction. Ultrasound-guided prostate SBRT is a good option for intra-fraction motion monitoring with clinically acceptable efficiency.

Intrafraction Prostate Motion Management for Ultra-Hypofractionated Radiotherapy of Prostate Cancer.

Purpose: Determine the time-dependent magnitude of intrafraction prostate displacement and a cutoff for the tracking decision. Methods: Nine patients with localized prostate cancer were treated with ultra-hypofractionated radiotherapy (CyberKnife) with fiducial markers. Exact tract kV/kV imaging was used with an average interval of 19–92 s. A Gaussian distribution was calculated for the x-, y-, and z-directions (σx,y,z). The variation of prostate motion (μσ) was obtained by averaging the patients’ specifics, and the safety margin was calculated to be MAB = WYm + WBSs. Results: The calculated PTV safety margins were as follows: at 40 s: 0.55 mm (L/r), 0.85 mm (a/p), and 1.05 mm (s/i); at 60 s: 0.9 mm (L/r), 1.35 mm (a/p), and 1.55 mm (s/i); at 100 s: 1.5 mm (L/r), 2.3 mm (a/p), and 2.6 mm (s/i); at 150 s: 1.9 mm (L/r), 3.1 mm (a/p), and 3.6 mm (s/i); at 200 s: 2.2 mm (L/r), 3.8 mm (a/p), and 4.2 mm (s/i); and at 300 s: 2.6 mm (L/r), 5.3 mm (a/p), and 5.6 mm (s/i). A tracking cutoff of 2.5 min seemed reasonable. In order to achieve an accuracy of < 1 mm, tracking with < 50 s intervals was necessary. Conclusions: For ultra-hypofractionated radiotherapy of the prostate with treatment times > 2.5 min, intrafraction motion management is recommended.

Stereotactic body radiotherapy of prostate cancer: influence of intrafraction motion of prostate on final dose distribution

Purpose: To determine impact of various planning tumour volume (PTV) margins on final dose distribution in patients with maximal intrafraction prostate displacement. Materials: We analyzed data of 15 prostate cancer patients with maximal (значения) prostate intrafraction displacement registered during stereotactic body radiotherapy (SBRT) — 5 fractions of 7.25 Gy. Prostate displacement was determined by cone beam CT that was performed before and after each fraction. Modeling of dose distribution considering prostate displacement was performed for every fraction by isocenter shift. Final dose distribution was calculated as the sum of all fractions and was evaluated for PTV with various margins: 5-5-5-3, 3-3-3-1, 5-5-5 and cropped rectum. Results: The dosimetric impact of maximal intrafraction prostate motion was minimal for target coverage even for PTV with minimal margins (3 in all directions and 1 mm — posterior): CTV V100% varied from 97.5 to 100%. Prostate displacement reduced the dose to the rectum in all but minimal doses were detected for PTV 3-3-3-1: average D2cc — 31.87 Gy (28.41–34.05). For PTV 3-3-3-1 average bladder V100% volume slightly increased from 3.67 (SBRT plan) to 4.87 cc (simulation of intrafraction prostate displacement). Conclusions: The dosimetric impact of maximal intrafraction prostate motion was minimal for target coverage and doses in rectum and bladder even for PTV with minimal (3-3-3-1) margins.

Minimum non-isotropic and asymmetric margins for taking into account intrafraction prostate motion during moderately hypofractionated radiotherapy

PurposeTo investigate the impact on dose distribution of intrafraction motion during moderate hypofractionated prostate cancer treatments and to estimate minimum non-isotropic and asymmetric (NI-AS) treatment margins taking motion into account. MethodsProstate intrafraction 3D displacements were recorded with a transperineal ultrasound probe and were evaluated in 46 prostate cancer patients (876 fractions) treated by moderate hypofractionated radiation therapy (60 Gy in 20 fractions). For 18 patients (346 fractions), treatment plans were recomputed increasing CTV-to-PTV margins from 0 to 6 mm with an auto-planning optimization algorithm. Dose distribution was estimated using the voxel shifting method by displacing CTV structure according to the retrieved movements. Time-dependent margins were finally calculated using both van Herk’s formula and the voxel shifting method. ResultsMean intrafraction prostate displacements observed were −0.02 ± 0.52 mm, 0.27 ± 0.78 mm and −0.43 ± 1.06 mm in left–right, supero-inferior and antero-posterior directions, respectively. The CTV dosimetric coverage increased with increased CTV-to-PTV margins but it decreased with time. Hence using van Herk’s formula, after 7 min of treatment, a margin of 0.4 and 0.5 mm was needed in left and right, 1.5 and 0.7 mm in inferior and superior and 1.1 and 3.2 mm in anterior and posterior directions, respectively. Conversely, using the voxel shifting method, a margin of 0 mm was needed in left–right, 2 mm in superior, 3 mm in inferior and anterior and 5 mm in posterior directions, respectively. With this latter NI-AS margin strategy, the dosimetric target coverage was equivalent to the one obtained with a 5 mm homogeneous margin. ConclusionsNI-AS margins would be required to optimally take into account intrafraction motion.

Clinical evaluation of the impact of rectal and bladder filling on prostate position during hypofractionated radiotherapy for prostate cancer

Objective: To evaluate the impact of rectal and bladder filling on prostate position during hypofractionated radiotherapy for prostate cancer. Methods: Three gold fiducials were implanted into the prostate in 25 patients. Each patient underwent CT scanning under four different conditions: full rectum and bladder, full bladder and empty rectum, full rectum and empty bladder, and empty rectum and bladder (primary image). The other three scans were aligned with the primary image by pelvic bone, then by the implanted fiducials. Prostate displacements were determined by computing the difference between these two alignments. The magnitude and directions of displacement were analyzed. Results: A full rectum shifted the prostate most significantly in the anterior (0.93 ± 0.31 cm) and superior directions (0.48 ± 0.30 cm). A full rectum was associated with anterior shifts ≥0.5 cm in 92.0% of the patients, ≥1 cm in 44.0%, while superior shifts ≥0.5 cm were observed in 48.0% and ≥1 cm in 8.0%. A full bladder shifted the prostate mildly in the superior direction (0.19 ± 0.30 cm). A full rectum and full bladder shifted the prostate more in the anterior (1.19 ± 0.37 cm) and superior directions (0.49 ± 0.50 cm). 100% and 56.0% had ≥0.5 cm of anterior and superior displacements. 68.0% and 16.0% had ≥1 cm of anterior and superior shift. Conclusions: Our study demonstrated that a full rectum shifted the prostate mainly anterosuperiorly. The rectal volume’s impact on prostate movement is much larger than that of the bladder.

Role of magnetic resonance imaging in the management of male pelvic fracture urethral injury.

The management of male pelvic fracture urethral injury remains a urological challenge. Pelvic fracture urethral injury can be associated with sequelae, such as urethral gap, erectile dysfunction and urinary incontinence. Delayed anastomotic urethroplasty, the gold standard treatment for urethral gaps caused by pelvic fracture urethral injuries, is technically demanding, and reconstructive urologists should preoperatively obtain as much detailed anatomical information as possible. A combination of antegrade and retrograde urethrography is the fundamental preoperative evaluation, but it cannot accurately assess the urethral gap length, the degree of lateral prostatic displacement, the anatomical relationship of the urethra with its surrounding structures (such as the rectum and dorsal venous complex) or periurethral problems (such as minor fistulae or cavitation). To make up for these limitations of urethrography, magnetic resonance imaging has emerged as a non-invasive, multiplanar and high-resolution modality for the evaluation of pelvic fracture urethral injury. Magnetic resonance imaging has excellent soft-tissue contrast, and can clearly show the urethra and periurethral tissues without the effects of radiation, thus enabling clinicians to anticipate the required ancillary techniques for delayed anastomotic urethroplasty and to predict functional outcomes, such as erectile function and urinary continence, after delayed anastomotic urethroplasty. This review discusses the role of magnetic resonance imaging in the evaluation of pelvic fracture urethral injury and its impact on patient management.

Based on 0.35 T magnetic resonance-guided radiotherapy, what are the nonisotropic PTV margins required for conventional prostate radiotherapy?

This study aims to calculate planning target volume (PTV) margins for the prostate and seminal vesicles (SVs) from the use of magnetic resonance-guided radiation therapy (MRgRT). And whether nonisotropic PTV margins are beneficial for these structures. Organ motion is linked to the displacement of the prostate and SVs. From the use of MRgRT, the nearby organs at risk (OAR) can be visualized both inter- and intrafraction. This study looked to determine if there is a correlation between interfractional OAR changes and displacements to the prostate and SVs. Inter- and intrafractional data from 20 consecutive prostate cancer patients treated using extreme hypofractionated 0.35 T MRgRT indicated prostate and SV motion during treatment. Tracking points (TPs) on 2D sagittal cine-MRI enabled assessment of this intrafractional motion. To determine a correlation between rectal changes and target displacements, the rectal diameter (RD) changes were compared against the displacement differences (DDs) at the prostate and SVs. Eighty percent of patients required intrafractional imaging corrections during radiotherapy, including 16/100 fractions due to rectal volume increases and 24/100 fractions due to bladder volume increases. The frequency of ≥3 mm intrafraction displacement was considerably greater in TPs in the SV than in the prostate. A moderate positive correlation (R2 = 0.417) was shown between RD changes and DDs at the level of the prostate and SVs. The PTV margins required for 90% of the patient cohort for prostate and SVs are nonuniform in different directions, and the margin is larger for SVs. Organ motion contributed toward prostate and SV displacements and showed the importance of a robust bladder and rectal-filling protocol.

The effects of primary realignment or suprapubic cystostomy on prostatic displacement in patients with pelvic fracture urethral injury: a clinical study based on MR urethrography

BackgroundTo provide direct evidence of whether primary realignment (PR) or suprapubic cystostomy (SPC) had different effects on the prostatic displacement and prognosis in patients with pelvic fracture urethral injury who needed delay anastomotic urethroplasty based on Magnetic Resonance (MR) urethrography. MethodsWe screened the urethral stenosis database of our single institution from January 2016 to June 2020. Patients who underwent delayed anastomotic urethroplasty with a preoperative MR urethrography and no treatment history of urethra were included. We compared the urethral gap length and prostatic displacement between the PR and SPC group based on MR urethrography. The terminal outcomes such as stenosis-free rate, urinary continence and erectile function were also analyzed between two groups. Results66 patients were included in this retrospective study in which 36 were in PR group and 30 in SPC group. Mean follow-up time was 15.1 months (3-38 months). One and two patients experienced recurrence of stenosis after urethroplasty in two groups (p = 1.000). No difference of erectile dysfunction and urinary incontinence was found between two groups. Based on MR urethrography, the urethral gap length was 17.4 mm and 23.3 mm (p = 0.008) which presented a significant decrease in PR group. The superior prostatic displacement was similar in two groups (9.8 mm vs. 13.8 mm, p = 0.081). The numbers and distance of displacement on lateral aspect showed no difference, either. However, PR group had less anterior-posterior prostatic displacement (p = 0.005). Besides, the erectile function was significantly related to the lateral prostatic displacement (p = 0.030/0.047). ConclusionsBased on MR urethrography, patients in PR group showed shorter urethral gap distance and slighter anterior-posterior prostatic displacement without extra erectile dysfunction or incontinence. Besides, patients’ erectile function might be significantly related to the lateral prostatic displacement.

Design of a seed implantation robot with counterbalance and soft tissue stabilization mechanism for prostate cancer brachytherapy

This article focuses on the topic of the structural design of surgical radioactive surgery robot for prostate cancer. To improve the weight-to-payload ratio of surgery robot end-effector, the energy consumption and stability of robot joint drive and reducing the displacement and deformation of needle insertion in soft tissue. This article discusses the new static torque balancing method and multi-needle insertion soft tissue stabilization mechanisms that may be used in previously articulated seed implantation robots. Compared with the existing balancing system schemes, we adopt the idea of mutual conversion of gravitational potential energy and elastic potential energy and establish a static balancing model. With preloaded displacement parameter of the spring α, the variable gravity torque balance of robot arm can be achieved. Torque and equivalent gravity balancing distribution with the spring balance system and the quantitative evaluation experiment were performed, and experiment results provide evidence that these spring balance devices can basically compensate the gravity torque of the robot arm. In addition, we used nonlinear spring–damper model to establish multi-needles insertion soft tissue force model. Then, a variable multi-needle insertion soft tissue stabilization device is designed with six working modes. The innovative design of this device is the use of the first four needles that are introduced simultaneously on either side of the midline. Initially completed displacement simulation of different numbers of needle insertion prostate tissue, experiment results indicate that multi-needle puncture mechanism could reduce prostate displacement in the y- or z-direction. By this method, the prostate may be fixed, thus this mechanism maybe reduces rotation of the prostate and enabling subsequent needles to be inserted accurately.

P1137 - The effects of primary realignment or suprapubic cystostomy on prostatic displacement in patients with pelvic fracture urethral injury: A clinical study based on MR urethrography

P1137 - The effects of primary realignment or suprapubic cystostomy on prostatic displacement in patients with pelvic fracture urethral injury: A clinical study based on MR urethrography

First experimental evaluation of multi-target multileaf collimator tracking during volumetric modulated arc therapy for locally advanced prostate cancer

PurposeLocally advanced and oligometastatic cancer patients require radiotherapy treatment to multiple independently moving targets. There is no existing commercial solution that can simultaneously track and treat multiple targets. This study experimentally implemented and evaluated a real-time multi-target tracking system for locally advanced prostate cancer. MethodsReal-time multi-target MLC tracking was integrated with 3D x-ray image guidance on a standard linac. Three locally advanced prostate cancer treatment plans were delivered to a static lymph node phantom and dynamic prostate phantom that reproduced three prostate trajectories. Treatments were delivered using multi-target MLC tracking, single-target MLC tracking, and no tracking. Doses were measured using Gafchromic film placed in the dynamic and static phantoms. Dosimetric error was quantified by the 2%/2 mm gamma failure rate. Geometric error was evaluated as the misalignment between target and aperture positions. The multi-target tracking system latency was measured. ResultsThe mean (range) gamma failure rates for the prostate and lymph nodes, were 18.6% (5.2%, 28.5%) and 7.5% (1.1%, 13.7%) with multi-target tracking, 7.9% (0.7%, 15.4%) and 37.8% (18.0%, 57.9%) with single-target tracking, and 38.1% (0.6%, 75.3%) and 37.2% (29%, 45.3%) without tracking. Multi-target tracking had the lowest geometric error with means and standard deviations within 0.2 ± 1.5 for the prostate and 0.0 ± 0.3 mm for the lymph nodes. The latency was 730 ± 20 ms. ConclusionThis study presented the first experimental implementation of multi-target tracking to independently track prostate and lymph node displacement during VMAT. Multi-target tracking reduced dosimetric and geometric errors compared to single-target tracking and no tracking.

Dosimetric impact of rectum and bladder anatomy and intrafractional prostate motion on hypofractionated prostate radiation therapy.

The objective of this study was to evaluate the dosimetric impact on hypofractionated prostate radiation therapy of two geometric uncertainty sources: rectum and bladder filling and intrafractional prostate motion. This prospective study included 544 images (375 pre-treatment cone-beam CT [CBCT] and 169 post-treatment CBCT) from 15 prostate adenocarcinoma patients. We recalculated the dose on each pre-treatment CBCT once the positioning errors were corrected. We also recalculated two dose distributions on each post-treatment CBCT, either using or not intrafractional motion correction. A correlation analysis was performed between CBCT-based dose and rectum and bladder filling as well as intrafraction prostate displacements. No significant differences were found between administered and planned rectal doses. However, we observed an increase in bladder dose due to a lower bladder filling in 66% of treatment fractions. These differences were reduced at the end of the fraction since the lower bladder volume was compensated by the filling during the treatment session. A statistically significant reduction in target volume coverage was observed in 27% of treatment sessions and was correlated with intrafractional prostate motion in sagittal plane > 4mm. A better control of bladder filling is recommended to minimize the number of fractions in which the bladder volume is lower than planned. Fiducial mark tracking with a displacement threshold of 5mm in any direction is recommended to ensure that the prescribed dose criteria are met.

Evaluation of margins in pelvic lymph nodes and prostate radiotherapy and the impact of bladder and rectum on prostate position

PurposeThe aims of this study were: determination of the CTV to PTV margins for prostate and pelvic lymph nodes. Investigation of the impact of registration modality (pelvic bones or prostate) on the CTV to PTV margins of pelvic lymph nodes. Investigation of the variations of bladder and rectum over the treatment course. Investigation of the impact of bladder and rectum variations on prostate position. Patients and methodsThis study included 15 patients treated for prostate adenocarcinoma. Daily kilo voltage images and weekly CBCT scans were performed to assess prostate displacements and common and external iliac vessels motion. These data was used to calculate the CTV to PTV margins using Van Herk equation in the setting of a daily bone registration. We also compared the CTV to PTV margins of pelvic lymph nodes according to registration method; based on pelvic bone or prostate. We delineated bladder and rectum on all CBCT scans to assess their variations over treatment course at 4 anatomic levels [1.5cm above pubic bone (PB), superior edge, mid- and inferior edge of PB]. ResultsUsing Van Herk equation, the prostate CTV to PTV margins (bone registration) were 8.03mm, 5.42mm and 8.73mm in AP, ML and SI direction with more than 97% of prostate displacements were less than 5mm. The CTV to PTV margins ranged from 3.12mm to 3.25mm for external iliac vessels and from 3.12mm to 4.18mm for common iliac vessels. Compared to registration based on prostate alignment, bone registration resulted in an important reduction of the CTV to PTV margins up to 54.3% for external iliac vessels and up to 39.6% for common iliac vessels. There was no significant variation of the mean bladder volume over the treatment course. There was a significant variation of the mean rectal volume before and after the third week of treatment. After the third week, the mean rectal volume seemed to be stable. The uni- and multivariate analysis identified the anterior wall of rectum as independent factor acting on prostate motion in AP direction at 2 levels (superior edge of, mid PB). The right rectal wall influenced the prostate motion in ML direction at inferior edge of PB. The bladder volume tends toward significance as factor acting on prostate motion in AP direction. ConclusionsWe recommend CTV to PTV margins of 8mm, 6mm and 9mm in AP, ML and SI directions for prostate. And, we suggest 4mm and 5mm for external and common iliac vessels respectively. We also prefer registration based on bony landmarks to minimize bowel irradiation. More CBCT scans should be performed during the first 3weeks and especially the first week to check rectum volume.

Evaluation Of Intra-Fraction Motion Of Prostate Gland During Moderately Hypofractionated External Beam Radiotherapy Using Four Dimensional Trans Perineal Ultrasound (TPUS)

The purpose of the study is to monitor the intra fraction movements of prostate during hypo fractionated EBRT in real time using noninvasive 4D trans perineal ultra sound (Elekta clarity TPUS auto scan system). A total of 1986 trans perineal ultrasound sound (TPUS) monitorings were studied. We analyzed TPUS monitoring data of 100 treatment sessions from five of our patients treated with 60Gy/20 fractions over four weeks. Planning CT scan and reference TPUS was acquired in same position. Bladder and rectal protocols were reproduced in all treatment sessions. Treatment was delivered with VMAT technique under TPUS guidance with Gating. During treatment continuous monitoring of prostate motion is done with TPUS in three direction Superior- Inferior (SI), Right-Left (RL), Anterior-Posterior (AP). The treatment time for each session ranged from 220 to 660 seconds. The prostate displacement in every 20 second interval was taken for evaluation in this study. The mean, median, maximum displacements in each direction were calculated. Percentage of time the prostate moved within 1mm, 3mm, 6mm, 10mm, >10mm and percentage of time prostate moved in SI, RL, AP direction were assessed for each patient. The treatment was automatically stopped (gating) if the displacement of prostate is more than 3mm for more than 3 seconds. The mean prostate displacement of (1.14±0.80) mm, (-1.77±2.57) mm, (-1.96±1.46) mm were observed in SI, RL, AP directions. The prostate moved within 3mm in 88.58%, 90.16% ,75.76% and within 6 mm in 98.94%, 97.24%, 92.96% of treatment time in SI, RL, AP directions respectively. Prostate displacement was noted in inferior: superior (86%:13.9%); right: left (47.02%:52.98%); anterior: posterior (11.64%:88.36%) directions respectively. The maximum duration of prostate displacement was seen in posterior and inferior direction. Maximum displacement up to 13.65 mm was detected. Deviations more than 10mm in SI, RL, AP directions were 0%, 0.2% and 3.5% respectively. Maximum displacement was seen in AP direction. Maximum duration of prostate displacement was seen in inferior and superior direction. Real time monitoring of prostate motion during treatment is warranted during hypo fractionated radiotherapy while using tight margins.

Preliminary Clinical Evaluation of Intrafraction Prostate Displacements for Two Immobilization Systems.

Immobilization systems and their corresponding set-up errors influence the clinical target volume to the planning target volume (CTV-PTV) margins, which is critical for hypofractionated prostate stereotactic body radiotherapy (SBRT). This preliminary study evaluates intrafraction prostate displacement for two immobilization systems (A and B). Six consecutive patients having localized prostate cancer and implanted prostate marker seeds were studied. Planar X-ray images were acquired pre- and post-treatment to find the intrafraction prostate displacement. The average absolute displacements (lateral, longitudinal, vertical) were 0.9 ± 0.4 mm, 1.7 ± 0.1 mm, 1.3 ± 0.3 mm (system A), and 0.5 ± 0.2 mm, 0.6 ± 0.1 mm, 0.8 ± 0.3 mm (system B), with average three-dimensional displacements of 2.6 ± 0.2 mm (system A) and 1.3 ± 0.2 mm (system B). The computed CTV-PTV margins (lateral, longitudinal, vertical) were 2.5 mm, 2.5 mm, 3.6 mm and 1.4 mm, 1.6 mm, 2.4 mm for systems A and B, respectively. This suggests that the immobilization system influences intrafraction prostate displacement and, therefore, the margins applied. However, the margins found for both systems are comparable to the margins used for hypofractionated prostate SBRT.

Mosquito proboscis-inspired needle insertion to reduce tissue deformation and organ displacement

This study investigates mosquito proboscis-inspired (MPI) insertion applied to the clinically used biopsy needle to reduce tissue deformation and organ displacement. Advanced medical imagining has enabled early-stage identification of cancerous lesions that require needle biopsy for minimally invasive tissue sampling and pathological analysis. Accurate cancer diagnosis depends on the accuracy of needle deployment to the targeted cancerous lesion site. However, currently available needle delivery systems deform and move soft tissue and organs, leading to a non-diagnostic biopsy or undersampling of the target. Two features inspired by the mosquito proboscis were adopted for MPI insertion in prostate biopsy: (1) the harpoon-shape notches at the needle tip and (2) reciprocating needle-cannula motions for incremental insertion. The local tissue deformation and global prostate displacement during the MPI vs. traditional direct insertions were quantified by optically tracking the displacement of particle-embedded tissue-mimicking phantoms. Results show that the MPI needle insertion reduced both local tissue deformation and global prostate displacement because of the opposite needle-cannula motions and notches which stabilized and reduced the tissue deformation during insertion. Findings provide proof of concept for MPI insertion in the clinical biopsy procedures as well as insights of needle–tissue interaction for future biopsy technology development.