Permanent Prostate Research Articles

Comparison of prostate contours between conventional stepping transverse imaging and Twister-based sagittal imaging in permanent interstitial prostate brachytherapy.

PurposeTo compare prostate contours on conventional stepping transverse image acquisitions with those on twister-based sagittal image acquisitions.Material and methodsTwenty prostate cancer patients who were planned to have permanent interstitial prostate brachytherapy were prospectively accrued. A transrectal ultrasonography probe was inserted, with the patient in lithotomy position. Transverse images were obtained with stepping movement of the transverse transducer. In the same patient, sagittal images were also obtained through rotation of the sagittal transducer using the “Twister” mode. The differences of prostate size among the two types of image acquisitions were compared. The relationships among the difference of the two types of image acquisitions, dose-volume histogram (DVH) parameters on the post-implant computed tomography (CT) analysis, as well as other factors were analyzed.ResultsThe sagittal image acquisitions showed a larger prostate size compared to the transverse image acquisitions especially in the anterior-posterior (AP) direction (p < 0.05). Interestingly, relative size of prostate apex in AP direction in sagittal image acquisitions compared to that in transverse image acquisitions was correlated to DVH parameters such as D90 (R = 0.518, p = 0.019), and V100 (R = 0.598, p = 0.005).ConclusionsThere were small but significant differences in the prostate contours between the transverse and the sagittal planning image acquisitions. Furthermore, our study suggested that the differences between the two types of image acquisitions might correlated to dosimetric results on CT analysis.

Prostate cancer-specific death in brachytherapy treated high-risk patients stratified by pre-treatment PSA.

PurposeTo evaluate prostate-cancer specific mortality (PCSM) in a cohort of high-risk patients treated with a permanent prostate brachytherapy approach, stratified by pre-treatment PSA.Material and methods448 high-risk patients (NCCN criteria) underwent permanent prostate brachytherapy. High risk patients were stratified by pre-treatment PSA (≤ 10.0, 10.1-20, and > 20 ng/ml). Biochemical failure (BF), prostate cancer-specific mortality (PCSM), distant failure (DM), and overall mortality (OM) were assessed as a function of prognostic group. Multiple clinical, treatment, and dosimetric parameters were evaluated for impact on outcome.ResultsThe 10-year OM, BF, and PCSM for the entire cohort were 28.5%, 13.3%, and 4.9%, respectively. At 10 years, PCSM was 2.5%, 10.7%, and 4.5% in the PSA ≤ 10, 10.1-20, and > 20 ng/ml groups, respectively. No statistically significant differences in BF or overall survival (OS) were noted when stratified by pre-treatment PSA. DF was the most common in the 10.1-20 ng/ml cohort (8.6% at 10 years). In multivariate analysis, PCSM was most closely related to percent positive biopsies (p = 0.001) and tobacco (p = 0.042).ConclusionsHigh-risk prostate cancer treated with permanent prostate brachytherapy and supplemental external beam radiotherapy resulted in excellent long-term biochemical control and PCSM. Overall, PCSM was low in all cohorts but highest in the intermediate PSA group (10.1-20 ng/ml).

Dosimetry advantages of intraoperatively built custom-linked seeds compared with loose seeds in permanent prostate brachytherapy.

PurposeThe aim of this study was to compare the implant quality between intraoperatively built custom-linked seeds (IBCL) and loose seeds (LS) retrospectively.Material and methodsThis study included 74 prostate cancer patients who were treated with permanent prostate brachytherapy (PPB) using IBCL (n = 37) or LS (n = 37) between July 2014 and June 2016. Dose-volume histogram (DVH) parameters, seed migration, and operation time were compared between the IBCL and LS groups. In addition to the standard target volume of the whole prostate gland, DVH parameters for prostate plus a 3 mm margin (CTV) were evaluated.ResultsIn intraoperative planning, prostate V150 was lower (54.8% vs. 59.6%, p = 0.027), and CTV V100 (88.1% vs. 85.6%, p = 0.019) and D90 (98.5% vs. 92.6%, p = 0.0033) were higher in the IBCL group compared with in the LS group. In post-implant dosimetry, prostate V100 (96.9% vs. 95.2%, p = 0.020), CTV V100 (85.6% vs. 81.7%, p = 0.046), and CTV D90 (94.2% vs. 86.5%, p < 0.001) were higher, and prostate V150 (57.1% vs. 64.5%, p = 0.0051) and CTV V150 (31.5% vs. 35.7%, p = 0.046) were lower in the IBCL group compared with in the LS group. Regarding DVH changes between intraoperative planning and post-implant dosimetry, the decrease in prostate D90 was significantly lower in the IBCL group than in the LS group (–1.16% vs. –4.17%, p < 0.001). For the IBCL group, the operation time was slightly but significantly longer than that for the LS group (50.5 minutes vs. 43.7 minutes, p = 0.011). However, the seed migration rate was significantly lower in the IBCL group than in the LS group (5% vs. 41%, p < 0.001).ConclusionsIntraoperatively built custom-linked is more advantageous than LS in terms of dosimetric parameters and migration.

Does supplemental external beam radiation therapy impact urinary, bowel, and erectile function following permanent prostate brachytherapy?: results of two prospective randomized trials.

PurposeTo evaluate the impact of supplemental external beam radiation therapy (EBRT) prior to permanent prostate brachytherapy on long term urinary, bowel, and erectile function.Material and methodsPatient administered urinary, bowel, and erectile quality of life (QoL) instrument were obtained prior to treatment and following brachytherapy. The study population was comprised of the 457 patients who were alive as of June 2016, had been randomized to two markedly different supplemental EBRT dose regimens and a third arm without supplemental EBRT, and had completed the June 2016 QoL survey. The need for urinary or bowel surgical intervention was prospectively recorded during routine follow-up. Multiple parameters were evaluated for effect on outcomes.ResultsThe urinary catheter was removed on day 0 in 92.1% of patients and 0.4% required a post-implant transurethral prostatic resection (TURP). On average, the International Prostate Symptom Score (IPSS) normalized at week 14. The 10-year rate of urethral strictures was 5.3%. No significant differences were discerned between baseline and post-implant rectal function assessment score (RFAS), and no patient developed a rectal ulcer or fistula. The 10-year potency preservation rate was 50.3%. Supplemental EBRT did not affect urinary, bowel, or erectile function. Urethral strictures were most closely related to bulbomembranous urethral brachytherapy doses, post-implant rectal function to pre-implant hemorroidal bleeding, and RFAS and erectile function to pre-brachytherapy international index of erectile function and age.ConclusionsSupplemental EBRT did not significantly effect catheter dependency, IPSS resolution, urethral stricture rate, the need for post-implant TURP, bowel, or erectile function. Careful attention to brachytherapy dose distributions appears to be most important in minimizing post-brachytherapy morbidity.

Use of novel thermobrachytherapy seeds for realistic prostate seed implant treatments.

A practical means of delivering both therapeutic radiation and hyperthermia to a deep-seated target has been identified in the literature as highly desirable, provided it is capable of generating sufficient temperatures over the defined target volume. The authors present continued development of a dual-modality thermobrachytherapy (TB) seed, investigating its capabilities in delivering prescribed hyperthermia to realistic deep-seated targets. The TB seed is based on the ubiquitous low dose-rate (LDR) brachytherapy permanent implant. Heat is generated by incorporating a ferromagnetic core within the seed and placing the patient in an oscillating external magnetic field, producing eddy currents within the core and hence Joule heating. A strategically selected Curie temperature results in thermal self-regulation. The magnetic and thermal properties of the TB seed were studied experimentally by means of seed prototypes placed in a tissue-mimicking phantom and heated with an industrial induction heater, as well as computationally in the finite element analysis solver COMSOL Multiphysics. Patient-specific seed distributions derived from LDR permanent prostate implants previously conducted at their institution were modeled in COMSOL to evaluate their ability to adequately cover a defined target volume and to overcome the loss of heat due to blood perfusion within tissue. The calculated temperature distributions were analyzed by generating temperature-volume histograms, which were used to quantify coverage and temperature homogeneity for varied blood perfusion rates, seed Curie temperatures, and thermal power production rates. Use of additional hyperthermia-only (HT-only) seeds in unused spots within the implantation needles was investigated, as was an increase in these seeds' core size to increase their power. The impact of the interseed attenuation and scatter (ISA) effect on radiation dose distributions of this seed was also quantified by Monte Carlo studies in the software package Monte Carlo N-Particle Version 5. Increasing the power production of the seeds, as well as increasing their Curie point, would increase the maximum blood perfusion rate that a given seed distribution could overcome to obtain an acceptable temperature distribution. However, this would also increase the maximum temperatures generated at the seed surfaces. Auxiliary HT-only seeds serve to improve the temperature uniformity within the target, as well as decrease the seed power generation requirements. Both an increase in their core size and an increase in both seed types' Curie temperatures enhance the resulting temperature coverage. The interseed and scatter effect caused by both the TB and HT-only seeds was found to reduce the dose to 90% of the target volume (D90) by a factor of 1.10 ± 0.02. A systematic approach of combining LDR prostate brachytherapy with hyperthermia is described, and its ability to provide sufficient and uniform temperature distributions in realistic patient-specific implants evaluated. A combination of TB and HT-only seeds may be used to produce a uniform temperature distribution in a defined target. Various modeled changes to their design, such as optimization of their Curie temperature, improve their ability to overcome the thermal effects of blood perfusion. The enhanced ISA of the TB and HT-only seeds must be taken into account for dose calculations, but is manageable.

The impact of timing of salvage hormonal therapy on survival after brachytherapy for prostate cancer

PurposeWe aimed to evaluate the impact of timing of androgen deprivation therapy (ADT) on survival in a cohort of patients with biochemical recurrence (BCR) after brachytherapy treatment for prostate cancer. Methods and MaterialsWe retrospectively identified 2366 men receiving permanent prostate brachytherapy with or without external beam radiation therapy. Patients experiencing BCR were stratified by receipt of immediate or delayed (≥3 months) ADT and prostate-specific antigen (PSA) failure threshold of 10 ng/mL. Prostate cancer–specific mortality (PCSM) and all-cause mortality (ACM) were evaluated using Fine–Gray's competing risks regression and Cox proportional hazard model, respectively. ResultsWe identified 109 patients in the study cohort treated with ADT for BCR, followed for a median of 11.4 years. Competing risk regression revealed that there was no difference in PCSM for patients receiving delayed vs. immediate ADT (hazard ratio [HR], 0.94; 95% confidence interval [CI]: 0.44–2.00: p = 0.871) or for those initiating hormonal therapy at PSA threshold of 10 vs. <10 ng/mL (HR, 0.85; 95% CI: 0.41–1.75; p = 0.649); similarly, there was no difference in ACM. PSA doubling time <6 months (HR, 2.52; 95% CI: 1.22–5.23; p = 0.013), time to BCR <3 years (HR, 3.27; 95% CI: 1.67–6.42; p = 0.003), and permanent prostate brachytherapy with external beam radiation therapy (HR, 5.21; 95% CI: 2.05–13.26; p = 0.001) were significantly associated with PCSM, as well as ACM. ConclusionsAmong a cohort of brachytherapy patients, we identified no significant difference in survival for delayed salvage hormonal therapy. Shorter PSA doubling time and time to BCR are significantly associated with adverse outcomes, and these patients should be considered for immediate salvage therapy.

Long-Term Prostate-Specific Antigen Stability and Predictive Factors of Failure After Permanent Seed Prostate Brachytherapy

Long-Term Prostate-Specific Antigen Stability and Predictive Factors of Failure After Permanent Seed Prostate Brachytherapy

Dosimetric Consequences and Acute Toxicity Following Perirectal Hydrogel Spacer Injection During Permanent Prostate Brachytherapy

Dosimetric Consequences and Acute Toxicity Following Perirectal Hydrogel Spacer Injection During Permanent Prostate Brachytherapy

Autologous fat transfer as prostate-rectal spacer: Technique description and early results

Purpose: Several attempts have been made to increase the distance between the prostate and the rectum through injection of different synthetic compounds, generating space between organs. To report an original technique to increase the distance between the rectum and the prostate, by autologous fat implantation into the rectoprostatic space, with the aim of providing physical dosimetry protection and rectal dose sparing. Methods: We prospectively evaluated twelve patients subjected to autologous fat implantation as recto-prostatic spacer subsequently receiving prostate either radical (n = 6), or salvage brachytherapy for local recurrence after external beam radiation therapy (EBRT) (n = 6). Standard permanent prostate brachytherapy seed implantation was performed through transperineal approach and under transrectal ultrasonography (TRUS) and template guidance. Prescribed D90 dose for Iodine - 125 monotherapy was 140 - 160 Gy, reduced by 30% for rescue cases to obtain a Rectum V100 under 1 cc. Results: Lipo-transfer was completed in all 12 patients. Control CT scan at 1 month showed average distances of: 10.7 mm (range) (2.8 - 15.9 mm), 7.6 (1.8 - 11.6 mm) and 6.8 (4.2 - 8.3) mm at prostate base, middle and apex, respectively. Shortest separation distance observed was at apex and midline, while largest was observed the sides and at seminal vesicles level. Control CT at 3 months showed average distances of 9.6 mm (1.9 - 14.6 mm), 6.3 mm (1.8 - 10.2 mm) and 5.4 mm (3.8 - 7.2 mm) at prostate base, middle and apex, respectively. Most complications were minor. Conclusion: Autologous fat transfer is a feasible and simple procedure for experienced practitioners with low complication rates, which allows dose escalation to the prostate.

Prostate-specific antigen nadir concentration, hypertension and diabetes as risk factors for biochemical failure after permanent 125I seed brachytherapy for prostate cancer.

The aim of this study was to evaluate risk factors for biochemical failure (BF) following permanent prostate seed 125I brachytherapy for prostate cancer. The study reviewed the medical records of 607 patients with biopsy-proven prostate adenocarcinoma who were treated at Oulu University Hospital between 2001 and 2014. Clinical characteristics at diagnosis, treatment-related data and follow-up data were collected to identify potential risk factors for BF, which was defined using the Phoenix criteria [prostate-specific antigen (PSA) increase >2 µg/l from the PSA nadir concentration, which defined as the lowest PSA concentration observed after BT]. The median follow-up was 81 months. BF was detected in 117 (19.3%) patients. The PSA nadir concentration was associated with BF. The mean times to BF were 114 [95% confidence interval (CI): 112-116] and 55 (95% CI: 47-63) months for patients with PSA nadir concentrations <0.5 and ≥0.5 µg/l, respectively (P<0.001). Patients with underlying hypertension or diabetes tended to develop BF more rapidly. For patients without and with hypertension, the mean times to BF were 104 (95% CI: 100-107) and 98 (95% CI: 93-103) months, respectively (P=0.035). For patients without and with diabetes, the mean times to BF were 103 (95% CI: 100-106) and 89 (95% CI: 77-102) months, respectively (P=0.006). The overall survival and prostate cancer-specific survival rates were 90.3 and 98.0%, respectively. The mean overall survival and prostate-cancer specific survival times were 147 and 158 months, respectively. Therefore, PSA nadir level was identified as a clear risk factor for BF. In addition, BF tended to develop more rapidly among patients with underlying hypertension or diabetes. These risk factors should be considered, and individually tailored follow-up may be useful for identifying patients requiring more intense follow-up for early BF detection.

94: Long-Term PSA Stability and Predictive Factors of Failure after Permanent Seed Prostate Brachytherapy

94: Long-Term PSA Stability and Predictive Factors of Failure after Permanent Seed Prostate Brachytherapy

Stranded seed displacement, migration, and loss after permanent prostate brachytherapy as estimated by Day 0 fluoroscopy and 4-month postimplant pelvic x-ray

PurposeThe aim of the study was to determine the incidence of local displacement, distant seed migration to the chest, and seed loss after permanent prostate brachytherapy (PPB) with stranded seeds (SSs) using sequential two-dimensional fluoroscopic pelvic and chest x-rays. Methods and MaterialsBetween October 2010 and April 2014, a total of 137 patients underwent PPB and 4-month followup pelvic and chest x-ray imaging. All patients had exclusively SSs placed and an immediate postimplant fluoroscopic image of the seed cluster. Followup x-ray images were evaluated for the number, location, and displacement of seeds in comparison to Day 0 fluoroscopic images. Significant seed displacement was defined as seed displacement >1 cm from the seed cluster. Followup chest x-rays were evaluated for seed migration to the chest. ResultsSeed migration to the chest occurred in 3 of the 137 patients (2%). Seed loss occurred in 38 of the 137 patients (28%), with median loss of one seed (range, 1–16), and total seeds loss of 104 of 10,088 (1.0%) implanted. Local seed displacement was seen in 12 of the 137 patients (8.8%), and total seeds displaced were 0.15% (15/10,088). ConclusionsSS placement in PPB is associated with low rates of substantial seed loss, local displacement, or migration to the chest. Comparing immediate postimplant fluoroscopic images to followup plain x-ray images is a straightforward method to supplement quality assurance in PPB and was found to be useful in identifying cases where seed loss was potentially of clinical significance.

Testing and evaluation of image registration brachytherapy

Real-time ultrasound (US) is used to guide implantation for temporary and permanent prostate brachytherapy treatment. MRI, CT and US fusion is available in dedicated treatment planning systems used for these procedures. The registration of these imaging modalities requires additional image verification and tests to ensure accuracy. Using a CIRS Tissue Equivalent Ultrasound Prostate Phantom we evaluated the accuracy of the registration system of a Hitachi Preirus US scanner for fusing MRI and live US images. The phantom contains 3 lesions, a urethra and a prostate volume of 53 cm3. The MRI and US images were registered using the urethra as a marker in the central slice of the image. The registration was then checked at the base and apex of the prostate. Along the urethra the registration was accurate to within 2mm. Another common fusion software, Variseed™, was assessed by measuring the percentage of overlapping volumes for the prostate and a lesion within the prostate for CT, US and MRI images. The overlapping volumes were compared for CT–MRI, CT–US (un-deformed prostate), CT–US (deformed prostate), MRI-US (un-deformed prostate), MRI-US (deformed prostate) and US–US(un-deformed prostate and deformed prostate). Contour overlap varied from 90% to 40% for the lesion, which was approximately 1 cm3, and 96% to 78% contour overlap for the whole prostate. This study demonstrates how a tissue equivalent phantom can be used for testing and commissioning of multi-modality registration systems in brachytherapy.

SU-G-201-02: Application of RayStretch in Clinical Cases: A Calculation for Heterogeneity Corrections in LDR Permanent I-125 Prostate Brachytherapy

Purpose: Tissue heterogeneities and calcifications have significant impact on the dosimetry of low energy brachytherapy (BT). RayStretch is an analytical algorithm developed in our institution to incorporate heterogeneity corrections in LDR prostate brachytherapy. The aim of this work is to study its application in clinical cases by comparing its predictions with the results obtained with TG-43 and Monte Carlo (MC) simulations. Methods: A clinical implant (71 I-125 seeds, 15 needles) from a real patient was considered. On this patient, different volumes with calcifications were considered. Its properties were evaluated in three ways by i) the Treatment planning system (TPS) (TG-43), ii) a MC study using the Penelope2009 code, and iii) RayStretch. To analyse the performance of RayStretch, calcifications located in the prostate lobules covering 11% of the total prostate volume and larger calcifications located in the lobules and underneath the urethra for a total occupied volume of 30% were considered. Three mass densities (1.05, 1.20, and 1.35 g/cm3) were explored for the calcifications. Therefore, 6 different scenarios ranging from small low density calcifications to large high density ones have been discussed. Results: DVH and D90 results given by RayStretch agree within 1% with the full MC simulations. Although no effort has been done to improve RayStretch numerical performance, its present implementation is able to evaluate a clinical implant in a few seconds to the same level of accuracy as a detailed MC calculation. Conclusion: RayStretch is a robust method for heterogeneity corrections in prostate BT supported on TG-43 data. Its compatibility with commercial TPSs and its high calculation speed makes it feasible for use in clinical settings for improving treatment quality. It will allow in a second phase of this project, its use during intraoperative ultrasound planning. This study was partly supported by a fellowship grant from the Spanish Ministry of Education, by the Generalitat Valenciana under Project PROMETEOII/2013/010, by the Spanish Government under Project No. FIS2013-42156 and by the European Commission within the SeventhFramework Program through ENTERVISION (grant agreement number 264552).

SU‐F‐T‐42: MRI and TRUS Image Fusion as a Mode of Generating More Accurate Prostate Contours

Purpose:Transrectal Ultrasound (TRUS) imaging is utilized intra‐operatively for LDR permanent prostate seed implant treatment planning. Prostate contouring with TRUS can be challenging at the apex and base. This study attempts to improve accuracy of prostate contouring with MRI‐TRUS fusion to prevent over‐ or under‐estimation of the prostate volume.Methods:14 patients with previous MRI guided prostate biopsy and undergone an LDR permanent prostate seed implant have been selected. The prostate was contoured on the MRI images (1 mm slice thickness) by a radiologist. The prostate was also contoured on TRUS images (5 mm slice thickness) during LDR procedure by a urologist. MRI and TRUS images were rigidly fused manually and the prostate contours from MRI and TRUS were compared using Dice similarity coefficient, percentage volume difference and length, height and width differences.Results:The prostate volume was overestimated by 8 ± 18% (range: 34% to −25%) in TRUS images compared to MRI. The mean Dice was 0.77 ± 0.09 (range: 0.53 to 0.88). The mean difference (TRUS‐MRI) in the prostate width was 0 ± 4 mm (range: −11 to 5 mm), height was −3 ± 6 mm (range: −13 to 6 mm) and length was 6 ± 6 (range: −10 to 16 mm). Prostate was overestimated with TRUS imaging at the base for 6 cases (mean: 8 ± 4 mm and range: 5 to 14 mm), at the apex for 6 cases (mean: 11 ± 3 mm and range: 5 to 15 mm) and 1 case was underestimated at both base and apex by 4 mm.Conclusion:Use of intra‐operative TRUS and MRI image fusion can help to improve the accuracy of prostate contouring by accurately accounting for prostate over‐ or under‐estimations, especially at the base and apex. The mean amount of discrepancy is within a range that is significant for LDR sources.

SU-G-201-09: Evaluation of a Novel Machine-Learning Algorithm for Permanent Prostate Brachytherapy Treatment Planning

Purpose: A novel, automated, algorithm for permanent prostate brachytherapy (PPB) treatment planning has been developed. The novel approach uses machine-learning (ML), a form of artificial intelligence, to substantially decrease planning time while simultaneously retaining the clinical intuition of plans created by radiation oncologists. This study seeks to compare the ML algorithm against expert-planned PPB plans to evaluate the equivalency of dosimetric and clinical plan quality. Methods: Plan features were computed from historical high-quality PPB treatments (N = 100) and stored in a relational database (RDB). The ML algorithm matched new PPB features to a highly similar case in the RDB; this initial plan configuration was then further optimized using a stochastic search algorithm. PPB pre-plans (N = 30) generated using the ML algorithm were compared to plan variants created by an expert dosimetrist (RT), and radiation oncologist (MD). Planning time and pre-plan dosimetry were evaluated using a one-way Student's t-test and ANOVA, respectively (significance level = 0.05). Clinical implant quality was evaluated by expert PPB radiation oncologists as part of a qualitative study. Results: Average planning time was 0.44 ± 0.42 min compared to 17.88 ± 8.76 min for the ML algorithm and RT, respectively, a significant advantage [t(9), p = 0.01]. A post-hoc ANOVA [F(2,87) = 6.59, p = 0.002] using Tukey-Kramer criteria showed a significantly lower mean prostate V150% for the ML plans (52.9%) compared to the RT (57.3%), and MD (56.2%) plans. Preliminary qualitative study results indicate comparable clinical implant quality between RT and ML plans with a trend towards preference for ML plans. Conclusion: PPB pre-treatment plans highly comparable to those of an expert radiation oncologist can be created using a novel ML planning model. The use of an ML-based planning approach is expected to translate into improved PPB accessibility and plan uniformity.

SU-G-JeP1-10: Feasibility of CyberKnife Tracking Using the Previously-Implanted Permanent Brachytherapy Seed Cloud

Purpose: Robotic radiosurgery is a salvage treatment option for patients with recurrent prostate cancer. We explored the feasibility of tracking the bolus of permanent prostate implants (PPI) using image recognition software optimized to track spinal anatomy. Methods: Forty-five inert iodine seeds were implanted into a gelatin-based prostate phantom. Four superficial gold seeds were inserted to provide ground-truth alignment. A CT scan of the phantom (120 kVp, 1 mm slice thickness) was acquired and a single-energy iterative metal artifact reduction (MAR) algorithm was used to enhance the quality of the DRR used for tracking. CyberKnife treatment plans were generated from the MAR CT and regular CT (no-MAR) using spine tracking. The spine-tracking grid was centered on the bolus of seeds and resized to encompass the full seed cloud. A third plan was created from the regular CT scan, using fiducial tracking based on the 4 superficial gold seeds with identical align-center coordinates. The phantom was initially aligned using the fiducial-tracking plan. Then the MAR and no-MAR spine-tracking plans were loaded without moving the phantom. Differences in couch correction parameters were recorded in the case of perfect alignment and after the application of known rotations and translations (roll/pitch of 2 degrees; translations XYZ of 2 cm). Results: The spine tracking software was able to lock on to the bolus of seeds and provide couch corrections both in the MAR and no-MAR plans. In all cases, differences in the couch correction parameters from fiducial alignment were <0.5 mm in translations and <1 degree in rotations. Conclusion: We were able to successfully track the bolus of seeds with the spine-tracking grid in phantom experiments. For clinical applications, further investigation and developments to adapt the spine-tracking algorithm to optimize for PPI seed cloud tracking is needed to provide reliable tracking in patients. One of the authors (MD) has received research support and speaker honoraria from Accuray.

WE‐AB‐BRA‐11: Improved Imaging of Permanent Prostate Brachytherapy Seed Implants by Combining an Endorectal X‐Ray Sensor with a CT Scanner

Purpose:To test feasibility of the use of a digital endorectal x‐ray sensor for improved image resolution of permanent brachytherapy seed implants compared to conventional CT.Methods:Two phantoms simulating the male pelvic region were used to test the capabilities of a digital endorectal x‐ray sensor for imaging permanent brachytherapy seed implants. Phantom 1 was constructed from acrylic plastic with cavities milled in the locations of the prostate and the rectum. The prostate cavity was filled a Styrofoam plug implanted with 10 training seeds. Phantom 2 was constructed from tissue‐equivalent gelatins and contained a prostate phantom implanted with 18 strands of training seeds. For both phantoms, an intraoral digital dental x‐ray sensor was placed in the rectum within 2 cm of the seed implants. Scout scans were taken of the phantoms over a limited arc angle using a CT scanner (80 kV, 120–200 mA). The dental sensor was removed from the phantoms and normal helical CT and scout (0 degree) scans using typical parameters for pelvic CT (120 kV, auto‐mA) were collected. A shift‐and add tomosynthesis algorithm was developed to localize seed plane location normal to detector face.Results:The endorectal sensor produced images with improved resolution compared to CT scans. Seed clusters and individual seed geometry were more discernable using the endorectal sensor. Seed 3D locations, including seeds that were not located in every projection image, were discernable using the shift and add algorithm.Conclusion:This work shows that digital endorectal x‐ray sensors are a feasible method for improving imaging of permanent brachytherapy seed implants. Future work will consist of optimizing the tomosynthesis technique to produce higher resolution, lower dose images of 1) permanent brachytherapy seed implants for post‐implant dosimetry and 2) fine anatomic details for imaging and managing prostatic disease compared to CT images.Funding: LSU Faculty Start‐up Funding. Disclosure: XDR Radiography has loaned our research group the digital x‐ray detector used in this work. CoI: None.

SU‐F‐T‐39: Comparing Nomograms for Ordering of Palladium‐103 Seeds for Dynamic Intraoperative Prostate Seed Implantation

Purpose:Several nomograms exist for the purpose of ordering palladium‐ 103 seeds for permanent prostate seed implants. Excess seeds pose additional radiation safety risks and increase the cost of care. This study compared three seed ordering nomograms with seed counts from dynamic intra‐operative PSI to determine (1) the cause of excess seeds and (2) the optimal nomogram for our institution.Methods:Pre‐operative and intra‐operative clinical data were collected for 100 Gy (n=151) and 125 Gy (n=224) prostate seed implants. The number of implanted seeds which would have given D90=100% was normalized to that criteria and seed strength of 2U. This was plotted against intra‐operative prostate volume and compared to two previously published nomograms and an in‐house nomogram. A linear fit was produced and confidence intervals were calculated. The causes of excess seeds were assessed by comparing pre‐ and intra‐operative prostate volumes, variability of D90 around 100%, and variance of seed strength from 2U.Results:Of the 375 total cases, 97.6% had excess seeds. On average, 27.17±12.91% of ordered seeds were wasted. Of this percentage, 6.98±5.47% of excess seeds were due to overestimation of pre‐operative prostate volume, 1.10±0.88% were due to D90&lt;100%, 1.17±0.67% were due to seed strength over 2U, and 17.36±7.79% could not be directly attributed to a specific reason. The latter percentage may be due to overestimation of the in‐house nomogram. Two of three nomograms substantially overestimated the number of seeds required. The third nomogram underestimated the required seed number for smaller prostate treatment volume. A linear fit to the clinical data was derived and 99.9% confidence intervals were calculated.Conclusion:Over 85% of clinical cases wasted over 15% of ordered seeds. Two of three nomograms overestimated the required number of seeds. The upper 99.9% C.I. of the clinical data may provide a more reasonable nomogram for Pd‐103 seed ordering.

SU‐F‐J‐167: Use of MR for Permanent Prostate Implant Preplanning

Purpose:To study the feasibility using MR imaging to improve target definition on ultrasound during permanent prostate implants and aid in source strength determination for treatment planning in the OR.Methods:Patients who receive permanent prostate implants undergo MR and CT imaging prior to the implant procedure to determine the volume of the prostate, bony restriction to the procedure, bladder extension, external sphincter length and neurovascular bundle. The volume of the prostate is generally used to order seeds for the procedure. In 10 patients, the MR was used as the preplanning study with the PTV defined as a 2 mm expansion of the MR prostate in all directions except the posterior. Various dose volume parameters for the MR prostate and the PTV were compared to the actual preplan developed and executed in the OR. In addition, there parameters were compared to the post implant dosimetry performed 3 weeks after the implant procedure.Results:The results show that the number of seeds used using MR and US (ultrasound) planning was generally with 2 seeds and the maximum difference was 7 seeds. There is no significant difference between any of the dose index parameters of V100, V150, V200, D99 and D90 parameters between MR planning, US planning and postimplant evaluation There was a significant difference between planned D99 (avg of 105%) and achieved D99 (avg 91%).Conclusion:MR imaging is an invaluable tool to improve target definition for permanent prostate implants. Use of MR images for preplanning improves the confidence with which source can be ordered for the procedure that is OR planned. Ordering a maximum of 10 seeds more than planned would be sufficient to deliver a plan in the OR using US. Moving ahead to non‐rigid registration between MR ad US images could further increase the confidence level of MR planning.