Interstitial Catheter Research Articles

Proof-of-concept of real-time electromagnetic guidance for gynecologic interstitial catheters in high dose rate brachytherapy

Background and PurposeThe addition of interstitial needles to intracavitary gynecologic (GYN) high dose rate (HDR) brachytherapy has been shown to improve target coverage and organs-at-risk (OAR) sparing. However, no commercial solution allows real-time guidance of interstitial catheter placement. This phantom study aimed to evaluate the feasibility of an electromagnetic (EM) tracking system guidance workflow for GYN HDR brachytherapy treatment in a magnetic resonance imaging (MRI) and real-time transrectal ultrasound (TRUS) fusion scenario. Materials and MethodsA clinical investigational system combining a treatment planning system and the EM tracking technology was used. The 3D T2 weighted magnetic resonance (MR) image set of a patient treated with intracavitary and interstitial HDR brachytherapy was retrospectively chosen. The MR image set was used to delineate the target and the OARs. A preplan was generated to determine needles positions in advance. The implant was reproduced in a water phantom. A 3D TRUS scan was acquired, and a rigid registration between the MR and the TRUS images was performed. ResultsThe accuracy of the EM tracking system was < 1 mm for both the sagittal and the transverse modes of the TRUS probe. Contours that were delineated on the MRI were propagated on the TRUS images after the rigid registration. Needle insertion was successfully guided in real time with the EM tracking system on the TRUS live image using the MRI contours for guidance. ConclusionBased on this proof-of-concept, real-time EM-guidance of interstitial needle for GYN HDR brachytherapy appears to be feasible.

Saturday, June 18, 20227:40 AM - 5:00 PMPO22 Presentation Time: 7:40 AM: A Novel Algorithm for Automatic Interstitial Needle Tracking on PETRA MRI for HDR Brachytherapy

<h3>Purpose</h3> Current practice for interstitial high-dose-rate (HDR) brachytherapy treatment planning involves manual tracking of needle positions on CT images. Recently, PETRA MRI showed the potential to detect empty interstitial gynecological brachytherapy needles owing to low needle signal, intermediate tissue contrast and high spatial resolution. We aimed to develop an algorithm for automatic interstitial needle tracking on PETRA images by employing their negative contrast against surrounding tissue. <h3>Materials and Methods</h3> Fourteen ProGuide Sharp Needles 6Fx294mm were implanted in an endometrial adenocarcinoma patient using a Syed-Neblett template. One of the needles lay in the obturator center, and six inside the obturator slots. The patient underwent standard CT imaging with copper-filled needles. After marker removal, 3D PETRA images of the patient's pelvis (TR\TE 3.32\0.07 ms, voxel size 0.9 mm³ isotropic, 416 slices) were acquired on a 3T Siemens Vida MR scanner. PETRA MR images were analyzed for interstitial needle detection using custom code in MATLAB R2022a. A rectangular part of all axial slices where needles may be contained (slices 149-310) was selected. For each slice part, corner points were extracted from the original part and from its sharpened gradient magnitude image by detecting Harris features. Points found within Euclidean distance (ED) of 3 pixels on both images were matched, and the pixel with minimum signal intensity closest to each such point on the original part was selected. Minimum intensity points lying within 2 pixels ED between subsequent slices were considered as possible catheter coordinates. Such points appearing on at least 10 continuous slices were designated as true catheters, and their positions were compared to those visible on CT. <h3>Results</h3> Figure 1a) displays the selected MR image parts for two example slices. Pixels with detected Harris features and their closest signal minima are marked by red and green crosses, respectively, in b). Pixels accepted as needle positions are shown as magenta crosses in c). Matching CT image parts with bright marker-filled needles are displayed in d). Empty interstitial catheters on PETRA images corresponded to local minima of signal intensity, located near Harris features. The assumption of needle position continuity within an allowed distance along subsequent slices helped avoid spurious signal minima, while following needle position variations caused by different deflection angles. Needles guided through the obturator grooves and the central needle were detected only after they became detached from the obturator (ex. figure left). All 14 needles were tracked along their visible length inside tissue (ex. figure right). Visual comparison to CT images confirmed interstitial catheter detection on MRI. Selecting a range of slices and zooming on a part of each slice for analysis reduced computational time and output data size. <h3>Conclusions</h3> Automated detection of interstitial needles is feasible on PETRA MR images and may facilitate MR-only treatment planning in interstitial HDR brachytherapy. The newly developed algorithm was able to track all needles inside tissue based on their signal intensity characteristics, without requiring manual seed position placement.

First pointwise encoding time reduction with radial acquisition (PETRA) implementation for catheter detection in interstitial high-dose-rate (HDR) brachytherapy

PURPOSEA pointwise encoding time reduction with radial acquisition (PETRA) sequence was optimized to detect empty catheters in interstitial (HDR) brachytherapy with clinically acceptable spatial accuracy for the first time. Image quality and catheter detectability were assessed in phantoms, and the feasibility of PETRA's clinical implementation was assessed on a gynecological cancer patient. METHODS AND RESULTSEmpty catheters embedded in a gelatin phantom displayed positive signal on PETRA and more accurate cross-sections than on clinically employed T2-weighted sequences, differing by 0.4 mm on average from their nominal 2 mm diameter. PETRA presented minimal susceptibility differences and a symmetric metal artifact, contrary to the clinical sequences. The PETRA-CT catheter tip position differences assessed by a treatment planning system (TPS) were < 1 mm. PETRA also detected an interstitial template with empty catheters penetrating a poultry phantom and fused very well with CT. Interstitial catheter positional difference between PETRA and CT images was < 1 mm on average, increasing with distance from isocenter. All interstitial catheters and the employed interstitial template were detected on PETRA images of an endometrial adenocarcinoma patient. Empty needles were traceable using a TPS, with higher spatial resolution and more favorable contrast than on T2-weighted images used for contouring. A treatment plan could be produced by combining information from PETRA for catheter detection and from T2-weighted images for tumor and organs delineation. CONCLUSIONSPETRA detected successfully and accurately interstitial catheters in phantoms. Its first clinical implementation shows a potential for MR-only treatment planning in interstitial HDR brachytherapy.

The combined use of 2D scout and 3D axial CT images to accurately determine thecathetertips for high-dose-rate brachytherapy plans.

PurposeTo develop a method combining CT scout images with axial images to improve the localization accuracy of catheter tips in high‐dose‐rate (HDR) brachytherapy treatments.Materials and MethodsCT scout images were utilized along with conventionally reconstructed axial images to aid the localization of catheter tips used during HDR treatment planning. A method was developed to take advantage of the finer image resolution of the scout images to more precisely identify the tip coordinates. The accuracies of this method were compared with the conventional method based on the axial CT images alone, for various slice thicknesses, in a computed tomography dose index (CTDI) head phantom. A clinical case which involved multiple interstitial catheters was also selected for the evaluation of this method. Locations of the catheter tips were reconstructed with the conventional CT‐based method and this newly developed method, respectively. Location coordinates obtained via both methods were quantitatively compared.ResultsCombination of the scout and axial CT images improved the accuracy of identification and reconstruction of catheter tips along the longitudinal direction (i.e., head‐to‐foot direction, more or less parallel to the catheter tracks), compared to relying on the axial CT images alone. The degree of improvement was dependent on CT slice thickness. For the clinical patient case, the coordinate differences of the reconstructed catheter tips were 2.6 mm ± 0.9 mm in the head‐to‐foot direction, 0.4 mm ± 0.2 mm in the left‐to‐right direction, and 0.6 mm ± 0.2 mm in the anterior‐to‐posterior direction, respectively.ConclusionCombining CT scout and axial images demonstrates the ability to provide a more accurate identification and reconstruction of the interstitial catheter tips for HDR brachytherapy treatment, especially in the longitudinal direction. The method developed in this work has the potential to be implemented clinically together with automatic segmentation in modern brachytherapy treatment planning systems, in order to improve the reconstruction accuracy of HDR catheters.

100: Electromagnetic-Guided Interstitial Catheter Navigation for Gynecological Brachytherapy: A Phase I Trial (E-Mint)

100: Electromagnetic-Guided Interstitial Catheter Navigation for Gynecological Brachytherapy: A Phase I Trial (E-Mint)

Using infrared depth-sensing technology to improve the brachytherapy operating room experience

PurposeThe purpose of this study was to discuss the merits of using depth-sensing infrared camera technology in the brachytherapy operating room during interstitial brachytherapy for gynecologic malignancies. Materials and MethodsThe infrared depth-sensing camera from a Microsoft Kinect that had been adapted for surgical use was introduced into a high-volume interstitial brachytherapy operating room. Brachytherapists then used the touchless, gestural interface to review preoperative MRI in real time to guide needle insertion. ResultsThe interface was used for 10 consecutive procedures by 4 separate brachytherapists. The initial training and adjustment to the technology was variable among brachytherapists. All brachytherapists found the controls intuitive and were able to successfully navigate MRI on the system after 1, 30, 30, and 45 min. Qualitatively, brachytherapists found the system helpful for interpretation of intraoperative ultrasound imaging. Furthermore, it ensured adequate needle positioning and deposition was maintained for large tumors. Surgeons involved in its use agreed on potential for considerable benefit when performing interstitial brachytherapy. ConclusionsAdapting this technology for use in the brachytherapy suite provided a higher level of comfort with interstitial catheter placement. This novel tool or similar technology might be considered within other brachytherapy suites.

Robust Optimization for Gynecological High-Dose Rate Interstitial BrachytherapyUsing Post-Hoc Uniformity Correction

Graphical optimization (GO) is commonly used during forward planning high-dose rate (HDR) interstitial brachytherapy (IB) to conform prescription dose to high-risk clinical target volume (HRCTV) while limiting organs-at-risk (OAR) doses. However, this typically Results in variations in dwell times between adjacent dwell positions even within an interstitial catheter (Figure 1a). When using IB for locally advanced/recurrent gynecological cancers, a common fractionation approach involves 5 fractions delivered twice daily over 3 days. During this time, day-to-day variations in internal normal tissue anatomy (bowel/bladder filling) can occur. Connecting and disconnecting transfer tubes for each treatment may result in longitudinal movement of individual catheters. Above factors could impact actual dose delivered. To mitigate the impact of these variations, we seek to explore the impact of a post-hoc uniformity correction (PHUC) on the GO plan and report an initial clinical experience with using this robust optimized (RO) approach.

In vivo dose verification method in catheter based high dose rate brachytherapy

In vivo dosimetry is a powerful tool for dose verification in radiotherapy. Its application in high dose rate (HDR) brachytherapy is usually limited to the estimation of gross errors, due to inability of the dosimetry system/ method to record non-uniform dose distribution in steep dose gradient fields close to the radioactive source. In vivo dose verification in interstitial catheter based HDR brachytherapy is crucial since the treatment is performed inserting radioactive source at the certain positions within the catheters that are pre-implanted into the tumour. We propose in vivo dose verification method for this type of brachytherapy treatment which is based on the comparison between experimentally measured and theoretical dose values calculated at well-defined locations corresponding dosemeter positions in the catheter. Dose measurements were performed using TLD 100-H rods (6 mm long, 1 mm diameter) inserted in a certain sequences into additionally pre-implanted dosimetry catheter. The adjustment of dosemeter positioning in the catheter was performed using reconstructed CT scans of patient with pre-implanted catheters.Doses to three Head&Neck and one Breast cancer patient have been measured during several randomly selected treatment fractions. It was found that the average experimental dose error varied from 4.02% to 12.93% during independent in vivo dosimetry control measurements for selected Head&Neck cancer patients and from 7.17% to 8.63% - for Breast cancer patient. Average experimental dose error was below the AAPM recommended margin of 20% and did not exceed the measurement uncertainty of 17.87% estimated for this type of dosemeters. Tendency of slightly increasing average dose error was observed in every following treatment fraction of the same patient. It was linked to the changes of theoretically estimated dosemeter positions due to the possible patient’s organ movement between different treatment fractions, since catheter reconstruction was performed for the first treatment fraction only. These findings indicate potential for further average dose error reduction in catheter based brachytherapy by at least 2–3% in the case that catheter locations will be adjusted before each following treatment fraction, however it requires more detailed investigation.

Intracavitary/Interstitial MR-Based Cervix Brachytherapy: First Look at Implant Quality

Image-guided adaptive brachytherapy (BT) holds promise for improved cervical cancer outcomes, with lesser normal tissue toxicity. Key to this are better tumor visualization (via MRI), defined dose-volume targets (via international recommendations), and plan conformity (via interstitial (IS) sources added to traditional intracavitary (IC) applicators). Hybrid IC/IS implant quality is not well characterized, nor its impact on overall BT plan quality. Our institutional experience with IC/IS MRI-based cervix BT (no volumetric preplanning; post-implant planning on MRI assisted by CTsim) was reviewed. Tandem-ring (T&R) and tandem-ovoid (T&O) based IC/IS implant quality was evaluated for variability in the IS component, with attention to intent at implant vs post-implant geometry. Descriptive statistics were performed. From 07/2013 – 12/2016, IC/IS technique was used in n=43 single-fraction pulsed dose rate BT boost cases, during curative (chemo)radiotherapy for locally advanced cervix cancer. Median HR-CTV D90 (EQD2) was 90.7 Gy [76.4 – 96.6], median D2cc 75.8 Gy [43.2 – 90.4] for bladder, 64.3 Gy [52.3 – 74.2] rectum, 62.2 Gy [46.6 – 73.6] sigmoid, and ICRU rectovaginal point dose, 64.2 Gy [52.0 – 82.1]. Of a median of 3 [1 – 6] IS catheters implanted per case (79% T&R), 2 [1 – 5] were loaded, for an overall load rate of 82%, with no appreciable difference by applicator type. More IS catheters (N=10, in 6 unique implants) remained unused among our first 15 cases, compared to the latest 15 (N=7, in 6 implants) in our evolving experience. Radial IS positions, selected based on pre-BT clinical/radiological tumor residuum and patient anatomy, were loaded most frequently lateral for T&O, and lateral more than anterior for T&R. Least loaded were posterior (T&R) and medial (T&O) positions. There was no change in IS catheter depth on CTsim vs MRI, suggesting no significant movement. Median IS depth beyond ring/ovoid surface was 26.0 mm [7.5 – 47.1], closely matching intended insertion depths, with mean difference of 1.4 ± 3.0 mm. IS catheter deflection was observed (median 1.7 deg [0 – 35.6] anterior-posterior; 1.0 deg [0 – 34.4] medial-lateral), reaching > 5 deg for median insertion depths of 25.6 mm [11.5 – 43.0]. IS weighting ranged from 0.5% to 70.2%, although the median was 7.7% relative to the IC component, with outliers reflecting individual anatomic and tumor topographies. The technical quality of IC/IS cervix BT implants improves with experience, but small variabilities persist in measured IS catheter positions. To what extent post-implant BT planning processes can safely mitigate for suboptimal IS tracks (assuming IC applicator selection appropriate to the target) remains unknown.

Prospective Clinical Implementation of a Novel Magnetic Resonance Tracking Device for Real-Time Brachytherapy Catheter Positioning

We designed and built dedicated active magnetic resonance (MR)-tracked (MRTR) stylets. We explored the role of MRTR in a prospective clinical trial. Eleven gynecologic cancer patients underwent MRTR to rapidly optimize interstitial catheter placement. MRTR catheter tip location and orientation were computed and overlaid on images displayed on in-room monitors at rates of 6 to 16 frames per second. Three modes of actively tracked navigation were analyzed: coarse navigation to the approximate region around the tumor; fine-tuning, bringing the stylets to the desired location; and pullback, with MRTR stylets rapidly withdrawn from within the catheters, providing catheter trajectories for radiation treatment planning (RTP). Catheters with conventional stylets were inserted, forming baseline locations. MRTR stylets were substituted, and catheter navigation was performed by a clinician working inside the MRI bore, using monitor feedback. Coarse navigation allowed repositioning of the MRTR catheters tips by 16mm (mean), relative to baseline, in 14±5s/catheter (mean±standard deviation [SD]). The fine-tuning mode repositioned the catheter tips by a further 12mm, in 24±17s/catheter. Pullback mode provided catheter trajectories with RTP point resolution of ∼1.5mm, in 1 to 9s/catheter. MRTR-based navigation resulted in rapid and optimal placement of interstitial brachytherapy catheters. Catheters were repositioned compared with the initial insertion without tracking. In pullback mode, catheter trajectories matched computed tomographic precision, enabling their use for RTP.

Chronic Renal Medullary Infusion of Interleukin‐1 Receptor Antagonist Delays the Onset of Salt Sensitive Hypertension in Uninephrectomized Dahl SS Rats

The Dahl SS rat is a well‐established model of salt‐sensitive hypertension and renal disease with the immune system contributing in the pathology of the disease. Recent work from our laboratory demonstrated that in response to a high salt challenge, in addition to increases in blood pressure and urinary albumin excretion, there is an upregulation of the Nod‐like receptor protein‐3 (NLRP3) inflammasome in the renal medulla. This upregulation of the NLRP3 inflammasome leads to a subsequent increase in interleukin 1 beta (IL‐1β) production. This proinflammatory cytokine has been shown to be elevated in hypertension in humans making it a potential therapeutic target for salt sensitive hypertension. Therefore, we tested the hypothesis that chronic renal medullary infusion of IL‐1 receptor antagonist (IL‐1RA) would attenuate the development of salt sensitive hypertension in the Dahl SS rat. Animals underwent a right uninephrectomy at 7 weeks of age to avoid compensatory changes in blood pressure from the contralateral kidney. After a week of recovery, the left femoral artery was cannulated to measure mean arterial pressure (MAP) while a chronically implanted medullary interstitial catheter was placed in the left kidney for continuous infusion IL‐1RA (600μg/day, n=5) or vehicle (0.9% NaCl saline, n=6). MAP was measured during a 4‐day period while animals were maintained on 0.4% NaCl chow then switched to a high salt (4.0% NaCl) challenge for a 10‐day. MAP did not differ between saline and IL‐1RA treated animals during the 0.4% diet period (127±3 mmHg vs 121±4 mmHg, P&gt;0.05). However, following a 10‐day challenge of 4.0% NaCl diet, MAP was significantly reduced in the IL‐1RA treated rats compared to the saline‐treated rats (157±9 mmHg vs 176±5 mmHg, P&lt;0.05). Despite seeing a reduction in MAP, urinary albumin (118±18 vs 126±10 mg/day) and protein (284±28 vs 277±19 mg/day) excretion in IL‐1RA treated did not differ from saline‐treated rats. Furthermore, when medullary IL‐1β levels were measured by ELISA, there was no difference between the IL‐1RA treated rats compared to the saline‐treated rats (76±25 pg/mL vs. 83±11 pg/mL). In contrast to the effects of intarenal infusion, systemic administration of the same dose of IL‐1RA did not alter salt‐sensitive hypertension compared to vehicle‐treated control SS (132±8mmHg vs 141±mmHg, n=5–6/group), demonstrating that the effects observed with medullary interstitial infusion are due to intrarenal effects. These data indicate that blockade of the IL‐1 receptor in the renal medulla attenuates salt‐sensitive hypertension in the Dahl SS rat. Further studies are required to understand the mechanism by which renal medullary inhibition of IL‐1β results in reduction in blood pressure in response to a high salt diet.Support or Funding InformationSupported by DK96859, HL116264, and 15SFRN2391002.

SU-G-JeP2-14: MRI-Based HDR Prostate Brachytherapy: A Phantom Study for Interstitial Catheter Reconstruction with 0.35T MRI Images

Purpose: To evaluate the accuracy of interstitial catheter reconstruction with 0.35T MRI images for MRI-based HDR prostate brachytherapy. Methods: Recently, a real-time MRI-guided radiotherapy system combining a 0.35T MRI system and three cobalt 60 heads (MRIdian System, ViewRay, Cleveland, OH, USA) was installed in our department. A TrueFISP sequence for MRI acquisition at lower field on Viewray was chosen due to its fast speed and high signal-to-noise efficiency. Interstitial FlexiGuide needles were implanted into a tissue equivalent ultrasound prostate phantom (CIRS, Norfolk, Virginia, USA). After an initial 15s pilot MRI to confirm the location of the phantom, planning MRI was acquired with a 172s TrueFISP sequence. The pulse sequence parameters included: flip angle = 60 degree, echo time (TE) =1.45 ms, repetition time (TR) = 3.37 ms, slice thickness = 1.5 mm, field of view (FOV) =500 × 450mm. For a reference image, a CT scan was followed. The CT and MR scans were then fused with the MIM Maestro (MIM software Inc., Cleveland, OH, USA) and sent to the Oncentra Brachy planning system (Elekta, Veenendaal, Netherlands). Automatic catheter reconstruction using CT and MR image intensities followed by manual reconstruction was used to digitize catheters. The accuracy of catheter reconstruction was evaluated from the catheter tip location. Results: The average difference between the catheter tip locations reconstructed from the CT and MR in the transverse, anteroposterior, and craniocaudal directions was −0.1 ± 0.1 mm (left), 0.2 ± 0.2 mm (anterior), and −2.3 ± 0.5 mm (cranio). The average distance in 3D was 2.3 mm ± 0.5 mm. Conclusion: This feasibility study proved that interstitial catheters can be reconstructed with 0.35T MRI images. For more accurate catheter reconstruction which can affect final dose distribution, a systematic shift should be applied to the MR based catheter reconstruction in HDR prostate brachytherapy.

Use of a 3-dimensional lumpectomy marker for targeting interstitial accelerated partial breast irradiation (APBI).

42 Background: APBI via high-dose-rate (HDR) interstitial catheter implants is an effective, highly customizable method of delivering radiotherapy in breast cancer patients. The technique is amenable to challenging anatomy such as pendulous and/or very small breasts, augmented breasts or superficial lumpectomy sites. The challenge for any APBI technique is identification of the lumpectomy cavity, which can be difficult to visualize after surgery due to post-surgical changes or tissue mobilization for oncoplastic closure. In the past we have used x-ray contrast injected into the cavity to facilitate the radiographic visualization of the cavity or individual clips. A new 3-D tissue marker (BioZorb, Focal Therapeutics, Inc.) has recently been used by surgeons to mark the area of the lumpectomy cavity at greatest risk for recurrence. In effect this acts as a communication tool to help guide the radiation oncologist for treatment planning and delivery. We examined this device for target volume localization in 15 patients receiving interstitial HDR APBI. Methods: The marker mimicking the tumor size was surgically sutured at the base of the lumpectomy cavity in 15 patients with T1T2N0N1 breast cancer with a variety of closure techniques. The clinical target volume (CTV) was taken as the 3-D outline made by the six embedded titanium markers and a 2 cm margin expanded around that structure (the planning target volume, PTV). Multiple interstitial catheters were spaced 1.5 cm apart within the PTV and 34 Gy was delivered in 10 fractions delivered over 5 treatment days. Results: The marker/CTV was easily visualized on CT images, without clips or injected contrast, making catheter insertion and planning more efficient, easier, and reproducible. The CTV volume was small (12.5 +/- 8.7cc; mean +/- SD, range 4.4–33.4cc) as was the PTV (137 +/- 60cc; mean +/- SD, range 75–327cc), relative to typical HDR APBI implants. Conclusions: The technique facilitated identification of the lumpectomy cavity in all patients treated regardless of surgical closure technique. The unambiguous margin demarcation facilitated target contouring and reproducibility for APBI.

Novel high dose rate lip brachytherapy technique to improve dose homogeneity and reduce toxicity by customized mold.

Purpose/ObjectivesThe purpose of this study is to describe a novel brachytherapy technique for lip Squamous Cell Carcinoma, utilizing a customized mold with embedded brachytherapy sleeves, which separates the lip from the mandible, and improves dose homogeneity.Materials and methodsSeven patients with T2 lip cancer treated with a “sandwich” technique of High Dose Rate (HDR) brachytherapy to the lip, consisting of interstitial catheters and a customized mold with embedded catheters, were reviewed for dosimetry and outcome using 3D planning. Dosimetric comparison was made between the “sandwich” technique to “classic” – interstitial catheters only plan. We compared dose volume histograms for Clinical Tumor Volume (CTV), normal tissue “hot spots” and mandible dose. We are reporting according to the ICRU 58 and calculated the Conformal Index (COIN) to show the advantage of our technique.ResultsThe seven patients (ages 36–81 years, male) had median follow-up of 47 months. Four patients received Brachytherapy and External Beam Radiation Therapy, 3 patients received brachytherapy alone. All achieved local control, with excellent esthetic and functional results. All patients are disease free.The Customized Mold Sandwich technique (CMS) reduced the high dose region receiving 150% (V150) by an average of 20% (range 1–47%), The low dose region (les then 90% of the prescribed dose) improved by 73% in average by using the CMS technique. The COIN value for the CMS was in average 0.92 as opposed to 0.88 for the interstitial catheter only. All differences (excluding the low dose region) were statistically significant.ConclusionThe CMS technique significantly reduces the high dose volume and increases treatment homogeneity. This may reduce the potential toxicity to the lip and adjacent mandible, and results in excellent tumor control, cosmetic and functionality.

Development and Evaluation of an Automatic Interstitial Catheter Digitization Tool for HDR Brachytherapy of Gynecologic Cancers

Establish and evaluate software to automatically digitize interstitial catheters used in HDR brachytherapy for gynecologic cancers. The goal is to reduce planning time and enable efficient adaptive re-planning in interstitial HDR Brachytherapy. The digitization technique developed in this study is a semi-automatic method using a region growing algorithm in conjunction with a spline based model. CT images were processed to enhance the contrast between the catheters (flexi-needles) and soft tissue. For each catheter, several points within the catheter were used as seed positions for the region growing algorithm. A cubic polynomial spline was used to prevent inter-catheter region growing cross-over near air or metal artifacts. This method was applied to 10 patients who had received HDR interstitial brachytherapy on an IRB approved image-guided radiation therapy protocol. The prescribed dose was 18.75 or 20 Gy delivered in 5 fractions (3.75 or 4 Gy per fraction) twice daily over 3 consecutive days. The first CT image for each patient after implantation was used for evaluation. The automatically digitized plans were compared to the plans created via manual digitization using the same source dwell parameters. The mean and standard deviation of differences in catheter positions were calculated for each catheter. Dosimetric indicators compared included D90% of CTV and D2cc of bladder and rectum. The region growing algorithm was successful in resolving and digitizing all catheters using the multi-seed region growing/spline approach. The difference between automatic and manually digitized positions was 0.8±0.3 mm. The time of digitization ranged from 34 minutes to 43 minutes with a mean digitization time of 37 minutes. The bulk of the time was spent on manual selection of initial seed positions and spline parameter adjustments. Catheter digitization time has been reduced compared to manual digitization (1-2 hours). The dosimetric results are summarized in the table below.Scientific Abstract 2729; TableD90% CTVD2cc BladderD2cc RectumManual digitization91.5±4.4%971±236 cGy997±367 cGyAutomatic digitization91.4±4.4%970±235 cGy997±367 cGyp-value0.560.420.27 Open table in a new tab A region growing algorithm was developed to semi-automatically digitize interstitial catheters in HDR brachytherapy using the Syed-Neblett template. This automatic digitization tool was shown to be accurate compared to manual digitization. The reduction in digitization time will enable efficient evaluation and practical daily adaptive re-planning compared to manual methods.

Abstract 026: Renal Medullary (Pro)Renin Receptor Mediates Angiotensin II-Induced Hypertension via Enhancement of Local Renin Response and Renal Medullary α-ENaC Expression

(Pro)renin receptor (PRR) is predominantly expressed in the collecting duct and is stimulated by angiotensin II (AngII) via the COX-2/PGE2/EP4 pathway but the function of PRR is unknown. We examined the effect of intramedullary delivery of a novel PRR decoy peptide PRO20 on AngII hypertension via an interstitial catheter chronically placed in the rat medulla. Telemetry showed that 1-wk AngII infusion (100 ng/kg/min) elevated MAP from 108 ± 5.8 to 164.7 ± 6.2 mmHg and this value was lowered to 110.2 ± 4.8 mmHg (p&lt;0.05) by intramedullary PRO20 infusion (IMPRO) at 120μg/kg/d but was only modestly affected by intravenous PRO20 infusion (IVPRO) (day 7: 151.7 ± 4.4 mmHg). The indices of kidney injury including proteinuria (2.7-fold increase in urinary protein), glomerulosclerosis and interstitial fibrosis following AngII infusion were completely normalized by IMPRO so were the polyuria and downregulation of renal AQP2 protein expression. AngII infusion elevated urinary renin activity from 0.17 ± 0.013 to 9.3 ± 1.7 AngI ng/24h, which was reduced to 0.09 ± 0.04 AngI ng/24h by IMPRO. A similar pattern of changes in renin activity was observed in the inner medulla, contrasting to opposite changes in renal cortex and plasma. α-ENaC mRNA and protein were elevated 158% and 180%, respectively, in the inner medulla but not in the cortex or plasma, and the elevations were abolished by IMPRO. By chopstick electrodes, amiloride-sensitive sodium transport was increased from 13.06 ± 1.2 to 115.19 ± 7.5 Ieq μA/cm 2 by aldosterone, which was abolished by PRO20 (10.5 ± 3.75 Ieq μA/cm 2 ). Together, these results suggest that renal medullary PRR determines the hypertension likely via mediating the local renin response and the direct activation of ENaC during AngII infusion.

SU-E-T-574: Fessiblity of Using the Calypso System for HDR Interstitial Catheter Reconstruction

Purpose: It is always a challenge to reconstruct the interstitial catheter for high dose rate (HDR) brachytherapy on patient CT or MR images. This work aims to investigate the feasibility of using the Calypso system (Varian Medical, CA) for HDR catheter reconstruction utilizing its accuracy on tracking the electromagnetic transponder location. Methods: Experiment was done with a phantom that has a HDR interstitial catheter embedded inside. CT scan with a slice thickness of 1.25 mm was taken for this phantom with two Calypso beacon transponders in the catheter. The two transponders were connected with a wire. The Calypso system was used to record the beacon transponders’ location in real time when they were gently pulled out with the wire. The initial locations of the beacon transponders were used for registration with the CT image and the detected transponder locations were used for the catheter path reconstruction. The reconstructed catheter path was validated on the CT image. Results: The HDR interstitial catheter was successfully reconstructed based on the transponders’ coordinates recorded by the Calypso system in real time when the transponders were pulled in the catheter. After registration with the CT image, the shape and location of the reconstructed catheter are evaluated against the CT image and the result shows an accuracy of 2 mm anywhere in the Calypso detectable region which is within a 10 cm X 10 cm X 10 cm cubic box for the current system. Conclusion: It is feasible to use the Calypso system for HDR interstitial catheter reconstruction. The obstacle for its clinical usage is the size of the beacon transponder whose diameter is bigger than most of the interstitial catheters used in clinic. Developing smaller transponders and supporting software and hardware for this application is necessary before it can be adopted for clinical use.

WE-A-17A-06: Evaluation of An Automatic Interstitial Catheter Digitization Algorithm That Reduces Treatment Planning Time and Provide Means for Adaptive Re-Planning in HDR Brachytherapy of Gynecologic Cancers

Purpose: To evaluate an automatic interstitial catheter digitization algorithm that reduces treatment planning time and provide means for adaptive re-planning in HDR Brachytherapy of Gynecologic Cancers. Methods: The semi-automatic catheter digitization tool utilizes a region growing algorithm in conjunction with a spline model of the catheters. The CT images were first pre-processed to enhance the contrast between the catheters and soft tissue. Several seed locations were selected in each catheter for the region growing algorithm. The spline model of the catheters assisted in the region growing by preventing inter-catheter cross-over caused by air or metal artifacts. Source dwell positions from day one CT scans were applied to subsequent CTs and forward calculated using the automatically digitized catheter positions. This method was applied to 10 patients who had received HDR interstitial brachytherapy on an IRB approved image-guided radiation therapy protocol. The prescribed dose was 18.75 or 20 Gy delivered in 5 fractions, twice daily, over 3 consecutive days. Dosimetric comparisons were made between automatic and manual digitization on day two CTs. Results: The region growing algorithm, assisted by the spline model of the catheters, was able to digitize all catheters. The difference between automatic and manually digitized positions was 0.8±0.3 mm. The digitization time ranged from 34 minutes to 43 minutes with a mean digitization time of 37 minutes. The bulk of the time was spent on manual selection of initial seed positions and spline parameter adjustments. There was no significance difference in dosimetric parameters between the automatic and manually digitized plans. D90% to the CTV was 91.5±4.4% for the manual digitization versus 91.4±4.4% for the automatic digitization (p=0.56). Conclusion: A region growing algorithm was developed to semi-automatically digitize interstitial catheters in HDR brachytherapy using the Syed-Neblett template. This automatic digitization tool was shown to be accurate compared to manual digitization.

Ten-year outcomes of accelerated partial breast irradiation compared with whole breast irradiation: A matched-pair analysis.

55 Background: Breast conserving therapy (BCT) represents a standard of care in the management of early stage breast cancer; while adjuvant radiation therapy was traditionally delivered using whole breast irradiation (WBI), accelerated partial breast irradiation (APBI) offers an alternative to WBI that shortens the duration of treatment and may improve toxicity profiles and quality of life. The purpose of this analysis is to compare clinical outcomes of patients treated with WBI versus APBI. Methods: A total of 3,009 patients were treated with BCT at single institution between 1980 and 2012 with 2,528 patients receiving WBI and 481 patients receiving APBI (interstitial or balloon-based). A matched-pair analysis was performed with patients matched according to age (+/- 3 years), T stage (Tis vs T1 vs T2), and estrogen receptor (ER) status (+/-). All patients had a minimum of 12 months of follow up. A total of 247 matches were made with clinical outcomes compared using the Kaplan-Meier method. Results: Mean follow-up was 8.1 years for WBI vs. 7.8 years for APBI (p&lt;0.001), a difference of less than 4 months. There were no differences with respect to age (p=0.88), tumor stage (p=1.0), or ER status (p=1.0). Long-term cosmesis was good to excellent in 94% vs. 95% of patients (p=0.78). WBI patients demonstrated a trend for slightly larger tumors (13.0 vs. 11.4 mm, p=0.06). At 10 years, no difference in ipsilateral breast tumor recurrence (4% vs. 4%, p=0.11), regional recurrence (1% vs. 1%, p=0.20), distant metastases (3% vs. 6%, p=0.47), disease free survival (93% vs. 91%, p=0.10), or contralateral breast failure (9% v. 3%, p=0.06) was noted when comparing WBI and APBI. In addition, 10 year cause-specific survival (94% v. 93%, p=0.72) and overall survival (83% vs. 75%, p=0.34) were similar. Conclusions: At 10 years, no differences in locoregional recurrence, distant metastasis or survival were found between patients undergoing whole breast irradiation or accelerated partial breast irradiation using interstitial catheter or balloon-based brachytherapy. These data represent one of the only APBI series with prolonged follow-up and show similar outcomes in a matched group of patients undergoing WBI or APBI.

SU-E-T-343: Dosimetric Analysis of Catheter Displacement in High Dose Rate Prostate Brachytherapy

Purpose: To evaluate the dosimetric effect of catheter displacement on target coverage and doses to organs at risks (OARs) in high dose rate prostate brachytherapy. Methods: CT simulations from 21 prostate cancer patients treated with HDR monotherapy (7.25 Gy × 6 fractions) were used. The prostate CTV and OARs were contoured on the 3D‐CT. Treatment plans were optimized using an inverse planning simulated annealing algorithm and graphical optimization to ensure dosimetry objectives: target coverage (CTV D90=100–115%, V100 >97%, and V150 <35%) and OAR dose constraints (D0.1cc <85% (rectum), 80&–95% (bladder), and <110% (urethra)). Craniocaudal catheter movements from 1 to 10 mm in 1 mm increments were simulated by simultaneously shifting all active dwell positions in the initial treatment plan using catheter offset in the Oncentra MasterPlan (Nucletron). Target coverage (D90 and V100) and OAR doses (D0.1cc and D1cc) were evaluated and compared to no displacement plans. Results: The mean prostate CTV volume was 74.7±22.8 cc (range: 24.8–113.7 cc). Initial treatment plans provided target D90 = 107.7±2.0% (103.0–111.2%) and V100 = 98.5±0.8% (97.1–99.5%). The D0.1cc to OARs was 77.3±2.3% (rectum), 84.2±2.0% (bladder), and 106.8±1.6% (urethra). The mean target coverage was not significantly different for 1–2 mm shifts. Shifts between 3 and 6 mm still met most dosimetry objectives, but provided progressively less good target coverage and doses to OARs. Displacements of greater than or equal to 7 mm resulted in dosimetry that did not meet our dosimetry objectives. Conclusion: Small changes in catheter position Result in significant alterations in dosimetry and treatment delivery. The target coverage (D90 and V100) and bladder dose are reduced and the rectal and urethra doses are higher in direct proportion to the degree of displacement. It is essential to check and correct interstitial catheter positions before each HDR fraction to accurately deliver the planned radiation dose.