Frameless image guidance improves accuracy in three-dimensional interstitial brachytherapy needle placement

PURPOSE: The aim of this work was to adapt a computer-assisted real-time three-dimensional (3D) navigation system for interstitial brachytherapy procedures. METHODS AND MATERIALS: The 3-D navigation system Surgical Planning and Orientation Computer System (SPOCS; Aesculap, Tuttlingen, Germany) was adapted for use in interstitial brachytherapy. A special needle holder with mounted infrared-emitting diodes (IRED) for 3D navigation-based needle implantation was developed. Measurements were made on a series of different phantoms to study the feasibility and the overall accuracy and precision of the navigation system with regard to single-needle application and volume implants (multiple-needle implantations). In all, 250 single implants and 20 volume implants were performed. Accuracy was measured as the target registration error (TRE) between the preoperatively defined and the achieved target position. RESULTS: Analyses of the 250 different targets showed a mean TRE for single-needle applications of 1.1 mm (SD +/- 0.4 mm), 0.9 mm (SD +/- 0.3 mm), and 0.7 mm (SD +/- 0.3 mm) in the x, y, and z direction, respectively. The maximal deviation was 2.3 mm. The corresponding TRE in the x, y, and z direction for volume implants was 1.6 mm (SD +/- 0.4 mm), 1.9 mm (SD +/- 0.6 mm), and 1.0 mm (SD +/- 0.4 mm), respectively. The maximum deviation was 2.9 mm. CONCLUSIONS: The adaptation of a commercially available surgical planning and navigation system to interstitial brachytherapy is feasible. It enables virtual planning and improved accuracy in 3D interstitial needle implantation.     

Reconstruction and navigation system for intraoperative brachytherapy using the flab technique for colorectal tumor bed irradiation

Purpose: To present the development of a new navigation and reconstruction system based on an electromagnetic free-hand tracker and on CT imaging for treatment planning of intraoperative high-dose-rate brachytherapy (IORT-HDRB) in the sacral region. Our aim is to improve accuracy and to enable individualized treatment planning and dose documentation to be performed for IORT-HDRB using a flab technique.

Methods and Materials: The material consists of an electromagnetic 3D tracker system, a PC workstation with Microsoft Windows NT 4.0 operating system, and a recognition program for continuous speech. In addition, we designed an external reference system constructed of titanium and Perspex, which is positioned in the pelvis, and a special digitizer pen for reconstruction of the flab geometry. The flab design incorporates a series of silicon 10-mm-diameter spherical pellets. Measurements were made with a pelvic phantom in order to study the accuracy of the system. The reconstruction results are stored and can be exported via network or floppy to our different treatment planning systems.

Results: Our results for the reconstruction of a flab with six catheters and a total of 100 spherical pellets give mean errors in the range (2.5 ± 0.6) mm to (3.5 ± 0.8) mm depending on the positions of the pelvic phantom and transmitter relative to the operation table. These errors are calculated by comparing the reconstruction results of our system with those using a CT-based reconstruction of the flab geometry. For the accuracy of the navigation system for the pelvic phantom, we obtained mean errors in the range (2.2 ± 0.7) mm to (3.1 ± 1.0) mm.

Conclusions: The new system we have developed enables navigation and reconstruction within the surgical environment with a clinically acceptable level of accuracy. It offers the possibility of individualized treatment planning and effective documentation of the 3D dose distribution in IORT-HDRB using a flab technique.     

New interstitial HDR brachytherapy technique for prostate cancer: CT based 3D planning after transrectal implantation.

We have developed a new interstitial HDR brachytherapy technique for the treatment of prostate cancer using CT based 3D planning after transrectal implantation of four non-parallel needles. CT based needle reconstruction, target definition, evaluation and documentation, including DVHs and 3D imaging, is a feasible, safe and well tolerated treatment concept.     

Projector-based augmented reality for intuitive intraoperative guidance in image-guided 3D interstitial brachytherapy

PURPOSE: The aim of this study is to implement augmented reality in real-time image-guided interstitial brachytherapy to allow an intuitive real-time intraoperative orientation. METHODS AND MATERIALS: The developed system consists of a common video projector, two high-resolution charge coupled device cameras, and an off-the-shelf notebook. The projector was used as a scanning device by projecting coded-light patterns to register the patient and superimpose the operating field with planning data and additional information in arbitrary colors. Subsequent movements of the nonfixed patient were detected by means of stereoscopically tracking passive markers attached to the patient. RESULTS: In a first clinical study, we evaluated the whole process chain from image acquisition to data projection and determined overall accuracy with 10 patients undergoing implantation. The described method enabled the surgeon to visualize planning data on top of any preoperatively segmented and triangulated surface (skin) with direct line of sight during the operation. Furthermore, the tracking system allowed dynamic adjustment of the data to the patient's current position and therefore eliminated the need for rigid fixation. Because of soft-part displacement, we obtained an average deviation of 1.1 mm by moving the patient, whereas changing the projector's position resulted in an average deviation of 0.9 mm. Mean deviation of all needles of an implant was 1.4 mm (range, 0.3-2.7 mm). CONCLUSIONS: The developed low-cost augmented-reality system proved to be accurate and feasible in interstitial brachytherapy. The system meets clinical demands and enables intuitive real-time intraoperative orientation and monitoring of needle implantation.     

Risk Factors for Operation Complications of High Dose Rate 3-Dimensional Interstitial Brachytherapy for Lung Cancer

BackgroundThe risk factors for operation complications of high-dose-rate dimensional (3D) interstitial brachytherapy for lung malignant tumors are still unclear. We aimed to provide a reliable reference for the preoperative safety assessment of interstitial brachytherapy.Patients and MethodsWe analyzed the degree and incidence of operational complications in 120 eligible patients with lung carcinoma who underwent computed tomography (CT)-guided HDR interstitial brachytherapy. Univariate and multivariate analyses were used to study the relationships between patient-related factors, tumor-related factors, operation-related factors, and operational complications.ResultsThe most frequent complications of CT-guided HDR interstitial brachytherapy were pneumothorax and hemorrhage. In univariate analysis, smoking, emphysema, distance of implanted needles through the normal lung tissue, number of implanted needle adjustments, and distance of the lesion from the pleura were the risk factors for pneumothorax; the tumor size, distance of the tumor from the pleura, number of implanted needle adjustments, and distance of the implanted needle through the normal lung tissue were risk factors for hemorrhage. In multivariate analysis, the depth of the implanted needle through the normal lung tissue and distance of the lesion from the pleura were independent risk factors for pneumothorax. Tumor size, number of implanted needle adjustments, and distance through normal lung tissue were independent risk factors for hemorrhage.ConclusionThis study provides a reference for the clinical treatment of lung cancer by analyzing the risk factors for complications of interstitial brachytherapy.     

Computed Tomography–Guided Optimization of Needle Insertion for Combined Intracavitary/Interstitial Brachytherapy With Utrecht Applicator in Locally Advanced Cervical Cancer

PurposeThere are no international guidelines for optimal needle insertion during interstitial intracavitary brachytherapy (IS-ICBT) for cervical cancer. We aimed to investigate the clinical feasibility and added value of computed tomography (CT) guidance to optimize needle insertion in IS-ICBT using the Utrecht applicator and to evaluate needle shifts.Methods and MaterialsWe enrolled 24 patients who were treated with interstitial-brachytherapy. Two CT scans each were performed for every patient: (1) after applicator insertion without needles (CT_preneedle) and (2) after needle insertion (CT_postneedle). In addition to magnetic resonance imaging after external-beam radiation therapy, CT_preneedle was used to determine optimal needle locations and insertion lengths based on applicator and organs at risk positioning on the day of treatment; CT_postneedle was used for IS-ICBT planning. The needle-channel axis was used as a reference to determine needle-shift evolution.ResultsA total of 266 interstitial needles were inserted in 76 of 93 BT fractions with high intra- and interpatient variations in the number of inserted needles. Based on CT_preneedle findings, needle insertion was avoided in 9, 4, 2, and 2 patients at the first, second, third, and fourth fractions, respectively. The unloaded needle frequency was 4%. Average needle contribution to total dwell time was 37.2% ± 19.2%. Shifting was observed in 68% of the needles (mean shift 2.0 ± 2.3 mm), mostly in the posterior direction, and in needles with a larger insertion length. Needle reinsertion was not needed in any patient. No complication due to needle insertion was observed, except for minor vaginal bleeding in 1 patient after needle removal.ConclusionsThe adaptive CT-guided IS-ICBT application was feasible and resulted in fewer unloaded needle insertions or complications and more efficient use with higher needle contribution to the treatment. Needle shift was frequent but did not require needle reinsertion with the proposed method.     

后装施源器Offset值验证研究

目的 研究后装治疗中多种施源器的Offset值。方法 选取插植钢针(Part#083.062)、插植塑料圆针(Part#189.608)、插植塑料尖针(Part#189.601)、多通道施源器软管(Part#110.800)、塑料宫腔管(Part#189.745)、金属宫腔管(Part#110.437)施源器。根据源在荧光胶片放射性成像,确定施源器顶端驻留点位置以及到施源器顶端的距离。在施源器顶端驻留点位置贴铅珠,将施源器置入盆腔体模中进行CT扫描。然后在计划系统中重建施源器,通过调整Offset值使铅珠与施源器顶端驻留点对准,从而得到施源器Offset值。塑料材质施源器由于密度与人体组织接近,施源器顶端难以准确重建,因此利用挡块或者假源重建施源器,得到塑料材质施源器Offset值。根据验证结果分析比较不同施源器Offset值差异。结果 不同施源器Offset值存在较大差异,其中插植钢针为-11.4 mm,插植塑料圆针为-4.1 mm,插植塑料尖针为-3.5 mm,多通道施源器软管为0 mm或-5.0 mm,塑料宫腔管为-6.5 mm,金属宫腔管为-7.5 mm。结论 为了适应精确放疗的发展趋势,有必要对后装中施源器Offset值进行测量验证。     

后装施源器Offset值验证研究

目的 研究后装治疗中多种施源器的Offset值。方法 选取插植钢针(Part#083.062)、插植塑料圆针(Part#189.608)、插植塑料尖针(Part#189.601)、多通道施源器软管(Part#110.800)、塑料宫腔管(Part#189.745)、金属宫腔管(Part#110.437)施源器。根据源在荧光胶片放射性成像,确定施源器顶端驻留点位置以及到施源器顶端的距离。在施源器顶端驻留点位置贴铅珠,将施源器置入盆腔体模中进行CT扫描。然后在计划系统中重建施源器,通过调整Offset值使铅珠与施源器顶端驻留点对准,从而得到施源器Offset值。塑料材质施源器由于密度与人体组织接近,施源器顶端难以准确重建,因此利用挡块或者假源重建施源器,得到塑料材质施源器Offset值。根据验证结果分析比较不同施源器Offset值差异。结果 不同施源器Offset值存在较大差异,其中插植钢针为-11.4 mm,插植塑料圆针为-4.1 mm,插植塑料尖针为-3.5 mm,多通道施源器软管为0 mm或-5.0 mm,塑料宫腔管为-6.5 mm,金属宫腔管为-7.5 mm。结论 为了适应精确放疗的发展趋势,有必要对后装中施源器Offset值进行测量验证。     

3D打印微创导向模板在术后复发性宫颈癌近距离治疗中的临床应用

  目的  探讨3D打印微创导向模板在术后复发性宫颈癌三维插植后装治疗中的临床应用。  方法  收集2017年7月至2018年4月10例就诊于河北省沧州中西医结合医院,术后复发的宫颈癌患者行个体化3D打印微创导向模板辅助下三维插植后装治疗的临床资料。根据患者具体情况选用不同阴道定位模板,行CT模拟定位,勾画靶区,设计主要导向针道空间分布,打印出3D微创导向模板。根据预设针道植入插植针,制定治疗计划,高危临床靶区（high risk-clinical target volume,HR-CTV）处方剂量为6 Gy/次,共4~6次。  结果  10例患者共行插植治疗52次,每次插植治疗平均扫描CT次数为（1.58±0.70）次,每次插植治疗从插植针植入至插植针到达满意位置的平均消耗时间为（10.88±2.94）min,每次治疗插植针的使用针数为（5.69±1.91）根。剂量参数HR-CTV包绕90%靶区体积的剂量（D90）为（6.41±0.29）Gy,包绕膀胱、直肠、乙状结肠的2 cm3体积的剂量（D_2cm3）分别为（4.75±0.37）、（3.93± 0.26）、（4.33±0.24）Gy。10例患者治疗结束3个月后进行疗效评价,8例达完全缓解（complete response,CR）、2例达部分缓解（par tial response,PR）。  结论  3D打印微创导向模板应用于术后中心型复发性宫颈癌三维插植后装治疗,定位准确,可重复治疗,插植操作时间短,插植针数少,患者痛苦小,并发症少而轻,肿瘤缩小明显,具有良好的应用前景。      

Technical Feasibility of Transperineal MR-Guided Prostate Interventions in a Low-Field Open MRI Unit: Canine Study

Magnetic resonance imaging (MRI) provides superior visualization of the prostate, its substructure, surrounding tissues, and, most important, focal lesions or cancer. The purpose of our canine study was to demonstrate the feasibility of a low-field (0.35 T) transperineal system that enables precise MR image guidance of prostate interventions. The canines were placed in the right lateral decubitus position. Template reconstruction, trajectory planning, contouring were based on T2-weighted FSE images. For image guidance and target confirmation, fast gradient spoiled-echo (FSPGR) sequence was used. MR compatible coaxial needles were manually inserted through the perineum to the base of the prostate. After satisfactory position was confirmed, brachytherapy catheters were placed through the coaxial needles. The mean deviation of the needle displacements was 2.9 mm with a median value of 2.7 mm. 97% of the errors were less than 4.0 mm. The needle placement accuracy was modelled by the Rayleigh distribution with a sigma value of 2.3 mm. Visual confirmation of needle placements was demonstrated on pathology tissue slices. The time needed for each step was: anaesthesia - 15 min, setup and positioning - 15 min, initial imaging - 15 min, template registration, projection - 15 min, contouring, trajectory planning, insertion of 12 needles - 60 min Based on our canine experiences our method seems to be a promising approach for performing feasible, accurate, reliable and high-quality prostate MR guidance within a reasonable time span.     

肺癌插植放疗中插植针排列规则对肺受量影响研究

目的 分析肺部肿瘤的近距离组织间插植放疗插植针的排列规则对肺受照剂量影响。方法 针对15例近距离组织间插植放疗肺癌患者病例,设计不受肋骨限制的插植针规则排列的放疗计划,命名为虚拟计划并与原实际计划进行比较。分别统计当两种计划方案的处方剂量为 10、30、60、120 Gy时肺V5、V20、V30、MLD。采用Wilcoxon符号秩检验。结果 虚拟计划方案的肺V5、V20、V30、MLD均小于实际计划方案,差异均有统计学意义(P<0.05)。结论 插植针的不规则排列限制了近距离组织间插植放疗在肺受量上进一步降低;所以在插植手术中应尽可能使得插植针规则排列。     

In vivo thermoluminescence dosimetry dose verification of transperineal 192Ir high-dose-rate brachytherapy using CT-based planning for the treatment of prostate cancer

PURPOSE: To evaluate the potential of in vivo thermoluminescence dosimetry to estimate the accuracy of dose delivery in conformal high-dose-rate brachytherapy of prostate cancer. METHODS AND MATERIALS: A total of 50 LiF, TLD-100 cylindrical rods were calibrated in the dose range of interest and used as a batch for all fractions. Fourteen dosimeters for every treatment fraction were loaded in a plastic 4F catheter that was fixed in either one of the 6F needles implanted for treatment purposes or in an extra needle implanted after consulting with the patient. The 6F needles were placed either close to the urethra or in the vicinity of the median posterior wall of the prostate. Initial results are presented for 18 treatment fractions in 5 patients and compared to corresponding data calculated using the commercial treatment planning system used for the planning of the treatments based on CT images acquired postimplantation. RESULTS: The maximum observed mean difference between planned and delivered dose within a single treatment fraction was 8.57% +/- 2.61% (root mean square [RMS] errors from 4.03% to 9.73%). Corresponding values obtained after averaging results over all fractions of a patient were 6.88% +/- 4.93% (RMS errors from 4.82% to 7.32%). Experimental results of each fraction corresponding to the same patient point were found to agree within experimental uncertainties. CONCLUSIONS: Experimental results indicate that the proposed method is feasible for dose verification purposes and suggest that dose delivery in transperineal high-dose-rate brachytherapy after CT-based planning can be of acceptable accuracy.     

Impact of oedema on implant geometry and dosimetry for temporary high dose rate brachytherapy of the prostate

The optimal timing of dosimetry for permanent seed prostatic implants remains contentious given the half life of post‐implant oedema resolution. The aim of this study was to establish whether prostatic oedematous change over the duration of a temporary high dose rate (HDR) interstitial brachytherapy (BR) boost would result in significant needle displacement, and whether this change in geometry would influence dosimetry. Two CT scans, one for dosimetric purposes on the day of the implant and the second just prior to implant removal, were obtained for four patients receiving transperineal interstitial prostate brachytherapy. The relative changes in cross‐sectional dimensions of the implants were calculated by establishing the change in mean radial distance (MRD) of the needle positions from the geometric centre of the implant for each patient's pair of CT studies. The treatment plan, as calculated from the first CT scan, was used in the second set of CT images to allow a comparison of dose distribution. The percentage change in MRD over the duration of the temporary implants ranged from ?1.91% to 1.95%. The maximum change in estimated volume was 3.94%. Dosimetric changes were negligible. In the four cases studied, the degree of oedematous change and consequent displacement of flexiguide needle positions was negligible and did not impact on the dosimetry. The rate and direction of oedematous change can be extremely variable but on the basis of the four cases studied and the results of a larger recent study, it might not be necessary to re‐image patients for dosimetric purposes over the duration of a fractionated HDR BT boost to the prostate where flexiguide needles are utilized. Nevertheless, further investigation with larger patient numbers is required.     

The Vienna applicator for combined intracavitary and interstitial brachytherapy of cervical cancer: clinical feasibility and preliminary results

PURPOSE: The aims of this study were to investigate the clinical feasibility and to report on preliminary treatment outcomes of combined intracavitary/interstitial brachytherapy, using a novel applicator and magnetic resonance imaging (MRI)-based treatment planning in patients with locally advanced cervical cancer. METHODS AND MATERIALS: A total of 22 cervical cancer patients with insufficient response and/or unfavorable topography after external-beam irradiation were included in this study. Parametrial extent of the disease in these patients was judged to exceed the coverage limit of intracavitary brachytherapy alone. A modified tandem/ring (T/R) applicator for guidance of parametrial needles (N) was used to perform high-dose-rate-brachytherapy with MRI-based treatment planning. Clinical feasibility and preliminary treatment outcomes were assessed. RESULTS: A total of 44 interstitial needle implants were performed. The spatial relations between the T/R + N applicator, high-risk clinical target volume, and organs at risk were visible clearly in all cases. Accurate and reproducible needle placement could be achieved in the majority of cases. No severe adverse events were caused by the intervention. The mean follow-up period was 20 months (range, 5-35 months). No G3 to G4 early or persistent late side effects were observed. Complete remission was achieved in 21 patients (95%). One local recurrence was observed within the high-risk clinical target volume area during follow-up. CONCLUSIONS: Our preliminary clinical experience indicates that combined intracavitary and interstitial MRI-based brachytherapy in patients with significant residual disease after external-beam therapy extending up to the distal third of parametria is feasible and allows excellent local control and a low rate of morbidity.     

Correlating the degree of needle trauma during prostate brachytherapy and the development of acute urinary toxicity

PURPOSE: To determine if there is an association between the degree of prostate trauma during prostate brachytherapy and development of acute urinary toxicity. METHODS AND MATERIALS: In a consecutive prospective cohort of permanent (125)I prostate brachytherapy patients, the number of times each needle was repositioned was tracked, and the dosimetry plans were used to determine the number of times needles within 1 cm of the urethra were manipulated. Additionally, prostate volume, total number of needles, number of needles/prostate volume, and the number of periurethral needle manipulations/prostate volume were determined. The need for catheterization beyond 24 hours and the Radiation Therapy Oncology Group (RTOG) urinary toxicity score at 4 weeks were recorded. The independent samples t test was used to search for a correlation between these parameters and the recorded toxicity scores. RESULTS: Twenty-eight consecutive implant patients were evaluated in the study. Median (range) values were as follows: prostate volume 35 cc ( range, 15-51 cc), number of needles per patient 32 (range, 21-41), number of needle manipulations per patient 94.5 ( range, 55-147), and number of periurethral needle manipulations 42 (range, 17-65). The only significant association between urinary toxicity and these variables was for the number of periurethral needle manipulations (p = 0.025). CONCLUSIONS: These data provide evidence that needle prostate trauma during brachytherapy contributes to acute urinary toxicity.     

Phantom investigations on CT seed imaging for interstitial brachytherapy.

BACKGROUND AND PURPOSE: The Braphyqs group (BRAchytherapy PHYsics Quality System, the brachytherapy physicist's task group of GEC-ESTRO) investigated the quality of CT- and X-ray based seed reconstruction procedures using the Kiel-phantom. In this study systematic phantom investigations on CT post-planning and the results of a mailed multi-centre inter-comparison are presented. MATERIALS AND METHODS: The phantom was equipped with a test configuration composed of 17 non-radioactive seeds. To investigate the quality of seed reconstruction CT measurements with varying CT parameters and different seed models were carried out. In a mailed multi-centre approach the phantom was sent to six European seed centres. The centres performed a typical CT- or X-ray based post-planning. The coordinates of the reconstructed sources were compared with the known positions in the phantom. RESULTS: In the systematic study it was found for the used CT scanner and seed models that when the slice thickness or the table index (respectively, an appropriate pitch for helical scans) reaches 4 or 5mm the accuracy of the CT seed reconstruction decreases in longitudinal direction. No influences of scanned field of view, tube current, kV(p), or scan type (axial or spiral) on seed reconstruction accuracy were detected. This finding was confirmed by the multi-centre evaluation. It was demonstrated that the Kiel-phantom is a suitable quality assurance (QA) tool for the assessment of the seed reconstruction accuracy in post-implant procedures and that it is a feasible QA test tool for a mailed multi-centre approach. CONCLUSIONS: QA of seed post-planning is necessary. A trend was observed that when the slice thickness and table index is 4 or 5mm the standard deviation of the reconstructed seeds increases for CT-based post-planning. Individual optimizations can be performed with dedicated phantoms.     

Measurement of prostate rotation during insertion of needles for brachytherapy.

BACKGROUND AND PURPOSE: The purpose of this study is to investigate whether prostate rotation due to needle insertion for prostate brachytherapy is predictable and if so, to quantify this rotation, and to see whether locking needles reduce the magnitude of prostate rotation. PATIENTS AND METHODS: The measurements are done at the beginning of the procedure for brachytherapy with a Foley catheter in situ. After a needle is inserted into the prostate, a 3D ultrasound scan is made. Then the seeds are delivered using RAPID Strands (Oncura), and the needle is withdrawn. A second 3D scan is made. The needle and seed positions are determined in these scans. To determine the rotation of the prostate, the angle between the needle and the seed trajectory is calculated. RESULTS: The prostate rotations have been measured in 16 patients, eight without the use of locking needles and eight with locking needles. In total 62 needles were inserted. The maximum rotation was 13.8 degrees and occurred in the coronal plane when no locking needles were used with a significant correlation (P<0.01, R=0.637) between the place of insertion and rotation. It was shown that the method (with or without locking needles) had a significant (P<0.001) influence on the rotation in the coronal plane. Rotations in the sagittal plane ranged from -8.5 degrees to +10.2 degrees without correlation with the insertion point of the needle or the use of locking needles. CONCLUSIONS: This study showed that prostate rotation during needle insertion for prostate brachytherapy is relatively large and unpredictable. Locking needles reduce prostate rotation in the coronal plane, but not in the sagittal plane. Minimising this rotation is necessary for accurate seed delivery, especially when a robotic implantation technique is used.     

Needle displacement during HDR brachytherapy in the treatment of prostate cancer

Purpose: We used clinical patient data to examine implant displacement between high dose rate (HDR) brachytherapy fractions for prostate cancer to determine its impact on treatment delivery.

Materials and Methods: We analyzed the verification films taken prior to each fraction for 96 consecutive patients treated with HDR brachytherapy boosts as part of their radiation therapy for definitive treatment of organ-confined prostate cancer at our institution. Patients were treated with 18–24 Gy in 4 fractions of HDR delivered in 40 hours followed by 36–39.6 Gy external beam radiation to the prostate. We determined the mean and maximum displacement distances of marker seeds placed in the prostate and of the implanted needles between HDR fractions.

Results: Mean and maximum displacement distances between fractions were documented up to 7.6 mm and 28.5 mm, respectively, for the implant needles and 3.6 mm and 11.4 mm, respectively, for the gold marker seeds. All displacement of implant needles occurred in the caudal direction. At least 1 cm caudal displacement of needles occurred prior to 15.5% all fractions. Manual adjustment of needles was required prior to 15% of fractions, and adjustment of the CLP only was required in 24%. Most of the displacement for both the marker seeds and needles occurred between the first and second fractions.

Conclusions: There is significant caudal displacement of interstitial implant needles between HDR fractions in our prostate cancer patients. Obtaining verification films and making adjustments in the treatment volume prior to each fraction is necesary to avoid significant inaccuracies in treatment delivery.     

Ultrasonography and fluoroscopic fusion for prostate brachytherapy dosimetry

: To investigate the feasibility of performing postimplant and intraoperative dosimetry for prostate brachytherapy by fusing transrectal ultrasound (TRUS) and fluoroscopic data.

: Registration of ultrasound (prostate boundary) and fluoroscopic (seed) data requires spatial markers that are detectable by both imaging modalities. In this study, the needle tips were considered as such fiducials. Prostate phantoms were implanted with the seeds, and four localization needles were inserted. In the TRUS frame of reference, the longitudinal coordinate of the needle tip was determined by advancing the needle until the echo from its tip just registered at a known probe depth. The tip’s transverse coordinates were determined from the associated TRUS slice. The three-dimensional needle tip positions were also calculated in the fluoroscopic coordinate system using a seed reconstruction method. The transformation between the TRUS and fluoroscopy coordinate systems was established by the least-squares solution using the singular value decomposition.

: With three of four needle tips as fiducials and the one remaining needle as a test target, the mean fiducial registration error was 0.8 mm and the test target registration error was 2.5 mm. When all four points were used for registration, the errors decreased to 1.1 mm. A comparison between the proposed method and CT-based dosimetry yielded a percentage of prostate volume receiving 100% and 150% of the prescribed minimal peripheral dose and minimal dose received by 90% of the prostate gland that agreed within 0.4%, 2.7%, and 4.2%, respectively.

: The combination of TRUS and fluoroscopy is a feasible alternative to the currently used CT-based postimplant dosimetry. Furthermore, because of online imaging capability, the method lends itself to real-time intraoperative applications.