Robotic system for prostate brachytherapy.

In contemporary brachytherapy procedures, needle placement at the desired target is challenging for a variety of reasons. A robot-assisted brachytherapy system can potentially improve needle placement and seed delivery, resulting in enhanced therapeutic outcome. In this paper we present a robotic system with 16 degrees of freedom (DOF) (9 DOF for the positioning module and 7 DOF for the surgery module) that has been developed and fabricated for prostate brachytherapy. Strategies to reduce needle deflection and target movement were incorporated after extensive experimental validation. Provision for needle motion and force feedback was included in the system to improve robot control and seed delivery. Preliminary experimental results reveal that the prototype system is sufficiently accurate in placing brachytherapy needles.

Efficacy of prostate stabilizing techniques during brachytherapy procedure.

During the prostate brachytherapy procedure, multiple needles are inserted into the prostate and radioactive seeds are deposited. Stabilizing needles are first inserted to provide some rigidity and support to the prostate, ideally this will provide better seed placement and an overall improved treatment. However, there is much speculation regarding the effectiveness of using regular brachytherapy needles as stabilizers. In this study, we explored the efficacy of (1) two types of needles--18 gauge brachytherapy needle vs. 18 gauge hooked needle; and (2) parallel vs. angulated needle configurations to stabilize the prostate. Prostate phantom movement and needle insertion progression were imaged using ultrasound (US). The recorded images were analyzed and prostate displacement was computed from images using implanted artifacts. Experimentation allowed us to further understand the mechanics behind prostate stabilization. We observed superior stabilization by the hooked needles compared to the regular brachytherapy needles (more than 40% for parallel stabilization). Prostate movement was also reduced significantly when regular brachytherapy needles were in an angulated configuration as compared to the parallel configuration (approximately 40%). When the hooked needles were angled for stabilization, further improvement in decreased displacement was observed. In general, for convenience of dosimetric planning, all needles are desired to be in parallel and in this case, hooked needles are better suited to improve stabilization of the prostate. On the other hand, both regular and hooked needles appear to be equally effective in reducing prostate movement when they are in angulated configurations, which will be useful in robotic permanent seed implantation (PSI).

Needle insertion force estimation model using procedure-specific and patient-specific criteria.

Placement accuracy of different types of surgical needles in soft biological tissues depends on a variety of factors. The needles used for prostate brachytherapy procedures are typically about 200 mm in length and 1.27-1.47 mm in diameter. These needles are prone to deflection and thereby depositing the seeds at a location other than the planned one. Thus tumorous tissues may not receive the planned dose whereas the critical organs may be over-dosed. A significant amount of needle deflection and target movement is related to some procedure-specific criteria and some patient-specific criteria. In this paper we have developed needle insertion force models taking both procedure-specific criteria and patient-specific criteria. These statistical models can be used to estimate the force that the needle will experience during insertion and thereby control the needle to reduce the needle deflection and enhance seed delivery accuracy.

In-vivo measurement of surgical needle intervention parameters: a pilot study.

Percutaneous intervention is essential in numerous medical diagnostic and therapeutic procedures. In these procedures, accurate insertion of the surgical needle is very important. But precise interstitial intervention is quite challenging. Robot-assisted needle intervention can significantly improve accuracy and consistency of various medical procedures. To design and control any robotic system, the design and control engineers must know the forces that will be encountered by the system and the motion trajectories that the needling mechanism will have to follow. Several researchers have reported needle insertion forces encountered while steering through soft tissue and soft material phantoms, but hardly any in-vivo force measurement data is available in the literature. In this paper, we present needle insertion forces and motion trajectories measured during actual brachytherapy needle insertion while implanting radioactive seeds in the prostate glands of twenty five patients.

Real-time US versus CT determination of pubic arch interference for brachytherapy.

PURPOSE: Part 1, to determine whether transrectal ultrasonography (US) enables accurate determination of pubic arch interference (PAI) for prostate brachytherapy (PBT); part 2, to compare the accuracy of transrectal US with that of computed tomography (CT) for PAI determination; and part 3, to determine the cost savings of PAI determination with transrectal US versus that with CT. MATERIALS AND METHODS: Part 1: The pubic arch was identified intraoperatively with transrectal US and compared with attempted needle passage (14 patients). Part 2: Planning CT with the patient supine was compared with planning transrectal US with patients in the dorsal lithotomy position (nine patients). Part 3: Cost savings were calculated for PAI determination with transrectal US versus that with CT (32 patients per group). RESULTS: Part 1: Transrectal US accurately showed the pubic arch relative to the prostate. Part 2: CT resulted in PAI overestimation by 11.8 mm. Part 3: Cost savings with transrectal US were $1,465 per patient. CONCLUSION: Transrectal US PAI determination is easily performed, intraoperatively useful, and accurate. CT can result in PAI overestimation. Reducing direct CT costs and the indirect costs of unnecessary hormonal therapy for false-positive PAI will reduce expense and improve patient care. Transrectal US should replace CT for PAI determination.

Intraoperative optimized inverse planning for prostate brachytherapy: early experience.

PURPOSE: To demonstrate the feasibility of an intraoperative inverse planning technique with advanced optimization for prostate seed implantation. METHODS AND MATERIALS: We have implemented a method for optimized inverse planning of prostate seed implantation in the operating room (OR), based on the genetic algorithm (GA) driven Prostate Implant Planning Engine for Radiotherapy (PIPER). An integrated treatment planning system was deployed, which includes real-time ultrasound image acquisition, treatment volume segmentation, GA optimization, real-time decision making and sensitivity analysis, isodose and DVH evaluation, and virtual reality navigation and surgical guidance. Ten consecutive patients previously scheduled for implantation were included in the series. RESULTS: The feasibility of the technique was established by careful monitoring of each step in the OR and comparison with conventional preplanned implants. The median elapsed time for complete image capture, segmentation, GA optimization, and plan evaluation was 4, 10, 2.2, and 2 min, respectively. The dosimetric quality of the OR-based plan was shown to be equivalent to the corresponding preplan. CONCLUSION: An intraoperative optimized inverse planning technique was developed for prostate brachytherapy. The feasibility of the method was demonstrated through an early clinical experience.

Automated treatment planning engine for prostate seed implant brachytherapy.

PURPOSE: To develop a computer-intelligent planning engine for automated treatment planning and optimization of ultrasound- and template-guided prostate seed implants. METHODS AND MATERIALS: The genetic algorithm was modified to reflect the 2D nature of the implantation template. A multi-objective decision scheme was used to rank competing solutions, taking into account dose uniformity and conformity to the planning target volume (PTV), dose-sparing of the urethra and the rectum, and the sensitivity of the resulting dosimetry to seed misplacement. Optimized treatment plans were evaluated using selected dosimetric quantifiers, dose-volume histogram (DVH), and sensitivity analysis based on simulated seed placement errors. These dosimetric planning components were integrated into the Prostate Implant Planning Engine for Radiotherapy (PIPER). RESULTS: PIPER has been used to produce a variety of plans for prostate seed implants. In general, maximization of the minimum peripheral dose (mPD) for given implanted total source strength tended to produce peripherally weighted seed patterns. Minimization of the urethral dose further reduced the loading in the central region of the PTV. Isodose conformity to the PTV was achieved when the set of objectives did not reflect seed positioning uncertainties; the corresponding optimal plan generally required fewer seeds and higher source strength per seed compared to the manual planning experience. When seed placement uncertainties were introduced into the set of treatment planning objectives, the optimal plan tended to reach a compromise between the preplanned outcome and the likelihood of retaining the preferred outcome after implantation. The reduction in the volatility of such seed configurations optimized under uncertainty was verified by sensitivity studies. CONCLUSION: An automated treatment planning engine incorporating real-time sensitivity analysis was found to be a useful tool in dosimetric planning for prostate brachytherapy.

Autotransplantation for relapsed or refractory Hodgkin's disease: long-term follow-up and analysis of prognostic factors.

Seventy consecutive patients with refractory or relapsed Hodgkin's disease who received high-dose chemotherapy followed by autologous stem cell rescue were analyzed to identify clinically relevant predictors of long-term event-free survival. High-dose therapy consisted primarily of carmustine (BCNU), etoposide, cytarabine and cyclophosphamide (BEAC). The 5-year Kaplan-Meier event-free survival (EFS) for the entire cohort was 32% (95% confidence interval; 18-45%) with a median follow-up of 3.6 years (range 7 months-7.6 years). The most significant predictor of improved survival was the presence of minimal disease (defined as all areas < or =2 cm) at the time of transplant: the 5 years EFS was 46 vs 10% for patients with bulky disease (P = 0.0002). Other independent predictors identified by step-wise regression analysis included the presence of non-refractory disease and the administration of post-transplant involved-field radiotherapy (XRT). Treatment-related mortality occurred in 13 of 70 patients: nine patients (13%) died within the first 100 days, mainly from cardiopulmonary toxicity. However, only one of 24 patients (4%) transplanted during the last 4.5 years died from early treatment-related complications. While high-dose therapy followed by autotransplantation led to long-term EFS of 50% for patients with favorable prognostic factors, a substantial proportion of patients relapsed, indicating that new therapeutic strategies are needed.