Arvind Soni

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.

The molecular and cellular biologic basis for the radiation treatment of benign proliferative diseases.

Since its discovery, radiation has been used to treat numerous ailments, including many benign conditions. The most susceptible disorders have included keloids, heterotopic bone formation, and, most recently, vascular restenosis. These disorders are proliferative in nature and fall under the category of excessive wound healing or scar formation after trauma. In addition, radiation has been used for its immunosuppressive quality, eg, in organ transplantation to suppress graft rejection and in the treatment of autoimmune diseases. In this article, we have chosen keloids as an archetype for radiation use with benign conditions; the radiation inhibition of vascular restenosis will be used as a prototype to explore a paradigm for the molecular and cellular basis of radiation treatment for selected benign disorders. Vascular restenosis is currently one of the new frontiers of radiation therapy and offers opportunities to explore the role of inflammatory or immune cell responses in benign conditions that lead to excessive fibrogenesis and require treatment. The pathophysiology of surgical wound healing has not been avidly studied in the radiobiologic laboratory setting. However, the paradigm we propose for the effectiveness of radiation treatment for benign conditions is based on the model offered by Clark. He describes three phases of molecular and cellular events in which an inflammatory phase precedes the fibrogenic phase, occurs within hours of injury, and continues for weeks. We postulate that the radiosensitive targets within the vascular milieu are the monocyte/macrophages that would otherwise act as the trigger for the induced cytokine cascade, leading to the myofibroblast being recruited from a quiescent to a proliferative phase, resulting in fibrogenesis.

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.

Benefits of external beam irradiation for peripheral arterial bypass: preliminary report on a phase I study

PURPOSE To perform a Phase I study to determine the safety and feasibility of using external beam radiotherapy to prevent neointimal hyperplasia in patients after surgical bypass of occluded infrainguinal arteries. METHODS AND MATERIALS All patients undergoing operative infrainguinal bypass for chronic ischemia were eligible for enrollment, although those requiring a prosthetic graft were preferentially considered. Immediately after bypass, the distal anastomosis was marked with clips, and the baseline anatomy of the anastomosis was documented with an intraoperative angiogram. The distal anastomotic site and 2 cm of surrounding tissues were irradiated to a total dose of 30 Gy, delivered in 10 fractions. The first dose was given within 48 h of surgery. RESULTS Twenty-one patients were enrolled in this study. No anastomotic or wound problems or any other short-term complications of the treatment developed. However, at a mean follow-up of 10 months (range 3-18), 12 (57%) of the 21 grafts had occluded. Angiography was performed in 2 patients after successful thrombolysis and demonstrated normal anastomoses without residual stenosis. Evidence of stenosis at the irradiated anastomosis was seen in only 1 of the 21 patients by ongoing ultrasound surveillance. CONCLUSION Fractionated external irradiation to a total dose of 30 Gy delivered to the distal surgical anastomosis immediately after operative bypass has no short-term complications and was associated with an apparently low rate of intimal hyperplasia. However, any possible gains made by reducing the neointimal hyperplasia at the site of anastomosis were significantly diminished by the high frequency of thrombotic events.