Frontiers of Radiation Therapy and Oncology最新文献

What are the limitations to the accuracy of our current technologies in radiation oncology? The immobilization of the patient, definition of the target, motion of the target and localization of the target are the major concerns that must be addressed. Current approaches to meet these needs have brought new technical systems with greater precision and new clinical procedures with higher expectations of practice. This text offers discussions on these issues, including advances in intensity-modulated radiotherapy planning, clinical target definition for the major tumor sites, management of organ motion, target localization and image guidance systems, and the expanding applications of high-precision treatment with stereotactic body radiotherapy.

Four-dimensional CT acquisition is commercially available, and provides important information on the shape and trajectory of the tumor and normal tissues. The primary advantage of four-dimensional imaging over light breathing helical scans is the reduction of motion artifacts during scanning that can significantly alter tumor appearance. Segmentation, image registration, visualization are new challenges associated with four-dimensional data sets because of the overwhelming increase in the number of images. Four-dimensional dose calculations, while currently laborious, provide insights into dose perturbations due to organ motion. Imaging before treatment (image guidance) improves accuracy of radiation delivery, and recording transmission images can provide a means of verifying gated delivery.

Stanford University has a long legacy of contributions to the field of radiation therapy. The Cyberknife image-guided robotic radiosurgery is the latest in a series of radiation advancements that allows for improved treatment of tumors. Here we present a decade of experience in using robotic radiosurgery to treat 295 spinal and paraspinal lesions including spinal metastases, benign intradural tumors, and arteriovenous malformations. Our analysis of clinical outcomes confirms the promise of this technology in terms of efficacy and safety.

Image-guided radiation therapy implies the use of a variety of imaging techniques in the treatment room to determine the location of target areas with the patient in the treatment position. This is particularly relevant for prostate cancer radiation therapy since the prostate gland can differ in its position within the pelvis from one treatment to another. The different imaging techniques include transabdominal ultrasound, in-room X-rays with and without the use of intraprostatic implanted fiducials, kilovoltage and megavoltage CT techniques, and even in-room MRI. The workflow and capabilities of each imaging system need to be evaluated and investigated individually.

Stereotactic body radiation therapy (SBRT) is a potent noninvasive means of administering high-dose radiation to demarcated tumor deposits in extracranial locations. The treatments use image guidance and related treatment delivery technology for the purpose of escalating the radiation dose to the tumor itself with as little radiation dose to the surrounding normal tissue as possible. The local tumor control for SBRT has been higher than anything previously published for radiotherapy in treating typical carcinomas. In addition, the pattern, timing and severity of toxicity have been very different than what was seen with conventional radiotherapy. In this review, the clinical characteristics and outcomes of SBRT are presented in the context of their underlying mechanisms. While much of the material is unproven and speculative, it at least qualitatively searches for understanding as to the biological basis for the observed clinical effects. Hopefully, it will serve as a motivation for more sophisticated biological research into the effects of SBRT.

Stereotactic body radiation therapy (SBRT) is currently under active study at numerous centers for clinical application in the management of patients with primary or metastatic tumors of the liver, primary or metastatic tumors of the kidney, and selected other retroperitoneal tumors. Accurate patient positioning and tumor relocalization are essential for SBRT use in the liver and other abdominal and retroperitoneal sites, as at other tumor sites. In a phase I clinical trial at the University of Colorado, patients with liver metastases have received SBRT. Eligible patients had 1-3 discrete liver metastases and no prior radiotherapy to the liver. The aggregate tumor diameter (sum of diameters) was <6 cm. Respiratory control was used. Normal liver volume to be preserved was determined prior to therapy. Dose was prescribed to a planning target volume that included the gross tumor volume plus at least a 5-mm radial and 10-mm superior-inferior margin. SBRT was administered with 6- to 15-MV beams through either dynamic conformal arcs or a combination of multiple noncoplanar static beams. The dose was safely escalated to 60 Gy in 3 fractions. After SBRT to hepatic lesions, it is extremely difficult to radiographically evaluate tumor response within the first few months, and radiographic response analysis may require 4-6 months after SBRT. Care must be taken to avoid focal high-dose therapy to the gastrointestinal mucosa, where the maximum point dose is likely to be the major limitation rather than the mean dose. SBRT has a potential role in the management of renal cell carcinoma, either as an alternative to surgery to the primary site or as cytoreductive therapy directed toward metastatic sites, and in the management of selected retroperitoneal tumors.

Radiation therapy treatment planning and delivery capabilities have changed dramatically since the introduction of three-dimensional treatment planning in the 1980s and continue to change in response to the implementation of new technologies. CT simulation and three-dimensional radiation treatment planning systems have become the standard of practice in clinics around the world. Medical accelerator manufacturers have employed advanced computer technology to produce treatment planning/delivery systems capable of precise shaping of dose distributions via computer-controlled multileaf collimators, in which the beam fluence is varied optimally to achieve the plan prescription. This mode of therapy is referred to as intensity-modulated radiation therapy (IMRT), and is capable of generating extremely conformal dose distributions including concave isodose volumes that provide conformal target volume coverage and avoidance of specific sensitive normal structures. IMRT is rapidly being implemented in clinics throughout the USA. This increasing use of IMRT has focused attention on the need to better account for both intrafraction and interfraction spatial uncertainties, which has helped spur the development of treatment machines with integrated planar and volumetric advanced imaging capabilities. In addition, advances in both anatomical and functional imaging provide improved ability to define the tumor volumes. Advances in all these technologies are occurring at a record pace and again pushing the cutting-edge frontiers of radiation oncology from IMRT to what is now referred to as image-guided IMRT, or simply image-guided radiation therapy (IGRT). A brief overview is presented of these latest advancements in conformal treatment planning and treatment delivery.