Intensity-modulated radiotherapy (IMRT) can improve dose distributions through the treated breast and also reduce radiation doses to adjacent normal tissues including the contralateral breast, heart and lung with appropriate planning. Analyses demonstrate that the quality of radiation dose distribution does affect clinical results, and that outcomes are enhanced through improved planning and dose delivery methods. To achieve these results, it is essential to carefully define tissue volumes for treatment or avoidance, select technologies that can potentially conform fields to those volumes, use comprehensive planning methods, and assess their results in terms of objective dose constraints. IMRT can also be used to boost the region of tumor excision concurrently with whole breast treatment, an approach now being evaluated in on-going clinical studies. Partial breast irradiation (PBI) has been proposed as an alternative to irradiation of the entire breast for early-stage breast cancer patients undergoing breast conservation treatment. Numerous single institution phase II studies have demonstrated promising results, and the American Society of Radiation Oncology (ASTRO) has defined a suitable group of low-risk patients for PBI treatment off protocol at this time. IMRT has been proposed as an alternative to 3D conformal radiotherapy (3DCRT) for external beam PBI to improve the dose conformality to target volumes and the sparing of normal tissues. There are an increasing number of institutions evaluating and using IMRT instead of 3DCRT for PBI because of the potential treatment advantages for the breast cancer patient.
Organ motion due to breathing, peristalsis and deformation presents challenging problems for the delivery of highly conformal radiotherapy to upper abdominal targets, despite the many advancements in the technology of radiation planning and delivery. It is important to understand and account for this motion to avoid treatment inaccuracies, especially systematic errors that could potentially impact the probability of tumor control or increase the risk of normal tissue toxicity. Various image guidance tools can be utilized from the outset of radiation planning through treatment to minimize introducing such errors. These strategies include: assessment of breathing motion (with or without breath hold) prior to simulation, 4D CT simulation and cine MRI to evaluate tumor/organ motion, and image guidance on the treatment unit using kV fluoroscopy and 4D cone-beam CT. Together, image guidance methods can provide greater assurance that concordance exists between planned and delivered doses during a course of radiotherapy.
Delineation of the targets for intensity-modulated radiation therapy (IMRT) of the head and neck is a crucial step in treatment planning, determining the risks of marginal or out-of-field local/regional recurrences. Delineation of the gross tumor volumes needs to take into account both radiological (CT, MRI, PET) and clinical findings, discussed in this paper. In contrast, the delineation of the clinical target volumes depends solely on the physician's judgement and knowledge of the natural history and spread pattern of head and neck cancer. While much of this information exists in older literature, new information has been gained from the pattern of recurrences observed after IMRT of head and neck cancer. This review concentrates on this information and on the lessons gained from these recurrences at our institution.
Healthcare economists generally agree that the development and rapid introduction of new technologies and the expanding utilization of existing ones in national healthcare systems have been significant factors in the dramatic and potentially unsustainable growth in healthcare spending. Creating a rational system for evaluation of emerging technologies in this country has been complicated by 3 broad issues: the often conflicting needs and expectations of the variety of stakeholders; an arcane and often illogical system of service valuation and payment; and the lack of a standardized, transparent and validated approach to the measurement of 'value.' Recent discussions on reforming the elements of healthcare delivery have increased focus on these systemic shortcomings and conflicts. As a specialty that is clinically wedded to modern and increasingly expensive technology, radiation oncology has often been singled out for scrutiny. A thorough examination and understanding of the various factors and controversies involved in technology development, implementation and valuation analysis is essential to rational growth and development of the specialty.
Managing target motion first requires understanding the nature of the motion characteristic of the tumor in the individual patient. It is important to have effective immobilization and patient training strategies to help reduce motion, and then to design appropriate margins and compensation for the residual motion that is quantified. Especially when considering complex, technically demanding treatments that require a degree of patient cooperation, careful patient selection is needed to ensure that the potential benefits of the treatment design are actually realized. Finally, accurate treatment hinges critically on verification - of overall positioning, of target and organ motion at the time of treatment, and of the performance of the selected treatment strategy. Properly selected imaging methods are central to this verification process. This discussion will present practical solutions for motion management and image guidance of radiotherapy for thoracic tumors, and most of these concepts are widely applicable to treatment of other tumor sites as well.
The current climate of rapid technological evolution is reflected in newer and better methods to modulate and direct radiation beams for cancer therapy. This Vision 20/20 paper focuses on part of this evolution, locating and targeting moving tumors. The two processes are somewhat independent and in principle different implementations of the locating and targeting processes can be interchanged. Advanced localization and targeting methods have an impact on treatment planning and also present new challenges for quality assurance (QA), that of verifying real-time delivery. Some methods to locate and target moving tumors with radiation beams are currently FDA approved for clinical use-and this availability and implementation will increase with time. Extensions of current capabilities will be the integration of higher order dimensionality, such as rotation and deformation in addition to translation, into the estimate of the patient pose and real-time reoptimization and adaption of delivery to the dynamically changing anatomy of cancer patients.
Intensity-modulated arc therapy (IMAT) is a rotational approach to radiation therapy delivered on a conventional linear accelerator using a conventional multileaf collimator. There are 2 key advantages of IMAT. First, the rotational nature of the delivery provides great flexibility in shaping each dose distribution. As a result, IMAT can provide dosimetric advantages relative to fixed-field intensity-modulated radiation therapy (IMRT). The second advantage is the highly efficient nature of the delivery. For centers with an active IMRT program, the clinical implementation of IMAT should be relatively straightforward. For clinical implementation of IMAT, it is important to fully characterize the accuracy of the dose model used, and the performance of the quality assurance equipment.
