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Publications relating brainstem radiation toxicity to quantitative dose and dose-volume measures derived from three-dimensional treatment planning were reviewed. Despite the clinical importance of brainstem toxicity, most studies reporting brainstem effects after irradiation have fewer than 100 patients. There is limited evidence relating toxicity to small volumes receiving doses above 60-64 Gy using conventional fractionation and no definitive criteria regarding more subtle dose-volume effects or effects after hypofractionated treatment. On the basis of the available data, the entire brainstem may be treated to 54 Gy using conventional fractionation using photons with limited risk of severe or permanent neurological effects. Smaller volumes of the brainstem (1-10 mL) may be irradiated to maximum doses of 59 Gy for dose fractions ≤2 Gy; however, the risk appears to increase markedly at doses >64 Gy. KeywordsBrainstem; Radiation; Tolerance; NTCP CLINICAL SIGNIFICANCECentral nervous system (CNS) tolerance to radiation therapy (RT) is of concern for patients treated for primary or meta-static disease involving the brain and head and neck. ENDPOINTSThe common toxicity criteria of the Cancer Therapy Evaluation Program (CTEP) grades brainstem injury on the basis of symptoms (Grade 1-mild or asymptomatic; Grade 2-moderate, not interfering with activities of daily living (ADLs); Grade 3-severe interference with ADLs, possible intervention; Grade 4-life-threatening or disabling, intervention indicated; and Grade 5-Death) (1). Severe RT-induced CNS injury is typically manifest months to years after treatment. Tumor recurrence and constitutional symptoms from other diseases and treatments may confound the diagnosis. The study of RT-induced CNS injury is challenging because (1) the incidence of injury is generally low, (2) survivals are short for most patients, (3) formal grading of brainstem effects is subjective and is often characterized categorically (yes-no) for cranial neuropathy, and (4) for patients with intracranial tumors, it is often difficult to distinguish between side effects and disease progression. For patients CHALLENGES OF DEFINING VOLUMESDefining the brainstem on axial imaging is usually straightforward, although it requires special attention to the superior extent and interfaces at the cerebral and cerebellar peduncles where the brainstem borders are indistinct. The brainstem includes the midbrain, pons, and medulla. The midbrain is inferior to the third ventricle and the optic tracts. The inferior border of brainstem is at the pyramidal decussation found at the level of the foramen magnum where the brainstem becomes the spinal cord. Segmentation or visualization of coronal or sagittal planes may be helpful when defining the brainstem on neuroimaging. The brainstem is a stable structure; however, anatomic shift may occur from tumor and after surgery. REVIEW OF DOSE-VOLUME DATAA literature review was undertaken to extract relevant brainstem tolerance data from studies published in the era of CT-...

Treatment planning tools that use biologically related models for plan optimization and/or evaluation are being introduced for clinical use. A variety of dose-response models and quantities along with a series of organ-specific model parameters are included in these tools. However, due to various limitations, such as the limitations of models and available model parameters, the incomplete understanding of dose responses, and the inadequate clinical data, the use of biologically based treatment planning system (BBTPS) represents a paradigm shift and can be potentially dangerous. There will be a steep learning curve for most planners. The purpose of this task group is to address some of these relevant issues before the use of BBTPS becomes widely spread. In this report, the authors (1) discuss strategies, limitations, conditions, and cautions for using biologically based models and parameters in clinical treatment planning; (2) demonstrate the practical use of the three most commonly used commercially available BBTPS and potential dosimetric differences between biologically model based and dose-volume based treatment plan optimization and evaluation; (3) identify the desirable features and future directions in developing BBTPS; and (4) provide general guidelines and methodology for the acceptance testing, commissioning, and routine quality assurance (QA) of BBTPS.

A substantial barrier to the single- and multi-institutional aggregation of data to supporting clinical trials, practice quality improvement efforts, and development of big data analytics resource systems is the lack of standardized nomenclatures for expressing dosimetric data. To address this issue, the American Association of Physicists in Medicine (AAPM) Task Group 263 was charged with providing nomenclature guidelines and values in radiation oncology for use in clinical trials, data-pooling initiatives, population-based studies, and routine clinical care by standardizing: (1) structure names across image processing and treatment planning system platforms; (2) nomenclature for dosimetric data (eg, dose-volume histogram [DVH]-based metrics); (3) templates for clinical trial groups and users of an initial subset of software platforms to facilitate adoption of the standards; (4) formalism for nomenclature schema, which can accommodate the addition of other structures defined in the future. A multisociety, multidisciplinary, multinational group of 57 members representing stake holders ranging from large academic centers to community clinics and vendors was assembled, including physicists, physicians, dosimetrists, and vendors. The stakeholder groups represented in the membership included the AAPM, American Society for Radiation Oncology (ASTRO), NRG Oncology, European Society for Radiation Oncology (ESTRO), Radiation Therapy Oncology Group (RTOG), Children's Oncology Group (COG), Integrating Healthcare Enterprise in Radiation Oncology (IHE-RO), and Digital Imaging and Communications in Medicine working group (DICOM WG); A nomenclature system for target and organ at risk volumes and DVH nomenclature was developed and piloted to demonstrate viability across a range of clinics and within the framework of clinical trials. The final report was approved by AAPM in October 2017. The approval process included review by 8 AAPM committees, with additional review by ASTRO, European Society for Radiation Oncology (ESTRO), and American Association of Medical Dosimetrists (AAMD). This Executive Summary of the report highlights the key recommendations for clinical practice, research, and trials.