What is plan quality in radiotherapy? The importance of evaluating dose metrics, complexity, and robustness of treatment plans

Plan evaluation is a key step in the radiotherapy treatment workflow. Central to this step is the assessment of treatment plan quality. Hence, it is important to agree on what we mean by plan quality and to be fully aware of which parameters it depends on. We understand plan quality in radiotherapy as the clinical suitability of the delivered dose distribution that can be realistically expected from a treatment plan. Plan quality is commonly assessed by evaluating the dose distribution calculated by the treatment planning system (TPS). Evaluating the 3D dose distribution is not easy, however; it is hard to fully evaluate its spatial characteristics and we still lack the knowledge for personalising the prediction of the clinical outcome based on individual patient characteristics. This advocates for standardisation and systematic collection of clinical data and outcomes after radiotherapy. Additionally, the calculated dose distribution is not exactly the dose delivered to the patient due to uncertainties in the dose calculation and the treatment delivery, including variations in the patient set-up and anatomy. Consequently, plan quality also depends on the robustness and complexity of the treatment plan. We believe that future work and consensus on the best metrics for quality indices are required. Better tools are needed in TPSs for the evaluation of dose distributions, for the robust evaluation and optimisation of treatment plans, and for controlling and reporting plan complexity. Implementation of such tools and a better understanding of these concepts will facilitate the handling of these characteristics in clinical practice and be helpful to increase the overall quality of treatment plans in radiotherapy

Current treatment options for recurrent nasopharyngeal cancer

Loco-regional control rate of nasopharyngeal carcinoma (NPC) has improved significantly in the past decade. However, local recurrence still represents a major cause of mortality and morbidity in advanced stages, and management of local failure remains a challenging issue in NPC. The best salvage treatment for local recurrent NPC remains to be determined. The options include brachytherapy, external radiotherapy, stereotactic radiosurgery, and nasopharyngectomy, either alone or in different combinations. In this article we will discuss the different options for salvage of locally recurrent NPC. Retreatment of locally recurrent NPC using radiotherapy, alone or in combination with other treatment modalities, as well as surgery, can result in long-term local control and survival in a substantial proportion of patients. For small-volume recurrent tumors (T1–T2) treated with external radiotherapy, brachytherapy or stereotactic radiosurgery, comparable results to those obtained with surgery have been reported. In contrast, treatment results of advanced-stage locally recurrent NPC are generally more satisfactory with surgery (with or without postoperative radiotherapy) than with reirradiation

Need of causal analysis for assessing phase relationships in closed loop interacting cardiovascular variability series

The phase spectra obtained by the classical closed loop autoregressive model (2AR) and by an open loop autoregressive model (ARXAR) were compared to shed light on the need of introducing causality in the assessment of the delay between RR and arterial pressure oscillations. The reliability of the two approaches was tested in simulation and real data setting. In simulation, the coupling strength of a bivariate closed loop process was adjusted to obtain a range of working conditions from open to closed loop. In open loop condition, 2AR and ARXAR phases were comparable and in agreement with the imposed delay. In closed loop condition, ARXAR model returned the imposed delays, while 2AR showed an intermediate value of delay. Real data were chosen to represent comparable physiological condition. The use of cross spectrum for calculating the delay from arterial peressure to RR oscillations seems adequate only in particular condition of open-loop relationship as it happens during head up tilt in young healthy subjects

Cardiovascular response to sinusoidal neck suction in healthy volunteers and orthostatic intolerance patients

The dynamic response to sinusoidal neck suction, of the RR interval, systolic arterial blood pressure and muscle sympathetic nerve activity series, was studied in 10 controls and 5 patients with orthostatic intolerance. By using different spectral techniques (autoregressive, short time Fourier transformation), the cardiovascular and MSNA variability were analyzed during 0.1 Hz and 0.2 Hz frequency of neck suction. Moreover, by using the autoregressive model, a quantitative analysis of particular power spectral frequency bands was done. Finally, a chirp neck suction input signal was applied to qualitatively compare the frequency response. The patients with orthostatic intolerance showed a partial blood pressure response to NS, particularly over 0.1 Hz compared to controls

Spectral decomposition of RR-variability obtained by an open loop parametric model for the diagnosis of neuromediate syncope

The role of the cardiovascular regulatory mechanism in patients with neuromediate syncope (NS) is poorly understood. Aim of this study was to accomplish continuous non-invasive analysis of the baroreflex mechanism in patients during head-up tilt-table test (HTT) using an open loop autoregressive model with exogenous input. The model describes the causal dependence of the RR interval on the systolic arterial pressure (SAP) variability. Thus, RR variability results as the linear composition of SAP-dependent (Pdep) and SAP-independent parts. Further, the model allows the estimation of the baroreflex gain using the modulus of the transfer function (G) from SAP to RR in the low frequency band. Results showed a significant decrease of both Pdep and G immediately before syncope. Thus, a reduced functionality of the baroreflex and of the sympathetic tone seemed to be the mechanism responsible for the NS event