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- A heuristic based on fuzzy inference systems for multiobjective IMRT treatment planningPublication . Dias, Joana; Rocha, Humberto; Ventura, Tiago; Costa Ferreira, Brigida; Lopes, Maria do CarmoRadiotherapy is one of the treatments used against cancer. Each treatment has to be planned considering the medical prescription for each specific patient and the information contained in the patient’s medical images. The medical prescription usually is composed by a set of dosimetry constraints, imposing maximum or minimum radiation doses that should be satisfied. Treatment planning is a trial-and-error time consuming process, where the planner has to tune several parameters (like weights and bounds) until an admissible plan is found. Radiotherapy treatment planning can be interpreted as a multiobjective optimization problem, because besides the set of dosimetry constraints there are also several conflicting objectives: maximizing the dose deposited in the volumes to treat and, at the same time, minimizing the dose delivered to healthy cells. In this paper we present a new multiobjective optimization procedure that will, in an automated way, calculate a set of potential non-dominated treatment plans. It is also possible to consider an interactive procedure whenever the planner wants to explore new regions in the non-dominated frontier. The optimization procedure is based on fuzzy inference systems. The new methodology is described and it is applied to a head-and-neck cancer case.
- A derivative-free multistart framework for an automated noncoplanar beam angle optimization in IMRTPublication . Rocha, Humberto; Dias, Joana; Ventura, Tiago; BC Ferreira; Lopes, Maria do CarmoThe inverse planning of an intensity-modulated radiation therapy (IMRT) treatment requires decisions regarding the angles used for radiation incidence, even when arcs are used. The possibility of improving the quality of treatment plans by an optimized selection of the beam angle incidences-beam angle optimization (BAO)-is seldom done in clinical practice. The inclusion of noncoplanar beam incidences in an automated optimization routine is even more unusual. However, for some tumor sites, the advantage of considering noncoplanar beam incidences is well known. This paper presents the benefits of using a derivative-free multistart framework for the optimization of the noncoplanar BAO problem.
- Noncoplanar beam angle optimization in IMRT treatment planning using pattern search methodsPublication . Rocha, Humberto; Dias, Joana M; Costa Ferreira, Brigida; Lopes, Maria CRadiation therapy is used to treat localized cancers, aiming to deliver a dose of radiation to the tumor volume to sterilize all cancer cells while minimizing the collateral effects on the surrounding healthy organs and tissues. The planning of radiation therapy treatments requires decisions regarding the angles used for radiation incidence, the fluence intensities and, if multileaf collimators are used, the definition of the leaf sequencing. The beam angle optimization problem consists in finding the optimal number and incidence directions of the irradiation beams. The selection of appropriate radiation incidence directions is important for the quality of the treatment. However, the possibility of improving the quality of treatment plans by an optimized selection of the beam incidences is seldom done in the clinical practice. Adding the possibility for noncoplanar incidences is even more rarely used. Nevertheless, the advantage of noncoplanar beams is well known. The optimization of noncoplanar beam incidences may further allow the reduction of the number of beams needed to reach a clinically acceptable plan. In this paper we present the benefits of using pattern search methods for the optimization of the highly non-convex noncoplanar beam angle optimization problem.
- SPIDERplan: A tool to support decision-making in radiation therapy treatment plan assessmentPublication . Ventura, Tiago; Lopes, Maria do Carmo; Costa Ferreira, Brigida; Khouri, LeilaAim In this work, a graphical method for radiotherapy treatment plan assessment and comparison, named SPIDERplan, is proposed. It aims to support plan approval allowing independent and consistent comparisons of different treatment techniques, algorithms or treatment planning systems. Background Optimized plans from modern radiotherapy are not easy to evaluate and compare because of their inherent multicriterial nature. The clinical decision on the best treatment plan is mostly based on subjective options. Materials and methods SPIDERplan combines a graphical analysis with a scoring index. Customized radar plots based on the categorization of structures into groups and on the determination of individual structures scores are generated. To each group and structure, an angular amplitude is assigned expressing the clinical importance defined by the radiation oncologist. Completing the graphical evaluation, a global plan score, based on the structures score and their clinical weights, is determined. After a necessary clinical validation of the group weights, SPIDERplan efficacy, to compare and rank different plans, was tested through a planning exercise where plans had been generated for a nasal cavity case using different treatment planning systems. Results SPIDERplan method was applied to the dose metrics achieved by the nasal cavity test plans. The generated diagrams and scores successfully ranked the plans according to the prescribed dose objectives and constraints and the radiation oncologist priorities, after a necessary clinical validation process. Conclusions SPIDERplan enables a fast and consistent evaluation of plan quality considering all targets and organs at risk.
- Beam angle optimization in IMRT: are we really optimizing what matters?Publication . Rocha, Humberto; Dias, Joana Matos; Ventura, Tiago; BC Ferreira; Lopes, Maria do CarmoIntensity‐modulated radiation therapy (IMRT) is a modern radiotherapy modality that uses a multileaf collimator to enable the irradiation of the patient with nonuniform maps of radiation from a set of distinct beam irradiation directions. The aim of IMRT is to eradicate all cancerous cells by irradiating the tumor with a prescribed dose while simultaneously sparing, as much as possible, the neighboring tissues and organs. The optimal choice of beam irradiation directions—beam angle optimization (BAO)—can play an important role in IMRT treatment planning by improving organ sparing and tumor coverage, increasing the treatment plan quality. Typically, the BAO search is guided by the optimal value of the fluence map optimization (FMO)—the problem of obtaining the most appropriate radiation intensities for each beam direction. In this paper, a new score to guide the BAO search is introduced and embedded in a parallel multistart derivative‐free optimization framework that is detailed for the extremely challenging continuous BAO problem. For the set of 10 clinical nasopharyngeal tumor cases considered, treatment plans obtained for optimized beam directions clearly outperform the benchmark treatment plans obtained considering equidistant beam directions typically used in clinical practice. Furthermore, treatment plans obtained considering the proposed score clearly improve the quality of the plans resulting from the use of the optimal value of the FMO problem to guide the BAO search.
- Compliance to radiation therapy of head and neck cancer patients and impact on treatment outcomePublication . Costa Ferreira, Brigida; Sá-Couto, P.; Lopes, M. C.; Khouri, L.The aims of the study were to evaluate head and neck cancer (HNC) patient's compliance to the planned radiation therapy (RT) using the department policy established in 2005 at IPOCFG and to estimate the impact on treatment outcome due to failure in receiving RT as prescribed.
- Comparison of two beam angular optimization algorithms guided by automated multicriterial IMRTPublication . Ventura, Tiago; Rocha, Humberto; Costa Ferreira, Brigida; Dias, Joana; Lopes, Maria do CarmoTo compare two beam angle optimization (BAO) algorithms for coplanar and non-coplanar geometries in a multicriterial optimization framework.
- Biological dose-escalated definitive radiation therapy in head and neck cancerPublication . Costa Ferreira, Brigida; Sá-Couto, Pedro; Khouri, Leila; Lopes, Maria do CarmoTo compare treatment outcome of patients with head and neck (HN) tumours treated with definitive radiation therapy that, mainly owing to differences in the fractionation scheme used with simultaneous integrated boost techniques, resulted in a different biological dose.
- Incorporating the Local Biological Effect of Dose Per Fraction in IMRT Inverse OptimizationPublication . BC Ferreira; Mavroidis, Panayiotis; Dias, Joana; Rocha, Humberton intensity modulated radiation therapy (IMRT), the dose in each voxel of the organs at risk (OAR) can be strongly reduced compared to conformal radiation therapy (RT). Due to the sensitivity of late side-effects to fraction size, a smaller dose per fraction in the normal tissues represent an increased tolerance to RT. This expected reduction in biological effect may then be used as an additional degree of freedom during IMRT optimization. In this study, the comparison between plans optimized with and without a voxel-based fractionation correction was made. Four patients diagnosed with a head and neck (HN), a breast, a lung or a prostate tumor were used as test cases. Voxel-based fractionation corrections were incorporated into the optimization algorithm by converting the dose in each normal tissue voxel to EQD2 (equivalent dose delivered at 2 Gy per fraction). The maximum gain in the probability of tumor control (PB), due to the incorporation of the correction for fractionation in each voxel, was 1.3% with a 0.1% increase in the probability of complications (PI) for the HN tumor case. However, in plan optimization and evaluation, when tolerance doses were compared with the respective planned EQD2 (calculated from the 3-dimensional dose distribution), PB increased by 19.3% in the HN, 12.5% in the lung, 6.2% in the breast and 2.7% in the prostate tumor case, respectively. The corresponding increases in PI were 2.3%, 6.2%, 1.0% and 0.7%, respectively. Incorporating voxel-based fractionation corrections in plan optimization is important to be able to show the clinical quality of a given plan against established tolerance constraints. To properly compare different plans, their dose distributions should be converted to a common fractionation scheme (e.g. 2 Gy per fraction) for which the doses have been associated with clinical outcomes.
- Automated fluence map optimization based on fuzzy inference systemsPublication . Dias, Joana; Rocha, Humberto; Ventura, Tiago; BC Ferreira; Lopes, Maria do CarmoThe planning of an intensity modulated radiation therapy treatment requires the optimization of the fluence intensities. The fluence map optimization (FMO) is many times based on a nonlinear continuous programming problem, being necessary for the planner to define a priori weights and/or lower bounds that are iteratively changed within a trial-and-error procedure until an acceptable plan is reached. In this work, the authors describe an alternative approach for FMO that releases the human planner from trial-and-error procedures, contributing for the automation of the planning process.
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