A new detector for the beam energy measurement in proton therapy: a feasibility study.

The proof of concept of a new device, capable of determining in a few seconds the energy of clinical proton beams by measuring the time of flight (ToF) of protons, is presented. The prototype consists of two thin ultra fast silicon detector (UFSD) pads, aligned along the beam direction in a telescope configuration and readout by a digitizer. The method developed for extracting the energy at the isocenter from the measured ToF, validated by Monte Carlo simulations, and the procedure used to calibrate the system are also presented and discussed in detail. The prototype was tested at the Centro Nazionale di Adroterapia Oncologica (CNAO, Pavia, Italy), at several beam energies, covering the entire clinical range, and using different distances between the sensors. The measured beam energies were benchmarked against the nominal CNAO energy values, obtained during the commissioning of the centre from the measured ranges in water. Deviations of few hundreds of keV have been achieved for all considered proton beam energies for distances between the two sensors larger than 60 cm, indicating a sensitivity to the corresponding beam range in water smaller than the clinical tolerance of 1 mm. Moreover, few seconds of irradiation were necessary to collect the required statistics. These preliminary results indicate that a telescope of UFSDs could achieve in a short time the accuracy required for the clinical application and therefore encourage further investigations towards the improvement and the optimization of the present prototype.

RIDOS: A new system for online computation of the delivered dose distributions in scanning ion beam therapy.

PURPOSE: To describe a new system for scanned ion beam therapy, named RIDOS (Real-time Ion DOse planning and delivery System), which performs real time delivered dose verification integrating the information from a clinical beam monitoring system with a Graphic Processing Unit (GPU) based dose calculation in patient Computed Tomography. METHODS: A benchmarked dose computation algorithm for scanned ion beams has been parallelized and adapted to run on a GPU architecture. A workstation equipped with a NVIDIA GPU has been interfaced through a National Instruments PXI-crate with the dose delivery system of the Italian National Center of Oncological Hadrontherapy (CNAO) to receive in real-time the measured beam parameters. Data from a patient monitoring system are also collected to associate the respiratory phases with each spot during the delivery of the dose. Using both measured and planned spot properties, RIDOS evaluates during the few seconds of inter-spill time the cumulative delivered and prescribed dose distributions and compares them through a fast γ-index algorithm. RESULTS: The accuracy of the GPU-based algorithms was assessed against the CPU-based ones and the differences were found below 1‰. The cumulative planned and delivered doses are computed at the end of each spill in about 300 ms, while the dose comparison takes approximatively 400 ms. The whole operation provides the results before the next spill starts. CONCLUSIONS: RIDOS system is able to provide a fast computation of the delivered dose in the inter-spill time of the CNAO facility and allows to monitor online the dose deposition accuracy all along the treatment.

External sensory-motor cues while managing unexpected slippages can violate the planar covariation law.

This study was aimed at investigating the intersegmental coordination of six older adults while managing unexpected slippages delivered during steady walking, and wearing an Active Pelvis Orthosis (APO). The APO was setup either to assist volunteers at the hip levels during balance loss or to be transparent. The Planar Covariation Law (PCL) of the lower limb elevation angles was the main tool used to assess the intersegmental coordination of both limbs (i.e., the perturbed and unperturbed ones). Results revealed that, after the onset of the perturbation, elevation angles of both limbs do not covary, a part from the robot-mediated assistance. These new evidences suggest that external sensory-motor cues can alter the temporal synchronization of elevation angles, thus violating the PCL.

Pre-impact detection algorithm to identify lack of balance due to tripping-like perturbations.

This study investigates the performance of an updated version of our pre-impact detection algorithm while parsing out hip kinematics in order to identify unexpected tripping-like perturbations during walking. This approach grounds on the hypothesis that due to unexpected gait disturbances, the cyclic features of hip kinematics are suddenly altered thus promptly highlighting that the balance is challenged. To achieve our goal, hip angles of eight healthy young subjects were recorded while they were managing unexpected tripping trials delivered during the steady locomotion. Results showed that the updated version of our pre-impact detection algorithm allows for identifying a lack of balance due to tripping-like perturbations, after a suitable tuning of the algorithm parameters. The best performance is represented by a mean detection time ranging within 0.8-0.9 s with a low percentage of false alarms (i.e., lower than 10%). Accordingly, we can conclude that the proposed strategy is able to detect lack of balance due to different kinds of gait disturbances (e.g., slippages, tripping) and that it could be easily implemented in lower limb orthoses/prostheses since it only relies on joint angles.

Evaluation of time-frequency features as detectors of lack of balance due to tripping-like perturbations.

Unbalancing events during gait can end up in falls and, thus, injury. Detecting events that could bring to fall and consequently activating fall prevention systems before the impact may help to mitigate related injuries. However, there is uncertainty about signals and methods that could offer the best performance. In this paper we investigated a novel trip detection method based on time-frequency features to evaluate the performances of these features as trip detectors. Hip angles of eight healthy young subjects were recorded while performing unexpected tripping trials delivered during steady locomotion. Then the Short-Time Fourier Transform (STFT) of the hip angle was estimated. Median frequency, power, centroidal frequency as well as frequency dispersion were computed for each time sliced power spectrum. These features were used as input for a trip detection algorithm. We assessed detection time (Tdetect), specificity (Spec) and sensitivity (Sens) for each feature. Performances obtained with median frequencies over time(Tdetect 0.91 ± 0.47 s; Sens 0.96) were better than those obtained using the hip angle signal in time domain (Tdetect 1.19 ± 0.27 s; Sens 0.83). Other features did not show significant results. Thus, median frequency over time expected to achieve effective real-time event detection systems, with the aim of a future on-board application concerning detection and prevention measures.

'Survival': a simulation toolkit introducing a modular approach for radiobiological evaluations in ion beam therapy.

One major rationale for the application of heavy ion beams in tumour therapy is their increased relative biological effectiveness (RBE). The complex dependencies of the RBE on dose, biological endpoint, position in the field etc require the use of biophysical models in treatment planning and clinical analysis. This study aims to introduce a new software, named 'Survival', to facilitate the radiobiological computations needed in ion therapy. The simulation toolkit was written in C++ and it was developed with a modular architecture in order to easily incorporate different radiobiological models. The following models were successfully implemented: the local effect model (LEM, version I, II and III) and variants of the microdosimetric-kinetic model (MKM). Different numerical evaluation approaches were also implemented: Monte Carlo (MC) numerical methods and a set of faster analytical approximations. Among the possible applications, the toolkit was used to reproduce the RBE versus LET for different ions (proton, He, C, O, Ne) and different cell lines (CHO, HSG). Intercomparison between different models (LEM and MKM) and computational approaches (MC and fast approximations) were performed. The developed software could represent an important tool for the evaluation of the biological effectiveness of charged particles in ion beam therapy, in particular when coupled with treatment simulations. Its modular architecture facilitates benchmarking and inter-comparison between different models and evaluation approaches. The code is open source (GPL2 license) and available at https://github.com/batuff/Survival.

Altered miR-193a-5p expression in children with cow's milk allergy.

BACKGROUND: Cow's milk allergy (CMA) is one of the most common food allergies in children. Epigenetic mechanisms have been suggested to play a role in CMA pathogenesis. We have shown that DNA methylation of Th1/Th2 cytokine genes and FoxP3 affects CMA disease course. Preliminary evidence suggests that also the miRNome could be implicated in the pathogenesis of allergy. Main study outcome was to comparatively evaluate miRNome in children with CMA and in healthy controls. METHODS: Peripheral blood mononuclear cells were obtained from children aged 4-18 months: 10 CMA patients, 9 CMA patients who outgrew CMA, and 11 healthy controls. Small RNA libraries were sequenced using a next-generation sequencing-based approach. Functional assessment of IL-4 expression was also performed. RESULTS: Among the miRNAs differently expressed, 2 were upregulated and 14 were downregulated in children with active CMA compared to healthy controls. miR-193a-5p resulted the most downregulated miRNA in children with active CMA compared to healthy controls. The predicted targets of miR-193a-5p resulted upregulated in CMA patients compared to healthy controls. Peripheral blood CD4+ T cells transfected with a miR193a-5 inhibitor showed a significant upregulation of IL-4 mRNA and its protein expression. Children who outgrew CMA showed miRNA-193a-5p level, and its related targets expression, similar to that observed in healthy controls. CONCLUSIONS: Our results suggest that miR-193a-5p is a post-transcriptional regulator of IL-4 expression and could have a role in IgE-mediated CMA. This miRNA could be a novel diagnostic and therapeutic target for this common form of food allergy in childhood.

An ecologically-controlled exoskeleton can improve balance recovery after slippage.

The evolution to bipedalism forced humans to develop suitable strategies for dynamically controlling their balance, ensuring stability, and preventing falling. The natural aging process and traumatic events such as lower-limb loss can alter the human ability to control stability significantly increasing the risk of fall and reducing the overall autonomy. Accordingly, there is an urgent need, from both end-users and society, for novel solutions that can counteract the lack of balance, thus preventing falls among older and fragile citizens. In this study, we show a novel ecological approach relying on a wearable robotic device (the Active Pelvis Orthosis, APO) aimed at facilitating balance recovery after unexpected slippages. Specifically, if the APO detects signs of balance loss, then it supplies counteracting torques at the hips to assist balance recovery. Experimental tests conducted on eight elderly persons and two transfemoral amputees revealed that stability against falls improved due to the "assisting when needed" behavior of the APO. Interestingly, our approach required a very limited personalization for each subject, and this makes it promising for real-life applications. Our findings demonstrate the potential of closed-loop controlled wearable robots to assist elderly and disabled subjects and to improve their quality of life.

Quality assurance of carbon ion and proton beams: A feasibility study for using the 2D MatriXX detector.

PURPOSE: The quality assurance (QA) procedures in particle therapy centers with active beam scanning make extensive use of films, which do not provide immediate results. The purpose of this work is to verify whether the 2D MatriXX detector by IBA Dosimetry has enough sensitivity to replace films in some of the measurements. METHODS: MatriXX is a commercial detector composed of 32×32 parallel plate ionization chambers designed for pre-treatment dose verification in conventional radiation therapy. The detector and GAFCHROMIC® films were exposed simultaneously to a 131.44MeV proton and a 221.45MeV/u carbon-ion therapeutic beam at the CNAO therapy center of Pavia - Italy, and the results were analyzed and compared. RESULTS: The sensitivity MatriXX on the beam position, beam width and field flatness was investigated. For the first two quantities, a method for correcting systematic uncertainties, dependent on the beam size, was developed allowing to achieve a position resolution equal to 230µm for carbon ions and less than 100µm for protons. The beam size and the field flatness measured using MatriXX were compared with the same quantities measured with the irradiated film, showing a good agreement. CONCLUSIONS: The results indicate that a 2D detector such as MatriXX can be used to measure several parameters of a scanned ion beam quickly and precisely and suggest that the QA would benefit from a new protocol where the MatriXX detector is added to the existing systems.

Axis II disorders, body image and childhood abuse in bariatric surgery candidates.

BACKGROUND AND AIMS: Psychiatric disorders are common in obese patients and they are often considered contraindications for bariatric surgery. In this patients Axis I profile has been widely investigated, while only few studies on Axis II profile are reported. Aim of the study was to examine the prevalence of Axis II psychopathology, to describe the typical body image and to evaluate the prevalence of childhood abuse in bariatric surgery candidates. MATERIALS AND METHODS: A total of 102 consecutive obese patients (77 females) were evaluated by the Structured Clinical Interview for DSM IV which assessed Axis I Disorders. After the exclusion of Axis I Disorders, 50 patients (36 females, BMI: 44.68 ± 9.48 Kg/m2, age: 44.5 ± 11.7 years) were enrolled. All 50 patients received a psychiatric assessment including the Structured Clinical Interview for DSM-IV Axis II Disorders (SCID-II); the Body Uneasiness Test, part a (BUT-A), which assesses body image disorders; the Childhood Trauma Questionnaire (CTQ) as a screening test of childhood maltreatment histories. RESULTS: Nineteen patients (38%) were affected by Axis II disorders. Cluster C disorders, including avoidant, dependent and obsessive-compulsive personality disorders, represented the most common diagnosis (24%). Moreover, 34 patients (68%) showed body image disorders (BID), with a GSI score ≥1.2 and 24 (48%) referred an abuse during childhood. Patients with Axis II disorder or a body image uneasiness or a history of maltreatment during childhood, showed higher BMI in adulthood. CONCLUSIONS: Psychiatric comorbidities in obese patients were not only represented by depression or anxiety (Axis I disorders), but also by personality disorders (Axis II), body image disorders and childhood abuse. The identification of these conditions could improve outcomes of bariatric surgery and represent an indication for a most important psychiatric support before, during and after surgery.

Metabolic syndrome in patients with coeliac disease on a gluten-free diet.

BACKGROUND: Several studies have shown that weight changes are common in patients with coeliac disease after starting a gluten-free diet (GFD), but data on the prevalence of metabolic syndrome in this population are still scarce. AIMS: To assess the prevalence of metabolic syndrome in patients with CD at diagnosis and 1 year after starting GFD. METHODS: We enrolled all consecutive patients with newly diagnosed coeliac disease (CD) who were referred to our third-level CD Unit. For all patients we collected: waist circumference, BMI, blood pressure, lipid profile (HDL cholesterol, triglycerides) and levels of blood glucose. Diagnosis of metabolic syndrome was made according to the International Diabetes Federation (IDF) criteria for European countries. The prevalence of metabolic syndrome was re-assessed after 12 months of GFD. RESULTS: Ninety-eight patients with CD were assessed, two patients with CD (2%) fulfilled the diagnostic criteria for metabolic syndrome at diagnosis and 29 patients (29.5%) after 12 months of GFD (P < 0.01; OR: 20). With regard to metabolic syndrome sub-categories 1 year after GFD compared to baseline respectively: 72 vs. 48 patients exceeded waist circumference cut-off (P < 0.01; OR: 2.8); 18 vs. 4 patients had high blood pressure (P < 0.01; OR: 5.2); 25 vs. 7 patients exceeded glycemic threshold (P = 0.01; OR: 4.4); 34 vs. 32 patients with CD had reduced levels of HDL cholesterol (P = 0.7); and 16 vs. 7 patients had high levels of triglycerides (P = 0.05). CONCLUSIONS: Patients with coeliac disease show a high risk of metabolic syndrome 1 year after starting a gluten-free diet. We suggest that an in-depth nutritional assessment is undertaken for all patients with coeliac disease.

The CNAO dose delivery system for modulated scanning ion beam radiotherapy.

PURPOSE: This paper describes the system for the dose delivery currently used at the Centro Nazionale di Adroterapia Oncologica (CNAO) for ion beam modulated scanning radiotherapy. METHODS: CNAO Foundation, Istituto Nazionale di Fisica Nucleare and University of Torino have designed, built, and commissioned a dose delivery system (DDS) to monitor and guide ion beams accelerated by a dedicated synchrotron and to distribute the dose with a full 3D scanning technique. Protons and carbon ions are provided for a wide range of energies in order to cover a sizable span of treatment depths. The target volume, segmented in several layers orthogonally to the beam direction, is irradiated by thousands of pencil beams which must be steered and held to the prescribed positions until the prescribed number of particles has been delivered. For the CNAO beam lines, these operations are performed by the DDS. The main components of this system are two independent beam monitoring detectors, called BOX1 and BOX2, interfaced with two control systems performing the tasks of real-time fast and slow control, and connected to the scanning magnets and the beam chopper. As a reaction to any condition leading to a potential hazard, a DDS interlock signal is sent to the patient interlock system which immediately stops the irradiation. The essential tasks and operations performed by the DDS are described following the data flow from the treatment planning system through the end of the treatment delivery. RESULTS: The ability of the DDS to guarantee a safe and accurate treatment was validated during the commissioning phase by means of checks of the charge collection efficiency, gain uniformity of the chambers, and 2D dose distribution homogeneity and stability. A high level of reliability and robustness has been proven by three years of system activity needing rarely more than regular maintenance and working with 100% uptime. Four identical and independent DDS devices have been tested showing comparable performances and are presently in use on the CNAO beam lines for clinical activity. CONCLUSIONS: The dose delivery system described in this paper is one among the few worldwide existing systems to operate ion beam for modulated scanning radiotherapy. At the time of writing, it has been used to treat more than 350 patients and it has proven to guide and control the therapeutic pencil beams reaching performances well above clinical requirements. In particular, in terms of dose accuracy and stability, daily quality assurance measurements have shown dose deviations always lower than the acceptance threshold of 5% and 2.5%, respectively.

Robot-assisted gait training improves motor performances and modifies Motor Unit firing in poststroke patients.

BACKGROUND: Robotics and related technologies are realizing their promise to improve the delivery of rehabilitation therapy but the mechanism by which they enhance recovery is still unknown. The electromechanical-driven gait orthosis Lokomat has demonstrated its utility for gait rehabilitation after stroke. AIM: To test the efficacy of Lokomat in gait retraining and to investigate the neurophysiological mechanisms underlying the recovery process. DESIGN: Case series study. SETTING: Unit of Neurorehabilitation of a University Hospital. POPULATION: Fifteen patients with post-stroke hemiparesis. METHODS: Patients underwent a six weeks rehabilitative treatment provided by Lokomat. The outcome measures were: Fugl-Meyer Motor Scale (FMMS), Berg Balance Scale (BBS), 10 metres Walking Test (10mWT), Timed Up and Go test (TUG), 6 Minute Walking Test (6MWT). Strength and Motor Unit firing rate of vastus medialis (VM) were analyzed during isometric knee extension through an isokinetic dynamometer and surface EMG recording. RESULTS: An increase of duration and covered distance, a decrease of body weight support and guidance force on the paretic side along the sessions were observed. The FMMS, the BBS, the TUG and the 6MWT demonstrated a significant improvement after the training. No increase of force was observed whereas a significant increase of firing rate of VM was recorded. CONCLUSION: The evidence that the improvement of walking ability observed in our study determines a significant increase of firing rate of VM not accompanied by an increase of force could suggest an effect of training on motorneuronal firing rate that thus contributes to improve motor control. CLINICAL REHABILITATION IMPACT: Given the current wide use of robotics in gait retraining after stroke, our approach can contribute to clarify the mechanisms underlying its rehabilitative impact so as to incorporate the findings of evidence-based practice into appropriate treatment plans for persons poststroke.

Age-related neuromuscular adaptation does not affect the mechanical efficiency of lower limbs during walking.

Ageing involves modifications of the locomotor system which is believed to increase energy consumption. This study aimed at verifying whether neuromuscular adaptation due to ageing, in conjunction with age-related modifications of the muscle-tendon actuators, involves greater muscle-tendon workload. Ten young and 7 elderly healthy subjects were assessed using gait analysis while walking at comparable speed. Planar models of muscle-driven locomotion, accounting for 14 muscles grouped into 9 equivalent actuators, were developed. Muscle-tendon forces were estimated by using the inverse-dynamic based static optimization where cost functions were tuned to capture the different muscle co-activation between groups. Following this, tendon and muscle shortening/lengthening was computed, and muscle-tendon work was estimated and compared between groups. Results showed that both groups produced comparable muscle mechanical work, though shared differently among muscles. In particular, young subjects showed a greater workload of ankle plantaflexor muscles and older subjects used greater eccentric energy at the knee extensors during stance phase. Moreover, young people used more elastic energy than older people. These findings suggest that the combination adaptation due to ageing, in conjunction with age-related modifications of the muscle-tendon actuators, do not significantly increase the overall energetic output of locomotion. Moreover, the motor control system appears to be characterised by a degree of adaptation which allows older individuals to achieve biomechanical efficiency comparable to younger subjects.

Modifications of muscle synergies and spinal maps due to absence of visual feedback in patients with unilateral vestibular disease.

The present study aimed at describing the modifications of muscle synergies and spinal activity due to the absence of visual feedback, in patients affected by unilateral vestibular disease. Patients were tested both during unperturbed quite stance and walking while the activity of 7 bilateral muscles, from the leg to the trunk, were recorded for the estimation of muscle synergies and spinal activity. Results showed that during locomotion the absence of visual feedback did not significantly modify either the principal roles underlying muscle activity (i.e., synergies) or the spinal bursts. Conversely, during the upright stance, the absence of visual feedback involved a significant coupling of ankle dorsi- and plantar-flexor muscle groups with a consequent shift of the motoneuronal (MN) activity toward most caudal segments. Results revealed that the muscle synergies are able to document an increased activity of sensory-motor afferences leading a more intense role of the forward based mechanism underlying balance control in vestibular patients.

Relevance of orthostatic posturography for clinical evaluation of hip and knee joint arthroplasty patients.

In order to verify whether orthostatic posturography (OP) can support clinical assessment of total hip (THA) and knee arthroplasty (TKA), 81 subjects with THA and 100 with TKA were recruited and compared with 59 healthy volunteers. All patients were tested one or two days prior to surgery; 42 subjects (20 THA and 22 TKA) were tested again after six months, and 34 (14 THA and 20 TKA) yet again after 12 months. OP was performed using a Kistler 9286A piezoelectric force plate and the following postural parameters (PPs) were adopted on account of their functional meaning: mean velocity and the root mean square of the distance of the centre of pressure (CoP), sway area, and 95% of the CoP power frequency. Eye condition and fatigue related to the test duration were also examined. The three most meaningful PPs were identified and a logarithmic transformation was then applied to these, as well as standardization. Almost all the PP values were higher preoperatively in the patients as compared with the healthy subjects and it was possible to detect many statistically significant differences between patients and healthy subjects. However, when examining the 181 subjects at the preoperative stage, the PPs did not show congruence with the clinical scores as well as they did during follow-up. Therefore, the use of the OP is not recommended to monitor patients undergoing THA or TKA.

Online beam monitoring in the treatment of ocular pathologies at the INFN Laboratori Nazionali del Sud-Catania.

A detector (MOPI) has been developed for the online monitoring of the beam at the Centro di AdroTerapia e Applicazioni Nucleari Avanzate (CATANA), where shallow tumours of the ocular region are treated with 62 MeV protons. At CATANA the beam is passively spread to match the tumour shape. The uniformity of the delivered dose depends on beam geometrical quantities which are checked before each treatment. However, beam instabilities might develop during the irradiation affecting the dose distribution. This paper reports on the use of the MOPI detector to measure the stability of the beam profile during the irradiation in the clinical practice. The results obtained in the treatment of 54 patients are also presented.

Cost function tuning improves muscle force estimation computed by static optimization during walking.

Muscle force estimation while a dynamic motor task is carried out still presents open questions. In particular, concerning locomotion, although the inverse dynamic based static optimization has been widely accepted as a suitable method to obtain reliable results, appropriate modifications of the object function may improve results. This paper was aimed at analyzing the sensitivity of estimated muscle forces when modifications of the objective function are adopted to better fit EMG signals of healthy subjects. A 7 links and 9 degrees of freedom biomechanical model accounting for 14 lower limb muscles, grouped in 9 equivalent actuators, was developed. Muscle forces were estimated by using the inverse dynamic based static optimization in which the performance criteria was the sum of muscle stresses raised to a certain n power. This exponent was gradually changed (from 2 to 100) and the agreement between force patterns and EMG signals was estimated by both the correlation coefficient and the Coactivation Index. Results suggested that force estimation can be improved by slightly modifying the cost function. In particular, with respect to adopted data, when the exponent belong to the interval between 2.75 and 4, estimated forces better captured general features of EMG signals. Concluding, a more reliable solution can be obtained by suitably tuning the cost function in order to fit EMG signals.

Evaluation of leg joint trajectories while carrying out passive manipulation by NEUROBike.

During the last decades, many robotic platforms aimed at post-stroke neurorehabilitation of locomotion have been developed. These devices have been designed to enhance the possibilities of conventional rehabilitation providing safe, highly accurate, intensive and prolonged treatments. Nevertheless, up to now, robotic aided therapy has not yet promoted improvements of the motor performance significantly greater than those achieved by the conventional therapy. According to previous studies, we believe that this result may be partially ascribed to two main issues: the rehabilitation mediated by robots is usually provided too late from the trauma and it mainly consists of passive and cyclic manipulation of the legs. Our proposal to overcome some of the supposed limits is NEUROBike, an operative mechatronic platform able to lead leg manipulation as soon as possible after the trauma, that is when patients still lie on their own beds. Moreover, NEUROBike has been designed to provide both passive and cyclic manipulation of leg joints with trajectories similar to those related to natural walking, and motor task involving random efforts. This work presents the comparison between desired and measured leg joint trajectories while NEUROBike provides cyclic and passive leg manipulation. The results show that angular excursions at proximal joints were reasonably comparable with those obtained by the velocity based model even though they were affected by a positive offset involving emphasized flexion of hip and knee during the gait cycle.

Heuristic optimization of the scanning path of particle therapy beams.

Quasidiscrete scanning is a delivery strategy for proton and ion beam therapy in which the beam is turned off when a slice is finished and a new energy must be set but not during the scanning between consecutive spots. Different scanning paths lead to different dose distributions due to the contribution of the unintended transit dose between spots. In this work an algorithm to optimize the scanning path for quasidiscrete scanned beams is presented. The classical simulated annealing algorithm is used. It is a heuristic algorithm frequently used in combinatorial optimization problems, which allows us to obtain nearly optimal solutions in acceptable running times. A study focused on the best choice of operational parameters on which the algorithm performance depends is presented. The convergence properties of the algorithm have been further improved by using the next-neighbor algorithm to generate the starting paths. Scanning paths for two clinical treatments have been optimized. The optimized paths are found to be shorter than the back-and-forth, top-to-bottom (zigzag) paths generally provided by the treatment planning systems. The gamma method has been applied to quantify the improvement achieved on the dose distribution. Results show a reduction of the transit dose when the optimized paths are used. The benefit is clear especially when the fluence per spot is low, as in the case of repainting. The minimization of the transit dose can potentially allow the use of higher beam intensities, thus decreasing the treatment time. The algorithm implemented for this work can optimize efficiently the scanning path of quasidiscrete scanned particle beams. Optimized scanning paths decrease the transit dose and lead to better dose distributions.