Computer- and robot-assisted Medical Intervention

Medical robotics includes assistive devices used by the physician in order to make his/her diagnostic or therapeutic practices easier and more efficient. This chapter focuses on such systems. It introduces the general field of Computer-Assisted Medical Interventions, its aims, its different components and describes the place of robots in that context. The evolutions in terms of general design and control paradigms in the development of medical robots are presented and issues specific to that application domain are discussed. A view of existing systems, on-going developments and future trends is given. A case-study is detailed. Other types of robotic help in the medical environment (such as for assisting a handicapped person, for rehabilitation of a patient or for replacement of some damaged/suppressed limbs or organs) are out of the scope of this chapter.Comment: Handbook of Automation, Shimon Nof (Ed.) (2009) 000-00

Online adaptive planning methods for intensity-modulated radiotherapy

Online adaptive radiation therapy aims at adapting a patient's treatment plan to their current anatomy to account for inter-fraction variations before daily treatment delivery. As this process needs to be accomplished while the patient is immobilized on the treatment couch, it requires time-efficient adaptive planning methods to generate a quality daily treatment plan rapidly. The conventional planning methods do not meet the time requirement of online adaptive radiation therapy because they often involve excessive human intervention, significantly prolonging the planning phase. This article reviews the planning strategies employed by current commercial online adaptive radiation therapy systems, research on online adaptive planning, and artificial intelligence's potential application to online adaptive planning.<br/

ESTRO-ACROP guideline on surface guided radiation therapy

Surface guidance systems enable patient positioning and motion monitoring without using ionising radiation. Surface Guided Radiation Therapy (SGRT) has therefore been widely adopted in radiation therapy in recent years, but guidelines on workflows and specific quality assurance (QA) are lacking. This ESTRO-ACROP guideline aims to give recommendations concerning SGRT roles and responsibilities and highlights common challenges and potential errors. Comprehensive guidelines for procurement, acceptance, commissioning, and QA of SGRT systems installed on computed tomography (CT) simulators, C-arm linacs, closed-bore linacs, and particle therapy treatment systems are presented that will help move to a consensus among SGRT users and facilitate a safe and efficient implementation and clinical application of SGRT. Keywords: ACROP; ESTRO; Guideline; SGRT; Surface guided radiation therapy

Assessment of and improvements to a stereophotogrammetric patient positioning system for proton therapy

Summary in English.Bibliography: pages 125-129.This thesis describes the construction and use of the facemask at the National Accelerator Centre (NAC) as used to both immobilise and position patients for precision proton radiotherapy. The precision achieved using the stereophotogrammetric (SPG) positioning system is measured, and the shortcomings and errors in using the facemask by the SPG system are measured and analysed. The implementation of improvements made to the SPG system is reported upon, and alternative means of both supporting the fiducial markers and immobilising the patient are investigated and evaluated. The accuracy of positioning a facemask using the SPG system is 1.4 mm and of positioning a newly designed frame is 1.6 mm. These measurements were made without using a patient. It is estimated that the total uncertainty of positioning a patient's tumour at the isocentre is 1.6 (1SD) mm using the facemask and it is estimated that the precision using the frame will be less than this value. The largest component of this error (1.39 mm) is due to the error in obtaining the CT scanner co-ordinates. These results are comparable to those obtained by other investigators. The movement of patient bony landmarks within the facemask was measured to be 1.0 ± 0.8 mm. Three main recommendations are that the CT scanner co-ordinating procedure be improved, the SPG computer program be rewritten in parts to achieve greater speed and accuracy, and that the new frame be used. The frame is easier to manufacture than the facemask and allows real time monitoring of the position of the patient's head by the SPG system thus allowing faster throughput of patients and better positioning quality control

Physical and Clinical Potential of offline PET/CT Imaging after Proton Radiotherapy

Bei der Behandlung von Krebserkrankungen mit Protonenstrahlen können empindliche Gewebestrukturen direkt hinter dem Zielvolumen durch den schnellen Dosisabfall am Ende der Reichweite von Protonen vor Strahlung geschützt werden. Dieser ernorme Vorteil von Protonen wird jedoch nicht immer voll genutzt, da die Behandlungsplanung und -durchführung oft schwer einschätzbare Unsicherheiten beinhaltet. Die erfolgversprechendste In-Vivo-Methode zur nicht invasiven Kontrolle von Protonenstrahlbehandlungen ist die Positron Emissions Tomographie (PET). Positronenemitter, wie zum Beispiel 11C und 15O, werden bei nuklearen Reaktionen entlang des Strahlengangs produziert und können als räumliche Indikatoren für die deponierte Dosis genutzt werden. So lassen sich PET/CT-Messungen als Qualität sichernde Maßnahme zur Überprüfung der tatsächlich verabreichte Dosis und zur Quantifizierung von Unsicherheiten nutzen. In dieser Arbeit werden die physikalischen und klinischen Möglichkeiten von zeitversetzten PET/CT-Messungen zur Behandlungskontrolle untersucht. In einer Phantom-Studie wird die physikalische Reproduzierbarkeit, die Konsistenz und die Sensivität der Methode erkundet. In einer Patienten-Studie wird ihre klinische Leistungsfähigkeit qualitativ und quantitativ betrachtet. Dafür werden Daten von 23 Patienten (9 Patientendatensätze wurden vor, 14 im Rhamen dieser Arbeit gesammelt) mit vielfältigen Tumorerkrankungen unterschiedlicher Art und Lokalitätern analysiert. Es werden Patientenuntergruppen bestimmt, die aus der Anwendung der Methode am meisten profitieren. Darüber hinaus werden technische und methodische Verbesserungen untersucht, die eine breitere Anwendbarkeit von PET/CT-Messungen zur Behandlungskontrolle bei der Strahlentherapie mit Protonen ermöglichen

Optimization of high precision stereotactic body radiotherapy with photons and ions for non-small-cell-lung cancer

This work presents a contribution in two different aspects required for the implementation of scanned-beam particle therapy for lung tumors. The first part of this work investigates the reproducibility of the calculated particle therapy dose distribution for early stage non-small cell lung cancer (NSCLC) tumors in a clinical scenario. These calculations were carried out based on data sets of patients treated with single dose photon stereotactic body radiotherapy (SBRT) under high frequency jet ventilation (HFJV) in order to achieve near-total tumor fixation. A dosimetric evaluation of calculated proton and carbon ion plans was performed, to fulfill clinical plan acceptance criteria with emphasis on target coverage. By simulating the inter-fractional anatomical changes in a short time scale between planning and delivery-time anatomies as imaged by the planning and localization computed tomography (CT) data sets, we carried out an investigation of the deterioration in target coverage. The anatomical changes (e.g. tumor position, patient setup) were quantified through water equivalent path length (WEPL) calculations within the beam entrance channels and correlated with the loss in dosimetric coverage. In addition, we identified beam and planning settings, which also help to reduce dosimetric deterioration, such as best choice of beam angle, higher number of beams, larger spot sizes and larger allowances for beam spots outside the target. We demonstrated reproducible tumor fixations through HFJV. Such technique warranted excellent target coverage in proton SBRT in the majority of the investigated patients. However, for a minor number of cases, unacceptable dosimetric deviations were observed, illustrating the need for imaging prior to each dose delivery with dedicated protocols, together with the development of intervention thresholds in case of anatomical discrepancies based on their potential impact on the dose distribution. HFJV seems a suitable technique to reduce interplay effects. Newer assisted ventilation techniques which do not require use of anesthesia might be more suitable for fractionated radiotherapy. Biological treatment planning for carbon ion therapy requires a model of the radiobiological effects of high linear energy transfer (LET) radiation. One approach in the context of scanned beam ion therapy is built upon the local effect model (LEM). Within this approach, the description of the radiosensitivity and the behavior versus fractionated photon radiotherapy of both tumor and normal tissue requires input of α/β ratios, usually obtained from in vitro studies. Obtaining tumor-specific, realistic, clinical α/β values is urgently required. This topic is also relevant in hypofractionated photon radiotherapy, where there is an ongoing discussion, if the linear-quadratic (LQ) model represents adequately dose responses at high doses per fraction or if the linear-quadratic-linear (LQ-L) correction is necessary, and which α/β ratio describes better the fractionation effect for NSCLC tumors. The second part of this work presents a review of local control data of early stage NSCLC and models of these dose response data using the LQ and LQ-L approaches. Both, the LQ and LQ-L models can be fitted to clinical normo- and hypofractionated NSCLC outcome data. The LQ-L model yielded a significant value for the Dt of 11.0 Gy for the model based on biologically effective dose (BED) at the isocenter with α/β equal to 10 Gy for the full hypofractionation range; it produced a comparable tumor control probability (TCP) fit to the LQ model. We found a clear dose-effect relationship, which in the high BED region was weaker due to considerable dispersion in the data. For the application of BED (α/β=10 Gy) in the range of 100–150 Gy in three fractions or more, the differences in isoeffects predicted by both models can be neglected. Our findings therefore do not allow us to suggest use of the LQ-L model for an improved fitting compared to the LQ model of local control data in case of hypofractionation. A tentative analysis to establish the optimal α/β ratio in the frame of the LQ model for the full fractionation range did not produce significant estimates, although it showed a trend for α/β values lower than 10 Gy

Treatment plan robustness in pancreatic patients treated with scanned ion-beam therapy: Inter- and intra-fractional aspects

Pancreatic cancer is still an unsolved oncological challenge, however radiotherapy with charged particles has been considered a promising approach to improve the patients overall survival. These patients might benefit from dose escalation, although uncertainties during the beam delivery (intra-fractional) or along the treatment course (inter-fractional) can compromise the accuracy of the treatment. In this thesis, inter- and intra-fractional anatomy changes are explored in order to define the potential source of uncertainties, quantify their effect, and to define strategies towards their reduction. Anatomical changes along the course of the treatment showed to lead target under-dosages up to 20% and an increase in the dose to the normal tissues. However, this can be lowered through the selection of beam arrangements from the patient's posterior side and beam-specific margins. From the results of this work, it was concluded that a combination of an Internal Target Volume (ITV), obtained by a geometric expansion of 3 mm from the Clinical Target Volume (CTV), and two oblique posterior beams can reduce the mean V95CTV variations to less than 1%. For other beam directions, the calculation of ITVs including the water-equivalent path length (WEPL), suggested the need for a CTV asymmetric expansion in depth, and minimal in lateral beam direction. Additionally, weekly monitoring of the patient anatomy using computed tomography (CT) might easily be included in the clinical workflow and will assist in the decision of treatment re-planning, when substantial anatomical changes occur. The suggested prediction model was based on the variations of the accumulated WEPL (∆accWEPL) relative to the planning CT, and showed a strong correlation between the ∆accWEPL and the gamma index of the dose distributions. The gamma criterion was selected as dose distribution quality metric, since it includes dosimetric changes in the target and normal tissues. Regarding intra-fractional variations, the induced breathing motion together with a dynamic beam delivery, affect the dose distribution in terms of homogeneity and target coverage. This effect is stronger (∆V95CTV > 10%) for patients with a tumor motion amplitude superior to 5 mm and a highly modulated dose distribution intra- and inter-fields. The concept of modulation index was employed, it showed that different optimisers produce plans with contrasting distribution of the number of particles, resulting in unlike robustness against range and positioning uncertainties. It was concluded that under internal motion, the use of homogeneous plans, multiple beams, and geometric ITVs, originated dose distributions exhibiting a slight mean decrease of the dose homogeneity (H_CTV) and V95CTV of 4% and 1%, respectively. Finally, a first approach to the use of 4D-Magnetic Resonance Imaging (MRI) for motion detection was performed. The results revealed cases of non-linear correlation between the breathing signal (diaphragm position) and the pancreas motion, and variability of the motion amplitude along the acquisition time and between sessions. This reinforces the need of an alternative method, comparative to the use of external surrogates, for simulation of a 4D dose distribution. Therefore, MRI will allow to include baseline drifts, amplitude variations and anatomical alterations in the 4D dose distribution assessment. In summary, the key for a precise delivery of the treatment is the monitoring of anatomical changes, and a prompt reaction in order to minimise or eliminate potential uncertainties. In future, it is expected that the methods suggested in this thesis, the experience gained at HIT on treating moving organs and, the developments in treatment planning and treatment delivery will allow us to move towards the robust plan optimisation, prediction of changes in the dose distribution, and enable treatment without a constant and complex monitoring of the patient's movement