Towards unlocking the full potential of Multileaf Collimators

International audienceA central problem in the delivery of intensity-modulated radiation therapy (IMRT) using a multileaf collimator (MLC) relies on fi nding a series of leaves confi gurations that can be shaped with the MLC to properly deliver a given treatment. In this paper, we analyse, from an algorithmic point of view, the power of using dual-layer MLCs and Rotating Collimators for this purpose

Static and dynamic beam intensity modulation in radiotherapy using a multileaf collimator

Investigations on computer optimization of radiotherapy treatment planning (inverse planning) have demonstrated that dose distributions can often be conformed tightly to a target volume by customizing the beam intensity profiles within the treatment field. The aim of this study was the development and clinical implementation of static and dynamic intensity modulated treatment techniques using a multileaf collimator. Using static beam intensity modulation, a technique for penumbra enhancement at the superior and inferior field edges of axial coplanar treatment plans was developed. Due to penumbra enhancement, the length of all treatment fields could be reduced by typically 1.5 cm, while still achieving an adequate dose in the planning target volume. As a result, the dose delivery to critical structures could often be reduced with respect to our (previous) standard treatment without intensity modulation. A dosimetrical study showed that application of this technique in lung treatments could also compensate for the increased lateral secondary electron transport in lung tissue. For calculation of the required leaf motions to generate optimized intensity modulated beam profiles by means of dynamic multileaf collimation an algorithm was developed that fully avoids tongue-and-groove underdosage effects. Dose measurements showed that, using these leaf motions, the accuracy and stability of intensity modulated profiles was generally within 2%. For individual patients, a fast and accurate method for pretreatment verification of each optimized beam was implemented, based on absolute dose measurements with an electronic portal imaging device. Static and dynamic beam intensity modulation is presently applied routinely in our institution for treatment of head and neck cancer patients and prostate cancer patients

Applications of mathematical network theory

This thesis is a collection of papers on a variety of optimization problems where network structure can be used to obtain efficient algorithms. The considered applications range from the optimization of radiation treatment plkans in cancer therapy to maintenance planning for maximizing the throughput in bulk good supply chains

Dose Conformation in Tumor Therapy with External Ionizing Radiation: Physical Possibilities and Limitations

The central problem in tumor irradiation is to deposit a high and spatially uniform dose in the tumor target volume while sparing the surrounding normal tissue as much as possible. The present work investigates how such an adaptation ("conformation") of the spatial dose distribution to arbitrarily shaped target volumes can be achieved, and where the physical limits lie. In particular, the specific possibilities of irradiation with different types of radiation are determined under these aspects, whereby a rough distinction is made between irradiation with charged and uncharged particles. Due to the different mechanisms of radiation-tissue interaction, a conformal dose distribution can be achieved with only one radiation field in the case of heavy charged particles; in the case of uncharged particles, several radiation fields from different directions are required. First, the possibilities and limits of dose conformation are evaluated theoretically. Analytical approximations for modeling dose distributions with uncharged and charged particles are developed. Within the framework of these approximations, the theory of the exponential Radon transform is used to determine the optimal parameters for obtaining a desired dose distribution. It is shown that for an infinite number of radiation fields in the plane, it is possible to adapt the high-dose region to arbitrarily shaped target volumes for both uncharged and charged particles. The dose in a small radiation-sensitive organ at risk in the immediate vicinity of the target volume can be reduced to small scatter contributions. In the case of charged particles, this is also possible for multiple organs at risk. Furthermore, the non-conformal "dose background" is always smaller for charged particles than for uncharged particles. In a more application-oriented chapter, an algorithm is developed for the optimization of dose distributions under practical boundary conditions, i.e. in three dimensions, with finitely many radiation fields and for finite resolutions of the beam shaping devices. To achieve optimal dose distributions, the use of fluence- and (in the case of charged particles) energy-modulated radiation fields is necessary. Especially in the case of uncharged particles, the technical prerequisites for this are not yet available in clinical practice. Therefore, newly developed approaches to fluence modulation for uncharged particles using a dynamically or quasi-dynamically driven "multileaf collimator" are presented. Furthermore, the first phantom experiment is described in which these generalized methods for achieving the best possible conformal dose distribution were realized with high-energy photons (15-MV bremsstrahlung spectrum). The high degree of practically achievable dose conformation is thus verified. Finally, a comparison of the optimized dose distributions achievable with photons and protons is performed for challenging clinical cases where conventional radiotherapy reaches its limits. The most important result is that irradiation with uncharged particles, and in particular with high-energy X-rays, can be optimized in such a way that, in all clinically relevant cases, tumor-conformal dose distributions can be achieved with relatively few (less than ten) radiation fields. The exposure of healthy tissue is naturally higher than for heavy charged particles. However, the tolerance dose values are not exceeded. Exceptions are the rare cases in which the target volume is surrounded on almost all sides by particularly radiation-sensitive risk organs. Only in these cases can a much better result be achieved with the technically more demanding heavy charged particle therapy

Moderne metode radioterapije

The aim of this review article is to present new sophisticated techniques in radiotherapy, which occurred due to the advancement of technology over the past few decades. The paper will provide insight into their advantages and disadvantages, the importance of diagnostic imaging modality, precise contouring, treatment planning and control of patients’ position during radiation treatment. The transition from two-dimensional to three-dimensional radiotherapy has allowed contouring of target volume and organs at risk and accurate information on radiation dosage delivered. With a further desire for more precision and protection of healthy tissues, techniques such as intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) have been developed with the ability to modulate beam intensity. Quality imaging diagnostics is an infallible part of the modern radiotherapy. Image-guided radiotherapy (IGRT) and adaptive radiotherapy enable the delivery of high precision radiation to the target volume and spares organs at risk by correcting interfractional and intrafractional variations. Respiratory gating and tracking technique are useful for tumours that change their position during respiratory cycle. Stereotactic ablative radiotherapy (SABR) is a technique that uses highly conformal high-dose hypofractionated radiation to treat small tumours. In some indication such as the treatment of early stage non small lung cancer, it competes with radical surgery. SABR is also an important therapeutic modality in the management of oligometastatic disease. This paper will briefly discuss proton therapy and its unique physical properties.Cilj ovog preglednog rada je prikazati nove sofisticirane metode radioterapije koje su se razvile zahvaljujući napretku tehnologije unazad par desetljeća. Osvrnut ćemo se na njihove prednosti i nedostatke, važnost slikovne obrade, preciznog konturiranja, planiranja radioterapije i kontrole pozicije pacijenta tijekom radioterapije. Prijelaz s konvencionalne dvodimenzionalne na konformalnu trodimenzionalnu radioterapiju je omogućio konturiranje ciljnog volumena i organa od rizika te praćenje isporučene radioterapijske doze. Daljnjom željom za još većom preciznošću i poštedom zdravih tkiva razvile su se još naprednije tehnike poput radioterapije snopovima promjenjivog intenziteta (IMRT) i volumetrijski modulirane lučne terapije (VMAT) koje imaju mogućnost moduliranja intenziteta snopa. Kvalitetna slikovna dijagnostika je neizostavan dio moderne radioterapije. Radioterapija vođena slikom (IGRT) i adaptivna radioterapija omogućuju isporuku visokopreciznog zračenja na ciljni volumen i poštedu organa od rizika korigiranjem interfrakcionarnih i intrafrakcionarnih varijacija. Gating tehnika i tracking tehnika su korisne kod pomičnih tumora tijekom ciklusa disanja. Stereotaktička ablativna radioterapija (SABR) je tehnika koja koristi visokokonformalno, visokodozno hipofrakcionirano zračenje u liječenju malih tumora. U nekim indikacijama, kao npr. liječenje karcinoma nemalih stanica pluća ranog stadija, ova metoda može zamijeniti kirurški zahvat. Važan je terapijski modalitet u liječenju oligometastatske bolesti. U ovom radu će biti govora i o protonskoj terapiji i njenim jedinstvenim fizikalnim svojstvima