Simulaciones Monte Carlo para radioterapia intraoperatoria con haces de electrones

Intraoperative Radiation Therapy (IORT) is a special modality for cancer treatment that combines radiation therapy with surgery. This technique delivers a single high dose of radiation directly to the tumor bed, during surgery right after tumor resection (Palta et al. 1995, Lamana et al. 2012, Calvo et al. 2006, Beddar et al. 2006). The objective is to achieve a higher dose in the target volume, while minimal exposure of surrounded tissues is granted either by displacing them or by shielding them with attenuation plates that protect organs at risk (Russo et al. 2012). Therefore, IORT facilitates an integrated approach to the multidisciplinary treatment of cancer and emphasises the interaction between surgery and radiotherapy in three principal aspects: reducing the chance of residual disease at the site of surgery by eliminating microscopic tumor foci, maximizing the radiobiological effect of a single high dose of irradiation with attainment of total dosage levels that exceed those of standard conformal external beam irradiation and optimizing the timing of the combined surgery and radiotherapy with earlier irradiation. Nevertheless, currently, one of the main limitations in IORT lies in the difficulties that the planning process entails, which limits the widespread of this technique (Pascau et al. 2012, Lamanna et al. 2012)]. The retraction of the structures of the patient and the removal of affected tissues modify his/her geometry. Therefore, it is difficult to carry out a feasible dosimetry calculation from pre-operative images. In addition, as IORT is an invasive technique that introduces an applicator to reach the tissues to be irradiated, the operatory area has to be adapted in order to reach an ideal position of the remaining parts of the tumor. Therefore, it is difficult to plan the radiotherapy process beforehand because the surgeons must choose during surgery the cone dimension, its positioning, the bevel angle and the electron beam ́s energy according to their medical and surgical experience and the information gathered during the procedure..

Validation of a phase space determination algorithm for intraoperative radiation therapy

Monte-Carlo (MC) methods are a valuable tool for dosimetry in radiotherapy, including Intra-Operative Electron Radiotherapy (IOERT), since effects such as inhomogeneities or beam hardening may be realistically reproduced

Optimization of Monte Carlo code for clinical simulation of electron beams

The aim of this work is to optimize a Monte Carlo (MC) kernel for electron radiation therapy (IOERT) compatible with intraoperative usage and to integrate it within an existing IOERT dedicated treatment planning system (TPS

Iterative determination of clinical beam phase space from dose measurements

Monte Carlo (MC) method can accurately compute the dose produced by medical linear accelerators. However, these calculations require a reliable description of the electron and/or photon beams delivering the dose, the phase space (PHSP), which is not usually available. A method to derive a phase space model from reference measurements that does not heavily rely on a detailed model of the accelerator head is presented. The iterative optimization process extracts the characteristics of the particle beams which best explains the reference dose measurements in water and air, given a set of constrain

Feasibility assessment of the interactive use of a Monte Carlo algorithm in treatment planning for intraoperative electron radiation therapy

This work analysed the feasibility of using a fast, customized Monte Carlo (MC) method to perform accurate computation of dose distributions during pre- and intraplanning of intraoperative electron radiation therapy (IOERT) procedures. The MC method that was implemented, which has been integrated into a specific innovative simulation and planning tool, is able to simulate the fate of thousands of particles per second, and it was the aim of this work to determine the level of interactivity that could be achieved. The planning workflow enabled calibration of the imaging and treatment equipment, as well as manipulation of the surgical frame and insertion of the protection shields around the organs at risk and other beam modifiers. In this way, the multidisciplinary team involved in IOERT has all the tools necessary to perform complex MC dosage simulations adapted to their equipment in an efficient and transparent way. To assess the accuracy and reliability of this MC technique, dose distributions for a monoenergetic source were compared with those obtained using a general-purpose software package used widely in medical physics applications. Once accuracy of the underlying simulator was confirmed, a clinical accelerator was modelled and experimental measurements in water were conducted. A comparison was made with the output from the simulator to identify the conditions under which accurate dose estimations could be obtained in less than 3 min, which is the threshold imposed to allow for interactive use of the tool in treatment planning. Finally, a clinically relevant scenario, namely early-stage breast cancer treatment, was simulated with pre- and intraoperative volumes to verify that it was feasible to use the MC tool intraoperatively and to adjust dose delivery based on the simulation output, without compromising accuracy. The workflow provided a satisfactory model of the treatment head and the imaging system, enabling proper configuration of the treatment planning system and providing good accuracy in the dosage simulation