Simulaciones Monte Carlo para radioterapia intraoperatoria con haces de electrones

Abstract

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...