Grisel Mora

University of Lisbon | UL · Faculty of Science

Abstract Purpose Gamma-ray stereotactic radiosurgery systems available commercially contain either stationary or rotational source configuration. Rotational systems reduce the number of sources utilized and can also provide beneficial dosimetric properties. In this study, we explore the dosimetric advantage of a novel rotating gamma-ray design for...

Purpose The trend today in modern radiation therapy is toward conformal therapy with segmented or moving field techniques. Generally, this requires multifield irradiation or the use of arc/rotation therapy. Many authors have pointed out in literature that if the Co-60 machines were modernized with state of the art devices, it may be able to provide...

Purpose: Stereotactic radiosurgery with Gamma ray systems (GRS) has been very successful in treating many intracranial patients. However, the cone collimation utilized in those systems makes treatment of some lesions challenging owing to their complex irregular shapes. In this study we explore the dosimetric advantage of a novel rotating GRS equipp...

Introduction A new design of Gamma Knife consist of 30 ⁶⁰C0 source capsules, two circular primary collimators (diameter of 6.60 mm and 6.10 mm) and four different changeable collimators. The sources (diameter of 2.8 mm) are distributed in six groups of five sources in the spherical geometry. Each source is individually collimated to obtain four dif...

Purpose:Dose-volume-histogram (DVH) is widely used for plan evaluation in radiation treatment. The concept of dose-mass-histogram (DMH) is expected to provide a more representative description as it accounts for heterogeneity in tissue density. This study is intended to assess the difference between DVH and DMH for evaluating treatment planning qua...

Purpose:Stereotactic intra and extra-cranial body radiation therapy has evolved with advances in treatment accuracy, effective radiation dose, and parameters necessary to maximize machine capabilities. Novel gamma systems with a ring type gantry were developed having the ability to perform oblique arcs. The aim of this study is to explore the dosim...

Co-60 beams have unique dosimetric properties for cranial treatments and thoracic cancers. The conventional concern about the high surface dose is overcome by modern system designs with rotational treatment techniques. This work investigates a novel rotational Gamma ray system for image-guided, external beam radiotherapy. The CybeRT system (Cyber M...

Co-60 beams have unique dosimetric properties that are ideally suited for cranial treatments. Co-60 sources with cone-shaped collimators provide conformal dose distributions allowing for ablative treatments with rapid dose falloff to spare nearby critical structures. This work investigates a novel, image-guided, rotational Gamma ray system that pro...

A new modernized design for cobalt 60 (Co-60) machines is being developed with a ring type gantry. In this study we investigate the beneficial outcome of the new design for conformal arc therapy for various clinical sites. The new modality was evaluated based on isodose distributions and dose volume histograms as compared to 6MV photon beams from c...

Introduction: The 60 Co beam emerging from the Gamma- Tomo source assembly was simulated in a previous study [1] and the authors reported the spectra of particles reaching the plane immediately (1mm) before the collimation system entrance. In the present work, we simulate the 60Co beam emerging from a novel Gamma-Tomo SBRT collimation system and ca...

Purpose: to determine the characteristics of the 60Co beam emerging from a new design of a rotating Gamma Knife system and to calculate 3D dose distributions at the isocenter for different source configurations and collimator openings. Methods: We employed the BEAM-Monte Carlo code to realistically model the geometry design, including 30 60Co sourc...

Purpose: Estimation of Cerenkov dose from high-energy megavoltage photon and electron beams in tissue and its impact on the radiosensitization using Protoporphyrine IX (PpIX) for tumor targeting enhancement in radiotherapy. Methods: The GEPTS Monte Carlo code is used to generate dose distributions from 18MV Varian photon beam and generic high-energ...

Purpose: Modulated electron radiotherapy (MERT) has the potential to achieve better treatment outcome for shallow tumors such as those of breast and scalp. In a separate study with scalp lesions, MERT was compared to volumetric modulated arc therapy. Our results showed a reduction in the dose reaching the brain with MERT. However dose calculation a...

Purpose To simulate the 60Co beam from a novel Gamma—Tomo SBRT system and to calculate the output factors and dose rates for different source configurations and collimator sizes. Methods The BEAM-Monte Carlo code is used to realistically model the system geometry, including 32 source capsules, source housing, primary collimator and 4 different cha...

This study evaluates the dosimetric impact caused by an air cavity located at 2 mm depth from the top surface in a PMMA phantom irradiated by electron beams produced by a Siemens Primus linear accelerator. A systematic evaluation of the effect related to the cavity area and thickness as well as to the electron beam energy was performed by using Mon...

Purpose: The use of DMH as an alternative method to validate the treatment plans of the head and neck region has been investigated in the past[1].For patient geometry contains large air cavities,high statistical uncertainties were found in dose distributions calculated using MC method in air cavities and tissues that surround air cavities.These pr...

Monte Carlo (MC) dose calculation algorithms have been widely used to verify the accuracy of intensity-modulated radiotherapy (IMRT) dose distributions computed by conventional algorithms due to the ability to precisely account for the effects of tissue inhomogeneities and multileaf collimator characteristics. Both algorithms present, however, a pa...

Purpose: Previous studies [1] demonstrated that Dose Volume Histogram (DMH) is a better parameter than DVH for evaluating treatment plans calculated by Monte Carlo(MC) simulations that may have large statistical uncertainties in low‐density regions such as air cavities and lungtissues. On other hand, it has been showed [2] that the voxel size may a...

In the present work, we studied the effect of a multileaf collimator (MLC) on the build-up region. Ionization measurements (PDI) were performed in a water phantom for a 6 MV photon beam emerging from a Varian 2100C/D accelerator with a 120 – MILLENIUM MLC. We used two different detectors: a PTW 31002 cylindrical ionization chamber (IC) and a Roos p...

Purpose:Dose volume histograms (DVH) represent an important tool for the clinical evaluation of radiotherapy treatment plans. For head and neck regions, however, the presence of air cavities makes the DVH tool less adequate for Monte Carlo calculated IMRT plans. The air cavities may introduce high dose uncertainties in both air cavities and surroun...

Previous Monte Carlo studies have investigated the multileaf collimator (MLC) contribution to the build-up region for fields in which the MLC leaves were fully blocking the openings defined by the collimation jaws. In the present work, we investigate the same effect but for symmetric and asymmetric MLC defined field sizes (2×2, 4×4, 10×10 and 3×7 c...

The conversion of computed tomography (CT) numbers into material composition and mass density data influences the accuracy of patient dose calculations in Monte Carlo treatment planning (MCTP). The aim of our work was to develop a CT conversion scheme by performing a stoichiometric CT calibration. Fourteen dosimetrically equivalent tissue subsets (...

The ability of CT (Computer Tomography) to measure the distribution of absorption coefficient in the patient body opens up the possibility of improving the accuracy of the dose calculation. On the other hand, the implementation of the Monte Carlo (MC) techniques in the treatment planning system is becoming a practical possibility [1]. The actual tr...

from Grisel Mora

from Grisel Mora

The BEAM Monte Carlo code is used to simulate the 60Co beam from an Eldorado 6 radiotherapy unit and to calculate the relative air-kerma output factors as a function of field size. The unit is realistically modeled, including source capsule, housing and collimator assembly. The calculated relative air-kerma output factors at SSD=80.5 cm agree to wi...