Dose distribution changes with shielding disc misalignments and wrong orientations in breast IOERT: a Monte Carlo – GEANT4 and experimental study

Abstract

One of the most relevant risks in breast intraoperative electron radiotherapy (IOERT) is the incorrect positioning of the shielding disc. If such a setup error occurs, the treatment zone could receive a nonuniform dose delivery, and a considerable part of the electron beam could hit — and irradiate — the patient's healthy tissue. However misalignment and tilt angle of the shielding disc can be evaluated, but it is not possible to measure the corresponding in vivo dose distribution. This led us to develop a simulation using the Geant4 Monte Carlo toolkit to study the effects of disc configuration on dose distribution. Some parameters were investigated: the shielding factor (SF), the radiation back scattering factor (BSF), the volume–dose histogram in the treatment zone, and the maximum leakage dose (MLD) in normal tissue. A lateral shift of the disc (in the plane perpendicular to the beam axis) causes a decrease in SF (from 4% for a misalignment of 5 mm to 40% for a misalignment of 40 mm), but no relevant dose variations were found for a tilt angle until 10°. In the same uncorrected disc positions, the BSF shows no significant change. MLD rises to 3.45 Gy for a 14 mm misalignment and 4.60 Gy for 30° tilt angle when the prescribed dose is 21 Gy. The simulation results are compared with the experimental ones, and allow an a posteriori estimation of the dose distribution in the breast target and underlying healthy tissue. This information could help the surgical team choose a more correct clinical setup, and assist in quantifying the degree of success or failure of an IOERT breast treatment.PACS number: 87.53.Jw, 87.55.dk, 87.55.Gh, 87.55.K‐, 87.55.N‐

Comparing the dosimetric characteristics of the electron beam from dedicated intraoperative and conventional radiotherapy accelerators

“…Intraoperative radiation therapy (IORT) is designed to deliver a high single fraction of radiation dose to the patient after surgery and under anesthesia (1‐3) . There are three different methods to perform this kind of radiotherapy: IOERT, HDR‐IORT, and Low KV IORT, (4,5) of which, IOERT is the most popular, because of the desired dose distribution, (6) limited penetration of the electron beam, and treatment time.…”

In vivo dosimetry and shielding disk alignment verification by EBT3 GAFCHROMIC film in breast IOERT treatment

“…In vivo dosimetry (IVD) is particularly needed in IORT because of the absence of software systems of treatment planning based on computed tomography. (2,3) As described in recent studies, (4,5) the setup of normal tissue protection and applicator placement are closely correlated with two very relevant risks in IOERT treatments: misalignment and wrong orientation of the shielding disk.…”

Dosimetry for electron Intra-Operative RadioTherapy: Comparison of output factors obtained through alanine/EPR pellets, ionization chamber and Monte Carlo-GEANT4 simulations for IORT mobile dedicate accelerator

“…We used a web version Geant4 application, named iort_therapy, and developed by IBFM-CNR-LATO researchers. The software was published in the advanced examples of the official Geant4 release (from 9.5 version) and today it is available by users on the Italian Grid Infrastructure (IGI) through the Catania Science Gateway [32,33].…”

“…Moreover, in the last years there is an increasing interest in evaluating dose distributions for IORT treatments through Monte Carlo (MC) simulations [32,33]. Indeed, a Geant4 Monte Carlo toolkit iort_therapy has been developed with the aims at calculating dose distribution curves in water or other materials, investigating different clinical setups, and studying various radioprotection devices [32].…”

“…Indeed, a Geant4 Monte Carlo toolkit iort_therapy has been developed with the aims at calculating dose distribution curves in water or other materials, investigating different clinical setups, and studying various radioprotection devices [32].…”