Roberta Castriconi

Dose–response of EBT3 radiochromic films to proton and carbon ion clinical beams

We investigated the dose-response of the external beam therapy 3 (EBT3) films for proton and carbon ion clinical beams, in comparison with conventional radiotherapy beams; we also measured the film response along the energy deposition-curve in water. We performed measurements at three hadrontherapy centres by delivering monoenergetic pencil beams (protons: 63-230 MeV; carbon ions: 115-400 MeV/u), at 0.4-20 Gy dose to water, in the plateau of the depth-dose curve. We also irradiated the films to clinical MV-photon and electron beams. We placed the EBT3 films in water along the whole depth-dose curve for 148.8 MeV protons and 398.9 MeV/u carbon ions, in comparison with measurements provided by a plane-parallel ionization chamber. For protons, the response of EBT3 in the plateau of the depth-dose curve is not different from that of photons, within experimental uncertainties. For carbon ions, we observed an energy dependent under-response of EBT3 film, from 16% to 29% with respect to photon beams. Moreover, we observed an under-response in the Bragg peak region of about 10% for 148.8 MeV protons and of about 42% for 398.9 MeV/u carbon ions. For proton and carbon ion clinical beams, an under-response occurs at the Bragg peak. For carbon ions, we also observed an under-response of the EBT3 in the plateau of the depth-dose curve. This effect is the highest at the lowest initial energy of the clinical beams, a phenomenon related to the corresponding higher LET in the film sensitive layer. This behavior should be properly modeled when using EBT3 films for accurate 3D dosimetry.

Dose Volume Distribution in Digital Breast Tomosynthesis: A Phantom Study

Monte Carlo (MC) calculations for breast dosimetry in digital breast tomosynthesis (DBT) require experimental validations. We measured the 3-D dose distribution in breast phantoms, using XR-QA2 radiochromic films, compared to dose maps obtained with a previously validated MC code. Film sheets were positioned at the entrance surface, at the bottom surface as well as at four depths between adjacent slabs in the five-slabs 50-mm-thick phantoms simulating a compressed breast. We employed a homogeneous PMMA phantom, for the method validation, and a heterogeneous (BR 50/50) phantom for a preliminary study in a complex breast phantom. Irradiations were made at 40 kV at ±25° and 0° in craniocaudal view. A continuous scan over 15° was carried out for the homogeneous phantom. In the direction of the beam axis the dose decreases down to 12% of the entrance value. In the transverse planes, the dose varies up to 17%; in the heterogeneous phantom, it decreases to 25% in the direction of the beam axis. In transverse planes the maximum dose variations are up to 18% at

Evaluation of the BreastSimulator software platform for breast tomography.

{\theta = 0^\circ }

Image Quality and Radiation Dose in Propagation Based Phase Contrast Mammography with a Microfocus X-ray Tube: A Phantom Study

, whereas the dose varies up to 22% in angular views. The simulations agreed with the measured values within the measurement uncertainties.

In-line phase contrast tomography of the breast with a dedicated micro-CT scanner

The aim of this work was the evaluation of the software BreastSimulator, a breast x-ray imaging simulation software, as a tool for the creation of 3D uncompressed breast digital models and for the simulation and the optimization of computed tomography (CT) scanners dedicated to the breast. Eight 3D digital breast phantoms were created with glandular fractions in the range 10%-35%. The models are characterised by different sizes and modelled realistic anatomical features. X-ray CT projections were simulated for a dedicated cone-beam CT scanner and reconstructed with the FDK algorithm. X-ray projection images were simulated for 5 mono-energetic (27, 32, 35, 43 and 51 keV) and 3 poly-energetic x-ray spectra typically employed in current CT scanners dedicated to the breast (49, 60, or 80 kVp). Clinical CT images acquired from two different clinical breast CT scanners were used for comparison purposes. The quantitative evaluation included calculation of the power-law exponent, β, from simulated and real breast tomograms, based on the power spectrum fitted with a function of the spatial frequency, f, of the form S(f)  =  α/f   β . The breast models were validated by comparison against clinical breast CT and published data. We found that the calculated β coefficients were close to that of clinical CT data from a dedicated breast CT scanner and reported data in the literature. In evaluating the software package BreastSimulator to generate breast models suitable for use with breast CT imaging, we found that the breast phantoms produced with the software tool can reproduce the anatomical structure of real breasts, as evaluated by calculating the β exponent from the power spectral analysis of simulated images. As such, this research tool might contribute considerably to the further development, testing and optimisation of breast CT imaging techniques.

Volume dose distribution in digital breast tomosynthesis: A phantom study

Digital mammography has limitations in sensitivity, in particular for patients with a dense breast. Phase contrast techniques phase contrast mammography, PCM might increase the tissue contrast for breast imaging. Propagation based PCM with a dedicated 0.1-mm-focal spot size mammography unit was investigated in past years, showing higher image quality in magnification PCM than in absorption based DM. In this work the authors investigated, using breast phantoms, the dependence of image quality on increasing mean glandular dose with a 0.007-mm-focal spot size W-anode microfocus X-ray tube. They compared PCM imaging magnification Mi¾?i¾?i¾?2 to absorption based contact imaging Mi¾?i¾?i¾?1 and then to phase retrieval for phase imaging, at low 40 kV as well as high 80 kV beam energy. Phase imaging shows higher image contrast for glandular masses and microcalcifications with MGD similar to one-view mammography. The phase contrast power spectrum assumes higher values than for absorption imaging. Possibility of dose reduction was suggested by the adoption of phase retrieval PCM.

A.34 – Characterization of the energy dependent response of EBT3 radiochromic film to proton and carbon ion beams

We performed laboratory investigations of the image quality for in-line phase contrast micro tomography dedicated to the breast, using a 3D breast phantom. We employed the cone-beam, microfocus (7-micrometer focal spot size) computed tomography (CT) scanner developed in-house for investigation of high resolution, absorption based, and phase contrast based, X-ray imaging of the breast for cancer diagnosis, at dose levels comparable to two-view mammography. CT slices were reconstructed (FDK algorithm) from phase contrast projection images as well as from phase retrieved projections (ANKAphase algorithm), under the assumption of spatially uniform distribution in the object volume of the ratio of the X-ray optical coefficients of the sample material, at the effective energy of the X-ray beam (80 kV, HVL = 6.11 mm Al). Microcalcifications were best visible after phase retrieval, down to 0.23 mm size.

[OA192] Kilovoltage rotational radiotheraphy with the marix/brixs source for partial breast irradiation

Monte Carlo calculations for breast dosimetry in Digital Breast Tomosynthesis (DBT) may require experimental validations, e.g. via the assessment of the calculated and measured dose volume distribution in the breast. This might also take into account any uneven distribution of the beam intensity in the entrance plane, not usually considered in Monte Carlo simulations, e.g. as determined by the heel effect. We measured the 3D dose distribution in a breast phantom, using XR-QA2 radiochromic films calibrated in free-in-air air kerma. Film sheets were positioned at the entrance surface, at the bottom surface as well as at four depths between adjacent slabs in the 5-slabs, 5-cm-thick phantom simulating a compressed breast with 50% glandular fraction. By varying the irradiation angle, the basic requirements of a DBT scan were simulated. The irradiations were made at 40 kV (HVL 1.1 mm Al) for three angular positions of the beam central axis (θ = ±25 deg and θ = 0 deg normal incidence, simulating a craniocaudal view). Results show that it is possible to determine the transverse and longitudinal distribution of the average dose in the phantom (in terms of kerma in simulated breast tissue 50/50 normalized to the entrance kerma), showing the angular dependence of the depth-resolved dose. In the direction of the beam axis, the dose decreases down to about 26% of the entrance value without the phantom. The backscatter fraction was 8%. In transverse planes the maximum dose variations are between 6% and 18% at θ = 0 deg, whereas the dose varies up to 22% in angular views.