Biomedical subjects

Emiliano Spezi

Publications and source records attributed to Emiliano Spezi.

3 recordsLinked to original sources

PubMed2007

Conversion of CT numbers into tissue parameters for Monte Carlo dose calculations: a multi-centre study.

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 (bins), of which ten bone bins, were created. After validating the proposed CT conversion scheme on phantoms, it was compared to a conventional five bin scheme with only one bone bin. This resulted in dose distributions D(14) and D(5) for nine clinical patient cases in a European multi-centre study. The observed local relative differences in dose to medium were mostly smaller than 5%. The dose-volume histograms of both targets and organs at risk were comparable, although within bony structures D(14) was found to be slightly but systematically higher than D(5). Converting dose to medium to dose to water (D(14) to D(14wat) and D(5) to D(5wat)) resulted in larger local differences as D(5wat) became up to 10% higher than D(14wat). In conclusion, multiple bone bins need to be introduced when Monte Carlo (MC) calculations of patient dose distributions are converted to dose to water.

Biophysical Phenomena↗

PubMed2006

Gamma histograms for radiotherapy plan evaluation.

BACKGROUND AND PURPOSE: The technique known as the 'gamma evaluation method' incorporates pass-fail criteria for both distance-to-agreement and dose difference analysis of 3D dose distributions and provides a numerical index (gamma) as a measure of the agreement between two datasets. As the gamma evaluation index is being adopted in more centres as part of treatment plan verification procedures for 2D and 3D dose maps, the development of methods capable of encapsulating the information provided by this technique is recommended. PATIENTS AND METHODS: In this work the concept of gamma index was extended to create gamma histograms (GH) in order to provide a measure of the agreement between two datasets in two or three dimensions. Gamma area histogram (GAH) and gamma volume histogram (GVH) graphs were produced using one or more 2D gamma maps generated for each slice of the irradiated volume. GHs were calculated for IMRT plans, evaluating the 3D dose distribution from a commercial treatment planning system (TPS) compared to a Monte Carlo (MC) calculation used as reference dataset. RESULTS: The extent of local anatomical inhomogenities in the plans under consideration was strongly correlated with the level of difference between reference and evaluated calculations. GHs provided an immediate visual representation of the proportion of the treated volume that fulfilled the gamma criterion and offered a concise method for comparative numerical evaluation of dose distributions. CONCLUSIONS: We have introduced the concept of GHs and investigated its applications to the evaluation and verification of IMRT plans. The gamma histogram concept set out in this paper can provide a valuable technique for quantitative comparison of dose distributions and could be applied as a tool for the quality assurance of treatment planning systems.

Head and Neck Neoplasms↗

PubMed2006

A multiple acquisition sequence for IMRT verification with a 2D ion chamber array.

This investigation deals with the implementation of a multiple acquisition (MA) sequence for radiotherapy beam verification with a 2-dimensional (2D) ion chamber array. The acquisition is carried out through multiple beam deliveries with the 2D detector array in different positions. The MA sequence is performed through remote-controlled movements of the treatment couch. In this work, the MA dose map of an intensity-modulated radiotherapy (IMRT) modulated beam is presented and compared to standard acquisition mode data and ion chamber measurements. The implementation of MA sequence increases the number of measurement points and therefore the efficiency of the detection system and the final imaging resolution. Results from this investigation show that the imaging resolution of the system used in standard acquisition mode can be increased up to 4 times. The procedure described in this work can be automated, including couch movements in the radiotherapy plan sent to the treatment workstation. Furthermore, this specific solution could be successfully applied to matrices of detector with a different construction design.

Humans↗