F. Di Rosa

Experimental validation of the filtering approach for dose monitoring in proton therapy at low energy

The higher physical selectivity of proton therapy demands higher accuracy in monitoring of the delivered dose, especially when the target volume is located next to critical organs and a fractionated therapy is applied. A method to verify a treatment plan and to ensure the high quality of the hadrontherapy is to use Positron Emission Tomography (PET), which takes advantage of the nuclear reactions between protons and nuclei in the tissue during irradiation producing beta(+)-emitting isotopes. Unfortunately, the PET image is not directly proportional to the delivered radiation dose distribution; this is the reason why, at the present time, the verification of depth dose profiles with PET techniques is limited to a comparison between the measured activity and the one predicted for the planned treatment by a Monte Carlo model. In this paper we test the feasibility of a different scheme, which permits to reconstruct the expected PET signal from the planned radiation dose distribution along beam direction in a simpler and more direct way. The considered filter model, based on the description of the PET image as a convolution of the dose distribution with a filter function, has already demonstrated its potential applicability to beam energies above 70 MeV. Our experimental investigation provides support to the possibility of extending the same approach to the lower energy range ([40, 70] MeV), in the perspective of its clinical application in eye proton therapy.

Monte Carlo Studies of a Proton Computed Tomography System

Proton therapy is a precise forms of radiation therapy that makes use of high energy proton compared to the conventional, more commonly used and less precise x-ray and electron beams. On the other hand, to fully exploit the proton therapy advantages, very accurate quality controls of the treatments are required. These are mainly related to the dose calculations and treatment planning. Actually dose calculations are routinely performed on the basis of X-ray computed tomography while a big improvement could be obtained with the direct use of protons as the imaging system. In this work we report the results of Monte Carlo simulations for the study of an imaging system based on the use of high energy protons: the proton computed tomography (pCT). The main limitation of the pCT and the current adopted technical solutions, based on the use of the most likely path (MLP) approximation are illustrated. Simulation results are compared with experimental data obtained with a first prototype of pCT system tested with 200 MeV proton beams available at the Loma Linda University Medical Center (LLUMC) (CA).

A PET Prototype for “In-Beam” Monitoring of Proton Therapy

The in-beam PET is a novel PET application to image the beta+ activity induced in biological tissues by hadronic therapeutic beams. Thanks to the correlation existing between beam-delivered dose profiles and beam-induced activity profiles, in vivo information about the effective ion paths can be extracted from the in-beam pet image. in situ measurements, immediately after patient irradiation, are recommended in order to exploit the maximum statistics, by also detecting the contribution provided by the very short lived isotopes, e.g. 15O. A compact, dedicated tomograph should then be developed for such an application, so as to be used in the treatment room. We developed a small PET prototype in order to demonstrate the feasibility of such a technique for the monitoring of proton therapy of ocular tumors at the CATANA facility (Catania, Italy). The prototype consists of two planar heads with an active area of about 5 cm times 5 cm. Each head is made up of a square position sensitive photomultiplier (Hamamatsu H8500) coupled to a matrix of the same size of LYSO scintillating crystals (2 mm times 2 mm times 18 mm pixel dimensions). Dedicated, compact electronic boards are used for the signal multiplexing, amplification and digitization. The distance between the pair can be varied from 10 cm up to a maximum of about 20 cm. The validation of the prototype was performed on plastic phantoms using 62 MeV protons at the CATANA beam line. Different dose distributions were delivered and a good correlation between the distal fall-off of the activity profiles and of the dose profiles was found, i.e., better than 2 mm along the beam direction.

Validation of Geant4 Physics Models for the Simulation of the Proton Bragg Peak

A comprehensive, rigorous validation of Geant4 electromagnetic and hadronic models pertinent to the simulation of the proton Bragg peak in water is presented. Geant4 simulation results are validated against high precision experimental data taken in the CATANA hadrontherapy facility.

Detailed Monte Carlo investigation of a proton computed tomography system

Proton therapy is a precise form of radiation therapy and thus it requires accurate quality control of patients treatment. Protons may be more suitable than conventional X-rays for this task since the relative electron density distribution can be measured directly with proton computed tomography (pCT). However, proton CT has its own limitation. The main limit is that of spatial resolution limited by multiple coulomb scattering of proton inside the body of patient. In order to improve spatial resolution we need to determine the most likely path of single proton inside the body. In this work we realized a set of Monte Carlo simulations for the calculation of the most likely path

Monte Carlo based implementation of an energy modulation system for proton therapy

A certain numbers of radiation therapy techniques, requires that the treatment setup, varies in time during the dose delivery. This can be the case of the proton therapy where an uniform dose can be obtained using the movement of special element during the patient irradiation. Hadron therapy is a special radiotherapeutic treatment based on the use of high energy proton beams. Thanks to their specific interaction with matter, hadrons release all their energy at the end of their paths (Bragg peak). The Bragg peak permits to irradiate selectively tumors sparing the surrounding normal tissues. The full width half maximum of a typical Bragg peak is usually of the order of 1 mm: completely insufficiently to cover a tumor region (of the order of 20 mm for the case of the eye melanoma). In order to form an homogeneous dose distribution within the tumor volume, individual pristine beams have to be added up. Most proton therapy facilities are currently using a broad beam modulation technique where a spread-out Bragg peak (SOBP) is generated by a set of absorbers having different thickness. Technical solutions are ridge filters or modulator wheels ensuring temporal variation of the beam energy. In our previous work, using the GEANT4 Monte Carlo package, we simulated all the elements of the CATANA proton therapy facility (G.A.P. Cirrone et al.). CATANA is the first and actually unique proton therapy center in Italy. Now we show the possibility to use the GEANT4 toolkit also to design and simulate the time-dependent geometry of the modulator wheel. Simulated results are reported and compared with the experimental ones. The implemented solution for the time-dependent geometry, can represents an useful example for the GEANT4 users that want use this feasibility in a different environment.

Dosimetric and clinical experience in eye proton treatment at INFN-LNS

After six years of activity 155 patients have been treated inside the CATANA (Centro di AdroTerapia ed Applicazioni Nucleari Avanzate) facility. CATANA is the first and unique proton therapy facility in which the 62 MeV proton beams, accelerated by a Superconducting Cyclotron, are used for the radio‐therapeutic treatments of choroidal and iris melanomas. Inside CATANA new absolute and relative dosimetric techniques have been developed in order to achieve the best results in terms of treatment precision and dose release accuracy. The follow‐up results for 42 patients demonstrated the efficacy of high energy protons in the radiotherapeutic field and encouraged us in our activity in the battle against cancer

Residual energy measurements for proton computed tomography

We present a preliminary study on proton calorimetry for pCT (proton computed tomography) system. In a pCT scanner there are a tracking system for proton-path reconstruction and a calorimeter for measurement of residual proton energy. We set up a prototype system using a silicon tracker and a scintillator crystal . In particular, we show the measurements obtained with YAG:Ce scintillator crystal and therapeutic proton beams.

A multimodality network platform for oncologic solution

Introduction Two facilities, located in different geographical areas and related to a single Radiotherapy Department, need a massive storage of multimodal DICOM images. A network connection is required in order to share all clinical, physical and dosimetric information. Purpose We design and implement a server infrastructure to perform a real time connection for the full management of a Radiotherapy Department. Materials and methods We developed a server architecture dedicated to radiotherapy requirements based on an advanced DICOM forwarding rules: RTPACS. The combination of this system with an advanced DICOM viewer assures a full support of DICOM standard extension. The use of a DICOM server, embedded with programmable SQL databases, offers all solutions to satisfy the requirements for a long-term storage allowing the clinical plan evaluation free by TPS vendor. Results RTPACS provides easy access to the single patient waiting list and a multidisciplinary and multicenter study of a same patient: a treatment can be planned, valued, approved and delivered independently in both facilities. Such system ensures a continuative service avoiding treatment interruptions caused by machine maintenance or downtime. Moreover, RTPACS constitutes a tool to manage, compare and storage the quality controls results performed by images. Conclusion A network implementation joining two far facilities of the same Department answers to the needs and cares of the oncologic patient. It represents an innovative, easy and affordable solution that provides a service we cannot find in our territorial area. A unique radiotherapy data management permits a better organization of human resources. Disclosure Authors disclose any relationship that may prejudice their presentation.