Optimization of Radiation Therapy
System for Optimization of Radiation Therapy Planning by Photon and Electron Beams on the Basis of a Pencil Beam Algorithm
Tech Area / Field
8 Project completed
Senior Project Manager
Tocheny L V
MIFI, Russia, Moscow
- Cancer Research Center / Scientific Research Institute of Clinical Oncology, Russia, Moscow\nVNIIEF, Russia, N. Novgorod reg., Sarov
- Forschungszentrum Rossendorf / Institut für Sicherheitsforschung, Germany, Dresden\nCEA / IPSN (Institut de Protection et Sûreté Nucléaire), France, Fontenay aux Roses\nDeutsches Zentrum für Luft- und Raumfahrt e.V. / Institut für Technische Physik, Germany, Stuttgart
Project summaryOne of the most urgent problems of beam therapy at the present stage becomes optimization of beam therapy, the purpose of which is on the one hand maintenance of a required high dose in tumor volume, and on the other hand - minimum irradiation of healthy tissues and especially of critical organs.
In the last five years some known scientists developed several mathematical models and algorithms to solve the problem of beam therapy optimization. However methods and algorithms published in the literature are not effective to solve many problems and first of all to deal with three - dimensional optimization problems.
In this project elaboration and creation of the system for optimization of radiation therapy by photon and electron beams on the basis of algorithm of a generalized pencil beam and large-scale element method are suggested.
The system is intended for effective and economic solution of 3-D optimization problems by use a few fields (3 - 5) and by modulation of beam intensities by profiling compensatory blocks.
The authors in the previous project ISTC (N 144-94, ending 30.09.1997) have created first in Russia the system of 3-D dosimetry planning for remote gamma-therapy based on the algorithm of a pencil beam. In the project also the fast computer code for full-scale calculation of three-dimensional dose distributions by a Monte Carlo method and mock-up of dose field analyzer of gamma-radiation were developed. The new project is a logic continuation of the previous one. In this project the solution of the following problems is suggested:
- Elaboration of an algorithm and computer code for the effective solution of three-dimensional optimization problems on the basis of a large-scale elements method and the algorithm of a pencil beam;
- Selection and specification of appropriate physical and radiobiological objective functions in the optimization problem;
- Creation of an automated installation for manufacturing moulds to cast shielding blocks and compensating filters for formation of the optimum shape and profiles of irradiation beams;
- Development of the effective code for calculation of dose volume distributions by a Monte Carlo method using a PL-estimation to examine the results of optimization;
- Improvement of the dose field analyzer and creation of the installation for experimental check of optimization and planning results on its basis;
- Elaboration of the quality guarantee of the optimum irradiation plans realization.
The major advantage of the suggested project lies hi the most economical way of minimization integral beam dose delivered to a patient to obtain uniform dose distribution in a tumor and to take into account clinical indications of patients. It is achieved by means of new methods of dose distribution formation in the body of a patient from radiation beams with modulation of intensity.
For acceleration of the three-dimensional problems solution a method of large elements will be applied, allowing without essential loss of accuracy to decrease dimension of spaces, to which vectors of required distributions of primary beam intensity and doses of irradiation belong. This method is based on fixing of the rings of discrete conformal image of tumor contour projection onto plane that are normal to irradiating beam axis. This allows to decrease essentially the calculation time and dimensionality of solution vector and to keep the requested accuracy of final result. The realization of large-scale method consists in calculation of weight factors for elementary meshes of each ring in accordance with mesh contribution to total dose delivered to tumor. The method allows to choose different objective functions to solve optimization problem (physical, geometrical, biological etc.) and to realize effective iteration schemes for numerical determination of objective function optimum.
One of the important moments under elaboration of optimization complex is the development of the program block, "quickly" calculating three-dimensional dose distribution from beams of modulated intensity. The technique of calculation, used in this program, will be based on the algorithm of a generalized pencil beam and appropriate analytical approximation of pencil beam dose distributions.
It is very important, that in the project it is suggested to create a really complex system of beam therapy optimization, including not only program of optimization and the machine for manufacture of compensating filters, but also the means for calculational and experimental check of how dose distributions, which result from "optimized irradiation", conform to criteria of optimization.
For calculational checking the full-scale computer code is developed to simulate the problem by Monte Carlo method. The main peculiarity of this code will be the use of PL-estimators, developed by the authors in the previous project N 144-94. The method of PL-estimators is based on the use of properties of local invariance concerning shifts over space of trajectories, connected to the transport equation of Markovian process and allows without adapting any simplified assumptions to reduce time of the calculation by a few order in comparison with known code EGS4.
The creation of the system for optimization of radiation therapy by photon and electron beams will allow to increase considerably the efficiency and quality of cancer patient treatment by means of ionizing radiation. The estimations carried out by the authoritative foreign experts’ show that this increase of treatment efficiency resulted from the optimum irradiation plans realization makes 15 - 20 %.
Scientists and the engineers, who worked earlier in the field of weapon design, and began to work on the ISTC project N144-94, in the beginning of 1994 have come in the new field of medical physics. Now, getting the experience during the development of a dosimetry planning system, this collective proposes the new project in one of the most urgent directions of medical physics - beam therapy optimization. Even partial success in this field gives a real opportunity to increase the efficiency of beam therapy during treatment of patients. It is of special importance for Russia because of lagging behind the advanced countries of the world in the field of high medical technologies.