Transcript Document
Use of accelerators for medical treatment in Tomsk region (Russia) Tomsk Polytechnic University
A.P. Potylitsyn
Cyclotron U-120 is operated in NPI TPU from the beginning of 1960’s.
• • • • • • • • The main parameters: Magnet diameter Magnet field Acceleration radius RF system 120 cm; 14,5 T; 53 cm; 9-17 MHz; Beam density on the external target ~ 10 uA/cm 2 ; Number of experimental channels 5; Accelerated ions Max energy p, d, He 2 , N, O, Ne, Ar; 1,2 MeV ∕ nucleon.
Actuality
Since 1984 Cancer research institute of Тomsk Scientific Center of Russian Academy of Medical Science uses the cyclotron U-120 of Tomsk Polytechnic university for realization of neutron therapy program, preoperative or postoperative neutron therapy as a method of combined treatment of various localizations of cancer with photon therapy; For last 10 years in Cancer research institute of TSC RAMS fast neutron beam is applied to treatment cancer of a mammary gland and its relapses as an independent method of cancer therapy or in a combination with electron or gamma therapy; Since 1989 betatron PMB-6 is used for intra-surgical therapy in operational room.
MAINTENANCE OF NEUTRON THERAPY HARDWARE AND THEORETICAL DOSIMETRY NEUTRONS RADIOBIOLOGICAL ASPECTS OF NEUTRON THERAPY COMPUTER DOSE CALCULATION AND RADIOBIOLOGICAL PLANNING METHODS OF NEUTRON THERAPY
deuterons The neutron channel diagram for neutron therapy Radiation protection
NEUTRONS
collimator patient Beryllium target 3 mm
The deuterons beam (40 uA) hits the beryllium target.
Neutrons are formed at deuterons and beryllium nucleus interaction. The neutron beam is formed by collimator and acts upon malignant tumour of a patient.
The neutron channel drawing
(using beam of the cyclotron U – 120 for neutron therapy ) Dose field min – 4x4cm 2 ; Dose field max – 15x15cm 2 .
Measuring system diagram
1- deuterons beam; 2- target; 3-beam current monitor; 4- collimator; 5-phantom; 6,11- ionization chambers; 7,12- preamplifiers; 8,13- dosimeters; 9,10- ionization chambers moving mechanism.
Dosimetric and radiobiological researches
1 – field S=225 cm 2 ; 2 – field S=48 cm 2 .
cm
Neutrons doze distribution vs. tissue depth
The neutron doze distribution in tissue-equivalent media calculated for 6×8 сm 2 radiated aria in plane which parallel to 8 сm side .
cm
The neutron absorbed doze distribution in skin near its surface
1 – 0 cm; 2 – 20 cm.
mm
Average specific KERMa of neutrons for various tissues and materials СРЕДНЯЯ УДЕЛЬНАЯ КЕРМА (фГр* м^2) НЕЙТРОНОВ ДЛЯ РАЗЛИЧНЫХ ТКАНЕЙ И МАТЕРИАЛОВ
SBT BT Adipose tissue Brain Polyethylene Water 4.5
3.8
5.6
4.8
6.3
4.8
2 1 0 7 4 3 6 5
Influence of a adipose tissue layer on doze distribution of neutrons g/cm 2
Distribution of the neutrons absorbed doze in view of and without taking into account heterogeneity in a pulmonary tissue.
1,2 1 0,8 0,6 0,4 0 2 6 10 14 18 20
Dependence of a relative number of surviving cells on the absorbed doze gamma-radiation (1) and neutrons (2).
Doze, Gy
Total distribution of equal-effective dozes at neutrons and gamma – radiations treatments
Conclusions
For last 20 years treatment of 1000 patients is done on a cyclotron U-120; Efficiency of neutron therapy at separate localizations of cancerous growth allows prolonging non-relapse period and the general life expectancy of patients; In 2007 - 2011гг perspective scientific researches on neutron therapy of resistant cancerous growth are planned in Cancer research institute of TSC RAMS.
In additional to neutron therapy we are engaged dosimetric planning of intra-surgical radiation therapy and remote gamma-therapy, and also their combination.
For this aim we are planning to use electron accelerators: - Betatron PMB –6 with energy 6 MeV (electron beam); - Linac CL75 –5–MT with energy 6 MeV (gamma beam).
Linear accelerator СL75 – 5 – МТ
D = 5 Gy/min at distance 1 m.
The main tasks: Ranging of a maximum permissible single doze in view of type and volume of an irradiated tissue; Choice of a total doze for postoperative distant gamma-therapy (DGT), for supplementing intra surgical radiation therapy (ISRT) after some time interval; Choice of admissible value of the single doze ISRT spent after preoperative DGT; Calculation of distribution of the total absorbed doze of electron beam and gamma - radiations.
Distant gamma-therapy (DGT)
Лшр Ла Ллла Радиальное распределение и изодозные кривые в плоскости, проходящей через ось симметрии пучка в водном фантоме, облучаемом коническим пучком гамма-излучения.
Distant gamma-therapy, multiple-fields irradiation 4-fields irradiation diagram
Small-sized betatron in operating-room
Betatron features: Electron energy – 6 MeV Electron beam power at 70 cm distance – up to 6 Gy/min Frequency – 200 Hz Consumption power – 2 kWt
Diagram of electron outlet from small-sized betatron
1 – electromagnet 2 – accelerating chamber 3 – outlet winding
Irradiation by electron beam
Longitudinal absorbed doze distribution of an electron beam in the water phantom on an axis of the beam.
Profile absorbed doze distribution of an electron beam in a water phantom.
Irradiation by electron beam
Isodoze distribution at interaction electron beam with 5,4 MeV energy and a water phantom
1.4
1.2
1 0.8
0.6
0.4
0.2
0 -15 Total distribution of the absorbed electron beam doze and gamma - radiations doze along a line, which perpendicular to axis of a electron beam • 8 Gy • 10 Gy • 15 Gy • Gamma radiation -10 -5 0
X [см]
5 10 15
Total distribution of the absorbed electron beam doze and gamma - radiations doze along a axis of a electron beam 1,4 1,2 1 0,8 0,6 0,4 0,2 0 -15 -10 -5 0
Y [см]
5 10 15 • 8 Gy • 10 Gy • 15 Gy • Gamma radiation
Comparison of the absorbed dozes and corresponding biological effects
80 60 40 20
42
0
8 10 15 70 29 41 77
Isodoze distribution of total absorbed electron beam and gamma - radiations dozes
Contour Graph 1 6 4 2 14 12 10 8 0 6 8 20 40 60 80 100 10 12 14 16
X, сm
18 20 22 e
Distribution of radiation in non-uniform media at implants presence
Development Parallel Monte-Carlo application for the cancer treatment planning by means high performance clusters with geometry reconstruction from DICOM images. Simulation and experimental study of transition effects for the absorbed dose in tissues adjacent to metal implants.
It is well known that in homogeneous media the absorbed dose is smooth function of coordinates. But near the interfaces with dissimilar media dose varies steeply. For particle energies, applicable for radiation treatment, absorbed dose essentially increases near upstream side of metal implant, it has deep minimum near downstream side of metal plate and then with increasing distance from plate it tends to the value corresponding to homogeneous media. As it was shown in our calculations this behavior is due to perturbation in the charged particles flux caused by high Z material.
Most powerful and exact method allowing to take in to account the effect described above in the radiation treatment planning is method of statistical simulation – Monte Carlo (MC).
Disadvantage of the method is slow convergence, it is very time expensive.
Because of this fact a high performance cluster or grid is suggested as way to obtain exact solution for acceptable time.
Radiation acts upon water phantom in which on some depth there is a plate from a titanium-nickel alloy.
NiTi d - depth, 3 or 10 cm.
d
NiTi layers are placed at 3 cm and 10 cm depth. Kjdhkl Доза на оси конического пучка гамма-квантов в водном фантоме (гистограмма) со слоями NiTi (точки).
designated by a dotted line)
Penetration of radiation through a matter is studied in Tomsk Polytechnic University for years. Monte Carlo simulation and analytical methods such as the perturbation theory are used for calculations of spatial, angular and energy distributions of photons and electrons in energy interval 10^3 - 10^{12} eV. New effective methods have been developed for solution of a great variety of scientific and applied problems. Two candidates for realization parallel MC code could be considered. First – GEANT4 code system. There is even example of realization radiation treatment planner with DICOM images as source for the geometry construction in GEANT4 source tree. Second candidate under consideration is our home made code system, which we call CASCADE.
It is based on original algorithms, developed on the basis of strict solution of kinetic equations for the transition probability densities of charged particles.
As result it is much more fast as compared with corresponding application based parallel radiation treatment planner.
on GEANT4.
Although we intensively use GEANT4 for simulation of high energy experiments and detectors, but for low energies which are used in radiation treatment we assume CASCADE as good base for realization of the For Geant4 based parallel treatment planning system any can use DINE environment or ParGeant interfaces based on TOPC. For now in our cluster applications we use TOPC tools.
TPU cluster consists of 24 computational nodes.
Each of the nodes has two dual core processors. Total performance of the cluster is about 1TFLOP.
Summary: For last 15 years treatment of 1200 patients is done on a betatron PMB-6; The linear accelerator СL75–5–МТ is exploited for 3 years, time of operation ~30 %, treatment of 300 patients is done; The method providing a choice of maximum permissible dozes on the basis of several radiobiological models is developed; The approaches received; providing radiobiological planning at combination ISRT and an distant gamma irradiation are The method and the program of calculation of gamma- and electron distributions in tissue-equivalent media is developed; The researches of laws of distribution of radiation in non uniform media at implants presence made from NiTi are carried out; Training on master's degree courses « Medical physics» is carried out; students may prepare the final qualifying works using the neutron-,gamma and electron beams of accelerators.