- Email: [email protected]
Feasibility and dosimetric characterization of single convergent beam teletherapy device
Abstracts / Physica Medica 30 (2014) e45ee74
Figure 4. Cluster size (Number of pixels from each particle hit) vs. energy distribution of correlated events in two of the hodoscope detection layers.
ELECTRON BEAM DOSE DISTRIBUTION ANALYSIS FOR IRREGULAR FIELDS IN TREATMENT OF SUPERFICIAL TUMORS: A MONTE CARLO STUDY M.B. Tavakoli, P. Shokrani, K. Bamneshin. Department of Medical Physics and Medical Engineering, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran Introduction: In superficial treatments with electron beam, irregular fields are usually produced by using lead shields which are placed either at the end of the applicator or on the surface of the patient body. For these fields the amount of scatter and therefore the dosimetric parameters such as PDD, profiles and output factor may change with respect to the regular fields. The objective of this research was to investigate the effect of shielding on electron field using Monte-Carlo method. Materials and methods: DOSXYZnrc code were used for simulating Nepton 10PC linac head and BEAMnrc code for simulating irregular fields obtained from 1515cm2, 2020cm2, 2525cm2 to calculate dosimetric parameters of percentage depth dose (PDD), dose profiles and output factors for different field configurations. A total number of 60 irregular fields were investigated. The calculated results were compared with equivalent field methods. To evaluate the accuracy of calculation, the calculated results of PDD were compared with the measured results obtained with a Scanditronix p-type silicon diode in a phantom. Results and conclusion: The study, showed that maximum changes for 90% depth dose of 6MeV electron is 2.2mm. Maximum change in output factor for the mentioned energy when maximum shielding was applied is 6.3%. The results also showed that using equivalent square field method is not an appropriated method for dose calculation when irregular field is used especially when PDD is considered. The percentage of error increases with increasing percentage of the shielding. Keywords: Dosimetry, irregular fields, Linear accelerator, percentage depth dose, FEASIBILITY AND DOSIMETRIC CHARACTERIZATION CONVERGENT BEAM TELETHERAPY DEVICE
OF
SINGLE
Rodolfo G. Figueroa a, Mauro Valente b. a Physics Department, Universidad de La Frontera, Temuco Chile; b CONYCET, Fa.M.A.F. Universidad Nacional de rdoba, Co rdoba, Argentina Co Background: Currently X-photons teletherapy utilizes divergent beams, which implies a non-negligible irradiation of healthy tissues. A convergent beam would allow a greater radiation focalization. This work aimed to determine feasibility and characteristics of a new type of radiation therapy based on the application of a convergent beam of photons, using a device capable of generating a convergent X-ray beam of energies. We named this technique RTHC.
e73
Materials and Methods: An analytical method was developed to determine dosimetric characteristics of an ideal convergent X photon beam in a hypothetical water phantom. Then, using Monte Carlo (MC) code, PENELOPE, an ideal convergent beam was applied to a water phantom using a specially adapted geometry; results were compared with those of the analytical method. MC simulations were performed in a vacuum, using a more realistic geometry. These simulations were performed for a largesize thin spherical anodic target (30 cm radius). Thus, the electrons perpendicularly impact upon various points of the cap (RTHC condition, convergent beam radiotherapy), mainly at the focal point in the water phantom center. The X radiation (bremsstrahlung) is generated toward the focus. A spherical collimator coaxial to the cap, with many holes, allows a clean convergent X-ray beam output. On the other hand, magnitudes of the electric / magnetic fields necessary for a clinical use electron beam (0.1 to 20 MeV) are determined using electromagnetism equations with relativistic corrections. Results: In-depth dose peaks similar in shape to hadron therapy were shown. This remarks that in-depth dose peaks are generated at the focus point/isocenter. The electric and magnetic fields needed to control the deflection of the electron beams in the RTHC geometry were calculated. Discussion: Results are consistent with those obtained with PENELOPE code. Peak-focus is independent of the X photon beam energy, though its intensity is not. Aperture angle at each impact point depends on the energy beam, the atomic Z number and the target thickness. Electric and magnetic fields necessary to control the X-ray beam are highly feasible by means of a specially designed electric/magnetic device. Electric fields are much more difficult to achieve than magnetic ones, especially at high energies. In conclusion, is possible to generate a device with the abovementioned characteristics (Pat.Pending-CoverayTM) POLIMER GAFCHROMIC EBT3 FILM FOR ELECTRON DOSIMETRY OF BETATRON BEAM Evgeniia Sukhikh a, b, Leonid Sukhikh b, Evgeniy Malikov b. a Research Institute for Oncology, Kooperativnyy st., 5, Tomsk, 634050, Russia; b National Research Tomsk Polytechnic University, Lenin ave., 30, Tomsk, 634050, Russia Keywords: radiation therapy, Gafchromic EBT3 polymer films, cylindrical and plane-parallel ionization chamber, a linear accelerator, betatron, X-ray tube Background: Intraoperative radiotherapy is a treatment modality for a locally advanced tumor of the abdomen, pelvis and breast, which involves the use of large single dose of radiation delivered to the tumor or bed of tumor and areas of potential regional spread during the surgical operation. The modality is based on electron beams of MeV energies due to particular dose distribution in the tissue-equivalent environment [1,2]. Nowadays, most of the clinics worldwide carry on the IORT procedure using the electron sources based on the compact linear accelerators. However, in Russia historically several clinics have been using the sources based on betatrons. The main advantages of the betatrons are the possibility to change the beam energy in a wide range with small steps (e.g. 2-6 MeV with spacing 0.5 MeV), low energy spread of the beam and the relatively low cost of a device (typically $ 200 000). These days our team develops new generation of betatrons with extracted electron beam for IORT and skin cancer treatment. Materials and Methods: The investigation of 3D dose distributions generated by new prototype of IORT source based on betatron was carried out in the energy range 2-6 MeV with 500 keV steps. The dose distributions were measured using plane-parallel and cylindrical ionization chambers and Unidose-E electrometer [3-5] and radiochromic films Gafchromic EBT-3 [6-9]. The films were calibrated using 10 MeV electron beam of Electa Axcess accelerator and 2 MeV beam of our betatron. . All measurements were performed in tissue-equivalent phantom with zero air gap. Results: The results of radiochromic film calibration are shown in Fig.1. The calibration was carried out for both red and green channels of the film. Basing on obtained calibration the measurements of absolute dose distributions were carried out. Fig. 2 shows the 2D distribution of the absolute
Figure 4. Cluster size (Number of pixels from each particle hit) vs. energy distribution of correlated events in two of the hodoscope detection layers.
ELECTRON BEAM DOSE DISTRIBUTION ANALYSIS FOR IRREGULAR FIELDS IN TREATMENT OF SUPERFICIAL TUMORS: A MONTE CARLO STUDY M.B. Tavakoli, P. Shokrani, K. Bamneshin. Department of Medical Physics and Medical Engineering, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran Introduction: In superficial treatments with electron beam, irregular fields are usually produced by using lead shields which are placed either at the end of the applicator or on the surface of the patient body. For these fields the amount of scatter and therefore the dosimetric parameters such as PDD, profiles and output factor may change with respect to the regular fields. The objective of this research was to investigate the effect of shielding on electron field using Monte-Carlo method. Materials and methods: DOSXYZnrc code were used for simulating Nepton 10PC linac head and BEAMnrc code for simulating irregular fields obtained from 1515cm2, 2020cm2, 2525cm2 to calculate dosimetric parameters of percentage depth dose (PDD), dose profiles and output factors for different field configurations. A total number of 60 irregular fields were investigated. The calculated results were compared with equivalent field methods. To evaluate the accuracy of calculation, the calculated results of PDD were compared with the measured results obtained with a Scanditronix p-type silicon diode in a phantom. Results and conclusion: The study, showed that maximum changes for 90% depth dose of 6MeV electron is 2.2mm. Maximum change in output factor for the mentioned energy when maximum shielding was applied is 6.3%. The results also showed that using equivalent square field method is not an appropriated method for dose calculation when irregular field is used especially when PDD is considered. The percentage of error increases with increasing percentage of the shielding. Keywords: Dosimetry, irregular fields, Linear accelerator, percentage depth dose, FEASIBILITY AND DOSIMETRIC CHARACTERIZATION CONVERGENT BEAM TELETHERAPY DEVICE
OF
SINGLE
Rodolfo G. Figueroa a, Mauro Valente b. a Physics Department, Universidad de La Frontera, Temuco Chile; b CONYCET, Fa.M.A.F. Universidad Nacional de rdoba, Co rdoba, Argentina Co Background: Currently X-photons teletherapy utilizes divergent beams, which implies a non-negligible irradiation of healthy tissues. A convergent beam would allow a greater radiation focalization. This work aimed to determine feasibility and characteristics of a new type of radiation therapy based on the application of a convergent beam of photons, using a device capable of generating a convergent X-ray beam of energies. We named this technique RTHC.
e73
Materials and Methods: An analytical method was developed to determine dosimetric characteristics of an ideal convergent X photon beam in a hypothetical water phantom. Then, using Monte Carlo (MC) code, PENELOPE, an ideal convergent beam was applied to a water phantom using a specially adapted geometry; results were compared with those of the analytical method. MC simulations were performed in a vacuum, using a more realistic geometry. These simulations were performed for a largesize thin spherical anodic target (30 cm radius). Thus, the electrons perpendicularly impact upon various points of the cap (RTHC condition, convergent beam radiotherapy), mainly at the focal point in the water phantom center. The X radiation (bremsstrahlung) is generated toward the focus. A spherical collimator coaxial to the cap, with many holes, allows a clean convergent X-ray beam output. On the other hand, magnitudes of the electric / magnetic fields necessary for a clinical use electron beam (0.1 to 20 MeV) are determined using electromagnetism equations with relativistic corrections. Results: In-depth dose peaks similar in shape to hadron therapy were shown. This remarks that in-depth dose peaks are generated at the focus point/isocenter. The electric and magnetic fields needed to control the deflection of the electron beams in the RTHC geometry were calculated. Discussion: Results are consistent with those obtained with PENELOPE code. Peak-focus is independent of the X photon beam energy, though its intensity is not. Aperture angle at each impact point depends on the energy beam, the atomic Z number and the target thickness. Electric and magnetic fields necessary to control the X-ray beam are highly feasible by means of a specially designed electric/magnetic device. Electric fields are much more difficult to achieve than magnetic ones, especially at high energies. In conclusion, is possible to generate a device with the abovementioned characteristics (Pat.Pending-CoverayTM) POLIMER GAFCHROMIC EBT3 FILM FOR ELECTRON DOSIMETRY OF BETATRON BEAM Evgeniia Sukhikh a, b, Leonid Sukhikh b, Evgeniy Malikov b. a Research Institute for Oncology, Kooperativnyy st., 5, Tomsk, 634050, Russia; b National Research Tomsk Polytechnic University, Lenin ave., 30, Tomsk, 634050, Russia Keywords: radiation therapy, Gafchromic EBT3 polymer films, cylindrical and plane-parallel ionization chamber, a linear accelerator, betatron, X-ray tube Background: Intraoperative radiotherapy is a treatment modality for a locally advanced tumor of the abdomen, pelvis and breast, which involves the use of large single dose of radiation delivered to the tumor or bed of tumor and areas of potential regional spread during the surgical operation. The modality is based on electron beams of MeV energies due to particular dose distribution in the tissue-equivalent environment [1,2]. Nowadays, most of the clinics worldwide carry on the IORT procedure using the electron sources based on the compact linear accelerators. However, in Russia historically several clinics have been using the sources based on betatrons. The main advantages of the betatrons are the possibility to change the beam energy in a wide range with small steps (e.g. 2-6 MeV with spacing 0.5 MeV), low energy spread of the beam and the relatively low cost of a device (typically $ 200 000). These days our team develops new generation of betatrons with extracted electron beam for IORT and skin cancer treatment. Materials and Methods: The investigation of 3D dose distributions generated by new prototype of IORT source based on betatron was carried out in the energy range 2-6 MeV with 500 keV steps. The dose distributions were measured using plane-parallel and cylindrical ionization chambers and Unidose-E electrometer [3-5] and radiochromic films Gafchromic EBT-3 [6-9]. The films were calibrated using 10 MeV electron beam of Electa Axcess accelerator and 2 MeV beam of our betatron. . All measurements were performed in tissue-equivalent phantom with zero air gap. Results: The results of radiochromic film calibration are shown in Fig.1. The calibration was carried out for both red and green channels of the film. Basing on obtained calibration the measurements of absolute dose distributions were carried out. Fig. 2 shows the 2D distribution of the absolute