Wyniki wyszukiwania - BazTech

1

Evaluation of jaws-only intensity modulated radiation therapy treatment plans using Octavius 4D system

Than Tai D., Oanh L. T., Son N. D., Loan T. T. H.

Polish Journal of Medical Physics and Engineering

|

2018

|

Vol. 24, Iss. 2

75--78

EN

Introduction: Jaws-Only Intensity modulated radiation therapy (JO-IMRT) is a technique uses the collimator jaws of the linear accelerator (LINAC) to delivery of complex intensity patterns. In previous studies, pretreatment patient specific quality assurance for those JO-IMRT were also performed using ionization chamber, MapCHECK2, and Octavius 4D and good agreements were shown. The aim of this study is to further verify JO-IMRT plans in 2 different cases: one with the gantry angle set equal to beam angle as in the plans and the other with gantry angle set to zero degree. Materials and Methods: Twenty-five JO-IMRT, previously verified, were executed twice for each plan. The first one used a real gantry angle, and the second one used a 0° gantry angle. Measurements were performed using Octavius 4D 1500. Results: The results were analyzed using Verisoft software. The results show that the Gamma average was 97.32 ± 2.21% for IMRT with a 0° gantry angle and 94.72 ± 2.67% for IMRT with a true gantry angle. Conclusion: In both cases, gamma index of more than 90% were found for all of our 25 JO-IMRT treatment plans.

2

Monte Carlo study on a new concept of a scanning photon beam system for IMRT

Wysocka-Rabin A. M., Hartmann G. H.

Nukleonika

|

2011

|

Vol. 56, No. 4

291-297

EN

Intensity-modulated radiation therapy (IMRT) is almost exclusively realized using a multi-leaf collimator (MLC). In this work we investigated alternative approaches to realize an IMRT - scanning photon beam system. The technical realization of this concept required investigating the influence of various design parameters on the final small photon beam. This was done using Monte Carlo (MC) simulation methods. The resulting photon beam that is to be scanned should have a diameter well less than 10 mm at a source-surface distance (SSD), and the penumbra should be as small as possible. A first draft for this system, based on the PRIMUS 6 MV accelerator at DKFZ (Deutsches Krebsforshungszentrum), was proposed and modeled using the BEAMnrc/EGSnrc MC code. We then proposed and studied a new geometry of the source-target-collimator system. Calculations were done for 108 particles, using an electron energy cut-off (ECUT) = 0.7 MeV, and a photon energy cut-off (PCUT) = 0.01 MeV. The influence of different collimator parameters, different target construction and various incident electron beam characteristics was studied. Calculations of the dose absorbed in the water were performed for 8 different collimators at a distance of 40 cm from the collimator exit, which is the medical requirement. Results of the dose distribution calculations are presented as photon beam profiles with the values of full width at half-maximum (FWHM) and penumbra (PM) for every beam profile. The influence of target construction was studied for different thicknesses of target and material minimizing electron contamination. The influence of the following characteristics of the incident electron beam was also investigated: size of electron beam, energy, displacement of the beam from the axis of target-collimator system, shape of the electron beam profile. The field dose distribution of the photon beam was calculated for the collimators giving the beam profiles. Basing on the work performed in this investigation, it will be possible to define adequate parameters for the target-collimator system as well as on the scanning electron beam for new IMRT system.

3

Evaluation of set-up verification with the analysis of systematic and random errors in radiotherapy - a study of the Great Poland Cancer Centre

Szczurek Ł., Skrobała A., Piotrowski T., Jodda A.

Nukleonika

|

2008

|

Vol. 53, No. 4

167-171

EN

The aim of this study was the examination of influence of location tumors and methods of immobilizing on values of geometrical errors during treatment, and the analysis of set-up errors in reference to the method of irradiation in three groups of patients before and after corrections. This study included three groups of patients with prostate cancer (59 patients, 277 portal images), head and neck (60 patients, 285 portal images) and brain tumor (45 patients, 175 portal images). Ratios of IMRT vs. 3D-CRT were respectively: in I group 76% vs. 24%, in II group 95% vs. 5% and III group 83% vs. 17%. Set-up errors were compared in reference to the technique of irradiation and stage of treatment. The displacements were significantly higher in the first group compared with head, neck and brain tumors; 5.66, 4.05, 3.93 mm, respectively. The values of the vector lengths were significantly dependent on the type of irradiation technique (3D-CRT vs. IMRT) only in the first group (p < 0.001). The average of vector length in I, II and III group were significantly reduced from; 5.67, 4.02, 3.91 mm to 5.13, 3.63, 3.57 mm after correction, respectively. The Spearman test is indicating a low negative correlation between set-up errors and the following fractions. The applied methods of patients positioning with prostate cancer produce a worse repeatability than the ones used for patients with head, neck and brain cancers. Portal verification reduces values of set-up errors. Significant differences in the magnitude of displacements before and after correction were observed. No significant differences between value of displacement and number of fraction were revealed.