Speaker
Elena Morozova
Description
The study of dose transmission is a vital topic because the number of patients who have developed delayed radiation injuries increases every year [2,3].
Recently commissioned linear accelerator Varian Halcyon V1.0 (Varian Medical Systems, Palo Alto, Calif., USA) without collimation shutters is now gaining popularity in oncology clinics. The Halcyon MLC System features the stacked and staggered dual‐layer multileaf collimator. The primary and secondary collimators are fixed; there is no flattering filter [1, 4].
This study aims to measure dose transmission from a Varian Halcyon multileaf collimator experimentally. Our experiments were carried out on the Varian Halcyon linear accelerator with a boundary photon energy of 6 MeV:
- Investigation of the effect of field size on dose transmission. IMRT plans were created to irradiate the phantom with different sized fields in the treatment planning system Eclipse. The dose profile was measured with an IC Profiler SunNuclear array detector. A water-equivalent Solid Water GAMMEX phantom was used. The data obtained were used to plot the beam profiles. All received doses were normalized to a absorbed dose in a 10 × 10 cm2 reference field at a depth of 10 cm.
- Measurement of dose transmission at a small field size. In this experiment, a plan was created to irradiate the 3D Scanner SunNuclear water phantom. The multileaf collimator was positioned to create a rectangular beam size 1x2 cm2. The SNC125c ionization chamber was used.
The experiment showed that despite the fact that in all experiments, the same dose of 200 monitor units was applied, the dose transmission becomes larger with increasing field size. At a distance of 16 cm from the central axis, doses of 0.003, 0.012, 0.029, 0.052, 0.092, 0.128 Gy are observed for fields with sizes 5x5, 10x10, 15x15, 20x20, 25x25 cm2, respectively.
The results of the current study are essential for understanding how field size affects dose transmission.
Bibliography:
- Lim TY, Dragojević I, Hoffman D, Flores‐Martinez E, Kim GY. Characterization of the Halcyon TM multi-leaf collimator system. J Appl Clin Med Phys. 20: 106– 114 (2019);
- NCRP, NCRP Report 170. Second Primary Cancers and Cardiovascular Disease After Radiation Therapy. Bethesda, Md: National Council on Radiation Protection and Measurements (2011);
- Takam R, Bezak E, Marcu LG, Yeoh E. Out-of-field neutron and leakage photon exposures and the associated risk of second cancers in high-energy photon radiotherapy: current status. Radiat Res. 176:508–520 (2011);
- Varian Medical Systems. Halcyon Brochure. 2017 URL: https://www.varian.com/sites/default/files/resource_attachments/Halcyon_brochure_RAD10443B_092417.pdf.
Primary authors
Alexander Chernyaev
(Moscow State University)
Aytalyna Petrova
Ekaterina Lykova
(Lomonosov Moscow State University)
Elena Morozova
Nadezhda Gromova
