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Study of dosimetry techniques applied to electron beams with high dose rate
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Orientador(es)
Resumo(s)
Electron beams of 4-20 MeV are used for Total Skin Electron Irradiation (TSEI) of T-cell
lymphomas like the mycosis fungoides type. High dose rate electron (HDRE) beams show
effectiveness in achieving local control rates close to 100% and low rates of acute and late toxicity. An
Elekta Infinity Agility machine was modeled without manufacturer information and the resulting 6
MeV (TSEI compatible energy) beam was compared with reference experimental beam. The
dosimetric study was conducted using Advanced Markus® Type 34045 plane-parallel ionization
chamber (IC) and GafChromicTM EBT-XD films. Both water (MP3) and solid water (RW3) were used,
and beam evaluation involved reference 10x10 cm2
fields and 100 cm SSD as well as open fields and
240 cm SSD TSEI compatible. Functional performance testing was done for evaluation of beam
constancy in HDRE operating mode. Results show a 0.983 Gy per 100 MU in reference conditions and
a 9.115 times higher dose using HDRE mode. Gamma analysis passing of 100 % (2 mm DTA / 2 %
DD) was obtained, for comparison between MP3 and RW3 HDRE beams in an open field
configuration and for an SSD of 100 cm. The working range was within the effective range of EBTXD films. On a 240 cm spaced perpendicular plane, relative dose was verified as symmetrical within a
15 % tolerance. In an anthropomorphic phantom, dose was analyzed using the dual-field Stanford
technique and dmax shift was seen to occur, discarding interface artifacts, from 1.40 ± 0.05 cm (SSDref)
to 0.7 ± 0.2 cm. From TOPAS MC simulation, gamma analysis has shown that the model agrees
completely with reference beam. Limited agreement was seen using SSD of 240 cm. MC model
mimics the studied linac using reference conditions and SSD of 240 cm is adequate for TSEI
implementation. More studies for confirmation of results and others focusing on non-reference
conditions are needed.
Descrição
Tese de mestrado, Engenharia Física, 2023, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Electrões Dosimetria TSEI Elekta TOPAS Teses de mestrado - 2023