The variation of HVL with focal spot to chamber distance as a function of beam quality for the Pantak Therapax 150 X-ray unit and the implications on dose to water determination using the IPEMB code of practice

Baines, John and Sim, Lucy (2014) The variation of HVL with focal spot to chamber distance as a function of beam quality for the Pantak Therapax 150 X-ray unit and the implications on dose to water determination using the IPEMB code of practice. Australasian Physical and Engineering Sciences in Medicine, 37 3: 559-566. doi:10.1007/s13246-014-0289-2


Author Baines, John
Sim, Lucy
Title The variation of HVL with focal spot to chamber distance as a function of beam quality for the Pantak Therapax 150 X-ray unit and the implications on dose to water determination using the IPEMB code of practice
Journal name Australasian Physical and Engineering Sciences in Medicine   Check publisher's open access policy
ISSN 1879-5447
0158-9938
Publication date 2014-09-01
Sub-type Article (original research)
DOI 10.1007/s13246-014-0289-2
Open Access Status Not yet assessed
Volume 37
Issue 3
Start page 559
End page 566
Total pages 8
Place of publication Dordrecht, Netherlands
Publisher Springer Netherlands
Language eng
Formatted abstract
Using a Pantak Therapax SXT 150 system HVL values for clinical beams generated with filters 4–8, were determined as a function of FCD (30–130 cm). Aluminium absorbers were placed midway between the focus and chamber with collimation to define both narrow and broad beam geometries. For filters 4–7 with broad beam geometry the HVL initially decreases as the FCD is increased from 30 cm and then increases as the FCD approaches 130 cm. In contrast filter 8 exhibits a reduction in HVL with increasing FCD attributed to the decreasing influence of absorber scatter. With narrow beam geometry the HVL of filter 4 increases as the FCD is increased. For other filters the HVL variation is similar to that for the broader beam albeit that for a given FCD the HVL is smaller, a consequence of reduced absorber scatter. Monte Carlo BEAMnrc simulations of filter 4–8 beams demonstrated a quality dependent air attenuation effect associated with an increase in HVL for lower quality beams with increasing FCD. Thus for the beams investigated in this work the variation of HVL with FCD can be interpreted in terms of the competing influences of absorber scatter, which tends to decrease the measured HVL, and a quality dependent in air attenuation that tends to increase the HVL with increasing FCD. In terms of an absorbed dose determination it is shown that changes of HVL with FCD resulted in variations of Dw,z = 0 < ±0.5 %.
Keyword Absorbed dose
HVL
Superficial
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ

Document type: Journal Article
Sub-type: Article (original research)
Collection: Mater Research Institute-UQ (MRI-UQ)
 
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