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Prostate Helical Tomotherapy: A semi-empirical estimation of the scaling factor based on 2D approximating field
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G. Grigorov   , J.C.L. Chow |
| , grigorovgn@yahoo.ca |
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Abstract: (11688 Views) |
| Background: In Helical Tomotherapy (HT), the
scaling factor (SF) is the time in seconds that each
leaf viewing a target would need to be open to deliver
the prescribed dose. The SF is patient-specific and is
used to calculate the rotational period of the gantry,
and the total treatment time (TTT) of the HT. The SF is
generally difficult to estimate. Currently, it takes
about one hour to fully optimize a prostate HT plan
and to calculate the corresponding TTT. The aim of
this study is to develop a method for estimation of
the SF directly using a patient-specific approximating
function. Materials and Methods: The SFs of ten
randomly selected patients were used to build the
approximation model. For the entire group of patients
the PTV1 ranged from 57 to 396 cm3 for PTV1 margins
from 2 to 10 mm. The discrete data for every patient
is represented by an individual function, SF=f (k×
PTV1). The values of the function were rescaled to a
special unit which represents the target volume irradiated
with the prescribed dose per second. The values
were normalized with two “geometric” parameters,
namely, the target-to-target and the body-to-body
ratios. After the normalization, the function for every
patient was ordered in the file by the volume of the
prostate and seminal vesicles. Results: For prostate
HT planning, it was found that the planning target
volume (PTV1) has a higher impact on the SF values
than the size of the patient's bodies. The function
SF=f (k×PTV1) was found smooth and continuous over
the given interval. The rescaled and normalized
functions for all patients were represented as delimiters
of a 2D field. Conclusion: The method proposed
for determination of the SF and TTT for HT prostate
planning covers PTV1 of four margins and a volume of
prostate and seminal vesicles ranging from 42.8 to
161 cm3. Using these approximations, the TTTs for a
second group of patients were determined in several
minutes with deviation ranging from −2.8% to +7.1%
compared to that of the TTTs calculated using the HT
planning system. Iran. J. Radiat. Res., 2010 7 (4): 177-185 |
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| Keywords: Helical tomotherapy, prostate treatment, scaling factor. |
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Full-Text [PDF 342 kb]
(2252 Downloads)
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Type of Study: Original Research |
Subject:
Radiation Biology
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