Biomedical subjects

Fumio Komai

Publications and source records attributed to Fumio Komai.

4 recordsLinked to original sources

PubMed2006

[Two approximations to obtain the collimator scatter factor (Sc) for MLC irregular fields].

The collimator scatter factor (S(c)(MLC)) at MLC irregular fields for high-energy X-ray irradiation is generally assumed to be equal to the jaw collimator scatter factor (S(c)(jaw)) of the square field equivalent to the rectangular field produced using pairs of jaw collimators. However, this assumption becomes strained as the ratio of the MLC equivalent square field side to the jaw collimator equivalent square field side decreases. In this study, for 4 MV and 10 MV X-rays, the collimator scatter factor (S(c)(MLC)) for an MLC irregular field could be evaluated with a high degree of accuracy using the MLC irregular correction (F(MIC)) factor or the jaw collimator correction (F(JCC)) factor.

Phantoms, Imaging↗

PubMed2004

[Method of estimating 10 MV X-ray irregular field dose using the collimator scatter factor (Sc) and phantom scatter factor (Sp)].

It has been found that in general 10 MV X-ray dose calculation can be made accurately for multi-leaf collimator irregular fields by using the total scatter factor (S(cp)), collimator scatter factor (S(c)), and phantom scatter factor (S(p)) proposed by Khan et al. With respect to the collimator scatter factor (S(c)), we used the field-mapping method of Kim et al. to obtain equivalent square fields of irregular fields (the collimator reverse effect can be accurately dissolved using the field-mapping method). Even for extremely small multi-leaf fields compared with the main collimator opening, X-ray output calculations could be made accurately by introducing the small segment correction (SSC) factor. With respect to the phantom scatter factor (S(p)), highly accurate calculations could be made for irregular field irradiation by applying an F(MLC) (MLC radiation leakage) factor to the equivalent square field (in cases in which the ratio of the multi-leaf equivalent square field side to the main collimator equivalent square field side is less than 0.6). However, it has been found that highly accurate dose calculations can, in general, be performed when the main collimator is limited just at the opening determined by the multi-leaf collimator field.

Phantoms, Imaging↗

PubMed2004

[Method for estimating 4 MV X-ray irregular field dose using the collimator scatter factor (Sc) and phantom scatter factor (Sp)].

Calculation of in-air or in-water dose for 4 MV X-ray irregular fields could be accurately performed using the collimator scatter factor (S(c)) and phantom scatter factor (S(p)) concepts. It has been revealed that the equivalent square field for a multi-leaf collimator (MLC) irregular field can be evaluated accurately by using the S(p)-Clarkson or S(c)-Clarkson integration method; however, the S(c)-Clarkson integration method is more straightforward because the S(c) factor expresses the in-air X-ray output factor. It has been found that when the MLC field is relatively much smaller than the main collimator field, the Sc factor can be accurately evaluated by introducing the small segment correction (SSC) factor (except for the case in which the MLC field is less than 1 x 1 cm(2)). It has also been found that both the S(p) factor and the tissue-phantom ratio (TPR) can be precisely evaluated by introducing the F(MLC) factor in cases in which the ratio of the MLC equivalent square field side to the main collimator equivalent square field side is less than about 0.7.

Phantoms, Imaging↗

PubMed2002

[Comments on evaluation method for equivalent square fields to the collimator scatter factors of rectangular fields].

In the measurement of 4 MV and 10 MV X-ray collimator scatter factors (S(c)), the method of using an acrylic mini-phantom showed no significant differences between cases in which the chamber axis was either parallel or perpendicular to the beam axis. Chamber readings with an aluminum or acrylic build-up cap were not reflected by contaminant electrons when the chamber axis was parallel to the beam axis. On the basis of the data on 4 MV and 10 MV X-ray collimator Sc measured using an acrylic mini-phantom, we examined three methods of obtaining square fields equivalent to rectangular fields, and reached the following conclusions: (1) The A/P method was not accurate because it did not take into account the structure of the radiation head. (2) Regarding the geometrical weight factor (k) used in the field-mapping method, more accurate k values were obtained when using the geometrical places of the flattening filter (or the second source, taken from the concept of extra-focal radiation), the upper and lower collimators, and the chamber, rather than when using the geometrical places of the source, the upper and lower collimators, and the chamber. (3) The most accurate k values could, in general, be obtained when determined on the basis of measured S(c) data.

Phantoms, Imaging↗