Transmission Dose Estimation Algorithm for Irregularly Shaped Radiation Field / 대한방사선종양학회지

PURPOSE: Measurement of transmission dose is useful for in vivo dosimetry. In this study, the algorithm for estimating the transmission dose for open radiation fields was modified for application to partially blocked radiation fields. MATERIALS AND METHODS: The beam data was measured with a flat solid phantom with various blocked fields. A new correction algorithm for partially blocked radiation field was developed from the measured data. This algorithm was tested in some settings simulating clinical treatment with an irregular field shape. RESULTS: The correction algorithm for the beam block could accurately reflect the effect of the beam block, with an error within +/-1.0%, with both square fields and irregularly shaped fields. CONCLUSION: This algorithm can accurately estimate the transmission dose in most radiation treatment settings, including irregularly shaped field.

A Study on the Effect of Field Shaping on Dose Distribution of Electron Beams / 대한치료방사선과학회지

In electron therapy, lead cutout or low-melting alloy block is used for shaping the field. Material for shaping electron field affects the output factor as well as the collimation system. The authors measured the output factors of electron beams for shaped fields from Clinac-18 using ionization chamber of Farmer type on polystyrene phantom. They analyzed the incident energy, collimation system and size of shaped field. For shaped field the variation of output factor for the field (A/P) has appearance of a smooth curve for all energy and all applicator collimator combination. The output factors for open field deviate from the curves for shaped fields. An output factor for a given field can be calculated by equivalent field method such as A/P method, if a combination of applicator and collimator is fixed.