Total scatter factor (S_cp), head scatter factor (S_c) and phantom scatter factor (S_p) are very important for accurate radiation therapy at stereotactic radiosurgery (SRS) with irregular field shape using micro-MLC and intensity modulated radiation therapy (IMRT) including many small field sizes. In this study we measured and compared S_cp with reference ion chamber, pinpoint chamber and diode detector and adapted the resuls form diode detector. Head scatter factors for small field sizes were also measured with diode detector covered 1.5 cm-thick solid water build-up cap. Some errors like as electron contamination of 1∼3% were included in the values of Sc but trend of total results of S_c was coincided with basic theory. Phantom scatter factors for small field sizes were calculated form S_cp and S_c. The results of S_p were compared and were well-agreed with those of other authors.

KeywordsSmall field size, Output factor, Head scatter factor, Phantom scatter factor