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Execution of a single-isocenter three-field technique, using a multileaf collimator or tray-mounted cerrobend blocks:
G O De Meerleer1, C M Derie, L Vakaet
1Division of Radiotherapy, University Hospital, Gent, Belgium.
Purpose:
In this article, we studied the total treatment time of a single-isocenter three-field irradiation of breast and axilla, using either tray-mounted cerrobend blocks, or a multileaf collimator (MLC) for field shaping.
Methods And Materials:
A total of 20 female, unselected patients were given 50 Gy (2 Gy/fraction) on breast and 46 Gy on axilla and supraclavicular region (2 Gy/fraction). Patients were randomized between two different treatment groups. The first group (n = 10) was treated on a Philips SL-75 linear accelerator (SL-75), using 5 MV photons with tray-mounted cerrobend blocks. The second group (n = 10) was treated on a Philips SL-25 linear accelerator, using 6 MV photons and a MLC (SL-25-MLC).
Results:
Although the beam-on time on the SL-25-MLC was significantly higher (p < 0.0001) compared to the SL-75, overall treatment time was significantly shorter using a MLC instead of tray-mounted cerrobend blocks (p < 0.0001). The difference in total treatment time was in the range of 100 s per patient per day. The main difference between the two accelerators was observed when setup of the second and third field was done using the automatic setup facility of the SL-25-MLC (avoids entering the treatment room). A mean time gain of 124 s per treatment session was observed using automatic setup. Considering the yearly number of patients receiving this treatment, a total time gain equivalent to 16.15 8-h workdays was calculated.
Conclusions:
Compared to a technique using tray-mounted cerrobend blocks in the single-isocenter three-field irradiation of a breast and axilla, a MLC combined with automatic field setup provides a significant time advantage, by reducing the number of manipulations inside the treatment room.