Journal List > Prog Med Phys > v.25(4) > 1098446

Kim, Lee, Moon, Seol, and Lee: Characteristics of Photon Beam through a Handmade Build-Up Modifier as a Substitute of a Bolus

Abstract

We evaluated the effect of scatter on a build-up region based on the measured percent depth dose (PDD) of high-energy photon beams that penetrated a handmade build-up modifier (BM) as a substitute of bolus. BM scatter factors (SBM) were calculated based on the PDDs of photon beams that penetrated through the BM. The calculated SBM values were normalized to 1 at the square field side (SFS) of 30 mm without a BM. For the largest SFS (200 mm), the SBM values for a 6-MV beam were 1.331, 1.519, 1.598, 1.641, and 1.657 for the corresponding BM thickness values. For a 10-MV beam, the SBM values were 1.384, 1.662, 1.825, 1.913, and 2.001 for the corresponding BM thickness values. The BM yielded 76% of the bolus efficiency. We expect BM to become useful devices for deep-set patient body parts to which it is difficult to apply a bolus.

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Fig. 1.
Handmade build-up modifier (BM) designed and manufactured at our institute.
pmp-25-225f1.tif
Fig. 2.
Schematic showing the locations of the build-up modifier (BM) and the water phantom in the linear accelerator for percent depth dose (PDD) measurements.
pmp-25-225f2.tif
Fig. 3.
Treatment plans for (a) “no build-up modifier (BM) no bolus” (open), (b) BM application (BM), (c) bolus application (Bolus), and the resulting dose distributions in Eclipse. The figures show sample treatment plans for the 6-MV photon beam in Eclipse.
pmp-25-225f3.tif
Fig. 4.
Percent depth dose curves for (a) 6-MV and (b) 10-MV photon beams penetrating through various build-up modifier (BM) thicknesses, for a square field side (SFS) of 200 mm.
pmp-25-225f4.tif
Fig. 5.
Build-up modifier (BM) scatter factors for (a) 6-MV and (b) 10-MV photon beams, as a function of depth, for different values of square field side (SFS).
pmp-25-225f5.tif
Fig. 6.
Build-up modifier (BM) scatter factors at the square field side (SFS) of 200 mm, as a function of thickness.
pmp-25-225f6.tif
Fig. 7.
Relative absorption doses at different depths (0, 5, 10, 15, and 50 mm) and for different square field sides (SFSs) ((a) 30, (b) 100, (c) 150, and (d) 200 mm), for the 6-MV photon beam in a radiation treatment planning system (RTPS).
pmp-25-225f7.tif
Fig. 8.
Relative absorption doses at different depths (0, 5, 10, 15, and 50 mm) and for different SFSs ((a) 30, (b) 100, (c) 150, and (d) 200 mm), for the 10-MV photon beam in a radiation treatment planning system (RTPS).
pmp-25-225f8.tif
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