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. 2012 Sep;85(1017):1263–1271. doi: 10.1259/bjr/27924223

Figure 1.

Figure 1

Grey line indicates the measured beam penumbra data for a 9×9 cm field at a depth of 10 cm and focus-to-skin distance of 90 cm; only one half of the beam is shown. The dose levels and lateral extent of the 2 planning target volumes (PTVs) are shown by the bold horizontal lines indicating that 95% of the isocentric dose is required to enclose PTV2, and 72% is required to enclose PTV1. Note that, if PTV2 is just covered by this beam, PTV1 is covered by a dose in excess of 72%. CTV, clinical target volume.