Figure 4From: Functional intercomparison of intraoperative radiotherapy equipment – Photon Radiosurgery SystemComparison of normalised Half Value Layers (HVL). The HVLs for all the x-ray sources was determined by a broad beam method, in which the x-ray probe is placed 20 cm away from the ionisation chamber, with high purity aluminium attenuators placed near the midpoint. The HVL for each x-ray source was approximately 0.1 mm Al.Back to article page