In vivo diode dosimetry proved its efficacy as a patient-specific quality assurance tool for 3DCRT. Its usefulness in IMRT is not sufficiently investigated.

Four step-and-shoot IMRT plans were generated for different treatment sites using an Alderson Rando anthropomorphic phantom. Two in vivo semiconductor diodes were used to perform 33 entrance radiation dose measurements at central axis and max beam point dose on a water-equivalent slabs based on the anthropomorphic plans. Measured values were compared to planned ones, and detailed analysis per segment of each IMRT field was made to infer the reason behind the discrepancies of measurements from expectations.

Point dose measurements were performed on a beam and a segment basis. Agreement within ±5% action level with planned dose was 27% of beams at central axis versus 45% at max point dose and 10% of segments at central axis versus 25% at max point dose. For ±10% action level, 70% of beams at central axis versus 73% at max point dose, and 15% of segments at central axis versus 41% at max point dose. Classification of segments resulted in a significance of .021 for measuring at positions unaffected by the MLC partial and total blockage.

Diode measurements are recommended at maximum dose coordinates for open beams/segments for more accurate patient dose verification results as part of in vivo dosimetry. This is important for limited resources centres treating with sMLC IMRT.