- •Comparing Iris and MLC plan quality for 56 CyberKnife abdominal and prostate SBRT cases.
- •Comparison based on a overall mathematical scoring index and on clinical scoring.
- •Iris and MLC comparison was not straightforward when based on multiple parameters.
- •Mathematical and clinical scoring proved essential to evaluate MLC plans advantages.
- •Time reduction achievable by MLC is highly variable among different published studies.
This study evaluated the plan quality of CyberKnife MLC-based treatment planning in comparison to the Iris collimator for abdominal and pelvic SBRT. Multiple dosimetric parameters were considered together with a global scoring index validated by clinical scoring.
Methods and materials
Iris and MLC plans were created for 28 liver, 15 pancreas and 13 prostate cases including a wide range of PTV sizes (24–643 cm3). Plans were compared in terms of coverage, conformity (nCI), dose gradient (R50%), homogeneity (HI), OAR doses, PTV gEUD, MU, treatment time both estimated by TPS (tTPS) and measured. A global plan quality score index was calculated for IRIS and MLC solutions and validated by a clinical score given independently by two observers.
Compared to Iris, MLC achieved equivalent coverage and conformity without compromising OAR sparing and improving R50% (p < 0.001). MLC gEUD was slightly lower than Iris (p < 0.05) for abdominal cases. MLC reduced significantly MU (−15%) and tTPS (−22%). Time reduction was partially lost when measured. The global score index was significantly higher for MLC solutions which were selected in 73% and 64% of cases respectively by the first and second observer.
Iris and MLC comparison was not straightforward when based on multiple dosimetric parameters. The use of a mathematical overall score index integrated with a clinical scoring was essential to confirm MLC plans advantages over Iris solutions.
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Accepted: November 17, 2018
Received in revised form: November 13, 2018
Received: June 13, 2018
© 2018 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.