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Dosimetric impact of systematic MLC positional errors on step and shoot IMRT for prostate cancer: a planning study

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Abstract

The positional accuracy of multileaf collimators (MLC) is crucial in ensuring precise delivery of intensity-modulated radiotherapy (IMRT). The aim of this planning study was to investigate the dosimetric impact of systematic MLC positional errors on step and shoot IMRT of prostate cancer. A total of 12 perturbations of MLC leaf banks were introduced to six prostate IMRT treatment plans to simulate MLC systematic positional errors. Dose volume histograms (DVHs) were generated for the extraction of dose endpoint parameters. Plans were evaluated in terms of changes to the defined endpoint dose parameters, conformity index (CI) and healthy tissue avoidance (HTA) to planning target volume (PTV), rectum and bladder. Negative perturbations of MLC had been found to produce greater changes to endpoint dose parameters than positive perturbations of MLC (p < 0.01). Negative and positive asynchronised MLC perturbations of −1 mm resulted in median changes in D95 of −1.2 and 0.9% respectively. Negative and positive synchronised MLC perturbations of 1 mm in one direction resulted in median changes in D95 of −2.3 and 1.8% respectively. Doses to rectum were generally more sensitive to systematic MLC errors compared to bladder (p < 0.01). Negative and positive synchronised MLC perturbations of 1 mm in one direction resulted in median changes in endpoint dose parameters of rectum and bladder from 1.0 to 2.5%. Maximum reduction of −4.4 and −7.3% were recorded for conformity index (CI) and healthy tissue avoidance (HTA) respectively due to synchronised MLC perturbation of 1 mm. MLC errors resulted in dosimetric changes in IMRT plans for prostate.

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Acknowledgments

The authors acknowledge the assistance of Sara Lyons Hackett and Simon Woodings in the preparation of this manuscript. This research has been supported by an academic Ph.D scholarship from the Malaysian Ministry of Higher Education and the University of Malaya.

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Authors and Affiliations

  1. School of Physics, The University of Western Australia, 35 Stirling Highway, Crawley, WA, 6009, Australia

    N. M. Ung & L. Wee

  2. Perth Radiation Oncology, Wembley, WA, 6014, Australia

    N. M. Ung, C. S. Harper & L. Wee

  3. Clinical Oncology Unit, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia

    N. M. Ung

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  1. N. M. Ung
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  3. L. Wee
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Correspondence to N. M. Ung.

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Ung, N.M., Harper, C.S. & Wee, L. Dosimetric impact of systematic MLC positional errors on step and shoot IMRT for prostate cancer: a planning study. Australas Phys Eng Sci Med 34, 291–298 (2011). https://doi.org/10.1007/s13246-011-0062-8

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  • DOI: https://doi.org/10.1007/s13246-011-0062-8

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