The Dosimetric Effects of Different Multileaf Collimator Widths on Physical Dose Distributions

Document Type: Original Paper

Authors

1 Prof. of Medical physics ; National Cancer Institute, cairo university & Children Cancer Hospital , Egypt

2 Cairo University, Cairo, Egypt

Abstract

Introduction: Geometric changes in the multileaf collimator (MLC) led to dosimetric considerations in intensity-modulated radiation therapy (IMRT) due to the number and size of the pixels in the intensity map, which are determined by the MLC leaf width. In this study, we evaluated the dosimetric effects of different MLC widths on physical dose distributions for IMRT plans.
Materials and Methods: Forty-two IMRT plans based on different MLC devices were generated and analyzed to study the effect of MLC width on plan quality.
Results: Improvements in IMRT plan quality using 0.4 cm leaf width in comparison with 1 cm leaf width were evaluated. The 0.4 cm leaf-based plans resulted in significantly higher Dmean, D98%, D95% , D5%, and V95 (58.86 Gy, 95.11%, 96.57%, 104%, and 97.92%, respectively) compared to the 1 cm leaf plans (58.66 Gy, 92.56%, 94.56%, 104.14%, and 95.72%, respectively). Conformation number (CN) for planning target volume in 0.4 cm leaf plans was significantly higher than the 1 cm leaf plans (0.74 vs. 0.67; P<0.05). In addition, the 0.4 cm leaf plans significantly improved dose homogeneity compared to the 1 cm leaf plans (1.08 vs. 1.10; P<0.05). We found that 0.4 cm leaf width significantly decreased the integral dose to normal tissue compared to the 1 cm leaf width (from 56.09 to 49.46 Gy.Kg P<0.05).  Conclusion: No significant clinical differences were observed between the two plans for a serially functioning tissue, while the differences in mean doses were statistically significant for parallel functioning normal tissues.

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References

 

  1. Fiveash JB, Murshed H, Duan J, Hyatt M, Caranto J, Bonner JA, Popple RA. Effect of multileaf collimator leaf width on physical dose distributions in the treatment of CNS and head and neck neoplasms with intensity modulated radiation therapy. Medical physics. 2002 Jun 1;29(6):1116-9.
  2. Burmeister J, Mc Dermott PN, Bossen berger T, Ben Josef E, Levin K, Forman JD. Effect of MLC leaf width on the planning and delivery of SMLC IMRT using the CORVUS inverse treatment planning system. Medical physics. 2004 Dec 1;31(12):3187-93.
  3. International Commission on Radiation Units and Measurements ICRU report 50: prescribing, recording, and reporting photon beam therapy. Bethesda: ICRU, 1993.
  4. International Commission on Radiation Units and measurements ICRU report 62: prescribing, recording, and reporting photon beam therapy (supplement to ICRU report 50). Bethesda: ICRU, 1999.
  5. Deshpande S, Sathiyanarayanan VK, Bhangle J, Swamy K, Basu S. Dosimetric and QA aspects of Konrad inverse planning system for commissioning intensity-modulated radiation therapy. Journal of Medical Physics/Association of Medical Physicists of India. 2007 Apr;32(2):51.
  6. Kim HJ, Kim S, Park YK, Kim JI, Park JM, Ye SJ. Multileaf collimator tongue-and-groove effect on depth and off-axis doses: A comparison of treatment planning data with measurements and Monte Carlo calculations. Medical Dosimetry. 2015 Dec 1;40(4):271-8.
  7. Van’t Riet A, Mak AC, Moerland MA. A conformation number to quantify the degree of conformality in brachytherapy and external beam irradiation: Application to the prostate. International Journal of Radiation Oncology* Biology* Physics. 1997 Feb 1;37(3):731-6.
  8. Aoyama H, Westerly DC, Mackie TR, Olivera GH, Bentzen SM, et al. Integral radiation dose to normal structures with conformal external beam radiation. International Journal of Radiation Oncology* Biology* Physics. 2006 Mar 1;64(3):962-7.
  9. Huang EH, Pollack A, Levy L, Starkschall G, Dong L, Rosen I, Kuban DA. Late rectal toxicity: dose–volume effects of conformal radiotherapy for prostate cancer. International Journal of Radiation Oncology* Biology* Physics. 2002 Dec 1;54(5):1314-21.
  10. Hall EJ, Wuu CS. Radiation-induced second cancer: the impact of 3D-CRT and IMRT.  International Journal of Radiation Oncology* Biology* Physics. 2003 May 1;56(1):83-8.
  11. Gong Y, Wang S, Zhou L, Liu Y, Xu Y, Lu Y, et al. Dosimetric comparison using different multileaf collimeters in intensity-modulated radiotherapy for upper thoracic esophageal cancer. Radiation Oncology. 2010 Jul 15;5(1):65.