IJMPCERO  Vol.2 No.1 , February 2013
Effects of Beam Startup Characteristics on Dose Delivery Accuracy at Low Monitor Units in Step-and-Shoot Intensity Modulated Radiation Therapy
ABSTRACT

Intensity modulated radiation therapy (IMRT) is a highly accurate technique that is usually implemented in either dynamic or step-and-shoot fashion with many segments each having low monitor units (MUs). The present study evaluated the effects of beam startup characteristics on the dose delivery accuracy for each segment at low MUs for step-and-shoot IMRT with an Elekta Precise accelerator at the highest dose rates. We used a two-dimensional semi-conductor detector for the dose measurements. The field size of each segment was assumed to be 20 ×20 cm2 and each segment was set to deliver 1 - 10 MUs. Our results show a variation in dose delivery accuracy between segments for the same IMRT beam, which can be attributed to the beam startup characteristics. This variability is attributed to the changes in the transient changes in the temperatures of the electron gun filament and the magnetron. That is, the transient increase in the temperature of the filament leads to increasing doses with time and that of the magnetron leads to decreasing doses with time during the first few MUs.


Cite this paper
K. Fujimoto, K. Tateoka, Y. Yaegashi, K. Shima, J. Suzuki, Y. Saito, A. Nakata, T. Nakazawa, T. Abe, M. Yano, M. Someya, K. Nakata, M. Hori, M. Hareyama and K. Sakata, "Effects of Beam Startup Characteristics on Dose Delivery Accuracy at Low Monitor Units in Step-and-Shoot Intensity Modulated Radiation Therapy," International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, Vol. 2 No. 1, 2013, pp. 1-5. doi: 10.4236/ijmpcero.2013.21001.
References
[1]   V. Y. Kuperman and W.-C. Lam, “Improving Delivery of Segments with Small MU in Step-and-Shoot IMRT,” Medical Physics, Vol. 33, No. 4, 2006, pp. 1067-1073. doi:10.1118/1.2174128

[2]   R. D. Wiersma and L. Xing “Examination of Geometric Accuracies of Gated Step-and-Shoot Intensity Modulated Radiation Therapy,” Medical Physics, Vol. 34, No. 10, 2007, pp. 3962-3970. doi:10.1118/1.2776671

[3]   G. A. Ezzell and S. Chungbin, “The Overshoot Phenomenon in Step-and-Shoot IMRT Delivery,” Journal of Applied Clinical Medical Physics, Vol. 2, No. 3, 2001, pp. 138-148. doi:10.1120/1.1386508

[4]   S.-K. Kang, K.-H. Cheong, T. Hwang, B. C. Cho, S. S. Kim, K. J. Kim, D. H. Oh and H. Bae, “Dosimetric Characteristics of Linear Accelerator Photon Beams with Small Monitor Unit Setting,” Medical Physics, Vol. 35, No. 11, 2008, pp. 5172-5178. doi:10.1118/1.2995759

[5]   V. N. Hansen, P. M. Evans, G. J. Budgell, J. H. L. Mott, P. C. Williams, M. J. P. Brugmans, F. W. Wittk?mper, B. J. Mijnheer and K. Brown, “Quality Assurance of the Dose Delivery by Small Radiation Segments,” Physics in Medicine and Biology, Vol. 43, No. 9, 1998, pp. 2665-2675. doi:10.1088/0031-9155/43/9/017

[6]   M. Ravikumar, M. A. Al Asmary, R. a. A. Sultan and H. A. Al Ghamdi, “Dose Delivery Accuracy of Therapeutic Photon and Electron Beams at Low Monitor Unit Setting,” Strahlentherapie und Onkologie, Vol. 181, No. 12, 2005, pp. 796-799. doi:10.1007/s00066-005-1412-9

[7]   P. Mohr, S. Brieger, J. Stahl and G. Witucki, “Linearity of the Dose Monitor System at Low Monitor Units,” Strahlentherapie und Onkologie, Vol. 183, No. 6, 2007, pp. 327-331. doi:10.1007/s00066-007-1596-2

[8]   V. Moiseenko, C. Duzenli and R. E. Durand, “In Vitro Study of Cell Survival Following Dynamic MLC Intensity-Modulated Radiation Therapy Dose Delivery,” Medical Physics, Vol. 34, No. 4, 2007, pp. 1514-1520. doi:10.1118/1.2712044

[9]   J. Z. Wang, X. A. Li, W. D. D’Souza and R. D. Stewart, “Impact of Prolonged Fraction Delivery Times on Tumor Control: A Note of Caution for Intensity-Modulated Radiation Therapy (IMRT),” International Journal of Radiation Oncology, Biology, Physics, Vol. 57, No. 2, 2003, pp. 543-552. doi:10.1016/S0360-3016(03)00499-1

[10]   H. Paganetti, “Changes in Tumor Cell Response Due to Prolonged Dose Delivery Times in Fractionated Radiation Therapy,” International Journal of Radiation Oncology, Biology, Physics, Vol. 63, No. 3, 2005, pp. 892900. doi:10.1016/j.ijrobp.2005.07.953

[11]   M. Buchgeister and F. Nüsslin, “Startup Performance of the Traveling Wave versus Standing Wave Linear Accelerator,” Medical Physics, Vol. 25, No. 4, 1998, pp. 493495. doi:10.1118/1.598225

[12]   E. E. Klein, et al., “Task Group 142 report: Quality AsSurance of Medical Accelerator,” Medical Physics, Vol. 36, No. 9, 2009, pp. 4197-4212. doi:10.1118/1.3190392

[13]   C. B. Saw, S. Li, K. M. Ayyangar, M. Yoe-Sein, S. Pillai, C. A. Enke and J. C. Celi, “Dose Linearity and Uniformity of a Linear Accelerator Designed for Implementation of Multileaf Collimation System-Based Intensity Modulated Radiation Therapy,” Medical Physics, Vol. 30, No. 8, 2003, pp. 2253-2256. doi:10.1118/1.1592640

[14]   D. Greene and P. C. Williams, “Linear Accelerators for Radiation Therapy,” 2nd Edition, Taylor & Francis, New York, 1997.

 
 
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