AbstractObjective To simulate the possible systematic delivery errors introduced by monitor units (MU) and multi-leaf collimator (MLC) in radiotherapy plans for nasopharyngeal carcinoma (NPC), and to analyze the dosimetric sensitivity of static intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) with these errors. Methods Five IMRT plans were replanned using VMAT modality with the same physical parameters, and then MU errors of 1.25%, 2.50%, and 5.00% were introduced into IMRT and VMAT plans. Meanwhile, to simulate leaf position errors during delivery, MLC position errors (0.25 mm, 0.50 mm, 1.00 mm, 1.50 mm, and 2.00 mm) were introduced by modifying the original plan documents. The types of MLC errors were as follows:(1) the MLC banks moved in the same direction;(2) the MLC banks moved in opposing directions (expand or contract the MLC gaps). The differences in dosimetric sensitivity introduced by MU and MLC errors between IMRT and VMAT plans for NPC were calculated by linear regression analysis. Results With the increase in MU errors, the doses to target and organs at risk (OARs) of IMRT and VMAT plans increased in a linear way, and met R2=0.992-1.000(P<0.05). For MLC errors, the average dosimetric sensitivity for target and OARs of IMRT and VMAT were -0.26%/mm and -0.65%/mm in case of offset errors, 4.87%/mm and 8.68%/mm in case of expansion errors, and -6.04%/mm and -9.88%/mm in case of indentation errors. In addition, the dosimetric sensitivity with the three types of MLC errors was greater for VMAT plan than for IMRT plan. Conclusions MU and MLC errors have a significant effect on the dose distribution of IMRT, and particularly VMAT, for NPC. It is important to execute routine quality assurance of MLC to ensure accurate radiotherapy.
Cheng Yanming,Hu Cairong,Yin Xiaojuan et al. Dosimetric sensitivity with MU and MLC errors in IMRT versus VMAT plan for nasopharyngeal carcinoma[J]. Chinese Journal of Radiation Oncology, 2017, 26(10): 1199-1203.
Cheng Yanming,Hu Cairong,Yin Xiaojuan et al. Dosimetric sensitivity with MU and MLC errors in IMRT versus VMAT plan for nasopharyngeal carcinoma[J]. Chinese Journal of Radiation Oncology, 2017, 26(10): 1199-1203.
[1] McGrath SD,Matuszak MM,Yan D,et al. Volumetric modulated arc therapy for delivery of hypofractionated stereotactic lung radiotherapy:a dosimetric and treatment efficiency analysis[J].Radiother Oncol,2010,95(2):153-157.DOI:10.1016/j.radonc.2009.12.039. [2] Otto K.Volumetric modulated arc therapy:IMRT in a single gantry arc[J].Med Phys,2008,35(1):310-317.DOI:10.1118/1.2818738. [3] Study#RTOG0615,A phase Ⅱ study of concurrent chemoradiotherapy using three-dimensional conformal radiotherapy (3D-CRT) or intensity-modulated radiation therapy (IMRT)+ Bevacizumab (BV) for locally or regionally advanced nasopharyngeal cancer[J].2006. [4] Yu CX,Amies CJ,Svatos M.Planning and delivery of intensity-modulated radiation therapy[J].Med Phys,2008,35(12):5233-5241.DOI:10.1118/1.3002305. [5] Bertelsen A,Hansen CR,Johansen J,et al. Single arc volumetric modulated arc therapy of head and neck cancer[J].Radiother Oncol,2010,95(2):142-148.DOI:10.1016/j.radonc.2010.01.011. [6] Oliver M,Bush K,Zavgorodni S,et al. Understanding the impact of RapidArc therapy delivery errors for prostate cancer[J].J Appl Clin Med Phys,2011,12(3):32-43.DOI:10.1120/jacmp.v12i3.3409. [7] LoSasso T.IMRT delivery performance with a varian multileaf collimator[J].Int J Radiat Oncol Biol Phys,2008,71(1 Suppl):S85-S88.DOI:10.1016/j.ijrobp.2007.06.082. [8] Ling CC,Zhang PP,Archambault Y,et al. Commissioning and quality assurance of RapidArc radiotherapy delivery system[J].Int J Radiat Oncol Biol Phys,2008,72(2):575-581.DOI:10.1016/j.ijrobp.2008.05.060. [9] Boylan C,McWilliam A,Johnstone E,et al. The impact of continuously-variable dose rate VMAT on beam stability,MLC positioning,and overall plan dosimetry[J].J Appl Clin Med Phys,2012,13(6):254-266.DOI:10.1120/jacmp.v13i6.4023. [10] Bayouth JE,Wendt D,Morrill SM.MLC quality assurance techniques for IMRT applications[J].Med Phys,2003,30(5):743-750.DOI:10.1118/1.1564091. [11] Mu G,Ludlum E,Xia P.Impact of MLC leaf position errors on simple and complex IMRT plans for head and neck cancer[J].Phys Med Biol,2008,53(1):77-88.DOI:10.1088/0031-9155/53/1/005. [12] Heilemann G,Poppe B,Laub W.On the sensitivity of common gamma-index evaluation methods to MLC misalignments in Rapidarc quality assurance[J].Med Phys,2013,40(3):031702.DOI:10.1118/1.4789580. [13] Oliver M,Gagne I,Bush K,et al. Clinical significance of multi-leaf collimator positional errors for volumetric modulated arc therapy[J].Radiother Oncol,2010,97(3):554-560.DOI:10.1016/j.radonc.2010.06.013. [14] Qi P,Xia P.Relationship of segment area and monitor unit efficiency in aperture-based IMRT optimization[J].J Appl Clin Med Phys,2013,14(3):232-243.DOI:10.1120/jacmp.v14i3.4056.
2017, Vol. 26 
