Abstract：Objective To study a new quantitative method—arc-beam modulation complexity score (AMCS) to evaluate the plan complexity of volumetric-modulated arc therapy (VMAT), and the effect of the six metrics on VMAT dosimetric verification. Methods The six metrics, which contain the average of beam area (ABA), the average of leaf travel (ALT), the average of beam width (ABW), the modulation complexity score (MCS), the leaf travel and modulation complexity score (LTMCS) and AMCS, was calculated to quantify the plan complexity of VMAT for 127 selected patients. Delta4 system was used for verifying the VMAT plans and the γ pass rate was calculated. The relativity between the six metrics and the pass rates or between the 6 parameters were analyzed with Pearson method. Results The average of ABA, ALT, ABW, MCS, LTMCS and AMCS were (73.5±24.1) cm2, (69.6±9.8) cm, (3.63±1.03) cm, 0.33±0.05, 0.14±0.04 and 0.16±0.05, respectively. A negative correlation was observed for ALT and the pass rate, and the other metrics had a positive correlation with it (P=0.000).The correlation between AMCS and the pass rate was the strongest with Pearson’s (r=0.637) in the six metrics. The percentage of arcs with a pass rate lower the 95% was 60.7 when AMCS is lower than the average, while it was 9.9% when AMCS is higher than the average. Both ABA and ABW had no significant correlation with ALT (P=0.720, 0.073), and the other metrics had significant correlations (P=0.000-0.003). Conclusions AMCS is a suitable quantitative metric to evaluate the plan complexity of VMAT, and could be used to forecast the result of dosimetric verification of VMAT plans. It could be also use to compare the multiple VMAT plans complexity and help us to choose the best plan.
Li Guangjun,Li Yanlong,Wang Xuetao et al. The quantitative method to evaluate the plan complexity of volumetric-modulated arc therapy[J]. Chinese Journal of Radiation Oncology, 2015, 24(6): 712-713.
[1] 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. [2] Cozzi L,Dinshaw KA,Shrivastava SK,et al. A treatment planning study comparing volumetric arc modulation with RapidArc and fixed field IMRT for cervix uteri radiotherapy[J].Radiother Oncol,2008,89(2):180-191.DOI:10.1016/j.radonc.2008.06.013. [3] Verbakel WFAR,Cuijpers JP,Hoffmans D,et al. Volumetric intensity-modulated arc therapy vs.conventional IMRT in head-and-neck cancer:a comparative planning and dosimetric study[J].Int J Radiat Oncol Biol Phys,2009,74(1):252-259.DOI:10.1016/j.ijrobp.2008.12.033. [4] Mcniven AL,Sharpe MB,Purdie TG.A new metric for assessing IMRT modulation complexity and plan deliverability[J].Med Phys,2010,37(2):505-515.DOI:10.1118/1.3276775. [5] Masi L,Doro R,Favuzza V,et al. Impact of plan parameters on the dosimetric accuracy of volumetric modulated arc therapy[J].Med Phys,2013,40(7):071718.DOI:10.1118/1.4810969. [6] Mohan R,Arnfield M,Tong SD,et al. The impact of fluctuations in intensity patterns on the number of monitor units and the quality and accuracy of intensity modulated radiotherapy[J].Med Phys,2000,27(6):1226-1237.DOI:10.1118/1.599000. [7] Matuszak MM,Larsen EW,Fraass BA.Reduction of IMRT beam complexity through the use of beam modulation penalties in the objective function[J].Med Phys,2007,34(2):507-520.DOI:10.1118/1.2409749. [8] Dai JR,Zhu YP.Minimizing the number of segments in a delivery sequence for intensity-modulated radiation therapy with a multileaf collimator[J].Med Phys,2001,28(10):2113-2120.DOI:10.1118/1.1406518. [9] Webb S.Use of a quantitative index of beam modulation to characterize dose conformality:illustration by a comparison of full beamlet IMRT,few-segment IMRT (fsIMRT) and conformal unmodulated radiotherapy[J].Phys Med Biol,2003,48(14):2051-2062.DOI:10.1088/0031-9155/48/14/301. [10] Giorgia N,Antonella F,Eugenio V,et al. What is an acceptably smoothed fluence
Dosimetric and delivery considerations for dynamic sliding window IMRT[J].Radiat Oncol,2007,2:42.DOI:10.1186/1748-717X-2-42. [11] Coselmon MM,Moran JM,Radawski JD,et al. Improving IMRT delivery efficiency using intensity limits during inverse planning[J].Med Phys,2005,32(5):1234-1245.DOI:10.1118/1.1895545. [12] McGarry CK,Chinneck CD,O′Toole MM,et al. Assessing software upgrades,plan properties and patient geometry using intensity modulated radiation therapy (IMRT) complexity metrics[J].Med Phys,2011,38(4):2027-2034.DOI:10.1118/1.3562897.
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