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Volumetric modulated arc therapy for recurrent nasopharyngeal carcinoma: a dosimetric comparison with intensity-modulated radiation therapy

WU Fu-rong1,2, TAN Bing2, QIU Da2, WANG Ying2   

  1. 1.Postgraduate College, Guangxi Medical University, Nanning 530021, China; 2.Department of Radiotherapy, Chongqing Cancer Hospital, Chongqing 400030, China
  • Online:2014-03-28 Published:2014-04-02

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Abstract:

Objective To explore the dosimetric characteristics of volumetric modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT) during the treatment of recurrent nasopharyngeal carcinoma (rNPC). Methods Thirty patients with rNPC were selected. The target areas received two dose levels using simultaneous integrated boosts (SIB) technique, i.e. PGTV 2.26Gy/F and PCTV 2Gy/F in 30 fractions. VMAT and IMRT treatment plans were designed with the same dosimetric constraints for each patient. Dosimetric comparisons between VMAT and IMRT plans were analyzed to evaluate ①target coverage, and homogeneity and conformity of PTV, ②sparing of OARs, and ③monitor units (MUs). Results The average dose of planning clinical target, dose received by 2% (D2), and 98% (D98) of the planning clinical target volume of VMAT were higher than those of IMRT (P<0.05). The target conformity index (CI) of VMAT was higher than that of IMRT (P<0.05) and the heterogeneity index (HI) of VMAT was lower than that of IMRT (P<0.05). The right temporal lobe D1 of VMAT was lower than that of IMRT (P<0.05), while brainstem Dmax and D1 of VMAT were higher than those of IMRT (P<0.05). The right temporal lobe D1 of VMAT was lower than that of IMRT (P<0.05), while brainstem Dmax and D1 of VMAT were higher than those of IMRT (P<0.05). The left temporomandibular joint Dmax and left temporal lobe Dmax of VMAT were higher than those of IMRT (P<0.05). The differences of spinal cord Dmax, optic nerve Dmax, crystal Dmax, and parotid gland D50 between VMAT and IMRT were not statistically significant (P>0.05). Compared to IMRT, the total MU of VMAT reduced by an average of 33.2% (P<0.05). Conclusion The results indicate that VMAT provides a better average dose of planning clinical target, conformity, and homogeneity, and fewer MUs than IMRT for recurrent nasopharyngeal carcinoma patients. But for normal tissue sparing, VMAT is similar to IMRT.

Key words: recurrent nasopharyngeal carcinoma, volumetric modulated arc therapy, intensity-modulated radiation therapy, dosimetry