A Dosimetric Comparison Of Intensity Modulated Radiation Therapy And Three-dimensional Conformal Therapy For Maxillary Sinus Carcinoma

PurposeTo compare the homogeneity and conformity of dose distribution in the target,and thedose to the organs at risk among three dimensional conformal radiation therapy(3D-CRT)and intensity modulated radiation therapy, and then to evaluate the clinical value of IMRTfor maxillary sinus carcinoma, to investigate the dosimetry advantages and disadvantagesof the four plans.Methodwe retrospectively selected5patients,who had been recently treated for maxillarysinus carcinoma in our hospital from2010to2012．all patients had a pathologically orbiopsy-proven diagnosis of squamous carcinoma．The CT-Sim images of the patients wereavailable on the hard disk of the3D-TPS．The contours of target volumes，normal tissueand critical organs were based on patients’ pre-radiotherapy MRI images．For each patient,four treatment plans，including a6field3D plan, a5field IMRT plan，a7field IMRT planand a9field IMRT plan were generated．We compared dose distribution of target(Dmax, Dmin, Dmean, D95, V95, dose conformity and homogeneity index),organs at risk(Dmax and Dmean) between the four plans．Results1.Compared with the3D-CRT, IMRT significantly improved the Dmax、V95%andCI value of PTV-G(P<0.05),and the Dmax、Dmin and CI value of PTV-C(P<0.05);compared3D-CRT and IMRT plans all showed no statistical difference (P value were0.596,0.103). Compared with the3D-CRT, IMRT significantly reduced the V95%value ofPTV-C（P<0.05）.Compared IMRT-5F,IMRT-7F and IMRT-9F, IMRT-5F reduced the CIvalue(P<0.05). 2. IMRT enabled dose reductions of normal tissues, including brainstem(Dmean by32.25%), optic chiasm(Dmax by7.66%and Dmean by20.62%), pituitary(Dmax by17.19%and Dmean by34.10%), ipsilateral optic nerve(Dmax by5.19%and Dmean by15.53%), and contralateral optic nerve(Dmax by7.20%and Dmean by12.80%).But IMRTplans to protect crystal around the3D-CRT planning, makes its illuminated dose increasessignificantly, the maximum dose and the mean dose showed significant difference.0．05)．Then, in all the IMRT plans，there was equivalent maximum and mean in all OARsexcept brainstem, which IMRT-7F significantly discrease mean with IMRT-5F andIMRT-9F.Conclusions1. Both IMRT and3DCRT can be good to satisfy the requirement of Clinic dosimetryin the target coverage, homogeneity and conformity．But IMRT spares better critical tissueto the3DCRT, IMRT-7F planning is feasible for clinical use．2. The numbers of field from5to9, increasing the field numbers of IMRT can neitherimprove target conformity, coverage and homogeneity, nor discrease the irradiation inOARs．...