Dosimetric Comparison Of CRT, IMRT And3D-CRT In Advanced Cervical Cancer Patients

Purpose1. To compare the homogeneity and conformity of dose distribution in the target,thetreatment period of patients and the dose to the organs at risk among conventional radiationtherapy(CRT),three dimensional conformal radiation therapy(3D-CRT) and intensitymodulated radiation therapy(IMRT), and then to evaluate the clinical value of IMRT forcervical cancer.2. To compare bone marrow-sparing intensity-modulated radiotherapy (BM-IMRT)and IMRT techniques in reducing the volume and dose of bone marrow of patients withadvanced cervical cancer. The prescribed dose was45Gy, to evaluate the dose distributiondifference in OAR and PTV in IMRT and BM-IMRT.3. To evaluate the organ sparing effect to different plan target volume margin size inintensity-modulated radiotherapy (IMRT) in cervical carcinoma.Method1. Ten patients with advanced cervical cancer were selected. Before the treatment,computed tomography scan image were transferred to an IMRT planning system, Theclinical target volume (CTV) including the uterus, vagina and GTV and internal, externaliliac, obturator, presacral lymph node region and its surrounding tissues, The planningtarget volume (PTV) was generated using a10mm uniform expansion of the CTV. Theprescribed dose to the PTV was45Gy in1.8Gy daily fractions. All plans were optimized toassure that more than95%of PTV volume received the prescribed dose.Plans werecompared according to dose-volume histogram analysis in terms of PTV homogeneity andconformity indices(HI and CI) as well as OARs dose and volume parameters and the treatment period of patients, Comparing of several treatment technology advantages anddisadvantages.2. For a cohort of10patients, BM-IMRT and IMRT planning were designed. Planswere compared according to dose-volume histogram (DVH) analysis in terms of PTVhomogeneity and conformity indices (HI and CI) as well as OARs dose and volumeparameters.3. Three different margins were added to CTV to generate PTV7f.，PTV0.5,PTV1.0,0.5。PTV7fconsisted CTV with1cm margin at all direction. PTV0.5consisted CTV with0.5cmmargin at all direction. PTV0.5,1.0consisted CTV with0.5cm margin at lateral and posteriorand1cm margin at other direction. The irradiated normal tissues volume was comparedwhen different PTVs were used for treatment planning.Results1. Compared with CRT and3D-CRT, IMRT reduced the volume of small bowel,bladder, rectum at nearly all dose levels. At the same prescribed dose of45Gy,there wereno significant differences on PTV and GTV(including Dmax, Dmin) dose amongIMRT,3D-CRT and CRT plans(P>0.05).Among IMRT,3D-CRT and CRT plans, Theconformity index(CI)of IMRT plans were inferior than the3D-CRT and CRTplans.However Beyond5F,the advantage of increasing fields was not significant. Theadvantage of IMRT at dosimeter was significant compared with conventional or3D-CRTby means of sparing normal tissues.2. The conformity index of BM-IMRT shows more advantages than IMRT7f（P=0.029）. There is no difference （P>0.05）between the intensity modulatedradiotherapy of bone marrow and the protection of bladder and rectal. There is no evidentreduction（P<0.05）on V30,V20and V10. In the level of V30, BM-IMRT generallydecreases a volume of10%than that of IMRT; in the levels of V20and V10, BM-IMRTgenerally decreases a volume of16%than that of IMRT.3. In comparison of the three IMRT plans in PTV, IMRT0.5and IMRT0.5,1.0protectrectal better than IMRT7Fin both high dose regions and low ones. For different IMRT planning, there is no evident statistics significance in the protection of small intestine andbladder.Conclusions1. IMRT has reduced the volume of intention,small bowel,rectum and bladder in highdose area and low ones, In IMRT planning, IMRT7fplanning is feasible for clinical use.2. Compared with IMRT, BM-IMRT can guarantee better target dose distribution, lessirradiation volume and lower dose of bone marrow in advanced cervical cancer.3. PTV could be contoured by adding0.5-1.0cm margin to CTV. Different marginsadded to CTV to generate PTV will influence the irradiated normal tissues. It wasimportant to select appropriate PTV for different patients.