Dosimetric Comparison Of IMRT、CRT And3D-CRT In Early Anal Cancer Patients

Purpose1.To compare the homogeneity and conformity of dose distribution in the target, the treatment period of patients and the dose to the organs at risk among conventional radiation therapy(CRT),three dimensional conformal radiation therapy(3D-CRT)and intensity modulated radiation therapy(IMRT),and then to evaluate the clinical value of IMRT for anal cancer.2.To evaluate the organ sparing effect to different plan target volume margin size in intensity modulated radiotherapy (IMRT)in anal carcinoma.Method1.Ten patients with early anal cancer were selected.Before the treatment, computed tomography scan image were transferred to an IMRT planning system,The clinical target volume(CTV) including the uterus, vagina and GTV and mesorectum,presacral space,internal iliac lymph nodes ischiorectal,fossa obturator nodes,external iliac lymph nodes,nguinal lymph nodes and its surrounding tissues,The planning target volume(PTV)was generated using a10mm uniform expansion of the CTV.The prescribed dose to the PTV was54Gy in1.8Gy daily fractions. All plans were optimized to assure that more than95%of PTV volume received the prescribed dose. Plans were compared according to dose volume histogram analysis in terms of PTV homogeneity and conformity indices(HI and CI)as well as OARs dose and volume parameters and the treatment period of patients, Comparing of several treatment technology advantages and disadvantages.2.Three different margins were added to CTV to generate PTV7f, PTV0.5,PTV1.5.PTV7f consisted CTV with lcm margin at all direction.PTVo.5consisted CTV with0.5cm margin at all direction.PTV1.5consisted CTV with0.5cm margin at all direction.The irradiated normal tissues volume was compared when 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 of54Gy,there were no significant differences on PTV and GTV(including Dmax, Dmin)dose among IMRT,3D-CRT and CRT plans.Among IMRT,3D-CRT and CRT plans, The conformity index(CI)of IMRT plans were inferior than the3D-CRT and CRT plans.However Beyond5F,the advantage of increasing fields was not significant.The advantage of IMRT at dosimeter was significant compared with conventional or3D-CRT by means of sparing normal tissues.2.In comparison of the three IMRT plans in PTV,IMRT0.5and IMRT1.0protect medulla spinalis better than IMRT1.5in both high dose regions and low ones.For different IMRT planning,there is no evident statistics significance in the protection of small intestine and bladder.Conclusions1.IMRT has reduced the volume of intention,small bowel,rectum and bladder in high dose area and low ones,In IMRT planning,IMRT7f planning is feasible for clinical use.2.PTV could be contoured by adding0.5-1.0cm margin to CTV.Different margins added to CTV to generate PTV will influence the irradiated normal tissues.It was important to select appropriate PTV for different patients.