Dosimetric Comparison Of Different Radiotherapy Techniques For Patients With Locally Advanced Hypopharyngeal Carcinoma

Purpose:The comparison of local advanced hypopharyngeal cancer IMRT treatment planning with 2D-RT and 3D-CRT between treatment plans in tumor target dose distribution of conformal,uniformity and dose coverage rate;the critical organ dose、volume,the possibility to explore the characteristics and advantages of the three kinds of radiation dosimetry technique,for the future clinical research and application basis provides dosimetry.Materials and methods:We selected 8 cases of locally advanced cases from the First Affiliated Hospital of Soochow University(T3-4N1-2M0) in hypopharyngeal carcinoma postoperative patients entered the dosimetric study.Using three dimensional treatment planning system, the same set of target area of every patient were completed in conventional analog of conventional radiotherapy(2D-RT group), three dimensional conformal radiotherapy(group 3D-CRT)and intensity modulated radiotherapy(IMRT5f and IMRT7f). The dose prescribed to high-risk plan target volume(PTV1) was 66 Gy,which to low-risk plan target volume(PTV2)was 50 Gy.The evaluate indicator of PTV contained the volume percentage of which coverd by 93%,95% and 107% respectively(V95, V95, V107),inhomogeneity coefficient(IC) and conformity index(CI).The evaluate indicator of parotid gland were mean dose(Dmean),the volume percentage of receiving more than 15 Gy,30Gy and 45 Gy respeetively(V15, V30,V45) and normal tissue complication probability(NTCP).The evaluate indicator of other normal tissues were the doses delivered to lcm3,5%and 33%of planning organ at risk volume respectively(Dlcc,D5,D33).To compared the indicators above for the three different radiotherapy techniques.Results:The average values of IMRT7 f group, IMRT5 f group, 3D-CRT group and 2D-RT group PTV1 V95 were 99.38%, 98.12%, 97.23% and 87.68%(P<0.05),the average values of V93 were 99.63%, 99.24%, 97.82% and 92.48%(P<0.05), the average values of V107 were0.37%, 0.46%, 4.60% and 11.20%(P<0.05), the average values of IC were 0.136, 1.168,0.221 and 0.453, the average values of CI were 0.848, 0.742, 0.586 and 0.442. PTV2 the average values of V95 were 98.92%, 97.34%, 96.46% and 88.21%, the average values of V93 were 99.90%, 98.12%, 97.24% and 90.61%(P<0.05), the average values of CI were0.646, 0.612, 0.568 and 0.547,the above indexes between four groups had significant difference(P<0.05). The above results show that: in group 3D-CRT, more than 95%isodose line within the coverage of target volume percentage and the target area uniformity,conformal were significantly higher than that of 2D-RT group,while the IMRT7 f and IMRT5 f group was significantly higher than that of group 3D-CRT and group 2D-RT,wherein IMRT7 f in the comparison of optimal.In the organs at risk protection,on the side of the parotid gland Dmean average value,average value of V15, the average values of V30, V45 average, IMRT7f(respectively24.48%, 56.46%, 43.26%, 24.42%) than IMRT5f(respectively 27.23%, 62.48%, 46.30%,28.62%) than 3D-CRT(respectively 42.67%, 95.96%, 87.62%, 52.68%) and more than2D-RT(respectively 54.16%, 98.24%, 93.54%, 87.34%)..Four groups of NTCP average value is 24.50~32.30%, 32.80~37.60%, 62.60~98.70% and 78.60~99.90%, the index in the four groups were significant difference between(P<0.05).Four groups of spinal cord D1 cc mean values were 37.24 Gy, 40.02 Gy, 47.96 Gy and 45.35 Gy, the difference was statistically significant(P<0.05), and brain stem, TMJ, mandible, tongue and middle dose group showed no significant differences between the four groups.Conclusions:1.The radiotherapy for local advanced hypopharyngeal cancer patients after surgery,IMRT7 f and IMRT5 f technology in the target coverage or the normal organ protection is superior to 3D-CRT and 2D-RT,at the same time IMRT7 f from either or the target coveragewere superior to those of normal organ protection IMRT5 f.2.IMRT can significantly reduce the mean dose and irradiated volume of parotid gland to offer better parotid sparing,nevertheless,both 3DCRT and 2D-RT techniques are inadequate for fully preserving parotid gland function.3. IMRT offers the best spinal cord sparing,followed by 3D-CRT,2D-RT is the worst.4.There is no significant difference of the other normal organs sparing between the three radiotherapy techniques.