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Dosimetric study of inverse-planed intensity modulated, forward-planned intensity modulated and conventional
Kanisa Rongsriyam1, Prayuth Rojpornpradit, Chawalit Lertbutsayanukul
1Division of Therapeutic Radiology and Oncology, Department of Radiology, King Chulalongkorn Memorial Hospital, Bangkok, Thailand.
Objective:
The authors present the result of a dosimetric comparison of inverse-planed intensity modulated, forward-planned intensity modulated, and conventional tangential technique in breast conserving radiotherapy.
Method And Material:
The breasts (Right side: Left side = 1:1), heart, and lungs of 28 patients were contoured on all the computed tomography (CT)-slice. Three different treatment plans were created: (1) inverse IMRT (iIMRT), (2) forward IMRT (fIMRT), and (3) conventional tangential technique (CVT). The total prescribed dose for all plans was 50 Gy/25 fractions. All treatment plans were normalized at 95% of the prescribed dose covered the entire PTV and used inhomogeneity corrections.
Results:
For the entire group, the mean breast volume was 517 cc. The V105% for iIMRT, fIMRT and conventional plans was 1.12%, 2.36% and 16.81%, which iIMRT better than fIMRT and CVT (p < 0.001) and fIMRT better than CVT (p < 0.05). The Dmax for the iIMRT plan received 105.03%, which was significantly less than those from the fIMRT(106.6%, p < 0.001) and the conventional (110.68%, p < 0.001) plan. The PTV coverage (V95-105%) for the iIMRT, fIMRTand conventional was 96%, 91% and 87%, which iIMRT better than fIMRT and CVT (p < 0.05) and fIMRT better than CVT (p < 0.05). The PTV CI for the iIMRT technique was 0.704, which was significantly more conformity than those from the fIMRT (0.639, p < 0.001) and the conventional (0.539, p < 0.001) techniques. The PTV CI of fIMRT is significantly better than CVT (p < 0.005). Mean ipsilateral lung dose was 642.7 cGy, 747.6 cGy and 882.25 cGy for iIMRT fIMRT and CVT respectively (p < 0.05) The V20Gy reduced from 14.87% for conventional plan to 12.82% for the fIMRT plan, while 0.88% was obtained for the iIMRT plan (P<0.05). The heart V30 Gy value was 3.124%, 4.65%, and 5.84% for iIMRT, fIMRT and conventional plans, respectively (p < 0.05). The mean dose of contralateral breast was 55.86 cGy, 60.33 cGy, 68.57 cGy for iIMRT, fIMRT and conventional plans, respectively (p < 0.05 both). The mean contralateral lung dose was 57.8 cGy, 43.87 cGy, and 32.28 cGy for iIMRT, fIMRT and conventional plans, respectively (p < 0.005 both).
Conclusion:
The iIMRT technique provides significantly improved PTV Dmax, PTV V105%, PTV V110%, target volume coverage, dose homogeneity and dose conformity throughout the target volume of breast and reduced doses to all critical structures, compared to the fIMRT and conventional techniques. In view of fIMRT technique, it significantly improved the dose distribution and reduced dose to OARs compared to conventional technique, although not better than iIMRT technique.
