Abstract Book

S1036

ESTRO 37

of normal tissues treated based on dose-volume histograms (DVHs). DVHs were calculated for the PTV, heart, and the bilateral lungs, contralateral breast.

Figure1. Beam arrangements of hybrid IMRT (left), and inverse-fields IMRT (right) Results Maintaining the coverage of PTV, hybrid IMRT and inverse-fields IMRT plans have the equivalent homogeneity (HI) because inverse fields, but the inverse- fields IMRT plans improved the plan dose conformity. The hybrid IMRT plans have higher volume of 20Gy but lower volume of 5Gy for ipsilateral lung than inverse-fields IMRT plans because using two tangential fields by 80% of prescribe dose. The volume of 20Gy and 5Gy for contralateral lung, the mean dose for heart and contralateral breast both are lower in the hybrid IMRT technique.

Figure. Results of 4D dose calculation. (a) representative case and (b) average of 10 patients Conclusion This study determined how respiratory motion affects whole breast IMRT with SIB and this motion resulted in blurred dose distribution with the consequence of increased CTV dose heterogeneity and a loss in target coverage. Therefore, even though breast IMRT can improve dose conformity and reduce the maximum dose to the target by sparing the OARs compared to 3D-CRT, breast IMRT with SIB should be seriously considered and respiration control during the treatment should be needed because respiration motion can degrade the CTV dose distribution. EP-1909 Dosimetric comparison of whole breast irradiation with hybrid IMRT and inverse-fields IMRT P.C. Tu 1 , C.H. Lin 1 , S. Shaw 1 , C.J. Wu 2 1 Sijhih Cathay General Hospital, Radiation Oncology, New Taipei City, Taiwan 2 Cathay General Hospital, Radiation Oncology, Taipei, Taiwan Purpose or Objective We compared the dosimetric characteristics in whole breast irradiation using hybrid IMRT (2 tangential 3D fields(80%) + IMRT fields(20%) )and inverse-fields IMRT We analyzed the two different planning techniques for 10 early stage breast cancer patients(six right and four left) with breast conserving surgery. The treatment plans of these patients were replanned using the same contours based on the computed tomography(CT) image sets by using pinnacle planning system in our department. The hybrid IMRT plans combined two tangential 3D fields by 80% of the prescribe dose and another four to five inverse intensity fields by 20% of the prescription dose which angles distribution between the tangential angles. The inverse-fields IMRT plans selected 5 to 7 different angles based on tumor shape by 100% of prescription dose. Plans were compared on the planning target volume (PTV), dose conformity(CI) , homogeneity(HI) , and the volumes planning techniques. Material and Methods

Table 1. Dose characteristics of normal organs Conclusion

Because there are intensity modulated fields to improve the equivalent conformity and homogeneity, hybrid IMRT technique needed less MUs and treatment time, and achieved superior outcome of dose of normal tissues than inverse-fields IMRT technique. The hybrid IMRT technique is a good choice for early stage whole breast irradiation. EP-1910 single-isocenter volumetric-modulated Dynamic WaveArc therapy in brain metastases M. Uto 1 , K. Ogura 1 , Y. Miyabe 1 , M. Nakamura 1 , N. Mukumoto 1 , H. Hirashima 1 , T. Katagiri 1 , K. Takehana 1 , M. Hiraoka 2 , T. Mizowaki 1 1 Kyoto University Graduate School of Medicine, Radiation Oncology and Image-Applied Therapy, Kyoto, Japan 2 Japanese Red Cross Wakayama Medical Center, Director, Wakayama, Japan Purpose or Objective Volumetric radiosurgery for patients with multiple brain metastases is typically performed using single-isocenter volumetric-modulated arc therapy (VMAT) with multiple non-coplanar straight arcs. The Vero4DRT (Mitsubishi Heavy Industries, Ltd., Tokyo, Japan, and Brainlab,