ESTRO 37 Abstract book

S1037

ESTRO 37

Results Treatment plans generated using IMRT resulted in CN and HI for PTV and CTV superior to those of 3D-CRT. On average, doses for ipsilateral lung and heart were lower in IMRT technique. For all DI and EI phases of static dose distributions, CN and HI were significantly lower than those of EE phase. For IMRT with 4D plan, V 95% significantly decreased from 95.0% (EE) to 94.1 ± 1.6 % (EE:EI(1:1)) for PTV and from 99.2 ± 1.3% (EE) to 93.4 ±8.3% (EE:EI(1:1)) for CTV. V 100% of CTV was 85.0 ± 13.0 % (EE), 79.2 ± 14.2% (5:1), 78.4 ± 14.4% (4:1), 77.2 ± 14.8 % (3:1), 75.4 ± 15.8% (2:1), 72.0 ± 18.0 % (1:1), and the differences were statistically significant (p = 0.05). The mean dose, V 5Gy , V 10Gy , and V 20Gy of ipsilateral lung were significantly higher in all 4D plans compared to the reference plan. There was no significant difference in parameters related to heart.

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