Abstract Book

S1035

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.

EP-1908 Assessment of dosimetric impact of respiratory motion during breast IMRT using 4D calculation Y.E. Choi 1 , K. Sung 1 1 Gil Medical Hospital, Radiation Oncology, Incheon, Korea Republic of Purpose or Objective In this study, we aimed to generate 4D dose distributions by incorporating each static dose distribution of three consecutive computed tomography (CT) scans using deformable image registration. The ultimate goal was to evaluate the dosimetric impact of respiratory motion on breast intensity modulated radiation therapy (IMRT) with simultaneous integrated boost (SIB). Material and Methods CT images of ten consecutive patients treated according to our institutional DIBH protocol were retrospectively re- planned using IMRT and 3-dimensinal conformal radiation therapy (3D-CRT). Using the RPM systems for detecting the breathe amplitude, multiple CT scans were performed in distinct respiratory phases: end-expiration (EE), end-inspiration (EI), and deep-inspiration (DI). EE- CT scan was used to develop treatment plan as a reference and then this static dose distribution was projected to EI and DI-CT scans, separately. The prescription was to deliver 50 Gy and 57.5 Gy in 25 fractions to PTV and CTV. The dose distribution projected to EI-CT was deformably registered to EE-CT using Mirada RTx. The ratio of EE to EI used to generate 4D dose distributions was 1:1, 2:1, 3:1, 4:1 and 5:1. The dosimetric parameters of three static dose distributions for each plan (IMRT and 3D-CRT), and 4D dose distributions with different ratio of EE to EI (EE:EI) were compared: conformity number (CN) and homogeneity index (HI) of target volumes, and the dose-volume parameters of the heart, each lung, and contralateral breast.