ESTRO 2021 Abstract Book

S1606

ESTRO 2021

Conclusion The results support the hypothesis that the h3DVM technique is feasible for treating whole breast cancer patients. The optimal proportion was found to be 80% 3DCRT and 20% VMAT as it enables a balance between dose coverage, conformality and exposure of the organs at risks. Also, any potential interplay effects are minimized by using only a small proportion of VMAT. Keywords: Breast cancer, Radiotherapy, VMAT, breath-hold, COVID-19 PO-1886 Dosimetric Analysis of Sequential IMRT (SeB) Versus SIB for Lymph nodes in Cervical Cancer d. aravindakshan 1 , l. guram 2 , r. hazare 3 , s. mohanty 4 , s. chopra 5 , r. kinhikar 1 , u. mahantshetty 6 1 tata memorial hospital, medical physics, mumbai, india; 2 tata memorial hospital, radiation oncology , mumbai, india; 3 hbch&rc,tata memorial centre, medical physics, vishakapatnam, india; 4 tata memorial hospital, radiation oncology, mumbai, india; 5 actrec,tata memorial centre, radiation oncology, mumbai, india; 6 hbch&rc,tata memorial centre, radiation oncology, vishakapatnam, india Purpose or Objective To dosimetrically evaluate and compare Sequential IMRT boost (SeB) of lymph nodes with simultaneously integrated boost(SIB) plans for target coverage and organs at risk doses inLACC . Materials and Methods CT planning paired (one done for phase I and second for phase2 SeB) datasets of 40 cervical cancer patients with metastatic lymph nodes proven by imaging or biopsy, who were treated SeB were utilized for the study. Targets and OAR (bladder, rectum, femoral heads, kidneys and bowel bag) were delineated. VMATwith two full rotations were generated for SIB and SeB on Eclipse( v.13.5 )using Accuros (V.13.5) with 6MV photons. SIB IMRT 1(45Gy in 25 Fr to the cervix and elective nodal volumes, 55Gy to nodal boost PTV generated in CT 1)and SeB IMRT (Phase I 45Gy in 25 fractions to the cervix and elective nodal volumes including the metastatic lymph nodes was generated on CT 1 and Phase II 12.6 Gy/ 7 Fr to the nodal boost PTV was generated on CT dataset 2.) and SIB IMRT 2( summation of SIB plan (44 Gy/20 Fr) generated on CT dataset 1 and SIB plan (11 Gy/ 5 Fr) in CT2, generated by copying the SIB IMRT1in CT dataset2 for 5Fr) were evaluated .The EQD2 of the prescription doses irrespective of the techniques were 55.9 Gy for SIB and 55.4 Gy for SeB (for alpha/beta ratio: 10) and 57.2 Gy for SIB and 54.6 Gy for SeB ( for alpha/beta ratio: 3). Composite doses for SeB were assessed on the initial planning CT by registering the sequential CT scan rigidly to initial scan. Both plans were optimised to achieve atleast 95%coverage of the PTV with 95% of the prescribed dose while minimising the dose to OARs. The three treatment plans were compared with each other for PTV coverages and OARs using the Friedman test since the data was not normally distributed and had paired