ESTRO 2022 - Abstract Book

S802

Abstract book

ESTRO 2022

Results On pre-ICR MRI, 26/38(72.72%) patients fitted into Group-1 and 12/38(27.28%) into Group-2. Three months post-treatment, all patients had complete response, both clinical and radiological. The pre-treatment Mean ADC (MADC) value was 0.8441±0.1064x10 -3 m 2 /s, with mean as well as maximum and minimum values increasing after EBRT and further after treatment completion. Whereas, baseline MADC was higher, both Mean Blood Flow(MBF) and Mean Blood Volume(MBV) were lower in Group-1. Although there was no significant difference in the pre-EBRT values of MADC, MBF and MBV, there was significant difference in pre-ICT and post-treatment values of these, between Groups 1&2. With regard to percentage change in MADC, 13/26(50%) patients in Group-1 and 5/12(41.6%) patients in Group-2 had >30% increment (p=0.089). Significant difference in MADC of mid-treatment values was significant for patients with and without vaginal involvement (p=0.037), and of mid and post-treatment values for patients with or without bladder involvement (p=0.005 and p<0.001, respectively). The percentage change of both MBF and MBV, between pre-ICT and post-treatment values was significantly higher in Group- 1. With regard to percentage change in MBF, 23/26(88.46%) Group-1 patients and 2/12(16.67%) Group-2 patients, had >60% decrement (p<0.001). 25/26(96.15%) Group-1 patients of and 5/12(41.6%) Group-2 patients, had >50% decrement in MBV(p<0.001). Conclusion With help of Functional MRI, tumour response can be assessed by values of and percentage changes of ADC. The percentage increase of ADC with treatment reflected the disease outcome. Blood Flow and Blood Volume could serve as markers of Hypoxia and can predict response to radiotherapy. Use of functional MRI may act as an important tool for assessing tumour response in carcinoma cervix by studying both anatomical and physiological parameters. Purpose or Objective IMRT with IGRT followed by brachytherapy and concurrent chemotherapy is usually the mainstay of treatment in locally advanced cancer cervix (LACC). IMRT plans are usually generated on snapshot pre-external radiotherapy (ERT) CECT scans taken 1-2 weeks before starting ERT. These IMRT plans are generally considered to be applicable throughout the entire course of ERT. However, the gross tumor volume (GTV) in LACC is expected to undergo dynamic regression during the usual 5 weeks of ERT, representing a sigmoid dose-response curve. The study aims to analyze the accuracy of pre-ERT IMRT plans on various dose-volume histogram (DVH) parameters with the transposed GTV on re-CECT taken at 3-4 weeks of ERT. Materials and Methods 15 consecutive patients of LACC were included in this prospective study. IMRT plans were generated 1-2 weeks before starting ERT to deliver 50Gy in 25 fractions over 5 weeks to 98% of the planning target volume (PTV). The same IMRT plan was superimposed on a re-CECT taken at 3-4 weeks of ERT. GTV and DVH parameters - V 50 , V 95 , D 95 , D 98 , D 50 , D 5 , D 2 , conformity index (CI), homogeneity index (HI) and concordance index (ConI) were assessed and compared between pre- ERT and re-CECT scans. Additionally the V 50 of bladder and rectum; V 45 and D 190cc of small bowel were also evaluated. Before IMRT delivery, biweekly positional accuracy of the patient setup was monitored using portal imaging. Results A total of 159 shifts in 15 consecutive patients before delivery of IMRT, each in X, Y and Z axes were recorded. The mean±SD of these shifts in X, Y and Z axes were 0.09±0.5cm, 0.12±0.5cm and 0.08±0.3cm respectively. Compared to pre-ERT IMRT, significant reduction in GTVs at 3-4 weeks were observed (p<0.0001). This resulted in significant differences in various DVH parameters between those of the pre-ERT PTV s vs. PTV s on re-CECT at 3-4 weeks of ERT V 95 (p<0.001), D 98 (p=0.011), CI(p=0.002), HI(p=0.009) and ConI (p<0.001), V 50 bladder (p= 0.003) and V 45 of small bowel (p<0.001)(Table). The mean differences inV 50 , D 2 , D 5 and D 50 were insignificant. PD-0907 Are set-up corrections adequate enough to ensure an optimal dose delivery by IMRT in cancer cervix? P. Kale 1 , P. Kalbande 1 , N. Shanmugam 1 , B. Mahindrakar Jain 1 , A. Singh 1 , Z. Mathi 1 , V. Hatekar 1 , N.R. Datta 1 1 Mahatma Gandhi Institute of Medical Sciences, Radiotherapy, Wardha, India