Abstract book - ESTRO meets Asia

S95 ESTRO meets Asia 2018

PO-232 Texture analysis to identify pelvic active bone marrow for bone marrow sparing IMRT approaches P. Franco 1 , C. Fiandra 1 , F. Arcadipane 1 , P. Silvetti 1 , S. Rosati 2 , G. Balestra 3 , U. Ricardi 1 1 University of Turin, Department of Oncology- Radiation Oncology, Turin, Italy 2 Politechnic University, Depatment of Electronics and Informatics, Turin, Italy 3 Polytechnic University, Depatment of Electronics and Informatics, Turin, Italy Purpose or Objective Concurrent chemo-radiation (CT-RT) is the standard of care for anal cancer patients. IMRT is frequently used. Even when this approach is employed, acute hematologic toxicity remains an issue. Bone marrow (BM) sparing IMRT decreases this type of toxicity. This strategy requires the correct identification of active BM within the pelvis. Functional imaging with 18 FDG-PET has been explored for this purpose. We compared a radiomic approach based on texture analysis to a 18 FDG-PET-based strategy to identify pelvic BM in anal cancer patients treated with concurrent CT-RT. Material and Methods A total of 5 patients submitted to IMRT was analyzed. Several bony structures were defined: pelvic and lumbar- sacral (LSBM), lower pelvis (LPBM) and iliac (IBM) bone marrow. Active BM characterized employing 18 FDG-PET was defined as all subregions within pelvic bone marrow having Standard Uptake Values (SUVs) higher than SUV mean. For the radiomic approach, an octagonal element made of 5-by-5 pixels moving by 1 pixel at time in both directions was considered. A set of 36 features was computed for each octagonal element: 4 statistics (mean, standard deviation, skewness and kurtosis) and 32 texture features were analyzed. Five texture features were extracted with the Gray Level Difference Method. We extracted: contrast, angular second moment, entropy, mean, and inverse difference moment. The training set and the classifier were constructed. The discrete training set was used for constructing a Decision Tree for each patient. We employed the CART algorithm for the tree construction and the Gini Index for the identification of the best splitting rule for each node. We then compared the active bone marrow masks obtained from PET with those returned by radiomics. The comparison was carried out using three indices: Dice index (overall overlap between the two segmentations); Precision (over-segmentation); Recall (under-segmentation). Results Results are shown in Table 1.

compared the PTV coverage and OAR sparing between the different techniques. Results Both IMRT and VMAT were superior to 3DCRT in PTV coverage (PTV D98% and PTV V27.5Gy), demonstrating superior coverage of tumor and nodal basin. D98 can be interpreted as the minimum doe received by the PTV. V27.5Gy indicated the dose hotspot area that received 110% of the prescribed dose. VMAT and IMRT were equivalent to each other but were superior to 3DCRT in the sparing of the OARs. Both IMRT and VMAT provided significantly more sparing of the bowel, bladder, femoral head and bone marrow compared to 3DCRT. VMAT also has a significantly shorter treatment time compared to IMRT. Conclusion This is the first dosimetric study to demonstrate the superiority of VMAT and IMRT over 3DCRT in the setting of neoadjuvant short course radiotherapy for locally advanced rectal cancer. PO-231 combined EBRT and HDREBT boost in elderly or medically inoperable Asian rectal cancer patients C.L. Chiang 1,2,3 , V.W.Y. Lee 2 , C.S.Y. Yeung 2 , M.Y.P. Wong 2 , S.K.T. Cheung 2 , C.H.M. Ho 2 , M.S.F. Lee 2 , F.A.S. Lee 2 , F.C.S. Wong 2 1 University of Hong Kong, Department of Clinical Oncology, Hong Kong, Hong Kong SAR China 2 Tuen Mun Hospital, Department of Clinical Oncology, Hong Kong, Hong Kong SAR China 3 University of Hong Kong-Shenzhen Hospital, Department of Clinical Oncology, Shenzhen, China Purpose or Objective To evaluate the efficacy and toxicity of the combined external beam radiotherapy (EBRT) followed by high-dose- rate endorectal brachytherapy (HDREBT) boost in elderly or medically inoperable patients with rectal cancer among Asian population. Material and Methods We retrospectively review the clinical records of sixteen patients with T3N0-2 rectal cancer patients treated with EBRT and HDREBT. Eleven because of medical inoperability, while five due to refusal of surgery. HDRBET boost was performed at 8 weeks after EBRT. Brachytherapy boost of 10Gy for 1, 2, or 3 weekly fraction(s) were given in six, five, and five patients respectively. Primary endpoint was tumor response. Secondary endpoints were toxicity, local- progression free survival (L-PFS), cancer specific survival (CSS), and overall survival (OS). Results Sixteen patients with median age of 80 (range: 70-95) were included in the analysis. Ten were T3N1-2, while six were T3N0; median size of tumor was 4.2cm (range: 3- 6.7cm). Median equivalent dose of 2Gy per fraction (EQD2) (a/b=10) delivered was 66Gy (range: 48-92). Tumor responses occurred in fourteen of sixteen patients (87.5%) with 31.3% complete response (CR). The median OS, CSS, and L-PFS were 25 months, 28.1 months and 19.2 months respectively. Patients with CR had a significantly better L- PFS (median 29.5 months, p=0.015) and a trend in improved CSS (median 33.6 months, p=0.17). Acute grade 2 and grade 3 procitis occurred in 43.8% and 6.2% respectively, while late ≥ grade 3 procitis occurred in 18.8%. Most severe toxicity was observed at around 12 months. Conclusion In elderly or medically inoperable patients, combined EBRT and HDREBT can provide good tumor response, with improved L-PFS in patients with CR. The treatment was associated with acceptable toxicity. Further prospective trial is justified.

Conclusion A radiomic approach based on texture analysis has a good performance in identifying active BM within the pelvis compared to 18 FDG-PET for LSBM and IBM. The poor performance for LPBM needs further evaluation. PO-233 Predictors of DFS in Carcinoma rectum patients treated with neo-adjuvant chemo-radiation- An audit N. Anjum 1 , T. Kataria 1 , S. Bisht 1 , S. Goyal 1 1 Medanta The Medicity, Radiation Oncology, Haryana, India