ESTRO 2021 Abstract Book

S83

ESTRO 2021

Materials and Methods Patients with locally advanced tumor without metastases (Stage T2, T3 or T4, whatever N stage, stage N1-N3 whatever T stage) were treated with two RT periods (45Gy in 5 weeks and a boost of 20Gy in 2 weeks) with concomitant CT sessions of 5FU/MMC at RT weeks 1 and 5. Pmab was administered on RT weeks 1, 3, 5 and 7 according to the doses defined by a previous phase 1 study (MMC: 10 mg/m² at J1 and J29; 5FU: 400 mg/m² from J1 to J4 and from J29 to J32, Pmab: 3mg/kg) (1). The expected rate of CR at 8 weeks to continue in phase III was 80%. Results Forty-five patients (male: 9 (20%), female: 36 (80%); median age: 60.1 [41.5-81]) were enrolled in 15 French centers. Three patients were HIV positive. All patients but one completed the CRT. Median duration of CRT was 52 days [30-76].Fourteen patients had a RT interruption because of toxicity. Most common related grade 3-4 toxicities observed were digestive (51.1%), hematologic (lymphopenia: 73.4%; neutropenia: 11.1%), radiation dermatitis (28.8%) and asthenia (11.1%). One patient died because of mesenteric ischemia during the CRT (total dose: 36 Gy), non-related to treatment. In ITT analysis, the CR rate at 8 weeks after CRT was 66.7% [90%CI: 53.4-78.2]. Median follow-up was 43.6 months [IC 95%: 38.61 – 47.01]. Overall survival, recurrence- free and colostomy-free survival at one year were 94.6% [95%CI: 75.8-98.7], 72.2% [95%CI: 55.0-83.7] and 78.2% [95%CI: 60.6 – 88.6] respectively. Overall survival, recurrence-free and colostomy-free survival at 3 years were 80% [95%CI: 65.1-89], 62.2% [IC95%: 46.5- 74.6] and 68.8 % [IC95%: 53.1 – 80.2] respectively. Eight (17.7%) patients had a colostomy with abdomino-perineal amputation due to a tumor recurrence for 7 and to functional sequelae for one patient. Conclusion Despite a significant toxicity , panitumumab in combination with CRT for locally advanced anal cancer failed to meet the expected CR rate to justify further clinical trials PH-0114 Pelvic insufficiency fractures detected by MRI one-year after chemoradiotherapy for anal cancer. C. Kronborg 1 , B.G. Pedersen 2 , J. Klemmensen 3 , A.C. Lefévre 3 , K.L. Wind 4 , K.G. Spindler 4 1 Danish Centre for Particle Therapy, Danish Centre for Particle Therapy, Aarhus N, Denmark; 2 Aarhus University Hospital, Department of Radiology, Aarhus N, Denmark; 3 Aarhus University Hospital, Department of Oncology, Aarhus N, Denmark; 4 Aarhus University Hospital, Department of Oncology, Aarhus N, Denmark Purpose or Objective Pelvic insufficiency fracture (PIF) is a well-known late complication to pelvic radiotherapy (RT). PIF can cause pain and decreased mobility and be clinically be misinterpreted as a local recurrence. PIFs are described in 1.4-14% of anal cancers after RT. However, studies are mainly retrospective and characterized by heterogeneity in definition, timing, imaging, RT techniques and follow up (FU). Imaging method is important, and MRI is estimated to have a sensitivity of 99-100 % and a specificity of 85 % for stress fractures in general. Furthermore, relations to dose volume parameters are not well described for anal cancer. Materials and Methods Patients, treated with RT for anal cancer, were enrolled into a prospective toxicity (CTCAE) trial, and asked at their one-year FU to participate in this study with supplementary MRIs to detect PIFs. RT was planned with 2 or 3 arc VMAT and doses 60-64 Gy to tumor and pathological lymph nodes and 48-51.2 Gy for elective nodal areas. Identification of PIFs: The MRIs were performed at 1.5T platforms including a sagittal STIR 5 mm and coronal T1 FSE 7mm of total bony pelvis and proximal femoral bone. High signal intensity changes in the bone marrow at the STIR sequence, indicating bone marrow edema, with accompanying subtle linear, low signal intensity changes at T1 weighted images were regarded as suggestive of the presence PIF. As most patients had multiple fractures, fracture sites were divided into following areas: alae of the sacrum, acetabulum, femoral heads, pubic bone, iliac bone near joint, and midline of sacral bone. Delineation: Sacral bone outer contour was delineated from S1 to S5. Wilcoxon rank sum or Pearson's Chi 2 tests were used for comparison between PIF vs. no PIF. A p-value <0.05 was considered statistically significant. Results 27 patients were included, (81% female, n=22). PIFs were identified in 52% (n=14). The most frequent site was alae of the sacral bone (L/R) n=20, followed by acetabulum (L/R) n=11, femoral head (L/R) n=4, Pubic bone (L/R) n=4, iliac bone near sacroiliac joint (L/R) n=4, sacral bone midline n=1. RT doses to sacral bone were significantly higher in patients with PIF for: max and mean dose, V20Gy, V30Gy and V40 Gy, p=0.01, p=0.04, p=0.037, p=0.02, p=0.048 but not for V50Gy p=0.062. Significantly more patients with PIF had pain (85% vs 23%), p=0.001 . Ten complained about pain in the sacral area, 8 in hip area, and one in symphyseal area. Seven (50%) patients had grade I bone pain, 7 (50%) patients grade II. Six (46%) patients had pain while resting, 11 (85%) pain with activity. Conclusion We found a very high incidence of PIFs on MRI 1 year after RT for anal cancer. Importantly, a significant proportion of patients had symptoms affecting daily living indicating symptomatic PIF. Higher RT dose to sacral bone was associated to increased risk of PIF. These results suggest that future studies should consider including specific constraints to pelvic bones primarily in weight bearing areas. PH-0115 Bone marrow-sparing IMRT in anal cancer patients: final results of a prospective phase II trial P. Franco 1 , F. Arcadipane 2 , F. Olivero 3 , P. Silvetti 3 , I. Chiovatero 3 , L. Spinelli 3 , R. Carlevato 3 , E. Gallio 4 , F.R. Giglioli 5 , C. Fiandra 3 , U. Ricardi 3 1 University fo Turin, Department of Oncology, Turin, Italy; 2 AOU Citta' della Salute e della Scienza, Radiation Oncology, Turin, Italy; 3 University of Turin, Department of Oncology, Turin, Italy; 4 AOU Citta' della Salute e