ESTRO 38 Abstract book

S791 ESTRO 38

LNs. PTV1 and PTV2 corresponded to GTV and CTV, respectively, adding 0.5 cm. RT dose was 50.4 Gy/28 fractions (fr) to PTV2 and 64.8 Gy/36 fr to PTV1, delivered with 3DCRT, VMAT (RA) or Tomotherapy, concomitant to NIGRO scheme chemotherapy. Results FDG showed inguinal uptake in 20/69 pts (29%) and in 11/20 pts lymphoscintigraphy was performed: SLNB confirmed inguinal mts in 4/11 (36%) pts, 6/11 (54.5%) pts were false positive and SLN not found in 1 pt. FDG-PET was negative in 49/69 pts (71%) and in 30/49 (61%) lymphoscintigraphy was performed: 6/30 (20%) showed mts, 23/30 (77%) were true negative and SLN not found in 1 pt. PET was false positive in 50% HIV- pts versus no HIV+ pts. Fifty-four/80 pts (67.5%) received RT on groin (RA: 26 pts, 3DCRT: 14 pts, Tomotherapy: 14 pts); 19/54 pts were HIV+. Pts treated vs no treated on groin showed more inguinal dermatitis toxicity (G1-G2: 27 (50%) vs 3 pts (11.5%) and G3-G4: 9 pts (17%) vs 0%. HIV+ pts treated on groin had more G3-G4 perineal dermatitis toxicity (9 (33.5%) vs 5 pts (18.5%). All pts treated on groin showed higher G3-G4 hematological toxicity vs not treated pts independently of HIV status. RA better avoid inguinal region than 3DCRT. Tomotherapy was better than 3DCRT and RA in perineal toxicity (28.5% vs 43% and 42.5%, respectively), and was superior to 3DCRT in inguinal toxicity (14% vs 36%). All pts were evaluated for responses, at a median follow- up of 36.8 months (5-128 m): 70 pts (87.5%) showed a complete response, 9 pts (11.25%) a partial response, 1pt (1.25%) a stable disease, while 11 pts (13.75%) had a local relapse (3 with distant mts), median time to local relapse was 9.3 months (6.2-25.5). Twelve pts (5%) had a distant progression, median time to distant progression was 11.16 months (1.4-20.53). No pts treated or not on groin showed inguinal relapse. Conclusion SLNB improve FDG-PET inguinal LNs staging which has a large false positive and false negative rate, independently of HIV status and guides decision in inguinal RT. Inguinal irradiation could be avoided based on negativity of imaging and SLNB. Advanced RT techniques should better avoid toxicity especially in HIV+ pts. EP-1460 Internal Margin evaluation in prone or supine rectal cancer patients using CBCT C. Rosa 1 , L. Gasparini 1 , S. Di Biase 1 , C. Di Carlo 1 , A. Allajbej 1 , F. Patani 1 , D. Fasciolo 1 , A. Vinciguerra 1 , L. Caravatta 1 , D. Genovesi 1 1 Ospedale Clinicizzato S.S. Annunziata, Department of Radiation Oncology- SS. Annunziata Hospital- "G. D'Annunzio" University- Chieti- Italy, Chieti, Italy Purpose or Objective Due to a reported dose-response relationship in rectal cancer radiotherapy, a greater interest in dose intensification on small boost volume arises. When conformational techniques, as IMRT and VMAT, are used an accurate delineation of gross tumor volume (GTV) and an appropriate organ motion evaluation are suggested. Our previous study evaluated internal movement (IM) of GTV and mesorectum in patients in prone position on CBCTs. Now, this study aimed to use CBCT for GTV and mesorectal IM evaluation, in rectal cancer patient treated with neoadjuvant radiochemotherapy, examining the differences in prone and supine position. Material and Methods Thirty-two locally advanced rectal cancer patients (M:22, W:10) underwent CT scan simulation, 16 in prone and 16 in supine position, with controlled bladder filling. Co- registrating MRI imaging with CT scan simulation, GTV (tumor site plus corresponded rectum) and mesorectum (from the sacral promontory to the level where the levator

FU-based radio-chemotherapy with 50.4 Gy in 28 fractions followed by surgery and adjuvant chemotherapy. Radiation dose was delivered using conventional radiotherapy (3D-CRT) with posterior-anterior and opposed lateral field arrangement (with additional segments) in prone treatment position using a belly board. For CT-planning and each treatment fraction, a full bladder was required. Small bowel loops were individually contoured up to 3 cm above the cranial PTV border. The 3D treatment plans were compared to retrospectively calculated VMAT plans with equal dose prescription. Values for Dmean and Dmax for bladder and small bowel were calculated. Additionally the small bowel volume receiving doses between 5 and 50 Gy (V 5-50 ) in 5 Gy intervals were recorded. Acute bladder and small bowel toxicities were classified according to CTCAE v4.03 Comparison of mean values was done by using t-test statistics, with p-values < 0.05 regarded as significant. Results Median patient age was 62.7 years. Nineteen patients were female and 16 male. Tumor stage was T3 100%, N0 3%, N1 14% and N2 83%. Nine patients (26%) developed acute cystitis Grade 1 and 18 patients (51%) acute diarrhea ≥ 2. While occurrence of cystitis did not depend on bladder and PTV volume (p=0.442; p=0.943), there was a significant dependence on higher Dmean values to the bladder (grade 0: 25.2 Gy vs. grade 1: 29.4 Gy; p=0,009). Neither the PTV volume nor the bladder volume correlated with acute diarrhea (p=0.395 and p=0.303). If larger small bowel volumes were close to the PTV, higher grades of diarrhea occurred (grade 0-1: 648.8 ml vs. grade > 2: 846.1 Gy; p=0.021). This relation was also true for almost all dose levels (V5-50): V5 grade 1: 425.5 ml vs. grade 2: 606.6 ml; p=0.017. After re-planning the 3D plans with a VMAT technique dose to bladder and small bowel could be significantly reduced: Dmean bladder 26.3 Gy vs. 21.9 Gy (p<0.01) and Dmean small bowel 11.3 Gy vs. 7.7 Gy (p<0.01). Also, the other small bowel volumes receiving 5 to 45 Gy could be spared by VMAT (p<0.01). Conclusion Acute cystitis and gastrointestinal toxicities are dose and volume dependent. Irradiated volumes can be sufficiently reduced with VMAT planning compared to 3D-CRT. This effort might reduce urinary and gastrointestinal toxicities. EP-1459 Impact of sentinel lymph-node biopsy and FDG-PET in staging and radiation treatment of anal cancer N. Slim 1 , P. Passoni 1 , R. Tummineri 1 , C. Gumina 1 , G.M. Cattaneo 2 , P. De Nardi 3 , C. Canevari 4 , M. Ronzoni 5 , C. Fiorino 2 , E. Incerti 4 , A.M. Tamburini 3 , L. Gianolli 4 , L. Gianni 5 , R. Rosati 3 , N. Di Muzio 1 1 San Raffaele Scientific Institute- Milano- Italy, Radiation Oncology, Milan, Italy ; 2 San Raffaele Scientific Institute- Milano- Italy, Medical physics, Milan, Italy ; 3 San Raffaele Scientific Institute- Milano- Italy, Surgery, Milan, Italy ; 4 San Raffaele Scientific Institute- Milano- Italy, Nuclear Medecin, Milan, Italy ; 5 San Raffaele Scientific Institute- Milano- Italy, Medical Oncology, Milan, Italy Purpose or Objective To assess the role of sentinel lymph-node biopsy (SLNB) and FDG-PET in staging and radiation treatment (RT) of anal cancer patients (pts). Material and Methods 80 pts (m:32, f:48), median age 61 years (38-87y) with anal squamous cell carcinoma were treated from 3/2008 to 3/2018. Twenty-seven/80 pts (34%) were HIV+. Pts without evident clinical inguinal LN metastases (mts) and/or with discordance between clinical and imaging were considered for SLNB. FDG-PET was performed in 69/80 pts. Pts with negative imaging in inguinal LNs and negative SLNB could avoid RT on groin. CTV included GTV (primary tumour and positive LNs) and pelvic ± inguinal