Abstract Book

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ESTRO 37

dose with mucosal parameters (BED) (α/β=10 Gy, α=0.3 Gy -1 , T k =7 days, T p =2.5 days) and BED modified to take in to account the effect of synchronous chemotherapy (mcBED) (T p =5 days) and the duration of grade 3 reactions (v3 and v4) and severe throat or mouth sores (PRO) was investigated using spearman’s rho correlation coefficients. Results The study is ongoing but 44 patients have completed the post treatment phase. Prescription doses were 70Gy/35# (n=6), 65 Gy/30# (n=35), 64Gy/25# (n=2) and 55Gy/20# (n=1). Synchronous chemotherapy was cisplatin (n=35), carboplatin (n=3), cetuximab (n=1), radiotherapy alone (n=5). Mean high dose CTV volume was 200cm 3 (range 29- 533cm 3 ). Median duration of grade 3 reactions was 7 weeks (wks) (0-14 wks) (v3), 8 wks (0-15wks) (v4). Median duration of severe mouth or throat sores was 7.5 wks (0- 15 wks) (PRO). There was no significant correlation between high dose CTV volume, BED, and mcBED with duration of grade 3 mucositis as measured using CTC v3 or v4. However, there was a significant correlation between both high dose CTV volume (p=0.006) and mcBED (p=0.044) with duration of mouth and throat sores (PRO). Conclusion Early results from this ongoing study suggest that the duration of patient reported severe mouth or throat sores correlates with the volume of the high dose CTV and the prescription dose when this is converted into BED using mucosal parameters corrected for synchronous chemotherapy. Given that this relationship was not seen with v3 and v4 it is possible that this patient reported outcome may be more sensitive to changes in mcBED and CTV volume and has a potential as an endpoint in both volumetric and dosimetric escalation/de-escalation studies. OC-0096 Late toxicity of prostate stereotactic ablative radiotherapy treated with flattening filter free A. Duffton 1 , L. Devlin 1 , A. Sadozye 2 , P. McLoone 3 , N. MacLeod 2 , C. Lamb 2 , S. Currie 4 , D. Dodds 2 1 Beatson West of Scotland Cancer Centre, Radiotherapy, Glasgow, United Kingdom 2 Beatson West of Scotland Cancer Centre, Clinical Oncology, Glasgow, United Kingdom 3 University of Glasgow, Institute of Health & Wellbeing, Glasgow, United Kingdom 4 Beatson West of Scotland Cancer Centre, Clinical Physics and Bioengineering, Glasgow, United Kingdom Purpose or Objective Stereotactic ablative radiotherapy (SABR) for prostate cancer allows high doses of radiotherapy to be delivered with high precision over a short course of treatment. Here, we report the clinical outcomes at 12 month follow-up in a prospective safety and feasibility study where patients were treated with Rapidarc® and flattening filter free (FFF). Material and Methods Male patients with low-intermediate risk prostate cancer were enrolled in this prospective, ethically approved study. Initial PSA (iPSA) of ≤20ng/ml, Gleason score 6-7. Patients had MR/CT fusion for delineation of prostate +/- seminal vesicles. CT/MR fusion images were used for delineation of the target volume and planned using Rapidarc® FFF. Patients received 35Gy in 5 fractions. On treatment CBCT imaging with fiducial markers were used for set-up correction. For late toxicity (≥ 90 days after radiotherapy) GU and GI symptoms were assessed and recorded 6 monthly following treatment using RTOG scoring criteria. Results Forty-one patient treated for low-intermediate risk prostate cancer were recruited to the study. 24 (58.5%)

patients had a Gleason score of 7, all other patients (17 (41.5%)) were Gleason score 6. Low grade acute genito-urinary symptoms were prevalent among 53.7% of patients (22/41) at baseline. At six months 47.5% (95% CI 31.5-63.9%) of patients experienced GU symptoms, and this declined to 22.5% (10.8-38.4) by 12 months. At six and 12 months 3 and 2 patients respectively experienced grade 2 symptoms. Five percent (2/41) of patients reported acute gastrointestinal symptoms at baseline. At 6 months 22.5% (10.8-38.4%) of patients reported GI symptoms, 1 patient grade 2. At 12 months the same proportion 22.5% (10.8- 38.4%) reported GI symptoms, 2 patients with grade 2. No patients experienced grade 3 GI toxicity. At baseline the median PSA was 10.5 (IQR 8.0-13.3) and ranged from a minimum of 4.3 to 29.9 ng/ml. At 6 months median PSA was 0.5 (IQR 0.2-1.1) and ranged from a minimum of 0.1 to 3.9 ng/ml. At 12 months the median was 0.5 (0.2-0.8) and ranged from 0.1 to 3.6 ng/ml. Conclusion SABR for this group of patients was delivered safely using Rapidarc® FFF for treatment and online CBCT for set-up correction. Few patients presented with grade 2 GU/GI symptoms and none with grade 3 at 6 or 12 months. Longer follow-up is required to further assess PSA response and freedom from biochemical failure. OC-0097 Awareness and surveillance reduces head and neck radiotherapy treatment length J. Gornitzka 1 , P. Andersen 1 , M. Nielsen 2 , A. Bertelsen 2 , L. Johnsen 2 , J. Johansen 1,3 , C. Rønn Hansen 2,3 1 Odense University Hospital, Department of Oncology, Odense, Denmark 2 Odense University Hospital, Laboratory of Radiation Physics, Odense, Denmark 3 University of Southern Denmark, Institute of Clinical Research, Odense, Denmark Purpose or Objective Treatment course length is of essential importance in radiotherapy of head and neck cancer patients. National guidelines prescribe a maximum course length of 41 days for moderate accelerated treatments (6 fractions/week), and 48 days for non-accelerated treatments (5 fractions/week). The purpose of this study is to measure the time from the first to last fraction in a cohort of head and neck cancer patients treated 2003-2017, and to evaluate the effect of increased awareness of the importance of treatment course length. Material and Methods The study included 2,011 head and neck cancer patients treated between 2003 to 2017 to 66-68 Gy in 33-34 fractions and never re-irradiated. As a part of a National Cancer Plan in 2005 the focus increased on the “Patient pathways in packages”. From 2011 the department scheduled QA and service on treatment machines outside clinical hours to reduce non-treatment days. In February 2016, a systematic weekly review of the planned treatment course was introduced, where total radiation treatment course length was checked, and it was ensured that the first treatment was not on a Friday and the last treatment not on a Monday. Patients with scheduled treatment violations, according to national guidelines, are conferred with the responsible oncologist and the treatment plan is compensated with an extra fraction in the last week of treatment. Results The mean length of accelerated treatment courses was reduced from 40.9 days in 2007 to 38.3 days in 2017. For non-accelerated courses, the mean was reduced from 50.3 days in 2007 to 45.9 days in 2017 (fig. 1), making the treatment approximately 2 Gy more effective due to the reduced repopulation of the tumour.