ESTRO 37 Abstract book

ESTRO 37

S610

(CBCT) images were evaluated in terms of internal target volume (ITV) changes, center of mass (COM) displacement, Dice similarity coefficient (DSC) of ITV and planning target volume (PTV). Deformable registration was used to deform the planning computed tomography (PCT) images to the CBCT images for more accurate dose calculation with the original treatment plan. Dosimetric comparison was carried out between the planned dose and actual dose regarding dose per fraction and accumulated dose. The relationship between the anatomic variation and dosimetric deviation was then analyzed by correlation test. Results No statistically significant trend was found in the ITV volume, COM displacement, ITV DSC and PTV DSC over the treatment course. However, twelve patients (63%) demonstrated similar tendency of ITV volume changes, with tumor expansion from the first fraction and tumor shrinkage by the final fraction. The largest tumor expansion found in this study was 20% of the initial volume. From dosimetric evaluation, the actual delivered dose in terms of PTV coverage, dose conformity and low dose spillage significantly deteriorated from the planned dose, but ITV coverage was not significantly compromised. All patients could maintain 100% of ITV receiving the full prescription dose in accumulated dose evaluation. The dosimetric deviation of target coverage was found to be significantly correlated with ITV volume, ITV DSC and PTV DSC. Conclusion Although significant anatomic and dosimetric variations were observed in some patients during the course of lung SBRT, it should be noted that re-planning was not deemed necessary for at least half of the patients because the final dosimetric deviation was found to be minimal. The action of adaptive planning should be based on the individual anatomic variation of each patient. ITV DSC and PTV DSC might serve as a quick online assessment for the degree of anatomic variation which could reflect the associated dosimetric deviation. M.S. Assenholt 1 , A. Vestergaard 2 , E.B. Kjærsgaard 3 , A. Schouboe 2 , L. Nyvang 1 , J.C. Lindegaard 3 , K. Tanderup 1 , L.U. Fokdal 3 , N.B.K. Jensen 3 1 Aarhus University Hospital, Department of Medical Physics, Aarhus N, Denmark 2 Aarhus University Hospital, Danish Center for Proton Therapy, Aarhus N, Denmark 3 Aarhus University Hospital, Department of Oncology, Aarhus N, Denmark Purpose or Objective To evaluate an image-guided and adaptive EBRT workflow in locally advanced cervical (LACC) patients treated according to EMBRACE II guidelines in terms of individualized ITV margins and new criteria for dose coverage. Interfractional target (cervix/uterus) motion and organ filling was monitored on a daily basis and investigated along with the impact of daily patient feedback on organ fillings. Material and Methods Patients treated with definitive chemoradiotherapy were included. Pretreatment MRI- and (PET)-CT scans with full and empty bladder were performed and a bladder-filling protocol applied. VMAT plans were used to deliver 45Gy/25 fractions with daily onboard cone beam CT (CBCT) scans. Contouring was according to EMBRACE II PO-1082 Adaptation of EBRT through daily CBCT monitoring for cervical cancer patients

guidelines with individualized ITV margin and 5mm PTV margin. Trained RTTs monitored the interfractional target motion, and scored the target coverage in every fraction. A clinical workflow including thresholds for re-planning if target was not inside PTV was designed and followed. Daily patient feedback was given in order to optimize the bladder/rectal filling. CBCTs were retrospectively reviewed, and the accuracy of the RTT scorings analyzed. Target motion was characterized measuring ITV margins and target motion at treatment planning. Minimum target doses were estimated for re-planned patients. Results Twenty-three patients were monitored and analyzed. RTT scoring of target coverage was correct in 93% of the CBCTs (505/546), incorrect in <1%, and in 7% of the CBCTs the RTTs could not score primary due to compromised image quality. Seven patients were re- planned because of uterus (7) and/or cervix (2) motion. The dosimetric benefit of re-planning was 0-2Gy for uterus, and above 3.5Gy for cervix. Large target motion was found in 7 patients at planning and in 4 without target motion at planning, significant motion occurred during radiotherapy. Loss in target coverage was most often caused by rectal/bowel filling. A trend towards an increase in bladder volume with daily patient feedback The study proposes a practical adaptive approach for EBRT in LACC patients with daily IGRT monitoring supporting the EMBRACE II guidelines. This can be done with high accuracy by RTTs. In most cases a tissue- sparing VMAT plan with individualized margins was sufficient with respect to target dose coverage. In patients with unpredictable interfractional target- and organ motion, the compromised coverage benefitted from re-planning. The approach has limited workload and is relevant for other pelvic diagnoses was found. Conclusion PO-1083 “De gode strålene” – a book for children as next of kin to cancer patients in Norway K. Farstad 1 , S.K. Bergene 2 , I. Garseg 2 , S. Moen 2 , G. Bekkevold 2 , K.E. Rennan 2 , M.H. Normann 2 1 Ålesund Hospital, Radiotherapy, Ålesund, Norway 2 Oslo University Hospital, Radiotherapy, Oslo, Norway Purpose or Objective 350,000 children are next of kin to patients with severe somatic disease in Norway. 'De gode strålene” (which translates 'the helpful rays”) is a book written by a radiation therapist published in 2015. The book explains and illustrates cancer, radiotherapy (RT) and side effects. The book’s intention is to help children as next of kin to patients in the radiation department.To be able to recommend 'De gode strålene” to different radiation departments, we needed to examine if the book could be a useful tool for adults when they communicate with children regarding cancer. Material and Methods Two radiation departments cooperated to develop a questionnaire. All patients undergoing radiation therapy with the custody of children under the age of 18 received 'De gode strålene” and the questionnaire. This was Poster: RTT track: Patient care, side effects and communication

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