ESTRO 37 Abstract book

ESTRO 37

S606

Poster: RTT track: Image guided radiotherapy and verification protocols

Group two. 367/420 (87%) of image reviews concurred with the gold-standard. Individual concordance rates ranged from 80-100%; all achieved parity. Group two results supported the clinical implementation of Radiographer-led soft tissue review under prospective audit conditions. Conclusion A dedicated TCP facilitated implementation of Radio- grapher-led cervical cancer soft tissue verification. Result variability bolsters the necessity for Radiographer training and competency assessment before role- extension in this area. Currently, two competent Radiographers complete each image review, with initial prospective results indicating a high level of concordance (103/107 images reviewed: 96% agreement) with clinicians. PO-1076 Action levels for local expansions of the body outline during radiotherapy of the residual breast M. Berg 1 , L. Jeppesen 1 , K. Drevsfeldt 1 , H.D. Nissen 1 1 Vejle Hospital, Department of Medical Physics, Vejle, Denmark Purpose or Objective Local expansions of the body outline are commonly observed during the radiotherapy (RT) course for patients with breast cancer. Causes include tissue swelling, edemas and variations in the position of the ipsilateral arm. Enlargement in the anterio-lateral direction can be taken into account by applying a skin flash. This does however not ensure sufficient target coverage deep in the breast in case of tissue enlargement during RT. The present study investigates target coverage as a function of simulated tissue enlargement. The results can be used for setting up action levels for rescanning and re-planning based on daily positioning CBCTs. Material and Methods 15 consecutive patients, treated for right sided breast cancer with 40 Gy in 15 fractions, were retrospectively selected. The CTV of the residual breast was delineated according to the ESTRO guidelines and cropped to 5 mm beneath the skin. Original dose plans were made with the field-in-field technique using a mixture of 6MV and 18MV beams. A bolus of 3, 6, 9, 12 and 15 mm on the medial, lateral and combined medial and lateral part of the breast was simulated and the original plan recalculated with unchanged MU for each bolus setup. As tissue enlargement typically results in under dosage in the deepest part of the CTV a CTVdeep consisting of the most dorsal 1 cm of the CTV in every slice was created. Finally V38Gy was evaluated as a function of bolus thickness for the CTVdeep. Results Median volume of CTV (range) was 748 mL (341-1401) and 266 mL (168-364) for the CTV and CTVdeep, respectively. Median V38Gy for the original plan was for the CTV and the CTVdeep 99.2% (97.3-99.6) and 98.9% (98.3-99.3), respectively. The number of patients having V38Gy < 95% for CTVdeep as a function of bolus thickness and position is given in Table 1. Example of V38Gy for CTVdeep for bolus applied both medially and laterally is shown in Figure 1. Conclusion If local expansion of the body outline is seen medially or laterally only changes up to about 9 mm can be accepted while still maintaining V38Gy ≥ 95% of CTVdeep. For expansions both medially and laterally the corresponding

PO-1075 Implementation and validation of radiographer-led IGRT for cervix cancer S. Alexander 1 , N. Hopkins 1 , S. Lalondrelle 2 , A. Taylor 3 , K. Titmarsh 4 , H. McNair 2 1 The Royal Marsden NHS Foundation Trust, Department of Radiation Oncology, Sutton, United Kingdom 2 The Royal Marsden NHS Foundation Trust / The Institute of Cancer Research, Department of Radiation Oncology, Sutton, United Kingdom 3 The Royal Marsden NHS Foundation Trust / The Institute of Cancer Research, Department of Radiation Oncology, Chelsea, United Kingdom 4 Kingston University & St George's- University of London, Faculty of Health- Social Care and Education, London, United Kingdom Purpose or Objective IGRT in cervical cancer treatment delivery is complex due to significant target and OAR motion. Implementing image assessment of soft tissue target and OAR position to improve accuracy is recommended 1 yet no standard IGRT solution or guidelines for Radiographer review exist. We introduced a dedicated training and competency programme (TCP), with the aim of implementing soft tissue assessment on CBCT into routine practice. Material and Methods The TCP comprised inter-professional didactic lectures and practical sessions, supported by a comprehensive workbook. Content was decided by a multi-disciplinary team comprising Clinical Oncologists, Radiographers, and Physicists. The TCP was delivered twice, six months apart. More stringent review guidelines and greater anatomy teaching was added in advance of the second session. Nineteen and twenty-one radiographers volunteered for the first and second TCP respectively. In both groups, on completion of training, soft-tissue review proficiency (after bony anatomy registration) was assessed against a Consultant Clinical Oncologist gold-standard from a database of 20 cervical cancer CBCT images. Group one focussed on offline verification and decision making. Assessment of PTV coverage, bladder and rectal volume, pelvic pitch and body contour was guided by a traffic-light decision support system. Decision choices comprised: no action, intervene before next fraction or seek advice. Group two focussed on online verification and decision making. Image review was supported by a decision flowchart, directing the Radiographer to: assess pelvic pitch and PTV coverage, identify causes of sub-optimal CTV coverage and resolve to continue treatment or intervene before treatment. All reviews were graded pass or fail based on PTV coverage assessment and decision taken in concordance with the gold-standard. Parity was set at ≥ 80% agree- ment. Results Sixteen Radiographers completed the TCP in group one, twenty-one in group two. Collectively 740 images were reviewed. Group one. 231/320 (72%) of image reviews co ncurred with the gold-standard. Individual concordance with gold- standard ranged from 60-90%, four achieved ≥ 80%, signifying parity. This was not sufficient to support clinical implementation.