ESTRO 2020 Abstract book

S1080 ESTRO 2020

PO‐1843 Bladder and rectum volume control at the CT simulation stage of curative pelvic patients protocol M. Berg 1 , T. H Herbst 1 , C. J Skovgaard 1 , C. Krog 1 , J.S. Rasmussen 1 , K. Edwardsen 1 , M. Christensen 1 , S.D. Hansen 1 1 Vejle Hospital, Department of Medical Physics, Vejle, Denmark Purpose or Objective For patients with prostate and recti cancer, the variation in rectum size between the planning CT (pCT) and daily treatments should be as small as possible in order to target prostate / elective lymph nodes and/or rectum, with the smallest margin possible. Therefore, the pCT maximum permissible rectum diameter is 3 cm (prostate) and 4 cm (rectal) in our ward. To obtain this current practice is that patients take microlax ® at home on the day of pCT. Furthermore, patients with prostate cancer drink up to 500 mL of water 30 minutes before the pCT. Some patients still had an excessive rectum diameter so another round of microlax ® and water is used to empty the rectum and refill the bladder before scanning the patient again. This imparts a delay of up to 30 minutes before the patient is ready for a new pre‐scan. Therefore we have investigated whether it is advantageous the patients to meet 30‐45 minutes before their scheduled pCT time to take microlax ® A new practice has been introduced in which patients take a microlax ® at home the evening before pCT. On the day of pCT, the patient meets 30‐45 minutes before the pCT and is met by a radiographer. The patient is then given microlax ® while prostate cancer patients also receive water. In the spring of 2018, data for the old practice were collected for 29 and 22 randomly selected patients with prostate and rectal cancer, respectively, while in the spring / summer 2019, after the introduction of the new practice, data were also collected for 27 and 17 randomly selected patients. Results With the old practice, 22% of patients had not taken microlax ® at home, and approximately every third patient had to leave the CT for both diagnostic groups ‐ see Table 1. The new practice resulted in only four out of 44 patients leaving the CT. This is a drop from 31 % to 9 % for postponing the pCT. and water in the ward. Material and Methods Conclusion Since the patients themselves were responsible for taking microlax ® , only about75% of patients complied, resulting in approximately one third of them having to leave the CT to take another microlax ® , leading to delays in the CT‐MR program of about 30 minutes per patient. With the introduction of the new practice where patients are met by a radiographer in the ward immediately before the pCT and take microlax ® and possibly drinking water, only 15% of patients with prostate cancer and 0% with recti cancer were postponed. Therefore, the change has resulted in great satisfaction among both patients and staff, as the number of delays has been reduced from 31% to 9% for the two groups together. PO‐1844 Service evaluation of a new bladder filling protocol for radical prostate radiotherapy D. Burns 1 , K. Rosbottom 2 , J. Mitchell 1 1 NHS Lothian, Edinburgh Cancer Centre, Edinburgh, United Kingdom ; 2 Sheffield Hallam University, Radiotherapy, Sheffield, United Kingdom

Purpose or Objective Purpose

Conventional radiotherapy for prostate cancer has been planned with a full bladder based on the rationale that this will move the small bowel out of the treatment field and result in greater sparing of the bladder itself[1]. Our department has moved from a comfortably full (CF) bladder to a strict drinking protocol (DP) of emptying the bladder, drinking three cups of water and waiting 30 minutes prior to treatment. A service evaluation was carried out to determine if this change in practice results in a more consistent bladder volume from CT panning to treatment. [1] Tsang, Y.M., & Hoskin, P. (2017) the impact of bladder preparation protocols on post treatment toxicity in radiotherapy for localised prostate cancer patients. Technical Innovations & Patient support in Radiation Based on 233 prostate patients treated per year a sample size of 146 was determined to result in a 95% confidence level with a 5% margin of error[1]. The last 73 patients on the CF protocol and the first 73 patients on the DP bladders were compared. The bladder volume from CT and on CBCT fraction one was outlined by one observer to ascertain the difference in bladder volume and assess if an increase in consistency had been achieved with the addition of the DP. Each bladder protocol was also assessed to ascertain which protocol results in the most consistent bladder volume at treatment. [1] Sample size calculator, Raosoft, 2004 The addition of the DP does not result in a statistically significant ( P = ‐0.984) difference in bladder volume from CT to CBCT fraction one compared to CF. Each bladder protocol was evaluated for consistency and it was found that neither protocol results in a consistent volume and a statistically significant result (CF: p = 0.857) and (DP: p = 0.201). The results illustrate that there is statistically no benefit gained from moving from CF to the DP in terms of consistency of bladder volume achieved. In the UK there are currently no official guidelines on what is the optimal volume of bladder for prostate cancer patients[1]. To attend a busy regional cancer centre patients may have had to travel a long distance. This coupled with any unintended delays can result in patients having to empty their bladder or be taken of the treatment couch, therefore a strict drinking protocol may not be feasible .The results of this study that there is no statistically significant difference in consistency gained from employing a strict drinking protocol compared to maintaining a comfortably full bladder. [1] Nightingale, H., Conroy, R., Elliot, T., Coyle, C., Wylie, J. P., & Choudhury, A. (2017) A national survey of current practices of preparation and management of radical prostate radiotherapy patients during treatment. Radiography, 23, 87‐93 Oncology, 3‐4, 37‐40 Material and Methods Method and Materials Results Results Conclusion Conclusion

Poster: RTT track: Imaging acquisition and registration, OAR and target definition

PO‐1845 Time trend analysis of target volume auto‐ contouring in locally advanced NSCLC over the course of RT S. Barrett 1 , M. Leech 1 , L. Marignol 1 1 Trinity College Dublin, Applied Radiation Therapy Trinity, Dublin, Ireland

Purpose or Objective