1. Does my bum look big in this? Audit of rectal volumes and AP diameter in planning scans for radical prostate radiotherapy Tse V, Lorimer CFK, Parker R, Robinson A Sussex Cancer Centre, Royal Sussex County Hospital, Brighton, UK 53 consecutive radical prostate patients were identified from our radiotherapy database from 2010 (Group A). This group had had no rectal intervention prior to planning CT and treatment. 45 consecutive patients were then identified from the same database from 2013 post implementation of the micro-enema protocol (Group B). Rectal volumes were calculated from the organs at risk outlining records and AP diameters at the base of the seminal vesicles were measured. Radiotherapy treatment notes were analysed for number of rescans. The data was analysed using Microsoft Excel and the statistical analysis performed using Mann-Whitney and Fisher’s exact test of proportions. Introduction Method Conclusion Microenemas are highly effective in reducing rectal volume and AP diameter for patients due to have radical radiotherapy for prostate cancer. Patients were issued with a prescription for microenemas when they were consented for radiotherapy so that no delays were introduced into the system. The microenemas were generally well tolerated by the patient group. This data is consistent with other studies and supports a movement towards national guidelines for rectal preparation prior to radical radiotherapy for prostate cancer. Results References Rectal volumes AP diameter 1.Dearnaley DP et al. Lancet Oncol 2014 2.Yahya S et al. Br J Radiol 2013 3.Thomas SJ et al. Radiother Oncol. 2013 4.De Crevoisier et al. IJOBP. 2005 5.Heemsbergen et al. IJOBP 2007 6.Engels at al IJOBP 2008 Increasing dose and tighter planning margins used in radical external beam radiotherapy (EBRT) for prostate cancers necessitates more accurate PTV delineation and more reproducible PTV position. Several papers have quantified intra-fraction prostate motion and also shown that increased rectal distension on planning CT reduced local tumour control. Rectal volume and anterior-posterior (AP) diameter are important anatomical considerations in planning patients for EBRT. Volumes of under 60cm 3 are thought to be optimal and <100cm 3 mandatory. The AP diameter at the level of the base of seminal vesicles should ideally be < 5cm to avoid anterior displacement of the prostate. Until 2009, no rectal preparation was given prior to planning scans or treatment at our centre. An unacceptable number of rescans were seen raising concern about possible movement of the prostate. Diet sheets were trialled with poor patient compliance. As a result, microenemas were introduced as standard from 2012. Our aim was to assess whether this intervention reduced rectal volumes, AP diameter and number of rescans. Rectal Volumes (cm3) No rectal preparation N = 53 cases Microlette enemas N = 45 cases Mean89.763.2 Range38.4 – 185.136.6 – 144 AP diameter (cm)NMeanSDT-test Before534.21.0 <0.001 After453.60.8 The median rectal volume in Group A was 85.3cm 3 (interquartile range 58.6 - 112.7) versus 61.3cm 3 (interquartile range 48.3 - 72.3) in Group B (p<0.001). 34% of patients in Group A had rectal volumes over 100cm 3 compared to 4% in Group B (P<0.001). Volumes over 60cm 3 were 71% and 51% respectively (p=0.04). The mean AP diameter was 4.2cm (SD +/- 1.0) in Group A compared to 3.6 (SD +/- 0.8) in Group B (p<0.001). The percentage of patients with an AP diameter over 5cm in Group A was 28% versus 4.4% in Group B (p<0.002). 8% of patients in Group A had to be rescanned during treatment due to rectal distension versus 2% in Group B. Volume (cm3) Min25 th Median75thMax Before 38.458.685.4112.7185.1 After 36.648.361.372.3144.4 p<0.001 p=0.04 Correspondence to: angus.robinson@nhs.net p=0.02 p<0.002 p<0.001