ESTRO 37 Abstract book

S161

ESTRO 37

Purpose or Objective The impact of environmental factors on error, efficiency and accuracy in image interpretation is widely addressed in diagnostic imaging (DI) by the provision of guidelines outlining the optimal environment under which image interpretation should occur; this is currently lacking for the Radiation Therapy environment. The aim of this research was to identify the opinions and perceptions of radiation therapists (RTTs) regarding the impact of environmental factors on image guided radiation therapy (IGRT) image interpretation. Material and Methods A mixed methods survey based on relevant DI literature was developed and distributed to RTTs worldwide. The survey was designed to collect qualitative and quantitative data regarding opinions and perceptions of the impact of environmental factors on IGRT image interpretation. Results Four hundred and thirty four RTTs fully completed the survey. 82% of RTTs identified environmental factors as having an impact on image interpretation. Figure 1 demonstrates the perceived impact of specific environmental factors on image interpretation. 10% of RTTs reported their work environment was unsuitable for image interpretation and 34% of respondents felt that changes were needed to facilitate image interpretation, these included provision of a designated room, or imaging workstation, removal of distractions/interruptions and lighting improvements. 69% surveyed identified that they believe the provision of guidelines would be beneficial to their image interpretation. Figure 1. Distribution of RTTs perceptions on the impact of specific environmental factors on their image interpretation

(IGRT) would better ensure toxicity is avoided. As the oesophagus is poorly seen on cone-beam computed tomography (CBCT), we assessed the extent to which this is improved using two oral contrast agents administered prior to treatment. Material and Methods Patients receiving contrast were enrolled into a prospective trial and were receiving radiotherapy for Stage I-III NSCLC. The first 6 patients were randomly assigned to 50mL Gastrografin or 50mL barium sulphate to determine which agent would be used going forward. Contrast was administered just prior to planning CT(PCT) and each daily/weekly pre-treatment CBCT. Three previously treated patients with matched baseline characteristics, who did not receive contrast were included as a control group. The ability to visualise the oesophagus was determined by assessing how similarly 6 observers (4 radiation oncologists and 2 dosimetrists) were able to contour the organ. Using all contours, a Simultaneous Truth and Performance Level Estimation (STAPLE) contour was created (CERR software) along with a generated Kappa statistic for each dataset. Individual contours were then compared to the STAPLE contour. Descriptive statistics were used and a Dice Coefficient(DC) & Hausdorff distance (HD) (95% CI) were calculated using 3DSlicer and compared using an independent t-test or Mann-Whitney U test. Each observer also scored the influence of any contrast- induced artefact on their ability to visualise the tumour and other critical organs. Results A total of 36 datasets were analysed and results summarised in table 1. Oesophagus contours were more similar between observers in the contrast patients compared to non-contrast patients, as evidenced by significantly higher Kappa, DC and HDs. Significantly higher concordance was seen with barium compared to Gastrografin. Compared to Gastrografin, barium enabled observers to identify the oesophagus with a smaller variation (p=0.002) with there being only 1.6mm between observers 95% of the time. Patient compliance as determined by the % of intended CBCTs given with contrast, was higher with the barium than with the Gastrografin (92% vs 52%), largely due to the occurrence of diarrhoea in 2 of the 3 Gastrografin patients. Some contrast-induced artefact was seen on the CBCTs with both agents, but the observers rated this as minimally affecting their ability to visualise the tumour and other organs.

Conclusion A wide range of environmental factors impact on RTTs’ ability to interpret images during IGRT. The introduction of guidelines outlining the optimal environment under which image interpretation should occur is needed based on the opinions and perceptions of RTTs and the literature identified from DI to improve image interpretation in Radiation Therapy. OC-0310 Contrast enhanced oesophageal avoidance for stereotactic body radiotherapy: Barium vs Gastrografin K. Woodford 1 , V. Panettieri 1 , J. Ruben 1 , S. Davis 1 , E. Sim 1 , T. Tran Le 1 , S. Senthi 1 1 The Alfred Hospital, Alfred Health Radiation Oncology, Melbourne, Australia Purpose or Objective Stereotactic body radiotherapy may facilitate treatment in a greater proportion of locally-advanced non-small cell lung cancers (NSCLC) patients, just as it has for early stage disease. The oesophagus is the key dose-limiting organ and visualisation during image-guided radiotherapy