(p¼0.018, 0.004) and left lung (p¼0.029, 0.022), and D0.1cc of the right mainstem (p¼0.049). All other results were unremarkable. Conclusion: The results produce statistically significant results when analyzing percent differences. However, it is observed that the difference is minimal in the context of absolute dose (cGy). It can be concluded that the current protocol of obtaining one CT scan per esophageal HDR-BT treat- ment is sufficient in evaluating dose to OARs. Can Conformity-Based Volumetric Modulated Arc Therapy Improve Dosimetry and Speed of Delivery in Radiation Therapy to Lumbosacral Spine Compared to Conventional Techniques? Joanna Javor 1 , Meagan Robbins 2 , Tara Rosewall 13 , Tim Craig 13 , Conrad Joseph Villafuerte 1 , Bernard Cummings 13 and Laura Dawson 13 1 - Princess Margaret Cancer Centre 2 - Eastern Health 3 - University of Toronto Purpose: VMAT is generally been perceived as too time and resource inten- sive for palliative radiation therapy (pRT), mainly due to the need for exten- sive OAR contouring. Dose limiting conformity objectives around the planning target volume can be automatically generated, and are commonly used to conform isodoses closely around the target volumes during inverse planning. The aim of this study is to determine if conformity based structures can be used to create VMAT plans for lumbosacral spine pRT without OAR contours, that will improve conformity, dose homogeneity and speed of de- livery compared to standard forward planning approaches. Methods: 25 patients were retrospectively re-planned using three different planning techniques: 1) anterior-posterior (AP/PA) parallel opposed pair (POP), 2) single isocenter AP/PA half beam block junctioned to 3 field, pos- terior and 2 laterals (JUNC), and 3) VMAT single arc. Treatment volume included L1-S5 vertebrae prescribed to 20 Gy in 5 fractions. Conformality index (CI), homogeneity index (HI), contour, planning and treatment time were compared for each technique. Results: PTV V95  95% was maintained for all 75 replans. VMAT was su- perior to POP and JUNC in terms of conformality (POP 2.0 vs. JUNC 1.8 vs. VMAT 1.2; p<0.01) and homogeneity (POP 1.1 vs. JUNC 1.1 vs. VMAT 1.0; p<0.01). Planning times for POP was the lowest (3.2 mins). VMAT and POP had similar delivery times (1.5 mins), which were approx- imately half the JUNC delivery time (3.2 mins). Conclusion: Conformity-based VMAT was dosimetrically superior to con- ventional field based planning, and reduced delivery time. This reduction in normal tissue dose, as well as reduced time spent on the treatment couch can potentially improve the quality of life in palliative patients receiving radiotherapy to the LS spine. Improving Patient Preparation for Prostate Radiotherapy Simulation and Treatment- Is There Anything That Can Be Done? Shannah Murland, Pamela Paterson, Winston Poon, Sonnia Valiquette-Fleury and Michael Piva Cross Cancer Institute Aim: The requirement for patients undergoing prostate radiotherapy to meet particular standards in bladder and bowel preparation for simulation and daily treatments can be challenging to patients and treatment units, and this has become even more significant with the use of reduced margins and hypofractionated regimes. While there may be slightly more flexibility in these parameters for daily treatment, it is crucial that the standards are met for treat- ment planning purposes and patients are required to prepare for simulation by achieving an empty rectum and a comfortably full bladder. Patients who cannot achieve these standards may need to have multiple simulation scans, occasionally returning on a different day, and may need to spend considerably more time at the cancer centre than expected. This is inconvenient for the patient and also very disruptive to CT simulator workflow, leading to delays for other patients. This project aimed to retrospectively evaluate the frequency of re-scanning and significant scan delays due to bladder-filling challenges in our department, and then evaluate the impact of two interventions alone and in combination on these parameters. Process: In January 2019, we began detailed tracking and found that 27/65 pa- tients (41.5%) experienced issues with bowel or bladder preparation. This included patients requiring multiple scans or patients who had to wait consider- ably past their appointment in order to fill their bladder. We then began having a radiation therapist telephone patients 3 days prior to their simulation appoint- ment to ensure that they had received their preparation instructions and under- stood what was required of them. For the next group of patients, they did not receive a phone call, but were booked for a preparation appointment 45 minutes ahead of their simulation to allow more time in the clinic for bladder-filling. For the final patient group, they received the phone call and the preparation appoint- ment. Each of the interventional groups consisted of 65 patients. Benefits / Challenges: Therapists were successful in contacting patients by phone within three attempts 73.9% of the time, and 70% of patients were reached on the first attempt. The frequency of re-scans was the same in the no intervention and phone call-only groups (27.7% and 27.8%), but dropped to 23.1% for preparation appointment only. The combination of phone call and preparation appointment was the most successful, with a re-scan rate of 13.8%. Patients being scanned significantly past their appointment times due to bladder emptiness also decreased with the introduction of the preparation appointment (from 43.1% to 23.1%), but the combination with the phone call was again the best intervention, dropping it further to 16.9%. Impact / Outcomes: The combination of the phone call and preparation appointment had the most impact on reducing re-scans and bladder delays, although the preparation appointment alone was successful in reducing bladder delays because of the extra time spent in the clinic. The phone call alone did not have much impact on re-scan and bladder delay frequency, but is still felt to be of value due to the other patient information that can be gathered and the benefits of educating patients on proper preparation. The process of phoning patients has been integrated into the simulator work- flow for a number of months and has been well-received. We have also measured a decrease in daily pre-treatment imaging re-scans due to this increased patient education. A Multi-Criteria Evaluation of Three Breath Hold Techniques for Left-sided Breast Radiation Therapy Franc ¸ois Gallant 1 , Stephen Breen 12 , Stephen Russell 1 , Glen Gonzalez 1 , Prashant Verma 1 , Shiangyee Yang 1 , Lisa Lalonde 1 and Matt Wronski 12 1 - Sunnybrook Health Sciences Centre 2 - University of Toronto, Department of Radiation Oncology Purpose: The risk of cardiac toxicity remains a clinical challenge for left- breast irradiation. Our institution evaluated three different breath hold tech- niques for cardiac sparing in patients receiving left-sided breast radiation ther- apy (RT): (1) the Active Breathing Coordinator (ABC); (2) an in-house- developed Visually-Monitored Voluntary Breath Hold (VM-VBH) technique and (3) a surface guided technique using the Align-RT system. The aim of this project was to select a primary breath hold technique option for future left-sided breast treatments. Methods: Eight evaluators including three frontline staff, one physicist, two supervisors and two managers from the RT and the Physics program partic- ipated in the evaluation of three different breath hold techniques (ABC, VM- VBH and Align-RT). A Pugh decision matrix was utilized with weighted eval- uation criteria. Nine evaluation criteria were utilized; 1) clinical effectiveness, 2) patient factors, 3) operator human factors, 4) planning factors, 5) contin- gency, 6) quality assurance resources, 7) transferability, 8) capital cost and 9) operating expenses. Each breath-hold technique was rated in each of these cat- egories using a five-point scale based on programmatic experience. The ABC system was used as a baseline as this technique was our standard of care at the time of evaluation. Technique ratings were multiplied by evaluation criteria weights to produce a final score for all three techniques. Conference Proceedings from RTi3 2020/Journal of Medical Imaging and Radiation Sciences 51 (2020) S1-S17 S7