ESTRO 37 Abstract book

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ESTRO 37

At our center, all prostate cancer patients are treated by arc based IMRT (VMAT) radiotherapy. The fractionation regimen used is either 78Gy in 39 fractions, 60Gy in 20 fractions (hypo-fractionation) or 66Gy in 33 fractions (post-op). Our current standard (STD) bladder filling protocol requires a patient drink 500cc of water 1 hour prior to each treatment and bladder filling is evaluated on daily CBCT prior to treatment. When the bladder is less than 50% of the planning CT volume, treatment is postponed and given later the same day when the bladder at least 50% full. Our goal was to develop an evaluation volume that could ensure a safe minimal bladder filling. Our dose constraints require that no more than 50% of the bladder can receive 60-65Gy with standard fractionation (2Gy/day) or 50Gy with the hypo-fractionation regimen (3Gy/day). We created a structure defined as a Virtual Bladder (VB) using the V60 isodose line from each patient’s respective treatment plan. The V50 isodose was used for patient receiving the hypo-fractionation regimen. This structure was than used to prospectively evaluate the bladder volume during each treatment and this was compared to our STD protocol. The VB protocol requires that the radiation therapist must evaluate the sagittal plane of the CBCT containing the largest bladder volume. The therapist than ensures that less than 50% of the bladder is found within the VB volume. The radiation therapists were instructed to follow the STD protocol in our center; however, they were also asked to prospectively determine whether the VB protocol would have changed their conduct. Results Between June and September 2017, 38 patients were evaluated with the VB protocol. Of these, 9 received 78Gy, 17 received 60Gy and 12 received 66Gy. With our STD protocol, 18 instances occurred where the criteria were not met in 6 (16%) patients. Of the 6 patients, there were 2 from each fractionation regimen. With our VB protocol, only 2 (5%) patients did not meet the criteria. Both received 66Gy and had no bladder filling issues with the STD protocol. The VB protocol changed the radiation therapists conduct in 8 (21%) of patients. Conclusion The Virtual Bladder protocol is a novel method to evaluate bladder filling, customized to each patient based on dose constraints derived from their treatment plan. Application of this protocol would likely result in a reduced number of postponed treatments and decrease the need for repeat imaging. This tool could allow us to target patients needing stricter bladder constraints with the goal of reducing bladder dose and toxicity. Further studies are warranted. OC-0312 Inter- and Intra-fraction setup errors in patients of HCC with PVTT treated with SBRT using ABC system T. Teekendra Singh 1 , T. Kataria 1 , K. Narang 1 1 Medanta The Medicity, DIVISION OF RADIATION ONCOLOGY, Gurgaon, India Purpose or Objective With the technologic advancements in image guidance and dose delivery, stereotactic body radiotherapy (SBRT) is being widely used in Hepato cellular carcinoma with Portal Vein TumourThrombosis (HCC with PVTT) cases as a noninvasive alternative to surgery. The purpose of this study was to evaluate the daily setup accuracy, inter & intra-fraction motion in these patients treated with Linac based SBRT using Active Breathing Co-ordinator (ABC), and to calculate the PTV margins required to account for the same. Material and Methods 22 Treatment fraction datasets for 5 patients of HCC with PVTT treated with SBRT to a total dose of40–60 Gy in 3-5 treatment fractions, were available. All patients were

Conclusion Barium produced lower delineation uncertainties, compared to Gastrografin and no contrast and can therefore be considered superior at highlighting the oesophagus on CBCT images. It is feasible to use oral contrast as a tool in IGRT to help guide clinicians and therapists with online matching and monitoring of the oesophageal position. OC-0311 Optimal bladder filling using CBCT based “virtual bladder” volume L. Igidbashian 1 , F. Girard 1 , M. Hinse 1 , E. Plouffe 1 , J. Tremblay 1 1 Hôpital de la Cité de la Santé de Laval - CSSSL, Radiation Oncology, Laval, Canada Purpose or Objective To develop a dosimetry based evaluation volume that could ensure an optimal bladder filling during Most published data evaluating bladder filling use ultrasound based pre-treatment evaluation with a pre- defined volume cut-off. Several variables including initial bladder filling and dosimetric constraints are often not taken into account . prostate radiotherapy. Material and Methods