ESTRO 2021 Abstract Book

S1082

ESTRO 2021

Health Evidence, Nijmegen, The Netherlands; 4 University Medical Center Utrecht, Julius Center for Health Sciences and Primary Care, The Netherlands, The Netherlands; 5 University Medical Center Utrecht, Julius Center for Health Sciences and Primary Care, Utrecht, The Netherlands Purpose or Objective 1.5 Tesla magnetic resonance imaging radiotherapy linear accelerator (MR-Linac) is gaining interest for treatment of localized prostate cancer. Evidence of clinical effectiveness is still lacking and it therefore remains uncertain whether MR-Linac is cost-effective. An early health economic analysis was performed to calculate the necessary relative reduction in complications and the maximum price of MR-Linac treatment (5 fractions) to be cost-effective compared to 5, 20 and 39 fractionation schedules of external beam radiotherapy (EBRT) and low-dose-rate (LDR) brachytherapy. Materials and Methods A state transition model was developed for men with localized prostate cancer. Quality adjusted life years (QALYs), costs and incremental cost-effectiveness ratios of MR-Linac and comparators were calculated over lifetime. Complication rates such as grade ≥2 urinary, grade ≥2 bowel and sexual complications, and utilities were based on systematic literature searches. Costs were estimated from literature using a Dutch healthcare perspective. Threshold analyses were performed to identify the thresholds of complications and costs for MR- Linac to be cost-effective. One-way sensitivity analyses were performed to outline uncertainty outcomes of all parameters. Results At a cost price of €6,460 per patient, no reductions in complications were needed to consider MR-Linac cost- effective compared to EBRT 20 and 39 fractions. Compared to EBRT 5 fractions and LDR brachytherapy, MR- Linac is found to be cost-effective when complications are relatively reduced by 54% and 66% respectively. Sensitivity analyses showed that the results are highly sensitive to the utilities of urinary, bowel and sexual complications and the probability of biochemical progression. Conclusion MR-Linac is likely to be cost-effective compared to 20 and 39 fractions EBRT. For MR-Linac to become cost- effective compared to 5 fractions EBRT and LDR brachytherapy, it has to either reduce complications substantially or be offered at limited costs. PO-1320 Infectious Risk After Prostatic Transrectal Fiducial Marker Implantation in Radiation Therapy T. Reynaud 1 , I. Ben Aicha 1 , D. Carignan 2 , C. Pelchat 1 , C. Fiset 1 , W. Foster 1 , A. Martin 3 , E. Vigneault 1 1 CHU de Québec-Université Laval, Department of Radiation Oncology, Québec, Canada; 2 CHU de Québec- Université Laval, Research Centre, Québec, Canada; 3 CHU de Québec-Université Laval, Departement of Radiation Oncology, Québec, Canada Purpose or Objective The aim of this study is to report the infection risk in transrectal ultrasound-guided fiducial marker (FM) insertion for image-guided radiotherapy (IGRT) in prostate cancer. Materials and Methods Between January 2016 and December 2020, 835 patients scheduled for intensity-modulated radiation therapy for treatment of prostate cancer had an intraprostatic FM transrectal implantation under ultrasound guidance by radiation oncologists specialized in brachytherapy. Patients had a standard oral prophylactic antibiotic with quinolone. If quinolone-resistant bacteria were detected at the time of the prostate cancer biopsies, the prophylactic antibiotic regimen was modified accordingly. The quinolone-resistant bacteria screening test was not repeated in this cohort of patients before FM insertion. The infectious complications were assessed with questionnaires at the time of planning CT and medical record reviewed. Toxicities were evaluated according to CTCAE v5.0. Results The median time between FM implantation and evaluation was 10 days (range, 0-165). Four (0.48%) patients experienced pollakiuria and painful urination after the procedure, one (0.12%) patient also had fever, but the infectious assessment was negative. Four (0.48%) patients developed urinary tract infection related to the procedure, mostly with quinolone-resistant bacteria (75%). Three had a grade 2 infection, and one patient experienced a grade 3 urosepsis by quinolone-resistant E. coli. The quinolone-resistance status was known for 2 patients (one positive and one negative) and was unknown for the other 2 patients prior to FM implantation. Conclusion Intraprostatic transrectal FM implantation for IGRT is well tolerated with a low rate of infection compared to the prostate biopsies' literature (2%-7%). Yet, an infection could be potentially fatal, and it is important to prevent sepsis with the appropriate antimicrobial prophylaxis. The necessity of repeating the quinolone- resistance test prior to FM insertion remains unclear and needs to be validated.

PO-1321 A Simple Method to Visualize and to Spare the Ureters During SBRT for Oligo Metastatic Patients

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