ESTRO 2022 - Abstract Book

S495

Abstract book

ESTRO 2022

(in mV) corresponds to when irradiated. Stage three consisted of measuring dose in the Venezia™ applicator by placing the MOSFET device into an interstitial needle within the applicator. The applicator was partially submerged in a water tank for the purpose of replicating a patient. Results The mean dose from applicator measurements resulted in a -1.8% difference (with STDEV of 1.5) from the Oncentra® treatment planning system (TPS) dose. The total plan uncertainty ( k= 2), including MOSFET angular dependence uncertainties acquired from commissioning measurements, calibration uncertainties and TPS dose uncertainties, was calculated to be ±11.2%. This compares to prostate IVD measurements which resulted in -6.4% mean dose (range +5.1% to -15.2%) compared to TPS dose and total plan uncertainty ( k= 2) between 11-17% [1] . Conclusion Use of the MOSFET device for IVD in HDR gynaecological brachytherapy applicators in a water tank showed good agreement with predicted dose (extracted from the TPS) within measurement uncertainties. These results provide confidence in the accuracy of dose delivery for brachytherapy. The next stage of this project will implement real-time IVD measurements in patients during cervix brachytherapy treatments, based on MOSFET readings taken automatically every 20 seconds. 1 National Institute of Oncology, Centre of Radiotherapy, Budapest, Hungary; 2 Eötvös Loránd University, Faculty of Natural Sciences, Department of Biophysics, Budapest, Hungary; 3 Semmelweis University, Faculty of Medicine, Department of Oncology, Budapest, Hungary; 4 Semmelweis University, Faculty of Medicine, Department of Oncology, Budapest, Hungary Purpose or Objective A detailed dosimetric comparison of the intensity-modulated-arc-therapy (IMAT), CyberKnife therapy (CK), single fraction interstitial high-dose-rate (HDR) and low-dose-rate (LDR) brachytherapy (BT) in low-risk prostate cancer. Materials and Methods Treatment plans of twenty patients treated with CK were selected and additional plans using IMAT, HDR and LDR BT were created on the same CT images (Figure). The prescribed dose was 2.5/70Gy in IMAT, 8/40Gy in CK (according to an ongoing phase II prospective trial at our institute), 21Gy in HDR and 145Gy in LDR BT to the prostate gland (according to our PROMOBRA prospective randomized study). EQD2 dose-volume parameters were calculated for each technique and compared using Friedman ANOVA and Fisher-LSD post-hoc tests. 1 year was estimated in LDR BT as overall treatment time, as during this time 89% of the prescribed dose is delivered. PD-0565 Which is the most appropriate treatment modality in the radiotherapy of low-risk prostate cancer? G. Fröhlich 1,2 , P. Ágoston 1,3 , K. Jorgo 1 , G. Stelczer 1 , C. Polgár 1,4 , Z. Takácsi-Nagy 1,4 , T. Major 1,4

Results EQD2 total dose of the prostate was significantly lower with IMAT and CK than with HDR and LDR BT, D90 was 79.5Gy, 116.4Gy, 169.2Gy and 157.9Gy (p<0.001), respectively. However, teletherapy plans were more conformal than BT, COIN was 0.84, 0.82, 0.76 and 0.76 (p<0.001), respectively. The D 2 to rectum and bladder were lower with HDR BT than with IMAT, CK or LDR BT, it was 66.7Gy, 68.1Gy, 36.0Gy and 68.0Gy (p=0.0427), and 68.4Gy, 78.9Gy, 51.4Gy and 70.3Gy