Publications by authors named "Yagiz Yedekci"

5 Publications

  • Page 1 of 1

Factors affecting post-treatment radiation-induced lung disease in patients receiving stereotactic body radiotherapy to lung.

Radiat Environ Biophys 2021 03 24;60(1):87-92. Epub 2020 Oct 24.

Department of Radiation Oncology, Hacettepe University Faculty of Medicine, 06100, Ankara, Turkey.

The aim of the study is to investigate factors that may cause radiation-induced lung disease (RILD) in patients undergoing stereotactic body radiotherapy (SBRT) for lung tumors. Medical records of patients treated between May 2018 and June 2019 with SBRT were retrospectively evaluated. All patients should have a diagnosis of either primary non-small cell lung cancer (NSCLC) or less than three metastases to lung from another primary. The median treatment dose was 50 Gy in 4-5 fractions. Tumor response and RILD were evaluated in thoracic computer tomography (CT) using RECIST criteria. 82 patients with 97 lung lesions were treated. The median age was 68 years (IQR = 62-76). With a median follow-up of 7.2 months (3-18 months), three patients had grade 3 radiation pneumonitis (RP). RILD was observed in 52% of cases. Patients who had RILD had a higher risk of symptomatic RP (p = 0.007). In multivariate analyses older age, previous lung radiotherapy history, and median planning treatment volume (PTV) D95 value of ≥ 48 Gy were associated with RILD. Local recurrence (LR) was observed in 5.1% of cases. There was no difference in overall survival and LR with the presence of RILD. Older age, previous lung radiotherapy history, and median PTV D95 value of ≥ 48 Gy seems to be associated with post-SBRT RILD.
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http://dx.doi.org/10.1007/s00411-020-00878-3DOI Listing
March 2021

Role of 68-Ga-PSMA-PET/CT in pelvic radiotherapy field definitions for lymph node coverage in prostate cancer patients.

Radiother Oncol 2020 10 28;151:222-227. Epub 2020 Aug 28.

Department of Radiation Oncology, Hacettepe University, Faculty of Medicine, Ankara, Turkey.

Purpose: To evaluate the distribution of metastatic lymph nodes (LN) detected on Ga-PSMA-positron emission tomography/computed tomography (PET/CT) in treatment-naïve prostate cancer (PC) patients and to analyze the LN coverage rates of the pelvic fields defined in the GETUG trial and RTOG guidelines and a pelvic field extending superiorly from the L4/L5 interspace.

Materials And Methods: Ga-PSMA-PET/CT images obtained at diagnosis of 138 PC patients were retrospectively analyzed. The number and locations of Ga-PSMA-positive LNs were co-registered with one single-planning CT. The numbers, locations, and sizes of LNs located outside the three pelvic volumes were investigated for the entire cohort and for patients with LN metastasis in the pelvic area only.

Results: A total of 441 PSMA-PET-positive LN metastases were identified. The most frequent metastatic LNs were internal iliac LNs (25.2%). Para-aortic and presacral LNs outside the three pelvic fields were present in 20 (14.5%) and 22 patients (15.9%), respectively. The LN coverage rates according to the GETUG trial, the RTOG guidelines, and the pelvic field extending superiorly from L4/L5 were 44.2%, 52.2%, and 71, respectively, in the entire cohort and 51.7%, 61 and 83.1%, respectively, in patients with only pelvic LN metastasis. The number of metastatic LNs was a predictive factor for LNs located outside the three pelvic fields.

Conclusions: Extending the cranial margin of the pelvic field from L5/S1 to L4/L5 increases the accuracy of pelvic field irradiation in approximately 20% of patients, highlighting the importance of proximal common iliac irradiation, particularly in patients with multiple LN metastasis.
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http://dx.doi.org/10.1016/j.radonc.2020.08.021DOI Listing
October 2020

Feasibility of novel in vivo EPID dosimetry system for linear accelerator quality control tests.

Australas Phys Eng Sci Med 2019 Dec 12;42(4):995-1009. Epub 2019 Sep 12.

Department of Radiation Oncology, Faculty of Medicine, Hacettepe University, 06100, Ankara, Turkey.

The main aim was to validate the capability of a novel EPID-based in vivo dosimetry system for machine-specific quality control (QC) tests. In current study, two sets of measurements were performed in Elekta Versa HD linear accelerator using novel iViewDose™ in vivo dosimetry software. In the first part, measurements were carried out to evaluate the feasibility of novel in vivo system for daily dosimetric QC tests including output constancy, percentage depth dose (PDD) and beam profile measurements. In addition to daily QC tests, measured output factor as a function of field size, leaf transmission and tongue and groove effect were compared with calculated TPS data. In the second part of the measurements, detection capability of iViewDose software for basic mechanical QC tests were investigated for different setup conditions. In dosimetric QC tests, measured output factor with changing field size, PDD, beam profile and leaf transmission factors were found to be compatible with calculated TPS data. Additionally, the EPID-based system was capable to detect given dose calibration errors of 1% with ± 0.02% deviation. In mechanical QC tests, it was found that iViewDose software was sensitive for catching errors in collimator rotation (≥ 1°), changes in phantom thickness (≥ 1 cm) and major differences in irradiated field size down to 1 mm. In conclusion, iViewDose was proved to be as useful EPID-based software for daily monitoring of linear accelerator beam parameters and it provides extra safety net to prevent machine based radiation incidents.
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http://dx.doi.org/10.1007/s13246-019-00798-7DOI Listing
December 2019

Feasibility study of an electronic portal imaging based in vivo dose verification system for prostate stereotactic body radiotherapy.

Phys Med 2019 Aug 24;64:204-209. Epub 2019 Jul 24.

Hacettepe University, Faculty of Medicine, Department of Radiation Oncology, Ankara, Turkey.

Purpose: We evaluated the feasibility of electronic portal imaging based 3D in-vivo dosimetry for stereotactic body radiation therapy (SBRT) technique in prostate cancer.

Methods And Materials: To investigate error detectability limitations of iViewDose™ v.1.0.1 (Elekta, Stockholm, Sweden) for prostate SBRT cases, ten prostate cancer patients were selected and in-vivo electronic portal imaging devices dosimetry was performed. Also possible error scenarios including dose calibration, setup, collimator, multi leaf collimator and patient anatomy related inaccuracies were created to investigate detectability of EPID. For this purpose, a SBRT treatment was planned on BrainLab pelvis phantom (BrainLab Medical Systems, Westchester, IL) and irradiated after proving setup with cone beam computer tomography. After that incorrect plans were irradiated and obtained results were compared with original in vivo measurements.

Results: Mean gamma analysis (γ% ≤ 1) passing rate of ten patients was found as 96.2%. Additionally, mean dose reference point difference between measurement and calculated in treatment planning system for clinical target volume, rectum, bladder, left and right femur heads were found as 1.4%, 8%, 20.8%, 2.3% and 4.5%, respectively. Phantom measurements showed that positional errors can be escape from detection. However, the incorrect treated plans including linac calibration, MLC positions and patient anatomy based errors could not have passed the in vivo dosimetry analysis.

Conclusions: EPID-based 3D in vivo dosimetry software (iViewDose) provides an efficient safety check on the accuracy of dose delivery during prostate SBRT treatments. However, phantom results showed some limitation of the system.
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http://dx.doi.org/10.1016/j.ejmp.2019.07.008DOI Listing
August 2019

Evaluation of NanoDot Optically Stimulated Luminescence Dosimeter for Cone-shaped Small-field Dosimetry of Cyberknife Stereotactic Radiosurgery Unit: A Monte Carlo Simulation and Dosimetric Verification Study.

J Med Phys 2019 Jan-Mar;44(1):27-34

Institute of Nuclear Science, Hacettepe University, Ankara, Turkey.

Aim: The aim of this study was to investigate the adequacy of nanoDot optically stimulated luminescence (OSL) dosimeter for small field dosimetry before its applications in CyberKnife SRS unit.

Materials And Methods: A PTW 60018 SRS Diode, 60019 microDiamond, and Gafchromic EBT3 films were used along with a nanoDot carbon-doped aluminum oxide OSL dosimeter to collect and compare beam data. In addition, the EGSnrc/BEAMnrc code was employed to simulate 6-MV photon beams of CyberKnife SRS system.

Results: All detectors showed good consistency with each other in output factor measurements for cone sizes of 15 mm or more. The differences were maintained within 3% for these cones. However, OSL output factors showed higher discrepancies compared to those of other detectors for smaller cones wherein the difference reached nearly 40% for cone size of 5 mm. Depending on the performance of OSL dosimeter in terms of output factors, percentage depth doses (PDDs) were only measured for cones equal to or larger than 15 mm. The differences in PDD measurements were within 5% for depths in the range of 5-200 mm.

Conclusion: Its low reliable readings for cones smaller than 15 mm should be considered before its applications of Cyberknife system.
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http://dx.doi.org/10.4103/jmp.JMP_96_18DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6438048PMC
April 2019