Publications by authors named "Fatih Biltekin"

9 Publications

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A novel inverse optimization based three-dimensional conformal radiotherapy technique in craniospinal irradiation.

Phys Eng Sci Med 2021 Mar 8;44(1):265-275. Epub 2021 Feb 8.

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

Our aim was to develop a novel inverse optimization-based three-dimensional conformal radiotherapy (i3DCRT) technique for craniospinal irradiation. The imaging data of 20 patients with medulloblastoma were used retrospectively. The first group included 10 pediatric patients with supine position treated under anesthesia/sedation, and the second group included 10 young adult/adult patients treated with prone position. Three different treatment plans were created for each patient via i3DCRT, forward-planned three-dimensional conformal radiotherapy (f3DCRT) and intensity-modulated radiotherapy (IMRT) techniques. A total dose of 36 Gy was prescribed in 20 fractions for all plans. The comparative evaluation was conducted by using the parameters of conformity-index, homogeneity-index, and doses to the target volumes and organs at risk (OARs). The plans created with i3DCRT technique achieved better conformity and homogeneity compared to f3DCRT. In terms of OARs sparing, we found pronounced dose reductions in esophagus and heart in i3DCRT compared to f3DCRT plans. i3DCRT technique also provided a well-conformed dose distribution not superior, but comparable, to IMRT without increase in the total monitor unit per fraction (MU/fx) with respect to f3DCRT. The average monitor unit per fraction (MU/fx) for i3DCRT, f3DCRT and IMRT plans were found as 379.3, 378.0 and 1051.7 MU for the first group and 577.4, 563.5 and 1368.7 MU for the second group, respectively. Novel i3DCRT technique solves the problems associated with field junctions and beam edge matching encountered in f3DCRT plans. Additionally, i3DCRT technique can create almost similar plans as with IMRT with lower total MU/fx.
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http://dx.doi.org/10.1007/s13246-021-00976-6DOI Listing
March 2021

Adjuvant vaginal cuff brachytherapy: dosimetric comparison of conventional versus 3-dimensional planning in endometrial cancer.

J Contemp Brachytherapy 2020 Dec 16;12(6):601-605. Epub 2020 Dec 16.

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

Purpose: To evaluate dosimetric differences between point-based 2-dimensional (2D) vaginal brachytherapy (VBT) treatment planning technique and volume-based 3-dimensional (3D) VBT method for endometrial cancer (EC).

Material And Methods: Ten patients with uterine-confined EC treated with VBT were included in this study. All patients received 27.5 Gy in 5 fractions. Three different treatment plans were performed for each patient: plan A for dose prescribed to the entire vaginal wall thickness delineated via computed tomography guidance, plan B for dose prescribed to the vaginal mucosa/cylinder surface, and plan C for dose prescribed to 5 mm beyond the vaginal mucosa/cylinder surface. Dose-volume histograms (DVH) of treatment volumes and organs at risk (OARs) were evaluated and compared.

Results: DVH analysis of target volume doses (D, D, and D) showed a significant difference between plan A and plan B ( = 0.005), and plan B was found lower. D for plan C was significantly higher than plan A ( = 0.009), but for D and D, no statistically significant difference was found ( = 0.028 and = 0.028, respectively). In terms of OARs doses, including vagina, rectum, bladder, and sigmoid, D doses were significantly higher in plan A than plan B ( = 0.009, = 0.009, = 0.005, and = 0.005, respectively). All these doses were also significantly lower than in plan C ( = 0.005, = 0.012, and = 0.013, respectively), except for sigmoid ( = 0.155).

Conclusions: In this dosimetric analysis, we have shown that the volume-based 3D VBT technique provides the ability to balance the target dose against the sparing of OARs. Therefore, in the new modern 3D treatment era, instead of normalization of the dose to standard reference points, customized 3D volume-based VBT planning should be recommended.
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http://dx.doi.org/10.5114/jcb.2020.101694DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7787204PMC
December 2020

Characterization of 3D-printed bolus produced at different printing parameters.

Med Dosim 2021 Summer;46(2):157-163. Epub 2020 Nov 8.

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

We aimed to analyze the effects of printing parameters on characterization of three-dimensional (3D) printed bolus used in external beam radiotherapy. Two sets of measurements were performed to investigate the dosimetric and physical characterization of 3D-printed bolus at different printing parameters. In the first step, boluses were produced at different infill-percentages, infill-patterns and printing directions. Two-dimensional (2D) dose measurements were performed in Elekta Versa HD linear accelerator using 6 MV photon energy. Measured 2D dose maps for both printed and reference bolus materials were compared using the 2D gamma analysis method. Additionally, patient-specific bolus was produced with defined optimum printing parameters for anthropomorphic head and neck phantom. Then, point dose measurements were performed to evaluate the feasibility of printed bolus in clinical use. In the second step, physical measurements were carried out to evaluate the printing accuracy, the mean hounsfield unit (HU) value and the weight of 3D-printed boluses. According to our measurement, infill-percentage, infill-pattern and printing direction significantly changed the dosimetric and physical properties of the 3D-printed bolus independently. Maximum gamma passing rate at 1.5 and 5 cm depths were found as 93.8% and 98.8%, respectively, for 60% infill-percentage, sunglass fill infill-pattern and horizontal printing direction. The printing accuracy of the products was within 0.4 mm. Dosimetric and physical properties of the printed bolus material changed significantly with the selected printing parameters. Therefore, it is important to note that each combination of these printing parameters that will be used in the production of patient-specific bolus should be investigated separately.
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http://dx.doi.org/10.1016/j.meddos.2020.10.005DOI Listing
November 2020

Dosimetric comparison of two different applicators and rectal retraction methods used in inverse optimization-based intracavitary brachytherapy for cervical cancer.

J Contemp Brachytherapy 2020 Feb 28;12(1):35-43. Epub 2020 Feb 28.

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

Purpose: The purpose of this study was to evaluate the dosimetric differences between two different applicators and rectal-retraction methods used in image-guided brachytherapy (IGBT) for locally advanced cervical cancer (LACC).

Material And Methods: Ten patients with LACC treated with definitive chemoradiotherapy and inverse optimization-based IGBT were included in this study. In each patient, at least one fraction of IGBT was performed using tandem-ovoids (TO) with vaginal gauze packing (VGP) or tandem-ring (TR) with rectal-retractor (RR). High-risk clinical target volume (CTV) and intermediate-risk CTV (CTV) were defined as CTVs, and bladder, rectum, sigmoid, small bowel, urethra, and vaginal mucosa were defined as organs at risk (OARs). All patients received 50.4 Gy external beam radiotherapy (EBRT) in 28 fractions. After EBRT, 28 Gy high-dose-rate (HDR) IGBT in 4 fractions was delivered to central disease. A plan comparison was performed using dose-volume histogram (DVH) and treatment planning parameters for CTVs and OARs.

Results: There were no significant differences in D values of CTV. In terms of rectum dose, TR with RR was found to be significantly better than TO with VGP ( < 0.0001 for D and < 0.013 for V). Although, there were no statistically significant differences in D value of bladder, sigmoid, small bowel, upper vaginal mucosa, and urethra, mean value of D for all defined OARs were found lower in TR than in TO. Bladder V, upper vaginal mucosa V, middle and lower vaginal mucosa D values were all found to be significantly lower for TR than for TO ( < 0.035). CTV and CTV volumes contoured in TR were approximately 11% and 9% smaller than TO, respectively.

Conclusions: The results showed that there were no statistically differences in D value of CTV and CTV. However, all DVH parameters for OARs in TR with RR were found to be better than in TO with VGP.
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http://dx.doi.org/10.5114/jcb.2020.92699DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7073337PMC
February 2020

3D printer-based novel intensity-modulated vaginal brachytherapy applicator: feasibility study.

J Contemp Brachytherapy 2020 Feb 28;12(1):17-26. Epub 2020 Feb 28.

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

Purpose: To design a novel high-dose-rate intracavitary applicator which may lead to enhanced dose modulation in the brachytherapy of gynecological cancers.

Material And Methods: A novel brachytherapy applicator, auxiliary equipment and quality control phantom were modeled in SketchUp Pro 2017 modeling software and printed out from a MakerBot Replicator Z18 three-dimensional printer. As a printing material polylactic acid (PLA) filament was used and compensator materials including aluminum, stainless-steel and Cerrobend alloy were selected according to their radiation attenuation properties. To evaluate the feasibility of the novel applicator, two sets of measurements were performed in a Varian GammaMed iX Plus high-dose rate iridium-192 (Ir) brachytherapy unit and all of the treatment plans were calculated in Varian BrachyVision treatment planning system v.8.9 with TG43-based formalism. In the first step, catheter and source-dwell positioning accuracy, reproducibility of catheter and source positions, linearity of relative dose with changing dwell times and compensator materials were tested to evaluate the mechanical stability of the designed applicator. In the second step, to validate the dosimetric accuracy of the novel applicator measured point dose and two-dimensional dose distributions in homogeneous medium were compared with calculated data in the treatment planning system using PTW VeriSoft v.5.1 software.

Results: In mechanical quality control tests source-dwell positioning accuracy and linearity of the designed applicator were measured as ≤ 0.5 mm and ≤ 1.5%, respectively. Reproducibility of the treatment planning was ≥ 97.7% for gamma evaluation criteria of 1 mm distance to agreement and 1% dose difference of local dose. In dosimetric quality control tests, maximum difference between measured and calculated point dose was found as 3.8% in homogeneous medium. In two-dimensional analysis, the number of passing points was greater than 90% for all measurements using gamma evaluation criteria of 3 mm distance to agreement and 3% dose difference of local dose.

Conclusions: The novel brachytherapy applicator met the necessary requirements in quality control tests.
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http://dx.doi.org/10.5114/jcb.2020.92407DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7073342PMC
February 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 Photoneutron Dose Measured by Bubble Detectors in Conventional Linacs and Cyberknife Unit: Effective Dose and Secondary Malignancy Risk Estimation.

Technol Cancer Res Treat 2016 08 7;15(4):560-5. Epub 2015 Jul 7.

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

This study aims to reduce the uncertainty about the photoneutron dose produced over a course of radiotherapy with high-energy photon beams and evaluate photoneutron contamination-based secondary malignancy risk for different treatment modalities. Dosimetric measurements were taken in Philips SL25/75, Elekta Synergy Platform (Elekta AB, Stockholm, Sweden), Varian Clinac DHX High Performance systems (Varian Medical Systems, Palo Alto, CA), and Cyberknife Robotic Radiosurgery Unit (Accuray Inc., Sunnyvale, CA) using bubble detector for neutron dosimetry. The measurement data were used to determine in-field and out-of-field neutron equivalent dose in 6-MV 3D conformal radiotherapy, sliding window-intensity-modulated radiotherapy, and stereotactic body radiotherapy and to calculate the effective dose in 18-MV 3D conformal radiotherapy and sliding window-intensity-modulated radiotherapy techniques for patients with prostate cancer undergoing a standard treatment. For the 18-MV treatment techniques, the secondary malignancy risk due to the neutron contamination was estimated using the risk factors published by The International Commission on Radiological Protection. The neutron contamination-based secondary malignancy risk for the 18-MV 3D conformal radiotherapy and sliding window-intensity-modulated radiotherapy modalities was found to be 0.44% and 1.45% for Elekta Synergy Platform and 0.92% and 3.0% for the Varian Clinac DHX High Performance, respectively. For 6-MV 3D conformal radiotherapy, sliding window-intensity-modulated radiotherapy, and stereotactic body radiotherapy treatment techniques, neutron equivalent doses inside the treatment field were found to be lower than 40 mSv. Our measurements reveal that equivalent dose and effective dose due to the neutron contamination are at a considerable level for 18-MV sliding window-intensity-modulated radiotherapy treatments, while 6-MV photon beams used in different modalities still induce only negligible photoneutrons. The secondary malignancy risk based on photoneutron should be therefore taken into consideration in case of selecting 18-MV photons in a sliding window-intensity-modulated radiotherapy treatment instead of 6 MV.
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http://dx.doi.org/10.1177/1533034615592106DOI Listing
August 2016

Investigating in-field and out-of-field neutron contamination in high-energy medical linear accelerators based on the treatment factors of field size, depth, beam modifiers, and beam type.

Phys Med 2015 Jul 11;31(5):517-23. Epub 2015 Apr 11.

Department of Radiation Oncology, Faculty of Medicine, Hacettepe University, Sihhiye, Ankara, 06100, Turkey. Electronic address:

Purpose: We analysed the effects of field size, depth, beam modifier and beam type on the amount of in-field and out-of-field neutron contamination for medical linear accelerators (linacs).

Methods: Measurements were carried out for three high-energy medical linacs of Elekta Synergy Platform, Varian Clinac DHX High Performance and Philips SL25 using bubble detectors. The photo-neutron measurements were taken in the first two linacs with 18 MV nominal energy, whereas the electro-neutrons were measured in the three linacs with 9 MeV, 10 MeV, 15 MeV and 18 MeV.

Results: The central neutron doses increased with larger field sizes as a dramatic drop off was observed in peripheral areas. Comparing with the jaws-shaped open-field of 10 × 10 cm, the motorised and physical wedges contributed to neutron contamination at central axis by 60% and 18%, respectively. The similar dose increment was observed in MLC-shaped fields. The contributions of MLCs were in the range of 55-59% and 19-22% in Elekta and Varian linacs comparing with 10 × 10 and 20 × 20 cm open fields shaped by the jaws, respectively. The neutron doses at shallow depths were found to be higher than the doses found at deeper regions. The electro-neutron dose at the 18 MeV energy was higher than the doses at the electron energies of 15 MeV and 9 MeV by a factor of 3 and 50, respectively.

Conclusion: The photo- and electro-neutron dose should be taken into consideration in the radiation treatment with high photon and electron energies.
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http://dx.doi.org/10.1016/j.ejmp.2015.03.015DOI Listing
July 2015