PURPOSE:The Expanded Prostate Cancer Index Composite (EPIC) is a symptom scale that measures health-related quality of life (HRQoL) in prostate cancer (PCa) patients. This scale is translated into different languages and used in daily practice. This study aimed to translate the EPIC scale into Turkish and provide Turkish validation by conducting validity and reliability analyses. METHODS:Patients with biopsy-proven PCa who received definitive or postoperative radiotherapy (RT) at our department were included. All participants were evaluated using the Turkish EPIC, The European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC-QLQ) C30, and EORTC-QLQ PR25 questionnaires at five different time points. First, the original English version of the EPIC was translated into Turkish, and then, two reliability and five validity analyses were performed. RESULTS:One hundred-five patients were included in the study. In the reliability analyses, Cronbach's alpha values of the whole scale were measured at 0.866, and the main scales' Cronbach's alpha values were measured between 0.654 and 0.969. In the test-retest analysis, the correlation values of the main scales were measured between 0.413 and 0.861. The pilot study with 20 patients was completed, thus providing face validity. Sensitivity to change analysis, interscale correlation, criterion validity, and explanatory factor analyses were performed, and results proving the scale's validity were obtained in all analyses. CONCLUSION:The Turkish EPIC scale is applicable for patients in the Turkish population diagnosed with PCa who received either definitive or postoperative RT.

Purpose: The Expanded Prostate Cancer Index Composite (EPIC) is a symptom scale that measures health-related quality of life (HRQoL) in prostate cancer (PCa) patients. This scale is translated into different languages and used in daily practice. This study aimed to translate the EPIC scale into Turkish and provide Turkish validation by conducting validity and reliability analyses. Methods: Patients with biopsy-proven PCa who received definitive or postoperative radiotherapy (RT) at our department were included. All participants were evaluated using the Turkish EPIC, The European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC-QLQ) C30, and EORTC-QLQ PR25 questionnaires at five different time intervals. First, the original English version of the EPIC was translated into Turkish, and then, two reliability and five validity analyses were performed. Results: One hundred-five patients were included in the study. In the reliability analyses, Cronbach's alpha values of the whole scale were measured at 0.866, and the main scales' Cronbach's alpha values were measured between 0.654 and 0.969. In the test-retest analysis, the correlation values of the main scales were measured between 0.413 and 0.861. The pilot study with 20 patients was completed, thus providing face validity. Sensitivity to change analysis, interscale correlation, criterion validity, and explanatory factor analyses were performed, and results proving the scale's validity were obtained in all analyses. Conclusion: The Turkish EPIC scale is applicable for patients in the Turkish population diagnosed with PCa who received either definitive or postoperative RT.

Purpose To evaluate the outcomes of metastasis-directed treatment (MDT) using stereotactic body radiotherapy (SBRT) for bone-only oligometastasis (OM) detected with gallium prostate-specific membrane antigen ( 68 Ga-PSMA) PET/CT in castration-sensitive prostate cancer (PC) patients. Methods In this multi-institutional study, clinical data of 74 PC patients with 153 bone lesions who were undergoing MDT were retrospectively evaluated. Twenty-seven patients (36.5%) had synchronous, and 47 (63.5%) had metachronous OM. All patients had PC with 5 metastases or fewer detected by 68 Ga-PSMA PET/CT and treated using SBRT with a median dose of 20 Gy. The prognostic factors for PC-specific survival (PCSS) and progression-free survival (PFS) were analyzed. Results The median follow-up was 27.3 months. Patients with synchronous OM were older and received higher rates of androgen deprivation therapy after SBRT compared with patients with metachronous OM. The 2-year PCSS and PFS rates were 92.0% and 72.0%, respectively. A prostate-specific antigen (PSA) decline was observed in 56 patients (75.7%), and 48 (64.9%) had a PSA response defined as at least 25% decrease of PSA after MDT. The 2-year local control rate per lesion was 95.4%. In multivariate analysis, single OM and PSA response after MDT were significant predictors for better PCSS and PFS. In-field recurrence was observed in 4 patients (6.5%) with 10 lesions at a median of 13.1 months after MDT completion. No serious late toxicity was observed. Conclusions We demonstrated that SBRT is an efficient and well-tolerated treatment option for PC patients with 5 bone-only oligometastases or fewer detected with 68 Ga-PSMA PET/CT.

Neoadjuvant chemoradiotherapy (CRT) followed by surgical resection is the standard treatment for locally advanced rectal adenocarcinoma. In this study we evaluate our treatment results in patients treated with neoadjuvant radiotherapy (RT). Medical records of 144 patients treated between January 2009 and February 2019 were retrospectively evaluated. Most of the patients had (76%) MRI as a part of initial staging. Patients received either short course (25 Gy/5 fractions) (8%) or long course RT (92%) (median 50.4 Gy/28 fractions) +/- chemotherapy (ChT). Median age was 56 years (range, 24-90 years) and 131 patients received CRT. Most common concomitant ChT regime was oral capecitabine (48%). 26 patients refused the surgery. For rest of the patients, median time to surgery was 8 weeks. Sphincter was preserved in 19 patients (38%) who underwent surgery for distal tumors. With a median follow-up of 28 months, 19 patients had local recurrence and 30 patients had distant metastases. Two and five year estimated overall survival (OS), locoregional control (LRC) and distant metastases free survival (DMFS) rates were 88-67%, 78-62% and 74-57%, respectively. Presence of surgery significantly affect OS (HR= 0.147, 95% CI: 0.67-0.32, p< 0.001) , LRC (HR= 0.10, 95% CI: 0.05-0.2, p< 0.001) and DMFS (HR= 0.25, 95% CI: 0.13-0.49). Patients tolerated the treatment well with no grade 3 acute or late gastrointestinal and genitourinary system toxicities. Regardless of the schema neoadjuvant RT seems to be an efficient and safe treatment for patients with rectal adenocarcinoma. We found that surgery is the sole prognostic factor for better OS, LC and DMFS.

Background Metastasis-directed therapy (MDT) utilizing stereotactic body radiotherapy (SBRT) for oligoprogressive lesions could provide a delay in next-line systemic treatment (NEST) change while undergoing androgen receptor-targeted agents (ARTA) treatment. We evaluated prognostic factors for prostate cancer-specific survival (PCSS) and progression-free survival (PFS) to characterize patients receiving treatment with ARTA who may benefit from MDT for oligoprogressive lesions. The impact of MDT on delaying NEST and the predictive factors for NEST-free survival (NEST-FS) were also assessed. Materials and Methods The clinical data of 54 metastatic castration-resistant prostate cancer patients with 126 oligoprogressive lesions receiving abiraterone (1 g/day) or enzalutamide (160 mg/day) before or after systemic chemotherapy were analyzed. A median of three lesions (range: 1-5) were treated with MDT. The primary endpoints were PCSS and PFS. The secondary endpoints were time to switch to NEST and NEST-FS. Results The median follow-up time was 19.1 months. Univariate analysis showed that the number of oligoprogressive lesions treated with SBRT and the time between the start of ARTA treatment and oligoprogression were significant prognostic factors for PCSS, and the timing of ARTA treatment (before or after chemotherapy) and the prostate-specific antigen (PSA) response after MDT were significant prognostic factors for PFS. Multivariate analysis showed that early MDT for oligoprogressive lesions delivered less than 6 months after the beginning of ARTA and higher PSA levels after MDT were significant predictors of worse PCSS and PFS. The median total duration of ARTA treatment was 13.8 months. The median time between the start of ARTA treatment and the start of MDT for oligoprogressive lesions was 5.2 months, and MDT extended the ARTA treatment by 8.6 months on average. Thirty-two (59.3%) patients continued ARTA treatment after MDT. ARTA treatment after chemotherapy, early oligoprogression requiring MDT, and lower radiation doses for MDT were independent predictors of NEST-FS in multivariate analysis. Conclusions MDT for oligoprogressive lesions is effective and may provide several benefits compared to switching from ARTA treatment to NEST. Patients with early progression while on ARTAs and inadequate PSA responses after MDT have a greater risk of rapid disease progression and poor survival, which necessitates intensified treatment.

Background Defining the extent of disease spread with imaging modalities is crucial for therapeutic decision-making and definition of treatment. This study aimed to investigate whether clinical parameters and nomograms predict prostate-specific membrane antigen (PSMA)-positive lymph nodes in treatment-naive nonmetastatic prostate cancer (PC) patients. Materials and Methods The clinical data of 443 PC patients (83.3% high-risk and 16.7% intermediate-risk) were retrospectively analyzed. Receiver operating characteristic (ROC) curves with areas under the curve (AUC) were generated to evaluate the accuracy of clinical parameters (prostate-specific antigen [PSA], T stage, Gleason score [GS], International Society of Urological Pathology [ISUP] grade) and nomograms (Roach formula [RF], Yale formula [YF], and a new formula [NF]) in predicting lymph node metastasis. The AUCs of the various parameters and clinical nomograms were compared using ROC and precision-recall (PR) curves. Results A total of 288 lymph node metastases were identified in 121 patients (27.3%) using Ga-68-PSMA-11-positron emission tomography (PET)/computed tomography (CT). Most PSMA-avid lymph node metastases occurred in external or internal iliac lymph nodes (142; 49.3%). Clinical T stage, PSA, GS, and ISUP grade were significantly associated with PSMA-positive lymph nodes according to univariate logistic regression analysis. The PSMA-positive lymph nodes were more frequently detected in patients with PSA >20 ng/ml, GS >= 7 or high risk disease compared to their counterparts. The clinical T stage, serum PSA level, GS, and ISUP grade showed similar accuracy in predicting PSMA-positive metastasis, with AUC values ranging from 0.675 to 0.704. The median risks for PSMA-positive lymph nodes according to the RF, YF, and NF were 31.3% (range: 12.3%-100%), 22.3% (range: 4.7%-100%), and 40.5% (range: 12.3%-100%), respectively. The AUC values generated from ROC and PR curve analyses were similar for all clinical nomograms, although the RF and YF had higher accuracy compared to NF. Conclusion The clinical T stage, PSA, GS, and ISUP grade are independent predictors of PSMA-positive lymph nodes. The RF and YF can be used to identify patients who can benefit from Ga-68-PSMA-11 PET/CT for the detection of lymph node metastasis. Together with nomograms, Ga-68-PSMA-11 PET/CT images help to localize PSMA-positive lymph node metastases and can thus assist in surgery and radiotherapy planning.

Purpose To evaluate the outcomes of metastasis-directed treatment (MDT) using stereotactic body radiotherapy (SBRT) for bone-only oligometastasis (OM) detected with gallium prostate-specific membrane antigen (68Ga-PSMA) PET/CT in castration-sensitive prostate cancer (PC) patients. Methods In this multi-institutional study, clinical data of 74 PC patients with 153 bone lesions who were undergoing MDT were retrospectively evaluated. Twenty-seven patients (36.5%) had synchronous, and 47 (63.5%) had metachronous OM. All patients had PC with 5 metastases or fewer detected by 68Ga-PSMA PET/CT and treated using SBRT with a median dose of 20 Gy. The prognostic factors for PC-specific survival (PCSS) and progression-free survival (PFS) were analyzed. Results The median follow-up was 27.3 months. Patients with synchronous OM were older and received higher rates of androgen deprivation therapy after SBRT compared with patients with metachronous OM. The 2-year PCSS and PFS rates were 92.0% and 72.0%, respectively. A prostate-specific antigen (PSA) decline was observed in 56 patients (75.7%), and 48 (64.9%) had a PSA response defined as at least 25% decrease of PSA after MDT. The 2-year local control rate per lesion was 95.4%. In multivariate analysis, single OM and PSA response after MDT were significant predictors for better PCSS and PFS. In-field recurrence was observed in 4 patients (6.5%) with 10 lesions at a median of 13.1 months after MDT completion. No serious late toxicity was observed. Conclusions We demonstrated that SBRT is an efficient and well-tolerated treatment option for PC patients with 5 bone-only oligometastases or fewer detected with 68Ga-PSMA PET/CT.

We assessed the outcomes of stereotactic body radiotherapy (SBRT) to treat oligoprogressive castration-resistant prostate cancer (CRPC) patients with ≤5 lesions using gallium prostate–specific membrane antigen-positron emission tomography (68Ga-PSMA-PET/CT). The clinical data of 67 CRPC patients with 133 lesions treated with 68Ga-PSMA-PET/CT-based SBRT were retrospectively analyzed. All of the patients had oligoprogressive disease during androgen-deprivation therapy (ADT). The prognostic factors for overall- (OS) and progression-free survival (PFS) and the predictive factors for switching to next-line systemic treatment (NEST) and NEST-free survival (NEST-FS) were analyzed. With a median follow-up of 17.5 months, the 2-year overall survival (OS) and PFS rates were 86.9% and 34.4%, respectively. The PSA response was observed in 49 patients (73.1%). Progression was observed in 37 patients (55.2%) at a median of 11.0 months following SBRT. A total of 45 patients (67.2%) remained on ADT after SBRT, and 22 patients (32.8%) had a NEST change at a median of 16.4 months after metastasis-directed treatment (MDT). Patients with a NEST change had higher post-SBRT PSA values and fewer PSA nadirs after MDT than their counterparts. In multivariate analysis, higher pre-SBRT PSA values were the only significant predictor for worse OS and NEST-FS, and no significant factor was found for PFS. No serious acute or late toxicities were observed. This study demonstrated the feasibility of MDT using SBRT to treat oligoprogressive lesions by 68Ga-PSMA-PET/CT in CRPC patients is efficient and well-tolerated, prolonging the effectiveness of ADT by delaying NEST.

PURPOSE Stereotactic body radiotherapy (SBRT) is an effective treatment option for patients with early-stage non-small cell lung cancer (NSCLC). In this study, we evaluated the treatment results using two different SBRT techniques and the effect of beam-on time (BOT) on treatment outcomes. METHODS Between July 2007 and January 2018, 142 patients underwent SBRT for primary NSCLC. We have delivered SBRT using either respiratory tracking system (RTS) or internal-target-volume (ITV)-based motion management techniques. The effect of age, tumor size, pretreatment tumor SUVmax value, presence of tissue diagnosis, histopathological subtype, operability status, tumor location, motion management technique, BED10 value, BOT on overall survival (OS), loco-regional control (LRC), event-free survival (EFS) and primary tumor control (PTC) were evaluated. RESULTS Median age of the patients was 70 years (range, 39-91 years). Most of the patients were inoperable (90%) at the time of SBRT. Median BED10 value was 112.5 Gy. With a median follow-up of 25 months, PTC was achieved in 91.5% of the patients. Two-year estimated OS, LRC, PTC and EFS rates were 68, 63, 63 and 53%, respectively. For the entire group, OS was associated with BOT (P = 0.027), and EFS was associated with BOT (P = 0.027) and tumor size (P = 0.015). For RTS group, OS was associated with age (P = 0.016), EFS with BOT (P = 0.05) and tumor size (P = 0.024), LRC with BOT (P = 0.008) and PTC with BOT (P = 0.028). The treatment was well tolerated in general. CONCLUSION SBRT is an effective and safe treatment with high OS, LRC, EFS and PTC rates in patients with primary NSCLC. Protracted BOT might deteriorate SBRT outcomes.

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.

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-100, D-95, and D-90) showed a significant difference between plan A and plan B (p = 0.005), and plan B was found lower. D-100 for plan C was significantly higher than plan A (p = 0.009), but for D-95 and D-90, no statistically significant difference was found (p = 0.028 and p = 0.028, respectively). In terms of OARs doses, including vagina, rectum, bladder, and sigmoid, D-2cm3 doses were significantly higher in plan A than plan B (p = 0.009, p = 0.009, p = 0.005, and p = 0.005, respectively). All these doses were also significantly lower than in plan C (p = 0.005, p = 0.012, and p = 0.013, respectively), except for sigmoid (p = 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.

The aim of this study was to evaluate the outcomes of 68Ga prostate-specific membrane antigen (68Ga-PSMA) positron-emission tomography (PET)/CT-based metastasis-directed treatment (MDT) for oligometastatic prostate cancer (PC). In this multi-institutional study, clinical data of 176 PC patients with 353 lesions receiving MDT between 2014 and 2019 were retrospectively evaluated. All patients had biopsy proven PC with ≤5 metastases detected with 68Ga-PSMA-PET/CT. MDT was delivered with conventional fractionation or stereotactic body radiotherapy (SBRT) techniques. CTCAE v4.0 was used for acute and RTOG/EORTC Late Radiation Morbidity Scoring Schema was used for late toxicity evaluation. At the time of MDT, 59 patients (33.5%) had synchronous and 117 patients (66.5%) had metachronous metastases. Median number of metastases was one and the MDT technique was SBRT in 73.3% patients. The 2‑year overall survival (OS) and progression-free survival (PFS) rates were 87.6% and 63.1%, respectively. With a median follow-up of 22.9 months, 9 patients had local recurrence at the irradiated site. The 2‑year local control rate at the treated oligometastatic site per patient was 93.2%. In multivariate analysis, an increased number of oligometastases and untreated primary PC were negative predictors for OS; advanced clinical tumor stage, untreated primary PC, BED3 value of ≤108 Gy, and MDT with conventional fractionation were negative predictors for PFS. No patient experienced grade ≥3 acute toxicity, but one patient had a late grade 3 toxicity of compression fracture after spinal SBRT. 68Ga-PSMA-PET/CT-based MDT is an efficient and safe treatment for oligometastatic PC patients. Proper patient selection might improve treatment outcomes.

PURPOSE:Cisplatin based chemoradiation has been commonly used as a definitive treatment for muscle-invasive bladder cancer (MIBC). The aim of the current study is to evaluate oncologic results and toxicity profile of bladder-sparing treatment with external beam radiotherapy (EBRT) and gemcitabine chemotherapy (ChT) in patients with MIBC. MATERIALS AND METHODS:Between April 2005 and November 2018 44 patients with nonmetastatic and N0 MIBC were treated with transurethral resection of bladder (TURB), EBRT and concurrent gemcitabine. All patients were staged using thorax-abdomen-pelvic CT and pelvic MRI. EBRT was delivered using 3D conformal technique or intensity modulated radiotherapy. Patients received 50 Gy in 25 to 28 fractions to full bladder followed by a boost dose of 10 Gy in 5 fractions to empty bladder with weekly concurrent gemcitabine of 50 mg/m2. All patients were evaluated for age, gender, smoking status, neutrophil lymphocyte ratio (NLR) and platelet lymphocyte ratio (PLR) at diagnosis, presence of hydroureteronephrosis (HUN), preoperative tumor size, tumor multifocality, presence of CIS, clinical tumor stage. Acute/late genitourinary (GUS) and gastrointestinal (GIS) toxicity, recurrence status, cancer specific survival (CSS) and overall survival (OS) were evaluated. Statistical analysis was performed using SPSS v21.0. Kaplan-Meier survival estimates were calculated to describe CSS and OS. The effect of different parameters on survival was investigated using the log rank test. RESULTS:Median age of the patients was 72 years (interquartile [IQR]; 66-80). The median tumor size was 30 mm (IQR, 15-59 mm). Thirty-two (77%) patients had T2, 6 (14%) patients had T3, and 4 (9%) patients had T4a disease. Median NLR was 2.6 (IQR, 1.7-3.8) and median PLR was 126.47 (IQR, 77.4-184.8). Median follow-up time was 21 months (range, 6-153 months). At the first TURB performed 6 weeks after CRT, complete response, partial response, stable disease, and progression was detected in 37 (84%), 3 (7%), 1 (2%), and 3 (7%) patients, respectively. One- and 2-year OS, CSS, LRFS, and DMFS rates were 86% and 64%; 88% and 66%; 65% and 44%; 68% and 48%, respectively. In univariate analysis; prognostic factors were age and presence of HUN for OS and DMFS; age, HUN, presence of CIS, NLR, and PLR for DSS; HUN, NLR, and PLR for LRFS, respectively. In multivariate analysis, the independent predictor was the presence of HUN for OS, LRFS, and DMFS; NLR for DSS; PLR for LRFS and age for DMSF. For a subgroup of 17 patients with complete TURB and no CIS and HUN symptoms, 2-year OS, DSS, LRFS, and DMFS rates were 88%, 88%, 72%, and 79%, respectively. The treatment was well-tolerated and all patients completed the planned EBRT and ChT. No acute or late ≥ grade 3 toxicity was observed. Grade II acute GIS toxicity was detected in 3 (7%) patients and grade II acute GUS toxicity was detected in 9 (21%) patients, respectively. Grade II late GUS toxicity was observed in 2 (5%) patients. CONCLUSION:Gemcitabine based trimodality treatment is well-tolerated with similar oncologic outcomes reported in the literature. Older age, presence of CIS and high NLR and PLR values seem to deteriorate DSS.

OBJECTIVE This study aimed to evaluate the clinical effectiveness and cost of leuprorelin acetate Atrigel (Eligard (R)) in prostate cancer treatment and calculate its cost-effectiveness compared with other luteinizing hormonereleasing hormone (LHRH) agonists (leuprolide acetate microsphere [Lucrin (R)], goserelin [Zoladex LA (R)], and triptorelin [Decapeptyl (R)]). METHODS The primary health-related outcome was life-years gained, and effectiveness was measured through the difference between treatment options. Analyses were performed separately for testosterone suppression targets of <20 ng/dL and <50 ng/dL for disease risk groups (intermediate and high risk) and for disease periods (relapse-free, postrelapse, and postdistant metastasis). Only direct treatment costs were used for cost analyses. Resource utilization was estimated according to the National Comprehensive Cancer Network guidelines and expert opinion. RESULTS This study included 173 patients treated with definitive radiotherapy and maximal androgen blockade. The median follow-up duration was 125.37 (range 10.84-214.37) months. The percentages of patients whose testosterone levels decreased to <20 ng/dL and <50 ng/dL were higher with leuprorelin acetate Atrigel. Compared with leuprolide acetate microsphere, goserelin, and triptorelin, Leuprorelin acetate Atrigel provided cost savings of 8386.04 Turkish liras (TL), 3710.79 TL, and 8446.64 TL, respectively, in patients with testosterone levels of <20 ng/dL and 479.41 TL, 1142.13 TL, and 5490.79 TL, respectively, in patients with testosterone levels of <50 ng/dL. Deterministic sensitivity analysis showed that leuprorelin acetate Atrigel was superior to its comparators regarding incremental cost-effectiveness ratios at low-and high-sensitivity margins. CONCLUSION Leuprorelin acetate Atrigel was found to be clinically more effective and cost-saving than other LHRH agonists in the intermediate-and high-risk groups, regardless of testosterone suppression targets.

Aim: The aim of this study was to determine the Inflection Points (IPs) of flattening filter free (FFF) CyberKnife dose profiles for cone-based streotactic radiotherapy. In addition, dosimetric field sizes were determined. Background: The increased need for treatment in the early stages of cancer necessitated the treatment of smaller tumors. However, efforts in that direction required the modeling accuracy of the beam. Removal of the flattening filter (FF) from the path of x-ray beam has provided the solution to those efforts, but required a different normalization approach for the beam to ensure the delivery of the dose accurately. As a solution, researchers proposed a normalization factor based on IPs. Materials and methods: Measurements using microDiamond (PTW 60019), Diode SRS (PTW 60018) and Monte Carlo (MC) calculations of dose profiles were completed at SAD 80 cm and 5 cm depth for 15-60 mm cones. Performance analysis of detectors with respect to MC calculation was carried out. Gamma evaluation method was used to determine achievable acceptability criteria for FFF CyberKnife beams. Results: Acceptability within (3%-0.5 mm) was found to be anachievable criterion for all dose profile measurements of the cone beams used in this study. To determine the IP, the first and second derivatives of the dose profile were determined via the cubic spline interpolation technique. Conclusion: Derivatives of the interpolated profiles showed that locations of IPs and 50% isodose points coincide. (C) 2019 Greater Poland Cancer Centre. Published by Elsevier B.V. All rights reserved.