BACKGROUND: As radiotherapy techniques advance, so do planning methods for multi-target intracranial SRS cases. Multi-target-single-isocenter (MTSI) planning offers high-precision beam delivery with shortened duration. However, accommodating all targets in a single Patient-Specific-Quality-Assurance (PSQA) with QA devices like SRS MapCHECK (SRS MC) is generally impractical.
OBJECTIVE: Consequently, we conducted PSQA, using a custom script, by relocating each Target or Neighboring-Target-Group (T-NTG) relative to the beam isocenter on the PSQA device, ensuring each target\'s dose coverage at high precision.
METHODS: SRS treatment plans use 6MV-FFF beams, consisting of four Volumetric Modulated ARC Therapy (VMAT) arcs, including one full-arc and three half arcs with couch-kicks. A custom script calculated T-NTG coordinates relative to the beam isocenter. QA verification plans were created for each T-NTG, redefining the beam isocenter for precise alignment with the center of the SRS MC. CBCT images were acquired during PSQA for SRS MC alignment, and gamma-index analysis (GIA) was performed. A single-tail paired t-test assessed the passing rate (PR) for 75 QA verification plans.
RESULTS: GIA with l.0 mm/2.0% criteria for each QA plan yielded a PR > 95.5%, with an average of 98.9%. Plans achieving PR > 99.0% and > 97.0% constituted 63% and 92% of studied plans, respectively. Statistical significance was observed in a t-test with an ideal PR value of 100%, while insignificance was found with a PR value of 99%, suggesting that PSQA for individual targets consistently approaches 99% PR. In MTSI cases using 6MV-FFF beams, targets within the lateral dose-fall-off region require careful verification for acceptability. Our clinical study on individual T-NTG relocation demonstrates that the presented PSQA methods are generally acceptable, supported by a statistically insignificant PR against a 99% PR value.
CONCLUSIONS: Presented statistical analysis results indicate that the proposed PSQA approach can serve as a reliable tool in clinical settings.

OBJECTIVE: To characterize detector array spacing and gamma index for quality assurance (QA) of stereotactic radiosurgery (SRS) deliveries. Use the Nyquist theorem to determine the required detector spacing in SRS fields, and find optimal gamma indices to detect MLC errors using the SRS MapCHECK, ArcCHECK, and a portal imaging device (EPID).
METHODS: The required detector spacing was determined via Fourier analysis of small radiation fields and profiles of typical SRS treatment plans. The clinical impact of MLC errors of 0.5, 1, and 2 mm was evaluated. Global gamma (low-dose threshold 10%) was evaluated for the three detector systems using various combinations of the distance to agreement and the dose difference.
RESULTS: While MLC errors only slightly affected mean dose to PTV and a 2 mm thick surrounding structure (PTV_2 mm), significant PTV underdose incurred with increase in maximum dose to PTV_2 mm. Gamma indices with highest sensitivity to the introduced errors at 95% tolerance level for plans on target volumes of 3.2 cm3 (plan 3 cc) and 35.02 cm3 (plan 35 cc) were 2%/1 mm for the SRS MapCHECK and 2%/3 mm for the ArcCHECK, with 3%/1 mm (plan 3cc) and 2%/1 mm (plan 35cc) for the EPID. Drops in passing rates for a 2 mm MLC error were (46.2%, 41.6%) for the SRS MapCHECK and (12.2%, 4.2%) for the ArcCHECK for plan 3cc and plan 35cc, respectively. For Portal Dose, values were 4.5% (plan 3cc) and 7% (plan 35cc). The Nyquist frequency of two SRS dose distributions lie between 0.26  and 0.1 mm-1 , corresponding to detector spacings of 1.9 and 5 mm. Evaluation of SRS MapCHECK data with doubled detector density indicates that increased detector density may reduce the system\'s sensitivity to errors, necessitating a tighter gamma index.
CONCLUSIONS: The present results give insight on the performance of detector arrays and gamma indices for the investigated detectors during SRS QA.

UNASSIGNED: Virtual wedge (VW) is used in radiotherapy to compensate for missing tissues and create a uniform dose distribution in tissues. According to TECDOC-1583 and technical reports series no. 430, evaluating the dose calculation accuracy is essential for the quality assurance of treatment planning systems (TPSs). In this study, the dose calculation accuracy of the collapsed cone superposition (CCS) algorithm in the postmastectomy radiotherapy of the chest wall for breast cancer was evaluated by comparing the calculated and measured dose in VW fields.
UNASSIGNED: Two tangential fields with the typical VW angles were planned using ISOgray TPS in a thorax phantom. The CCS algorithm was used for dose calculation at 6 and 15 MV photon beams. The obtained dose distributions from EBT3 film spaces and TPS were evaluated using the gamma index.
UNASSIGNED: The measured and calculated dose values using VW in a heterogeneous medium with different beam energies were in a good agreement with each other (acceptance rate: 88.0%-93.4%). The calculated and measured data did not differ significantly with an increase/decrease in wedge angle. In addition, the results demonstrated that ISOgray overestimated and underestimated the dose of the soft tissue and lung in the planned volume, respectively.
UNASSIGNED: According to the results of gamma index analysis, the calculated dose distribution using VW model with the CCS algorithm in a heterogeneous environment was within acceptable limits.

In the present study, it was aimed to investigate the optimized plan of radiotherapy with dose modulation in the pelvis to reduce the dose on the skin in patients having pelvic region radiotherapy. The series of images of 45 pelvic cancer patients were selected, intensity-modulated radiation therapy (IMRT) plan was made, the skin dose reduction was optimized, and evaluated verifying the plan verification. As a result, skin volume receiving dose ≥10, ≥20, ≥30, ≥40 and ≥50 Gy of the IMRT Skin plan were all less than those of the IMRT plan. Particularly, skin volumes receiving doses ≥20, ≥30, ≥40 and ≥50 Gy of the Skin IMRT plan were markedly lower than those of the IMRT plan, the reduction values were 8.76, 18.83, 46.84 and 100%, respectively. Furthermore, the Skin IMRT plan was no longer affected by the 50 Gy dose. In conclusion, the present study revealed that the skin\'s dose can be decreased with optimal plan processing; thus, this decrease of the skin\'s dose ensures the continuation of radiotherapy and improved life quality of the patient.

UNASSIGNED: Most brachytherapy treatment planning system (TPS) commissioning requires data input based on the American Association of Physicists in Medicine Task Group-43 formalism. The commissioning accuracy is very important for dose calculation. The aim of this study is the implementation of a brachytherapy TPS into a clinical environment and check the TPS calculated dose accuracy.
UNASSIGNED: After introducing data of the different catheters (CIS Bio International, Saclay, France), composed of several Cesium-137 Eckert and Ziegler BEBIG CSM-11 radioactive sources; for XiO (CMS, St. Louis) brachytherapy TPS, the TPS dose calculation accuracy was investigated by comparing between the TPS calculated dose distribution (DD) for all the catheters with (1) the measuring DD using EBT3 GAFChromic film and (2) calculating DD by egs_brachy (Electron Gamma Shower, National Research Council of Canada) Monte Carlo simulation. The phantom used for this study consists of six PTW slabs 30 cm × 30 cm × 1 cm of polymethyl methacrylate with a Delouche MEDpro applicator on the top. The TPS DD was calculated on the computed tomography scan of this phantom.
UNASSIGNED: PTW VeriSoft version 6.0.1.7 (PTW-Freiburg, Germany) software was used for analyzing scanned films and to perform the comparison based on the gamma index distribution.
UNASSIGNED: For each catheter, the gamma index distribution showed agreement >95% of all pixels in both verification methods, with gamma ≤1.
UNASSIGNED: We confirm the commissioning accuracy and that the TPS can be used for clinical purposes.

Objective:The development of a stringent derivative-based gamma (DBG) index for patient-specific QA in stereotactic radiotherapy treatment planning (SRTP) to account for the spatial change in dose.Methods:Twenty-five patients of liver SBRT were selected retrospectively for this study. Deliberately, two different kinds of treatment planning approaches were used for each patient. Firstly, the treatment plans were generated using a conventional treatment planning (CTP) approach in which the target was covered with a homogeneous dose along with the nominal dose fall-off around the treatment field. Subsequently, the other treatment plans were generated using an SRTP approach with the intent of heterogeneous dose within the target region along with a steeper dose gradient outside the treatment field as much as possible. For both kinds of treatment plans, two dimensional (2D) conventional gamma (CG) and DBG analysis were performed using the 2D ion chamber array and radiochromic film.Results:Difference in the DBG index was statistically significant whereas, for CG analysis, the difference in CG index was insignificant for both types of treatment plans (CTP and SRTP). A significant positive correlation was observed between the difference in the DBG index and the difference in HI for high gamma criteria.Conclusion:The DBG evaluation is found to be more rigorous, and sensitive to the only SRTP. The proposed method could be opted-in the routine clinical practice in addition to CG.Advances in knowledge:DBG is more sensitive to detect the spatial change of dose, especially in high dose gradient regions.

OBJECTIVE: The quality of a measured distribution of dose delivered against its corresponding radiotherapy plan is routinely assessed by gamma index (GI) and dose-volume histogram (DVH) metrics. Any correlation between error detection rates, as based on either of these approaches, while argued, has never been convincingly demonstrated. The dependence of the strength of correlation between the GI passing rate ( γ P ) and DVH quality assurance (QA) metrics on various elements of the therapy plan has not been systematically investigated.
METHODS: A formal analysis of the relation between γ P and DVH metrics has been undertaken, leading to a relationship which may partly approximate γ P with respect to the DVH. This relationship was further validated by studying examples of simulated clinical radiotherapy plans and by studying the correlation between γ P and the derived relationship using a simple two-dimensional representations of the planning target volume (PTV) and organs at risk (OAR), where penumbra regions, distance-to-agreement tolerances and dose delivery errors were systematically varied.
RESULTS: It is shown formally that there cannot be any correlation between γ P and other commonly applied DVH-derived QA measures. However, γ P may be partly approximated given the planned and measured DVH. The derived γ P approximation (the \" γ -slope indicator\") may be clinically useful in some practical cases of radiotherapy plan QA.
CONCLUSIONS: In formal terms, there cannot be any correlation between γ P and any common DVH-calculated patient-specific measures, with respect to PTV or OAR. However, as demonstrated analytically and further confirmed in our simulation studies, the γ P approximation derived in this study (the \" γ -slope indicator\") may in some cases offer a degree of correlation between γ P and the PTV and OAR DVH QA metrics in measured and planned patient-specific dose distributions-which may be potentially useful in clinical practice.

UNASSIGNED: This study aimed to verify the dosimetric impact of Acuros XB (AXB) (AXB, Varian Medical Systems Palo Alto CA, USA), a two model-based algorithm, in comparison with Anisotropic Analytical Algorithm (AAA ) calculations for prostate, head and neck and lung cancer treatment by volumetric modulated arc therapy (VMAT ), without primary modification to AA. At present, the well-known and validated AA algorithm is clinically used in our department for VMAT treatments of different pathologies. AXB could replace it without extra measurements. The treatment result and accuracy of the dose delivered depend on the dose calculation algorithm.
UNASSIGNED: Ninety-five complex VMAT plans for different pathologies were generated using the Eclipse version 15.0.4 treatment planning system (TPS). The dose distributions were calculated using AA and AXB (dose-to-water, AXBw and dose-to-medium, AXBm), with the same plan parameters for all VMAT plans. The dosimetric parameters were calculated for each planning target volume (PTV) and involved organs at risk (OA R). The patient specific quality assurance of all VMAT plans has been verified by Octavius®-4D phantom for different algorithms.
UNASSIGNED: The relative differences among AA, AXBw and AXBm, with respect to prostate, head and neck were less than 1% for PTV D95%. However, PTV D95% calculated by AA tended to be overestimated, with a relative dose difference of 3.23% in the case of lung treatment. The absolute mean values of the relative differences were 1.1 ± 1.2% and 2.0 ± 1.2%, when comparing between AXBw and AA, AXBm and AA, respectively. The gamma pass rate was observed to exceed 97.4% and 99.4% for the measured and calculated doses in most cases of the volumetric 3D analysis for AA and AXBm, respectively.
UNASSIGNED: This study suggests that the dose calculated to medium using AXBm algorithm is better than AAA and it could be used clinically. Switching the dose calculation algorithm from AA to AXB does not require extra measurements.

Patient quality assurance (QA) is a required part of the treatment care path, and plan failure can lead to increased personnel hours or delay of treatment. The recommendation by the American Association of Physicists in Medicine is that gamma analysis be used to evaluate measured volumetric modulated arc therapy plans. Vendors have developed many different measurement geometries for patient QA devices which could yield varying pass rates when used with the recommended tolerances, normalization, and criterion. For this study, clinically treated stereotactic body radiation therapy plans were used to evaluate differences in gamma dose tolerances and sampled dose distribution complexity for centralized or peripheral measurement geometries on a cylindrical phantom. Random errors were then introduced into a subset of these plans, and the differences in pass rates between the geometries were correlated with differences in the observed mathematical differences. Finally, a single clinically relevant target coverage deviation was introduced to another subset of plans to evaluate whether a particular geometry is measurably better at identifying clinically relevant errors. It was found that centralized geometries resulted in more lenient dose tolerances and less complex sampled dose distributions compared to peripheral geometries. Pass rates were uniformly lower in the peripheral measurement geometry, and the difference in pass rates between the geometries correlated strongly with the difference in dose tolerance and weakly with the difference in the chosen complexity metrics. However, neither of the geometries were sufficiently sensitive enough to detect clinically relevant changes to target coverage when using recommended tolerances and criteria, and no statistically significant difference was found between their pass rates. Given these findings, the authors concluded that stereotactic body radiation therapy plans could fail patient QA when measured in the peripheral geometry but pass in the centralized geometry, with possibly neither having correlation to true clinical deviation.

The purpose of this study was to develop a novel quality assurance (QA) program to check the entire treatment chain of image-guided brachytherapy with dose distribution evaluation in a single setup and irradiation using a gel dosimeter.
A polymer gel was used, and the readout was performed by magnetic resonance scanning. A CT-based treatment plan was generated using the Oncentra planning system (Elekta, Sweden), and irradiation was performed three times using an afterloading device with an Ir-192 source. The dose-response curve of the gel was created using 6-MV X-ray, which is independent of the source beams. Planar gamma images on a coronal plane along the source transport axis were calculated using the measured dose as a reference, and the calculated doses were used in several error simulations (no error; 2.0 or 2.5 mm systematic and random source dwell mispositioning; and dose error of 2%, 5%, 10%, and 20%).
The dose-R2 (spin-spin relaxation rate) conversion table revealed that the uncertainty and dose resolution of 6-MV X-ray were better than those of Ir-192 and also constant between the three measurements. With the 3%/1 mm criteria, there were statistically significant differences between each pair of settings except dose error of 2% and 5%.
This work depicts a simple and efficient end-to-end test that can provide a clinically useful tool for QA of image-guided brachytherapy. In this QA program, air kerma strength and dwell position setting could also be verified. This test can also distinguish between different types of error.