Eclipse Treatment Planning System Research Articles

Yüksek Dereceli Glial Tümörlerin Radyoterapisinde VMAT Tekniği İle IMRT Tekniğinin Karşılaştırılması

The aim of radiotherapy is to protect critical organs sensitive to radiation and surrounding healthy tissues as much as possible, while giving the most appropriate dose on the specified target volume. The aim of this study is to provide the best plans of 10 brain tumor patients, whose computed tomography (CT) image was taken, using the best plans created using the VMAT technique in the Eclipse treatment planning system and the best plans created using the seven-field IMRT technique to compare doses in terms of target volume, duration of treatment and monitor unit (MU) values. The study is a retrospective study and patients were not treated with the plans and techniques used in the studies. Plans have been made so that 100% of the dose defined for the target volume will take at least 95% of the target volume. Using the Radiation Therapy Oncology Group (RTOG) protocol, the results obtained with the minitab program were statistically evaluated using the t-test for the matched data. PTV coverage, conformity and homogeneity index were equivalent for VMAT and IMRT plans. VMAT plans compared to IMRT, PTV max. 64,835±0,504 (p=0,039), Brain max. 64,378±0,565 (p=0,025), and Eye L. max. 20,39± 12,17 (p=0,046) The difference between the mean doses is statistically significant. Brain mean 26,74±3,42 (p=0,096), Brainstem max. 32,44±18,70 (p=0,178), Eye R. max. 32,90± 16,84 (p=0,076), Optic Nerve L.max. 23,17± 15,45 (p=0,851), Optic Nerve R. max. 22,63± 17,98 (p=0,688), Optic Chiasma max. 25,25± 20,24 (p=0,531) were found lower in VMAT plans but it was not statistically significant. It may be preferred in plans made with the VMAT technique due to less monitor units (MU) and shorter treatment time.

Assessing the out-of-field dose calculation accuracy by eclipse treatment planning system in sliding window IMRT of prostate cancer patients

AimThe objective of this study was to evaluate out-of-field dose distribution calculation accuracy by the Anisotropic Analytical Algorithm (AAA), version 13.0.26, in Eclipse TPS, (Varian Medical Systems, Palo Alto, Ca, USA) for sliding window IMRT delivery technique in prostate cancer patients. Materials and methodsProstate IMRT plans with nine coplanar were calculated with the AAA Eclipse treatment planning system. To assess the accuracy of dose calculation predicted by the Eclipse in normal tissue and OARs located out of radiation field areas, including the rectum, bladder, right and left head of the femur, absolute organ dose value, and dose distribution were measured using the Delta4+ IMRT phantom. ResultsIn the out-of-field areas, underestimation of −0.66% in organs near the field edge to −39.63% in organs far from the field edge (2.5 and 7.3 cm respectively) occurred in the TPS calculations. The percentage of dose deviation for the femoral heads was 95.7 on average while for the organ closer to the target (rectum) it was 79.81. ConclusionsAAA dosimetry algorithm (used in Eclipse TPS) showed poor dose calculation in areas beyond the treatment fields border where underestimation varies with the distance from the field edges. A significant underestimation was found for the AAA algorithm in the sliding window IMRT technique (P-value > 0.05).

Dosimetric comparison of intensity-modulated radiotherapy (IMRT) and RapidArc in low grade mucoepidermoid carcinoma of the salivary gland: a single institutional experience

AbstractPurpose:To report a single-institution experience of intensity-modulated radiotherapy (IMRT) and RapidArc treatment plans for the patients treated with low grade mucoepidermoid carcinoma (MEC) of the salivary gland while sparing the organs at risk (OARs) within tolerance limits.Material and Methods:Twenty-five patients with MEC were selected to develop and analyse the treatment plans using both of the techniques. Dose distributions were calculated using Eclipse treatment planning system (Varian Medical Systems, Palo Alto, CA). Plans were generated to deliver the dose of 6000 cGy in 30 fractions. For IMRT, seven angle plans were used and for RapidArc, two half arcs were used with the same 6 MV photon beam. Quality of treatment plans was evaluated by using parameters such as, coverage, conformity index (CI), homogeneity index (HI), gradient index (GI), unified dosimetry index (UDI), dose volume histogram, delivery time and OARs sparing for IMRT and RapidArc plans.Results:The analysis revealed that IMRT and RapidArc coverages are 0·90 and 0·94, respectively; CIs are 1·15 and 1·10, respectively; HIs are 1·12 and 1·07, respectively; GIs are 0·94 and 0·98, respectively. Average UDI values for RapidArc and IMRT are 1·09 and 1·11, respectively. Integral dose comparison shows better OAR sparing for RapidArc. RapidArc plans have the shorter beam on time (45%) in comparison with IMRT plans.Conclusion:Planning constraints were achieved in both techniques. However, RapidArc showed better quality treatment plan, OARs sparing and shorter delivery time as compared to IMRT.

Monte Carlo calculations of radiotherapy dose in "homogeneous" anatomy.

Given the substantial literature on the use of Monte Carlo (MC) simulations to verify treatment planning system (TPS) calculations of radiotherapy dose in heterogeneous regions, such as head and neck and lung, this study investigated the potential value of running MC simulations of radiotherapy treatments of nominally homogeneous pelvic anatomy. A pre-existing in-house MC job submission and analysis system, built around BEAMnrc and DOSXYZnrc, was used to evaluate the dosimetric accuracy of a sample of 12 pelvic volumetric arc therapy (VMAT) treatments, planned using the Varian Eclipse TPS, where dose was calculated with both the Analytical Anisotropic Algorithm (AAA) and the Acuros (AXB) algorithm. In-house TADA (Treatment And Dose Assessor) software was used to evaluate treatment plan complexity, in terms of the small aperture score (SAS), modulation index (MI) and a novel exposed leaf score (ELS/ELA). Results showed that the TPS generally achieved closer agreement with the MC dose distribution when treatments were planned for smaller (single-organ) targets rather than larger targets that included nodes or metastases. Analysis of these MC results with reference to the complexity metrics indicated that while AXB was useful for reducing dosimetric uncertainties associated with density heterogeneity, the residual TPS dose calculation uncertainties resulted from treatment plan complexity and TPS model simplicity. The results of this study demonstrate the value of using MC methods to recalculate and check the dose calculations provided by commercial radiotherapy TPSs, even when the treated anatomy is assumed to be comparatively homogeneous, such as in the pelvic region.

Measurement of the small field output factors for 10 MV photon beam using IAEA TRS-483 dosimetry protocol and implementation in Eclipse TPS commissioning

Dosimetry of small fields (SF) is vital for the success of highly conformal techniques. IAEA along with AAPM recently published a code of practice TRS-483 for SF dosimetry. The scope of this paper is to investigate the performance of three different detectors with 10 MV with-flatting-filter (WFF) beam using TRS-483 for SF dosimetry and subsequent commissioning of the Eclipse treatment planning system (TPS version-13.6) for SF data. SF dosimetry data (beam-quality TPR 20,10(10), cross-calibration, beam-profile, and field-output-factor (F.O.F)) measurements were performed for PTW31006-pinpoint, IBA-CC01 and IBA-EFD-3G diode detectors in nominal field size (F.S) range 0.5 × 0.5cm2 to 10 × 10 cm2 with water and solid water medium using Varian Truebeam linac. However, Eclipse-TPS commissioning data was acquired using IBA-EFD-3G diode, and absolute dose calibration was performed with FC-65G detector. The dosimetric performance of the Eclipse-TPS was validated using TLD-LiF chips, IBA-PFD, and IBA-EFD-3G diodes. Dosimetric performance of the PTW31006-pinpoint, IBA-CC01, and IBA-EFD-3G detectors was successfully tested for SF dosimetry. The F.O.Fs were generated and found in close agreement for all F.S except 0.5 × 0.5cm2. It is also found that TPR20,10(10) value can be derived within 0.5% accuracy from a non-reference field using Palmans equation. Cross-calibration can be performed in F.S 6 × 6 cm2 with a maximum variation of 0.5% with respect to 10 × 10cm2. During profile measurement, the full-width half-maxima (FWHM) of F.S 0.5 × 0.5cm2 was found maximum deviated from the geometric F.S. In addition, Eclipse-TPS was commissioned along with some limitations: F.O.F below F.S 1 × 1cm2 was ignored by TPS, PDD and profiles were dropped from configuration below F.S 2 × 2 cm2, and F.O.F which does not satisfy the condition 0.7 < A/B < 1.4 (A and B are FWHM in cross-line and in-line direction) have higher uncertainty than specified in TRS-483. Validation tests for Eclipse-TPS generated plans were also performed. The measured dose was in close agreement (3%) with TPS calculated dose up to F.S 1.5 × 1.5cm2.

Dosimetric comparison of three-dimensional conformal radiotherapy and static and dynamic intensity-modulated radiotherapy for the treatment of early-stage glottic cancer

The aim of this study was to compare dosimetric variations using the three-dimensional conformal radiotherapy (3DCRT), dynamic intensity-modulated radiation therapy (D-IMRT), and static intensity-modulated radiation therapy (S-IMRT) techniques for glottic cancer. Ten patients with early-stage glottic cancer were retrospectively selected and evaluated. The 3DCRT and IMRT treatment plans were performed using the solution commercialized by Varian with the Eclipse treatment planning system (TPS). For each patient, five different treatment plans were created and compared with respect to the doses received by the organs at risk (OARs) including the carotid arteries, thyroid gland, and spinal cord; the dose homogeneity index (DHI); conformity indexes (CI); and total monitor unit (MU) counts required for the treatment. The Mann-Whitney U test was used for statistical analyses. Statistically significant differences for the 3DCRT, D-IMRT, and S-IMRT techniques were observed for the planning target volume (PTV) mean and maximum doses. The results of this study indicated an increase in DHI for 3DCRT compared with D-IMRT and S-IMRT. Furthermore, the S-IMRT technique led to the superior decreased dose to the OAR. The 3DCRT plans performed better at the Dmax of the spinal cord and MU counts. The D-IMRT and S-IMRT techniques allowed more homogeneous dose distributions in PTV. Considering the dose to OAR, S-IMRT was more appropriate rather than 3DCRT and D-IMRT.

Comparison of VMAT complexity-reduction strategies for single-target cranial radiosurgery with the Eclipse treatment planning system.

Complexity in MLC‐based radiosurgery treatment delivery can be characterized by the efficiency of monitor unit (MU) utilization and the average MLC leaf separation distance for a treatment plan. A reduction in plan complexity may be desirable if plan quality is not impacted. In this study, a number of strategies are explored to determine how plan quality is affected by efforts to reduce plan complexity. Ten radiosurgery cases of varying complexity are retrospectively planned using six optimization strategies: an unconstrained volumetric modulated arc therapy (VMAT) technique, a MU‐constrained VMAT technique, three techniques using various strengths of the aperture shape controller (ASC), and a hybrid technique consisting of a final‐stage VMAT optimization applied to a dynamic conformal arc leaf sequence (ODCA). The plans are compared in terms of MU efficiency, MLC leaf‐separation, conformity index (CI), gradient index (GI), and QA measurement results. The five VMAT techniques exhibited only minor differences in CI and GI values, though the ASC and MU‐constrained techniques did require 6–20% fewer MU and had mean field apertures 5–19% larger. On average, the ODCA technique had CI values 3.5% lower and GI values 1.0–2.5% higher than the VMAT techniques, but also had a mean field aperture 24–47% larger and required 16–32% fewer MU. The QA measurement results showed a 0.61% variation in mean per‐field 2%/1 mm gamma passing rates across all techniques (range 96.81%–97.42%), with no observed correlation between passing rate and technique. For simple targets, the ODCA technique achieved CI results that were equivalent to the unconstrained VMAT technique with an average 30% reduction in required MU, an average 50% increase in mean leaf separation distance, and brain V12Gy values within 0.38 cc of the VMAT technique for targets up to approximately 2 cm diameter. For MLC‐based single‐target radiosurgery, plan complexity can often be significantly reduced without an equivalent reduction in plan quality.

The benefits evaluation of abdominal deep inspiration breath hold based on knowledge-based radiotherapy treatment planning for left-sided breast cancer.

PurposeTo study the impact of abdominal deep inspiration breath hold (DIBH) technique on knowledge‐based radiotherapy treatment planning for left‐sided breast cancer to guide the application of DIBH technology.Materials and methodsTwo kernel density estimation (KDE) models were developed based on 40 left‐sided breast cancer patients with two CT acquisitions of free breathing (FB‐CT) and DIBH (DIBH‐CT). Each KDE model was used to predict dose volume histograms (DVHs) based on DIBH‐CT and FB‐CT for another 10 new patients similar to our training datasets. The predicted DVHs were taken as a substitute for dose constraints and objective functions in the Eclipse treatment planning system, with the same requirements for the planning target volume (PTV). The mean doses to the heart, the left anterior descending coronary artery (LADCA) and the ipsilateral lung were evaluated and compared using the T‐test among clinical plans, KDE predictions, and KDE plans.ResultsOur study demonstrated that the KDE model can generate deliverable simulations equivalent to clinically applicable plans. The T‐test was applied to test the consistency hypothesis on another ten left‐sided breast cancer patients. In cases of the same breathing status, there was no statistically significant difference between the predicted and the clinical plans for all clinically relevant DVH indices (P > 0.05), and all predicted DVHs can be transferred into deliverable plans. For DIBH‐CT images, significant differences were observed between FB model predictions and clinical plans (P < 0.05). DIBH model prediction cannot be optimized to a deliverable plan based on FB‐CT, with a counsel of perfection.ConclusionKDE models can predict DVHs well for the same breathing conditions but degrade with different breathing conditions. The benefits of DIBH for a given patient can be evaluated with a quick comparison of prediction results of the two models before treatment planning.

Commissioning of total body irradiation using plastic bead bags.

The goal of total body irradiation (TBI) is to deliver a dose to the whole body with uniformity within ±10%. The purpose of this study was to establish the technique of TBI using plastic bead bags. A lifting TBI bed, Model ORP-TBI-MN, was used. The space between the patient’s body and the acrylic walls of the bed was filled with polyacetal bead bags. Patients were irradiated by a 10 MV photon beam with a source to mid-plane distance of 400 cm. The monitor unit (MU) was calculated by dose-per-MU, tissue-phantom-ratio and a spoiler factor measured in solid water using an ionization chamber. The phantom-scatter correction factor, off-center ratio and the effective density of the beads were also measured. Diode detectors were used for in vivo dosimetry (IVD). The effective density of the beads was 0.90 ± 0.09. The point doses calculated in an I’mRT phantom with and without heterogeneity material showed good agreement, with measurements within 3%. An end-to-end test was performed using a RANDO phantom. The mean ± SD (range) of the differences between the calculated and IVD-measured mid-plane doses was 1.1 ± 4.8% (−5.9 to 5.0%). The differences between the IVD-measured doses and the doses calculated with Acuros XB of the Eclipse treatment planning system (TPS) were within 5%. For two patients treated with this method, the differences between the calculated and IVD-measured doses were within ±6% when excluding the chest region. We have established the technique of TBI using plastic bead bags. The TPS may be useful to roughly estimate patient dose.

The dependence of inhomogeneity correction factors on photon beam quality index performed with the Anisotropic Analytical Algorithm

Abstract Purpose: The purpose of the study was to investigate the dependence of tissue inhomogeneity correction factors (ICFs) on the photon beam quality index (QI). Materials and Methods: Heterogeneous phantoms, comprising semi-infinite slabs of the lung (0.10, 0.20, 0.26 and 0.30 g/cm3), adipose tissue (0.92 g/cm3) and bone (1.85 g/cm3) in water, were constructed in the Eclipse treatment planning system. Several calculation models of 6 MV and 15 MV photon beams for quality index (TPR20,10) = 0.670±k*0.01 and TPR20,10 = 0.760±k*0.01, k = -3, -2, -1, 0, 1, 2, 3 respectively were built in the Eclipse. The ICFs were calculated with the anisotropic analytical algorithm (AAA) for several beam sizes and points lying at several depths inside of and below inhomogeneities of different thicknesses. Results: The ICFs increased for lung and adipose tissues with increasing beam quality (TPR20,10), while decreased for bone. Calculations with AAA predict that the maximum difference in ICFs of 1.0% and 2.5% for adipose and bone tissues, respectively. For lung tissue, changes of ICFs of a maximum of 9.2% (6 MV) and 13.8% (15 MV). For points where charged particle equilibrium exists, a linear dependence of ICFs on TPR20,10 was observed. If CPE doesn’t exist, the dependence became more complex. For points inside of the low-density inhomogeneity, the dependence of the ICFs on energy was not linear but the changes of ICFs were smaller than 3.0%. Measurements results carried out with the CIRS phantom were consistent with the calculation results. Conclusions: A negligible dependence of the ICFs on energy was found for adipose and bone tissue. For lung tissue, in the CPE region, the dependence of ICFs on different beam quality indexes with the same nominal energy may not be neglected, however, this dependence was linear. Where there is no CPE, the dependence of the ICFs on energy was more complicated.

Role of clip markers placed by endoscopic ultrasonography in contouring gross tumor volume for thoracic esophageal squamous cell carcinoma: one prospective study.

BackgroundWe aimed to analyze the value of metal clip markers guided and placed by endoscopic ultrasonography (EUS) in the delineation of gross tumor volume (GTV) for thoracic esophageal squamous cell carcinoma.MethodsFrom September 2016 to September 2018, patients with thoracic esophageal squamous cell carcinoma in Tianjin Medical University Cancer Institute and Hospital were recruited in the prospective trial, NCT02959385. They underwent titanium clips placement on tumor superior and inferior boundaries under EUS by a single expert endosonographer before radiotherapy computed tomography (CT) simulation. According to the clip markers, the reference GTVs were contoured by one experienced radiation oncologist. With the help of the Eclipse treatment planning system, clip markers on CT were concealed. Afterward, two other radiation oncologists with expertise in esophageal cancer delineated GTVs, defined as conventional GTVs, based on endoscopy and barium radiography findings. The two GTVs were compared and analyzed. Subgroup analysis was conducted in different T stage [early (T1 + T2) vs. advanced (T3 + T4)], focus location (upper vs. middle vs. lower segment), and tumor length (<5 vs. >5 cm) groups.ResultsThe trial recruited 55 patients with 60 thoracic esophageal cancer foci. A total of 111 titanium clips were guided and implanted by EUS. Before CT simulation, two titanium clips at two foci fell off. After the procedure, no case of intolerable esophageal pain, hemorrhage, or perforation occurred. Compared to reference GTVs’, discrepancies of conventional GTVs’ superior borders were 0.91±0.82 cm (P<0.001), while differences of inferior borders were 0.74±0.63 cm (P<0.001). On the contrary, conventional GTVs’ lengths were not significantly different from reference GTVs’ with discrepancies 0.08±1.30 cm (P=0.64). Regardless of T stage, tumor location, and tumor length, conventional GTVs’ superior and inferior borders were significantly different from reference GTVs’, while GTVs’ lengths differed insignificantly.ConclusionsThis study confirmed that EUS-placed titanium clips could correct contouring of GTVs in thoracic esophageal cancer in different T stages, tumor locations, and lengths.

FRoG: An independent dose and LETd prediction tool for proton therapy at ProBeam® facilities.

Particle therapy is becoming increasingly available world-wide for precise tumor targeting, its favorable depth dose deposition, and increased biological damage to tumor tissue compared to conventional photon therapy. As demand increases for improved robustness and conformality, next-generation secondary dose calculation engines are needed to verify treatment plans independently and provide estimates for clinical decision-making factors, such as dose-averaged linear energy transfer (LETd ) and relative biological effectiveness (RBE). FRoG (Fast dose Recalculation on GPU) has been installed and commissioned at the Danish Centre for Particle Therapy (DCPT). FRoG was developed for synchrotron-based facilities and has previously demonstrated good agreement with gold-standard Monte Carlo simulations and measurements. In this work, additions and modifications to FRoG's pencil beam algorithm to support the ion beam delivery with cyclotron-based technology as used at the DCPT, range shifter (RS) implementation, and robustness analysis methods are presented. FRoG dose predictions are compared to measurements and predictions of the clinical treatment planning system (TPS) Eclipse (Varian Medical Systems, Palo Alto, United States of America, CA, v.13.7.16) in both homogenous and heterogeneous scenarios using a solid-water/water and a half-head anthropomorphic phantom, respectively. Additional capabilities of FRoG are explored by performing a plan robustness analysis, analyzing dose and LETd for ten patients. Mid-target measurements in spread-out Bragg Peaks (SOBP) were on average within -0.19%±0.30% and ≤0.5% of FRoG predictions for irradiations withoutand with RS, respectively. Average 3%/2mm 3D γ-analysis passing rates were 99.1% for ~200 patient plan QA comparisons. Measurement with an anthropomorphic head-phantom yielded a γ-passing rate >98%. Overall, maximum target differences in D02% of <2% between the TPS and FRoG were observed for patient plans. The robustness analysis study accounting for range, delivery, and positioning uncertainties revealed small differences in target dose and a maximum LETd VH02% (LETd received by 2% of the volume having dose larger than 1% of maximum dose) values below 10.1keV/µm to the brain stem. We demonstrate that auxiliary dose calculation systems like FRoG can yield excellent agreement to measurements comparable to clinical beam models. Through this work, application of FRoG as a secondary engine at third party cyclotron-based particle treatment facilities is now established for dose verification as well as providing further insight on LETd and variable RBE distributions for protons, currently absent from the standard clinical TPS.

Voxel based evaluation of sequential radiotherapy treatment plans with different dose fractionation schemes.

This study presents a methodology for voxel-based evaluation of two phase sequential radiotherapy treatment plans having conventional dose scheme in the first phase and subsequent hypofractionation dose scheme in the second phase based upon different priority [planning target volume (PTV), clinical target volume (CTV) and organs at risk (OAR)] of display modes. A case of carcinoma prostate was selected for demonstration. Varian Eclipse treatment planning system (TPS) was used for contouring and planning. In the first phase, a dose of 52 Gy in 26 fractions to the PTV and in the second phase, a dose of 19.5 Gy in 3 fractions to the PTV Boost was planned on the same CT data set. Both the plans (Phase 1 and Phase 2) were exported and processed using "Voxel-based radiobiology display (VRb) tool". Plan Sum for Biologically effective dose (BED)-Cube and equivalent dose of 2Gy (EQD2)-Cube was reconstructed using a combination of linear quadratic (LQ) and linear quadratic-linear (LQ-L) radiobiological models. Tumor control probability (TCP) and normal tissue complication probability (NTCP) for different target volumes and organs were also calculated using EQD2-volume histograms of the Plan Sum. An in-house graphical user interface (GUI) is developed to present the qualitative and quantitative evaluation of the multiphase treatment plans with different display modes and dose regimens. The voxel based TCP obtained for the combined target volume was 90.56%. NTCP for the bladder and rectum was calculated from the Plan Sum histograms and found to be 0.33% and ~0.0% respectively. The proposed methodology using the VRb tool offers superior plan evaluation for multiphase sequential radiotherapy treatment plans over the existing methods. PTV, CTV and OAR priority based display modes in VRb tool offers better understanding of radiobiological evaluation of sequential radiotherapy treatment plans.

In search of a one plan solution for VMAT post-mastectomy chest wall irradiation.

PurposeThis study was designed to evaluate skin dose in both VMAT and tangent treatment deliveries for the purpose of identifying suitable bolus use protocols that should produce similar superficial doses.MethodsPhantom measurements were used to investigate skin dose in chest wall radiotherapy with and without bolus for 3D and rotational treatment techniques. Optically stimulated luminescence dosimeters (OSLDs) with and without housing and EBT3 film were used. Superflab (3, 5, and 10 mm) and brass mesh were considered. Measured doses were compared with predictions by the Eclipse treatment planning system. Patient measurements were also performed and the bolusing effect of hospital gowns and blankets were highlighted. The effect of flash for VMAT plans was considered experimentally by using 2 mm couch shifts.ResultsFor tangents, average skin doses without bolus were 0.64 (EBT3), 0.62 (bare OSLD), 0.77 (jacketed OSLD), and 0.68 (Eclipse) as a fraction of prescription. For VMAT, doses without bolus were 0.53 (EBT3), 0.53 (bare OSLD), 0.64 (jacketed OSLD), and 0.60 (Eclipse). For tangents, the average doses with different boluses as measured by EBT3 were 0.99 (brass mesh), 1.02 (3 mm), 1.03 (5 mm), and 1.07 (10 mm). For VMAT with bolus, average doses as measured by EBT3 were 0.83 (brass), 0.96 (3 mm), 1.03 (5 mm), and 1.04 (10 mm). Eclipse doses agreed with measurements to within 5% of measurements for all Superflab thicknesses and within 15% of measurements for no bolus. The presence of a hospital gown and blanket had a bolusing effect that increased the surface dose by approximately 10%.ConclusionsResults of this work allow for consideration of different bolus thicknesses, materials, and usage schedules based on desired skin dose and choice of either tangents or an arc beam techniques.

A preliminary study comparing planning target volume-based optimization and robust optimization

: Robust optimization (RO) makes intensity-modulated proton treatment (IMPT) plans has less sensitivity to proton uncertainties and provides better target dose coverage and even dose homogeneity without compromising critical-organ sparing compared to the plans generated by planning target volume (PTV)-based optimization. In this study, we compared the results between PTV-based and robust optimization on four cases including head-and-neck and lung regions for better understanding the difference in treatment planning optimization of IMPT on Eclipse treatment planning system. The planning results of RO demonstrated better robust outcome in defiance of proton uncertainties compared to PTV-based optimization. Besides, RO’s plans had better target dose coverage by increasing 1.5 Gy (RBE) on average to D95% of CTV than PTV-based optimization, and provide more homogeneous dose distributions by improving HI (D5%/D95%) from 0.03 to 0.04. The comparison results in this study show the superiority of RO was not due to incorporate safety margins for critical organs, but mainly the ability to compensate the dose perturbations caused by proton uncertainties.

A robust VMAT delivery solution for single-fraction lung SABR utilizing FFF beams minimizing dosimetric compromise.

Peripheral lung lesions treated with a single fraction of stereotactic ablative body radiotherapy (SABR) utilizing volumetric modulated arc therapy (VMAT) delivery and flattening filter‐free (FFF) beams represent a potentially high‐risk scenario for clinically significant dose blurring effects due to interplay between the respiratory motion of the lesion and dynamic multi‐leaf collimators (MLCs). The aim of this study was to determine an efficient means of developing low‐modulation VMAT plans in the Eclipse treatment planning system (v15.5, Varian Medical Systems, Palo Alto, USA) in order to minimize this risk, while maintaining dosimetric quality. The study involved 19 patients where an internal target volume (ITV) was contoured to encompass the entire range of tumor motion, and a planning target volume (PTV) created using a 5‐mm isotropic expansion of this contour. Each patient had seven plan variations created, with each rescaled to achieve the clinical planning goal for PTV coverage. All plan variations used the same field arrangement, and consisted of one dynamic conformal arc therapy (DCAT) plan, and six VMAT plans with varying degrees of modulation restriction, achieved through utilizing different combinations of the aperture shape controller (ASC) in the calculation parameters, and monitor unit (MU) objective during optimization. The dosimetric quality was assessed based on RTOG conformity indices (CI100/CI50), as well as adherence to dose–volume metrics used clinically at our institution. Plan complexity was assessed based on the modulation factor (MU/cGy) and the field edge metric. While VMAT plans with the least modulation restriction achieved the best dosimetry, it was found that there was no clinically significant trade‐off in terms of dose to organs at risk and conformity by reducing complexity. Furthermore, it was found that utilizing the ASC and MU objective could reduce plan complexity to near‐DCAT levels with improved dosimetry, which may be sufficiently robust to overcome the interplay effect.

Commissioning of Clinac IX Trilogy Linear Accelerator for Stereotactic Radiosurgery

Comprehensive quality assurance (QA) and beam data acquisition has been performed for commissioning of Varian Trilogy linear accelerator for stereotactic radiosurgery (SRS). Mechanical, electrical and radiological tests were performed to check linac performance as per American Association of Physicists in Medicine (AAPM) Task Group (TG) 142. The geometric isocentre accuracy, congruence check and calibration of kV and MV imager were performed using the Isocal QA device. The off axis ratio profiles, depth dose data and beam output factors of 6 MV SRS beam for the field sizes ranging from 2 × 2 cm2 to 15 × 15 cm2 were measured using SFD diode detector and cc13 semiflex ion chamber. The multileaf collimator (MLC) characterization was done in the treatment planning system (TPS) using the parameters measured with the CC13 semiflex ionisation chamber in water phantom. Dose measured with 2D ion chamber array was compared to that calculated in TPS. The maximum change in MV and kV imager isocentre was within ±0.03 cm. The variation between SFD measured and ion chamber measured beam data is in positive correlation for fields sizes down up to 2 × 2 cm2. Variation in output factors is ±0.56 ± 0.05 %. The measured beam data is imported and calculated in the Eclipse TPS and is found within 1% gamma agreement index (GAI) with the Analytical Anisotropic Algorithm (AAA) model data. GAI for TPS verification QA is 97.8%, 98.5% and 98.3% respectively for fix jaw 2 × 2 cm2, 5 × 5 cm2 and rapid arc SRS plan. Successful modelling of the photon beam for high dose rate SRS mode is achieved for clinical treatment of patients.

Dose Verification with diode versus TLD as in-vivo dosimeters for external radiotherapy

Background: Conformal radiotherapy was the first step toward patient-specific treatment, this is, in turn, arise the need to perform quality dose verification (DV) with in-vivo (IV) dosimetry. Aim: two common IV dosimeters were compared separately, diode and thermoluminescent dosimeters (TLD), the dose was compared with calculated dose and the isocenter dose measured with ion chamber (IC). Materials and Methods: First The absolute dose was measured in PTW Farmer IC (0.6 cc) on Varian machine model Unique for twenty cancer patients planned in 3D conformal radiotherapy, they were randomly selected to cover different clinical sites, the dose was calculated in Eclipse treatment planning system (TPS). Then in the treatment position, the in-vivo DV dosimetry was performed using: Sun nuclear Semiconductor diode and TLD. Results: the dose measured with Diode had less variance (-1.94±2.05) with TPS than dose measured with TLD/TPS (4.08 ±6.51), when comparing the dose measures with IC this discrepancy is not the case with IC/TPS as they were measured in the isocentre point and compared with prescribed doses Conclusion: patient specific DV performed with IC is the most accurate as a double check with prescribed dose. For IV dosimetry diode was closer to calculated dose, however, both diode and TLD characterized by uniform difference versus calculated dose within different clinical sites which keep each of them an accepted device especially when seeking their additive values either of small field dosimetry with TLD or skin dose measurement with diode. Those outcomes highlight the limitation of each device for IV dosimetry.

Comparison of Dose Volume Histogram (DVH) of Simulated Object Calculated by Analytically and Treatment Planning System (TPS): Preliminary Study

TPS is the key to the success of external radiotherapy medication, which directly affects the quality of treatment planning and accuracy of dose calculation within the plan. The output of TPS’s plan result is in form of DVH curve. DVH is the reference for dose dispersion on the target or healthy organ. Within this research, DVH result from the TPS and DVH result from analytical calculation were compared. The DVH comparison was started by creating a simulation object in form of virtual phantom using Matlab program in various geometrical shapes, which were sphere, cube, and cylinder. The planning on simulation object was conducted using TPS Eclipse. From the result of the plan using TPS Eclipse and analytical measurement, it can be concluded that the highest value difference was on the sphere object simulation. While for the Dmax and Dmin value comparison, the highest difference was in Dmin with the highest discrepancy. This was caused by the voxel size on each measurement. Besides, the dose value of interpolation and voxel determination on the surface of the geometrical simulation object also affected the value of analytical measurement, so it resulted in the higher value compared to the calculation result on each TPS.

Dosimetric comparison between single and double isocenters VMAT for SRT with multiple targets

The focal irradiation approach for brain metastasis (BMs) Stereotactic Radiosurgery (SRS) or Stereotactic Radiotherapy (SRT) has emerged as an important modality for multiple BMs. This study aimed to evaluate the dosimetric effects between single isocentre (SI) and double isocentres (DI) VMAT SRT of multiple brain metastases. Eighteen VMAT SRT plans with varying lesions size, number and distance were simulated on patient CT image using Eclipse treatment planning system version 15. The plan consists of 3 techniques in: 2 coplanar arcs SI, 1 coplanar combine with 2 non-coplanar arcs SI and 2 non-coplanar and 1 coplanar arc DI. The VMAT plans were generated with 21Gy prescription dose to all lesions in 3 fractions. The plans were evaluated in terms of Gradient index (Paddick GI), Conformity index (Paddick CI), and Homogeneity index (ICRU HI) for PTV and V12Gy and V6Gy for normal brain. The same dose constraints were used to optimize for all cases. On the average result from 3 techniques, 3 arcs SI plans and DI were better in GI (14.79±5.83, 13.70±4.72) and CI (0.63±0.08, 0.62±0.09) than 2 arcs SI (17.56±6.15, 0.62±0.11), while HI values was comparable for all techniques. For normal brain, V12Gy for 2 arcs and 3 arcs SI plans were comparable with DI and the volumes of normal brain receiving 6 Gy in 3 arcs SI and DI (77.40 ± 34.30 cm3, 68.94 ± 30.50 cm3) were better than 2 arcs SI (108.10 ± 57.20 cm3). Moreover, the number of arcs, monitoring units and treatment time were also increased and inconvenience in practice in DI. In conclusion, 3 arcs non-coplanar SI VMAT technique presents the suitable in dosimetric evaluation in 2-5 lesions metastases SRT.