Octavius 4D Phantom Research Articles

Dose measurement of optic chiasm and parotid organs using OCTAVIUS 4D phantom: a dynamic IMRT method for nasopharyngeal cancer treatment

IntroductionIn intensity-modulated radiation therapy (IMRT) techniques, although the dose conformity increases, the out-of-field doses would not decrease. This study aimed to assess the dose error calculated by the treatment planning system (TPS) in the out-of-field regions using the dynamic IMRT (D-IMRT) method in nasopharyngeal cancer (NPC) patients. MethodsThe out-of-field doses were measured for the chiasm and parotid organs using the D-IMRT technique (6 MV energy) with Monaco TPS. Computed tomography (CT) images of 10 NPC patients (54–77 years, mean: 61.6 ± 12.2 years) were considered and countered using 7-field and 11-field methods. The OCTAVIUS 4D phantom was utilized for dose assessment. ResultsAccording to the OCTAVIUS measurements, the Monaco TPS dose errors ranged from −58.8 to 105.5%. The average dose error for optic chiasm and parotid organs was −25% and 8.5%, respectively, with several cases falling within tolerance (±5%). ConclusionThere were considerable dose calculation errors by Monaco TPS for organs located in out-of-field regions (optic chiasm and parotid) during IMRT for NPC patients. Therefore, accurate dose estimation in the out-of-field regions should be considered in clinical practices.

PRIMO Monte Carlo software as a tool for commissioning of an external beam radiotherapy treatment planning system.

The purpose was to validate the PRIMO Monte Carlo software to be used during the commissioning of a treatment planning system (TPS). The Acuros XB v. 16.1 algorithm of the Eclipse was configured for 6 MV and 6 MV flattening-filter-free (FFF) photon beams, from a TrueBeam linac equipped with a high-definition 120-leaf multileaf collimator (MLC). PRIMO v. 0.3.64.1814 software was used with the phase space files provided by Varian and benchmarked against the reference dosimetry dataset published by the Imaging and Radiation Oncology Core-Houston (IROC-H). Thirty Eclipse clinical intensity-modulated radiation therapy (IMRT)/volumetric modulated arc therapy (VMAT) plans were verified in three ways: 1) using the PTW Octavius 4D (O4D) system; 2) the Varian Portal Dosimetry system and 3) the PRIMO software. Clinical validation of PRIMO was completed by comparing the simulated dose distributions on the O4D phantom against dose measurements for these 30 clinical plans. Agreement evaluations were performed using a 3% global/2 mm gamma index analysis. PRIMO simulations agreed with the benchmark IROC-H data within 2.0% for both energies. Gamma passing rates (GPRs) from the 30 clinical plan verifications were (6 MV/6MV FFF): 99.4% ± 0.5%/99.9% ± 0.1%, 99.8% ± 0.4%/98.9% ± 1.4%, 99.7% ± 0.4%/99.7% ± 0.4%, for the 1), 2) and 3) verification methods, respectively. Agreement between PRIMO simulations on the O4D phantom and 3D dose measurements resulted in GPRs of 97.9% ± 2.4%/99.7% ± 0.4%. The PRIMO software is a valuable tool for dosimetric verification of clinical plans during the commissioning of the primary TPS.

Application of a Comprehensive Treatment Planning Test for Credentialing Intensity-Modulated Radiotherapy and RapidArc in a TrueBeam Linear Accelerator Setup.

An extended version of task group report (TG)-119 dosimetric tests was introduced and tested on the TrueBeam linear accelerator setup. Treatment plan results and quality assurance (QA) results of RapidArc (RA) and intensity-modulated radiotherapy (IMRT) were compared to understand the limitation and efficacy of the RA and IMRT system of the linear accelerator. Test structure sets were drawn on OCTAVIUS four-dimensional (4D) phantom computed tomography scan data for this study. We generated treatment plans based on the specified goal in the Eclipse™ treatment planning system using RA and IMRT in the study phantom. We used the same planning objectives for RA and IMRT techniques. Planar dose verification was performed using electronic portal imaging device and OCTAVIUS 4D phantom. The treatment log file was further analyzed using Pylinac (V2.4.0 (Open Source Code library available on Github, runs under Python programming language)) to compare the dosimetric outcome of RA and IMRT. Dose to the planning target volume (PTV) 1-5 and organ at risk (OAR) were analyzed in this study for the efficiency comparison of RA and IMRT. The primary objective was accomplished by adhering to the dose constraints associated with PTV 2 and the OAR. RA and IMRT also met the secondary objective. The tertiary goal of dose delivery to PTV 4 was met with RA but not IMRT. This study can be utilized to compare different institutions' planning and patient-specific QA (PSQA) procedures. The findings of this study were in line with the published works of the literature. A multi-institutional planning and delivery accuracy audit can be built using this structure and set of planning objectives having similar PSQA phantom. The TG-119 report incorporated test challenges that were combined in a single study set and a single plan. This reduces the complexity of performing the original TG-119 tests, whereas keeping the challenges as introduced in the TG-119 report. This study's planning and dosimetric results could be further utilized for dosimetry audit with any institute having a linear accelerator and OCTAVIUS 4D phantom for PSQA.

Analysis of the interplay effect in lung stereotactic ablative radiation therapy based on both breathing motion and plan characteristics

Abstract Introduction: Stereotactic ablative radiotherapy (SABR) is susceptible to challenges for tumours affected by intrafraction organ motion. This study aims to investigate the effect of breathing characteristics and plan complexity on the interplay effect. Methods: A patient-specific interplay effect evaluation was performed using in-house software with an alpha version of the treatment planning verification software Verisoft (PTW-Freiburg, Germany) on VMAT plans. The OCTAVIUS 4D phantom was used to acquire the static dose distribution, and the simulation approach was utilised to generate the moving dose distribution. The influence of plan complexity, PTV size, number of breaths, and motion amplitudes on the interplay effect were examined. The dose distribution of two extreme phases—end-inhale and end-exhale—was considered using the gamma criteria of 2%/2 mm for the interplay effect evaluation. Results: A strong correlation was found between the motion amplitude (p < 0.001) and the NBs (p < 0.001) with the gamma-passing rate. No correlation was found between the gamma-passing rate and the PTV size or plan complexity. Conclusion: The simulation tool allowed the analysis of a large number of breathing traces, demonstrating how free-breathing patients, suspected of high interplay, could be selected for other motion management solutions. The simulated cases showed strong interplay effects for long breathing periods with extended motion amplitudes in a small group of patients.

Pretreatment Spinal Column Dose Estimation for Spinal SBRT Using Octavius Four-dimensional Phantom and Dose-volume Histograms Four-dimensional Feature: A Dosimetric Analysis.

The aim of this study was to estimate the spinal column dose for spinal Stereotactic body radiation therapy (SBRT) before patient treatment using the PTW dosimetry Octavius dose-volume histograms (DVH) four-dimensional (4D) feature. Twenty-three patients were included in the study, and a volumetric modulated arc therapy plan with 6MV flattening filter-free (6FFF) was generated for each patient in the Eclipse planning system using the Anisotropic Analytical Algorithm (AAA) algorithm (Varian Medical Systems, Palo Alto, CA) for the TrueBeam STx LINAC machine. The Octavius 4D system was used to estimate the spinal cord dose by delivering the plans to the 4D phantom. The measured dose was compared with the Eclipse treatment planning system (TPS) (Varian Medical Systems, Palo Alto, CA) dose. The spinal cord max and mean doses estimated using Varisoft DVH 4D are in close agreement with the TPS calculated max and mean doses. The deviation between measured dose and TPS dose is ±5% for the spinal max dose, and the deviation between measured dose and TPS dose is ± 3% for the spinal mean dose. The study demonstrates that the PTW Octavius 4D phantom and DVH 4D feature can be used as a tool to estimate spinal cord dose before the treatment in spinal SBRT plans. The system provides an independent dose measurement that is comparable to the TPS dose. The close agreement between measured and calculated doses validates the use of this system as a critical organ dose verification tool.

Dosimetric Comparison of Total Body Irradiation and Total Marrow Irradiation Using Volumetric Arc Therapy (VMAT)

Bu araştırmada tüm vücut ışınlaması (TVI) ve tüm kemik iliği ışınlaması (TKI) için, Volümetrik Ark Tedavi (VMAT) tekniği kullanılarak, hedef hacim ve kritik organ dozlarının karşılaştırılması amaçlanmıştır. Çalışmada, insan doku ve organ yoğunluklarına sahip, rando fantom kullanıldı. VMAT planları günlük fraksiyon dozu 6 Gy olmak üzere toplam doz 12 Gy olacak şekilde, oluşturuldu. Hedef hacimler ve risk altındaki organların (RAO) aldığı doz değerleri karşılaştırıldı. VMAT-TVI için ortalama akciğer dozu, 7.6 Gy ve lens dozu 4.4 Gy iken, VMAT-TKI için, RAO’nun dozları 2.7 ila 7.15 Gy aralığındadır. Ayrıca her iki plan için tedavi öncesi kalite kontrolü Octavius 4D fantom kullanılarak, planlanan ve verilen dozlar arasında doz doğruluğu, her 3 düzlemde 3mm ve %3 kriterleri ile gama indeks analizi, her iki tedavi planı için ≤1 olduğu saptanmıştır. Planlanan ve uygulanan tedavi arasında oldukça hassas doz dağılımı olduğu gözlemlendi. Her iki tedavi tekniğinde de hedef volüm istenilen dozu aldığı, fakat VMAT-TVI tekniğinde, doz homojenliği ve tedavi uygulama tekniklerinin iyileştirilmesi gerektiği sonucuna varıldı. TKI ile akciğer dışındaki diğer RAO'ların da daha iyi korunabildiği saptandı. Çalışmamızın sonucunda, VMAT'ın gelecekte geleneksel tekniklere göre hem TVI hem de TKI uygulaması için uygun bir teknik olabileceği görüşüne varıldı.

Craniospinal Irradiation: A Dosimetric Comparison Between O-Ring Linac and Conventional C-arm Linac

PurposeThe aim of this study was to perform a dosimetric evaluation between craniospinal irradiation volumetric modulated arc therapy plans designed for an O-Ring and a conventional C-arm Linac. Methods and MaterialsTwo adult patients were selected for this study. Two plans were designed one for a TrueBeam Edge and one for Halcyon O-ring Linac for each patient. The evaluation of the plans was conducted in terms of dose volume histogram analysis of the target volume and organs at risk (OARs) along with total plan monitor units and beam-on time. Paired sample t test was performed to compare Dmax and Dmean of OARs for each plan's comparison. The delivery of volumetric modulated arc therapy plans was evaluated using Octavius 4D phantom. ResultsAll plans demonstrated dose distributions with sufficient planned target volume conformity and homogeneity. The Homogeneity Index and Conformity Index for all plans were found comparable. The paired sample t test did not demonstrate significant difference in terms of Dmax and Dmean of OARs between plans for both patients. All plans met the threshold of 90%, with Halcyon plans having higher gamma passing rates. ConclusionsCraniospinal irradiation plans generated for Halcyon and Edge are equivalent in terms of plan quality and dose sparing at OARs. The small variations may have originated from the differences in beam profile or mean energy, the degree of the modulation for each plan and characteristics of multi leaf collimators for each treatment unit. Halcyon is able to deliver a distinctly faster treatment, but Edge provides an automatic rotational correction for patient positioning.

Automated hybrid volumetric modulated arc therapy (HVMAT) for whole-breast irradiation with simultaneous integrated boost to lumpectomy area : Atreatment planning study.

To develop anautomated treatment planning approach for whole breast irradiation with simultaneous integrated boost using an automated hybrid VMAT class solution (HVMAT). Twenty-five consecutive patients with left breast cancer received 50 Gy (2 Gy/fraction) to the whole breast and an additional simultaneous 10 Gy (2.4 Gy/fraction) to the tumor cavity. Ipsilateral lung, heart, and contralateral breast were contoured as main organs-at-risk. HVMAT plans were inversely optimized by combining two open fields with aVMAT semi-arc beam. Open fields were setup to include the whole breast with a2 cm flash region and to carry 80% of beams weight. HVMAT plans were compared with three tangential techniques: conventional wedged-field tangential plans (SWF), field-in-field forward planned tangential plans (FiF), and hybrid-IMRT plans (HMRT). Dosimetric differences among the plans were evaluated using Kruskal-Wallis one-way analysis of variance. Dose accuracy was validated using the PTW Octavius-4D phantom together with the 15002D-array. No significant differences were found among the four techniques for both targets coverage. HVMAT plans showed consistently better PTVs dose contrast, conformity, and homogeneity (p < 0.001 for all metrics) and statistically significant reduction of high-dose breast irradiation. V55 and V60 decreased by 30.4, 26.1, and 20.8% (p < 0.05) and 12.3, 9.9, and 6.0% (p < 0.05) for SWF, FIF, and HMRT, respectively. Pretreatment dose verification reported agamma pass-rate greater than the acceptance threshold of 95% for all HVMAT plans. In addition, HVMAT reduced the time for full planning optimization to about 20 min. HVMAT plans resulted in superior target dose conformity and homogeneity compared to other tangential techniques. Due to fast planning time HVMAT can be applied for all patients, minimizing the impact on human or departmental resources.

Comparative performance analysis of 2D and 3D gamma metrics for patient specific QA in VMAT using Octavius 4D with 2D-Array 1500.

Gamma pass percentage (GPP) is the predominant metric used for Patient Specific Quality Assurance (PSQA) in radiation therapy. The dimensionality of the measurement geometry in PSQA has evolved from 2D planar to 3D planar, and presently to state-of-the-art 3D volumetric geometry. We aim to critically examine the performance of the three-dimensional gammas vis-à-vis the older gamma metrics of lower dimensionality to determine their mutual fungibility in PSQA, using clinically approved Volumetric Arc Therapy (VMAT) plans. Gamma pass percentages derived from PSQA for VMAT plans using Octavius 4D phantom with 2D-Array 1500 and its proprietary software were recorded. 2D planar, 3D planar, and 3D volumetric gamma pass percentages were retrospectively extracted for multiple treatment plans at three sites, using three acceptance limits, and for two modes of normalization. The differences in mean pass percentages, and the pairwise correlation between geometries were calculated within limits of statistical significance. A significant increase in mean pass rates was observed from 2D planar to 3D planar geometries. The difference was less pronounced from 3D planar to 3D volumetric. 2D planar v/s 3D planar showed a significant degree of correlation among themselves, which was not seen against most of the 3D volumetric pass rates. The mean gamma pass rates show conclusive evidence of the benefits of shifting from 2D planar to higher dimensions measurement geometries, but the benefits of using 3D volumetric compared to 3D planar is not always unequivocal. The correlations show mixed results regarding the interdependence of pass percentages at different geometries.

Operation and calibration of the novel PTW 1600SRS detector for the verification of single isocenter stereotactic radiosurgery treatments of multiple small brain metastases.

Objectives:The aim of this work was to evaluate the operation of the 1600SRS detector and to develop a calibration procedure for verifying the dose delivered by a single isocenter stereotactic radiosurgery (SRS) treatment of small multiple brain metastases (BM).Methods:14 clinical treatment cases were selected with the number of BM ranging from 2 to 11. The dosimetric agreement was investigated between the calculated and the measured dose by an OCTAVIUS 1600SRS array detector in an OCTAVIUS 4D phantom equipped with dedicated SRS top. The cross-calibration procedure deviated from the manufacturer’s as it applied field sizes and dose rates corresponding to the volumetric modulated arc therapy segments in each plan.Results:Measurements with a plan specific cross-calibration showed mean ± standard deviation (SD) agreement scores for cut-off values 50%, 80%, 95%, of 98.6 ± 1.7%, 96.5 ± 4.6%, 97.3 ± 4.4% for the 6 MV plans respectively, and 98.6 ± 1.5%, 96.6 ± 4.0% 96.4 ± 6.3%, for the 6 MV flattening filter free (FFF) plans respectively. Using the default calibration procedure instead of the plan specific calibration could lead to a combined systematic dose offset of 4.1% for our treatment plans.Conclusion:The 1600SRS detector array with the 4D phantom offers an accurate solution to perform routine quality assurance measurements of single isocenter SRS treatments of multiple BM. This work points out the necessity of an adapted cross-calibration procedure.Advances in knowledge:A dedicated calibration procedure enables accurate dosimetry with the 1600SRS detector for small field single isocenter SRS treatment of multiple brain metastases for a large amount of BM.

RETRACTED ARTICLE: Dosimetric assessment of IMRT treatment planning for unilateral breast cancer patient using Octavius phantom detector

The goal of this research was to study the widely used criteria in Iraq and the suggested criteria from the American association of physics in medicine (AAPM). The breast cancer patients treated at Al-Andalus private hospital underwent a CT simulation. The data were exported to Monaco 5.1 treatment planning system for planning purposes using the intensity-modulated radiation therapy technique with X-ray energies of 6 or 10 MV. The planning was transferred to Agility linear accelerator for irradiation to Octavius-4D phantom detector for pre-treatment verification. The results show that there is no significant difference between the prescribed and measured point dose. In addition, the dose difference is acceptable and there was no significant correlation between the dose error and the result of gamma passing rates for all criteria. A high significant difference appeared between the 3%/2 mm and 3%/3 mm criteria for both local and global gamma passing rates at the two studied thresholds 5% and 10%. All the values of 10% thresholds were highly significant than 5% in local %GP but not significant for the global %GP. The number of segments and the total number of monitor units show an inverse relationship with gamma passing rates. The results clearly show that criteria and thresholds depend on the situation and health of the patient. This means the criteria are to be set at 3%/2 mm for plans which use high doses to organs at risk, while 3%/3 mm may be used for simpler plans with lower doses to organs at risk.

Personalized automation of treatment planning in head-neck cancer: A step forward for quality in radiation therapy?

To perform a comprehensive dosimetric and clinical evaluation of the new Pinnacle Personalized automated planning system for complex head-and-neck treatments. Fifteen consecutive head-neck patients were enrolled. Radiotherapy was prescribed using VMAT with simultaneous integrated boost strategy. Personalized planning integrates the Feasibility engine able to supply an "a priori" DVH prediction of the achievability of planning goals. Comparison between clinically accepted manually-generated (MP) and automated (AP) plans was performed using dose-volume histograms and a blinded clinical evaluation by two radiation oncologists. Planning time between MP and AP was compared. Dose accuracy was validated using the PTW Octavius-4D phantom together with the 1500 2D-array. For similar targets coverage, AP plans reported less irradiation of healthy tissue, with significant dose reduction for spinal cord, brainstem and parotids. On average, the mean dose to parotids and maximal doses to spinal cord and brainstem were reduced by 13-15% (p<0.001), 9% (p<0.001) and 16% (p<0.001), respectively. The integral dose was reduced by 16% (p<0.001). The dose conformity for the three PTVs was significantly higher with AP plans (p<0.001). The two oncologists chose AP plans in more than 80% of cases. Overall planning times were reduced to <30min for automated optimization. All AP plans passed the 3%/2mm γ-analysis by more than 95%. Complex head-neck plans created using Personalized automated engine provided an overall increase of plan quality, in terms of dose conformity and sparing of normal tissues. The Feasibility module allowed OARs dose sparing well beyond the clinical objectives.

Acuros® dose verification of ultrasmall lung lesions with EBT-XD film in a homogeneous and heterogeneous anthropomorphic phantom setup.

Modern type 'c' dose calculation algorithms like Acuros® can predict dose for lung tumors larger than approximately 4cm3 with a relative uncertainty up to 5%. However, increasingly better tumor diagnostics are leading to the detection of very small early-stage lung tumors that can be treated with stereotactic body radiotherapy (SBRT) for inoperable patients. This raises the question whether dose algorithms like Acuros® can still accurately predict dose within 5% for challenging conditions involving small treatment fields. Current recommendations for Quality Assurance (QA) and dose verification in SBRT treatments are to use phantoms that are as realistic as possible to the clinical situation, although water-equivalent phantoms are still largely used for dose verification. In this work we aim to demonstrate that existing dose verification methods are inadequate for accurate dose verification in very small lung tumors treated with SBRT. The homogeneous PTW Octavius4D phantom with the Octavius 1000 SRS detector ("Octavius4D phantom") and the heterogeneous CIRS Dynamic Thorax phantom ('CIRS phantom') were used for dose measurements. The CIRS phantom contained different lung-equivalent film-holding cylindrical phantom inserts ("film inserts") with water-equivalent spherical targets with diameters 0.5, 0.75, 1, 2, and 3cm. Plans were calculated for 6 and 10MV for each spherical target in the CIRS phantom, resulting in 14 treatment plans. The plans were delivered to both Octavius4D and CIRS phantom to compare measured dose in a commonly used homogeneous and more realistic heterogeneous phantom setup. In addition, treatment plans of seven clinical lung cancer patients with lung tumors below approximately 1.0cm3 were irradiated in the heterogeneous CIRS phantom. The actual tumor size within the clinical treatment plans determined the choice of the spherical target size, such that both measurement geometry and clinical target volumes match as closely as possible. The Acuros® dose algorithm (version 15.5.11) was used for all dose calculations reporting dose-to-medium using a 0.1-cm-grid size. The measurement discrepancies in the homogeneous Octavius4D phantom for the fourteen treatment plans were within 1.5%. Dose discrepancies between measurement and treatment planning systems (TPS) for the heterogeneous CIRS phantom increased for both 6 and 10MV with decreasing target diameters up to 23.7±1.0% for 6MV and 8.8±1.1% for 10MV for the smallest target of 0.5cm in diameter with a 2-mm-CTV-PTV margin. For the seven clinical plans this trend of increasing dose difference with decreasing tumor size is less pronounced although the smallest tumors show the largest differences between measurement and TPS up to 16.6±0.9%. Current verification methods using homogenous phantoms are not adequate for lung tumors with diameters below approximately 0.75cm. The current Acuros® dose calculation algorithm underestimates dose in very small lung tumors. Dose verification of small lung tumors should be performed in an anthropomorphic lung phantom incorporating a water-equivalent target that matches clinical tumor size as closely as possible.

Evaluation of the effect of random setup errors on dose delivery in Intensity Modulated Radiotherapy

Abstract Aim: To conduct a study on the effect of random setup errors inpatient for dose delivery in Intensity Modulated Radiotherapy plans using Octavius 4D phantom. Materials and methods: 11 patients with cancer of H&amp;N were selected for this study. An IMRT plan was created for each patient. The IMRT quality assurance plans were transferred to Mosaiq workstation in a linear accelerator. These plans were delivered at the reference treatment position. Subsequently, the QA plans were delivered on the Octavius 4D phantom after introducing errors in various translational and rotational directions. The setup inaccuracies introduced varied from 1 mm to 5 mm along X, Y. These setup uncertainties were then introduced along X and Y direction simultaneously in equal measures. Similarly, IMRT plans were delivered also after introducing roll and yaw rotation of 1, 2 and 3 degrees in phantom. The deviation of gamma indices at all these positions was analyzed with respect to the reference setup position. Results: The percentage of points passing the gamma acceptance criterion decrease as we increase the setup error. The change is found to be very insignificant with setup error up to 2 mm along X, Y or XY direction. Similarly, the rotational error of up to 3 degrees is found to be acceptable. Conclusions: Small setup (&lt; 2 mm) correction in patients may not adversely affect the dose delivery. But an error of similar magnitude in 2 directions simultaneously has a much greater impact on IMRT dose delivery.

Template-based automation of treatment planning in advanced radiotherapy: a comprehensive dosimetric and clinical evaluation

Despite the recent advanced developments in radiation therapy planning, treatment planning for head-neck and pelvic cancers remains challenging due to large concave target volumes, multiple dose prescriptions and numerous organs at risk close to targets. Inter-institutional studies highlighted that plan quality strongly depends on planner experience and skills. Automated optimization of planning procedure may improve plan quality and best practice. We performed a comprehensive dosimetric and clinical evaluation of the Pinnacle3 AutoPlanning engine, comparing automatically generated plans (AP) with the historically clinically accepted manually-generated ones (MP). Thirty-six patients (12 for each of the following anatomical sites: head-neck, high-risk prostate and endometrial cancer) were re-planned with the AutoPlanning engine. Planning and optimization workflow was developed to automatically generate “dual-arc” VMAT plans with simultaneously integrated boost. Various dose and dose-volume parameters were used to build three metrics able to supply a global Plan Quality Index evaluation in terms of dose conformity indexes, targets coverage and sparing of critical organs. All plans were scored in a blinded clinical evaluation by two senior radiation oncologists. Dose accuracy was validated using the PTW Octavius-4D phantom together with the 1500 2D-array. Autoplanning was able to produce high-quality clinically acceptable plans in all cases. The main benefit of Autoplanning strategy was the improvement of overall treatment quality due to significant increased dose conformity and reduction of integral dose by 6–10%, keeping similar targets coverage. Overall planning time was reduced to 60–80 minutes, about a third of time needed for manual planning. In 94% of clinical evaluations, the AP plans scored equal or better to MP plans. Despite the increased fluence modulation, dose measurements reported an optimal agreement with dose calculations with a γ-pass-rate greater than 95% for 3%(global)-2 mm criteria. Autoplanning engine is an effective device enabling the generation of VMAT high quality treatment plans according to institutional specific planning protocols.

Gamma Evaluation with Octavius 4D Phantom for PreTreatment of Modern Radiotherapy Treatment Techniques

Purpose: In modern radiotherapy techniques such as intensity-modulated radiation therapy (IMRT) and volume modulated arc therapy (VMAT), the quality assurance (QA) process is vital. The goal of the study was to verify the treatment planning dose delivered during delivery of complex treatment plans. The QA standard is to perform patient-specific comparisons between planned doses and doses measured in a phantom. Materials and Methods: Ninety-five complex IMRT and VMAT plans for different pathologies planned using Eclipse treatment planning system (TPS). The Octavius 4D phantom has been used to verify patient specific quality assurance of all VMAT plans calculating with different algorithms. Conclusion: Overall, good agreement was observed between measured and calculated doses in most cases with gamma values above 1 in >95% of measured points in volumetric 3D analysis and 1 in >90% in 2D analysis. The Octavius 4D phantom is an effective and efficient method for patient specific QA.

136. Which is the optimum cylindrical phantom grid size calculation to evaluate the accuracy of gamma index for times optimizing in the pre-treatment quality assurance procedure of VMAT and IMRT tecnique?

PurposeIMRT and VMAT are the state-of-the-art irradiation techniques for the delivery of highly conformal radiation fields to PTV. The use of QA tools for the verification of the planned dose distribution prior to the treatment of the patient has become a standard procedure in clinical routine. Aim of this study is to evaluate the optimal grid size calculation on cylindrical phantoms to determine the gamma index (γ) levels for the routinely pre-treatment dosimetric QA. Methods and materialsThe measurements were made on a Elekta Precise linear accelerator and compared with the created plans by the Philips Pinnacle3 TPS. The pre-treatment evaluations were made with the PTW_OCTAVIUS-4D phantom with the 729 cubical ion chambers arranged in the OCTAVIUS_Detector 2D_array of 27 cm × 27 cm. The beam incidence is always perpendicular to the surface of the detector panel and the data were collected and evaluated by means of the PTW_VeriSoft software package. On about 100 patients who underwent to radiotherapy with VMAT, were evaluated the γ between the dose deliveries and the dose calculations on the cylindrical phantom with cubic step size of 4 mm, 3 mm and 2 mm. For each phantom grid size the γ value with [3 mm;3%], [2 mm;2%] and [1 mm;1%] as distance and dose difference criteria respectively were determined. ResultsFor each fixed γ[d(mm);D(%)] criteria the γ global ratios to the 3 mm voxel phantom calculation, followed a Gaussian distribution. That mean that there isn’t a correlation between the used phantom grid size and γ accordance. The agreement in γ differences were found within 2%(2SD), 3%(2SD) and 5%(2SD) for γ[3 mm;3%], γ[2 mm;2%] and γ[1 mm;1%] respectively. ConclusionsDue to the computer limits and the large amount of calculation, the TPS algorithms are often time consuming, strongly depending on the set grid size calculation. For a busy Center a voxel grid size of 3–4 mm is enough appropriate.

5 Stereotactic treatments on standard accelerator: From implementing technique to treatment patient

Introduction Since 2015, the radiotherapy department of Reunion Island university hospital treats patients under stereotactic conditions on standard accelerators equipped with on-board imaging. We started our treatments under stereotactic intracranial in VMAT technique. In 2017, we implemented the 4D option with RPM material (Varian) on our scan and treated patients under extra-cranial stereotactic using dynamic arc therapy. Today, we routinely treat patients for stereotactic head, lung and bones localisation. This work provides a description of the implementation of this practice. Methods Our results concern 29 patients treated for intracranial stereotactic, 8 with tumor lung and 6 with bone metastasis. The Acuros AXB algorithm is defined as a reference for the intracranial and the AAA algorithm for extra-cranial treatments (1 mm resolution grid). The minimum jaw size we allow is 2x2cm2. We evaluate our dosimetry (calculated on Varian’s TPS Eclipse) according to the RTOG criteria, conformity and homogeneity indices, and tracking of OARs dose: R100, R50, RCI, CIp and GI indices. We also note the maximum dose 2 cm from PTV in any direction, percent of lung receiving 20 Gy for pulmonary tumors and percent of healthy brain receiving 12 Gy for intracranial stereotactic treatment. A mechanical quality control (QC) is performed, and, before each treatment, a patient QC is realized (Octavius 4D phantom SRS array PTW). Therefore, for each treatment session, CBCT imaging is acquired. Results For all patients the values (mean ± SD) of R100, R50, RCI, CIp and GI are 1,18 ± 0,16; 4,93 ± 0,90; 0,99 ± 0,01; 0,83 ± 0,09 and 4,14 ± 0,81 respectively. The mechanical precision tolerances (monthly controls) of linear accelerator are 1 mm per jaw size and 1 mm for isocenter (arm, collimator, table and OBI (kV and CBCT)). The results of gamma index for QC patients are 93.4% ± 10 (local dose 1 mm/ 3–5% with cut off at 50%). Conclusions Dosimetric indices and QC indicators are satisfactory. By now, our service can offer stereotactic intra and extra-cranial treatment on standard accelerator for patients who lives in Reunion island.

IMRT planning parameter optimization for spine stereotactic radiosurgery

Spine stereotactic radiosurgery (SSRS) is a noninvasive treatment for metastatic spine lesions. MD Anderson Cancer Center reports a quality assurance (QA) failure rate approaching 15% for SSRS cases, which we hypothesized is due to difficulties in accurately calculating dose resulting from a large number of small-area segments. Clinical plans typically use 9 beams with an average of 10 segments per beam and minimum segment area of 2-3 cm2. The purpose of this study was to identify a set of intensity-modulated radiation therapy (IMRT) planning parameters that attempts to optimize the balance among QA passing rate, plan quality, dose calculation accuracy, and delivery time for SSRS plans. Using Pinnacle version 9.10, we evaluated the effects of 2 IMRT parameters: maximum number of segments and minimum segment area. Initial evaluation of the data revealed that 5 segments per beam along with minimum segment area of 4 cm2 and 4 monitor units (MU) per segment (5-4-4 plans) was the most promising. IMRT QA was performed using a PTW OCTAVIUS 4D phantom with a 2D detector array. Our data showed no significant plan quality change with decreased number of segments and increased minimum segment area. The average coverage of GTV and CTV was 82.5 ± 13% (clinical) vs 82.5 ± 13% (5-4-4) and 92.3 ± 8% (clinical) vs 91.5 ± 8% (5-4-4). Maximum point dose to cord was 11.4 ± 3.5 Gy (clinical) vs 11.0 ± 4.0 Gy (5-4-4). Total plan delivery time was decreased by an average of 11.3% for the 5-4-4 plans. For IMRT QA, the gamma index passing rate (distance to agreement: 2.5 mm, local dose difference: 4%) for the original plans vs the 5-4-4 plans averaged 90.3% and 91.9%, respectively. In conclusion, IMRT parameters of 5 segments per beam and 4 cm2 minimum segment areas provided a better balance of plan quality, delivery efficiency, and plan dose calculation accuracy for SSRS.

IMRT Planning Parameter Optimization for Spine Stereotactic Radiosurgery

Spine stereotactic radiosurgery (SSRS) is a noninvasive treatment for metastatic spine lesions. MD Anderson Cancer Center reports a quality assurance (QA) failure rate approaching 15% for SSRS cases, which we hypothesized is due to difficulties in accurately calculating dose resulting from a large number of small-area segments. Clinical plans typically use 9 beams with an average of 10 segments per beam and minimum segment area of 2 to 3 cm2. The purpose of this study was to identify a set of intensity-modulated radiation therapy (IMRT) planning parameters that attempts to optimize the balance among QA passing rate, plan quality, dose calculation accuracy, and delivery time for SSRS plans. Using Pinnacle version 9.10, we evaluated the effects of 2 IMRT parameters: maximum number of segments and minimum segment area. Initial evaluation of the data revealed that 5 segments per beam along with minimum segment area of 4 cm2 and 4 minimum Monitor Units (MU) per segment (544 plans) was the most promising. IMRT QA was performed using an OCTAVIUS 4D phantom with a 2D detector array. Our data showed no significant plan quality change with decreased number of segments and increased minimum segment area. The average coverage of GTV and CTV was 82.5 ± 13% (clinical) vs 82.5 ± 13% (544) and 92.3 ± 8% (clinical) vs 91.5 ± 8% (544). Maximum point dose to cord was 11.4 ± 3.5 Gy (clinical) vs 11.0 ± 4.0 Gy (544). Total plan delivery time was decreased by an average of 11.3% for the 544 plans. In addition, the QA passing rate for the original plan vs the 544 plan averaged 90.3% and 91.9%, respectively. In conclusion, IMRT parameters of 5 segments per beam and 4 cm2 minimum segment area provided a better balance of plan quality, delivery efficiency, and plan dose calculation accuracy for SSRS.