Monaco Treatment Planning System Research Articles

Validation of two calculation options built in Elekta Monaco Monte Carlo based algorithm using MCNP code

IntroductionThe calculation algorithm for intensity modulated radiotherapy (IMRT) built in the Elekta Monaco treatment planning system (TPS) is based on Monte Carlo (MC) simulation. Absorbed dose is calculated as dose to medium in medium (Dm,m), but the conversion from Dm,m to dose to water in medium (Dw,m) is enabled. According to published data, differences between these two options exist, particularly in bony structures. In this study, comparisons between dose calculation options built in Elekta Monaco TPS and Monte Carlo N-Particle transport code® (MCNP) in different materials are shown. Furthermore, the majority of clinical experience is based on the dose to water in water (Dw,w) concept provided by analytical algorithms and has represented the standard for dose calculation over the past few decades. Additionally, MCNP calculation was performed to simulate the Dw,w concept. Therefore, the correlation between Dw,w concept, and both calculation options provided by the Elekta Monaco TPS was determined. Materials and methodsTo evaluate the accuracy of TPS calculation options for 6 MV photon beam, MCNP simulation was performed for 13 different materials with mass densities ranging from 0.2 g/cm3 to 2.17 g/cm3 using simplified geometry. The simulation was performed in two ways: with standard material representation taking into account their chemical compositions and corresponding mass densities and using non-standard material representation employing chemical composition of water with varying mass densities. Depth dose curves calculated by MCNP were compared to those obtained by two calculation options Dm,m and Dw,m using root mean square (RMS) deviations. ResultsRMS deviations between depth dose curves, for Dm,m and Dw,m become largest for mass density 2.17 g/cm3, up to RMS = 13%. Comparison for both calculation options to the MCNP defined for Dm,m shows very good agreement, with RMS deviation less than 3% for the majority of examined materials. For the Dw,m calculation option results are acceptable in mass density range from 0.5 g/cm3 (RMS = 1.4%) to 1.06 g/cm3 (RMS = 2.4%). For the rest of examined materials, RMS deviation increases, with a maximal value of 12.4%. Absorbed dose calculation comparison between Dw,m and non-standard MCNP shows large deviations for the majority of used materials, up to RMS = 13.1%. RMS deviations between Dm,m calculation option and non-standard MCNP are much lower than one might expect. For the highest mass density in this research (ρ = 2.17 g/cm3), the RMS deviation is 3.7%. ConclusionAlthough it does not take into account the chemical composition of the medium, TPS calculation option Dm,m shows very good agreement with standard MCNP calculations. Furthermore, it is demonstrated that the Dw,m calculation option differs substantially from Dw,w. Additionally, it was found that for different materials absorbed dose calculated as Dm,m shows better agreement to the algorithms that calculate absorbed dose using Dw,w approach. Although the research was performed on simplified geometry, the results indicate that the use of Dm,m could be preferable in order to allow better consistency with previous clinical data in radiation oncology.

Margin Reduction by Virtual Couch Shift in Prostate SBRT on a 1.5T MR-Linac

We treat localized prostate cancer on a 1.5T MR-Linac using plan re-optimization to the anatomy of the day in each fraction. We investigated the efficacy of a 2-stage, clinically available workflow to reduce intrafraction motion during the 40-minute patient on-couch time and potential margin reduction. Patients with intermediate risk prostate cancer (NCNN classification) were treated with 5 x 7.25 Gy on an MRL. Each fraction, an initial T2 weighed MR scan (‘INI’, 2 min scan time) was acquired, and pre-treatment contours were propagated and manually adapted to this scan, thus correcting for prostate rotation and organ deformation. Next, dose re-optimization (7 beam IMRT) was applied (Monaco treatment planning system), with a 5 mm CTV-PTV margin. Because the average time between the initial scan and beam on is approximately 30 minutes, prostate intrafraction motion can be considerable. Therefore, during the last minutes of this process, a position verification (‘PV’) MR scan was obtained to determine this motion. In our initial treatments (group 1, 26 patients) a virtual couch shift (VCS) was applied if part of the prostate was outside the PTV, (i.e., a prostate shift > 5 mm). The VCS involved a translation of the planned dose according to the PV to INI scan registration of the prostate, using a fast re-optimization method. In the subsequent 25 patients (group 2), the VCS was always applied, also for shifts below 5 mm, to further reduce the impact of pre-delivery intrafraction motion. Next, the plan was delivered in typically 7 minutes, while 3D cine-MR dynamics were acquired simultaneously (balanced turbo field echo). Each 3D dynamic spanned 9.4 seconds, and consisted of 448x448x45 voxels of 1.0x1.0x2.2mm. The prostate in all dynamics was automatically registered to INI and PV scans using a previously published method (D M de Muinck Keizer et al 2019 Phys. Med. Biol. 64 235008). In group 1, 24% of the patients required a VCS. In this group, intrafraction motion shifts relative to the treatment plan anatomy during dose delivery were 0.9±0.9 mm, 1.8±1.5 mm and 1.6±1.4 mm for respectively LR, AP and CC directions (mean ± SD of absolute values). In group 2, the VCS reduced the corresponding values to 0.4±0.4 mm, 1.4±1.2 mm and 1.3±1.3 mm. The average time between PV scan and beam on was 5 min, of which the VCS calculation time was below 1 min. An analysis of the required PTV margins in the corresponding directions showed that in group 2 margins could be safely reduced to 2, 4 and 4 mm in the LR, CC and AP directions. Daily VCS shortly before dose delivery allowed for a PTV margin reduction below conventionally applied 5 mm margins. However, due to the continuous and stochastical nature of intrafraction motion, margin reduction below 4 mm would require intrafraction plan adaptation. Presently, we develop such methods based on the high quality of the 1.5T 3D cineMR.

Clinical Outcomes, Cosmesis and Quality of Life in Hypofractionation Versus Conventional Fractionation Radiotherapy to Whole Breast and Regional Nodes: A Phase II Randomized Study

Whole Breast Radiotherapy (WBRT) is indicated as adjuvant treatment in the multimodality management of Breast Cancer after Breast Cancer Surgery (BCS). Regional Nodal Irradiation (RNI) improves outcomes in patients with positive nodes after axillary dissection. Hypofractionation in WBRT is equivalent to standard fractionation in terms of long-term outcomes, but the role of hypofractionation in the settings of RNI has not been explored. We prospectively conducted a phase II randomized study comparing Hypofractionation and Standard fractionation in WBRT with RNI to evaluate clinical outcomes, cosmesis and quality of life (QOL) between the two modalities. Women aged ≥ 18 years with breast cancer undergoing BCS and axillary dissection were recruited in the study after Institutional Ethics Committee approval. 52 patients were randomized into two groups, with 26 patients in arm 1 (standard fractionation) WBRT 50Gy/25fraction/5weeks followed by boost 16Gy/8fraction and other 26 patients in arm II (hypofractionation) WBRT 40Gy/15fraction/3 weeks followed by boost 10Gy/4fraction. Contouring was done as per the standard RTOG guidelines. WBRT was planned using forward planning IMRT. Direct or oblique photon fields were used for RNI of SCF/ Axillary region as clinically indicated. Contouring and planning was done on MONACO treatment planning system. Clinical acute toxicity, late toxicity was noted with RTOG acute toxicity criteria. Quality of life (QOL) was assessed with EORTC BR 23 questionnaire. Statistical analysis was done with SPSS v 21 and p-value < 0.05 was considered as significant. All patients received planned allocated treatment and were eligible for analysis. At treatment completion, the Grade II skin toxicity was higher in arm I compared to arm II, with 84% vs 11% (p <0.01), Grade III skin toxicity was not noted in arm II, but present in 3(11%) patients of arm I (p <0.01). The skin toxicity at 6 months was similar at 6 months with only Grade I skin toxicity. At completion of radiation, good cosmesis was noted in 8(32%) patients of arm I and 20(77%) patients of arm II, whereas fair cosmesis was observed in 17 (65%) patients of arm I and 6(23%) patients of arm II. The cosmesis at 6 months post radiation was excellent in 21(80%) patients of arm I and 23(88%) patients of arm II, and good cosmesis was seen in 5(20%) patients of arm I and 3(12%) patients of arm II. The cosmesis improved in both the arms at 6 months, and the results were comparable between the groups. There was no significant difference in subcutaneous toxicity, arm toxicity or lymphedema between the two arms at 3 and 6 months. There was no difference in QOL between two arms at 3 and 6 months. WBRT with RNI is feasible with hypofractionation and it is not associated with decreased clinical outcomes as compared to standard fractionation. Lymphedema was similar with hypofractionation. The clinical acute toxicity, cosmesis and QOL was similar with hypofractionation and standard fractionation.

Early Clinical Outcomes and Dosimetric Evaluation in Post Mastectomy Radiotherapy in Locally Advanced Breast Cancer: A Phase II Open Label Randomized Study between 3DCRT and VMAT

Post mastectomy Radiation (PMRT) is indicated as adjuvant treatment in the multimodality management of Locally Advanced Breast Cancer (LABC). Three-Dimensional Conformal Radiation (3DCRT) for PMRT is used with tangential fields for better target coverage and sparing of organs at risk (OAR). In comparison, VMAT has the potential to improve the coverage and decrease the OAR doses. We prospectively conducted a phase II randomized study comparing 3DCRT (Arm A) and VMAT (Arm B) in PMRT with regional nodal irradiation (RNI) to evaluate dosimetric and clinical differences between the two modalities. Women aged ≥ 18 years with locally advanced breast cancer undergoing MRM were recruited in the study. Forty patients were accrued after Institutional Ethics Committee approval. Contouring was done as per the standard RTOG guidelines. For 3DCRT, Planning was done with single isocenter technique. Two tangential fields with field in field were used for PTV-CW and AP-PA fields with higher AP weightage were used to cover PTV-RNI. For VMAT, two small partial arcs were used. The dose prescribed was 50 Gy in 25 fractions over 5 weeks. Contouring and planning was done on MONACO treatment planning system. Dosimetric analysis was done and compared between the arms. Clinical acute toxicity, late toxicity was noted with RTOG acute toxicity criteria. Quality of life (QOL) was assessed with EORTC BR 23 questionnaire. Statistical analysis was done with SPSS v 21 with chi square test and p-value < 0.05 was considered as significant. Between Jan 2018 to March 2019, forty patients were accrued in the study and twenty patients were randomized to each arm. All patients received planned allocated treatment and were eligible for analysis. PTV CW coverage was similar in both the arms. PTV RNI V95 coverage were better in VMAT arm (97.8%) than 3DCRT arm (94.5%) (p = <0.001). The ipsilateral lung V5 and V20 was 51.6% and 24.7% for VMAT and 47.1% and 27.8% for 3DCRT (p = 0.0185 and p = 0.167). The thyroid V45 was 51.3% for 3DCRT and 42% for VMAT arm (p = 0.018)]. The heart Dmean for 3DCRT and VMAT was 4.3Gy and 6.5Gy (p = 0.0372). There was no significant difference in skin, subcutaneous, lymphedema or lung toxicity between the two arms at 1, 3, and 6 months. There was no difference in global health status and QOL between two arms at 1, 3, and 6 months. No loco-regional recurrence was noted at 6 months. VMAT provides better coverage to lymph nodes with potential to decrease ipsilateral lung dose. The clinical acute toxicity, late toxicity and QOL was similar with VMAT and 3DCRT. A large prospective trial and longer follow-up is needed to confirm the findings.

Assessing the accuracy of treatment planning system based radiotherapy structure volumes

AbstractAim:The purpose of the present study was to assess the accuracy of radiotherapy (RT) structure volume generated by the Monaco treatment planning system (TPS) for three different computed tomography (CT) slice thicknesses. Further, this study addressed the important issue of ‘different volumes of the same RT structure shown at different places’ in the Monaco TPS. Also, the practical impact of this difference in structure volumes has been studied for brain or head and neck patients.Materials and Methods:Objects of known volumes were scanned with different CT slice thicknesses and contoured as an RT structure in Monaco TPS and two different volumes provided by the TPS for each RT structure were noted and compared with the real volumes of these objects. In addition, correlation was also assessed between TPS provided volumes and real volumes of these objects. The study was further extended to obtain correlation of volumes in cases of organs that exist in pairs (e.g., eye) in the human body.Results:Monaco TPS overestimates structure volumes except for objects with sharp corners. Although, volumes shown at different places of the same structure have nearly a linear correlation, volumes under structure table are more accurate than those shown under dose–volume histogram (DVH) statistics (total volume) table. Difference in magnitude between these two volumes has no correlation if this difference is analysed for paired organs.Findings:This study confirmed that Monaco TPS provides ‘different value at different places’ of the volume of a given contoured structure. It is recommended that this issue should be reviewed and resolved by the supplier.

Feasibility of using a single transmission factor for the Integral Quality Monitor ® on dynamic 15 MV photon beams

PurposeTo investigate the feasibility of using a single transmission factor (TF) to account for the attenuation of the iRT Systems Integral Quality Monitor (IQM) on dynamic 15 MV photon beams supported by Gafchromic EBT3 film measurements in a realistic pelvic prosthesis phantom. Materials and methodsIQM TFs for 2 × 2 to 20 × 20 cm2 15 MV photon beams produced by an Elekta Synergy linac were measured with a 0.6 cm3 cylindrical chamber inside RW3 phantom slabs. A Monaco treatment planning system (v. 5.00.00) that uses the X-ray voxel Monte Carlo algorithm was used to generate intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) plans in a computed tomography scanned-based model of the pelvic phantom. The phantom was irradiated according to the plans with and without the IQM mounted on the linac. In each case, the absorbed dose in the phantom was measured with EBT3 Gafchromic film. In a second step each plan was re-scaled to new monitor units (MUs) taking into account the IQM TF. The phantom was irradiated according to the plans that now have the re-scaled MUs. Again, film dosimetry was performed with the IQM mounted to the linac. Monaco dose values were compared with film measurements using percentage differences and gamma index criteria of 3%/3 mm. ResultsThe measured IQM TFs varied within 0.1% over the range of fields evaluated. For the treatment plans, inside the target area, dose differences ≥4% were found between Monaco and EBT3 film for plans with unscaled MUs with the IQM mounted. Plans delivered with unscaled MUs without the IQM as well as plans delivered with scaled MUs with the IQM showed dose differences within 2% between Monaco and film. In these cases, the corresponding gamma pass rate between Monaco and film data was ≥90%. ConclusionA single TF is sufficient to scale MUs of IMRT/VMAT plans so that the attenuation in IQM is taken into account for dynamic 15 MV photon beams. Dose differences between corrected plans and film measurements are then within 2%, as opposed to ≥4% when not taken into account.

Experimental validation of Monte Carlo based treatment planning system in bone density equivalent media.

IntroductionAdvanced, Monte Carlo (MC) based dose calculation algorithms, determine absorbed dose as dose to medium-in-medium (Dm,m) or dose to water-in-medium (Dw,m). Some earlier studies identified the differences in the absorbed doses related to the calculation mode, especially in the bone density equivalent (BDE) media. Since the calculation algorithms built in the treatment planning systems (TPS) should be dosimetrically verified before their use, we analyzed dose differences between two calculation modes for the Elekta Monaco TPS. We compared them with experimentally determined values, aiming to define a supplement to the existing TPS verification methodology.Materials and methodsIn our study, we used a 6 MV photon beam from a linear accelerator. To evaluate the accuracy of the TPS calculation approaches, measurements with a Farmer type chamber in a semi-anthropomorphic phantom were compared to those obtained by two calculation options. The comparison was made for three parts of the phantom having different densities, with a focus on the BDE part.ResultsMeasured and calculated doses were in agreement for water and lung equivalent density materials, regardless of the calculation mode. However, in the BDE part of the phantom, mean dose differences between the calculation options ranged from 5.7 to 8.3%, depending on the method used. In the BDE part of the phantom, neither of the two calculation options were consistent with experimentally determined absorbed doses.ConclusionsBased on our findings, we proposed a supplement to the current methodology for the verification of commercial MC based TPS by performing additional measurements in BDE material.

Application of dose-volume histogram prediction in biologically related models for nasopharyngeal carcinomas treatment planning

PurposeIn this study, we employed a gated recurrent unit (GRU)-based recurrent neural network (RNN) using dosimetric information induced by individual beam to predict the dose-volume histogram (DVH) and investigated the feasibility and usefulness of this method in biologically related models for nasopharyngeal carcinomas (NPC) treatment planning.Methods and materialsOne hundred patients with NPC undergoing volumetric modulated arc therapy (VMAT) between 2018 and 2019 were randomly selected for this study. All the VMAT plans were created using the Monaco treatment planning system (Elekta, Sweden) and clinically approved: > 98% of PGTVnx received the prescribed doses of 70 Gy, > 98% of PGTVnd received the prescribed doses of 66 Gy and > 98% of PCTV received 60 Gy. Of these, the data from 80 patients were used to train the GRU-RNN, and the data from the other 20 patients were used for testing. For each NPC patient, the DVHs of different organs at risk were predicted by a trained GRU-based RNN using the information given by individual conformal beams. Based on the predicted DVHs, the equivalent uniform doses (EUD) were calculated and applied as dose constraints during treatment planning optimization. The regenerated VMAT experimental plans (EPs) were evaluated by comparing them with the clinical plans (CPs).ResultsFor the 20 test patients, the regenerated EPs guided by the GRU-RNN predictive model achieved good consistency relative to the CPs. The EPs showed better consistency in PTV dose distribution and better dose sparing for many organs at risk, and significant differences were found in the maximum/mean doses to the brainstem, brainstem PRV, spinal cord, lenses, temporal lobes, parotid glands and larynx with P-values < 0.05. On average, compared with the CPs, the maximum/mean doses to these OARs were altered by − 3.44 Gy, − 1.94 Gy, − 1.88 Gy, 0.44 Gy, 1.98 Gy, − 1.82 Gy and 2.27 Gy, respectively. In addition, significant differences were also found in brainstem and spinal cord for the dose received by 1 cc volume with 4.11 and 1.67 Gy dose reduction in EPs on average.ConclusionThe GRU-RNN-based DVH prediction method was capable of accurate DVH prediction. The regenerated plans guided by the predicted EUDs were not inferior to the manual plans, had better consistency in PTVs and better dose sparing in critical OARs, indicating the usefulness and effectiveness of biologically related model in knowledge-based planning.

Impact of Magnetic Field on Dose Distribution in MR-Guided Radiotherapy of Head and Neck Cancer.

PurposeThis study investigates the impact of the magnetic field on plan quality and dose at the tissue–air interface in MR-guided radiotherapy of head and neck cancer.Materials and MethodsThe charts of 10 patients with hypopharyngeal carcinoma who were treated with conventional fractionated radiotherapy were collected and reviewed. The skin and tissues containing air cavities were contoured. Three plans using 9 fields of intensity-modulated radiation therapy were generated for each patient in the Monaco treatment planning system of an Elekta Unity MR-linac. The first plan was optimized without the magnetic field (plan0T). The second plan was recalculated in the presence of a 1.5-T magnetic field (plan1.5T_reCal) using the same segment shape and monitor units as the first plan. The third plan was reoptimized in the presence of a 1.5-T magnetic field (plan1.5T_reOpt) using the same cost function as the first plan. The dose to the skin and tissues containing air cavities were compared across the three types of plans. A plan-quality metric method was used to evaluate the plan quality according to the clinical requirements.ResultsThe skin dose was increased in the presence of the 1.5-T magnetic field, and the amplitude increase of plan1.5T_reOpt (ΔDmean 1.30 ± 0.42 Gy, ΔDmax 1.68 ± 1.36 Gy) was smaller than that of plan1.5T_reCal (ΔDmean 1.81 ± 0.79 Gy, ΔDmax 5.43 ± 2.26 Gy). There were no significant differences in terms of the metrics of interfaces of tissues containing air cavities except for an increased maximum dose to the larynx and trachea. The plan quality of plan1.5T_reCal (68.0 ± 9.2) was significantly worse than that of plan0T (82.2 ± 7.0), and the plan quality of plan1.5T_reOpt (80.0 ± 7.0) was similar to that of plan0T.ConclusionThe presence of a 1.5-T magnetic field had an apparent impact on the dose distribution, in particular, a significant increase in the skin dose. The plan quality of plan1.5T_reOpt was similar to that of the original plan0T when the same cost function was used.

Which Is Better for Liver SBRT: Dosimetric Comparison Between DCAT and VMAT for Liver Tumors.

Stereotactic body radiotherapy (SBRT) is currently well-adopted as a curative treatment for primary and metastatic liver tumors. Among SBRT methods, dynamic conformal arc therapy (DCAT) and volumetric-modulated arc therapy (VMAT) are the most preferred methods. In this study, we report a comparison study measuring the dose distribution and delivery efficiency differences between DCAT and VMAT for liver SBRT. All patients who were treated with SBRT for primary or metastatic liver tumors with a curative aim between January 2016 and December 2017 at DIRAMS were enrolled in the study. For all patients, SBRT plans were designed using the Monte Carlo (MC) algorithm in Monaco treatment planning system (version 5.1). The planning goals were set according to the RTOG 0813, RTOG 0915, and RTOG 1112 protocols. A plan comparison was made on the metrics of dose volume histogram, planning and delivery efficiency, monitor unit (MU), and dosimetric indices. PTV coverage was evaluated using the following: Dmean, D95%, D98%, D2%, D50%, Dmax, V95%, heterogeneity index (HI), and conformality index (CI). For DCAT and VMAT, respectively, the Dmean was 5942.8 ± 409.3 cGy and 5890.6 ± 438.8 cGy, D50% was 5968.8 ± 413.1 cGy and 5954.3 ± 405.2 cGy, and CI was 1.05 ± 0.05 and 1.03 ± 0.04. The D98% and V95% were 5580.0 ± 465.3 cGy and 20.4 ± 12.0 mL for DCAT, and 5596.0 ± 478.7 cGy and 20.5 ± 12.0 mL for VMAT, respectively. For normal liver, V40, V30, V20, V17, V5, Dmean, Dmax were evaluated for comparison. The V30, V20, and V10 were significantly higher in DCAT; other parameters of normal livers showed no statistically significant differences. For evaluation of intermediate dose spillage, D2cm(%) and R50% of DCAT and VMAT were 45.8 ± 7.9 and 5.6 ± 0.9 and 45.1 ± 6.7 and 5.5 ± 1.2, respectively. Planning and delivery efficiency were evaluated using MU, Calculation time, and Delivery time. DCAT had shorter Calculation time and Delivery time with smaller MU. MU was smaller in DCAT and the average difference was 300.1 MU. For liver SBRT, DCAT is an effective alternative to VMAT plans that could meet the planning goals proposed by the RTOG SBRT protocol and increases plan and delivery effectiveness, while also ignoring the interplay effect.

Study of out-of-field dose in photon radiotherapy: A commercial treatment planning system versus measurements and Monte Carlo simulations.

PurposeAn accurate assessment of out‐of‐field dose is necessary to estimate the risk of second cancer after radiotherapy and the damage to the organs at risk surrounding the planning target volume. Although treatment planning systems (TPSs) calculate dose distributions outside the treatment field, little is known about the accuracy of these calculations. The aim of this work is to thoroughly compare the out‐of‐field dose distributions given by two algorithms implemented in the Monaco TPS, with measurements and full Monte Carlo simulations.MethodsOut‐of‐field dose distributions predicted by the collapsed cone convolution (CCC) and Monte Carlo (MCMonaco) algorithms, built into the commercially available Monaco version 5.11 TPS, are compared with measurements carried out on an Elekta Axesse linear accelerator. For the measurements, ion chambers, thermoluminescent dosimeters, and EBT3 film are used. The BEAMnrc code, built on the EGSnrc system, is used to create a model of the Elekta Axesse with the Agility collimation system, and the space phase file generated is scored by DOSXYZnrc to generate the dose distributions (MCEGSnrc). Three different irradiation scenarios are considered: (a) a 10 × 10 cm2 field, (b) an IMRT prostate plan, and (c) a three‐field lung plan. Monaco's calculations, experimental measurements, and Monte Carlo simulations are carried out in water and/or in an ICRP110 phantom.ResultsFor the 10 × 10 cm2 field case, CCC underestimated the dose, compared to ion chamber measurements, by 13% (differences relative to the algorithm) on average between the 5% and the ≈2% isodoses. MCMonaco underestimated the dose only from approximately the 2% isodose for this case. Qualitatively similar results were observed for the studied IMRT case when compared to film dosimetry. For the three‐field lung plan, dose underestimations of up to ≈90% for MCMonaco and ≈60% for CCC, relative to MCEGSnrc simulations, were observed in mean dose to organs located beyond the 2% isodose.ConclusionsThis work shows that Monaco underestimates out‐of‐field doses in almost all the cases considered. Thus, it does not describe dose distribution beyond the border of the field accurately. This is in agreement with previously published works reporting similar results for other TPSs. Analytical models for out‐of‐field dose assessment, MC simulations or experimental measurements may be an adequate alternative for this purpose.

Experimental verification the electron return effect around spherical air cavities for the MR-Linac using Monte Carlo calculation.

Dose deposition around unplanned air cavities during magnetic resonance-guided radiotherapy (MRgRT) is influenced by the electron return effect (ERE). This is clinically relevant for gas forming close to or inside organs at risk (OARs) that lie in the path of a single beam, for example, intestinal track during pelvic treatment. This work aims to verify Monte Carlo calculations that predict the dosimetric effects of ERE around air cavities. For this, we use GafChromic EBT3 film inside poly-methyl methacrylate (PMMA) -air phantoms. Four PMMA phantoms were produced. Three of the phantoms contained centrally located spherical air cavities (0.5, 3.5, 7.5cm diameter), and one phantom contained no air. The phantoms were split to sandwich GafChromic EBT3 film in the center. The phantoms were irradiated on an Elekta Unity system using a single 10×10cm2 7-MV photon beam under the influence of a 1.5-T transverse magnetic field. The measurements were replicated using the Elekta Monaco treatment planning system (TPS). Gamma analysis with pass criteria 3%/3mm was used to compare the measured and calculated dose distributions. We also consider 3%/2mm, 2%/3mm, and 2%/2mm pass criteria for interest. The gamma analysis showed that >95% of the points agreed between the TPS-calculated and measured dose distributions, using 3%/3mm criteria. The phantom containing the largest air cavity had the lowest agreement, with most of the disagreeing points lying inside the air cavity (dose to air region). The dose effects due to ERE around spherical air cavities are being calculated in the TPS with sufficient accuracy for clinical use.

Development of a Fluence Generating Programme for Patient-Specific Quality Assurance and Calibration of an Amorphous Silicon EPID

Patient-specific quality assurance (QA) is an essential part of intensity-modulated radiotherapy (IMRT) and volumetric arc therapy (VMAT) treatments. This study aims to develop a Patient-specific QA system through the development of a fluence generating programme and utilization of amorphous silicon (aSi) electronic portal imaging device (EPID). The EPID was investigated on the dependency of dose rate, uniformity of detector sensitivity and output factor. A fluence generating programme was written using MATLAB. Five simple dynamic arc plans and one patient VMAT plan were created using the Monaco treatment planning system which were used in the programme to generate fluence maps. The accuracy of the programme was evaluated by performing gamma analysis between the generated and measured fluence. EPID signal was found to be linearly proportional to dose (1-1000 MU) and independent of dose rate. The mean uniformity ratio was 1.07 ± 0.04%. The measured fluence maps were corrected for uniformity before gamma analysis. Output factor and dose deposition were taken into account in the process. The average result of the gamma analysis passed the 95% threshold. A fluence generating programme was developed, serving as the foundation of the Patient-specific QA system using aSi EPID for IMRT/VMAT delivery in this centre.

Dose Calculation Comparisons between Three Modern Treatment Planning Systems.

Purpose:Monaco treatment planning system (TPS) version 5.1 uses a Monte-Carlo (MC)-based dose calculation engine. The aim of this study is to verify and compare the Monaco-based dose calculations with both Pinnacle3 collapsed cone convolution superposition (CCCS) and Eclipse anisotropic analytical algorithm (AAA) calculations.Materials and Methods:For this study, 18 previously treated lung and head-and-neck (HN) cancer patients were chosen to compare the dose calculations between Pinnacle, Monaco, and Eclipse. Plans were chosen from those that had been treated using the Elekta VersaHD or a Novalis Tx linac. All of the treated volumetric-modulated arc therapy plans used 6 MV or 10 MV photon beams. The original plans calculated with CCCS or AAA along with the recalculated ones using MC from the three TPS were exported into Velocity software for intercomparison.Results:To compare the dose calculations, Planning target volume (PTV) heterogeneity indexes and conformity indexes were calculated from the dose volume histograms (DVH) of all plans. While mean lung dose (MLD), lung V5 and V20 values were recorded for lung plans, the computed dose to parotids, brainstem, and mandible were documented for HN plans. In plan evaluation, percent differences of the above dosimetric values in Monaco computation were compared against each of the other TPS computations.Conclusion:It could be concluded through this research that there can be differences in the calculation of dose across different TPSs. Although relatively small, these differences could become apparent when compared using DVH. These differences most likely arise from the different dose calculation algorithms used in each TPS. Monaco employs the MC allowing it to have much more detailed calculations that result in it being seen as the most accurate and the gold standard.

Dosimetric study of the medical Agility grating system in radiotherapy of orbital lymphoma

AbstractObjectiveThe spatial location of the orbital lymphoma target area is special; improving the quality of the orbital lymphoma plan and protecting the eye are important focus areas for doctors and physicists. This study aimed to investigate the dosimetric characteristics of the Agility grating system in orbital lymphoma.MethodsA total of 10 patients with orbital lymphoma who underwent radiotherapy at the Ninth People's Hospital, affiliated with Shanghai Jiaotong University School of Medicine, from 1 May 2016 to 30 May 2018 were selected. The Monaco treatment planning system was used for calculation, and the MLCi2 and Agility grating data were selected, respectively. Dynamic intensity adjustment was carried out. In the calculation, the limit of other tissues is fixed, and only the limit of the patient's affected side crystal is changed. The limit range is changed from 4 to 20 Gy. The function is Serial, and each change is 2 Gy. The whole eye, the crystal, the optic nerve, and the target area's conformal index, homogeneity index, and planned hop count were calculated, respectively.ResultsWith increased limitation of the affected side crystal, Agility was more advantageous in the parameters of conformal index, homogeneity index, the affected side of the optic nerve, the average amounts of the affected eye and side of the eye, and the planned number of hops. The conformal index difference rate was 27.12%. After dropping to 5.11%, the difference rate of the homogeneity index decreased from 11.52% to 1.57%, and the downward trend gradually slowed down (P &lt; 0.01). There were statistically significant differences: the difference rate of the affected side optic nerve decreased from 11.99% to 1.53% (P &lt; 0.01); the mean difference rate of the affected side crystals decreased from 20.59% to 3.55% (P &lt; 0.01); and the mean value of the affected side eye was &lt;10 Gy when the crystal limit was &lt;10 Gy. The difference in learning was &gt;10 Gy, and there was no statistical difference. The calculation results of the contralateral crystal, MLCi2, are more advantageous (P &lt; 0.01), indicating there is a statistically significant difference.ConclusionThe results of Agility gratings are more dosimetric than MLCi2 gratings in the treatment of orbital lymphoma. Agility grating should be used for radiotherapy of orbital lymphoma.

PLA as a suitable 3D printing thermoplastic for use in external beam radiotherapy.

The purpose of this paper is to investigate the tissue equivalence and radiological properties of Polylactic Acid (PLA) to determine if this material is suitable for use as a 3D printing thermoplastic for radiotherapy applications. Profiles and percentage depth-dose measurements (PDDs) were analysed for photon and electron modalities with PLA samples (~ 1.25g/cm3) to determine material dosimeteric characteristics. Beam profiles and PDDs from treatment planning system (TPS) simulations, water tank measurements and radiochromic film measurements were compared. Tissue equivalence was determined through CT scanning several PLA samples and measuring the Hounsfield units (HUs) to determine relative electron density (RED), mass density and mass attenuation, these results were compared to several commercial tissue phantoms with varying properties. Geometric accuracy was tested by comparing digitally planned dimensions to physical and CT image measurements. Finally, resistance to radiation damage was tested by exposing PLA samples to several thousand monitor units (MUs) over several weeks and inspecting for damage. It was determined that PLA is a safe and effective thermoplastic for use as a patient specific bolus for both electron and photon treatment modalities. The material properties have been characterised and can be accurately modelled in the MONACO TPS.

Volumetric modulated arc therapy: a dosimetric comparison with dynamic IMRT and step-and-shoot IMRT

AbstractAim:The aim of this study was to compare volumetric modulated arc therapy (VMAT) with dynamic intensity-modulated radiation therapy (dIMRT) and step-and-shoot IMRT (ssIMRT) for different treatment sites.Materials and methods:Twelve patients were selected for the planning comparison study. This included three head and neck, three brain, three rectal and three cervical cancer patients. Total dose of 50 Gy was given for all the plans. Plans were done for Elekta synergy with Monaco treatment planning system. All plans were generated with 6 MV photons beam. Plan evaluation was based on the ability to meet the dose volume histogram, dose homogeneity index, conformity index and radiation delivery time, and monitor unit needs to deliver the prescribed dose.Results:The VMAT and dIMRT plans achieved the better conformity (CI98% = 0·965 ± 0·023) and (CI98% = 0·939 ± 0·01), respectively, while ssIMRT plans were slightly inferior (CI98% = 0·901 ± 0·038). The inhomogeneity in the planning target volume (PTV) was highest with ssIMRT with HI equal to 0·097 ± 0·015 when compared to VMAT with HI equal to 0·092 ± 0·0369 and 0·095 ± 0·023 with dIMRT. The integral dose is found to be inferior with VMAT 105·31 ± 53·6 (Gy L) when compared with dIMRT 110·75 ± 52·9 (Gy L) and ssIMRT 115 38 ± 55·1(Gy L). All the techniques respected the planning objective for all organs at risk. The delivery time per fraction for VMAT was much lower than dIMRT and ssIMRT.Findings:Our results indicate that dIMRT and VMAT provide better sparing of normal tissue, homogeneity and conformity than ssIMRT with reduced treatment delivery time.

Validation of Dolphin dosimetry in three dimensional patient-specific quality assurance programme.

The aim of this study is to commission and validate Dolphin-Compass dosimetry as a patient-specific Quality Assurance (QA) device. The advancement of radiation therapy in terms of highly conformal delivery techniques demands a novel method of patient-specific QA. Dolphin-Compass system is a dosimetry solution capable of doing different QA in radiation therapy. Dolphin, air-vented ionization detector array mounted on Versa-HD Linear Accelerator (LINAC) was used for measurements. The Compass is a dose computation algorithm which requires modelling of LINAC head similar to other Treatment Planning Systems (TPS). The dosimetry system was commissioned after measuring the required beam data. The validation was performed by comparison of treatment plans generated in Monaco TPS against the measurement data. Different types of simple, complex, static and dynamic radiation fields and highly conformal treatment plans of patients were used in this study. For all field sizes, point doses obtained from Dolphin-Compass dosimetry were in good agreement with the corresponding TPS calculated values in most of the regions, except the penumbra, outside field and at build-up depth. The results of gamma passing rates of measurements by using different Multi-leaf Collimator patterns and Intensity Modulated Radiation Therapy fluence were also found to be in good correlation with the corresponding TPS values. The commissioning and validation of dosimetry was performed with the help of various fields, MLC patterns and complex treatment plans. The present study also evaluated the efficiency of the 3D dosimetry system for the QA of complex treatment plans.

Investigation of lung tumour peripheral doses using normoxic polymer gel and film dosimetry techniques

This paper describes the investigation of lung tumour peripheral doses for 6MV, 6MV FFF, 10MV FFF and 15MV conformal arc therapy (CAT) beams calculated in the Monaco® TPS and delivered using a flattening filter free capable Elekta® AgilityTM linac. Two independent high resolution dosimetry techniques were used for investigations. Measurements were performed using the normoxic PAG polymer gel dosimeter and GAFchromicTM EBT3 film and compared against the calculated dose plane from the Monaco treatment planning system. Both measurement methodologies indicate that Monaco is overestimating the lung tumour peripheral dose for the beams investigated in this study. It is shown that when using 10MV FFF in lung for arc deliveries, there is a dosimetric compromise compared with 6MV and 6MV FFF.

Evaluation of Dose Calculation Algorithms Accuracy for Eclipse, PCRT3D, and Monaco Treatment Planning Systems Using IAEA TPS commissioning tests in a Heterogeneous Phantom

Introduction: The accuracy of dose calculation algorithm (DCA) is highly considered in the radiotherapy sequences. This study aims at assessing the accuracy of five dose calculation algorithms in tissue inhomogeneity corrections, based on the International Atomic Energy Agency TEC-DOC 1583. Material and Methods: A heterogeneous phantom was scanned using computed tomography and tests were planned on three-dimensional treatment planning systems (3D TPSs) based on IAEA TEC-DOC 1583.Doseswere measured for 6- and 18-MV photon beams with ion chambers and then the deviation between measured and calculated TPS doses were reported. The evaluated five DCAs include Monte Carlo (MC) algorithm employed by Monaco, pencil beam convolution (PBC) and anisotropic analytical algorithms (AAA) employed by Eclipse and Superposition (SP), and Clarkson algorithms employed by PCRT3D TPSs. Results: In Clarkson algorithm, low and high energy photons indicated 7.1% and 14.8% deviations out of agreement criteria, respectively. The SP, AAA, and PBC algorithms indicated 0.9%, 7.4%, and 13.8% for low energy photon and 9.5%, 21.3%, and 23.2% for high energy photon deviations out of agreement criteria, respectively. However, MC algorithm showed 1.8% and less than 1% deviations at high and low energy photons, respectively. Conclusion: The DCAs had different levels of accuracy in TPSs. Some simple DCAs, such as Clarkson, showed large deviations in some cases. Therefore, the transition to more advanced algorithms, such as MC would be desirable, particularly for the calculation in the presence of inhomogeneity or high energy beams.