Monaco Treatment Planning System Research Articles

Bowel bag sparing in palliative radiotherapy (pRT) of rectal cancer (rCa): Tradeoff between organs at risk (OARs) and use of AI to reduce radiation oncologist (RO) workload.

e15615 Background: We retrospectively studied the potential to reduce bowel toxicity after pRT of rCa using a bowel dose (BD) minimization strategy; also its effect on dose to remaining normal tissues (NT) and pelvic bone marrow (PBM). Finally, we studied the use of AI to reduce the RO workload. Methods: 25 consecutive rCa patients (pts) previously treated with pRT were included. Their treatments were planned without consideration to BD. The following OARs were manually segmented retrospectively: Bowel Bag (BB-M) excluding PTV, PBM (PBM-M), and NT defined as the patient contour excluding PTV and BB-M. The AI-Rad Companion software was used to autosegment: Bowel Loops (BL-AI) and PBM (PBM-AI). For the 25 pts, two Pareto optimal treatment plans (5 Gy x 5) were generated with the Monaco treatment planning system. The first plan (Reference) was optimized aiming to limit dose outside the PTV. The second plan (Opt-BB-M) was optimized aiming firstly to limit BB-M dose and secondly to limit NT dose. A third plan (Opt-BL-AI) was generated for the 10 worst-off pts (in terms of BD) aiming instead to limit BL-AI dose. Two volume-at-dose (VD) metrics (V18Gy, V10Gy) were used as endpoints. Endpoint differences (ΔVD-OAR) were tested using one-sided Wilcoxon signed-rank tests. Spearman (rs) and Pearson (r) correlation coefficients were used to study correlation between variables (ΔVD-BB vs. ΔVD-BM, and ΔVD-BB vs. ΔVD-NT). Dice Similarity Coefficient (DCS) was used to compare PBM-M and PBM-AI. Results: After reoptimization, BB-M VD (V18Gy; V10Gy) was lower (p < 0.001; p < 0.001), PBM-M VD was higher (p = 0.002; p < 0.001), and NT VD was higher (p < 0.001; p < 0.001). For BB-M, ΔV18Gy and ΔV10Gy (median, min, max) were (-4, -46, 0) cm3 and (-33, -254, 0) cm3; for PBM-M: (+2, -4, +56) cm3 and (+33, -6, +189) cm3; for NT: (+10, -43, +194) cm3 and (+146, -18, +614) cm3. Table 1 presents results for the 10 worst-off pts. Medium/strong correlations were found for ΔV18Gy-BB vs. ΔV18Gy-PBM (rs = -0.72, p < 0.001; r = -0.74, p < 0.001), ΔV10Gy-BB vs. ΔV10Gy-PBM (rs = -0.66, p < 0.001; r = -0.32, p = 0.11), ΔV18Gy-BB vs. ΔV18Gy-NT (rs = -0.74, p < 0.001; r = -0.74, p < 0.001), ΔV10Gy-BB vs. ΔV10Gy-NT (rs = -0.74, p < 0.001; r = -0.51, p = 0.009). The DSC (median, min, max) for PBL was (92%, 87%, 94%). Conclusions: Bowel dose in pRT of rCa can be reduced at the expense of increasing dose to PBM and other NT. AI tools can be used effectively to limit RO workload. [Table: see text]

Validation of the Elekta iBEAM Evo couchtop modeling in the Monaco treatment planning system

IntroductionRecently, carbon fiber (CF) has prevailed as the primary material used in radiotherapy couchtops. Modern couchtops incorporate the CF sandwich design, in which two thin CF plates sandwich an air-equivalent polymeric foam. Developments in radiotherapy necessitate irradiation from posterior angles through the couchtop. However, the presence of the couchtop needs proper modeling in the Treatment Planning System (TPS) due to attenuation; otherwise, the tumor dose is reduced. In the current study, an effort was made with the intent of finding the optimum electron density (ED) values for Elekta's iBEAM Evo couchtop components (CF and Foam Core (FC)) for its proper modeling in Monaco TPS. Also, the attenuation of the beam due to the couchtop's presence was investigated. Materials and MethodsA cylindrical phantom with an ionization chamber positioned at the isocenter was utilized for the measurements. The phantom was placed centrally on the iBEAM Evo couchtop and was irradiated with an Elekta Infinity linear accelerator's 6, 10, and 15 MV photon beams. The gantry angle was set at 0o and from 120o to 180o with an increment of 10o. The same procedure was designed and followed in Monaco TPS. Measured and calculated dose values were compared by calculating percentage deviation (PD). Attenuation has also been calculated using the measurements of the experimental setup and the Monaco calculations. ResultsThe values of ED that provided the optimum agreement between measured and Monaco-calculated dose values while minimizing PD were 0.55 g/cm3 for CF, and 0.1 g/cm3 for FC. The maximum values of PD for the beams of 6, 10, and 15 MV were -0.62%, +1,78%, and +2.35% , respectively, for a 5x5 cm2 field size. Furthermore, Monaco predicted attenuation from 1.83% to 6.26% (calculated values), while from the measurements, an attenuation from 1.44% to 5.75% (measured values) regarding the posterior angles was found. Thus, good agreement was verified between the TPS calculations and experimental measurements. ConclusionsElekta's iBEAM Evo couchtop modeling was successfully validated in Monaco TPS. The couchtop's presence alters the patient's dose regarding irradiation from the posterior angles. Due to the attenuation of the beam, proper incorporation, modeling, and validation of the couchtop are necessary to improve the radiotherapy outcome and ensure that each patient receives the optimal treatment.

Evaluation of the Minimum Segment Width and Fluence Smoothing Tools for Intensity-modulated Techniques in Monaco Treatment Planning System

Purpose: This study aims to minimize monitor units (MUs) of intensity-modulated treatments in the Monaco treatment planning system while preserving plan quality by optimizing the “Minimum Segment Width” (MSW) and “Fluence Smoothing” parameters. Materials and Methods: We retrospectively analyzed 30 prostate, 30 gynecological, 15 breast cancer, 10 head and neck tumor, 11 radiosurgery, and 10 hypo-fractionated plans. Original prostate plans employed “Fluence Smoothing” = Off and were reoptimized with Low, Medium, and High settings. The remaining pathologies initially used MSW = 0.5 cm and were reoptimized with MSW = 1.0 cm. Plan quality, including total MU, delivery time, and dosimetric constraints, was statistically analyzed with a paired t-test. Results: Prostate plans exhibited the highest MU variation when changing “Fluence Smoothing” from Off to High (average ΔMU = −5.1%; P < 0.001). However, a High setting may increase overall MU when MSW = 0.5 cm. Gynecological plans changed substantially when MSW increased from 0.5 cm to 1.0 cm (average ΔMU = −29%; P < 0.001). Organs at risk sparing and planning target volumes remained within 1.2% differences. Replanning other pathologies with MSW = 1.0 cm affected breast and head and neck tumor plans (average ΔMU = −168.38, average Δt = −11.74 s, and average ΔMU = −256.56, average Δt = −15.05 s, respectively; all with P < 0.004). Radiosurgery and hypofractioned highly modulated plans did not yield statistically significant results. Conclusions: In breast, pelvis, head and neck, and prostate plans, starting with MSW = 1.0 cm optimally reduces MU and treatment time without compromising plan quality. MSW has a greater impact on MU than the “Fluence Smoothing” parameter. Plans with high modulation might present divergent behavior, requiring a case-specific analysis with MSW values higher than 0.5 cm.

MR-guided stereotactic radiation therapy for head and neck cancers

PurposeMR-guided radiotherapy (MRgRT) has the advantage of utilizing high soft tissue contrast imaging to track daily changes in target and critical organs throughout the entire radiation treatment course. Head and neck (HN) stereotactic body radiation therapy (SBRT) has been increasingly used to treat localized lesions within a shorter timeframe. The purpose of this study is to examine the dosimetric difference between the step-and-shot intensity modulated radiation therapy (IMRT) plans on Elekta Unity and our clinical volumetric modulated arc therapy (VMAT) plans on Varian TrueBeam for HN SBRT. MethodFourteen patients treated on TrueBeam sTx with VMAT treatment plans were re-planned in the Monaco treatment planning system for Elekta Unity MR-Linac (MRL). The plan qualities, including target coverage, conformity, homogeneity, nearby critical organ doses, gradient index and low dose bath volume, were compared between VMAT and Monaco IMRT plans. Additionally, we evaluated the Unity adaptive plans of adapt-to-position (ATP) and adapt-to-shape (ATS) workflows using simulated setup errors for five patients and assessed the outcomes of our treated patients. ResultsMonaco IMRT plans achieved comparable results to VMAT plans in terms of target coverage, uniformity and homogeneity, with slightly higher target maximum and mean doses. The critical organ doses in Monaco IMRT plans all met clinical goals; however, the mean doses and low dose bath volumes were higher than in VMAT plans. The adaptive plans demonstrated that the ATP workflow may result in degraded target coverage and OAR doses for HN SBRT, while the ATS workflow can maintain the plan quality. ConclusionThe use of Monaco treatment planning and online adaptation can achieve dosimetric results comparable to VMAT plans, with the additional benefits of real-time tracking of target volume and nearby critical structures. This offers the potential to treat aggressive and variable tumors in HN SBRT and improve local control and treatment toxicity.

Technical note: A simple method for patient-specific quality assurance for lateral targets on a 1.5 T MR-Linac.

The Elekta Unity magnetic resonance (MR) linac is limited to longitudinal couch motion and a sagittal-only laser, which restricts the ability to perform patient-specific quality assurance (PSQA) intensity-modulated radiotherapy (IMRT) measurements for very lateral targets. This work introduces a simple method to perform PSQA using the Sun Nuclear ArcCheck-MR phantom at left and right lateral positions without additional equipment or in-house construction. The proposed setup places the center of the phantom 1.3cm vertical and 12.9cm lateral to isocenter in either the left or right direction. Computed tomography (CT) scans are used to simulate the setup and create a QA plan template in the Monaco treatment planning system (TPS). The workflow is demonstrated for four patients, with an average axial distance from the center of the bore to the planning target volume (PTV) of 12.4cm. Gamma pass rates were above 94% for all plans using global 3%/2mm gamma criterion with a 10% threshold. Setup uncertainties are slightly larger for the proposed lateral setup compared to the centered setup on the Elekta platform (∼1mm compared to ∼0.5mm), but acceptable pass rates are achievable without optimizing shifts in the gamma analysis software. In general, adding the left and right lateral positions increases the axial area in the bore encompassed by the cylindrical measurement array by 147%, substantially increasing the flexibility of measurements for offset targets. Based on this work, we propose using the lateral QA setup if the closest distance to the PTV edge from isocenter is larger than the array radius (10.5cm) or the percent of the PTV encompassed by the diode array would be increased with the lateral setup compared to the centered setup.

A technique for creating wedge-shaped isodose distributions using multileaf collimators in the Monaco treatment planning system

A technique for creating wedge-shaped isodose distributions using multileaf collimators in the Monaco treatment planning system

First experience with the Monaco treatment planning system scripting application programming interface

First experience with the Monaco treatment planning system scripting application programming interface

Evolution of dosimetric treatment planning for pediatric total lymphoid irradiation (TLI): a single-institution experience.

Total lymphoid irradiation (TLI) is a conditioning regimen in allogeneic hematopoietic stem cell transplantation (allo-HSCT) which may reduce long-term toxicities attributed to other techniques, such as total body irradiation (TBI). At our institution, TLI treatments were first planned with the three-dimensional conformal radiation therapy (3D-CRT) technique and later with volumetric modulated arc therapy (VMAT). With the recent availability of a basic helical tomotherapy (HT), the possible dosimetric gain of the latter for TLI is studied. 22 pediatric patients were planned for VMAT and HT, prescribed to 8 Gy in 4 fractions. VMAT was planned with template based on a single cost function, using the Monaco treatment planning system (TPS). HT plans were planned using Accuray Precision TPS for a basic HT without the dynamic jaws feature or VOLO-Ultra algorithm. Plan quality was analyzed based on four quality indices, mean and maximum doses to planning target volume (PTV) and organs at risk (OARs), dose gradient and integral doses. Differences were analyzed with Wilcoxon signed-rank test. HT plans resulted in improved conformity (CI) and homogeneity indices (HI) (p < 0.05) but less steep dose gradient (p = 0.181). VMAT plans created larger areas with high doses within the PTV, while comparable doses to OARs, except mainly for the spinal marrow, for which a reduction of 37.7% in D2% was obtained (p < 0.05). Integral dose for non-tumor tissue was 11.3% lower with the VMAT template (p < 0.05). HT achieves better conformity and homogeneity even without its more advanced features. Nevertheless, the VMAT template achieves dosimetric results close to those of HT, both with similar clinical outcome.

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.

Evaluating the performance of automated external contouring tool on dose calculation of treatment planning system

Abstract Introduction The main goal of radiation therapy is to eradicate all cancer cells and minimize the damage to healthy tissues around the tumour. Treatment planning systems are used to predict the outcome of the treatment in terms of dose distribution prior to the treatment. One of the most reliable dose calculation algorithms is Monte Carlo. The aim of this study is to evaluate the performance of automated external contouring tool on dose calculation using Monte Carlo algorithm. Materials and methods The external contour of thorax phantom was created by automated tools of Monaco treatment planning system, and then, the IAEA-TECDOC-1583 quality assurance tests were created. Then, the treatment plans were delivered to the phantom, and the dose was measured by the Farmer ionization chamber at specific points. The external contour was corrected according to the source surface distances (SSD) which are mentioned in TECDOC-1583, and the dose was re-calculated. Finally, a comparison was made between the results. Results Dosimetric tests of TECDOC-1583 showed the errors ranged from −2·8% to +2·5%. In case of editing external contour and omitting fluctuations, the errors were decreased. The comparisons indicated that the most significant variation occurred in test 4 and the least changes were related to the tests 1 and 3. Conclusions The results of the study showed that the fluctuations of the external contour affect the calculated volume of the phantom and thus the dose. In order to obtain correct results, automated external contouring tools should be used with the correct instructions and re-checked before treatment planning.

Multi-institutional investigation into the robustness of intra-cranial multi-target stereotactic radiosurgery plans to delivery errors.

The use of modulated techniques for intra-cranial stereotactic radiosurgery (SRS) results in highly modulated fields with small apertures, which may be susceptible to uncertainties in the delivery device. This study aimed to quantify the impact of simulated delivery errors on treatment plan dosimetry and how this is affected by treatment planning system (TPS), plan geometry, delivery technique, and plan complexity. A beam modelling error was also included as context to the dose uncertainties due to treatment delivery errors. Delivery errors were assessed for multiple-target brain SRS plans obtained through the Trans-Tasman Radiation Oncology Group (TROG) international treatment planning challenge (2018). The challenge dataset consisted of five intra-cranial targets, each with a prescription of 20Gy. Of the final dataset of 54 plans, 51 were created using the volumetric modulated arc therapy (VMAT) technique and three used intensity modulated arc therapy (IMRT). Thirty-five plans were from the Varian Eclipse TPS, 17 from Elekta Monaco TPS, and one plan each from RayStation and Philips Pinnacle TPS. The errors introduced included: monitor unit calibration errors, multi-leaf collimator (MLC) bank offset, single MLC leaf offset, couch rotations, and collimator rotations. Dosimetric leaf gap (DLG) error was also included as a beam modelling error. Dose to targets was assessed via dose covering 98% of planning target volume (PTV) (D98%), dose covering 2% of PTV (D2%), and dose covering 99% of gross tumor volume (GTV) (D99%). Dose to organs at risk (OARs) was assessed using the volume of normal brain receiving 12Gy (V12Gy), mean dose to normal brain, and maximum dose covering 0.03cc brainstem (D0.03cc). Plan complexity was also assessed via edge metric, modulation complexity score (MCS), mean MLC gap, mean MLC speed, and plan modulation (PM). PTV D98% showed high robustness on average to most errors with the exception of a bank shift of 1.0mm and large rotational errors ≥1.0° for either the couch or collimator. However, in some cases, errors close to or within generally accepted machine tolerances resulted in clinically relevant impacts. The greatest impact upon normal brain V12Gy, mean dose to normal brain, and D0.03cc brainstem was found for DLG error in alignment with other recent studies. All delivery errors had on average a minimal impact across these parameters. Comparing plans from the Monaco TPS and the Eclipse TPS, showed a lesser increase to V12Gy, mean dose to normal brain, and D0.03cc brainstem for Monaco plans (p<0.01) when DLG error was simulated. Monaco plans also correlated to lower plan complexity. Using Spearman's correlation coefficient (r) a strong negative correlation (r≤-0.8) was found between the mean MLC gap and dose to OARs for DLG errors. Reducing MLC complexity and using larger mean MLC gaps is recommended to improve plan robustness and reduce sensitivity to delivery and modelling errors. For cases in which the calculated dose distribution or dose indices are close to the clinically acceptable limits, this is especially important.

A transformer-based hierarchical registration framework for multimodality deformable image registration.

Deformable image registration (DIR) between daily and reference images is fundamentally important for adaptive radiotherapy. In the last decade, deep learning-based image registration methods have been developed with faster computation time and improved robustness compared to traditional methods. However, the registration performance is often degraded in extra-cranial sites with large volume containing multiple anatomic regions, such as Computed Tomography (CT)/Magnetic Resonance (MR) images used in head and neck (HN) radiotherapy. In this study, we developed a hierarchical deformable image registration (DIR) framework, Patch-based Registration Network (Patch-RegNet), to improve the accuracy and speed of CT-MR and MR-MR registration for head-and-neck MR-Linac treatments. Patch-RegNet includes three steps: a whole volume global registration, a patch-based local registration, and a patch-based deformable registration. Following a whole-volume rigid registration, the input images were divided into overlapping patches. Then a patch-based rigid registration was applied to achieve accurate local alignment for subsequent DIR. We developed a ViT-Morph model, a combination of a convolutional neural network (CNN) and the Vision Transformer (ViT), for the patch-based DIR. A modality independent neighborhood descriptor was adopted in our model as the similarity metric to account for both inter-modality and intra-modality registration. The CT-MR and MR-MR DIR models were trained with 242 CT-MR and 213 MR-MR image pairs from 36 patients, respectively, and both tested with 24 image pairs (CT-MR and MR-MR) from 6 other patients. The registration performance was evaluated with 7 manually contoured organs (brainstem, spinal cord, mandible, left/right parotids, left/right submandibular glands) by comparing with the traditional registration methods in Monaco treatment planning system and the popular deep learning-based DIR framework, Voxelmorph. Evaluation results show that our method outperformed VoxelMorph by 6 % for CT-MR registration, and 4 % for MR-MR registration based on DSC measurements. Our hierarchical registration framework has been demonstrated achieving significantly improved DIR accuracy of both CT-MR and MR-MR registration for head-and-neck MR-guided adaptive radiotherapy.

Validation of a 2D dose verification systemfor intensity-modulated arc therapy

ObjectiveThe measured dose was shown to be dependent on the angle of beam incidence and influenced by couch absorption when a 2D detector was used in a stationary phantom. The use of a 2D array (MatriXX) in combination with a solid water phantom (RW3) dose verification system was explored, which could take into account the couch absorption influences, generate correction factors (CFs) for each detector element, and also calibrate the measured dose for accurate validation of intensity-modulated arc therapy (IMAT) treatment plans. MethodsBased on the introduction of a homogeneous treatment bed model in the Monaco treatment planning system, CFs(θ) were constructed for all incidence angles using 6 MV photon lines in a 28 cm × 28 cm field for MatriXX at different field incidence angles (0°–360°) as a relative ratio of simulated and measured values. The accuracy of the 2D array in combination with the solid water phantom (MatriXX/RW3) was systematically investigated by verifying 12 IMAT plans with and without CFs. In addition, the resulting assessments were evaluated by 40 additional IMAT plans of different tumor sites, using the COMPASS three-dimensional (3D) dose validation device measurements as a benchmark. ResultsAfter correction based on CFs(θ), the effect of the mean pass rates (3%/3 mm) of the MatriXX 2D array for 12 IMAT plan QA can be seenan explicit improvement of 6.1% was observed with the CFs(θ). The average pass rate increased from 92.0% to 98.1%, and the additional 40 IMAT plans QA γ(3mm/3%) matched well between COMPASS and the measurements for MatriXX/RW3, with CFs(θ)'s of 98.4 ± 1.5 vs. 99.1 ± 0.9 for the phantom plans. For different tumor sites, the cervical, thoracic, and abdominal cases for the 3D COMPASS validation devices were 97.9 ± 1.5 vs. 99.4 ± 0.3, 99.1 ± 0.9 vs. 98.6 ± 1.6, and 98.7 ± 0.9 vs. 99.3 ± 0.7, respectively, with P = 0.051, 0.420, and 0.175. For head tumors, the 2D MatriXX validation pass rate was slightly lower than 3D COMPASS (97.7 ± 2.0 vs. 99.2 ± 0.5, P = 0.048). ConclusionsThe combination of MatriXX with the solid water RW3 phantom and CFs(θ)'s incorporation of the main couch model (iBEAM evo Couchtop EP) proved to be a fast and reliable method for pre-treatment verification of arc therapy with sufficient accuracy. Slight deviations were found for patients with head tumors treated with the treatment bed extension plate assembly iBEAM® evo Extension 415. These could be minimized by constructing the extension plate couch model and then reconstructing the MatriXX/RW3 calibration factor.

Transmission probability filter optimization for Agility MLC in Monaco treatment planning system.

In the Monte Carlo-based treatment planning system (TPS) Monaco, transmission probability filters (TPF) are utilized to describe the transmission through the multi leaf collimator (MLC). By having knowledge of the TPF parameters for various photon beam energies, adjusting the MLC transmission parameters becomes easier, enhancing the accuracy of the Monte Carlo algorithm in achieving a dose distribution that closely aligns with the irradiated dose at the Versa HD linear accelerator (linac). The objective of this study was to determine the TPF parameters for 6MV, 10MV, 6MV flattening filter free (FFF) and 10MV FFF for a Versa HD linac equipped with Agility MLC. The TPF parameters were adjusted using point dose measurements and vendor-provided fields specifically designed to fine-tune the MLC. After adjusting the TPF parameters, a gamma passing rate (GPR) analysis was conducted on 25 treatment plans to ensure that the Monte Carlo model, with the updated TPF parameters, accurately matched the actual linac delivery. The TPF values ranged from 0.0018 to 0.0032 for leaf transmission and 1.15 to 1.25 for Leaf Tip leakage across the different energies. The average GPR ranged from 97.8% for 10MV FFF to 98.5% for 6MV photon energies. Additionally, the TPF parameters for 6MV obtained in this study were consistent with previously published TPF values for 6MV photon energy. Hence, it was concluded that optimizing the TPF does not need to be performed for every individual Versa HD linac with Agility MLC. Instead, the published parameters can be applied to other Versa HD linacs to enhance clinical accuracy. In conclusion, this study determined the TPF parameters for 6MV and previously unpublished photon energies 10MV, 6MV FFF and 10MV FFF. These parameters can be easily transferred to other facilities, resulting in improved agreement between the dose distribution from the TPS and the linac.

Dosimetric impact of hollow intraoral stents for head and neck cancer radiotherapy: A phantom study.

To investigate the dosimetric impact of the calculation boundaries and dose calculation algorithms of radiotherapy in head and neck cancer patients with an opened oral cavity connected to the exterior by a hollow intraoral positioning stent. A homemade silicone phantom with an opened oral cavity was placed in a CIRS head phantom to model head and neck cancer patients with a hollow intraoral positioning stent. 3D-CRT plans were designed on CT images of the phantom in Monaco and Pinnacle3 treatment planning systems (TPSs) with the same beam parameters. The default boundary and manually extrapolated boundary were both adopted in these two TPSs to explore the dosimetric impact on treatment plans. The nanoDot™ optically stimulated luminescence dosimeters (OSLDs) were chosen to measure the planned dose surrounding the oral cavity of the head phantom after calibration. The doses in the air cavity and two measuring points at the joint area were dramatically changed from 0.0, 92.4 and 148.8 cGy to 177.8, 244.2 and 244.1 cGy in Monaco after adopting the extrapolated boundary. While the calculated doses at the same place were changed from 61.2, 143.7 and 198.3 cGy to 175.4, 234.7 and 233.2 cGy in Pinnacle3 with a similar calculation boundary. For the Monaco TPS, the relative errors compared to the OSLD measured doses were 2.94±1.93%, 0.53±8.64%, 2.65±1.87% and 3.93±1.69% at 4 measuring positions. In contrast, the relative errors 4.03±1.93%, 4.85±8.64%, 7.61±1.87% and 5.61±1.69% were observed in Pinnacle3 . The boundary setting of an opened oral cavity in TPSs has a significant dosimetric impact on head and neck cancer radiotherapy. An extrapolated boundary should be manually set up to include the whole oral cavity in the dose calculation domain to avoid major dose deviations.

Comparison of Different Dosimetric Indices for Volumetric Arc Modulated Treatment Planning Using 2 Different Treatment Planning Systems: A Feasibility Study for Total Body Irradiation

Objective: To compare two different treatment planning systems (TPSs) for plan quality and to check the feasibility of VMAT TBI on the Elekta linear accelerator ‘Versa HD’. Methods: Ten clinical VMAT TBI plans were replanned in Monaco TPS version 5 for retrospective dosimetric analysis and to check the feasibility of treatment delivery in Elekta Versa HD. A dose of 12 Gy in 6 fractions was prescribed to cover 95% PTV. The OARs were the lungs, kidneys, heart, liver, and brain. Dosimetric optimization and calculation were performed in Monaco TPS with a statistical uncertainty of 1%, 2 mm grid. The chosen criterion for plan evaluation and comparison was based on plan quality, dosimetric indices like conformity and homogeneity index, and OAR doses. The comparison of time for optimization, monitor units, and beam on time was also analyzed. Pre-treatment verification using Octavious phantom and gamma analysis using Low’s method with a dose difference of 3% and distance to agreement 3mm criteria was done. The dosimetry of 2 VMAT TBI plans were compared using Wilcoxon signed rank test. Result: The calculated average maximum and mean doses of the PTV were 14.3321Gy and 12.235Gy for eclipse; and 14.428Gy and 12.198Gy for the Monaco system, respectively. The planning time in Monaco was approx. 4.5–6hrs compared to 14–18hrs for Eclipse TPS. Statistically significant difference was observed between the results of 2 TPSs in terms of monitor units, mean doses to lungs, kidneys, heart, and liver and planning time (P &lt; 0.05). However, calculated p values for HI, CI, and brain for both VMAT TBI plans were not statistically different. Conclusion: The study showed the feasibility of VMAT TBI for VERSA HD as it offers faster, better optimization in a single target compared to the Eclipse.

High-resolution entry and exit surface dosimetry in a 1.5 T MR-linac

The magnetic field of a transverse MR-linac alters electron trajectories as the photon beam transits through materials, causing lower doses at flat entry surfaces and increased doses at flat beam-exiting surfaces. This study investigated the response of a MOSFET detector, known as the MOSkin™, for high-resolution surface and near-surface percentage depth dose measurements on an Elekta Unity. Simulations with Geant4 and the Monaco treatment planning system (TPS), and EBT-3 film measurements, were also performed for comparison. Measured MOSkin™ entry surface doses, relative to Dmax, were (9.9 ± 0.2)%, (10.1 ± 0.3)%, (11.3 ± 0.6)%, (12.9 ± 1.0)%, and (13.4 ± 1.0)% for 1 × 1 cm2, 3 × 3 cm2, 5 × 5 cm2, 10 × 10 cm2, and 22 × 22 cm2 fields, respectively. For the investigated fields, the maximum percent differences of Geant4, TPS, and film doses extrapolated and interpolated to a depth suitable for skin dose assessment at the beam entry, relative to MOSkin™ measurements at an equivalent depth were 1.0%, 2.8%, and 14.3%, respectively, and at a WED of 199.67 mm at the beam exit, 3.2%, 3.7% and 5.7%, respectively. The largest measured increase in exit dose, due to the electron return effect, was 15.4% for the 10 × 10 cm2 field size using the MOSkin™ and 17.9% for the 22 × 22 cm2 field size, using Geant4 calculations. The results presented in the study validate the suitability of the MOSkin™ detector for transverse MR-linac surface dosimetry.

Dosimetric effects of the custom dose iteration times on stereotactic radiotherapy for lung cancer

PurposeTo evaluate the dosimetric effects of the custom dose iteration function in the Monaco 6.0 planning system on stereotactic radiotherapy for lung cancer. MethodsUsing the custom dose iterative function segment shape optimization (SSO) times in the Monaco 6.0 treatment planning system, the iterative times were set as 3, 5, 8, 10, and 12, respectively. Five volumetric modulated arc stereotactic body radiation therapy (SBRT) plans were made for each patient, and other optimization parameters and optimization functions were kept consistent. The dose volume histogram (DVH) statistical table was used to evaluate the dose of the target area and organs at risk (OAR). Statistical analysis was performed using SPSS 25 software, and the results were statistically different when p < 0.05. ResultsFor the target area dose analysis, SSO8, SSO10, and SSO12 groups showed similar results, significantly better than both SSO3 and SSO5 groups (p < 0.05). With the increase in the times of SSO, the protection of the heart was better, except for SSO3, the maximum dose of the esophagus and V47Gy of great vessels were significantly lower than SSO5 in all groups. The mean dose of heart was significantly lower in SSO10 and SSO12 than SSO5 (p < 0.05). There was no significant difference in other OAR among the groups. The optimization time (OT) of each group was statistically different, the maximum OT exceeded 1000s, the maximum deviation between groups exceeded 600s, and the OT increased significantly with the times of SSO (p < 0.05). There was no statistically significant difference between the 5 groups of monitor unit (MU), and segment was not significantly different between the groups except SSO3 which was significantly higher than SSO5 (p < 0.05). The delivery time (DT) was statistically different between the groups except for SSO3. ConclusionsIn the treatment of left-sided lung cancer patients with volumetric modulated arc SBRT, considering both calculation accuracy and clinical treatment efficiency, SSO times of 8 is recommended for designing SBRT for lung cancer with the Monaco treatment planning system.

Evaluation of Radiation Treatment Planning Algorithms in IMRT and VMAT: A Comparative Dosimetric Study in Lung Equivalent Heterogeneous Medium.

In Radiotherapy, computation of dose is important since in a small field with heterogeneity, dose is usually computed with discrepancies. The present study was aimed to evaluate the dosimetry of treatment planning algorithms in lung equivalent heterogeneous medium for Volumetric Modulated Arc Therapy (VMAT) with step and shoot Intensity-Modulated Radiation Therapy (ss-IMRT), and dynamic Intensity-Modulated Radiation Therapy (d-IMRT). In this experimental study, Computerized Imaging Reference System (CIRS) phantom was used with an inhomogeneous Racemosa wood cylinder for two types of tumors, namely, Left Lung Central Tumor (LCT) and Left Lung Peripheral Tumor (LPT) in the CIRS left lung cavity. The computed tomography (CT) datasets were employed with the generation of VMAT, d-IMRT and ss-IMRT plans for the LCT and LPT irradiated with 6 MV photon beams. In this study, the accuracy and efficacy of two algorithms: Monte Carlo (MC) and the Pencil Beam (PB), from the Monaco treatment planning system (TPS), were tested by using Gafchromic EBT3 films and CIRS thorax phantom. Regardless of treatment techniques, both algorithms exhibited higher divergence in LPT than LCT. In both LCT and LPT, the highest deviation was near the tumor-lung junction. However, the deviation was higher in the PB algorithm than MC algorithm, with a minimally acceptable variation of -0.8%. The MC algorithm shows more consistency for EBT3 measured dose in lung equivalent heterogeneous medium. However, accurate dose predictions are complicated due to electronic disequilibrium within and at the interface of inhomogeneity. These constraints may cause variations from the anticipated outcomes of the treatments.

An ultra-fast deep-learning-based dose engine for prostate VMAT via knowledge distillation framework with limited patient data

Objective. Deep-learning (DL)-based dose engines have been developed to alleviate the intrinsic compromise between the calculation accuracy and efficiency of the traditional dose calculation algorithms. However, current DL-based engines typically possess high computational complexity and require powerful computing devices. Therefore, to mitigate their computational burdens and broaden their applicability to a clinical setting where resource-limited devices are available, we proposed a compact dose engine via knowledge distillation (KD) framework that offers an ultra-fast calculation speed with high accuracy for prostate Volumetric Modulated Arc Therapy (VMAT). Approach. The KD framework contains two sub-models: a large pre-trained teacher and a small to-be-trained student. The student receives knowledge transferred from the teacher for better generalization. The trained student serves as the final engine for dose calculation. The model input is patient computed tomography and VMAT dose in water, and the output is DL-calculated patient dose. The ground-truth \\dose was computed by the Monte Carlo module of the Monaco treatment planning system. Twenty and ten prostate cases were included for model training and assessment, respectively. The model’s performance (teacher/student/student-only) was evaluated by Gamma analysis and inference efficiency. Main results. The dosimetric comparisons (input/DL-calculated/ground-truth doses) suggest that the proposed engine can effectively convert low-accuracy doses in water to high-accuracy patient doses. The Gamma passing rate (2%/2 mm, 10% threshold) between the DL-calculated and ground-truth doses was 98.64 ± 0.62% (teacher), 98.13 ± 0.76% (student), and 96.95 ± 1.02% (student-only). The inference time was 16 milliseconds (teacher) and 11 milliseconds (student/student-only) using a graphics processing unit device, while it was 936 milliseconds (teacher) and 374 milliseconds (student/student-only) using a central processing unit device. Significance. With the KD framework, a compact dose engine can achieve comparable accuracy to that of a larger one. Its compact size reduces the computational burdens and computing device requirements, and thus such an engine can be more clinically applicable.