A novel implementation of mARC treatment for non-dedicated planning systems using converted IMRT plans

Modulated Arc Therapy for hippocampal-avoidance whole brain radiation therapy: planning comparison with intensity modulated Radiation Therapy

This study aimed to evaluate the modulated arc therapy (mARC) technique as a planning and treatment option for hippocampal sparing whole brain radiotherapy (HS-WBRT) following the Radiation Therapy Oncology Group (RTOG) 0933 dosimetric criteria. Computed tomography (CT) and magnetic resonance imaging (MRI) were selected retrospectively for 15 patients. Two types of plans were created for each patient, namely an intensity-modulated radiation therapy (IMRT) and a mARC plan. IMRT and mARC plans were compared in terms of plan quality indices, absorbed dose to organs at risk (OARs), number of monitor units (MUs), and treatment time. All plans in both techniques were considered clinically acceptable for treatment. However, IMRT plans presented a higher conformity (p = 0.01) as well as a higher homogeneity as compared to mARC plans, but this difference was not statistically significant (p > 0.05). In terms of the preservation of the hippocampus, it was observed that the IMRT plans achieved significantly lower doses for both 100% of its volume and for its maximum dose (p < 0.001). The evaluation of the remaining OARs showed that the IMRT technique resulted in lower doses, and significant differences were observed for the following organs: left cochlea (p < 0.001), left eye (p < 0.001), right eye (p = 0.03), both lenses of the eye (p < 0.001), and right optic nerve (p = 0.02). Despite these differences, the absolute differences in all dosimetric parameters were low enough to bear any clinical relevance. A drastic (close to 65%) and significant (p < 0.001) decrease was observed in the number of MUs for the mARC plans. This resulted in a substantial decrease in treatment time (60.45%, p < 0.001). It is concluded that the mARC technique is a feasible planning and treatment solution for HS-WBRT that meets the RTOG 0933 criteria. The main advantage of using mARC over IMRT for HS-WBRT is the considerable reduction in MUs and treatment time.

Monte Carlo verification of radiotherapy treatments with CloudMC

Background

A new implementation has been made on CloudMC, a cloud-based platform presented in a previous work, in order to provide services for radiotherapy treatment verification by means of Monte Carlo in a fast, easy and economical way. A description of the architecture of the application and the new developments implemented is presented together with the results of the tests carried out to validate its performance.

Methods

CloudMC has been developed over Microsoft Azure cloud. It is based on a map/reduce implementation for Monte Carlo calculations distribution over a dynamic cluster of virtual machines in order to reduce calculation time. CloudMC has been updated with new methods to read and process the information related to radiotherapy treatment verification: CT image set, treatment plan, structures and dose distribution files in DICOM format. Some tests have been designed in order to determine, for the different tasks, the most suitable type of virtual machines from those available in Azure. Finally, the performance of Monte Carlo verification in CloudMC is studied through three real cases that involve different treatment techniques, linac models and Monte Carlo codes.

Results

Considering computational and economic factors, D1_v2 and G1 virtual machines were selected as the default type for the Worker Roles and the Reducer Role respectively. Calculation times up to 33 min and costs of 16 € were achieved for the verification cases presented when a statistical uncertainty below 2% (2σ) was required. The costs were reduced to 3–6 € when uncertainty requirements are relaxed to 4%.

Conclusions

Advantages like high computational power, scalability, easy access and pay-per-usage model, make Monte Carlo cloud-based solutions, like the one presented in this work, an important step forward to solve the long-lived problem of truly introducing the Monte Carlo algorithms in the daily routine of the radiotherapy planning process.

VMAT to arclet plan conversion in a treatment planning system : Feasibility and dosimetric relationship between VMAT, arclet, and stationary fields

AIM

The aim of this study was to make dynamic rotation treatment with mARC available for the non-dedicated Philips Pinnacle treatment planning system by converting SmartArc plans, offering insight into the relationship between SmartArc, mARC, and stationary field irradiation.

METHODS

A scripting solution is presented that can be run in the Pinnacle system. This allows for the conversion of SmartArc plans into mARC format. The dose distribution of the converted mARC plan can be evaluated both in the form of a "real" mARC plan with arclets and-as is generally done in treatment planning systems certified for mARC planning-by approximating the arclets as stationary fields. We present the proof of principle and dosimetric comparisons.

RESULTS

The converted plans were irradiated without problems. For the measured 3D dose distributions, on average over 90 % points agreed with the calculated dose distributions (mARC and stationary field plans) within the gamma criteria of 3 % deviation in the local dose, 3-mm distance to agreement, for all dose values above 10 % of the maximum. The agreement between the three calculated dose distributions (SmartArc with both converted plans) was above 87 % (above 92 % when comparing mARC with stationary fields).

CONCLUSION

Our solution offers the possibility of mARC planning in Pinnacle. The dose comparisons furthermore prove that the dosimetric differences between SmartArc and mARC, when appropriately translated, are minor.

Planning for mARC treatments with the Eclipse treatment planning system

While modulated arc (mARC) capabilities have been available on Siemens linear accelerators for almost two years now, there was, until recently, only one treatment planning system capable of planning these treatments. The Eclipse treatment planning system now offers a module that can plan for mARC treatments. The purpose of this work was to test the module to determine whether it is capable of creating clinically acceptable plans. A total of 23 plans were created for various clinical sites and all plans delivered without anomaly. The average 3%/3 mm gamma pass rate for the plans was 98.0%, with a standard deviation of 1.7%. For a total of 14 plans, an equivalent static gantry IMRT plan was also created to compare delivery time. In all but two cases, the mARC plans delivered significantly faster than the static gantry plan. We have confirmed the successful creation of mARC plans that are deliverable with high fidelity on an ARTISTE linear accelerator, thus demonstrating the successful implementation of the Eclipse mARC module.

mARC vs. IMRT radiotherapy of the prostate with flat and flattening-filter-free beam energies

BACKGROUND

There as yet exists no systematic planning study investigating the novel mARC rotational radiotherapy technique, which is conceptually different from VMAT. We therefore present a planning study for prostate cancer, comparing mARC with IMRT treatment at the same linear accelerator equipped with flat and flattening-filter-free (FFF) photon energies.

METHODS

We retrospectively re-contoured and re-planned treatment plans for 10 consecutive prostate cancer patients. Plans were created for a Siemens Artiste linear accelerator with flat 6 MV and FFF 7 MV photons, using the Prowess Panther treatment planning system. mARC and IMRT plans were compared with each other considering indices for plan quality and dose to organs at risk. All plans were exported to the machine and irradiated while measuring scattered dose by thermoluminescent dosimeters placed on an anthropomorphic phantom. Treatment times were also measured and compared.

RESULTS

All plans were found acceptable for treatment. There was no marked preference for either technique or energy from the point of view of target coverage and dose to organs at risk. Scattered dose was significantly decreased by the use of FFF energies. While mARC and IMRT plans were of very similar overall quality, treatment time could be markedly decreased both by the use of mARC and FFF energy.

CONCLUSIONS

Highly conformal treatment plans could be created both by the use of flat 6 MV and FFF 7 MV energy, using IMRT or mARC. For all practical purposes, the FFF 7 MV energy and mARC plans are acceptable for treatment, a combination of both allowing a drastic reduction in treatment time from over 5 minutes to about half this value.

Commissioning and first clinical application of mARC treatment

BACKGROUND

The modulated arc (mARC) technique has recently been introduced for Siemens ARTISTE linear accelerators. We present the first experiences with the commissioning of the system and first patient treatments.

PATIENTS AND METHODS

Treatment planning and delivery are presented for the Prowess Panther treatment planning system or, alternatively, an in-house code. Dosimetric verification is performed both by point dose measurements and in 3D dose distribution.

RESULTS

Depending on the target volume, one or two arcs can be used to create highly conformal plans. Dosimetric verification of the converted mARC plans with step-and-shoot plans shows deviations below 1 % in absolute point dose; in the 3D dose distribution, over 95 % of the points pass the 3D gamma criteria (3 % deviation in local dose and 3 mm distance to agreement for doses > 20 % of the maximum). Patient specific verification of the mARC dose distribution with the calculations has a similar pass rate. Treatment times range between 2 and 5 min for a single arc.

CONCLUSIONS

To our knowledge, this is the first report of clinical application of the mARC technique. The mARC offers the possibility to save significant amounts of time, with single-arc treatments of only a few minutes achieving comparable dose distribution to IMRT plans taking up to twice as long.