IOeRT conventional and FLASH treatment planning system implementation exploiting fast GPU Monte Carlo: The case of breast cancer

Partial breast irradiation for the treatment of early-stage breast cancer patients can be performed by means of Intra Operative electron Radiation Therapy (IOeRT). One of the main limitations of this technique is the absence of a treatment planning system (TPS) that could greatly help in ensuring a proper coverage of the target volume during irradiation. An IOeRT TPS has been developed using a fast Monte Carlo (MC) and an ultrasound imaging system to provide the best irradiation strategy (electron beam energy, applicator position and bevel angle) and to facilitate the optimisation of dose prescription and delivery to the target volume while maximising the organs at risk sparing. The study has been performed in silico, exploiting MC simulations of a breast cancer treatment. Ultrasound-based input has been used to compute the absorbed dose maps in different irradiation strategies and a quantitative comparison between the different options was carried out using Dose Volume Histograms. The system was capable of exploring different beam energies and applicator positions in few minutes, identifying the best strategy with an overall computation time that was found to be completely compatible with clinical implementation. The systematic uncertainty related to tissue deformation during treatment delivery with respect to imaging acquisition was taken into account. The potential and feasibility of a GPU based full MC TPS implementation of IOeRT breast cancer treatments has been demonstrated in-silico. This long awaited tool will greatly improve the treatment safety and efficacy, overcoming the limits identified within the clinical trials carried out so far.

New Advantage in Stereotactic Treatment of Lung and Pancreatic Cancer. Performance of Ultra-High Energy Electron (VHEE) Therapy Adjuvanted to the FLASH Effect: Clinical Implications and Treatment Plans Analysis

PURPOSE/OBJECTIVE(S)

Very High-Energy Electron (VHEE) beams delivered at ultra-high dose rates and hence profiting from the FLASH effect, may be a viable alternative to conventional treatment plans for the treatment of deep-seated tumors. Experimental data support the evidence of a considerable normal tissue sparing effect when treatments are delivered with dose rates much larger (100 times or more) compared to the conventional ones. Lung cancer and pancreatic cancer are considered the two biggest cancer killers. We urgently need more research in these areas, more awareness that support improvement in treatment strategies. To evaluate the potential of FLASH VHEE irradiation in these two clinical situations, we investigated the achievable sparing of healthy tissues and critical dose-limiting structures, with the goal of performing a higher dose prescription.

MATERIALS/METHODS

The study on the potential of VHEE for the stereotactic treatment of pancreatic and lung lesions was carried out on two clinical cases treated with Volumetric Modulated Arc Therapy (VMAT) techniques at University Hospital Campus Bio-Medico of Rome. The Planning Target Volume (PTV) was identified and the constraints on the Organs at Risk (OAR) and details on the irradiation approach were defined. The VHEE plan was designed to optimize the dose delivery to best activate the modelled FLASH effect based on the current experimental knowledge. In particular the impact on a dose threshold to activate the effect was studied. The VHEE treatment plan was based on an accurate Monte Carlo simulation of the electrons interactions and the results achievable with different FLASH effect models were studied. The simulation allowed the estimation of dose maps, which were used as input to an optimization algorithm that modified the fluence of each beam to meet treatment prescriptions in terms of dose to PTV. At the end the VHEE DVH plans were compared to VMAT plans.

RESULTS

The results demonstrated that FLASH therapy with VHEE beams of 70-130 MeV, could represent a promising alternative to standard radiotherapy allowing a comparable sparing of the healthy tissues. In the case of pancreatic cancer, the Dose Volume Histograms (DVH) showed how such a technique can be effective in sparing the duodenum. In case of lung cancers, the result showed how pulmonary tissue sparing can lead to a substantial reduction of pulmonary toxicity in comparison with the VMAT technique.

CONCLUSION

In the case of pancreatic cancer and assuming a non-negligible contribution from the FLASH effect, the DVH showed how the duodenum healthy tissue sparing could allow a higher dose to be prescribed at the target while keeping the constraints respected, improving the therapeutic ratio. In the case of lung cancer, the advantages of the technique are additionally increased by the significant benefit that could be related to the treatment delivery time reduction (<1s) and to the corresponding advantage coming from a reduced organ movement that translates in a lower risk of lung toxicity.

GPU-accelerated Monte Carlo simulation of electron and photon interactions for radiotherapy applications

Objective. The Monte Carlo simulation software is a valuable tool in radiation therapy, in particular to achieve the needed accuracy in the dose evaluation for the treatment plans optimisation. The current challenge in this field is the time reduction to open the way to many clinical applications for which the computational time is an issue. In this manuscript we present an innovative GPU-accelerated Monte Carlo software for dose valuation in electron and photon based radiotherapy, developed as an update of the FRED (Fast paRticle thErapy Dose evaluator) software.Approach. The code transports particles through a 3D voxel grid, while scoring their energy deposition along their trajectory. The models of electromagnetic interactions in the energy region between 1 MeV-1 GeV available in literature have been implemented to efficiently run on GPUs, allowing to combine a fast tracking while keeping high accuracy in dose assessment. The FRED software has been bench-marked against state-of-art full MC (FLUKA, GEANT4) in the realm of two different radiotherapy applications: Intra-Operative Radio Therapy and Very High Electron Energy radiotherapy applications.Results. The single pencil beam dose-depth profiles in water as well as the dose map computed on non-homogeneous phantom agree with full-MCs at 2% level, observing a gain in processing time from 200 to 5000.Significance. Such performance allows for computing a plan with electron beams in few minutes with an accuracy of ∼%, demonstrating the FRED potential to be adopted for fast plan re-calculation in photon or electron radiotherapy applications.

Perspectives in linear accelerator for FLASH VHEE: Study of a compact C-band system

PURPOSE

In order to translate the FLASH effect in clinical use and to treat deep tumors, Very High Electron Energy irradiations could represent a valid technique. Here, we address the main issues in the design of a VHEE FLASH machine. We present preliminary results for a compact C-band system aiming to reach a high accelerating gradient and high current necessary to deliver a Ultra High Dose Rate with a beam pulse duration of 3μs.

METHODS

The proposed system is composed by low energy high current injector linac followed by a high acceleration gradient structure able to reach 60-160 MeV energy range. To obtain the maximum energy, an energy pulse compressor options is considered. CST code was used to define the specifications RF parameters of the linac. To optimize the accelerated current and therefore the delivered dose, beam dynamics simulations was performed using TSTEP and ASTRA codes.

RESULTS

The VHEE parameters Linac suitable to satisfy FLASH criteria were simulated. Preliminary results allow to obtain a maximum energy of 160 MeV, with a peak current of 200 mA, which corresponds to a charge of 600 nC.

CONCLUSIONS

A promising preliminary design of VHEE linac for FLASH RT has been performed. Supplementary studies are on going to complete the characterization of the machine and to manufacture and test the RF prototypes.

Inter-fractional monitoring of [Formula: see text]C ions treatments: results from a clinical trial at the CNAO facility

The high dose conformity and healthy tissue sparing achievable in Particle Therapy when using C ions calls for safety factors in treatment planning, to prevent the tumor under-dosage related to the possible occurrence of inter-fractional morphological changes during a treatment. This limitation could be overcome by a range monitor, still missing in clinical routine, capable of providing on-line feedback. The Dose Profiler (DP) is a detector developed within the INnovative Solution for In-beam Dosimetry in hadronthErapy (INSIDE) collaboration for the monitoring of carbon ion treatments at the CNAO facility (Centro Nazionale di Adroterapia Oncologica) exploiting the detection of charged secondary fragments that escape from the patient. The DP capability to detect inter-fractional changes is demonstrated by comparing the obtained fragment emission maps in different fractions of the treatments enrolled in the first ever clinical trial of such a monitoring system, performed at CNAO. The case of a CNAO patient that underwent a significant morphological change is presented in detail, focusing on the implications that can be drawn for the achievable inter-fractional monitoring DP sensitivity in real clinical conditions. The results have been cross-checked against a simulation study.