Proton therapy facilities: an overview of the development in recent years

Since its discovery in 1946, Proton therapy has continued to overgrow from the number of units installed in various countries and the technology used. This paper aims to provide an overview of the development of proton therapy facilities to date based on a literature review. The results are discussed in several aspects, including its distribution across the globe, beam delivery techniques, dose verification, room layout, and shielding design considerations.

Further investigation of 3D dose verification in proton therapy utilizing acoustic signal, wavelet decomposition and machine learning

Online dose verification in proton therapy is a critical task for quality assurance. We further studied the feasibility of using a wavelet-based machine learning framework to accomplishing that goal in three dimensions, built upon our previous work in 1D. The wavelet decomposition was utilized to extract features of acoustic signals and a bidirectional long-short-term memory (Bi-LSTM) recurrent neural network (RNN) was used. The 3D dose distributions of mono-energetic proton beams (multiple beam energies) inside a 3D CT phantom, were generated using Monte-Carlo simulation. The 3D propagation of acoustic signal was modeled using the k-Wave toolbox. Three different beamlets (i.e. acoustic pathways) were tested, one with its own model. The performance was quantitatively evaluated in terms of mean relative error (MRE) of dose distribution and positioning error of Bragg peak (△BP ), for two signal-to-noise ratios (SNRs). Due to the lack of experimental data for the time being, two SNR conditions were modeled (SNR=1 and 5). The model is found to yield good accuracy and noise immunity for all three beamlets. The results exhibit an MRE below 0.6% (without noise) and 1.2% (SNR= 5), and △BP below 1.2 mm (without noise) and 1.3 mm (SNR= 5). For the worst-case scenario (SNR=1), the MRE and △BP are below 2.3% and 1.9 mm, respectively. It is encouraging to find out that our model is able to identify the correlation between acoustic waveforms and dose distributions in 3D heterogeneous tissues, as in the 1D case. The work lays a good foundation for us to advance the study and fully validate the feasibility with experimental results.

A Retrospective Study of Commercial Software System EDose in QA Application based on the Electronic Portal Imaging Device

Purpose: To evaluate the functions about the pre-treatment dose verification and, the in vivo dose verification for the commercial software EDose system based on Electronic Portal Imaging Device (EPID) retrospectively and establish the action limit level. Methods: The results of pre-treatment dose verification were compared with 2D array Seven29 and 3Dmap for 50 randomly selected IMRT plans of different lesions. A retrospective analysis was conducted for 287 radiotherapy plans using the EDose in pre-treatment dose verification, including 53 IMRT and 247 RapidArc plans, to establish the action limit level with statistical significance evaluation. 28 head and neck patients with different lesions were selected randomly for studying 3D online dose verification preliminary.Results: For pre-treatment dose verification, 50 plans’ average γ passing rates of the 3%/3mm criterion were > 98% for EDose, Seven29, 3Dmap, and 3%/2mm, 2%/2mm criteria were > 95%, 90%. The average γmean of the three verification methods were similar for the 3%/3mm criterion (0.35, 0.38, 0.35). Based on the 287 patients’ clinical data, the average γ passing rate was 97.5%, and the recommend clinical action level was established at 92% with a 95% confidence limit. The in vivo results showed that the γ pass rate had a decreasing trend as the 33 treatment fractions progressed. The γ passing rates means±SD of the first fraction was (91.92±3.31)% while the 33th fraction was (85.73±8.75)%. In addition, the standard deviation between the TPS calculations and the EDose measurement results indicated a higher value of the thirty-third treatment for PTVs and organ at risk compared to the first treatment.Conclusions: This study demonstrated that the EDose system is an accurate, efficient method for quality assurance of patient’ radiotherapy plans with remarkable consistency of treatment planning system (TPS).

Development of Patient Specific Conformal 3D-Printed Devices for Dose Verification in Radiotherapy

In radiation therapy, a bolus is used to improve dose distribution in superficial tumors; however, commercial boluses lack conformity to patient surface leading to the formation of an air gap between the bolus and patient surface and suboptimal tumor control. The aim of this study was to explore 3D-printing technology for the development of patient-specific conformal 3D-printed devices, which can be used for the radiation treatment of superficial head and neck cancer (HNC). Two 3D boluses (0.5 and 1.0 cm thick) for surface dose build-up and patient-specific 3D phantom were printed based on reconstruction of computed tomography (CT) images of a patient with HNC. The 3D-printed patient-specific phantom indicated good tissue equivalency (HU = −32) and geometric accuracy (DSC = 0.957). Both boluses indicated high conformity to the irregular skin surface with minimal air gaps (0.4–2.1 mm for 0.5 cm bolus and 0.6–2.2 mm for 1.0 cm bolus). The performed dose assessment showed that boluses of both thicknesses have comparable effectiveness, increasing the dose that covers 99% of the target volume by 52% and 26% for single field and intensity modulated fields, respectively, when compared with no bolus case. The performed investigation showed the potential of 3D printing in development of cost effective, patient specific and patient friendly conformal devices for dose verification in radiotherapy.