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We present the commissioning and quality assurance of our clinical protocol for respiratory gating in pencil beam scanning proton therapy for cancer patients with moving targets. In a novel approach, optical tracking has been integrated in the therapy workflow and used to monitor respiratory motion from multiple surrogates, applied on the patients’ chest. The gating system was tested under a variety of experimental conditions, specific to proton therapy, to evaluate reaction time and reproducibility of dose delivery control. The system proved to be precise in the application of beam gating and allowed the mitigation of dose distortions even for large (1.4 cm) motion amplitudes, provided that adequate treatment windows were selected. The total delivered dose was not affected by the use of gating, with measured integral error within 0.15 cGy. Analysing high-resolution images of proton transmission, we observed negligible discrepancies in the geometric location of the dose as a function of the treatment window, with gamma pass rate greater than 95% (2%/2 mm) compared to stationary conditions. Similarly, pass rate for the latter metric at the 3%/3 mm level was observed above 97% for clinical treatment fields, limiting residual movement to 3 mm at end-exhale. These results were confirmed in realistic clinical conditions using an anthropomorphic breathing phantom, reporting a similarly high 3%/3 mm pass rate, above 98% and 94%, for regular and irregular breathing, respectively. Finally, early results from periodic QA tests of the optical tracker have shown a reliable system, with small variance observed in static and dynamic measurements.

Shen (2019) commented on our paper ‘Lateral response heterogeneity of Bragg peak ionization chambers for narrow-beam photon and proton dosimetry’ regarding the impact of the low dose tail of the collimated x-ray beam we used to acquire individual response maps of large area ionization chambers. The behavior of this low dose tail was measured and compared to the simulations performed by Shen (2019). It was shown that the model of the tail by Shen (2019) is too simplistic and overestimates its effect. [ABSTRACT FROM AUTHOR]

While Monte Carlo (MC) codes are considered as the gold standard for dosimetric calculations, the availability of user friendly MC codes suited for particle therapy is limited. Based on the FLUKA MC code and its graphical user interface (GUI) Flair, we developed an easy-to-use tool which enables simple and reliable simulations for particle therapy. In this paper we provide an overview of functionalities of the tool and with the presented clinical, proton and carbon ion therapy examples we demonstrate its reliability and the usability in the clinical environment and show its flexibility for research purposes. The first, easy-to-use FLUKA MC platform for particle therapy with GUI functionalities allows a user with a minimal effort and reduced knowledge about MC details to apply MC at their facility and is expected to enhance the popularity of the MC for both research and clinical quality assurance and commissioning purposes. [ABSTRACT FROM AUTHOR]

Large area ionization chambers (LAICs) can be used to measure output factors of narrow beams. Dose area product measurements are proposed as an alternative to central-axis point dose measurements. Using such detectors requires detailed information on the uniformity of the response along the sensitive area. Eight LAICs were investigated in this study: four of type PTW-34070 (LAICThick) and four of type PTW-34080 (LAICThin). Measurements were performed in an x-ray unit using peak voltages of 100–200 kVp and a collimated beam of 3.1 mm (FWHM). The LAICs were moved with a step size of 5 mm to measure the chamber response at lateral positions. To account for beam positions where only a fraction of the beam impinged within the sensitive area of the LAICs, a corrected response was calculated which was the basis to calculate the relative response. The impact of a heterogeneous LAIC response, based on the obtained response maps was henceforth investigated for proton pencil beams and small field photon beams. A pronounced heterogeneity of the responses was observed in the investigated LAICs. The response of LAICThick generally decreased with increasing radius, resulting in a response correction of up to 5%. This correction was more pronounced and more diverse (up to 10%) for LAICThin. Considering a proton pencil beam the systematic offset for reference dosimetry was 2.4–4.1% for LAICThick and  −9.5 to 9.4% for LAICThin. For relative dosimetry (e.g. integral depth-dose curves) systematic response variation by 0.8–1.9% were found. For a decreasing photon field size the systematic offset for absolute dose measurements showed a 2.5–4.5% overestimation of the response for 6  ×  6 mm2 field sizes for LAICThick. For LAICThin the response varied even over a range of 20%. This study highlights the need for chamber-dependent response maps when using LAICs for absolute and relative dosimetry with proton pencil beams or small photon beams. [ABSTRACT FROM AUTHOR]

Objective: For the past 20 years, Paul Scherrer Institut (PSI) has treated more than 1500 patients with deep-seated tumors using PSI-Plan, an in-house developed treatment planning system (TPS) used for proton beam scanning proton therapy, in combination with its home-built gantries. The goal of the present work is to benchmark the performance of a new TPS/Gantry system for proton therapy centers which have established already a baseline standard of care., Methods and Materials: A total of 31 cases (=52 plans) distributed around 7 anatomical sites and 12 indications were randomly selected and re-planned using Eclipse™. The resulting plans were compared with plans formerly optimized in PSI-Plan, in terms of target coverage, plan quality, organ-at-risk (OAR) sparing and number of delivered pencil beams., Results: Our results show an improvement on target coverage and homogeneity when using Eclipse™ while PSI-Plan showed superior plan conformity. As for OAR sparing, both TPS achieved the clinical constraints. The number of pencil beams required per plan was on average 3.4 times higher for PSI-Plan., Conclusion: Both systems showed a good capacity to produce satisfactory plans, with Eclipse™ being able to achieve better target coverage and plan homogeneity without compromising OARs., Advances in Knowledge: A benchmark between a clinically tested and validated system with a commercial solution is of interest for emerging proton therapy, equipped with commercial systems and no previous experience with proton beam scanning.

The ratio of patients who need a treatment adaptation due to anatomical variations at least once during the treatment course is significantly higher in light ion beam therapy (LIBT) than in photon therapy. The ballistic behaviour of ion beams makes them more sensitive to changes. Hence, the delivery of LIBT has always been supported by state of art image guidance. On the contrary CBCT technology was adapted for LIBT quite late. Adaptive concepts are being implemented more frequently in photon therapy and also efficient workflows are needed for LIBT. The MedAustron Ion Beam Therapy Centre was designed to allow the clinical implementation of adaptive image-guided concepts. The aim of this paper is to describe the current status and the potential future use of the technology installed at MedAustron. Specifically addressed is the beam delivery system, the patient alignment system, the treatment planning system as well as the Record & Verify system. Finally, an outlook is given on how high quality X-ray imaging, MR image guidance, fast and automated treatment planning as well as in vivo range verification methods could be integrated., (Copyright © 2017. Published by Elsevier GmbH.)

Background: In proton radiation therapy a constant relative biological effectiveness (RBE) of 1.1 is usually assumed. However, biological experiments have evidenced RBE dependencies on dose level, proton linear energy transfer (LET) and tissue type. This work compares the predictions of three of the main radio-biological models proposed in the literature by Carabe-Fernandez, Wedenberg, Scholz and coworkers., Methods: Using the chosen models, a spread-out Bragg peak (SOBP) as well as two exemplary clinical cases (single field and two fields) for cranial proton irradiation, all delivered with state-of-the-art pencil-beam scanning, have been analyzed in terms of absorbed dose, dose-averaged LET (LET D ), RBE-weighted dose (D RBE) and biological range shift distributions., Results: In the systematic comparison of RBE predictions by the three models we could show different levels of agreement depending on (α/β) x and LET values. The SOBP study emphasizes the variation of LET D and RBE not only as a function of depth but also of lateral distance from the central beam axis. Application to clinical-like scenario shows consistent discrepancies from the values obtained for a constant RBE of 1.1, when using a variable RBE scheme for proton irradiation in tissues with low (α/β) x , regardless of the model. Biological range shifts of 0.6- 2.4 mm (for high (α/β) x ) and 3.0 - 5.4 mm (for low (α/β) x ) were found from the fall-off analysis of individual profiles of RBE-weighted fraction dose along the beam penetration depth., Conclusions: Although more experimental evidence is needed to validate the accuracy of the investigated models and their input parameters, their consistent trend suggests that their main RBE dependencies (dose, LET and (α/β) x ) should be included in treatment planning systems. In particular, our results suggest that simpler models based on the linear-quadratic formalism and LETD might already be sufficient to reproduce important RBE dependencies for re-evaluation of plans optimized with the current RBE = 1.1 approximation. This approach would be a first step forward to consider RBE variations in proton therapy, thus enabling a more robust choice of biological dose delivery. The latter could in turn impact clinical outcome, especially in terms of reduced toxicities for tumors adjacent to organs at risk.