This work tackles the commissioning and validation of a novel combination of a synchrotron-based proton beam therapy system (Hitachi, Ltd.) for use with a Monte Carlo treatment planning system (TPS). Four crucial aspects in this configuration have been investigated: (1) Monte Carlo-based correction performed by the TPS to the measured integrated depth-dose curves (IDD), (2) circular spot modelling with a single Gaussian function to characterize the synchrotron physical spot, which is elliptical, (3) the modelling of the range shifter that enables using only one set of measurements in open beams, and (4) the Monte Carlo dose calculation model in small fields.Integrated depth-dose curves were measured with a PTW Bragg peak chamber and corrected, with a Monte Carlo model, to account for energy absorbed outside the detector. The elliptical spot was measured by IBA Lynx scintillator, EBT3 films and PTW microDiamond. The accuracy of the TPS (RayStation, RaySearch Laboratories) at spot modelling with a circular Gaussian function was assessed.The beam model was validated using spread-out Bragg peak (SOBP) fields. We took single-point doses at several depths through the central axis using a PTW Farmer chamber, for fields between 2 x 2cm and 30 x 30cm. We checked the range-shifter modelling from open-beam data. We tested clinical cases with film and an ioni-zation chamber array (IBA Matrix).Sigma differences for spots fitted using 2D images and 1D profiles to elliptical and circular Gaussian models were below 0.22 mm. Differences between SOBP measurements at single points and TPS calculations for all fields between 5 x 5 and 30 x 30cm were below 2.3%. Smaller fields had larger differences: up to 3.8% in the 2 x 2cm field. Mean differences at several depths along the central axis were generally below 1%. Differences in range -shifter doses were below 2.4%. Gamma test (3%, 3 mm) results for clinical cases were generally above 95% for Matrix and film.Approaches for modelling synchrotron proton beams have been validated. Dose values for open and range -shifter fields demonstrate accurate Monte Carlo correction for IDDs. Elliptical spots can be successfully modelled using a circular Gaussian, which is accurate for patient calculations and can be used for small fields. A double-Gaussian spot can improve small-field calculations. The range-shifter modelling approach, which reduces clinical commissioning time, is adequate.

Objective. Periodic respiratory motion and inter-fraction variations are sources of geometric uncertainty in stereotactic body radiation therapy (SBRT) of pulmonary lesions. This study extensively evaluates and validates the separate and combined dosimetric effect of both factors using 4D-CT and daily 4D-cone beam CT (CBCT) dose accumulation scenarios. Approach. A first cohort of twenty early stage or metastatic disease lung cancer patients were retrospectively selected to evaluate each scenario. The planned-dose (3D(Ref)) was optimized on a 3D mid-position CT. To estimate the dosimetric impact of respiratory motion (4D(Ref)), inter-fractional variations (3D(Acc)) and the combined effect of both factors (4D(Acc)), three dose accumulation scenarios based on 4D-CT, daily mid-cone beam CT (CBCT) position and 4D-CBCT were implemented via CT-CT/CT-CBCT deformable image registration (DIR) techniques. Each scenario was compared to 3D(Ref.) A separate cohort of ten lung SBRT patients was selected to validate DIR techniques. The distance discordance metric (DDM) was implemented per voxel and per patient for tumor and organs at risk (OARs), and the dosimetric impact for CT-CBCT DIR geometric errors was calculated. Main results. Median and interquartile range (IQR) of the dose difference per voxel were 0.05/2.69 Gy and -0.12/2.68 Gy for 3DAcc-3DRef 4DAcc-3DRef. 4DRef-3DRef

Background It is widely accepted that Monte Carlo dose calculations offers a higher precision that the commercially available dose calculation algorithms. This advantage may be especially relevant for lung Stereotactic Body Radiation Therapy (SBRT), as this is a precise technique applied to an area of big inhomogeneity. Purpose We conducted a comparative study to reveal the differences between the doses calculated using the Collapsed Cone Convolution algorithm and the GAMOS/Geant4 Monte Carlo calculation for lung cancer patients treated with Stereotactic Body Radiation Therapy on an Elekta Versa HD linac. Methods For this study a set of ten patient treatments carried out at the Clínica Universidad de Navarra was selected. Theanalysis is based on the comparison of several dosimetric quantities for the Gross Tumor Volume (GTV) and several OrgansAt Risk (OARs), and also a gamma index calculation with distance-to-agreement set to 2 mm and dose difference to 3%, as recommended by ICRU to assess clinical impact. In order to guarantee a small uncertainty in the Monte Carlo calculation of the dosimetric quantities, we studied in detail the validity of different methods that may be used to determine this uncertainty. To compensate for lung movements, a 4D-Cone-beam Computed Tomography (CBCT) was acquired before treatment, whichallowed us to identify eight respiratory phases using a temporal binning. Using commercial MIM software®, we performed a deformable image registration between the eight CT respiration phases to construct the 4D doses. The same procedure was applied for the Treatment Planning System (TPS) dose files and for the Monte Carlo dose files. Results The differences between the two algorithms reveal the known weaknesses of the Collapsed Cone Convolution (CCC) algorithm for the calculation of lateral doses and in regions of large density change. The comparison between the two algorithms for individual phase doses shows differences up to 5% of the GTV D95 or 3¿4 Gy in some OARs, which may have a clinical impact. Nevertheless these differences are reduced for the 4D dose in most quantities under study. Conclusions Comparing the dose calculated with a Collapsed Cone Convolution algorithm with GAMOS/Geant4 for ten patients and eight respiratory phases, we found some differences that could have a clinical impact. When combining the eight temporal phases into a 4D dose using the MIM Deformable Image Registration software, the differences diminished substantially. Our statistical analysis concludes that dose uncertainty in the voxels with a maximum dose below a given percentage guarantees uncertainty in the dosimetric quantities below that figure.

Background The quality and quantity of tumor neoantigens derived from tumor mutations determines the fate of the immune response in cancer. Frameshift mutations elicit better tumor neoantigens, especially when they are not targeted by nonsense-mediated mRNA decay (NMD). For tumor progression, malignant cells need to counteract the immune response including the silencing of immunodominant neoantigens (antigen immunoediting) and promoting an immunosuppressive tumor microenvironment. Although NMD inhibition has been reported to induce tumor immunity and increase the expression of cryptic neoantigens, the possibility that NMD activity could be modulated by immune forces operating in the tumor microenvironment as a new immunoediting mechanism has not been addressed. Methods We study the effect of SMG1 expression (main kinase that initiates NMD) in the survival and the nature of the tumor immune infiltration using TCGA RNAseq and scRNAseq datasets of breast, lung and pancreatic cancer. Different murine tumor models were used to corroborate the antitumor immune dependencies of NMD. We evaluate whether changes of SMG1 expression in malignant cells impact the immune response elicited by cancer immunotherapy. To determine how NMD fluctuates in malignant cells we generated a luciferase reporter system to track NMD activity in vivo under different immune conditions. Cytokine screening, in silico studies and functional assays were conducted to determine the regulation of SMG1 via IL-6/STAT3 signaling. Results IL-6/STAT3 signaling induces SMG1, which limits the expression of potent frameshift neoantigens that are under NMD control compromising the outcome of the immune response. Conclusion We revealed a new neoantigen immunoediting mechanism regulated by immune forces (IL-6/STAT3 signaling) responsible for silencing otherwise potent frameshift mutation-derived neoantigens.

The purpose of this study was to devise and evaluate a method to quantify the dosimetric uncertainty produced by the interplay between the movement of multileaf collimator (MLC) and respiratory motion in lung stereotactic body radiation therapy (SBRT). The method calculates the dose distribution for all control points from a dynamic treatment in all respiratory phases. The methodology includes some characteristics of a patient's irregular breathing patterns. It selects, for each control point, the phases with maximum and minimum mean dose over the tumor and their corresponding adjacent phases, whenever necessary. According to this selection, the dose matrices from each control point are summed up to obtain two dose distributions in each phase, which are accumulated in the reference phase subsequently by Deformable Image Registration (DIR). D95 and Dmin,0.035cc were calculated over those accumulated dose distributions for Gross Tumor Volume (GTV), Planning Target Volume (PTV) - based on Internal Target Volume (ITV) approach - and Evaluation Target Volume (ETV), a novel concept that applies to 4D dose accumulation. With the ETV, DIR and interplay uncertainties are separated. The methodology also evaluated how variations in the breathing rate and field size affects the mean dose received by the GTV. The method was applied retrospectively in five patients treated with intensity modulated radiotherapy (IMRT) - minimum area defined by the leaves configuration at any control point was at least 4cm2-. Uncertainties in tumor coverage were small (in most patients, changes on D95 and Dmin,0.035cc were below 2% for GTV and ETV) but significant over- and under- dosages near ETV, which can be accentuated by highly irregular breathing. Uncertainties in mean dose for GTV tended to decrease exponentially with increasing field size and were reduced by an increase of breathing rate. The implementation of this method would be helpful to assess treatment quality in patients with irregular breathing. Furthermore, it could be used to study interplay uncertainties when small field sizes are used.

Purpose To use four-dimensional (4D) dose accumulation based on deformable image registration (DIR) to assess dosimetric uncertainty in lung stereotactic body radiation therapy (SBRT) treatment planning. A novel concept, the Evaluation Target Volume (ETV), was introduced to achieve this goal. Methods The internal target volume (ITV) approach was used for treatment planning for 11 patients receiving lung SBRT. Retrospectively, 4D dose calculation was done in Pinnacle v9.10. Total dose was accumulated in the reference phase using DIR with MIM. DIR was validated using landmarks introduced by an expert radiation oncologist. The 4D and three-dimensional (3D) dose distributions were compared within the gross tumor volume (GTV) and the planning target volume (PTV) using the D-95 and D-min (calculated as D-min,D-0.035cc) metrics. For lung involvement, the mean dose and V-20, V-10, and V-5 were used in the 3D to 4D dose comparison, and D-max (D-0.1cc) was used for all other organs at risk (OAR). The new evaluation target volume (ETV) was calculated by expanding the GTV in the reference phase in order to include geometrical uncertainties of the DIR, interobserver variability in the definition of the tumor, and uncertainties of imaging and delivery systems. D-95 and D-min,D-0.035cc metrics were then calculated on the basis of the ETV for 4D accumulated dose distributions, and these metrics were compared with those calculated from the PTV for 3D planned dose distributions.