Visually guided inspiration breath-hold facilitated with nasal high flow therapy in locally advanced lung cancer

Background and purpose Reducing breathing motion in radiotherapy (RT) is an attractive strategy to reduce margins and better spare normal tissues. The objective of this prospective study (NCT03729661) was to investigate the feasibility of irradiation of non-small cell lung cancer (NSCLC) with visually guided moderate deep inspiration breath-hold (IBH) using nasal high-flow therapy (NHFT). Material and methods Locally advanced NSCLC patients undergoing photon RT were given NHFT with heated humidified air (flow: 40 L/min with 80% oxygen) through a nasal cannula. IBH was monitored by optical surface tracking (OST) with visual feedback. At a training session, patients had to hold their breath as long as possible, without and with NHFT. For the daily cone beam CT (CBCT) and RT treatment in IBH, patients were instructed to keep their BH as long as it felt comfortable. OST was used to analyze stability and reproducibility of the BH, and CBCT to analyze daily tumor position. Subjective tolerance was measured with a questionnaire at 3 time points. Results Of 10 included patients, 9 were treated with RT. Seven (78%) completed the treatment with NHFT as planned. At the training session, the mean BH length without NHFT was 39 s (range 15-86 s), and with NHFT 78 s (range 29-223 s) (p = .005). NHFT prolonged the BH duration by a mean factor of 2.1 (range 1.1-3.9s). The mean overall stability and reproducibility were within 1 mm. Subjective tolerance was very good with the majority of patients having no or minor discomfort caused by the devices. The mean inter-fraction tumor position variability was 1.8 mm (-1.1-8.1 mm;SD 2.4 mm). Conclusion NHFT for RT treatment of NSCLC in BH is feasible, well tolerated and significantly increases the breath-hold duration. Visually guided BH with OST is stable and reproducible. We therefore consider this an attractive patient-friendly approach to treat lung cancer patients with RT in BH

Treatment planning comparison in the PROTECT-trial randomising proton versus photon beam therapy in oesophageal cancer:Results from eight European centres

PURPOSE To compare dose distributions and robustness in treatment plans from eight European centres in preparation for the European randomized phase-III PROTECT-trial investigating the effect of proton therapy (PT) versus photon therapy (XT) for oesophageal cancer. MATERIALS AND METHODS All centres optimized one PT and one XT nominal plan using delineated 4DCT scans for four patients receiving 50.4 Gy (RBE) in 28 fractions. Target volume receiving 95% of prescribed dose (V95%iCTVtotal) should be >99%. Robustness towards setup, range, and respiration was evaluated. The plans were recalculated on a surveillance 4DCT (sCT) acquired at fraction ten and robustness evaluation was performed to evaluate the effect of respiration and inter-fractional anatomical changes. RESULTS All PT and XT plans complied with V95%iCTVtotal >99% for the nominal plan and V95%iCTVtotal >97% for all respiratory and robustness scenarios. Lung and heart dose varied considerably between centres for both modalities. The difference in mean lung dose and mean heart dose between each pair of XT and PT plans was in median [range] 4.8 Gy [1.1;7.6] and 8.4 Gy [1.9;24.5], respectively. Patients B and C showed large inter-fractional anatomical changes on sCT. For patient B, the minimum V95%iCTVtotal in the worst-case robustness scenario was 45% and 94% for XT and PT, respectively. For patient C, the minimum V95%iCTVtotal was 57% and 72% for XT and PT, respectively. Patient A and D showed minor inter-fractional changes and the minimum V95%iCTVtotal was >85%. CONCLUSION Large variability in dose to the lungs and heart was observed for both modalities. Inter-fractional anatomical changes led to larger target dose deterioration for XT than PT plans

Optimization of dual-energy CT acquisitions for proton therapy using projection-based decomposition

International audiencePurposeDual-energy computed tomography (DECT) has been presented as a valid alternative to single-energy CT to reduce the uncertainty of the conversion of patient CT numbers to proton stopping power ratio (SPR) of tissues relative to water. The aim of this work was to optimize DECT acquisition protocols from simulations of X-ray images for the treatment planning of proton therapy using a projection-based dual-energy decomposition algorithm.MethodsWe have investigated the effect of various voltages and tin filtration combinations on the SPR map accuracy and precision, and the influence of the dose allocation between the low energy (LE) and the high energy (HE) acquisitions. For all spectra combinations, virtual CT projections of the Gammex phantom were simulated with a realistic energy-integrating detector response model. Two situations were simulated: an ideal case without noise (infinite dose) and a realistic situation with Poisson noise corresponding to a 20 mGy total central dose. To determine the optimal dose balance, the proportion of LE-dose with respect to the total dose was varied from 10% to 90% while keeping the central dose constant, for four dual-energy spectra. SPR images were derived using a two-step projection-based decomposition approach. The ranges of 70 MeV, 90 MeV and 100 MeV proton beams onto the adult female (AF) reference computational phantom of the ICRP were analytically determined from the reconstructed SPR maps.ResultsThe energy separation between the incident spectra had a strong impact on the SPR precision. Maximizing the incident energy gap reduced image noise. However, the energy gap was not a good metric to evaluate the accuracy of the SPR. In terms of SPR accuracy, a large variability of the optimal spectra was observed when studying each phantom material separately. The SPR accuracy was almost flat in the 30-70% LE-dose range, while the precision showed a minimum slightly shifted in favor of lower LE-dose. Photon noise in the SPR images (20 mGy dose) had lower impact on the proton range accuracy since comparable results were obtained for the noiseless situation (infinite dose). Root-mean-square range errors averaged over all irradiation angles associated to dual-energy imaging were comprised between 0.50 mm and 0.72 mm for the noiseless situation and between 0.51 mm and 0.77 mm for the realistic scenario.ConclusionsThe impact of the dual-energy spectra and the dose allocation between energy levels on the SPR accuracy and precision determined through a projection-based dual-energy algorithm were evaluated to guide the choice of spectra for dual-energy CT for protontherapy. The dose balance between energy levels was not found to be sensitive for the SPR estimation. The optimal pair of dual-energy spectra was material dependent but on a heterogeneous anthropomorphic phantom there was no significant difference in range accuracy and the choice of spectra could be driven by the precision, i.e., the energy gap

Dual-energy CT spectra optimization for proton treatment planning

International audienceThe purpose of this study was to determine the optimal dual-energy spectra for the treatment planning of proton therapy. We have evaluated the effect of various voltages and tin filtration combinations on the relative electron density (RED) map accuracy and precision. The RED is directly related to the stopping-power (SP) map and thus to the accuracy of the proton range estimation. An acquisition setup representing a medium-size body irradiation was evaluated. For all spectra combinations, virtual CT projections of the Gammex 467 tissue characterization phantom were simulated with realistic energy-integrating detector response model. Two situations were simulated: an ideal case without noise (infinite dose) and a realistic situation with a Poisson noise corresponding to a 20 mGy central dose. To derive the RED maps from dual-energy imaging, the projection-based basis material decomposition method proposed by Alvarez and Macovski (1976) was implemented. It was observed that the energy separation between the incident spectra had little influence on the RED accuracy but a strong influence on the precision. Different optimal ranges of low and high energy tube voltages and additional tin thicknesses that maximize the overall accuracy and the precision of RED maps were found. However, when studying each phantom material separately, a large variability of the optimal spectra was observed. An emphasis on the materials present in the anatomical region of interest must be made during the optimization process of the dual-energy spectra

Deriving the mean excitation energy map from dual-energy and proton computed tomography

International audienceThe mean excitation energy, I, is an essential quantity for proton treatment planning. This work investigated the feasibility of extracting the spatial distribution of I by combining two computed tomography (CT) modalities, dual-energy CT and proton CT, which provided the spatial distribution of the relative electron density and the stopping power relative to water, respectively. We provided the analytical derivation of I as well as its uncertainty. Results were validated on simulated X-ray and proton CT images of a digital anthropomorphic phantom. Accuracy was below 15% with a large uncertainty, which demonstrated the potential and limits of the technique

Implementation of a Compact Spot-Scanning Proton Therapy System in a GPU Monte Carlo Code to Support Clinical Routine

International audienceThe purpose of this work was to implement a fast Monte Carlo dose calculation tool, Fred, in the Maastro proton therapy center in Maastricht (Netherlands) to complement the clinical treatment planning system. Fred achieves high accuracy and computation speed by using physics models optimized for radiotherapy and extensive use of GPU technology for parallelization. We implemented the beam model of the Mevion S250i proton beam and validated it against data measured during commissioning and calculated with the clinical TPS. The beam exits the accelerator with a pristine energy of around 230 MeV and then travels through the dynamically extendable nozzle of the device. The nozzle contains the range modulation system and the multi-leaf collimator system named adaptive aperture. The latter trims the spots laterally over the 20 × 20 cm2 area at the isocenter plane. We use a single model to parameterize the longitudinal (energy and energy spread) and transverse (beam shape) phase space of the non-degraded beam in the default nozzle position. The range modulation plates and the adaptive aperture are simulated explicitly and moved in and out of the simulation geometry dynamically by Fred. Patient dose distributions recalculated with Fred were comparable with the TPS and met the clinical criteria. Calculation time was on the order of 10–15 min for typical patient cases, and future optimization of the simulation statistics is likely to improve this further. Already now, Fred is fast enough to be used as a tool for plan verification based on machine log files and daily (on-the-fly) dose recalculations in our facility.</jats:p

Comparison of projection- and image-based methods for proton stopping power estimation using dual energy CT

International audienceBackground and Purpose: Several strategies for estimating stopping power ratio (SPR) from dual-energy CT (DECT) have been proposed to improve accuracy of proton dose calculations. DECT methods can mainly be categorized into projection-based methods, where material decomposition is performed prior to image reconstruction, and image-based methods, where decomposition takes place after image reconstruction. With the advent of photon-counting and dual-layer technology, projection-based methods could be considered for SPR estimation. In this simulation-based study we compared the SPR accuracy of one projection-and three image-based DECT methods. Materials and Methods: X-ray CT projections of the female ICRP phantom were simulated using two different X-ray spectra with a realistic detector response and noise levels. ICRP slices at four different locations were selected. Reference SPR-maps were computed at 200 MeV. The SPR comparison was based on percentage deviation inside ROIs and relative range errors calculated with Radon transform of difference maps. Results: SPR root-mean-square errors (RMSE) over the selected ROIs were 0.54% for the projection-based method and 0.68%, 0.61% and 0.70% for the three image-based methods. The RMSE for the relative range errors were slightly smaller for the projection-based approach, but close to zero for all decomposition domains as positive and negative errors averaged out over the slice. Conclusions: SPR estimations with the projection-based method produced slightly better results (though not statistically significant) than the three image-based methods used in this simulation-based study, therefore, with the advent of technological developments, projection-based methods could be considered for SPR estimation if projection data is available

Decomposing a prior-CT-based cone-beam CT projection correction algorithm into scatter and beam hardening components

A scatter correction algorithm (SCA) for cone beam CT (CBCT) projections, making use of prior information obtained by deformable image registration of CT to CBCT, has recently been proposed and tested for particle therapy dose calculation. The SCA relies on subtraction of digitally reconstructed radiographs (DRR) from scaled measured projections and smoothing operations, followed by a subtraction correction and reconstruction. In this note, we compared the SCA’s correction to one based on a Monte Carlo simulation of the scatter, and a separate beam hardening correction. Agreement better than 3% between the two approaches was obtained when comparing corrected log-transformed projections. Keywords: CBCT, Scatter, Monte Carlo, Beam hardening, Proton therap