Brush head composition, wear profile, and cleaning efficacy: an assessment of three electric brush heads using in vitro methods.

OBJECTIVE: The objective of this research was to evaluate a current store brand (SB) brush head for composition/physical characteristics, Wear Index (WI), and cleaning efficacy versus the previous SB brush head refill design (SB control) and the Oral-B Precision Clean brush head (positive control, PC). METHODS: This research consisted of three parts: 1) Analytical analysis using Fourier Transform Infrared (FT-IR) spectrometry to evaluate the chemical composition of the current SB brush head bristles relative to the SB control. In addition, physical parameters such as bristle count and diameter were determined. 2) Wear Index (WI) investigation to determine the Wear Index scores of in vitro-aged brush heads at four weeks (one month) and 13 weeks (three months) by a trained investigator. To "age" the brush heads, a robot system was used as a new alternative in vitro method to simulate aging by consumer use. 3) Robot testing to determine the cleaning performance of in vitro-aged brush heads, comparing one month-aged current SB brush heads with the SB control (one and three months-aged) and the PC brush heads (three months-aged) in a standardized fashion. RESULTS: 1) FT-IR analysis revealed that the chemical composition of the current and control SB refill brush heads is identical. In terms of physical parameters, the current SB brush head has 12% more bristles and a slightly oval brush head compared to the round brush head of the SB control. 2) Wear Index analysis showed there was no difference in the one month-aged current SB brush head versus the one month-aged SB control (1.67 vs. 1.50, p = 0.65) or versus the three months-aged PC brush head (1.67 vs. 1.50, p = 0.65). The one month-aged current SB brush head demonstrated statistically significantly less wear than the three months-aged SB control (1.67 vs. 2.67, p = 0.01). 3) Analysis of cleaning efficacy shows that the one month-aged current SB brush head had improved cleaning performance over the one month-aged SB control brush head (p < 0.05), despite no statistically significant difference in wear. Both the one month-aged current and control SB brush heads showed statistically significantly lower cleaning performance compared to the three months-aged PC brush heads (p < 0.01). CONCLUSION: While the current SB brush head showed improved cleaning over the SB control, it demonstrated significantly lower durability and cleaning in comparison to the PC brush head. Dental professionals should be aware of these differences, both in durability and in cleaning performance, when recommending brush heads to their patients.

Particle arc therapy: Status and potential.

There is a rising interest in developing and utilizing arc delivery techniques with charged particle beams, e.g., proton, carbon or other ions, for clinical implementation. In this work, perspectives from the European Society for Radiotherapy and Oncology (ESTRO) 2022 physics workshop on particle arc therapy are reported. This outlook provides an outline and prospective vision for the path forward to clinically deliverable proton, carbon, and other ion arc treatments. Through the collaboration among industry, academic, and clinical research and development, the scientific landscape and outlook for particle arc therapy are presented here to help our community understand the physics, radiobiology, and clinical principles. The work is presented in three main sections: (i) treatment planning, (ii) treatment delivery, and (iii) clinical outlook.

Special report: workshop on 4D-treatment planning in actively scanned particle therapy--recommendations, technical challenges, and future research directions.

This article reports on a 4D-treatment planning workshop (4DTPW), held on 7-8 December 2009 at the Paul Scherrer Institut (PSI) in Villigen, Switzerland. The participants were all members of institutions actively involved in particle therapy delivery and research. The purpose of the 4DTPW was to discuss current approaches, challenges, and future research directions in 4D-treatment planning in the context of actively scanned particle radiotherapy. Key aspects were addressed in plenary sessions, in which leaders of the field summarized the state-of-the-art. Each plenary session was followed by an extensive discussion. As a result, this article presents a summary of recommendations for the treatment of mobile targets (intrafractional changes) with actively scanned particles and a list of requirements to elaborate and apply these guidelines clinically.

Reducing the sensitivity of IMPT treatment plans to setup errors and range uncertainties via probabilistic treatment planning.

Treatment plans optimized for intensity modulated proton therapy (IMPT) may be very sensitive to setup errors and range uncertainties. If these errors are not accounted for during treatment planning, the dose distribution realized in the patient may by strongly degraded compared to the planned dose distribution. The authors implemented the probabilistic approach to incorporate uncertainties directly into the optimization of an intensity modulated treatment plan. Following this approach, the dose distribution depends on a set of random variables which parameterize the uncertainty, as does the objective function used to optimize the treatment plan. The authors optimize the expected value of the objective function. They investigate IMPT treatment planning regarding range uncertainties and setup errors. They demonstrate that incorporating these uncertainties into the optimization yields qualitatively different treatment plans compared to conventional plans which do not account for uncertainty. The sensitivity of an IMPT plan depends on the dose contributions of individual beam directions. Roughly speaking, steep dose gradients in beam direction make treatment plans sensitive to range errors. Steep lateral dose gradients make plans sensitive to setup errors. More robust treatment plans are obtained by redistributing dose among different beam directions. This can be achieved by the probabilistic approach. In contrast, the safety margin approach as widely applied in photon therapy fails in IMPT and is neither suitable for handling range variations nor setup errors.

The method of long-term catheterization of the vena jugularis in pigs.

INTRODUCTION: The pig is one of the most valuable in vivo models in biomedical research, however with only a few well-accessible veins suitable for venipuncture. Moreover, most of the known methods of blood collection are suitable only for a limited time period. The aim of the study was to verify an improved method of long-term catheterization of the jugular vein in pigs. METHODS: A 420 mm polyurethane catheter 16G tube was surgically inserted using the Seldinger technique. The part of the tube that was not inserted into the vein was threaded through a subcutaneously introduced trocar into the occipital area, where it was well accessible and well protected from damage. The catheters were flushed with sterile 0.9% saline solution and locked with 4% citrate between frequent blood samplings, or with 30% citrate at intervals of 1-2-days. Once a week, the catheters were locked with 4% citrate containing taurolidine for 24 h in order to prevent infection. The method was verified in 14 pigs. RESULTS: The catheters were fully functional for up to 11 weeks and no infection or thrombus was observed. DISCUSSION: This method of catheterization and catheter care allows the realization of long-term experiments with comfortable and stress-free blood sampling.

Dose painting with IMPT, helical tomotherapy and IMXT: a dosimetric comparison.

PURPOSE: A planning study is presented in order to compare the suitability of intensity modulated photon radiotherapy (IMXT), helical tomotherapy (HTT) and intensity modulated protontherapy (IMPT) for dose painting. METHODS: For three HNC patients, nine different treatment plans were generated. Firstly, a uniform dose escalation (uniDE) of 10% was applied to the FDG PET positive region with step-and-shoot IMXT, HTT and IMPT. Secondly, dose painting by numbers (DPBN) was performed based on dose escalation maps determined from dynamic FMISO PET data for all three treatment modalities. Thirdly, the maximum PTV dose was not constrained while maximizing TCP, whereas the same organ at risk constraints as used for conventional IMXT had to be fulfilled. The dose distributions in spinal cord and parotids were optimized with equivalent uniform dose (EUD) constraints, expressing the risk of late reactions. RESULTS: The target coverage obtained with IMPT and HTT was more conformal regarding the inhomogeneous prescriptions than with IMXT for both uniDE and DPBN. IMPT allowed significantly higher levels of sparing normal tissues. In addition, the study showed that using IMXT, HTT or IMPT theoretically allows dose escalations of up to 50% under late reaction iso-toxicity conditions. CONCLUSION: The quality of dose painting treatment plans created for IMXT, HTT and IMPT is comparable. More accurate target coverage can be reached with HTT and IMPT, whereas IMPT allows to significantly reduce the dose to normal tissues.

Comparison of fixed-beam IMRT, helical tomotherapy, and IMPT for selected cases.

A growing number of advanced intensity modulated treatment techniques is becoming available. In this study, the specific strengths and weaknesses of four techniques, static and dynamic multileaf collimator (MLC), conventional linac-based IMRT, helical tomotherapy (HT), and spot-scanning proton therapy (IMPT) are investigated in the framework of biological, EUD-based dose optimization. All techniques were implemented in the same in-house dose optimization tool. Monte Carlo dose computation was used in all cases. All dose-limiting, normal tissue objectives were treated as hard constraints so as to facilitate comparability. Five patient cases were selected to offer each technique a chance to show its strengths: a deep-seated prostate case (for 15 MV linac-based IMRT), a pediatric case (for IMPT), an extensive head-and-neck case (for HT), a lung tumor (for HT), and an optical neurinoma (for noncoplanar linac-based IMRT with a miniMLC). The plans were compared by dose statistics and equivalent uniform dose metrics. All techniques delivered results that were comparable with respect to target coverage and the most dose-limiting normal tissues. Static MLC IMRT struggled to achieve sufficient target coverage at the same level of dose homogeneity in the lung case. IMPT gained the greatest advantage when lung sparing was important, but did not significantly reduce the risk of nearby organs. Tomotherapy and dynamic MLC IMRT showed mostly the same performance. Despite the apparent conceptual differences, all four techniques fare equally well for standard patient cases. The absence of relevant differences is in part due to biological optimization, which offers more freedom to shape the dose than do, e.g., dose volume histogram constraints. Each technique excels for certain classes of highly complex cases, and hence the various modalities should be viewed as complementary, rather than competing.

Influence of dose engine accuracy on the optimum dose distribution in intensity-modulated proton therapy treatment plans.

Analytical dose computation algorithms like pencil beam algorithms (PB) are presently used for clinical treatment planning in intensity-modulated proton therapy. PB offer fast computation times, but are based on substantial approximations. Monte Carlo algorithms (MC) offer better accuracy, but are slower. We present a comparison of optimized treatment plans for six patients computed either with PB or MC. Both PB and MC are used during optimization, plus MC is used to recompute PB results. PB is used with different accuracy settings that define the coarseness of approximation. We evaluate the errors of PB optimized treatment plans via comparison with MC optimized plans (convergence errors) and MC recomputed plans (systematic errors) occurring for different accuracy settings of the PB. The level of lateral heterogeneities, being one of the main sources of inaccuracies of the PB, is quantified by a formula. In geometries with high levels of lateral heterogeneities, the shortcomings of PB are most obvious. For these geometries, simple PB lead to clinically significant differences and more accurate PB settings have to be used to diminish the error. The most accurate PB settings lead however to longer computing times by approximately a factor of 2 to 4 compared to PB with simple settings. Although the errors can be diminished, they cannot be fully eliminated even with sophisticated PB. Further gain in accuracy can therefore only be reached with MC in optimization. The use of MC in optimization is technically feasible, the computing times are however about 25 to 50 times longer compared to PB with most accurate settings.

Conversion of CT numbers into tissue parameters for Monte Carlo dose calculations: a multi-centre study.

The conversion of computed tomography (CT) numbers into material composition and mass density data influences the accuracy of patient dose calculations in Monte Carlo treatment planning (MCTP). The aim of our work was to develop a CT conversion scheme by performing a stoichiometric CT calibration. Fourteen dosimetrically equivalent tissue subsets (bins), of which ten bone bins, were created. After validating the proposed CT conversion scheme on phantoms, it was compared to a conventional five bin scheme with only one bone bin. This resulted in dose distributions D(14) and D(5) for nine clinical patient cases in a European multi-centre study. The observed local relative differences in dose to medium were mostly smaller than 5%. The dose-volume histograms of both targets and organs at risk were comparable, although within bony structures D(14) was found to be slightly but systematically higher than D(5). Converting dose to medium to dose to water (D(14) to D(14wat) and D(5) to D(5wat)) resulted in larger local differences as D(5wat) became up to 10% higher than D(14wat). In conclusion, multiple bone bins need to be introduced when Monte Carlo (MC) calculations of patient dose distributions are converted to dose to water.

A pencil beam algorithm for intensity modulated proton therapy derived from Monte Carlo simulations.

A pencil beam algorithm as a component of an optimization algorithm for intensity modulated proton therapy (IMPT) is presented. The pencil beam algorithm is tuned to the special accuracy requirements of IMPT, where in heterogeneous geometries both the position and distortion of the Bragg peak and the lateral scatter pose problems which are amplified by the spot weight optimization. Heterogeneity corrections are implemented by a multiple raytracing approach using fluence-weighted sub-spots. In order to derive nuclear interaction corrections, Monte Carlo simulations were performed. The contribution of long ranged products of nuclear interactions is taken into account by a fit to the Monte Carlo results. Energy-dependent stopping power ratios are also implemented. Scatter in optional beam line accessories such as range shifters or ripple filters is taken into account. The collimator can also be included, but without additional scattering. Finally, dose distributions are benchmarked against Monte Carlo simulations, showing 3%/1 mm agreement for simple heterogeneous phantoms. In the case of more complicated phantoms, principal shortcomings of pencil beam algorithms are evident. The influence of these effects on IMPT dose distributions is shown in clinical examples.

A Monte Carlo dose calculation algorithm for proton therapy.

A Monte Carlo (MC) code (VMCpro) for treatment planning in proton beam therapy of cancer is introduced. It is based on ideas of the Voxel Monte Carlo algorithm for photons and electrons and is applicable to human tissue for clinical proton energies. In the present paper the implementation of electromagnetic and nuclear interactions is described. They are modeled by a Class II condensed history algorithm with continuous energy loss, ionization, multiple scattering, range straggling, delta-electron transport, nuclear elastic proton nucleus scattering and inelastic proton nucleus reactions. VMCpro is faster than the general purpose MC codes FLUKA by a factor of 13 and GEANT4 by a factor of 35 for simulations in a phantom with inhomogeneities. For dose calculations in patients the speed improvement is larger, because VMCpro has only a weak dependency on the heterogeneity of the calculation grid. Dose distributions produced with VMCpro are in agreement with GEANT4 results. Integrated or broad beam depth dose curves show maximum deviations not larger than 1% or 0.5 mm in regions with large dose gradients for the examples presented here.

Monte Carlo simulation of small electron fields collimated by the integrated photon MLC.

In this study, a Monte Carlo (MC)-based beam model for an ELEKTA linear accelerator was established. The beam model is based on the EGSnrc Monte Carlo code, whereby electron beams with nominal energies of 10, 12 and 15 MeV were considered. For collimation of the electron beam, only the integrated photon multi-leaf-collimators (MLCs) were used. No additional secondary or tertiary add-ons like applicators, cutouts or dedicated electron MLCs were included. The source parameters of the initial electron beam were derived semi-automatically from measurements of depth-dose curves and lateral profiles in a water phantom. A routine to determine the initial electron energy spectra was developed which fits a Gaussian spectrum to the most prominent features of depth-dose curves. The comparisons of calculated and measured depth-dose curves demonstrated agreement within 1%/1 mm. The source divergence angle of initial electrons was fitted to lateral dose profiles beyond the range of electrons, where the imparted dose is mainly due to bremsstrahlung produced in the scattering foils. For accurate modelling of narrow beam segments, the influence of air density on dose calculation was studied. The air density for simulations was adjusted to local values (433 m above sea level) and compared with the standard air supplied by the ICRU data set. The results indicate that the air density is an influential parameter for dose calculations. Furthermore, the default value of the BEAMnrc parameter 'skin depth' for the boundary crossing algorithm was found to be inadequate for the modelling of small electron fields. A higher value for this parameter eliminated discrepancies in too broad dose profiles and an increased dose along the central axis. The beam model was validated with measurements, whereby an agreement mostly within 3%/3 mm was found.

Helical tomotherapy vs. intensity-modulated proton therapy for whole pelvis irradiation in high-risk prostate cancer patients: dosimetric, normal tissue complication probability, and generalized equivalent uniform dose analysis.

PURPOSE: To compare intensity-modulated proton therapy (IMPT) and helical tomotherapy (HT) treatment plans for high-risk prostate cancer (HRPCa) patients. METHODS AND MATERIALS: The plans of 8 patients with HRPCa treated with HT were compared with IMPT plans with two quasilateral fields set up (-100°; 100°) and optimized with the Hyperion treatment planning system. Both techniques were optimized to simultaneously deliver 74.2 Gy/Gy relative biologic effectiveness (RBE) in 28 fractions on planning target volumes (PTVs)3-4 (P + proximal seminal vesicles), 65.5 Gy/Gy(RBE) on PTV2 (distal seminal vesicles and rectum/prostate overlapping), and 51.8 Gy/Gy(RBE) to PTV1 (pelvic lymph nodes). Normal tissue calculation probability (NTCP) calculations were performed for the rectum, and generalized equivalent uniform dose (gEUD) was estimated for the bowel cavity, penile bulb and bladder. RESULTS: A slightly better PTV coverage and homogeneity of target dose distribution with IMPT was found: the percentage of PTV volume receiving ≥ 95% of the prescribed dose (V(95%)) was on average > 97% in HT and > 99% in IMPT. The conformity indexes were significantly lower for protons than for photons, and there was a statistically significant reduction of the IMPT dosimetric parameters, up to 50 Gy/Gy(RBE) for the rectum and bowel and 60 Gy/Gy(RBE) for the bladder. The NTCP values for the rectum were higher in HT for all the sets of parameters, but the gain was small and in only a few cases statistically significant. CONCLUSIONS: Comparable PTV coverage was observed. Based on NTCP calculation, IMPT is expected to allow a small reduction in rectal toxicity, and a significant dosimetric gain with IMPT, both in medium-dose and in low-dose range in all OARs, was observed.

Study of robustness of IMPT and IMRT for prostate cancer against organ movement.

PURPOSE: Intensity-modulated radiotherapy with photons (IMRT) and protons (IMPT) produces dose distributions that have high conformality to the planning target volume and sufficient sparing of the organs at risk if calculated on a single static computed tomography (CT) scan. For prostate cancer patients, organ movement with related changes to the density distribution in the irradiated volume occurs during the treatment course. We evaluated the sensitivity of IMPT and IMRT plans to organ movement. METHODS AND MATERIALS: IMPT and IMRT treatment plans were evaluated for 4 patients with an average of 16 CT data sets per patient. The treatment plans were recalculated on all treatment CT scans, and the dose was accumulated in the reference geometry using a deformable registration algorithm. Accurate dose calculation methods were applied for both IMPT and IMRT. RESULTS: With IMPT, unacceptably low total doses in the gross tumor volume were observed for patients with gas in the rectum on the planning CT scan. To achieve a total equivalent uniform dose (EUD) and EUD spread similar to that with IMRT, two methods were crucial for IMPT-a rectal gas water-equivalent density overwrite in the original planning CT scan and initial beam weight setting to achieve a homogeneous dose distribution for the whole planning target volume for each field separately. An improvement in the total EUD for the prostate and rectal wall was also observed for IMRT with the water-equivalent density overwrite of the rectal cavities. CONCLUSION: The sensitivities of IMPT and IMRT to organ movement are of the same order if appropriate planning strategies are applied. The latter is especially crucial for IMPT.