Human Papillomavirus in Laryngeal Cancer in Northern Region of Turkey

Background and context: Human papilloma virus (HPV) has recently emerged as a new important etiological factor in the development of head and neck squamous cell carcinoma (HNSCC). The association of HPV in laryngeal squamous cell carcinoma (LSCC) is investigated in several studies but controversial results are established. Aim: This retrospective study aimed to evaluate the HPV DNA positivity in LSCC patients diagnosed and treated in 2 otorhinolaryngology referral center in northern region of Turkey. Strategy/Tactics: 52 formalin-fixed, paraffin-embedded (FFPE) tissue blocks of laryngeal cancers, diagnosed and treated between 2010 and 2016, were included. Detection and genotyping of HPV genotypes were done using a polymerase chain reaction (PCR) protocol. Program/Policy process: The study was planned as a retrospective investigation of laryngeal squamous cell cancer patients who had been diagnosed and treated in Samsun 19 Mayis University Hospital and Samsun Training and Research Hospital - otorhinolaryngology referral centers - between January 2010 and December 2016. Samsun is in the middle part of northern Turkey and stated as an oncology center in this region. Approval for the study was granted by the 19 Mayıs University Ethics Committee. The clinical characteristics of the patients were obtained from the computerized database. LSCC tissue samples fixed using 10% neutral buffered formalin and embedded blocks were used. Outcomes: PCR amplification was successful in 40 of 52 patients. Among the 40 LSCC samples HPV DNA was detected in 1 patient (2.5%). HPV 16 subtype was detected in this male patient aged 70 years, with a smoking history and stage III laryngeal cancer. After surgery, the patient received adjuvant radiotherapy and was still alive at 48 months without relapse. What was learned: In northern region of Turkey, this is the first study that evaluated HPV positivity in LSCC. Our results may suggest that HPV-related LSCC has not yet emerged as a significant health burden in our region. This finding may be due to the genetic, cultural or religious characteristics of our patients that are not conducive to oral HPV transmission. Unfortunately tobacco smoking is still the main reason for HNSCC in our city. There is a need for a nationwide screening study to investigate HPV prevalence variability among different regions in Turkey.

The alfa and beta of tumours: a review of parameters of the linear-quadratic model, derived from clinical radiotherapy studies

BACKGROUND

Prediction of radiobiological response is a major challenge in radiotherapy. Of several radiobiological models, the linear-quadratic (LQ) model has been best validated by experimental and clinical data. Clinically, the LQ model is mainly used to estimate equivalent radiotherapy schedules (e.g. calculate the equivalent dose in 2 Gy fractions, EQD₂), but increasingly also to predict tumour control probability (TCP) and normal tissue complication probability (NTCP) using logistic models. The selection of accurate LQ parameters α, β and α/β is pivotal for a reliable estimate of radiation response. The aim of this review is to provide an overview of published values for the LQ parameters of human tumours as a guideline for radiation oncologists and radiation researchers to select appropriate radiobiological parameter values for LQ modelling in clinical radiotherapy.

METHODS AND MATERIALS

We performed a systematic literature search and found sixty-four clinical studies reporting α, β and α/β for tumours. Tumour site, histology, stage, number of patients, type of LQ model, radiation type, TCP model, clinical endpoint and radiobiological parameter estimates were extracted. Next, we stratified by tumour site and by tumour histology. Study heterogeneity was expressed by the I² statistic, i.e. the percentage of variance in reported values not explained by chance.

RESULTS

A large heterogeneity in LQ parameters was found within and between studies (I² > 75%). For the same tumour site, differences in histology partially explain differences in the LQ parameters: epithelial tumours have higher α/β values than adenocarcinomas. For tumour sites with different histologies, such as in oesophageal cancer, the α/β estimates correlate well with histology. However, many other factors contribute to the study heterogeneity of LQ parameters, e.g. tumour stage, type of LQ model, TCP model and clinical endpoint (i.e. survival, tumour control and biochemical control).

CONCLUSIONS

The value of LQ parameters for tumours as published in clinical radiotherapy studies depends on many clinical and methodological factors. Therefore, for clinical use of the LQ model, LQ parameters for tumour should be selected carefully, based on tumour site, histology and the applied LQ model. To account for uncertainties in LQ parameter estimates, exploring a range of values is recommended.

The alfa and beta of tumours: a review of parameters of the linear-quadratic model, derived from clinical radiotherapy studies

Background

Prediction of radiobiological response is a major challenge in radiotherapy. Of several radiobiological models, the linear-quadratic (LQ) model has been best validated by experimental and clinical data. Clinically, the LQ model is mainly used to estimate equivalent radiotherapy schedules (e.g. calculate the equivalent dose in 2 Gy fractions, EQD₂), but increasingly also to predict tumour control probability (TCP) and normal tissue complication probability (NTCP) using logistic models. The selection of accurate LQ parameters α, β and α/β is pivotal for a reliable estimate of radiation response. The aim of this review is to provide an overview of published values for the LQ parameters of human tumours as a guideline for radiation oncologists and radiation researchers to select appropriate radiobiological parameter values for LQ modelling in clinical radiotherapy.

Methods and materials

We performed a systematic literature search and found sixty-four clinical studies reporting α, β and α/β for tumours. Tumour site, histology, stage, number of patients, type of LQ model, radiation type, TCP model, clinical endpoint and radiobiological parameter estimates were extracted. Next, we stratified by tumour site and by tumour histology. Study heterogeneity was expressed by the I² statistic, i.e. the percentage of variance in reported values not explained by chance.

Results

A large heterogeneity in LQ parameters was found within and between studies (I² > 75%). For the same tumour site, differences in histology partially explain differences in the LQ parameters: epithelial tumours have higher α/β values than adenocarcinomas. For tumour sites with different histologies, such as in oesophageal cancer, the α/β estimates correlate well with histology. However, many other factors contribute to the study heterogeneity of LQ parameters, e.g. tumour stage, type of LQ model, TCP model and clinical endpoint (i.e. survival, tumour control and biochemical control).

Conclusions

The value of LQ parameters for tumours as published in clinical radiotherapy studies depends on many clinical and methodological factors. Therefore, for clinical use of the LQ model, LQ parameters for tumour should be selected carefully, based on tumour site, histology and the applied LQ model. To account for uncertainties in LQ parameter estimates, exploring a range of values is recommended.

Electronic supplementary material

The online version of this article (10.1186/s13014-018-1040-z) contains supplementary material, which is available to authorized users.

The effect of time interval between radiotherapy and hyperthermia on planned equivalent radiation dose

PURPOSE

Thermoradiotherapy is an effective treatment for locally advanced cervical cancer. However, the optimal time interval between radiotherapy and hyperthermia, resulting in the highest therapeutic gain, remains unclear. This study aims to evaluate the effect of time interval on the therapeutic gain using biological treatment planning.

METHODS

Radiotherapy and hyperthermia treatment plans were created for 15 cervical cancer patients. Biological modeling was used to calculate the equivalent radiation dose, that is, the radiation dose that results in the same biological effect as the thermoradiotherapy treatment, for different time intervals ranging from 0-4 h. Subsequently, the thermal enhancement ratio (TER, i.e. the ratio of the dose for the thermoradiotherapy and the radiotherapy-only plan) was calculated for the gross tumor volume (GTV) and the organs at risk (OARs: bladder, rectum, bowel), for each time interval. Finally, the therapeutic gain factor (TGF, i.e. TER_GTV/TER_OAR) was calculated for each OAR.

RESULTS

The median TER_GTV ranged from 1.05 to 1.16 for 4 h and 0 h time interval, respectively. Similarly, for bladder, rectum and bowel, TER_OARs ranged from 1-1.03, 1-1.04 and 1-1.03, respectively. Radiosensitization in the OARs was much less than in the GTV, because temperatures were lower, fractionation sensitivity was higher (lower α/β) and direct cytotoxicity was assumed negligible in normal tissue. TGFs for the three OARs were similar, and were highest (around 1.12) at 0 h time interval.

CONCLUSION

This planning study indicates that the largest therapeutic gain for thermoradiotherapy in cervical cancer patients can be obtained when hyperthermia is delivered immediately before or after radiotherapy.

A novel controller based on state-transition models for closed-loop vagus nerve stimulation: Application to heart rate regulation

Vagus nerve stimulation (VNS) is an established adjunctive therapy for pharmacologically refractory epilepsy and depression and is currently in active clinical research for other applications. In current clinical studies, VNS is delivered in an open-loop approach, where VNS parameters are defined during a manual titration phase. However, the physiological response to a given VNS configuration shows significant inter and intra-patient variability and may significantly evolve through time. VNS closed-loop approaches, allowing for the optimization of the therapy in an adaptive manner, may be necessary to improve efficacy while reducing side effects. This paper proposes a generic, closed-loop control VNS system that is able to optimize a number of VNS parameters in an adaptive fashion, in order to keep a control variable within a specified range. Although the proposed control method is completely generic, an example application using the cardiac beat to beat interval (RR) as control variable will be developed in this paper. The proposed controller is based on a state transition model (STM) that can be configured using a partially or a fully-connected architecture, different model orders and different state-transition algorithms. The controller is applied to the adaptive regulation of heart rate and evaluated on 6 sheep, for 13 different targets, using partially-connected STM with 10 states. Also, partially and fully-connected STM defined by 30 states were applied to 7 other sheep for the same 10 targets. Results illustrate the interest of the proposed fully-connected STM and the feasibility of integrating this control system into an implantable neuromodulator.

Pulsed Cavitational Ultrasound Softening: a new non-invasive therapeutic approach of calcified bioprosthetic valve stenosis

BACKGROUND

The majority of prosthetic heart valves currently implanted are tissue valves that can be expected to calcify with time and eventually fail. Surgical or percutaneous redux valve replacement is associated with higher rate of complications. We propose a novel non-invasive therapeutic approach based on the use of pulsed cavitational ultrasound (PCU) to improve the valvular function of degenerative calcified bioprosthesis.

OBJECTIVES

Our study aims to demonstrate in vitro and in vivo on an ovine model that PCU can significantly improve the bioprosthesis opening by softening remotely the calcified stiff cusps.

METHODS

All the experiments were performed on calcified bioprosthetic valves explanted from human patients. PCU was performed in vitro on calcified bioprosthesis mounted on a hydraulic bench with pulsatile flow (n=8) and in vivo on an ovine model with implanted calcified bioprosthesis (n=7). We used 3D echocardiography, pressure and flow sensors, quantitative stiffness evaluation using shear wave elastography, micro-CT imaging and histology to evaluate in vitro and in vivo the effect of PCU.

RESULTS

The transvalvular gradient was found to decrease by a mean of 50% after PCU in both in vitro (from 21.1±3.9 to 9.6±1.7 mmHg, p<0.001) and in vivo setup (from 16.2±3.2 to 8.2±1.3 mmHg, p<0.001), with a decrease of valve stiffness (in vitro: from 105.8±9 to 46.6±4 kPa, p<0.001; in vivo: from 82.6±10 to 41.7±7 kPa, p<0.001) and an increase of valve area (from 1.10±0.1 to 1.58±0.1 cm2, p<0.001). Histology and micro-CT imaging showed modifications of calcification structure without loss of calcification volume or alteration of the leaflet superficial structures.

CONCLUSIONS

We have demonstrated in vitro and in vivo that PCU can decrease a calcified bioprosthesis stenosis by softening the leaflets remotely. This new non-invasive approach has the potential to improve the outcome of patients with severe bioprosthesis stenosis.

Measurement and analysis of the impact of time-interval, temperature and radiation dose on tumour cell survival and its application in thermoradiotherapy plan evaluation

PURPOSE

Biological modelling of thermoradiotherapy may further improve patient selection and treatment plan optimisation, but requires a model that describes the biological effect as a function of variables that affect treatment outcome (e.g. temperature, radiation dose). This study aimed to establish such a model and its parameters. Additionally, a clinical example was presented to illustrate the application.

METHODS

Cell survival assays were performed at various combinations of radiation dose (0-8 Gy), temperature (37-42 °C), time interval (0-4 h) and treatment sequence (radiotherapy before/after hyperthermia) for two cervical cancer cell lines (SiHa and HeLa). An extended linear-quadratic model was fitted to the data using maximum likelihood estimation. As an example application, a thermoradiotherapy plan (23 × 2 Gy + weekly hyperthermia) was compared with a radiotherapy-only plan (23 × 2 Gy) for a cervical cancer patient. The equivalent uniform radiation dose (EUD) in the tumour, including confidence intervals, was estimated using the SiHa parameters. Additionally, the difference in tumour control probability (TCP) was estimated.

RESULTS

Our model described the dependency of cell survival on dose, temperature and time interval well for both SiHa and HeLa data (R²=0.90 and R²=0.91, respectively), making it suitable for biological modelling. In the patient example, the thermoradiotherapy plan showed an increase in EUD of 9.8 Gy that was robust (95% CI: 7.7-14.3 Gy) against propagation of the uncertainty in radiobiological parameters. This corresponded to a 20% (95% CI: 15-29%) increase in TCP.

CONCLUSIONS

This study presents a model that describes the cell survival as a function of radiation dose, temperature and time interval, which is essential for biological modelling of thermoradiotherapy treatments.

Technical Aspects of Open Repair for Degenerative Aneurysmal Evolution Despite Early Thoracic Endovascular Repair of Type B Aortic Dissection

BACKGROUND

Closure of the proximal tear by thoracic endovascular aortic repair (TEVAR) at the acute phase appears to be a safe effective treatment to prevent aneurysmal degeneration type B dissection. However, it appears to be inefficient in up to a third of the patient. We report the technical aspects of our experience with patients undergoing secondary open repair after TEVAR for dissecting thoracoabdominal aneurysm despite early closure proximal tear by TEVAR.

METHODS

During a period of 5 years, 96 patients presenting acute type B aortic dissections were treated by TEVAR and followed-up in our institution. Among them, 5 patients experienced an evolution to a dissecting thoracoabdominal aortic aneurysm. Their demographic data and initial medical conditions, delay to reintervention, operative technical details, perioperative and mid-term outcomes were collected and analyzed.

RESULTS

All 5 patients (4 male, mean age 58 ± 9) were operated under peripheral normothermic bypass without deep circulatory arrest using the thoracic stent graft as an elephant trunk for completion of the proximal anastomosis. In cases of patency, the false lumen was reapproximated in the anastomosis, 6 visceral arteries were revascularized selectively. One patient died at day 1 of perioperative ventricular fibrillation due to an acute myocardial infarction. The 4 others are alive without complication after a median of 30 months, range (13-22).

CONCLUSIONS

In our experience, TEVAR was not only efficient at the acute phase to deal with complications, but in cases of subsequent aneurysmal evolution, it made open repair even easier by avoiding very proximal cross-clamping/anastomosis and circulatory arrest.

3D radiobiological evaluation of combined radiotherapy and hyperthermia treatments

PURPOSE

Currently, clinical decisions regarding thermoradiotherapy treatments are based on clinical experience. Quantification of the radiosensitising effect of hyperthermia allows comparison of different treatment strategies, and can support clinical decision-making regarding the optimal treatment. The software presented here enables biological evaluation of thermoradiotherapy plans through calculation of equivalent 3D dose distributions.

METHODS

Our in-house developed software (X-Term) uses an extended version of the linear-quadratic model to calculate equivalent radiation dose, i.e. the radiation dose yielding the same effect as the thermoradiotherapy treatment. Separate sets of model parameters can be assigned to each delineated structure, allowing tissue specific modelling of hyperthermic radiosensitisation. After calculation, the equivalent radiation dose can be evaluated according to conventional radiotherapy planning criteria. The procedure is illustrated using two realistic examples. First, for a previously irradiated patient, normal tissue dose for a radiotherapy and thermoradiotherapy plan (with equal predicted tumour control) is compared. Second, tumour control probability (TCP) is assessed for two (otherwise identical) thermoradiotherapy schedules with different time intervals between radiotherapy and hyperthermia.

RESULTS

The examples demonstrate that our software can be used for individualised treatment decisions (first example) and treatment optimisation (second example) in thermoradiotherapy. In the first example, clinically acceptable doses to the bowel were exceeded for the conventional plan, and a substantial reduction of this excess was predicted for the thermoradiotherapy plan. In the second example, the thermoradiotherapy schedule with long time interval was shown to result in a substantially lower TCP.

CONCLUSIONS

Using biological modelling, our software can facilitate the evaluation of thermoradiotherapy plans and support individualised treatment decisions.

Sensitivity Analysis of Vagus Nerve Stimulation Parameters on Acute Cardiac Autonomic Responses: Chronotropic, Inotropic and Dromotropic Effects

Although the therapeutic effects of Vagus Nerve Stimulation (VNS) have been recognized in pre-clinical and pilot clinical studies, the effect of different stimulation configurations on the cardiovascular response is still an open question, especially in the case of VNS delivered synchronously with cardiac activity. In this paper, we propose a formal mathematical methodology to analyze the acute cardiac response to different VNS configurations, jointly considering the chronotropic, dromotropic and inotropic cardiac effects. A latin hypercube sampling method was chosen to design a uniform experimental plan, composed of 75 different VNS configurations, with different values for the main parameters (current amplitude, number of delivered pulses, pulse width, interpulse period and the delay between the detected cardiac event and VNS onset). These VNS configurations were applied to 6 healthy, anesthetized sheep, while acquiring the associated cardiovascular response. Unobserved VNS configurations were estimated using a Gaussian process regression (GPR) model. In order to quantitatively analyze the effect of each parameter and their combinations on the cardiac response, the Sobol sensitivity method was applied to the obtained GPR model and inter-individual sensitivity markers were estimated using a bootstrap approach. Results highlight the dominant effect of pulse current, pulse width and number of pulses, which explain respectively 49.4%, 19.7% and 6.0% of the mean global cardiovascular variability provoked by VNS. More interestingly, results also quantify the effect of the interactions between VNS parameters. In particular, the interactions between current and pulse width provoke higher cardiac effects than the changes on the number of pulses alone (between 6 and 25% of the variability). Although the sensitivity of individual VNS parameters seems similar for chronotropic, dromotropic and inotropic responses, the interacting effects of VNS parameters provoke significantly different cardiac responses, showing the feasibility of a parameter-based functional selectivity. These results are of primary importance for the optimal, subject-specific definition of VNS parameters for a given therapy and may lead to new closed-loop methods allowing for the optimal adaptation of VNS therapy through time.

A biological modeling based comparison of two strategies for adaptive radiotherapy of urinary bladder cancer

Background Adaptive radiotherapy is introduced in the management of urinary bladder cancer to account for day-to-day anatomical changes. The purpose of this study was to determine whether an adaptive plan selection strategy using either the first four cone beam computed tomography scans (CBCT-based strategy) for plan creation, or the interpolation of bladder volumes on pretreatment CT scans (CT-based strategy), is better in terms of tumor control probability (TCP) and normal tissue sparing while taking the clinically applied fractionation schedules also into account. Material and methods With the CT-based strategy, a library of five plans was created. Patients received 55 Gy to the bladder tumor and 40 Gy to the non-involved bladder and lymph nodes, in 20 fractions. With the CBCT-based strategy, a library of three plans was created, and patients received 70 Gy to the tumor, 60 Gy to the bladder and 48 Gy to the lymph nodes, in 30-35 fractions. Ten patients were analyzed for each adaptive plan selection strategy. TCP was calculated applying the clinically used fractionation schedules, as well as a rescaling of the dose from 55 to 70 Gy for the CT-based strategy. For rectum and bowel, equivalent doses in 2 Gy fractions (EQD2) were calculated. Results The CBCT-based strategy resulted in a median TCP of 75%, compared to 49% for the CT-based strategy, the latter improving to 72% upon rescaling the dose to 70 Gy. A median rectum V30Gy (EQD2) of 26% [interquartile range (IQR): 8-52%] was found for the CT-based strategy, compared to 58% (IQR: 55-73%) for the CBCT-based strategy. Also the bowel doses were lower with the CT-based strategy. Conclusions Whereas the higher total bladder TCP for the CBCT-based strategy is due to prescription differences, the adaptive strategy based on CT scans results in the lowest rectum and bowel cavity doses.

Influence of Vagus Nerve Stimulation parameters on chronotropism and inotropism in heart failure

Vagus Nerve Stimulation (VNS) has been shown to be useful in heart failure patients, including antiarrhythmic effects, improvement of cardiac function and reduction of the mortality. However, the optimal configuration of VNS can be a difficult task, since there are several adjustable parameters, such as current amplitude (mA), pulse width (ms), burst frequency (Hz), number of pulses and, in the case of cardiac-triggered VNS, the delay (ms) between the R-wave and the beginning of the stimulation. The objective of this paper is to analyse the effect of these parameters, and their interaction, on the chronotropic and inotropic responses to vagal stimulation. 306 VNS sequences were tested on 12 sheep with induced heart failure. Autonomic markers of the chronotropic (changes in RR interval) and inotropic (changes in dP/dtmax) effects were extracted from the observed data. In order to analyse the influence of stimulation parameters on these markers, a sensitivity analysis method was applied. Results illustrate the strong interaction between the delay and the others parameters. The number of pulses, the current and the frequency seem to be particularly influent on chronotropism and inotropism although the effect of the frequency is highly non-linear or it depends on other parameters.

Shear Wave Imaging of Passive Diastolic Myocardial Stiffness: Stunned Versus Infarcted Myocardium

Objectives

The aim of this study was to investigate the potential of shear wave imaging (SWI), a novel ultrasound-based technique, to noninvasively quantify passive diastolic myocardial stiffness in an ovine model of ischemic cardiomyopathy.

Background

Evaluation of diastolic left ventricular function is critical for evaluation of heart failure and ischemic cardiomyopathy. Myocardial stiffness is known to be an important property for the evaluation of the diastolic myocardial function, but this parameter cannot be measured noninvasively by existing techniques.

Methods

SWI was performed in vivo in open-chest procedures in 10 sheep. Ligation of a diagonal of the left anterior descending coronary artery was performed for 15 min (stunned group, n = 5) and 2 h (infarcted group, n = 5). Each procedure was followed by a 40-min reperfusion period. Diastolic myocardial stiffness was measured at rest, during ischemia, and after reperfusion by using noninvasive shear wave imaging. Simultaneously, end-diastolic left ventricular pressure and segmental strain were measured with a pressure catheter and sonomicrometers during transient vena caval occlusions to obtain gold standard evaluation of myocardial stiffness using end-diastolic strain-stress relationship (EDSSR).

Results

In both groups, the end-systolic circumferential strain was drastically reduced during ischemia (from 14.2 ± 1.2% to 1.3 ± 1.6% in the infarcted group and from 13.5 ± 3.0% to 1.9 ± 1.8% in the stunned group; p <0.01). SWI diastolic stiffness increased after 2 h of ischemia from 1.7 ± 0.4 to 6.2 ± 2.2 kPa (p < 0.05) and even more after reperfusion (12.1 ± 4.2 kPa; p < 0.01). Diastolic myocardial stiffening was confirmed by the exponential constant coefficient of the EDSSR, which increased from 8.8 ± 2.3 to 25.7 ± 9.5 (p < 0.01). In contrast, SWI diastolic stiffness was unchanged in the stunned group (2.3 ± 0.4 kPa vs 1.8 ± 0.3 kPa, p = NS) which was confirmed also by the exponential constant of EDSSR (9.7 ± 3.1 vs 10.2 ± 2.3, p = NS).

Conclusions

Noninvasive SWI evaluation of diastolic myocardial stiffness can differentiate between stiff, noncompliant infarcted wall and softer wall containing stunned myocardium.

Beam configuration selection for robust intensity-modulated proton therapy in cervical cancer using Pareto front comparison

The Pareto front reflects the optimal trade-offs between conflicting objectives and can be used to quantify the effect of different beam configurations on plan robustness and dose-volume histogram parameters. Therefore, our aim was to develop and implement a method to automatically approach the Pareto front in robust intensity-modulated proton therapy (IMPT) planning. Additionally, clinically relevant Pareto fronts based on different beam configurations will be derived and compared to enable beam configuration selection in cervical cancer proton therapy. A method to iteratively approach the Pareto front by automatically generating robustly optimized IMPT plans was developed. To verify plan quality, IMPT plans were evaluated on robustness by simulating range and position errors and recalculating the dose. For five retrospectively selected cervical cancer patients, this method was applied for IMPT plans with three different beam configurations using two, three and four beams. 3D Pareto fronts were optimized on target coverage (CTV D(99%)) and OAR doses (rectum V30Gy; bladder V40Gy). Per patient, proportions of non-approved IMPT plans were determined and differences between patient-specific Pareto fronts were quantified in terms of CTV D(99%), rectum V(30Gy) and bladder V(40Gy) to perform beam configuration selection. Per patient and beam configuration, Pareto fronts were successfully sampled based on 200 IMPT plans of which on average 29% were non-approved plans. In all patients, IMPT plans based on the 2-beam set-up were completely dominated by plans with the 3-beam and 4-beam configuration. Compared to the 3-beam set-up, the 4-beam set-up increased the median CTV D(99%) on average by 0.2 Gy and decreased the median rectum V(30Gy) and median bladder V(40Gy) on average by 3.6% and 1.3%, respectively. This study demonstrates a method to automatically derive Pareto fronts in robust IMPT planning. For all patients, the defined four-beam configuration was found optimal in terms of plan robustness, target coverage and OAR sparing.