Comparison of Dynamic Trajectory Radiotherapy and Volumetric Modulated Arc Therapy for Loco-Regionally Advanced Oropharyngeal Cancer

PURPOSE/OBJECTIVE(S)

Dynamic trajectory radiotherapy (DTRT) extends volumetric modulated arc therapy (VMAT) with dynamic table and collimator rotation. We investigate the potential benefit of DTRT over VMAT with respect to organ-at-risk (OAR) sparing for patients with loco-regionally advanced oropharyngeal cancer (OPC).

MATERIALS/METHODS

We created DTRT and VMAT plans for 46 cases with prescribed doses of 50-70 Gy (2 Gy fractions, sequential boost) using 6 MV flattened beam on c-arm Linacs. For DTRT: case-specific collision avoidance maps were created and gantry-table paths were determined based on contoured structures to minimize fractional target/OAR overlap in beam's eye view. Gantry-collimator paths minimized field width in the leaf-travel direction. DTRT paths were imported in a research version of a commercial treatment planning system for intensity modulation optimization using the same optimizer and dose calculation algorithms as for VMAT. Plans at each dose level were normalized with 100% of the prescribed dose to 95% of the planning target volume (PTV). PTV coverage and OAR sparing for DTRT and VMAT were compared using Wilcoxon matched-pair signed rank test (5% significance level). The correlation between the fractional OAR/PTV50Gy volume overlap and difference in OAR Dmean between the two techniques was evaluated using Spearman's correlation coefficient.

RESULTS

Plans at each dose level were all acceptable and had D0.03cc<110% prescription dose (difference between DTRT and VMAT were not statistically significant). In the combined plans, PTV50Gy D95% and D98% and PTV70Gy D95% were significantly higher with DTRT compared to VMAT. Differences in PTV66Gy coverage and PTV70Gy D5% were not statistically significant. Mean Dmean to the contralateral (CL) parotid gland was 13.99 / 15.28 Gy for DTRT / VMAT respectively, it was 25.75 / 28.05 Gy for the CL submandibular gland, 44.88 / 45.82 Gy for the pharynx and 30.90 / 33.93 Gy for the oral cavity (all with p<.001). Mean Dmean to the ipsilateral (IL) parotid gland was 29.00 / 29.28 Gy for DTRT / VMAT respectively (p = .77) and 57.71 / 57.91 Gy for the IL submandibular gland (p = .99). Significantly higher doses were observed with DTRT than with VMAT for the optical and auditory OARs and for the brain, but well below the clinical goals. The difference in Dmean (VMAT-DTRT) was negatively correlated to the fractional OAR/PTV50Gy overlap for the CL parotid and submandibular gland and the IL submandibular gland (r = -0.55 to -0.51, p<.001) but not for IL parotid gland (r = -0.17, p = .26), oral cavity (r = -0.13, p = .41) or pharynx (r = -011, p = .47).

CONCLUSION

For at least the same target coverage, DTRT statistically significantly improves sparing for OARs related to salivary and swallowing functions compared to state-of-the-art VMAT. The advantage of DTRT decreases with increasing fractional OAR/PTV50Gy volume overlap for some salivary glands but not for pharynx or oral cavity. DTRT is promising to reduce treatment-related toxicity for patients with OPC.

Efficiency enhancements of a Monte Carlo beamlet based treatment planning process: implementation and parameter study

Objective.The computational effort to perform beamlet calculation, plan optimization and final dose calculation of a treatment planning process (TPP) generating intensity modulated treatment plans is enormous, especially if Monte Carlo (MC) simulations are used for dose calculation. The goal of this work is to improve the computational efficiency of a fully MC based TPP for static and dynamic photon, electron and mixed photon-electron treatment techniques by implementing multiple methods and studying the influence of their parameters.Approach.A framework is implemented calculating MC beamlets efficiently in parallel on each available CPU core. The user can specify the desired statistical uncertainty of the beamlets, a fractional sparse dose threshold to save beamlets in a sparse format and minimal distances to the PTV surface from which 2 × 2 × 2 = 8 (medium) or even 4 × 4 × 4 = 64 (large) voxels are merged. The compromise between final plan quality and computational efficiency of beamlet calculation and optimization is studied for several parameter values to find a reasonable trade-off. For this purpose, four clinical and one academic case are considered with different treatment techniques.Main results.Setting the statistical uncertainty to 5% (photon beamlets) and 15% (electron beamlets), the fractional sparse dose threshold relative to the maximal beamlet dose to 0.1% and minimal distances for medium and large voxels to the PTV to 1 cm and 2 cm, respectively, does not lead to substantial degradation in final plan quality compared to using 2.5% (photon beamlets) and 5% (electron beamlets) statistical uncertainty and no sparse format nor voxel merging. Only OAR sparing is slightly degraded. Furthermore, computation times are reduced by about 58% (photon beamlets), 88% (electron beamlets) and 96% (optimization).Significance.Several methods are implemented improving computational efficiency of beamlet calculation and plan optimization of a fully MC based TPP without substantial degradation in final plan quality.

Enabling non-isocentric dynamic trajectory radiotherapy by integration of dynamic table translations

Objective. The purpose of this study is to develop a treatment planning process (TPP) for non-isocentric dynamic trajectory radiotherapy (DTRT) using dynamic gantry rotation, collimator rotation, table rotation, longitudinal, vertical and lateral table translations and intensity modulation and to validate the dosimetric accuracy. Approach. The TPP consists of two steps. First, a path describing the dynamic gantry rotation, collimator rotation and dynamic table rotation and translations is determined. Second, an optimization of the intensity modulation along the path is performed. We demonstrate the TPP for three use cases. First, a non-isocentric DTRT plan for a brain case is compared to an isocentric DTRT plan in terms of dosimetric plan quality and delivery time. Second, a non-isocentric DTRT plan for a craniospinal irradiation (CSI) case is compared to a multi-isocentric intensity modulated radiotherapy (IMRT) plan. Third, a non-isocentric DTRT plan for a bilateral breast case is compared to a multi-isocentric volumetric modulated arc therapy (VMAT) plan. The non-isocentric DTRT plans are delivered on a TrueBeam in developer mode and their dosimetric accuracy is validated using radiochromic films. Main results. The non-isocentric DTRT plan for the brain case is similar in dosimetric plan quality and delivery time to the isocentric DTRT plan but is expected to reduce the risk of collisions. The DTRT plan for the CSI case shows similar dosimetric plan quality while reducing the delivery time by 45% in comparison with the IMRT plan. The DTRT plan for the breast case showed better treatment plan quality in comparison with the VMAT plan. The gamma passing rates between the measured and calculated dose distributions are higher than 95% for all three plans. Significance. The versatile benefits of non-isocentric DTRT are demonstrated with three use cases, namely reduction of collision risk, reduced setup and delivery time and improved dosimetric plan quality.

P06.08.B Radiation therapy enhances anti-tumor activity of a MET CAR T-based immunotherapy for glioblastoma

Background

Glioblastoma is the most frequent primary brain tumor with dismal prognosis after standard treatment with surgery, and chemoradiation (the Stupp protocol). After a decade of failed clinical trials, tumor-treating fields have been first to show the added benefit of improved overall survival compared to the Stupp protocol (20.9 months vs 16.0 months). However, GBM remains a devastating disease, with almost inevitable recurrence, and limited options for second-line therapy. Radiation therapy (RT), is a standard therapy option for GBM, and it is used in most GBM cases affecting tumor through induction of DNA-damage. Recently, RT has been investigated as a mediator of T cell-based therapies in the context of immunosuppressive GBM microenvironment. The findings have shown promise in combination of T cell-based therapies, such as chimeric antigen receptor (CAR) T cell therapies, in improving the tumor infiltration, and penetration with immune cells. MET is a relevant oncogene in the context of GBM, being involved in stem-like properties, radiation response and resistance․ Hence, MET appeared to be a plausible target for combination with RT. In our research, we use MET-targeting CAR T cells (MET-CAR T cells) combined with radiation, and hypothesize synergistic interaction for GBM treatment.

Material and Methods

We used adherent (2D) and stem-like (3D) human GBM cell lines with different levels of MET expression. For MET-CAR T cell generation we did retrovirus-mediated transduction of activated human T cells and sorted the CAR-positive cells. We co-cultured MET-CAR T cells with GBM cells with or without RT, and assessed the killing and cytokine production in CAR T cells.

Results

Our results indicated that 5Gy radiation combined with MET-CAR T cells increases their potential in tumor cell killing. We observed increased CAR T cells effect at lower CAR T to target cells ratios when combined with radiation, even when radiation treatment did not lead to a significant decrease in viability. This phenomenon was similar across different types of cell lines (adherent, stem-like), different levels of MET expression, and different sensitivity to CAR T cells. We investigated the underlying mechanisms via intracellular cytokine measurement. We observed the most prominent response in TNF-α-expression. We also observed an increase in Granzyme B expression in co-culture with some of the GBM cell lines, especially in CD8+ subpopulation of CAR T cells. IFN-gamma expression increased in some adherent glioma cell lines but not in stem-like cell lines.

Conclusion

In conclusion, our data demonstrates the potency of MET-CAR T cells against GBM, and increased efficiency when combined with radiation. The suggested mechanism is the increased activation of T cells in TNF-α-dependent-manner. To validate these results we are testing our setup in an orthotopic mouse GBM model.

Development of a Monte Carlo based robustness calculation and evaluation tool

Background

Evaluating plan robustness is a key step in radiotherapy.

Purpose

To develop a flexible Monte Carlo (MC)‐based robustness calculation and evaluation tool to assess and quantify dosimetric robustness of intensity‐modulated radiotherapy (IMRT) treatment plans by exploring the impact of systematic and random uncertainties resulting from patient setup, patient anatomy changes, and mechanical limitations of machine components.

Methods

The robustness tool consists of two parts: the first part includes automated MC dose calculation of multiple user‐defined uncertainty scenarios to populate a robustness space. An uncertainty scenario is defined by a certain combination of uncertainties in patient setup, rigid intrafraction motion and in mechanical steering of the following machine components: angles of gantry, collimator, table‐yaw, table‐pitch, table‐roll, translational positions of jaws, multileaf‐collimator (MLC) banks, and single MLC leaves. The Swiss Monte Carlo Plan (SMCP) is integrated in this tool to serve as the backbone for the MC dose calculations incorporating the uncertainties. The calculated dose distributions serve as input for the second part of the tool, handling the quantitative evaluation of the dosimetric impact of the uncertainties. A graphical user interface (GUI) is developed to simultaneously evaluate the uncertainty scenarios according to user‐specified conditions based on dose‐volume histogram (DVH) parameters, fast and exact gamma analysis, and dose differences. Additionally, a robustness index (RI) is introduced with the aim to simultaneously evaluate and condense dosimetric robustness against multiple uncertainties into one number. The RI is defined as the ratio of scenarios passing the conditions on the dose distributions. Weighting of the scenarios in the robustness space is possible to consider their likelihood of occurrence. The robustness tool is applied on IMRT, a volumetric modulated arc therapy (VMAT), a dynamic trajectory radiotherapy (DTRT), and a dynamic mixed beam radiotherapy (DYMBER) plan for a brain case to evaluate the robustness to uncertainties of gantry‐, table‐, collimator angle, MLC, and intrafraction motion. Additionally, the robustness of the IMRT, VMAT, and DTRT plan against patient setup uncertainties are compared. The robustness tool is validated by Delta4 measurements for scenarios including all uncertainty types available.

Results

The robustness tool performs simultaneous calculation of uncertainty scenarios, and the GUI enables their fast evaluation. For all evaluated plans and uncertainties, the planning target volume (PTV) margin prevented major clinical target volume (CTV) coverage deterioration (maximum observed standard deviation of D98%CTV was 1.3 Gy). OARs close to the PTV experienced larger dosimetric deviations (maximum observed standard deviation of D2%chiasma was 14.5 Gy). Robustness comparison by RI evaluation against patient setup uncertainties revealed better dosimetric robustness of the VMAT and DTRT plans as compared to the IMRT plan. Delta4 validation measurements agreed with calculations by >96% gamma‐passing rate (3% global/2 mm).

Conclusions

The robustness tool was successfully implemented. Calculation and evaluation of uncertainty scenarios with the robustness tool were demonstrated on a brain case. Effects of patient and machine‐specific uncertainties and the combination thereof on the dose distribution are evaluated in a user‐friendly GUI to quantitatively assess and compare treatment plans and their robustness.

A hybrid column generation and simulated annealing algorithm for direct aperture optimization

The purpose of this work was to develop a hybrid column generation (CG) and simulated annealing (SA) algorithm for direct aperture optimization (H-DAO) and to show its effectiveness in generating high quality treatment plans for intensity modulated radiation therapy (IMRT) and mixed photon-electron beam radiotherapy (MBRT). The H-DAO overcomes limitations of the CG-DAO with two features improving aperture selection (branch-feature) and enabling aperture shape changes during optimization (SA-feature). The H-DAO algorithm iteratively adds apertures to the plan. At each iteration, a branch is created for each field provided. First, each branch determines the most promising aperture of its assigned field and adds it to a copy of the current apertures. Afterwards, the apertures of each branch undergo an MU-weight optimization followed by an SA-based simultaneous shape and MU-weight optimization and a second MU-weight optimization. The next H-DAO iteration continues the branch with the lowest objective function value. IMRT and MBRT treatment plans for an academic, a brain and a head and neck case generated using the CG-DAO and H-DAO were compared. For every investigated case and both IMRT and MBRT, the H-DAO leads to a faster convergence of the objective function value with number of apertures compared to the CG-DAO. In particular, the H-DAO needs about half the apertures to reach the same objective function value as the CG-DAO. The average aperture areas are 27% smaller for H-DAO than for CG-DAO leading to a slightly larger discrepancy between optimized and final dose. However, a dosimetric benefit remains. The H-DAO was successfully developed and applied to IMRT and MBRT. The faster convergence with number of apertures of the H-DAO compared to the CG-DAO allows to select a better compromise between plan quality and number of apertures.

TriB-RT: Simultaneous optimization of photon, electron and proton beams

PURPOSE

To develop a novel treatment planning process (TPP) with simultaneous optimization of modulated photon, electron and proton beams for improved treatment plan quality in radiotherapy.

METHODS

A framework for fluence map optimization of Monte Carlo (MC) calculated beamlet dose distributions is developed to generate treatment plans consisting of photon, electron and spot scanning proton fields. Initially, in-house intensity modulated proton therapy (IMPT) plans are compared to proton plans created by a commercial treatment planning system (TPS). A triple beam radiotherapy (TriB-RT) plan is generated for an exemplary academic case and the dose contributions of the three particle types are investigated. To investigate the dosimetric potential, a TriB-RT plan is compared to an in-house IMPT plan for two clinically motivated cases. Benefits of TriB-RT for a fixed proton beam line with a single proton field are investigated.

RESULTS

In-house optimized IMPT are of at least equal or better quality than TPS-generated proton plans, and MC-based optimization shows dosimetric advantages for inhomogeneous situations. Concerning TriB-RT, for the academic case, the resulting plan shows substantial contribution of all particle types. For the clinically motivated case, improved sparing of organs at risk close to the target volume is achieved compared to IMPT (e.g. myelon and brainstem [Formula: see text] -37%) at cost of an increased low dose bath (healthy tissue V _10% +22%). In the scenario of a fixed proton beam line, TriB-RT plans are able to compensate the loss in degrees of freedom to substantially improve plan quality compared to a single field proton plan.

CONCLUSION

A novel TPP which simultaneously optimizes photon, electron and proton beams was successfully developed. TriB-RT shows the potential for improved treatment plan quality and is especially promising for cost-effective single-room proton solutions with a fixed beamline in combination with a conventional linac delivering photon and electron fields.

A cost-effectiveness analysis of consolidation immunotherapy with durvalumab in stage III NSCLC responding to definitive radiochemotherapy in Switzerland

BACKGROUND

Consolidation immunotherapy with the programmed death ligand 1 (PD-L1) inhibitor durvalumab improves survival in patients with stage III non-small-cell lung cancer responding to radiochemotherapy. The aim of this study was to assess the cost-effectiveness of durvalumab in Switzerland based on the most recent PACIFIC survival follow-up.

MATERIALS AND METHODS

We constructed a Markov model based on the 3-year follow-up data of the PACIFIC trial and compared consolidation durvalumab with observation. We used published utility values and assessed costs for treatment strategies from the perspective of the Swiss health care payers. Cost-effectiveness was tested both in the intention-to-treat population of the PACIFIC trial unselected for PD-L1 tumor expression and in patients with PD-L1-expressing tumors (≥1%).

RESULTS

In the unselected/PD-L1-positive patients, durvalumab showed an incremental effectiveness of 0.76/1.18 quality-adjusted life year (QALY) and incremental costs of Swiss Francs (CHF) 67 239/78 177, resulting in incremental cost-effectiveness ratios of CHF 88 703/66 131 per QALY gained, respectively. The most influential factors for the incremental cost-effectiveness ratio were the utility before first progression, costs for durvalumab, and the hazard ratio for overall survival under durvalumab versus observation. The cost-effectiveness of durvalumab was better than CHF 100 000 per QALY gained in 75% of the simulations in probabilistic sensitivity analysis.

CONCLUSION

Assuming a willingness-to-pay threshold of CHF 100 000 per QALY gained, consolidation durvalumab is likely to be cost-effective both in patients with inoperable stage III non-small-cell lung cancer (NSCLC) unselected for PD-L1 status and in patients with PD-L1-expressing tumors in Switzerland.

Benchmarking Monte-Carlo dose calculation for MLC CyberKnife treatments

Background

Vendor-independent Monte Carlo (MC) dose calculation (IDC) for patient-specific quality assurance of multi-leaf collimator (MLC) based CyberKnife treatments is used to benchmark and validate the commercial MC dose calculation engine for MLC based treatments built into the CyberKnife treatment planning system (Precision MC).

Methods

The benchmark included dose profiles in water in 15 mm depth and depth dose curves of rectangular MLC shaped fields ranging from 7.6 mm × 7.7 mm to 115.0 mm  × 100.1 mm, which were compared between IDC, Precision MC and measurements in terms of dose difference and distance to agreement. Dose distributions of three phantom cases and seven clinical lung cases were calculated using both IDC and Precision MC. The lung PTVs ranged from 14 cm³ to 93 cm³. Quantitative comparison of these dose distributions was performed using dose-volume parameters and 3D gamma analysis with 2% global dose difference and 1 mm distance criteria and a global 10% dose threshold. Time to calculate dose distributions was recorded and efficiency was assessed.

Results

Absolute dose profiles in 15 mm depth in water showed agreement between Precision MC and IDC within 3.1% or 1 mm. Depth dose curves agreed within 2.3% / 1 mm. For the phantom and clinical lung cases, mean PTV doses differed from − 1.0 to + 2.3% between IDC and Precision MC and gamma passing rates were > =98.1% for all multiple beam treatment plans. For the lung cases, lung V20 agreed within ±1.5%. Calculation times ranged from 2.2 min (for 39 cm³ PTV at 1.0 × 1.0 × 2.5 mm³ native CT resolution) to 8.1 min (93 cm³ at 1.1 × 1.1 × 1.0 mm³), at 2% uncertainty for Precision MC for the 7 examined lung cases and 4–6 h for IDC, which, however, is not optimized for efficiency but used as a gold standard for accuracy.

Conclusions

Both accuracy and efficiency of Precision MC in the context of MLC based planning for the CyberKnife M6 system were benchmarked against MC based IDC framework. Precision MC is used in clinical practice at our institute.

Impact of regular magnetic resonance imaging follow-up after stereotactic radiotherapy to the surgical cavity in patients with one to three brain metastases

BACKGROUND

Administering stereotactic radiotherapy to the surgical cavity and thus omitting postoperative whole brain radiotherapy (WBRT) is a favored strategy in limited metastatic brain disease. Little is known about the impact of regular magnetic resonance imaging follow-up (MRI FU) in such patient cohorts. The aim of this study is to examine the impact of regular MRI FU and to report the oncological outcomes of patients with one to three brain metastases (BMs) treated with stereotactic radiosurgery (SRS) or hypo-fractionated stereotactic radiotherapy (HFSRT) to the surgical cavity.

METHODS

We retrospectively analyzed patients who received SRS or HFSRT to the surgical cavity after resection of one to two BMs. Additional, non-resected BMs were managed with SRS alone. Survival was estimated by the Kaplan-Meier method. Prognostic factors were examined with the log-rank test and Cox proportional hazards model. Regular MRI FU was defined as performing a brain MRI 3 months after radiotherapy (RT) and/or performing ≥1 brain MRI per 180 days. Primary endpoint was local control (LC). Secondary endpoints were distant brain control (DBC), overall survival (OS) and the correlation between regular MRI FU and overall survival (OS), symptom-free survival (SFS), deferment of WBRT and WBRT-free survival (WFS).

RESULTS

Overall, 75 patients were enrolled. One, 2 and 3 BMs were seen in 63 (84%), 11 (15%) and 1 (1%) patients, respectively. Forty (53%) patients underwent MRI FU 3 months after RT and 38 (51%) patients received ≥1 brain MRI per 180 days. Median OS was 19.4 months (95% CI: 13.2-25.6 months). Actuarial LC, DBC and OS at 1 year were 72% (95% CI: 60-83%), 60% (95% CI: 48-72%) and 66% (95% CI: 53-76%), respectively. A planning target volume > 15 cm³ (p = 0.01), Graded Prognostic Assessment (GPA) score (p = 0.001) and residual tumor after surgery (p = 0.008) were prognostic for decreased OS in multivariate analysis. No significant correlation between MRI FU at 3 months and OS (p = 0.462), SFS (p = 0.536), WFS (p = 0.407) or deferment of WBRT (p = 0.955) was seen. Likewise, performing ≥1 MRI per 180 days had no significant impact on OS (p = 0.954), SFS (p = 0.196), WFS (p = 0.308) or deferment of WBRT (p = 0.268).

CONCLUSION

Our results regarding oncological outcomes consist with the current data from the literature. Surprisingly, regular MRI FU did not result in increased OS, SFS, WFS or deferment of WBRT in our cohort consisting mainly of patients with a single and resected BM. Therefore, the impact of regular MRI FU needs prospective evaluation.

TRIAL REGISTRATION

Project ID: 2017-00033, retrospectively registered.

Accuracy assessment of a potential clinical use of navigation-guided intra-operative liver metastasis brachytherapy-a planning study

For patients with inoperable liver metastases, intra-operative liver high dose-rate brachytherapy (HDR-BT) is a promising technology enabling delivery of a high radiation dose to the tumor, while sparing healthy tissue. Liver brachytherapy has been described in the literature as safe and effective for the treatment of primary or secondary hepatic malignancies. It is preferred over other ablative techniques for lesions that are either larger than 4 cm or located in close proximity to large vessels or the common bile duct. In contrast to external beam radiation techniques, organ movements do not affect the size of the irradiated volume in intra-operative HDR-BT and new technical solutions exist to support image guidance for intra-operative HDR-BT. We have retrospectively analyzed anonymized CT datasets of 5 patients who underwent open liver surgery (resection and/or ablation) in order to test whether the accuracy of a new image-guidance method specifically adapted for intra-operative HDR-BT is high enough to use it in similar situations and whether patients could potentially benefit from navigation-guided intra-operative needle placement for liver HDR-BT.

Part 2: Dynamic mixed beam radiotherapy (DYMBER): Photon dynamic trajectories combined with modulated electron beams

PURPOSE

The purpose of this study was to develop a treatment technique for dynamic mixed beam radiotherapy (DYMBER) utilizing increased degrees of freedom (DoF) of a conventional treatment unit including different particle types (photons and electrons), intensity and energy modulation and dynamic gantry, table, and collimator rotations.

METHODS

A treatment planning process has been developed to create DYMBER plans combining photon dynamic trajectories (DTs) and step and shoot electron apertures collimated with the photon multileaf collimator (pMLC). A gantry-table path is determined for the photon DTs with minimized overlap of the organs at risk (OARs) with the target. In addition, an associated dynamic collimator rotation is established with minimized area between the pMLC leaves and the target contour. pMLC sequences of photon DTs and electron pMLC apertures are then simultaneously optimized using direct aperture optimization (DAO). Subsequently, the final dose distribution of the electron pMLC apertures is calculated using the Swiss Monte Carlo Plan (SMCP). The pMLC sequences of the photon DTs are then re-optimized with a finer control point resolution and with the final electron dose distribution taken into account. Afterwards, the final photon dose distribution is calculated also using the SMCP and summed together with the one of the electrons. This process is applied for a brain and two head and neck cases. The resulting DYMBER dose distributions are compared to those of dynamic trajectory radiotherapy (DTRT) plans consisting only of photon DTs and clinically applied VMAT plans. Furthermore, the deliverability of the DYMBER plans is verified in terms of dosimetric accuracy, delivery time and collision avoidance. For this purpose, The DYMBER plans are delivered to Gafchromic EBT3 films placed in an anthropomorphic head phantom on a Varian TrueBeam linear accelerator.

RESULTS

For each case, the dose homogeneity in the target is similar or better for DYMBER compared to DTRT and VMAT. Averaged over all three cases, the mean dose to the parallel OARs is 16% and 28% lower, D2% to the serial OARs is 17% and 37% lower and V10% to normal tissue is 12% and 4% lower for the DYMBER plans compared to the DTRT and VMAT plans, respectively. The DYMBER plans are delivered without collision and with a 4-5 min longer delivery time than the VMAT plans. The absolute dose measurements are compared to calculation by gamma analysis using 2% (global)/2 mm criteria with passing rates of at least 99%.

CONCLUSIONS

A treatment technique for DYMBER has been successfully developed and verified for its deliverability. The dosimetric superiority of DYMBER over DTRT and VMAT indicates utilizing increased DoF to be the key to improve brain and head and neck radiation treatments in future.

Assessing dose rate distributions in VMAT plans

Dose rate is an essential factor in radiobiology. As modern radiotherapy delivery techniques such as volumetric modulated arc therapy (VMAT) introduce dynamic modulation of the dose rate, it is important to assess the changes in dose rate. Both the rate of monitor units per minute (MU rate) and collimation are varied over the course of a fraction, leading to different dose rates in every voxel of the calculation volume at any point in time during dose delivery. Given the radiotherapy plan and machine specific limitations, a VMAT treatment plan can be split into arc sectors between Digital Imaging and Communications in Medicine control points (CPs) of constant and known MU rate. By calculating dose distributions in each of these arc sectors independently and multiplying them with the MU rate, the dose rate in every single voxel at every time point during the fraction can be calculated. Independently calculated and then summed dose distributions per arc sector were compared to the whole arc dose calculation for validation. Dose measurements and video analysis were performed to validate the calculated datasets. A clinical head and neck, cranial and liver case were analyzed using the tool developed. Measurement validation of synthetic test cases showed linac agreement to precalculated arc sector times within ±0.4 s and doses ±0.1 MU (one standard deviation). Two methods for the visualization of dose rate datasets were developed: the first method plots a two-dimensional (2D) histogram of the number of voxels receiving a given dose rate over the course of the arc treatment delivery. In similarity to treatment planning system display of dose, the second method displays the dose rate as color wash on top of the corresponding computed tomography image, allowing the user to scroll through the variation over time. Examining clinical cases showed dose rates spread over a continuous spectrum, with mean dose rates hardly exceeding 100 cGy min(-1) for conventional fractionation. A tool to analyze dose rate distributions in VMAT plans with sub-second accuracy was successfully developed and validated. Dose rates encountered in clinical VMAT test cases show a continuous spectrum with a mean less than or near 100 cGy min(-1) for conventional fractionation.

Impact of p53 Status on Radiosensitization of Tumor Cells by MET Inhibition-Associated Checkpoint Abrogation

Signaling via the MET receptor tyrosine kinase has been implicated in crosstalk with cellular responses to DNA damage. Our group previously demonstrated that MET inhibition in tumor cells with deregulated MET activity results in radiosensitization via downregulation of the ATR-CHK1-CDC25 pathway, a major signaling cascade responsible for intra-S and G2-M cell-cycle arrest following DNA damage. Here we aimed at studying the potential therapeutic application of ionizing radiation in combination with a MET inhibitor, EMD-1214063, in p53-deficient cancer cells that harbor impaired G1-S checkpoint regulation upon DNA damage. We hypothesized that upon MET inhibition, p53-deficient cells would bypass both G1-S and G2-M checkpoints, promoting premature mitotic entry with substantial DNA lesions and cell death in a greater extent than p53-proficient cells. Our data suggest that p53-deficient cells are more susceptible to EMD-1214063 and combined treatment with irradiation than wild-type p53 lines as inferred from elevated γH2AX expression and increased cytotoxicity. Furthermore, cell-cycle distribution profiling indicates constantly lower G1 and higher G2-M population as well as higher expression of a mitotic marker p-histone H3 following the dual treatment in p53 knockdown isogenic variant, compared with the parental counterpart.

IMPLICATIONS

The concept of MET inhibition-mediated radiosensitization enhanced by p53 deficiency is of high clinical relevance, as p53 is frequently mutated in numerous types of human cancer. The current data point for a therapeutic advantage for an approach combining MET targeting along with DNA-damaging agents for MET-positive/p53-negative tumors.

Adjuvant therapy after resection of brain metastases. Frameless image-guided LINAC-based radiosurgery and stereotactic hypofractionated radiotherapy

BACKGROUND

Tumor bed stereotactic radiosurgery (SRS) after resection of brain metastases is a new strategy to delay or avoid whole-brain irradiation (WBRT) and its associated toxicities. This retrospective study analyzes results of frameless image-guided linear accelerator (LINAC)-based SRS and stereotactic hypofractionated radiotherapy (SHRT) as adjuvant treatment without WBRT.

MATERIALS AND METHODS

Between March 2009 and February 2012, 44 resection cavities in 42 patients were treated with SRS (23 cavities) or SHRT (21 cavities). All treatments were delivered using a stereotactic LINAC. All cavities were expanded by ≥ 2 mm in all directions to create the clinical target volume (CTV).

RESULTS

The median planning target volume (PTV) for SRS was 11.1 cm(3). The median dose prescribed to the PTV margin for SRS was 17 Gy. Median PTV for SHRT was 22.3 cm(3). The fractionation schemes applied were: 4 fractions of 6 Gy (5 patients), 6 fractions of 4 Gy (6 patients) and 10 fractions of 4 Gy (10 patients). Median follow-up was 9.6 months. Local control (LC) rates after 6 and 12 months were 91 and 77 %, respectively. No statistically significant differences in LC rates between SRS and SHRT treatments were observed. Distant brain control (DBC) rates at 6 and 12 months were 61 and 33 %, respectively. Overall survival (OS) at 6 and 12 months was 87 and 63.5 %, respectively, with a median OS of 15.9 months. One patient treated by SRS showed symptoms of radionecrosis, which was confirmed histologically.

CONCLUSION

Frameless image-guided LINAC-based adjuvant SRS and SHRT are effective and well tolerated local treatment strategies after resection of brain metastases in patients with oligometastatic disease.

Strahlentherapie der Prostata – alter Wein in neuen Schläuchen?

Technologische Weiterentwicklungen der letzten Jahre haben in der kurativen Radiotherapie des Prostatakarzinoms dazu geführt, dass gesundes Normalgewebe deutlich besser geschont werden kann. Dies ermöglicht einerseits eine Verminderung von Akut- und Langzeitnebenwirkungen, andererseits wird Spielraum gewonnen für eine Erhöhung applizierter Dosen mit dem Ziel, Tumorkontrollraten zu verbessern. Die wichtigsten neuen Bestrahlungstechniken werden vorgestellt und ihr klinischer Einsatz diskutiert.

Correlation between the tumoral expression of beta3-integrin and outcome in cervical cancer patients who had undergone radiotherapy

Integrins are cell-surface receptors, which mediate cell-to-cell and cell-to-extracellular matrix adhesion. Besides playing an important role in tumour angiogenesis, β3-integrin is also expressed in several types of epithelial cancer cells. It was the purpose of the present study to evaluate the prognostic value of β3-integrin expression in patients with cervical cancer. Biopsies were taken from 82 patients with squamous cell or adenocarcinomas of the uterine cervix who had undergone external-beam radiotherapy with or without brachytherapy. These tissue samples were analysed immunohistochemically for the expression of β3-integrin. The impact of immunoreactivity for β3-integrin on survival end points was assessed by univariate and multivariate analyses, and its correlation with clinicopathological characteristics evaluated by crosstabulations. β3-integrin was expressed in 61% (50 of 82) of the patients. Kaplan–Meier curves revealed local progression-free survival, distant metastasis-free survival and cause-specific survival to be significantly shorter (P-values according to the log-rank test: 0.002, 0.04 and 0.01, respectively) in patients with β3-integrin expression. The prognostic impact of this parameter was even higher than for other well-known prognostic parameters and remained statistically significant in the multivariate analyses. β3-integrin, which is expressed in the majority of patients with advanced cervical cancer, has a significant prognostic impact on outcome according to univariate and multivariate analyses.

Introduction of a novel dose saving acquisition mode for the PortalVision aS500 EPID to facilitate on-line patient setup verification

In external beam radiotherapy, electronic portal imaging becomes more and more an indispensable tool for the verification of the patient setup. For the safe clinical introduction of high dose conformal radiotherapy like intensity modulated radiation therapy, on-line patient setup verification is a prerequisite to ensure that the planned dosimetric coverage of the tumor volume is actually realized in the patient. Since the direction of setup fields often deviates from the direction of the treatment beams, extra dose is delivered to the patient during the acquisition of these portal images which may reach clinical relevance. The aim of this work was to develop a new acquisition mode for the PortalVision aS500 electronic portal imaging device from Varian Medical Systems that allows one to take portal images with reduced dose while keeping good image quality. The new acquisition mode, called RadMode, selectively enables and disables beam pulses during image acquisition allowing one to stop wasting valuable dose during the initial acquisition of "reset frames." Images of excellent quality can be taken with 1 MU only. This low dose per image facilitates daily setup verification with considerably reduced extra dose.

Altered regulation of ERK1b by MEK1 and PTP-SL and modified Elk1 phosphorylation by ERK1b are caused by abrogation of the regulatory C-terminal sequence of ERKs

ERK1b is an alternatively spliced form of ERK1, containing a 26-amino acid insertion between residues 340 and 341 of ERK1. Although under most circumstances the kinetics of ERK1b activation are similar to that of ERK1 and ERK2, we have previously found several conditions under which the activation of ERK1b by extracellular stimuli differs from that of other ERKs. We studied the molecular mechanisms that cause this differential regulation of ERK1b and found that ERK1b is altered in its ability to interact with MEK1 and this influenced its subcellular localization but not its kinetics of activation. ERK1b had a decreased ability to phosphorylate Elk1, but this did not change much the transcriptional activity of the latter. Importantly, the interaction of ERK1b with PTP-SL, which can act as a MAPK phosphatase, shortly after mitogenic stimulation, was significantly affected as well. Using mutants of ERK1b we found that the differential interaction of ERK1b with the three effectors is caused by the site of insertion that abrogates the cytosolic retention sequence/common docking motif of ERKs, and is not dependent on the actual sequence of the insert. Prolonged epidermal growth factor stimulation of Rat1 cells resulted in a differential inactivation and not activation of ERK1b as compared with ERK1 and ERK2. The reduced sensitivity to phosphatases without major differences in the kinetics of activation or activation of substrates, suggests that ERK1b plays a role in the transmission of extracellular signals under conditions of persistent stimulation, where ERK1b and MAPK phosphatases are induced, and the activity of ERK1 and ERK2 is suppressed.

Human papillomavirus positive squamous cell carcinoma of the oropharynx: a radiosensitive subgroup of head and neck carcinoma

BACKGROUND

Epidemiologic evidence points to a connection between viral infection by the human papillomavirus (HPV) and a subgroup of squamous cell carcinoma of the oropharynx. To assess the impact of HPV infection on the response of these tumors toward radiotherapy, the authors retrospectively determined the presence of the virus and the integrity of the viral E2 gene in tumors of patients who have undergone curative irradiation.

METHODS

Paraffin embedded biopsies from 99 patients were analyzed for HPV infection and E2 gene integrity by multiplex PCR. The experimental findings were correlated with clinical characteristics, known risk factors, and treatment outcome.

RESULTS

Fourteen of 99 tumors were HPV positive (11 HPV16, 1 HPV33, 1 HPV35, and 1 HPV45). Human papillomavirus positivity was closely linked to female gender (odds ratio [OR], 5.75; P = 0.004), age older than 56 years (OR, 7.42; P = 0.012), nonsmokers (OR, 21.33; P = 0.00001), and alcohol abstainers (OR, 5.35; P = 0.012). There was an inverse association with p53 nuclear immunoreactivity (OR, 0.06; P = 0.008). The Kaplan-Meier survival estimates showed a better local control (P = 0.050, log-rank) and a better overall survival (P = 0.046, log-rank) for patients with HPV positive tumors. In the multivariate analysis, HPV positivity remained to be associated with a lower risk of local failure (risk ratio [RR], 0.31; P = 0.048). Four of 11 HPV16 positive tumors had a disrupted E2 gene. Only tumors with a disrupted E2 gene manifested local treatment failure.

CONCLUSIONS

Human papillomavirus positivity designates a specific subgroup of oropharyngeal squamous cell carcinomas of the oropharynx that arise preferentially among individuals with no consumption of tobacco and alcohol and that have a favorable outcome attributable to an increased sensitivity toward radiotherapy.

Expression of hypoxia-inducible factor-1alpha: a novel predictive and prognostic parameter in the radiotherapy of oropharyngeal cancer

Hypoxia has long been recognized as detrimental to the successful treatment of malignant tumors with ionizing radiation. Because hypoxia-inducible factor (HIF)-1alpha plays an essential role in oxygen homeostasis in vitro, we explored the predictive potential of this factor in a cohort of 98 patients with squamous cell cancer of the oropharynx, who were treated by curative radiation therapy. Ninety-four % of the primary tumors showed overexpression of HIF-1alpha, relative to the surrounding tissue, as determined by immunohistochemistry. The degree of HIF-1alpha immunoreactivity correlated inversely with both the rate of complete remission of the primary tumor (odds ratio, 0.33; P = 0.03) and lymph node metastases (odds ratio, 0.34; P = 0.02) as well as with local failure-free survival (risk ratio, 2.15; P = 0.006), disease-free survival (risk ratio, 2.01; P = 0.008), and overall survival (risk ratio, 2.17; P = 0.002). The multivariate analysis revealed the predictive power of HIF-1alpha to be independent of other covariables. We conclude that HIF-1alpha is overexpressed in the vast majority of patients with squamous cell cancer of the oropharynx and that the degree of expression has predictive and prognostic significance in individuals undergoing curative radiation therapy.

Involvement of the hepatocyte growth factor/scatter factor receptor c-met and of Bcl-xL in the resistance of oropharyngeal cancer to ionizing radiation

The activation of cytoplasmic signal transduction pathways by a number of growth factors and their tyrosine-kinase receptors, including hepatocyte growth factor/scatter factor (HGF/SF) and its receptor c-met, exerts an inhibitory influence on apoptosis induced by ionizing radiation in vitro. The clinical relevance of the aforementioned ligand-receptor pair, of Bcl-xL, which is targeted by HGF/SF/c-met signaling, and of Bcl-2, was assessed by evaluating their predictive and prognostic impact in a cohort of 97 patients with radically irradiated squamous cell cancers of the oropharynx. Immunohistochemical expression of c-met and Bcl-xL was correlated with decreased rates of complete remission of the primary tumor in both the univariate (c-met: P = 0.01; Bcl-xL: P = 0.001) and multivariate analyses. Expression of c-met was, moreover, a significant and independent predictor of impaired local failure-free survival (P = 0.003), disease-free survival (P = 0.003) and overall survival (p = 0.001). Bcl-2 expression was, on the other hand, associated with a favorable outcome, in terms of both local failure-free survival (P = 0.01) and overall survival (P = 0.001). In accordance with in vitro data, c-met and Bcl-xL appear to be involved in the resistance of oropharyngeal cancers to ionizing radiation, and may therefore represent attractive targets for radiosensitization.

Intratumoral microvessel density predicts local treatment failure of radically irradiated squamous cell cancer of the oropharynx

PURPOSE

To determine the predictive value of intratumoral microvessel density (IMD), and of the expression of p53, vascular endothelial growth factor (VEGF) and thrombospondin-1 (TSP-1) for the radiocurability of patients with squamous cell cancer of the oropharynx.

MATERIALS AND METHODS

139 patients with squamous cell cancer of the oropharynx were radically irradiated (median dose, 74 Gy) between 1991 and 1997. Biopsies from 100 patients were processed for immunohistochemistry. IMD was determined in hot spot areas of tissue stained with anti-CD31 at a magnification of x200. Staining for p53 was considered positive if more than 10% of the cell nuclei overexpressed the protein. Immunostaining of VEGF and TSP-1 was assessed semiquantitatively.

RESULTS

Increasing IMD (range, 54-282) was strongly correlated with incomplete remission of both the primary tumors (p = 0.01) and lymph node metastases (p = 0.02). Moreover, multivariate Cox regression analysis revealed local failure-free survival to decline with increasing IMD (IMD continuous: risk ratio = 1.01 per increase of 1 microvessel, p = 0. 0001; IMD categorical: </= 80: baseline, 81-110: risk ratio = 2.71, 111-130: risk ratio = 4.55, > 130: risk ratio = 13.01). Neither the expression of p53, nor that of VEGF or TSP-1 was associated with the treatment outcome or IMD, but VEGF and TSP-1 expression were positively correlated (p = 0.02).

CONCLUSION

IMD represents a powerful and independent predictive factor for local treatment failure in radically irradiated patients with squamous cell cancer of the oropharynx.

Carcinoma of the oropharynx: local failure as the decisive parameter for distant metastases and survival

OBJECTIVE

How important and predictive are clinical parameters and locoregional failure after radical radiotherapy of oropharyngeal carcinomas for the probability of the occurrence of distant metastases?

PATIENTS AND METHODS

From 1 August 1990 to 1 October 1998, 139 patients with carcinomas of the oropharynx were treated in a prospective study by radical radiotherapy and evaluated in regard to the clinical parameters reflex-otalgia, predominant structure of tumor growth, T-category, presence of involved lymph nodes, and smoking and drinking habits. Twenty-nine patients received a concomitant chemotherapy. Twenty-five out of 139 patients had a planned neck dissection after completion of radiotherapy. Ten patients received a salvage operation.

RESULTS

The median follow up time was 24 months (range, 4 to 74). Two- and 5-year overall survival rates according to Kaplan Meier were 56.1 and 49.6%. The tumors were controlled in 77/139 patients (55%). The therapy failed in 62/139 patients (45%). Both groups, 62 patients with locoregional therapy failure and 77 patients with locoregionally control led tumors, were comparable in regard to performance status (Karnofsky index), age, gender, TNM-categories, histological differentiation, drinking habits, pretherapeutic diagnostics, total dose (Gy), and number of simultaneous chemotherapy cycles. Locoregional tumor control was significantly determined by the parameters reflex-otalgia (p < 0.0078), predominant growth pattern (p < 0.012), T-category (p < 0.03), and smoking (p < 0.0285). The median survival time of patients with locoregional failure is 17 months. At this moment 81% of locoregionally controlled patients are still alive. In 14/62 patients (23%) with locoregional failure, distant metastases were detectable against 4/77 (5%) of locally controlled patients, p < 0.0026. Probability of local control and distant metastases, predominantly pulmonary, reached a plateau after 24 months.

CONCLUSIONS

Locoregional tumor control, determined by several clinical parameters, is an important parameter for the probability of the development of distant metastases. Failure of local therapy is caused by the biologic aggressiveness of the tumor.

[Angiogenesis as prognostic factor in malignant tumors]

It is now generally accepted that angiogenesis is critical for tumor progression and metastasis. Angiogenic parameters like vascular density and expression of angiogenic factors have been linked to the outcome of a broad spectrum of cancers. Most of these studies report a worsening prognosis in cases of higher vascular density and increased expression of angiogenic factors. Furthermore, preliminary reports suggest that angiogenic activity may predict the success of some cytotoxic therapies. The evidence of angiogenesis as a fundamental process in cancer development led to a large number of studies testing anti-angiogenic strategies as monotherapy or in combination with radiation and chemotherapy.

V-Ha-ras-dependent expression of interleukin-3 mRNA in premalignant PB-3c mast cells correlates with the formation of tumors without interleukin-3 gene rearrangements

Retroviral transduction of v-Ha-ras into the interleukin-3 (IL-3) dependent PB-3c cells results in the generation of IL-3 autocrine tumors without (class-I tumors) or with (class-II tumors) insertion of endogenous retroviral elements into the IL-3 locus. In this study, we examined the frequency of both tumor classes arising from the IL-3-dependent PB-3c clone 15. This cell line was previously found to be unable to suppress IL-3 expression of class-I tumor cells after cell fusion and to be highly tumorigenic following ZIP-ras-neo transduction. To identify possible preexisting determinants of tumor progression, clone 15 cells were subcloned either before or after retroviral ZIP-ras-neo infection and tested for tumorigenicity. All 20 sublines with clonal cellular background, but with heterogeneous integration sites, were tumorigenic. In contrast, only 12 of 19 sublines with clonal integration sites formed tumors. None of the 42 tumor cell lines analyzed by Southern blotting showed evidence of IL-3 gene rearrangement. Only the tumorigenic sublines showed v-Ha-ras transcripts on Northern blots and low levels of IL-3 mRNA detectable by RT-PCR, as well as recovery of IL-3-independent cells after crisis in vitro. Expression of IL-3 mRNA and tumorigenicity were found in somatic cell hybrids of clone 15 with 15 v-Ha-ras, but not in cell hybrids with the class-I tumor suppressor-positive clone 20 v-Ha-ras. These data suggest that RT-PCR signals for IL-3 are a predictive marker in premalignant cells for the formation of tumors without IL-3 gene rearrangements, which depend on v-Ha-ras expression and a cooperating cellular function of recessive nature.