Planning Benchmark Study for Stereotactic Body Radiation Therapy of Pancreas Carcinomas with Simultaneously Integrated Boost and Protection: Results of the DEGRO/DGMP Working Group on Stereotactic Radiation Therapy and Radiosurgery.

PURPOSE/OBJECTIVE: The proximity or overlap of PTV and OAR poses a major challenge in SBRT of pancreatic cancer (PACA). This international treatment planning benchmark study investigates whether Simultaneously Integrated Boost (SIB) and Protection (SIP) concepts in PACA SBRT can lead to improved and harmonized plan quality. MATERIALS/METHODS: A multiparametric specification of desired target doses (GTVD50%, GTVD99%, PTVD95%, PTV0.5cc) with two prescription doses of GTVD50%=5×9.2Gy (46Gy) and GTVD50%=8×8.25Gy (66Gy) and OAR limits were distributed with planning CT and contours from 3 PACA patients. In phase 1, plans were ranked using a scoring system for comparison of trade-offs between GTV/PTV and OAR. In phase 2, re-planning was performed for the most challenging case and prescription with dedicated SIB and SIP contours provided for optimization after group discussion. RESULTS: For all 3 cases and both phases combined, 292 plans were generated from 42 institutions in 5 countries using commonly available treatment planning systems. The GTVD50% prescription was performed by only 76% and 74% of planners within 2% for 5 and 8 fractions, respectively. The GTVD99% goal was mostly reached, while the balance between OAR and target dose showed initial SIB/SIP-like optimization strategies in about 50% of plans. For plan ranking, 149 and 217 score penalties were given for 5 and 8 fractions, pointing to improvement possibilities. For phase 2, the GTVD50% prescription was performed by 95% of planners within 2% and GTVD99% as well as OAR doses were better harmonized with notable less score penalties. Fourteen of 19 planners improved their plan rank, 9 of them by at least 2 ranks. CONCLUSION: Dedicated SIB/SIP concepts in combination with multiparametric prescriptions and constraints can lead to overall harmonized and high treatment plan quality for PACA SBRT. Standardized SIB/SIP treatment planning in multicenter clinical trials appears feasible after group consensus and training.

The prognostic utility of the transcription factor SRF in docetaxel-resistant prostate cancer: in-vitro discovery and in-vivo validation.

BACKGROUND: Docetaxel based therapy is one of the first line chemotherapeutic agents for the treatment of metastatic castrate-resistant prostate cancer. However, one of the major obstacles in the treatment of these patients is docetaxel-resistance. Defining the mechanisms of resistance so as to inform subsequent treatment options and combinations represents a challenge for clinicians and scientists. Previous work by our group has shown complex changes in pro and anti-apoptotic proteins in the development of resistance to docetaxel. Targeting these changes individually does not significantly impact on the resistant phenotype but understanding the central signalling pathways and transcription factors (TFs) which control these could represent a more appropriate therapeutic targeting approach. METHODS: Using a number of docetaxel-resistant sublines of PC-3 cells, we have undertaken a transcriptomic analysis by expression microarray using the Affymetrix Human Gene 1.0 ST Array and in conjunction with bioinformatic analyses undertook to predict dysregulated TFs in docetaxel resistant prostate cancer. The clinical significance of this prediction was ascertained by performing immunohistochemical (IHC) analysis of an identified TF (SRF) in the metastatic sites from men who died of advanced CRPC. Investigation of the functional role of SRF was examined by manipulating SRF using SiRNA in a docetaxel-resistant PC-3 cell line model. RESULTS: The transcription factors identified include serum response factor (SRF), nuclear factor kappa-B (NFκB), heat shock factor protein 1 (HSF1), testicular receptor 2 & 4 (TR2 &4), vitamin-D and retinoid x receptor (VDR-RXR) and oestrogen-receptor 1 (ESR1), which are predicted to be responsible for the differential gene expression observed in docetaxel-resistance. IHC analysis to quantify nuclear expression of the identified TF SRF correlates with both survival from date of bone metastasis (p = 0.003), survival from androgen independence (p = 0.00002), and overall survival from prostate cancer (p = 0.0044). Functional knockdown of SRF by siRNA demonstrated a reversal of apoptotic resistance to docetaxel treatment in the docetaxel-resistant PC-3 cell line model. CONCLUSIONS: Our results suggest that SRF could aid in treatment stratification of prostate cancer, and may also represent a therapeutic target in the treatment of men afflicted with advanced prostate cancer.

Investigation of time-resolved proton radiography using x-ray flat-panel imaging system.

Proton beam therapy benefits from the Bragg peak and delivers highly conformal dose distributions. However, the location of the end-of-range is subject to uncertainties related to the accuracy of the relative proton stopping power estimates and thereby the water-equivalent path length (WEPL) along the beam. To remedy the range uncertainty, an in vivo measurement of the WEPL through the patient, i.e. a proton-range radiograph, is highly desirable. Towards that goal, we have explored a novel method of proton radiography based on the time-resolved dose measured by a flat panel imager (FPI). A 226 MeV pencil beam and a custom-designed range modulator wheel (MW) were used to create a time-varying broad beam. The proton imaging technique used exploits this time dependency by looking at the dose rate at the imager as a function of time. This dose rate function (DRF) has a unique time-varying dose pattern at each depth of penetration. A relatively slow rotation of the MW (0.2 revolutions per second) and a fast image acquisition (30 frames per second, ~33 ms sampling) provided a sufficient temporal resolution for each DRF. Along with the high output of the CsI:Tl scintillator, imaging with pixel binning (2 × 2) generated high signal-to-noise data at a very low radiation dose (~0.1 cGy). Proton radiographs of a head phantom and a Gammex CT calibration phantom were taken with various configurations. The results of the phantom measurements show that the FPI can generate low noise and high spatial resolution proton radiographs. The WEPL values of the CT tissue surrogate inserts show that the measured relative stopping powers are accurate to ~2%. The panel did not show any noticeable radiation damage after the accumulative dose of approximately 3831 cGy. In summary, we have successfully demonstrated a highly practical method of generating proton radiography using an x-ray flat panel imager.

Inter-comparison of relative stopping power estimation models for proton therapy.

Theoretical stopping power values were inter-compared for the Bichsel, Janni, ICRU and Schneider relative stopping power (RSP) estimation models, for a variety of tissues and tissue substitute materials taken from the literature. The RSPs of eleven plastic tissue substitutes were measured using Bragg peak shift measurements in water in order to establish a gold standard of RSP values specific to our centre's proton beam characteristics. The theoretical tissue substitute RSP values were computed based on literature compositions to assess the four different computation approaches. The Bichsel/Janni/ICRU approaches led to mean errors in the RSP of -0.1/+0.7/-0.8%, respectively. Errors when using the Schneider approach, with I-values from the Bichsel, Janni and ICRU sources, followed the same pattern but were generally larger. Following this, the mean elemental ionisation energies were optimized until the differences between theoretical RSP values matched measurements. Failing to use optimized I-values when applying the Schneider technique to 72 human tissues could introduce errors in the RSP of up to -1.7/+1.1/-0.4% when using Bichsel/Janni/ICRU I-values, respectively. As such, it may be necessary to introduce an additional step in the current stoichiometric calibration procedure in which tissue insert RSPs are measured in a proton beam. Elemental I-values can then optimized to match these measurements, reducing the uncertainty when calculating human tissue RSPs.

Dose ratio proton radiography using the proximal side of the Bragg peak.

PURPOSE: In recent years, there has been a movement toward single-detector proton radiography, due to its potential ease of implementation within the clinical environment. One such single-detector technique is the dose ratio method in which the dose maps from two pristine Bragg peaks are recorded beyond the patient. To date, this has only been investigated on the distal side of the lower energy Bragg peak, due to the sharp falloff. The authors investigate the limits and applicability of the dose ratio method on the proximal side of the lower energy Bragg peak, which has the potential to allow a much wider range of water-equivalent thicknesses (WET) to be imaged. Comparisons are made with the use of the distal side of the Bragg peak. METHODS: Using the analytical approximation for the Bragg peak, the authors generated theoretical dose ratio curves for a range of energy pairs, and then determined how an uncertainty in the dose ratio would translate to a spread in the WET estimate. By defining this spread as the accuracy one could achieve in the WET estimate, the authors were able to generate lookup graphs of the range on the proximal side of the Bragg peak that one could reliably use. These were dependent on the energy pair, noise level in the dose ratio image and the required accuracy in the WET. Using these lookup graphs, the authors investigated the applicability of the technique for a range of patient treatment sites. The authors validated the theoretical approach with experimental measurements using a complementary metal oxide semiconductor active pixel sensor (CMOS APS), by imaging a small sapphire sphere in a high energy proton beam. RESULTS: Provided the noise level in the dose ratio image was 1% or less, a larger spread of WETs could be imaged using the proximal side of the Bragg peak (max 5.31 cm) compared to the distal side (max 2.42 cm). In simulation, it was found that, for a pediatric brain, it is possible to use the technique to image a region with a square field equivalent size of 7.6 cm(2), for a required accuracy in the WET of 3 mm and a 1% noise level in the dose ratio image. The technique showed limited applicability for other patient sites. The CMOS APS demonstrated a good accuracy, with a root-mean-square-error of 1.6 mm WET. The noise in the measured images was found to be σ = 1.2% (standard deviation) and theoretical predictions with a 1.96σ noise level showed good agreement with the measured errors. CONCLUSIONS: After validating the theoretical approach with measurements, the authors have shown that the use of the proximal side of the Bragg peak when performing dose ratio imaging is feasible, and allows for a wider dynamic range than when using the distal side. The dynamic range available increases as the demand on the accuracy of the WET decreases. The technique can only be applied to clinical sites with small maximum WETs such as for pediatric brains.

Patient-specific stopping power calibration for proton therapy planning based on single-detector proton radiography.

A simple robust optimizer has been developed that can produce patient-specific calibration curves to convert x-ray computed tomography (CT) numbers to relative stopping powers (HU-RSPs) for proton therapy treatment planning. The difference between a digitally reconstructed radiograph water-equivalent path length (DRRWEPL) map through the x-ray CT dataset and a proton radiograph (set as the ground truth) is minimized by optimizing the HU-RSP calibration curve. The function of the optimizer is validated with synthetic datasets that contain no noise and its robustness is shown against CT noise. Application of the procedure is then demonstrated on a plastic and a real tissue phantom, with proton radiographs produced using a single detector. The mean errors using generic/optimized calibration curves between the DRRWEPL map and the proton radiograph were 1.8/0.4% for a plastic phantom and -2.1/ - 0.2% for a real tissue phantom. It was then demonstrated that these optimized calibration curves offer a better prediction of the water equivalent path length at a therapeutic depth. We believe that these promising results are suggestive that a single proton radiograph could be used to generate a patient-specific calibration curve as part of the current proton treatment planning workflow.

Invasive markers identified by gene expression profiling in pancreatic cancer.

BACKGROUND: Molecular profiling has proven utility as a diagnostic and predictive tool in clinical oncology. However, a clinically relevant gene expression profile in pancreatic cancer remains elusive. METHODS: Primary and metastatic pancreatic cancer cell lines (BxPC-3 and AsPC-1), were stimulated with phorbol-12-myristate 13-acetate (PMA), a known inducer of cell invasion. Affymetrix gene expression microarray analysis was performed, comparing gene expression to unstimulated controls. Differential expression was identified using ArrayAssist, and confirmed using quantitative real-time PCR. Bioinformatic analysis was performed using Pathway Studio and GOstat. The derived gene expression was further validated in fresh frozen pancreatic tumour samples. The ability of the derived 3 gene expression markersto differentiate between pancreatic adenocarcinoma (PDAC) and other neoplasms, and its association with clinicopathological variables was examined. RESULTS: PMA-induced significant changes in cell line gene expression, from which distinctive 3 potential invasive markers were derived. Expression of these genes, uPA, MMP-1 and IL1-R1 was confirmed in human pancreatic tumours, and was found to differentiate PDAC from other pancreatic neoplasms. The expression of IL1-R1 in PDAC is a novel finding. We found that the expression of MMP-1 was associated with high-grade PDAC (p = 0.035, Wilcoxon rank sum). CONCLUSION: We have identified three potential invasive markers, uPA, MMP-1 and IL1-R1, whose gene expression may differentiate PDAC from other pancreatic neoplasms, and potentially reflect a more invasive phenotype.

The human L1 element: a potential biomarker in cancer prognosis, current status and future directions.

The discovery of new biomarkers is a rapidly advancing area in cancer biology. The challenge of biomarker development for broad clinical use requires the translation of lab-based knowledge into clinical practice. The Long Interspersed Nuclear Elements-1 (LINE-1s or L1 elements) are active members of an autonomous family of non-LTR retrotransposons and occupy nearly 17% of the human genome. There is strong experimental evidence that the global hypomethylation of genomic DNA in cancer cells results in the activation of L1s and their expression is detectable at genome, transcriptome and proteome levels in human cancer cells. Thus, human L1s constitute a potential marker for cancer cells. In this review we have attempted to scrutinize L1 expression profiles in clinical cancer studies by undertaking a comprehensive systematic analysis of papers published in the field so far with a view to providing a more complete picture of the detection methods used, improvements achieved and potential future directions. Ultimately, we will try to evaluate the potential of L1s as a molecular marker in cancer detection.

Engineering CHO cell growth and recombinant protein productivity by overexpression of miR-7.

The efficient production of recombinant proteins by Chinese Hamster Ovary (CHO) cells in modern bioprocesses is often augmented by the use of proliferation control strategies. The most common method is to shift the culture temperature from 37 °C to 28-33 °C though genetic approaches to achieving the same effect are also of interest. In this work we used qRT-PCR-based expression profiling using TLDA™ cards to identify miRNAs displaying differential expression 24h after temperature-shift (TS) from 37 °C to 31 °C. Six miRNAs were found to be significantly up-regulated (mir-219, mir-518d, mir-126, mir-30e, mir-489 and mir-345) and four down-regulated (mir-7, mir-320, mir-101 and mir-199). Furthermore, qRT-PCR analysis of miR-7 expression over a 6 day batch culture, with and without TS, demonstrated decreased expression over time in both cultures but to a significantly greater extent in cells shifted to a lower culture temperature. Unexpectedly, when miR-7 levels were increased transiently by transfection with miR-7 mimic in CHO-K1 cells, cell proliferation at 37 °C was effectively blocked over a 96 h culture period. On the other hand, transient inhibition of endogenous miR-7 levels using antagonists had no impact on cell growth. The exogenous overexpression of miR-7 also resulted in increased normalised (per cell) production at 37 °C, though the yield was lower than cells grown at reduced temperature. This is the first report demonstrating a functional impact of specific miRNA disregulation on CHO cell behavior in batch culture and provides some evidence of the potential which these molecules may have in terms of engineering targets in CHO production clones. Finally, we report the cloning and sequencing of the hamster-specific cgr-miR-7.

MiRNA-29a regulates the expression of numerous proteins and reduces the invasiveness and proliferation of human carcinoma cell lines.

In this study we have identified a functional role for miR-29a in cancer cell invasion and proliferation. MiRNA expression profiling of human NSCLC cell lines indicated that miR-29a levels were reduced in more invasive cell lines. Exogenous overexpression of miR-29a in both lung and pancreatic cancer cell lines resulted in a significant reduction in the invasion phenotype, as well as in proliferation. 2D DIGE proteomic profiling of cells transfected with pre-miR-29a or anti-miR-29a resulted in the identification of over 100 differentially regulated proteins. The fold change of protein expression was generally modest--in the range 1.2-1.7-fold. Only 14 were predicted computationally to have miR-29a seed sequences in their 3' UTR region. Subsequent studies using siRNA to knock down several candidate proteins from the 2D DIGE experiment identified RAN (a member of the RAS oncogene family) which significantly reduced the invasive capability of a model lung cancer cell line. We conclude that miR-29a has a significant anti-invasive and anti-proliferative effect on lung cancer cells in vitro and functions as an anti-oncomir. This function is likely mediated through the post-transcriptional fine tuning of the cellular levels of several proteins, both directly and indirectly, and in particular we provide some evidence that RAN represents one of these.

TMEM25, REPS2 and Meis 1: favourable prognostic and predictive biomarkers for breast cancer.

BACKGROUND/AIMS: A panel of prognostic and predictive biomarkers would contribute to personalized treatment of breast cancer patients. However, many such biomarkers have yet to be identified and evaluated. The aim of this study was to investigate the relevance of 3 such putative biomarkers. METHODS: TMEM25, REPS2 and Meis 1 expression was investigated by qRT-PCR, in triplicate, in 103 breast tumour biopsies procured in 1993-1994. Normal breast tissue specimens were also analysed for comparative purposes. Univariate and multivariate analyses were used to identify associations between expression of these transcripts as well as patients' clinicopathological and survival data. RESULTS: TMEM25, REPS2 and Meis 1 transcripts were detected in approximately 52, 78 and 40% of tumour specimens, respectively. Expression of each of the 3 genes was indicative of extended survival times from diagnosis [association between relapse-free survival (RFS) and TMEM25, p = 0.0002; REPS2, p = 0.0287; association between overall survival (OS) and TMEM25, p = 0.001; REPS2, p = 0.0131; Meis 1, p = 0.0255]. Presence of TMEM25 and Meis 1 was associated with oestrogen receptor-positive (TMEM25, p < 0.0005; Meis 1, p = 0.011), lower-grade (TMEM25, p = 0.002; Meis 1, p = 0.001) tumours. Multivariate analysis indicated TMEM25 expression to be an independent prognostic factor for extended RFS (p = 0.011) and OS (p = 0.001). Furthermore, for patients who received adjuvant chemotherapy, significantly longer survival times were achieved if their tumours expressed TMEM25 (OS, p = 0.031; RFS, p = 0.0181) and REPS2 (OS, p = 0.011). While expression of these mRNAs was generally absent from triple-negative breast tumours, statistical significance was not achieved. CONCLUSION: Our results suggest that TMEM25, REPS2 and Meis 1 mRNAs may be useful members of a panel of favourable prognostic and predictive markers for breast cancer and an understanding of their function may provide useful information about this disease.

SNIP/p140Cap mRNA expression is an unfavourable prognostic factor in breast cancer and is not expressed in normal breast tissue.

The prevalence and clinical relevance of SNIP/p140Cap has not been extensively investigated. Here SNIP/p140Cap mRNA expression was studied in 103 breast tumour biopsies, where it was detected in approximately 37% of tumour specimens, but not in any normal breast specimens. Expression correlated significantly with unfavourable overall survival. This suggests that SNIP/p140Cap may be a useful diagnostic and prognostic marker for breast cancer and its expression in breast cancer, but not in normal breast tissue, suggests that it may have potential as a therapeutic target.

Techniques for clustering gene expression data.

Many clustering techniques have been proposed for the analysis of gene expression data obtained from microarray experiments. However, choice of suitable method(s) for a given experimental dataset is not straightforward. Common approaches do not translate well and fail to take account of the data profile. This review paper surveys state of the art applications which recognise these limitations and addresses them. As such, it provides a framework for the evaluation of clustering in gene expression analyses. The nature of microarray data is discussed briefly. Selected examples are presented for clustering methods considered.

Towards microbiological quality assurance in radiation sterilization processing: the limiting case model applied to a microbial population having a distribution of radiation responses.

A limiting case model, developed earlier to provide a conservative estimate of the proportion of non-sterile items (P) in an irradiated population of items contaminated with micro-organisms of a single type, has been extended to include items having organisms of different types. Estimates of P are compared with exact values derived on purely theoretical grounds and with values obtained by computer simulation of microbiological inactivation on items.

Net positives: conservative approach to measurement of proportions positive in substerilization process studies.

A method (designated the net positive approach) is described for scoring results of sterility tests done with more than one recovery condition on product items treated with inactivating agents at levels less than those used in sterilization processes proper (subprocess treatments). Three tests of sterility, one per recovery condition, constitute a single sample. A growth in one or more recovery conditions is scored as a net positive for that sample. The net positive approach reduces the occurrence of false-negatives and assigns a value to the proportion of items reported as nonsterile (proportions positive) that is conservative.