Mapping Local Failure Following Bladder Radiotherapy According to Dose.

AIMS: To determine the relationship between local relapse following radical radiotherapy for muscle-invasive bladder cancer (MIBC) and radiation dose. MATERIALS AND METHODS: Patients with T2-4N0-3M0 MIBC were recruited to a phase II study assessing the feasibility of intensity-modulated radiotherapy to the bladder and pelvic lymph nodes. Patients were planned to receive 64 Gy/32 fractions to the bladder tumour, 60 Gy/32 fractions to the involved pelvic nodes and 52 Gy/32 fractions to the uninvolved bladder and pelvic nodes. Pre-treatment set-up was informed by cone-beam CT. For patients who experienced local relapse, cystoscopy and imaging (CT/MRI) was used to reconstruct the relapse gross tumour volume (GTVrelapse) on the original planning CT . GTVrelapse D98% and D95% was determined by co-registering the relapse image to the planning CT utilising deformable image registration (DIR) and rigid image registration (RIR). Failure was classified into five types based on spatial and dosimetric criteria as follows: A (central high-dose failure), B (peripheral high-dose failure), C (central elective dose failure), D (peripheral elective dose failure) and E (extraneous dose failure). RESULTS: Between June 2009 and November 2012, 38 patients were recruited. Following treatment, 18/38 (47%) patients experienced local relapse within the bladder. The median time to local relapse was 9.0 months (95% confidence interval 6.3-11.7). Seventeen of 18 patients were evaluable based on the availability of cross-sectional relapse imaging. A significant difference between DIR and RIR methods was seen. With the DIR approach, the median GTVrelapse D98% and D95% was 97% and 98% of prescribed dose, respectively. Eleven of 17 (65%) patients experienced type A failure and 6/17 (35%) patients type B failure. No patients had type C, D or E failure. MIBC failure occurred in 10/17 (59%) relapsed patients; of those, 7/11 (64%) had type A failure and 3/6 (50%) had type B failure. Non-MIBC failure occurred in 7/17 (41%) patients; 4/11 (36%) with type A failure and 3/6 (50%) with type B failure. CONCLUSION: Relapse following radiotherapy occurred within close proximity to the original bladder tumour volume and within the planned high-dose region, suggesting possible biological causes for failure. We advise caution when considering margin reduction for future reduced high-dose radiation volume or partial bladder radiotherapy protocols.

A Comparison of Isotoxic Dose-escalated Radiotherapy in Lung Cancer with Moderate Deep Inspiration Breath Hold, Mid-ventilation and Internal Target Volume Techniques.

AIMS: With interest in normal tissue sparing and dose-escalated radiotherapy in the treatment of inoperable locally advanced non-small cell lung cancer, this study investigated the impact of motion-managed moderate deep inspiration breath hold (mDIBH) on normal tissue sparing and dose-escalation potential and compared this to planning with a four-dimensional motion-encompassing internal target volume or motion-compensating mid-ventilation approach. MATERIALS AND METHODS: Twenty-one patients underwent four-dimensional and mDIBH planning computed tomography scans. Internal and mid-ventilation target volumes were generated on the four-dimensional scan, with mDIBH target volumes generated on the mDIBH scan. Isotoxic target dose-escalation guidelines were used to generate six plans per patient: three with a target dose cap and three without. Target dose-escalation potential, normal tissue complication probability and differences in pre-specified dose-volume metrics were evaluated for the three motion-management techniques. RESULTS: The mean total lung volume was significantly greater with mDIBH compared with four-dimensional scans. Lung dose (mean and V21 Gy) and mean heart dose were significantly reduced with mDIBH in comparison with four-dimensional-based approaches, and this translated to a significant reduction in heart and lung normal tissue complication probability with mDIBH. In 20/21 patients, the trial target prescription dose cap of 79.2 Gy was achievable with all motion-management techniques. CONCLUSION: mDIBH aids lung and heart dose sparing in isotoxic dose-escalated radiotherapy compared with four-dimensional planning techniques. Given concerns about lung and cardiac toxicity, particularly in an era of consolidation immunotherapy, reduced normal tissue doses may be advantageous for treatment tolerance and outcome.

Feasibility of magnetic resonance guided radiotherapy for the treatment of bladder cancer.

Whole bladder magnetic resonance image-guided radiotherapy using the 1.5 Telsa MR-linac is feasible. Full online adaptive planning workflow based on the anatomy seen at each fraction was performed. This was delivered within 45 min. Intra-fraction bladder filling did not compromise target coverage. Patients reported acceptable tolerance of treatment.

A Dosimetric Comparison of Breast Radiotherapy Techniques to Treat Locoregional Lymph Nodes Including the Internal Mammary Chain.

AIMS: Radiotherapy target volumes in early breast cancer treatment increasingly include the internal mammary chain (IMC). In order to maximise survival benefits of IMC radiotherapy, doses to the heart and lung should be minimised. This dosimetry study compared the ability of three-dimensional conformal radiotherapy, arc therapy and proton beam therapy (PBT) techniques with and without breath-hold to achieve target volume constraints while minimising dose to organs at risk (OARs). MATERIALS AND METHODS: In 14 patients' datasets, seven IMC radiotherapy techniques were compared: wide tangent (WT) three-dimensional conformal radiotherapy, volumetric-modulated arc therapy (VMAT) and PBT, each in voluntary deep inspiratory breath-hold (vDIBH) and free breathing (FB), and tomotherapy in FB only. Target volume coverage and OAR doses were measured for each technique. These were compared using a one-way ANOVA with all pairwise comparisons tested using Bonferroni's multiple comparisons test, with adjusted P-values ≤ 0.05 indicating statistical significance. RESULTS: One hundred per cent of WT(vDIBH), 43% of WT(FB), 100% of VMAT(vDIBH), 86% of VMAT(FB), 100% of tomotherapy FB and 100% of PBT plans in vDIBH and FB passed all mandatory constraints. However, coverage of the IMC with 90% of the prescribed dose was significantly better than all other techniques using VMAT(vDIBH), PBT(vDIBH) and PBT(FB) (mean IMC coverage ± 1 standard deviation = 96.0% ± 4.3, 99.8% ± 0.3 and 99.0% ± 0.2, respectively). The mean heart dose was significantly reduced in vDIBH compared with FB for both the WT (P < 0.0001) and VMAT (P < 0.0001) techniques. There was no advantage in target volume coverage or OAR doses for PBT(vDIBH) compared with PBT(FB). CONCLUSIONS: Simple WT radiotherapy delivered in vDIBH achieves satisfactory coverage of the IMC while meeting heart and lung dose constraints. However, where higher isodose coverage is required, VMAT(vDIBH) is the optimal photon technique. The lowest OAR doses are achieved by PBT, in which the use of vDIBH does not improve dose statistics.

Evaluation of radiotherapy techniques for radical treatment of lateralised oropharyngeal cancers : Dosimetry and NTCP.

AIM: The aim of this study was to investigate potential advantages and disadvantages of three-dimensional conformal radiotherapy (3DCRT), multiple fixed-field intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) in terms of dose to the planning target volume (PTV), organs at risk (OARs) and normal tissue complication probability (NTCP) for delivering ipsilateral radiotherapy. MATERIALS AND METHODS: 3DCRT, IMRT and VMAT were compared in patients with well-lateralised primary tonsillar cancers who underwent primary radical ipsilateral radiotherapy. The following parameters were compared: conformity index (CI); homogeneity index (HI); dose-volume histograms (DVHs) of PTVs and OARs; NTCP, risk of radiation-induced cancer and dose accumulation during treatment. RESULTS: IMRT and VMAT were superior to 3DCRT in terms of CI, HI and dose to the target volumes, as well as mandible and dose accumulation robustness. The techniques were equivalent in terms of dose and NTCP for the contralateral oral cavity, contralateral submandibular gland and mandible, when specific dose constraint objectives were used on the oral cavity volume. Although the volume of normal tissue exposed to low-dose radiation was significantly higher with IMRT and VMAT, the risk of radiation-induced secondary malignancy was dependant on the mathematical model used. CONCLUSION: This study demonstrates the superiority of IMRT/VMAT techniques over 3DCRT in terms of dose homogeneity, conformity and consistent dose delivery to the PTV throughout the course of treatment in patients with lateralised oropharyngeal cancers. Dosimetry and NTCP calculations show that these techniques are equivalent to 3DCRT with regard to the risk of acute mucositis when specific dose constraint objectives were used on the contralateral oral cavity OAR.

Neurocognitive function after (chemo)-radiotherapy for head and neck cancer.

Radical radiotherapy has a pivotal role in the treatment of head and neck cancer (HNC) and cures a significant proportion of patients while simultaneously sparing critical normal organs. Some patients treated with radical radiotherapy for HNC receive significant radiation doses to large volumes of brain tissue. In fact, intensity-modulated radiotherapy techniques for HNC have been associated with a net increase in irradiated brain volumes. The increasing use of chemoradiotherapy for HNC has additionally exposed this patient population to potential neurotoxicity due to cytotoxic drugs. Patients with HNC may be particularly at risk for adverse late brain effects after (chemo)-radiotherapy, such as impaired neurocognitive function (NCF), as risk factors for the development of HNC, such as smoking, excess alcohol consumption and poor diet, are also associated with impaired NCF. The relatively good survival rates with modern treatment for HNC, and exposure to multiple potentially neurotoxic factors, means that it is important to understand the impact of (chemo)-radiotherapy for HNC on NCF, and to consider what measures can be taken to minimise treatment-related neurotoxicity. Here, we review evidence relating to the late neurotoxicity of radical (chemo)-radiotherapy for HNC, with a focus on studies of NCF in this patient population.

An experimental comparison of conventional two-bank and novel four-bank dynamic MLC tracking.

The AccuLeaf mMLC featuring four multileaf-collimator (MLC) banks has been used for the first time for an experimental comparison of conventional two-bank with novel four-bank dynamic MLC tracking of a two-dimensional sinusoidal respiratory motion. This comparison was performed for a square aperture, and for three conformal treatment apertures from clinical radiotherapy lung cancer patients. The system latency of this prototype tracking system was evaluated and found to be 1.0 s and the frequency at which MLC positions could be updated, 1 Hz, and therefore accurate MLC tracking of irregular patient motion would be difficult with the system in its current form. The MLC leaf velocity required for two-bank-MLC and four-bank-MLC tracking was evaluated for the apertures studied and a substantial decrease was found in the maximum MLC velocity required when four-banks were used for tracking rather than two. A dosimetric comparison of the two techniques was also performed and minimal difference was found between two-bank-MLC and four-bank-MLC tracking. The use of four MLC banks for dynamic MLC tracking is shown to be potentially advantageous for increasing the delivery efficiency compared with two-bank-MLC tracking where difficulties are encountered if large leaf shifts are required to track motion perpendicular to the direction of leaf travel.

4D planning over the full course of fractionation: assessment of the benefit of tumor trailing.

Tumor trailing techniques have been proposed as a method of reducing the problem of intrafraction motion in radiotherapy. However the dosimetric assessment of trailing strategies is complicated by the requirement to study dose deposition over a full fraction delivery. Common 4D planning strategies allowing assessment of dosimetric motion effects study a single cycle acquired with 4DCT. In this paper, a methodology to assess dose deposited over an entire treatment course is advanced and used to assess the potential benefit of tumor trailing strategies for lung cancer patients. Two digital phantoms mimicking patient anatomy were each programmed to follow the tumor respiratory trajectory observed from 33 lung cancer patients. The two phantoms were designed to represent the cases of a small (volume = 13.6 cm3) and large (volume = 181.7 cm3) lung lesion. Motion margins required to obtain CTV coverage by 95% of the prescription dose to 90% of the available cases were computed for a standard treatment strategy and a trailing treatment strategy. The trailing strategy facilitated a margin reduction of over 30% relative to the conventional delivery. When the dose was computed across the entire delivery for the 33 cases, the trailing strategy was found to significantly reduce the underdosage to the outlier cases and the reduced trailing margin facilitated a 15% (small lesion) and 4% (large lesion) reduction for the mean lung dose and 7% (small lesion) and 10% (large lesion) for the mean esophagus dose. Finally, for comparison an ideal continuous tracking strategy was assessed and found to further reduce the mean lung and esophagus dose. However, this improvement comes at the price of increased delivery complexity and increased reliance on tumor localization accuracy.

Dosimetric consequences of inter-fraction breathing-pattern variation on radiotherapy with personalized motion-assessed margins.

The data from eight patients who had undergone stereotactic body radiotherapy were selected due to their 4D-CT planning scans showing that their tumours had respiratory induced motion trajectories of large amplitude (greater than 9 mm in cranio-caudal direction). Radiotherapy plans with personalized motion-assessed margins were generated for these eight patients. The margins were generated by inverse 4D planning on an eight-bin phase-sorted 4D-CT scan. The planning was done on an in-house software system with a non-rigid registration stage being completed using freely available software. The resultant plans were then recalculated on a 4D-CT scan taken later during the course of treatment. Simulated image-guided patient set-up was used to align the geometric centres of the tumour region and minimize any misalignment between the two reconstructions. In general, the variation in the patient breathing patterns was found to be very small. Consequently, the degradation of the mean dose to the tumour region was found to be around a few percent (<3%) and hence was not a large effect.

Some considerations concerning volume-modulated arc therapy: a stepping stone towards a general theory.

In this paper it is formally shown that the dynamic multileaf collimator (MLC) IMRT delivery technique remains valid if the MLC is supported on a 1D moving platform. It is also shown that, in such circumstances, it is always time preferable to deliver overlapping modulating fields as a single swept field rather than as separate fields. The most general formulism is presented and then related to simpler equations in limiting cases. The paper explains in detail how a 'small-arc approximation' can be invoked to relate the 1D linear theory to the MLC-on-moving-platform-(gantry) delivery technique involving rotation therapy and known as volume-modulated arc therapy (VMAT). It is explained how volume-modulated arc therapy delivered with open unmodulated fields and which can deliver conformal dose distributions can be interpreted as an IMRT delivery. The (Elekta adopted) term VMAT will be used in a generic sense to include a similar (Varian) method known as RapidArc. Approximate expressions are derived for the 'amount of modulation' possible in a VMAT delivery. This paper does not discuss the actual VMAT planning but gives an insight at a deep level into VMAT delivery. No universal theory of VMAT is known in the sense that there is no theory that can predict precisely the performance of a VMAT delivery in terms of the free parameters available (variable gantry speed, variable fluence-delivery rate, set of MLC shapes, MLC orientation, number of arcs, coplanarity versus non-coplanarity, etc). This is in stark contrast to the situation with several other IMRT delivery techniques where such theoretical analyses are known. In this paper we do not provide such a theory; the material presented is a stepping stone on the path towards this.

Target-tracking deliveries on an Elekta linac: a feasibility study.

A target-tracking, intensity-modulated delivery on an Elekta MLCi system was assessed by film measurement with a simulated target-motion trajectory. A toroidally shaped idealized target surrounding an organ at risk necessitating multiple field segments to irradiate the target and spare the organ at risk was defined in a solid-water phantom. The phantom was programmed to move following a reproducible 2D elliptical trajectory in the beam's-eye view with a period of 10 s. Static and target-tracking treatments were planned for delivery on a standard Elekta Precise series linac with integrated MLCi system. Dose was delivered in three ways: (i) a static treatment to a static phantom, (ii) a static treatment to a moving phantom and (iii) a target-tracking treatment to a moving phantom. The dose delivered was assessed by film measurement on the central plane through the target and organ at risk. The target dose blurring was quantified by the standard deviation of the dose to the target which was evaluated as 2.8% for the static treatment to the static phantom, 7.2% for the static treatment to the moving phantom and 2.6% for the tracking treatment to the moving phantom. The mean organ-at-risk dose was 38.2%, 54.0% and 38.2% of the prescription dose for each delivery case. We have therefore shown that the linac is capable of delivering target-tracking fields with MLCs for the target trajectories tested.

Planning lung radiotherapy using 4D CT data and a motion model.

This work is a feasibility study to use a four-dimensional computed tomography (4D CT) dataset generated by a continuous motion model for treatment planning in lung radiotherapy. The model-based 4D CT data were derived from multiple breathing cycles. Four patients were included in this retrospective study. Treatment plans were optimized at end-exhale for each patient and the effect of respiratory motion on the dose delivery investigated. The accuracy of the delivered dose as determined by the number of intermediate respiratory phases used for the calculation was considered. The time-averaged geometry of the anatomy representing the mid-ventilation phase of the breathing cycle was generated using the motion model and a treatment plan was optimized for this phase for one patient. With respiratory motion included, the mid-ventilation plan achieved better target coverage than the plan optimized at end-exhale when standard margins were used to expand the clinical target volume (CTV) to planning target volume (PTV). Using a margin to account for set-up uncertainty only, resulted in poorer target coverage and healthy tissue sparing. For this patient cohort, the results suggest that conventional three-dimensional treatment planning was sufficient to maintain target coverage despite respiratory motion. The motion model has proved a useful tool in 4D treatment planning.

Target-tracking deliveries using conventional multileaf collimators planned with 4D direct-aperture optimization.

Respiratory motion-induced degradation of intensity-modulated radiotherapy can be corrected by the dynamic target-tracking motion of multileaf collimator equipment on a conventional linear accelerator. This paper presents a new system by which the motion of the tissue and the delivery equipment can be incorporated into the treatment optimization using a 4D direct-aperture optimization method. The program can optimize a static or dynamic delivery with respect to a 4D patient model. The individualized patient model consists of a series of discrete phases and describes changes in tissue: deformation, geometry, attenuation and scatter properties over the breathing cycle. A set of treatment apertures is matched to the respiratory phases of the motion model, and motion of the apertures between phases is constrained by the maximum leaf velocity. Plans with dynamic and static deliveries optimized on 4D patient models were compared to static plans optimized on a single phase. This investigation was carried out on a 4D digital motion phantom and repeated on a 4D patient model. The effect of motion of the static plan on the 4D phantom was evaluated by recalculating dose from all phases of the 4D model. The plan cost was evaluated as a combination of the rms spread in tumour dose from the prescribed dose and the volume of normal lung receiving doses above 10 Gy with relative weightings of 5 and 1 respectively. The motion was found to degrade the static plan by 30 +/- 4% with respect to the 3D cost function value. In contrast, the motion did not cause significant degradation to a treatment if the treatment was optimized on the 4D phantom and the cost was improved by 16 +/- 3% by optimizing with dynamic leaf tracking motion. All results are relative to the static single-phase plan. In the 4D patient model the observed tissue motion was considerably less and the measured benefit of 4D planning was consequently reduced. For the 4D patient the plan cost was not significantly changed by the tissue motion. Optimizing on 4D patient conferred an improvement of 7.5 +/- 0.3%, and the 4D plan with dynamic leaf motion improved the plan cost by 8.3 +/- 0.1%.

Potential role of high-mobility group box 1 in cystic fibrosis airway disease.

RATIONALE: High-mobility group box 1 (HMGB1) is a potent inflammatory mediator elevated in sepsis and rheumatoid arthritis, although its role in cystic fibrosis (CF) lung disease is unknown. OBJECTIVES: To determine whether HMGB1 contributes to CF lung inflammation, including neutrophil chemotaxis and lung matrix degradation. METHODS: We used sputum and serum from subjects with CF and a Scnn1b-transgenic (Scnn1b-Tg) mouse model that overexpresses beta-epithelial Na(+) channel in airways and mimics the CF phenotype, including lung inflammation. Human secretions and murine bronchoalveolar lavage fluid (BALF) was assayed for HMGB1 by Western blot and ELISA. Neutrophil chemotaxis was measured in vitro after incubation with human neutrophils. The collagen fragment proline-glycine-proline (PGP) was measured by tandem mass spectroscopy. MEASUREMENTS AND MAIN RESULTS: HMGB1 was detected in CF sputum at higher levels than secretions from normal individuals. Scnn1b-Tg mice had elevated levels of HMGB1 by Western blot and ELISA. We demonstrated that dose-dependent chemotaxis of human neutrophils stimulated by purified HMGB1 was partially dependent on CXC chemokine receptors and that this could be duplicated in CF sputum and BALF from Scnn1b-Tg mice. Neutralization by anti-HMGB1 antibody, in both the sputum and BALF-reduced chemotaxis, which suggested that HMGB1 contributed to the chemotactic properties of these samples. Intratracheal administration of purified HMGB1 induced neutrophil influx into the airways of mice and promoted the release of PGP. PGP was also elevated in Scnn1b-Tg mice and CF serum. CONCLUSIONS: HMGB1 expression contributes to pulmonary inflammation and lung matrix degradation in CF airway disease and deserves further investigation as a biomarker and potential therapeutic target.

A novel proteolytic cascade generates an extracellular matrix-derived chemoattractant in chronic neutrophilic inflammation.

Chronic neutrophilic inflammation is a manifestation of a variety of lung diseases including cystic fibrosis (CF). There is increasing evidence that fragments of extracellular matrix proteins, such as collagen and elastin, play an important role in inflammatory cell recruitment to the lung in animal models of airway inflammation. Unfortunately, the association of these peptides with human disease and the identification of therapeutic targets directed toward these inflammatory pathways have remained elusive. In this study, we demonstrate that a novel extracellular matrix-derived neutrophil chemoattractant, proline-glycine-proline (PGP), acts through CXC receptors 1 and 2 on neutrophils, similar to N-acetylated proline-glycine-proline (N-alpha-PGP). We describe the specific multistep proteolytic pathway involved in PGP generation from collagen, involving matrix metalloproteases 8 and 9 and prolyl endopeptidase, a serine protease for which we identify a novel role in inflammation. PGP generation correlates closely with airway neutrophil counts after administration of proteases in vivo. Using CF as a model, we show that CF sputum has elevated levels of PGP peptides and that PGP levels decline during the course of CF inpatient therapy for acute pulmonary exacerbation, pointing to its role as a novel biomarker for this disease. Finally, we demonstrate that CF secretions are capable of generating PGP from collagen ex vivo and that this generation is significantly attenuated by the use of inhibitors directed toward matrix metalloprotease 8, matrix metalloprotease 9, or prolyl endopeptidase. These experiments highlight unique protease interactions with structural proteins regulating innate immunity and support a role for these peptides as novel biomarkers and therapeutic targets for chronic, neutrophilic lung diseases.

Tracking 'differential organ motion' with a 'breathing' multileaf collimator: magnitude of problem assessed using 4D CT data and a motion-compensation strategy.

Intrafraction tumour (e.g. lung) motion due to breathing can, in principle, be compensated for by applying identical breathing motions to the leaves of a multileaf collimator (MLC) as intensity-modulated radiation therapy is delivered by the dynamic MLC (DMLC) technique. A difficulty arising, however, is that irradiated voxels, which are in line with a bixel at one breathing phase (at which the treatment plan has been made), may move such that they cease to be in line with that breathing bixel at another phase. This is the phenomenon of differential voxel motion and existing tracking solutions have ignored this very real problem. There is absolutely no tracking solution to the problem of compensating for differential voxel motion. However, there is a strategy that can be applied in which the leaf breathing is determined to minimize the geometrical mismatch in a least-squares sense in irradiating differentially-moving voxels. A 1D formulation in very restricted circumstances is already in the literature and has been applied to some model breathing situations which can be studied analytically. These are, however, highly artificial. This paper presents the general 2D formulation of the problem including allowing different importance factors to be applied to planning target volume and organ at risk (or most generally) each voxel. The strategy also extends the literature strategy to the situation where the number of voxels connecting to a bixel is a variable. Additionally the phenomenon of 'cross-leaf-track/channel' voxel motion is formally addressed. The general equations are presented and analytic results are given for some 1D, artificially contrived, motions based on the Lujan equations of breathing motion. Further to this, 3D clinical voxel motion data have been extracted from 4D CT measurements to both assess the magnitude of the problem of 2D motion perpendicular to the beam-delivery axis in clinical practice and also to find the 2D optimum breathing-leaf strategy. Issues relating to the practical calculation of the strategy, including effects on leaf velocity and effects of different spatial-sampling frequencies, have been investigated, and unattenuated-fluence maps have been produced showing the effects of the differential motion and tracking. It was discovered that large distances between adjacent leaf-ends could cause the tracking to fail when there was tissue motion across the leaf channels. To overcome this problem the use of 'synchronized' leaf trajectories, which ensure that adjacent leaf-ends are always close enough to each other to facilitate tracking, has also been investigated.

IMRT delivery to a moving target by dynamic MLC tracking: delivery for targets moving in two dimensions in the beam's eye view.

A new modification of the dynamic multileaf collimator (dMLC) delivery technique for intensity-modulated therapy (IMRT) is outlined. This technique enables the tracking of a target moving through rigid-body translations in a 2D trajectory in the beam's eye view. The accuracy of the delivery versus that of deliveries with no tracking and of 1D tracking techniques is quantified with clinically derived intensity-modulated beams (IMBs). Leaf trajectories calculated in the target-reference frame were iteratively synchronized assuming regular target motion. This allowed the leaves defined in the lab-reference frame to simultaneously follow the target motion and to deliver the required IMB without violation of the leaf maximum-velocity constraint. The leaves are synchronized until the gradient of the leaf position at every instant is less than a calculated maximum. The delivered fluence in the target-reference frame was calculated with a simple primary-fluence model. The new 2D tracking technique was compared with the delivered fluence produced by no-tracking deliveries and by 1D tracking deliveries for 33 clinical IMBs. For the clinical IMBs normalized to a maximum fluence of 200 MUs, the rms difference between the desired and the delivered IMB was 15.6 +/- 3.3 MU for the case of a no-tracking delivery, 7.9 +/- 1.6 MU for the case where only the primary component of motion was corrected and 5.1 +/- 1.1 MU for the 2D tracking delivery. The residual error is due to interpolation and sampling effects. The 2D tracking delivery technique requires an increase in the delivery time evaluated as between 0 and 50% of the unsynchronized delivery time for each beam with a mean increase of 13% for the IMBs tested. The 2D tracking dMLC delivery technique allows an optimized IMB to be delivered to moving targets with increased accuracy and with acceptable increases in delivery time. When combined with real-time knowledge of the target motion at delivery time, this technique facilitates improved target conformality relative to no-tracking deliveries and allows PTV margin reduction.

Array comparative genomic hybridisation (aCGH) analysis of premenopausal breast cancers from a nuclear fallout area and matched cases from Western New York.

High-resolution array comparative genomic hybridisation (aCGH) analysis of DNA copy number aberrations (CNAs) was performed on breast carcinomas in premenopausal women from Western New York (WNY) and from Gomel, Belarus, an area exposed to fallout from the 1986 Chernobyl nuclear accident. Genomic DNA was isolated from 47 frozen tumour specimens from 42 patients and hybridised to arrays spotted with more than 3000 BAC clones. In all, 20 samples were from WNY and 27 were from Belarus. In total, 34 samples were primary tumours and 13 were lymph node metastases, including five matched pairs from Gomel. The average number of total CNAs per sample was 76 (range 35-134). We identified 152 CNAs (92 gains and 60 losses) occurring in more than 10% of the samples. The most common amplifications included gains at 8q13.2 (49%), at 1p21.1 (36%), and at 8q24.21 (36%). The most common deletions were at 1p36.22 (26%), at 17p13.2 (26%), and at 8p23.3 (23%). Belarussian tumours had more amplifications and fewer deletions than WNY breast cancers. HER2/neu negativity and younger age were also associated with a higher number of gains and fewer losses. In the five paired samples, we observed more discordant than concordant DNA changes. Unsupervised hierarchical cluster analysis revealed two distinct groups of tumours: one comprised predominantly of Belarussian carcinomas and the other largely consisting of WNY cases. In total, 50 CNAs occurred significantly more commonly in one cohort vs the other, and these included some candidate signature amplifications in the breast cancers in women exposed to significant radiation. In conclusion, our high-density aCGH study has revealed a large number of genetic aberrations in individual premenopausal breast cancer specimens, some of which had not been reported before. We identified a distinct CNA profile for carcinomas from a nuclear fallout area, suggesting a possible molecular fingerprint of radiation-associated breast cancer.

Identification and characterisation of constitutional chromosome abnormalities using arrays of bacterial artificial chromosomes.

Constitutional chromosome deletions and duplications frequently predispose to the development of a wide variety of cancers. We have developed a microarray of 6000 bacterial artificial chromosomes for array-based comparative genomic hybridisation, which provides an average resolution of 750 kb across the human genome. Using these arrays, subtle gains and losses of chromosome regions can be detected in constitutional cells, following a single overnight hybridisation. In this report, we demonstrate the efficiency of this procedure in identifying constitutional deletions and duplications associated with predisposition to retinoblastoma, Wilms tumour and Beckwith-Wiedemann syndrome.