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.

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.

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.

Body image issues for children and adolescents with burns

Body image is a far-reaching, multidimensional, dynamic concept. Because burn injuries threaten the integrity of both the physical and psychologic identity, body-image issues related to burn injuries appear to be a meaningful area of investigation. Little research has been done to directly assess body-image issues for children and adolescents with burns. We reviewed the general findings that body-image adaptation occurs and is influenced by gender, social support, burn severity, overall adjustment, and developmental stage. It is suggested that body-image revision, if it occurs, is largely successful, but body-image issues may not be directly related to psychosocial adjustment after a burn injury.

Purification and molecular cloning of a novel group of BMPs and localization of BMP mRNA in developing bone

Using a novel purification scheme, we have characterized BMP as a 30kD fraction. After reduction, which destroys biological activity, this fraction was shown to be comprised of individual polypeptides with molecular weights of 30kD, 18kD and 16kD. Molecular cloning of these polypeptides resulted in the identification of 4 previously undescribed genes (BMP-1, BMP-2A, BMP-2B, and BMP-3) each of which is capable of directing de novo cartilage formation in vivo. While BMP-1 appears to be unrelated to other known growth factors, the derived amino acid sequence of BMP-2A, 2B, and 3 indicate that they are new members of the TGFb gene family. BMP-1, 2A and 2B are expressed in rat embryos during morphogenesis and can be localized by in situ hybridization to developing limb buds. BMP-3 localizes to neural ectoderm and later on in development to newly forming periosteum. Comparisons to other members of the TGFb family suggest that these newly identified BMPs are involved in pattern formation during early skeletal development.