Is tomotherapy the future of IMRT?

Helical tomotherapy for total lymphoid irradiation

Total lymphoid irradiation is employed in the preparative regimens for allogeneic bone marrow and solid organ transplantation, solid organ transplant rejection, and chronic graft-versus-host disease. Linear accelerator-based radiotherapy, typically involving opposed anteroposterior and posteroanterior beams, has been commonly used; however, extended source-to-skin patient setup and/or field matching are required, and all organs within the beam coverage receive the entire prescribed dose. Megavoltage helical tomotherapy represents a technological advance in terms of both treatment delivery and patient positioning. The continuously rotating multileaf collimated fan beam allows highly conformal coverage of complex target geometries, in turn allowing avoidance of radiosensitive adjacent organs. In addition, the megavoltage computed tomographic scans allow potentially more accurate, targetbased setup verification. The present case report describes tomotherapy-based total lymphoid irradiation in an adult patient with late-onset cardiac transplant rejection. Treatment planning allowed dose minimization to the spinal cord, kidneys, intestinal compartment, and lungs. The patient tolerated treatment well without acute adverse effects, and he is now in early follow-up.

Peripheral blood lymphocyte counts during standard conformal radiotherapy and TomoTherapy/IMRT for prostate cancer

Lymphopaenia is the earliest and the most sensitive routinely assessed biological parameter of corporeal radiation exposure in clinical practice; bone marrow, lymph nodes and peripheral blood lymphocyte populations are also at risk. During radical prostate radiotherapy, in 28 patients, the mean peripheral lymphocyte count fell from 1.76 × 109/l (standard deviation (SD) 0.63, 95% confidence interval (conf.) 0.23) to 1.10 × 109/l (SD 0.38, conf. 0.14), (p < 0.05). The question was asked as to whether intensity-modulated radiation therapy (IMRT) by TomoTherapy would cause more lymphopaenia than three-field conformal radiotherapy, bearing in mind the ‘low dose bath’ effect of IMRT and the long ‘beam-on’ times. Thirteen patients receiving three-field conformal radiotherapy experienced a fall in peripheral lymphocyte counts from 2.02 (SD: 0.62. conf. 0.43) to 1.17 × 109/l (SD: 0.47, conf. 0.26) after 34–38 Gy, as compared to a fall from 1.6 × 109/l (SD: 0.6, conf. 0.35) to 1.04 × 109/l (SD: 0.3, conf. 0.15) for 15 TomoTherapy patients—non-significant differences. We conclude that for this (approximately) standard, small-volume pelvic radiotherapy and to the dose under scrutiny, we cannot detect differences between the two radiotherapy techniques in terms of the lymphopaenia accruing. Neutrophil counts were similarly non-significantly different.

Dosimetric Impacts of Gantry Angle Misalignment on Prostate Cancer Treatment using Helical Tomotherapy

During helical tomotherapy, gantry angle accuracy is one of the vital geometric factors that assure accurate dose delivery to the target and organs at risk adjacent to it. The purpose of this study is to investigate the dosimetric impact of gantry angle misalignment on the target volume and critical organs during helical tomotherapy treatment. Five prostate cases were chosen to calculate the effects of gantry angle deviations on both patient-specific delivery quality assurance (DQA) and helical tomotherapy treatment plans. For DQA plans, the cheese phantom was rotated for up to +/- 5° from the preset position to simulate the gantry angle deviations during tomotherapy. Point doses at 5 mm below the isocenter and the dose distribution for each gantry angle were measured and reconstructed, respectively. For helical tomotherapy treatment plans, the same gantry misalignment effect was simulated by adjusting the automatic roll correction for up to +/- 5° using Planned Adaptive software. Variations of dose volume histograms (DVHs) and isodose lines were evaluated for both target and critical organs. There was no significant difference found, however, among the point dose measurements for gantry rotation up to +/- 5° in DQA plans. Shifts of isodose lines could be observed for gantry rotations larger than +/- 2°. Dosimetric discrepancies (less than 2%) were also found among DVHs of the PTV in the cases when gantry angle misalignment was larger than +/- 2°. However, for DVHs of either bladder or rectum under different gantry rotations, no significant differences were detected when gantry angle errors were up to +/- 5°. In summary, point dose measurements alone cannot reveal the dosimetric deviation due to gantry angle misalignment in DQA plans. For a 5° gantry deviation, the dose to PTV increased by 0.5% comparing to the planned dose. The influence on organs at risk, i.e., rectum and bladder, is also negligible. Further studies are needed on the dosimetric impacts of gantry angle deviations for other treatment sites.

Comparative analysis of 60Co intensity-modulated radiation therapy

In this study, we perform a scientific comparative analysis of using (60)Co beams in intensity-modulated radiation therapy (IMRT). In particular, we evaluate the treatment plan quality obtained with (i) 6 MV, 18 MV and (60)Co IMRT; (ii) different numbers of static multileaf collimator (MLC) delivered (60)Co beams and (iii) a helical tomotherapy (60)Co beam geometry. We employ a convex fluence map optimization (FMO) model, which allows for the comparison of plan quality between different beam energies and configurations for a given case. A total of 25 clinical patient cases that each contain volumetric CT studies, primary and secondary delineated targets, and contoured structures were studied: 5 head-and-neck (H&N), 5 prostate, 5 central nervous system (CNS), 5 breast and 5 lung cases. The DICOM plan data were anonymized and exported to the University of Florida optimized radiation therapy (UFORT) treatment planning system. The FMO problem was solved for each case for 5-71 equidistant beams as well as a helical geometry for H&N, prostate, CNS and lung cases, and for 3-7 equidistant beams in the upper hemisphere for breast cases, all with 6 MV, 18 MV and (60)Co dose models. In all cases, 95% of the target volumes received at least the prescribed dose with clinical sparing criteria for critical organs being met for all structures that were not wholly or partially contained within the target volume. Improvements in critical organ sparing were found with an increasing number of equidistant (60)Co beams, yet were marginal above 9 beams for H&N, prostate, CNS and lung. Breast cases produced similar plans for 3-7 beams. A helical (60)Co beam geometry achieved similar plan quality as static plans with 11 equidistant (60)Co beams. Furthermore, 18 MV plans were initially found not to provide the same target coverage as 6 MV and (60)Co plans; however, adjusting the trade-offs in the optimization model allowed equivalent target coverage for 18 MV. For plans with comparable target coverage, critical structure sparing was best achieved with 6 MV beams followed closely by (60)Co beams, with 18 MV beams requiring significantly increased dose to critical structures. In this paper, we report in detail on a representative set of results from these experiments. The results of the investigation demonstrate the potential for IMRT radiotherapy employing commercially available (60)Co sources and a double-focused MLC. Increasing the number of equidistant beams beyond 9 was not observed to significantly improve target coverage or critical organ sparing and static plans were found to produce comparable plans to those obtained using a helical tomotherapy treatment delivery when optimized using the same well-tuned convex FMO model. While previous studies have shown that 18 MV plans are equivalent to 6 MV for prostate IMRT, we found that the 18 MV beams actually required more fluence to provide similar quality target coverage.

Intensity-modulated radiation therapy and helical tomotherapy: its origin, benefits, and potential applications in veterinary medicine

Intensity-modulated radiation therapy (IMRT), especially image-guided IMRT as represented by helical tomotherapy, is a novel approach to therapy and is rapidly evolving. Both of these forms of therapy aim to allow targeted radiation delivery to the tumor volume while minimizing dose to the surrounding normal tissues. Adaptive radiation therapy and conformal avoidance are possible with intensity-modulated therapy and helical tomotherapy, which offer opportunities for improved local tumor control, decreased normal tissue toxicity, and improved survival and quality of life. Human and veterinary patients are likely to benefit from the continued development of this radiation delivery technique, and data over the next several years should be crucial in determining its true benefit.

Multibeam tomotherapy: a new treatment unit devised for multileaf collimation, intensity-modulated radiation therapy

A fully integrated system for treatment planning, application, and verification for automated multileaf collimator (MLC) based, intensity-modulated, image-guided, and adaptive radiation therapy (IMRT, IGRT and ART, respectively) is proposed. Patient comfort, which was the major development goal, will be achieved through a new unit design and short treatment times. Our device for photon beam therapy will consist of a new dual energy linac with five fixed treatment heads positioned evenly along one plane but one electron beam generator only. A minimum of moving parts increases technical reliability and reduces motion times to a minimum. Motion is allowed solely for the MLCs, the robotic patient table, and the small angle gantry rotation of +/- 36 degrees. Besides sophisticated electron beam guidance, this compact setup can be built using existing modules. The flattening-filter-free treatment heads are characterized by reduced beam-on time and contain apertures restricted in one dimension to the area of maximum primary fluence output. In the case of longer targets, this leads to a topographic intensity modulation, thanks to the combination of "step and shoot" MLC delivery and discrete patient couch motion. Owing to the limited number of beam directions, this multislice cone beam serial tomotherapy is referred to as "multibeam tomotherapy." Every patient slice is irradiated by one treatment head at any given moment but for one subfield only. The electron beam is then guided to the next head ready for delivery, while the other heads are preparing their leaves for the next segment. The "Multifocal MLC-positioning" algorithm was programmed to enable treatment planning and optimize treatment time. We developed an overlap strategy for the longitudinally adjacent fields of every beam direction, in doing so minimizing the field match problem and the effects of possible table step errors. Clinical case studies show for the same or better planning target volume coverage, better organ-at-risk sparing, and comparable mean integral dose to the normal tissue a reduction in treatment time by more than 50% to only a few minutes in comparison to high-quality 3-D conformal and IMRT treatments. As a result, it will be possible to incorporate features for better patient positioning and image guidance, while sustaining reasonable overall treatment times at the same time. The virtual multibeam tomotherapy design study TOM'5-CT contains a dedicated electron beam CT (TOM'AGE) and an objective optical topometric patient positioning system (TOPOS). Thanks to the wide gantry bore of 120 cm and slim gantry depths of 70 cm, patients can be treated very comfortably, in all cases tumor-isocentrically, as well as with noncoplanar beam arrangements as in stereotactic radiosurgery with a couch rotation of up to +/- 54 degrees. The TOM'5 treatment unit on which this theoretical concept is based has a stand-alone depth of 40 cm and an outer diameter of 245 cm; the focus-isocenter distance of the heads is 100 cm with a field size of 40 cm x 7 cm and 0.5 cm leaves, which operate perpendicular to the axis of table motion.

Phase II study of preoperative helical tomotherapy for rectal cancer

PURPOSE

To explore the efficacy and toxicity profile of helical tomotherapy in the preoperative treatment of patients with rectal cancer.

PATIENTS AND METHODS

Twenty-four patients with T3/T4 rectal cancer were included in this nonrandomized noncontrolled study. A dose of 46 Gy in daily fractions of 2 Gy was delivered to the presacral space and perineum if an abdominoperineal resection was deemed necessary. This dose was increased by a simultaneous integrated boost to 55.2 Gy when the circumferential resection margin was less than 2 mm on magnetic resonance imaging. Acute toxicity was evaluated weekly. Metabolic response was determined in the fifth week after the end of radiotherapy by means of fluorodeoxyglucose-positron emission tomography scan. A metabolic response was defined as a decrease in maximal standardized uptake value of more than 36%.

RESULTS

The mean volume of small bowel receiving more than 15 Gy and mean bladder dose were 227 ml and 20.8 Gy in the no-boost group and 141 ml and 21.5 Gy in the boost group. Only 1 patient developed Grade 3 enteritis. No other Grade 3 or 4 toxicities were observed. Two patients developed an anastomotic leak within 30 days after surgery. The metabolic response rate was 45% in the no-boost group compared with 77% in the boost group. All except 1 patient underwent an R0 resection.

CONCLUSIONS

Helical tomotherapy may decrease gastrointestinal toxicity in the preoperative radiotherapy of patients with rectal cancer. A simultaneous integrated radiation boost seems to result in a high metabolic response rate without excessive toxicity.

A study of prostate delineation referenced against a gold standard created from the visible human data

PURPOSE

To measure inter- and intra-observer variation and systematic error in CT based prostate delineation, where individual delineations are referenced against a gold standard produced from photographic anatomical images from the Visible Human Project (VHP).

MATERIALS AND METHODS

The CT and anatomical images of the VHP male form the basic data set for this study. The gold standard was established based on 1mm thick anatomical photographic images. These were registered against the 3mm thick CT images that were used for target delineation. A total of 120 organ delineations were performed by six radiation oncologists.

RESULTS

The physician delineated prostate volume was on average 30% larger than the "true" prostate volume, but on average included only 84% of the gold standard volume. Our study found a systematic delineation error such that posterior portions of the prostate were always missed while anteriorly some normal tissue was always defined as target.

CONCLUSIONS

Our data suggest that radiation oncologists are more concerned with the unintentional inclusion of rectal tissue than they are in missing prostate volume. In contrast, they are likely to overextend the anterior boundary of the prostate to encompass normal tissue such as the bladder.

Shielding requirements in helical tomotherapy

Helical tomotherapy is a relatively new intensity-modulated radiation therapy (IMRT) treatment for which room shielding has to be reassessed for the following reasons. The beam-on-time needed to deliver a given target dose is increased and leads to a weekly workload of typically one order of magnitude higher than that for conventional radiation therapy. The special configuration of tomotherapy units does not allow the use of standard shielding calculation methods. A conventional linear accelerator must be shielded for primary, leakage and scatter photon radiations. For tomotherapy, primary radiation is no longer the main shielding issue since a beam stop is mounted on the gantry directly opposite the source. On the other hand, due to the longer irradiation time, the accelerator head leakage becomes a major concern. An analytical model based on geometric considerations has been developed to determine leakage radiation levels throughout the room for continuous gantry rotation. Compared to leakage radiation, scatter radiation is a minor contribution. Since tomotherapy units operate at a nominal energy of 6 MV, neutron production is negligible. This work proposes a synthetic and conservative model for calculating shielding requirements for the Hi-Art II TomoTherapy unit. Finally, the required concrete shielding thickness is given for different positions of interest.

Quantifying Appropriate PTV Setup Margins: Analysis of Patient Setup Fidelity and Intrafraction Motion Using Post-Treatment Megavoltage Computed Tomography Scans

PURPOSE

To present a technique that can be implemented in-house to evaluate the efficacy of immobilization and image-guided setup of patients with different treatment sites on helical tomotherapy. This technique uses an analysis of alignment shifts between kilovoltage computed tomography and post-treatment megavoltage computed tomography images. The determination of the shifts calculated by the helical tomotherapy software for a given site can then be used to define appropriate planning target volume internal margins.

METHODS AND MATERIALS

Twelve patients underwent post-treatment megavoltage computed tomography scans on a helical tomotherapy machine to assess patient setup fidelity and net intrafraction motion. Shifts were studied for the prostate, head and neck, and glioblastoma multiforme. Analysis of these data was performed using automatic and manual registration of the kilovoltage computed tomography and post-megavoltage computed tomography images.

RESULTS

The shifts were largest for the prostate, followed by the head and neck, with glioblastoma multiforme having the smallest shifts in general. It appears that it might be more appropriate to use asymmetric planning target volume margins. Each margin value reported is equal to two standard deviations of the average shift in the given direction.

CONCLUSION

This method could be applied using individual patient post-image scanning and combined with adaptive planning to reduce or increase the margins as appropriate.

An assessment of the use of skin flashes in helical tomotherapy using phantom and in-vivo dosimetry

BACKGROUND AND PURPOSE

In helical tomotherapy the nature of the optimizing and planning systems allows the delivery of dose on the skin using a build-up compensating technique (skin flash). However, positioning errors or changes in the patient's contour can influence the correct dosage in these regions. This work studies the behavior of skin-flash regions using phantom and in-vivo dosimetry.

MATERIALS AND METHODS

The dosimetric accuracy of the tomotherapy planning system in skin-flash regions is checked using film and TLD on phantom. Positioning errors are induced and the effect on the skin dose is investigated. Further a volume decrease is simulated using bolus material and the results are compared.

RESULTS

Results show that the tomotherapy planning system calculates dose on skin regions within 2 SD using TLD measurements. Film measurements show drops of dose of 2.8% and 26% for, respectively, a 5mm and 10mm mispositioning of the phantom towards air and a dose increase of 9% for a 5mm shift towards tissue. These measurements are confirmed by TLD measurements. A simulated volume reduction shows a similar behavior with a 2.6% and 19.4% drop in dose, measured with TLDs.

CONCLUSION

The tomotherapy system allows adequate planning and delivery of dose using skin flashes. However, exact positioning is crucial to deliver the dose at the exact location.

IMAT-SIM: A new method for the clinical dosimetry of intensity-modulated arc therapy (IMAT)

Dynamic-gantry multi-leaf collimator (MLC)-based, intensity-modulated radiotherapy (IMAT) has been proposed as an alternative to tomotherapy. In contrast to fixed-gantry, MLC-based intensity-modulated radiotherapy (IMRT), where commercial treatment planning systems (TPS) or dosimetric analysis software currently provide many automatic tools enabling two-dimensional (2D) detectors (matrix or electronic portal imaging devices) to be used as measurement systems, for the planning and delivery of IMAT these tools are generally not available. A new dosimetric method is proposed to overcome some of these limitations. By converting the MLC files of IMAT beams from arc to fixed gantry-angle modality, while keeping the leaf trajectories equal, IMAT plans can be both simulated in the TPS and executed as fixed-gantry, sliding-window DMLC treatments. In support of this idea, measurements of six IMAT plans, in their double form of original arcs and converted fixed-gantry DMLC beams (IMAT-SIM), have been compared among themselves and with their corresponding IMAT-SIM TPS calculations. Radiographic films and a 2D matrix ionization chamber detector rigidly attached to the accelerator gantry and set into a cubic plastic phantom have been used for these measurements. Finally, the TPS calculation-algorithm implementations of both conformal dynamic MLC arc (CD-ARC) modalities, used for clinical IMAT calculations, and DMLC modalities (IMAT-SIM), proposed as references for validating IMAT plan dose-distributions, have been compared. The comparisons between IMAT and IMAT-SIM delivered beams have shown very good agreement with similar shapes of the measured dose profiles which can achieve a mean deviation (+/-2sigma) of (0.35+/-0.16) mm and (0.37+/-0.14)%, with maximum deviations of 1.5 mm and 3%. Matching the IMAT measurements with their corresponding IMAT-SIM data calculated by the TPS, these deviations remain in the range of (1.01+/-0.28) mm and (-1.76+/-0.42)%, with maximums of 3 mm and 5%, limits generally accepted for IMRT plan dose validation. Differences in the algorithm implementations have been found, but by correcting CD-ARC calculations for the leaf-end transmission offset (LTO) effect the IMAT and IMAT-SIM simulations agree well in terms of final dose distributions. The differences found between IMAT and the IMAT-SIM beam measurements are due to the different controls of leaf motion (via electron gun delay in the latter) that cannot be used in the former to correct possible speed variations in the rotation of the gantry. As the IMAT delivered beams are identical to what the patient will receive during the treatment, and the IMAT-SIM beam calculations made by the TPS reproduce exactly the treatment plans of that patient, the accuracy of this new dosimetric method is comparable to that which is currently used for static IMRT. This new approach of 2D-detector dosimetry, together with the commissioning, quality-assurance, and preclinical dosimetric procedures currently used for IMRT techniques, can be applied and extended to any kind of dynamic-gantry MLC-based treatment modality either CD-ARC or IMAT.

Simultaneous infield boost with helical tomotherapy for patients with 1 to 3 brain metastases

OBJECTIVE

We sought to model the feasibility of a simultaneous in field boost (SIB) to individual brain metastases during a course of whole brain radiotherapy (WBXRT) using helical tomotherapy (HT) intensity-modulated radiation therapy.

PATIENTS AND METHODS

Planning computed tomography data from 14 patients with 1 to 3 brain metastases were used to model an intralesional SIB delivery that yielded a total intralesional dose of 60 Gy with a surrounding whole brain dose of 30 Gy (designed to be isoeffective to WBXRT of 30 Gy with an 18 Gy in 1 fraction radiosurgery boost). Accuracy of treatment of a phantom on the HT unit was measured. Comparisons of HT delivery versus a conventional stereotactic radiotherapy technique for a particularly challenging simulated anatomy were made.

RESULTS

In all cases, SIB to 60 Gy with WBXRT to 30 Gy was possible while maintaining critical structures below assigned dose limits. Estimated radiation delivery time for the SIB treatment was approximately 10 minutes per fraction. Planning and treatment of the head phantom was associated with an overall accuracy of 2 mm. Comparison to conventional noncoplanar arc fractionated stereotactic radiotherapy plan demonstrated similar target coverage and improved critical tissue sparing even for a challenging anatomy with multiple lesions in the same plane as the optic apparatus.

CONCLUSIONS

Based on this study, use of an image guided SIB using HT seemed feasible and a phase I trial initiated at our institution is described. Potential advantages of this approach include frameless stereotaxis through daily megavoltage computed tomography localization, more efficient use of resources and exploitation of radiobiologic advantages of fractionation.

Research or reality: Within the context of UK radiotherapy and cancer services, where should research and investment be focused to best improve UK treatment outcomes?

Purpose: It is now six years since the publication of the NHS Cancer Plan. During this time, there has been considerable investment and research within UK cancer services. Some progress has been made towards improving treatment outcomes, but obstacles persist. This article explores some recent advances in cancer treatment and considers whether UK cancer treatment outcomes will best improve through the clinical advances being made in cancer research or whether improvement now needs to be more explicitly driven via a strategic approach.Methodology: The article explores this question from two differing perspectives. First, from a research perspective, it reviews briefly the evidence for a selection of clinical advancements in cancer therapy that have all been cited as providing breakthroughs in treatment outcomes. Second, it considers the investment in cancer research within a more strategic context, focusing on the reality of managing an improvement programme in UK cancer services. Here, some of the practical obstacles to improving treatment outcomes are highlighted.Findings: Significant progress has been made over the past six years towards improving UK treatment outcomes. Much of this is a direct result of international advances in clinical research. Further progress, however, is required. This article argues that progress will best be achieved by focusing resources and research investment on tackling some of the endemic strategic obstacles, highlighted in this article, that are the present reality within UK cancer services.

Opportunities for near-infrared thermal ablation of colorectal metastases by guanylyl cyclase C-targeted gold nanoshells

Colorectal cancer is the third most common malignancy and the second most common cause of cancer-related mortality worldwide. While surgery remains the mainstay of therapy, approximately 50% of patients who undergo resection develop parenchymal metastatic disease. Unfortunately, current therapeutic regimens offer little improvement to the survival of patients with parenchymal metastases in the liver and lung. In that context, there is a significant unrealized opportunity at the intersection of engineering and biology for the development of novel targeted therapeutic approaches to colorectal cancer metastases. This opportunity exploits the discovery that an intestinal receptor, guanylyl cyclase C, which mediates diarrhea induced by bacterial heat-stable enterotoxins (STs), is over-expressed by metastatic colorectal tumors only. Moreover, it leverages recent advances in the fabrication of metal nanoshells with defined thicknesses absorb near-infrared (NIR) light, resulting in resonance and transfer of thermal energies of more than 40 degrees C. Thus, the conjugation of ST to gold nanoshells, which can undergo resonance excitation by NIR light and emit heat, represents a previously unrecognized approach for the targeted therapy of parenchymal colorectal cancer metastases, specifically to the liver and lung. This article discusses the potential of ST-targeted nanoshells for NIR thermal ablation of metastatic colorectal tumors and highlights the significant challenges and solutions linked to the translation of this emerging technology to patient care.

An arc-sequencing algorithm for intensity modulated arc therapy

Intensity modulated arc therapy (IMAT) is an intensity modulated radiation therapy delivery technique originally proposed as an alternative to tomotherapy. IMAT uses a series of overlapping arcs to deliver optimized intensity patterns from each beam direction. The full potential of IMAT has gone largely unrealized due in part to a lack of robust and commercially available inverse planning tools. To address this, we have implemented an IMAT arc-sequencing algorithm that translates optimized intensity maps into deliverable IMAT plans. The sequencing algorithm uses simulated annealing to simultaneously optimize the aperture shapes and weights throughout each arc. The sequencer enforces the delivery constraints while minimizing the discrepancies between the optimized and sequenced intensity maps. The performance of the algorithm has been tested for ten patient cases (3 prostate, 3 brain, 2 head-and-neck, 1 lung, and 1 pancreas). Seven coplanar IMAT plans were created using an average of 4.6 arcs and 685 monitor units. Additionally, three noncoplanar plans were created using an average of 16 arcs and 498 monitor units. The results demonstrate that the arc sequencer can provide efficient and highly conformal IMAT plans. An average sequencing time of approximately 20 min was observed.

Présent et avenir de la radiothérapie guidée par l'image (IGRT) et ses applications possibles dans le traitement des cancers bronchiques

These last years, the new irradiation techniques as the conformal 3D radiotherapy and the IMRT are strongly correlated with the technological developments in radiotherapy. The rigorous definition of the target volume and the organs at risk required by these irradiation techniques, imposed the development of various image guided patient positioning and target tracking techniques. The availability of these imaging systems inside the treatment room has lead to the exploration of performing real-time adaptive radiation therapy. In this paper we present the different image guided radiotherapy (IGRT) techniques and the adaptive radiotherapy (ART) approaches. IGRT developments are focused in the following areas: 1) biological imaging for better definition of tumor volume; 2) 4D imaging for modeling the intra-fraction organ motion; 3) on-board imaging system or imaging devices registered to the treatment machines for inter-fraction patient localization; and 4) treatment planning and delivery schemes incorporating the information derived from the new imaging techniques. As this paper is included in the "Cancer-Radiotherapie" special volume dedicated to the lung cancers, in the description of the different IGRT techniques we try to present the lung tumors applications when this is possible.

[Helical tomotherapy: general methodology for clinical and dosimetric evaluation (national French project)]

The methodology and choice of criteria and indexes used for a common evaluation of helical tomotherapy by 3 French centres are described. After a selection of clinical indications and definition of the general purpose are successively described the criteria and index selected for: 1) description of volumes and adaptation for on board imaging; 2) dose prescription and constraints related to IMRT; 3) intercomparaison of volumes and doses and potential dosimetric gain with this new equipment.

Le système de tomothérapie hélicoïdale pour la radiothérapie modulée en intensité et guidée par l'image : développements récents et applications cliniques

The advent of 3D conformal radiotherapy and intensity modulated radiation therapy (IMRT) make possible the dose optimization to complex target volumes close to sane organs at risk. IMRT's introduction of numerous small radiation fields inherently increases delivery inaccuracies. As a consequence, the use of IMRT without precise localization of the tumor and sensitive structures, at both the planning and delivery stages, and the absence of continuous verification represent the most significant challenges to the implementation of IMRT in routine clinical use. Intensity modulated (or not) conformal radiotherapy delivery requires better precision in the definition of treatment volume, frequently if necessary. Helical tomotherapy has been designed to use CT imaging technology to plan, deliver, and verify that the delivery has been carried out as planned. The image-guided and intensity modulations processes of helical tomotherapy that enable this goal are described.

Dispelling the myths surrounding radiotherapy for treatment of cutaneous melanoma

The role of radiotherapy is well established in the management of most locally advanced and metastatic cancers; however, there has been reluctance to extend this role to melanoma. The reasons can be traced historically to in-vitro and in-vivo data suggesting that melanomas are resistant to radiation. Current findings indicate that these cancers have a wide range of sensitivity to radiation that overlaps extensively with those for common epithelial cancers: indeed, some melanomas show high sensitivity to radiation. Greater incorporation of radiotherapy into multidisciplinary management of melanoma is important because of the typical natural history of the disease (a propensity for both locoregional recurrence and distant metastases) and its poor response to systemic treatment. This review will discuss these issues and preview the strategies being developed for radiotherapy to further improve the care of patients with melanoma.

The IMRT information process—mastering the degrees of freedom in external beam therapy

The techniques and procedures for intensity-modulated radiation therapy (IMRT) are reviewed in the context of the information process central to treatment planning and delivery of IMRT. A presentation is given of the evolution of the information based radiotherapy workflow and dose delivery techniques, as well as the volume and planning concepts for relating the dose information to image based patient representations. The formulation of the dose shaping process as an optimization problem is described. The different steps in the calculation flow for determination of machine parameters for dose delivery are described starting from the formulation of optimization objectives over dose calculation to optimization procedures. Finally, the main elements of the quality assurance procedure necessary for implementing IMRT clinically are reviewed.

History of tomotherapy

Tomotherapy is the delivery of intensity modulated radiation therapy using rotational delivery of a fan beam in the manner of a CT scanner. In helical tomotherapy the couch and gantry are in continuous motion akin to a helical CT scanner. Helical tomotherapy is inherently capable of acquiring CT images of the patient in treatment position and using this information for image guidance. This review documents technological advancements of the field concentrating on the conceptual beginnings through to its first clinical implementation. The history of helical tomotherapy is also a story of technology migration from academic research to a university-industrial partnership, and finally to commercialization and widespread clinical use.

Defining the radiation target on a daily basis

The delineation of the target volume for irradiation is a critical step in the radiotherapy process. Delivery of radiotherapy occurs over a fractionated course of many treatments. Variations in the position of the target volume may occur on a daily basis during treatment and so the procedure for defining the target volume on a single initial ‘snapshot’ computed tomography scan has been re-evaluated. Newer technologies of image-guided radiotherapy allow the development of on-line daily definition of the target volume prior to radiotherapy delivery.

Targeted Total Marrow Irradiation Using Three-Dimensional Image-Guided Tomographic Intensity-Modulated Radiation Therapy: An Alternative to Standard Total Body Irradiation

Total body irradiation (TBI) is an important part of bone marrow transplantation conditioning regimens. In TBI, dose escalation is difficult, because of associated normal organ toxicities. A method to deliver a more targeted dose of TBI preferentially to sites of greatest tumor burden is needed to reduce the dose to normal organs, reduce toxicities, and permit dose escalation. The purpose of this study was to evaluate, through a dosimetric analysis, the potential advantages and feasibility of selectively delivering targeted myeloablative doses of radiation to bone and marrow using a recently developed image-guided tomographic intensity-modulated radiation therapy delivery system (helical tomotherapy). Whole-body computed tomography datasets from 3 patients, age 5, 20, and 53 years, were used for treatment planning studies to evaluate 2 targeted TBI strategies: total marrow irradiation (TMI), in which the target region was defined as the skeletal bone, and total marrow and lymphoid irradiation (TMLI), in which the target regions were defined as bone, major lymph node chains, liver, spleen, and sanctuary sites, such as brain. Organ doses and dose distributions were compared with those in conventional TBI. A 1.7- to 7.5-fold reduction in median organ doses was observed with TMI and TMLI compared with conventional TBI. With this more targeted approach, a dose-volume histogram analysis predicted the potential to escalate the dose to bone (and containing marrow) up to 20 Gy, while maintaining doses to normal organs at lower levels than in conventional TBI to 12 Gy. Results were similar for the adult and pediatric patients, indicating that this form of targeted TBI will be applicable to most patients regardless of frame size. TMI to 10 Gy was delivered as part of a tandem transplant regimen to the 53-year-old patient with multiple myeloma. Clinical results confirmed the treatment planning predictions. After TMI, the patient experienced the expected blood count nadir, followed by successful engraftment. Grade 2 nausea and grade 1 emesis occurred only briefly on day 2 of TMI. Skin erythema, oral mucositis, esophagitis, and enteritis were not observed. This report demonstrates the feasibility and potential dosimetric advantages of selectively delivering myeloablative doses of radiation to bone and marrow using an image-guided tomographic intensity-modulated radiation therapy delivery system. Organ doses are substantially lower than those associated with standard TBI and predict the potential to significantly reduce associated toxicities and allow for dose escalation. The results also suggest that this form of targeted TBI may have potential advantages over other forms of targeted TBI, such as radioimmunotherapy or bone-seeking radionuclide therapy. Ongoing clinical trials will define the maximum TMI and TMLI doses achievable and define the potential advantages and limitations of this new approach for patients undergoing hematopoietic stem cell transplantation.

Improving the morbidity of anorectal injury from pelvic radiotherapy

OBJECTIVE

Radiation anorectal injury due to pelvic radiotherapy for non intestinal cancer is a significant cause of morbidity which may limit the treatment dose required. Conservative treatment options are of limited value and surgery is reserved only for the most severe complications. This review addresses radioprotection of the anorectum and aims to increase awareness amongst surgeons of the strategies that have been in practice in order to minimize the side-effects of radiotherapy while preserving its therapeutic efficacy.

METHODS

This review is based on a literature search (Medline and NLM PubMed) with manual cross-referencing of all articles related to anorectal radiation injury.

RESULTS

Optimization of radiation dose, the use of radioprotective agents and improvement in radiation delivery are the main areas of development. There are few data on the potential of altered fractionation schedules in reducing anorectal injury. A few phase I and II studies suggest that the pharmacological agents amifostine and misoprostol could be beneficial in limiting radiation damage but larger phase III studies are awaited.

CONCLUSION

The introduction of 3-dimensional conformal radiation therapy and intensity modulated radiation therapy has been the most significant advance in reducing radiation morbidity.

Radiotherapeutic techniques for prostate cancer, dose escalation and brachytherapy

There is evidence to confirm a dose-response relationship in prostate cancer. The relative benefit is dependent on the clinical prognostic risk factors (T stage, Gleason score and presenting prostate-specific antigen [PSA]) being more favourable for intermediate-risk patients. Refinement of prognostic groups and clinical threshold parameters is ongoing. Escalation of dose in prostate radiotherapy using conventional techniques is limited by rectal tolerance. Substantial advances have been made in radiotherapy practice, such as the development of conformal radiotherapy (CFRT) and intensity-modulated radiotherapy (IMRT). Randomised data support the value of CFRT in reducing rectal toxicity. IMRT can permit higher-dose escalation while still respecting known rectal tolerance thresholds. Brachytherapy is a recognised alternative for low-risk prostate cancer subgroups. New radiotherapeutic strategies for prostate cancer include pelvic nodal irradiation, exploiting the presumed low alpha/beta ratio in prostate cancer for hypofractionation and combining external beam with high-dose-rate brachytherapy boosts. New image-guided methodologies will enhance the therapeutic ratio of any radiotherapy technique or dose escalation programme by enabling more reliable and accurate treatment delivery for improved patient outcomes.

Impact of margin on tumour and normal tissue dosimetry in prostate cancer patients treated with IMRT using an endorectal balloon for prostate immobilization

In IMRT treatment, margin for planning target volume is determined by organ motion and set-up error. The margin width that achieves the desired dose escalation, while minimizing normal tissue exposure is dependent upon patient immobilization and/or organ localization techniques. In this study, we compare the impact of margin width on the dosimetry of tumour and normal tissues using an endorectal balloon filled with 100 cc of air. Plans were generated for ten patients using margin widths of 0, 3, 5, 8 and 10 mm. The prescription dose to prostate and seminal vesicles was 70 Gy in 35 fractions with 15% of bladder allowed to receive above 65 Gy, 15% of rectum above 68 Gy and 10% of femurs above 45 Gy. Margins above 5 mm produced significantly lower mean doses for both prostate and seminal vesicles without affecting TCP. For normal tissues, mean doses, percent volumes above prescription constraints and NTCP increased as a function of margin width, especially when this was 5 mm or above. We conclude that planning with tighter margins of < or =5 mm improves IMRT dosimetry for prostate and normal tissues and is only possible when target localization and/or immobilization devices are routinely used.

Promising new advances in head and neck radiotherapy

Efforts to improve the efficacy of treatment for SCCHN have led to the use of multimodality approaches with combinations of surgery, radiotherapy and chemotherapy. Conventional head and neck radiotherapy, a standard approach for locoregionally advanced disease, is associated with a variety of well-known acute and long-term toxicities. These chronic toxicities (i.e. xerostomia, dysphagia, fibrosis) can impact negatively on patient quality of life. Altered radiation fractionation regimens that incorporate acceleration and/or hyperfractionation can improve locoregional control but also increase acute toxicities for head and neck cancer patients. Intensity modulated radiation therapy (IMRT) has emerged as a promising method for delivering effective radiation dose to head and neck tumour targets while reducing exposure of surrounding healthy tissue. Another method for improving head and neck cancer outcome with conventional radiotherapy is with the concurrent addition of chemotherapy. Indeed, chemoradiotherapy is now a standard treatment approach for locoregionally advanced disease. Molecular targeted agents, such as the epidermal growth factor receptor (EGFR) antagonist, cetuximab (Erbitux), have recently been shown to enhance the effects of radiotherapy, and reports to date suggest that this potentiation occurs without an increase in the characteristic toxicities associated with head and neck radiation.