The utility of atlas-assisted segmentation in the male pelvis is dependent on the interobserver agreement of the structures segmented.

OBJECTIVE: To investigate the relationship between the ability of atlas-based autosegmentation to reduce outlining time in the male pelvis (body, bladder, rectum, femoral heads, prostate and seminal vesicles) and the interobserver agreement in the delineation of these structures. To examine any increase of the interobserver agreement with the use of an autosegmentation tool. METHODS: We created atlases in the ABAS™ system v. 2.0 (Elekta, Crawley, UK) and recorded the time to delineate the above structures on eight patients with and without its aid. We also measured the interobserver agreement in the structure definitions using several metrics [Dice's similarity coefficient (DSC), mean distance to conformity, percentage volume difference] with and without the aid of ABAS. RESULTS: There is a high degree of correlation between the time saving with the use of ABAS and the degree of interobserver agreement (r = 0.90 for DSC). This indicates that for structures where the interobserver agreement is low (DSC < 0.65), the ABAS does not reduce outlining time. We found that the interobserver agreement is increased with ABAS only for the prostate. CONCLUSION: Outlining time saved in the male pelvis is highly correlated with the interobserver agreement of the structures. Only for the prostate does the use of ABAS significantly reduce the amount of interobserver variation in contouring. ADVANCES IN KNOWLEDGE: The use of autosegmentation software increases the outlining time for structures where the interobserver agreement is low. Any increase in the interobserver agreement in contouring with the aid of such software may be limited to those structures where there is currently mid-range agreement between observers.

The use of a commercial remote desktop program in the delineation of target volumes in radiotherapy.

Recent guidance from the Royal College of Radiologists suggests that there should be close collaboration between oncologists and radiologists in target volume determination. However, the guidance also states that there may be practical difficulties in achieving this. To ameliorate some of these difficulties, we have implemented a readily available remote desktop package, Microsoft NetMeeting, in conjunction with a commercial virtual simulation package, ProSoma. This allows radiologists to conference easily with oncologists on a particular patient, as the full functionality of the virtual simulator is available simultaneously to both parties. We have found that this solution is eminently practical and increases the amount of interaction between oncologists and radiologists during target volume definition.

Guidelines for dosimetry and calibration in ultraviolet radiation therapy: a report of a British Photodermatology Group workshop.

This report examines the dosimetry of ultraviolet (UV) radiation applied to dermatological treatments, and considers the definition of the radiation quantities and their measurement. Guidelines are offered for preferred measurement techniques and standard methods of dosimetry. The recommendations have been graded according to the American Joint Committee on Cancer classification of strength of recommendation and quality of evidence (summarized in Appendix 5).

Guidelines for topical photodynamic therapy: report of a workshop of the British Photodermatology Group.

Topical photodynamic therapy (PDT) is effective in the treatment of certain non-melanoma skin cancers and is under evaluation in other dermatoses. Its development has been enhanced by a low rate of adverse events and good cosmesis. 5-Aminolaevulinic acid (ALA) is the main agent used, converted within cells into the photosensitizer protoporphyrin IX, with surface illumination then triggering the photodynamic reaction. Despite the relative simplicity of the technique, accurate dosimetry in PDT is complicated by multiple variables in drug formulation, delivery and duration of application, in addition to light-specific parameters. Several non-coherent and coherent light sources are effective in PDT. Optimal disease-specific irradiance, wavelength and total dose characteristics have yet to be established, and are compounded by difficulties comparing light sources. The carcinogenic risk of ALA-PDT appears to be low. Current evidence indicates topical PDT to be effective in actinic keratoses on the face and scalp, Bowen's disease and superficial basal cell carcinomas (BCCs). PDT may prove advantageous where size, site or number of lesions limits the efficacy and/or acceptability of conventional therapies. Topical ALA-PDT alone is a relatively poor option for both nodular BCCs and squamous cell carcinomas. Experience of the modality in other skin diseases remains limited; areas where there is potential benefit include viral warts, acne, psoriasis and cutaneous T-cell lymphoma. A recent British Photodermatology Group workshop considered published evidence on topical PDT in order to establish guidelines to promote the efficacy and safety of this increasingly practised treatment modality.

Laser scanning of patient outlines for three-dimensional radiotherapy treatment planning.

In the planning of radiation treatments it is important to have a knowledge of the patient outline in order to correctly calculate the dose distribution that can be expected within the patient. This information is routinely obtained using x-ray computed tomography (CT). Although the CT data set is the ultimate data set, it can be impractical for economic and physical reasons. These impracticalities have been overcome using a commercial three dimensional (3D) laser scanning system. The system scans a laser line across the surface of the patient while a CCD camera views the patient from an offset angle. From a knowledge of the spatial orientation of the camera and the laser source, the system is able to detect the patient's surface and generate an equivalent 3D point cloud. Manipulation of 3D data sets allows the appropriate outlines of the patient to be obtained, that can then be used with the radiotherapy planning system. This has enabled the evaluation of 3D dose distributions for patients, and hence will allow the development of techniques for improving the uniformity of dose in breast treatments. The technique has no radiation overhead associated with it, is quick and is relatively cheap.

Portal imaging.

Portal imaging is the acquisition of images with a radiotherapy beam. Imaging theory suggests that the quality of portal images could be much higher if the efficiency of the imaging media in detecting radiation could be improved. Introduction of new media (films and electronic portal imaging devices) has confirmed this by markedly increasing the quality of portal images. Images from these devices can then be used to verify a patient's treatment. Geometric verification requires the portal image to be registered with a reference image. Dosimetric verification requires the portal imager to be calibrated for dose. This review gives a brief overview of the current areas of interest in portal imaging: imaging theory; imaging media, film and electronic portal imaging devices; image registration; and dosimetry using these devices.

Topical photodynamic therapy at low fluence rates--theory and practice.

Photodynamic Therapy (PDT), with topically applied 5-aminolaevulinic acid as the photosensitiser, is an effective treatment for various malignant and pre-malignant skin conditions. Several studies have shown the importance of fluence rate as well as fluence in the efficacy of PDT. We propose a measure of PDT efficacy, Photodynamic Damage Dose (PDD), which uses the product of instantaneous fluence rates, photosensitiser concentrations and oxygen concentrations in its calculation. We derive a qualitative numerical model of PDT and verify it by demonstrating an inverse fluence rate effect, increased efficacy of fractionated PDT, PDT induced hypoxia, and the dependence of photobleaching on fluence rate under certain circumstances. We recommend that fluence, fluence rate and any fractionation regime used should be detailed when reporting a trial as altering any of these has significant effects on PDT efficacy. The model predicts that low fluence rate irradiations should be as effective as high fluence rate irradiations if carried out over the same length of time. To test this we build a light emitting diode-based lamp (fluence rate of 7 mW cm(-2) at 635 nm) and used it to treat 32 superficial basal cell carcinomas on 22 patients (30 min treatment time, fluence 12.6 J cm(-2)). The complete response rate at one year was 84%, which is comparable to that achieved using higher fluence rate sources for similar treatment times. We conclude that this robust, inexpensive light source is effective for topical PDT.

Photodynamic therapy of feline superficial squamous cell carcinoma using topical 5-aminolaevulinic acid.

A study was undertaken to investigate the treatment of superficial squamous cell carcinoma of the nasal planum, pinna and eyelid in cats by photodynamic therapy, using topical 5-aminolaevulinic acid cream, with subsequent exposure to red light of wavelength 635 nm, supplied by a light-emitting diode source. A total of 13 squamous cell carcinomas were treated, including 10 nasal planum lesions, two pinnal lesions and one eyelid lesion. After a single treatment, complete responses were seen in nine out of 10 nasal planum lesions, one out of two pinnal lesions and the eyelid lesion. The overall complete response rate for lesions managed with a single photodynamic therapy treatment was 85 per cent. Seven of the 11 lesions (63.6 per cent) showing a complete response subsequently recurred; the time to recurrence ranged from 19 to 56 weeks (median 21 weeks, mean 26.7 weeks).

Post-partum retreatment with iridium-192 wire brachytherapy for meningioma recurring in pregnancy.

We report the case history of a female patient who had received radical radiotherapy for a malignant meningioma at the age of 11 years. Thirteen years later, during her first pregnancy, she presented with a recurrence. The tumour was surgically debulked, but complications related to postoperative sepsis, the location of the tumour, and the extent of her previous treatment made the delivery of adjuvant radiotherapy problematic. The tumour bed was treated using an interstitial implant of 192Ir wires to a dose of 60 Gy in 100 hours. The patient remains well with no evidence of tumour recurrence or brain necrosis 2 years later. We discuss the role of female sex hormones in meningioma and the difficulties of radical retreatment of tumours in the central nervous system. The various techniques of brachytherapy in the brain are highlighted. The specific advantages of 192Ir in this patient are discussed.

Characterization of new portal film systems for radiotherapy verification.

Portal images are an important verification tool in radiotherapy. Their use has been limited by their poor image quality, which is due to the inherent lack of contrast at megavoltage energies. Recently CEA and Kodak have introduced new portal film-cassette systems with much improved contrast. We have determined the H-D curves for these systems and found the gamma (gamma) for the CEA system (8.5) to be larger than that for the Kodak EC-L system (6.3). The optimal doses were CEA TLF 1.2 cGy, CEA TVS 15.9 cGy and Kodak EC-L 1.5 cGy. We also obtained phantom images that were evaluated by 11 radiotherapists. They ranked the CEA B High Plus cassette with CEA TVS film the highest, followed by the Kodak EC-L system. Some clinical films of a lateral pelvis are also presented, to demonstrate the improvement in image quality with these new film systems as compared with conventional portal films.

Calibration of strontium-90 eye applicator using a strontium external beam standard.

Four techniques for measuring the dose rate from Sr-90 concave eye plaques are presented. The techniques involve calibrating a concave eye plaque against a Sr-90 teletherapy unit using X-Omat film, radiochromic film, black LiF TLD discs and LiF chips. The mean dose rate predicted by these dosimeters is 7.5 cGy s(-1). The dose rate quoted by the manufacturer is 33% lower than this value, which is consistent with discrepancies reported by other authors. Calibration against a 6 MV linear accelerator was also carried out using each of the above dosimetric devices, and appropriate sensitivity correction factors have been presented.

Home phototherapy: report on a workshop of the British Photodermatology Group, December 1996.

Phototherapy is a popular and effective treatment for many patients with skin diseases. However, repeated journeys to hospital for phototherapy can be inconvenient and expensive. If it were available, many patients might prefer home-based phototherapy as long as it was safe and effective. Indeed, many psoriasis patients already self-treat with ultraviolet A sunbeds at home. This report represents a consensus view from a British Photodermatology Group workshop held in December 1996, the purpose of which was to examine the potential role of home-based phototherapy in dermatological practice. We conclude that home-based therapy represents a suboptimal treatment with greater attendant risks than phototherapy in a hospital environment. The level of medical supervision of the home treatment is crucial to its safety and effectiveness. Until further studies are forthcoming, home phototherapy should be largely restricted to those with overwhelming difficulties in attending hospital.

An investigation into the use of carbon fibre for megavoltage radiotherapy applications.

Properties of carbon fibre of relevance to its use for megavoltage radiotherapy applications have been investigated. Measurements have been made of the percentage transmission and percentage build-up of carbon fibre at energies of 5, 6 and 8 MV. The results are presented in comparison with those obtained for other materials commonly used in radiotherapy: polymethylmethacrylate (PMMA), PETG copolyester and expanded polystyrene foam. It was found that carbon fibre has a higher percentage transmission and a lower percentage build-up than either PMMA or PETG copolyester. It was also found that the build-up due to a combination of carbon fibre and 5 cm of polystyrene foam was less than 65% over the energy range for which measurements were made, and much lower than that due to PETG copolyester. It is thus proposed that carbon fibre is a suitable material from which to make devices for use in megavoltage radiotherapy.

An insight into the contributions of self-shielding and lamp reflectors to patient exposure in phototherapy units.

Calibration of phototherapy equipment can prove to be difficult. One problem is that the self-shielding produced by a patient reduces the irradiance relative to that determined when the cabinet is empty. A model has been developed to determine the factor to apply to the irradiance measured with the cabinet empty to give the irradiance with the patient present, i.e. the self-shielding correction factor. The model assumes that the cabinet consists of a number of discrete infinite line sources backed by perfect mirrors. The patient is treated as a barrier that prevents some of these sources being seen by the detector in the mirror it faces. The model was tested using a Waldmann 8001 K unit and three UV meters for UVA and UVB sources. The measurements suggested some modifications to the model--for UVA multiple reflections were important and for UVB the reflectors were only 30% efficient. The correction factors obtained were 0.87 for UVA and 0.96 for UVB.

Characterization and use of a commercial n-type diode system.

The characteristics of n-type diodes (linearity, temperature, dose rate, radiation damage response, directional dependence, output factors, wedge factors and percentage depth dose determinations) were investigated. Subsequently, the diodes were used clinically for in vivo dose verification during external megavoltage photon beam therapy. It has been shown that n-type diodes are easy to use and the results obtained are comparable to those reported for p-type diodes. On most occasions, n-type diodes can be used without any additional correction factors apart from regular monthly calibration. There is good agreement between the uncertainty limits estimated from the diodes' characteristics and those obtained on the basis of 2261 patient measurements.

Effect of the C-terminal proline repeats on ordered packing of squid rhodopsin and its mobility in membranes.

Negative stain electron microscopy and saturation transfer electron spin resonance spectroscopy have been used to compare the lattice ordering and in-plane membrane mobility of full-length and C-terminally cleaved squid rhodopsin. The C-terminus of squid rhodopsin contains a negatively charged region followed by 9-10 repeats of a proline-rich sequence, not found in rhodopsins other than those of cephalopod invertebrates, but similar proline repeats are found in other, unrelated membrane proteins. We find that the proline repeats cluster the rhodopsins into small groups, interfering with two-dimensional crystallization and maintaining their mobility in the membrane.

The application of dose-volume histograms to the Paris and Manchester systems of brachytherapy dosimetry.

When the geometry of an implant does not exactly follow a system of dosimetry problems arise in choosing a treatment dose rate. This study has investigated the use of natural dose-volume histograms (DVHs) as a means for choosing the treatment dose level in these cases. A number of ideal geometrical cases have been investigated. For these, where appropriate, the Paris or Manchester dose rates have been calculated and compared with the peak position of the natural DVH. The dose rate at the peak of the DVH was found to agree with the basal dose rate calculated according to the Paris rules. For implants that completely obeyed the Paris rules the mean ratio was 1.009 +/- 4%. A series of clinical implants was also examined. For these the mean ratio was 1.002 +/- 2.5%. It is concluded that the peak position of a DVH can be used to predict the Paris basal dose rate of an implant. There was no systematic relationship found between the Manchester dose rate and the peak position of the DVH. The mean ratio between the Manchester dose rate and the peak dose rate position of the DVH was 0.82 +/- 13% for a series of implants.

Signal transduction in photoreceptors.

The biochemical role of the visual-pigment protein, rhodopsin, is reviewed, with reference to vertebrate rods and cones and the microvillar photoreceptors of invertebrates. New results are presented on the structure of squid rhodopsin, which possesses an extensive proline-rich repeat at its C-terminus, using negative-stain electron microscopy.