• Robust three-dimensional best-path phase-unwrapping algorithm that avoids singularity loops.

      Abdul-Rahman, Hussein S; Arevalillo-Herráez, Miguel; Gdeisat, Munther A; Burton, David R; Lalor, Michael; Lilley, Francis; Moore, Christopher J; Sheltraw, Daniel; Qudeisat, Mohammed; Mobile Machine and Vision Lab, Sheffield Hallam University, Faculty of ACES, Showcase 4114, Pond Street, Sheffield S1 1WB, United Kingdom. (2009-08-10)
      In this paper we propose a novel hybrid three-dimensional phase-unwrapping algorithm, which we refer to here as the three-dimensional best-path avoiding singularity loops (3DBPASL) algorithm. This algorithm combines the advantages and avoids the drawbacks of two well-known 3D phase-unwrapping algorithms, namely, the 3D phase-unwrapping noise-immune technique and the 3D phase-unwrapping best-path technique. The hybrid technique presented here is more robust than its predecessors since it not only follows a discrete unwrapping path depending on a 3D quality map, but it also avoids any singularity loops that may occur in the unwrapping path. Simulation and experimental results have shown that the proposed algorithm outperforms its parent techniques in terms of reliability and robustness.
    • The use of computed radiography for routine linear accelerator and simulator quality control.

      Patel, I; Natarajan, T; Hassan, S S; Kirby, Mike C; North Western Medical Physics, Radiotherapy Department, Rosemere Cancer Centre, Lancashire Teaching Hospitals NHS Foundation Trust, Preston, UK. imran.patel@lthtr.nhs.uk (2009-10)
      Computed radiography (CR) systems were originally developed for the purpose of clinical imaging, and there has been much work published on its effectiveness as a film replacement for this end. However, there has been little published on its use for routine linear accelerator and simulator quality control, and therefore we have evaluated the use of the Kodak 2000RT system with large Agfa CR plates as a replacement for film for this function. A prerequisite for any such use is a detailed understanding of the system behaviour, hence characteristics such as spatial uniformity of response, reproducibility of spatial accuracy, plate signal decay with time and the dose-response of plates were investigated. Finally, a comparison of results obtained using CR for the measurement of radiation field dimensions was made against those from radiographic film, and found to be in agreement within 0.1 mm (mean difference for high-resolution images, 0.3 mm root mean square difference) for megavoltage images and 0.3 mm (maximum difference) for simulator images. In conclusion, the CR system has been shown to be a good alternative to radiographic film for routine quality control of linear accelerators and simulators.
    • Assessing the effect of a contouring protocol on postprostatectomy radiotherapy clinical target volumes and interphysician variation.

      Mitchell, Darren M; Perry, Lesley A; Smith, Steve; Elliott, Tony; Wylie, James P; Cowan, Richard A; Livsey, Jacqueline E; Logue, John P; Department of Clinical Oncology, Christie Hospital, Manchester, United Kingdom. dmmitchell@doctors.org.uk (2009-11-15)
      PURPOSE: To compare postprostatectomy clinical target volume (CTV) delineation before and after the introduction of a contouring protocol and to investigate its effect on interphysician variability METHODS AND MATERIALS: Six site-specialized radiation oncologists independently delineated a CTV on the computed tomography (CT) scans of 3 patients who had received postprostatectomy radiotherapy. At least 3 weeks later this was repeated, but with the physicians adhering to the contouring protocol from the Medical Research Council's Radiotherapy and Androgen Deprivation In Combination After Local Surgery (RADICALS) trial. The volumes obtained before and after the protocol were compared and the effect of the protocol on interphysician variability assessed. RESULTS: An increase in mean CTV for all patients of 40.7 to 53.9 cm(3) was noted as a result of observing the protocol, with individual increases in the mean CTV of 65%, 15%, and 24% for Patients 1, 2, and 3 respectively. A reduction in interphysician variability was noted when the protocol was used. CONCLUSIONS: Substantial interphysician variation in target volume delineation for postprostatectomy radiotherapy exists, which can be reduced by the use of a contouring protocol. The RADICALS contouring protocol increases the target volumes when compared with those volumes typically applied at our center. The effect of treating larger volumes on the therapeutic ratio and resultant toxicity should be carefully monitored, particularly if the same dose-response as documented in radical prostate radiotherapy applies to the adjuvant and salvage setting. Prostate cancer, Postprostatectomy, Radiotherapy, Target volume.
    • Spatial and temporal carrier fringe pattern demodulation using the one-dimensional continuous wavelet transform: recent progregg, challenges, and suggested developments.

      Gdeisat, Munther A; Abdulbasit, A; Burton, D R; Lalor, Michael; Lilley, Francis; Moore, Christopher J; Qudeisat, Mohammed (2009)
    • Assessment of bladder motion for clinical radiotherapy practice using cine-magnetic resonance imaging.

      McBain, Catherine A; Khoo, Vincent S; Buckley, David L; Sykes, Jonathan S; Green, Melanie M; Cowan, Richard A; Hutchinson, Charles E; Moore, Christopher J; Price, Patricia M; Academic Department of Radiation Oncology, The University of Manchester, Christie Hospital NHS Foundation Trust, Wilmslow Road, Manchester, United Kingdom. (2009-11-01)
      PURPOSE: Organ motion is recognized as the principal source of inaccuracy in bladder radiotherapy (RT), but there is currently little information on intrafraction bladder motion. METHODS AND MATERIALS: We used cine-magnetic resonance imaging (cine-MRI) to study bladder motion relevant to intrafraction RT delivery. On two occasions, a 28 minute cine-MRI sequence was acquired from 10 bladder cancer patients and 5 control participants immediately after bladder emptying, after abstinence from drinking for the preceding hour. From the resulting cine sequences, bladder motion was subjectively assessed. To quantify bladder motion, the bladder was contoured in imaging volume sets at 0, 14, and 28 min to measure changes to bladder volumes, wall displacements, and center of gravity (COG) over time. RESULTS: The dominant source of bladder motion during imaging was bladder filling (up to 101% volume increase); rectal and small bowel movements were transient, with minimal impact. Bladder volume changes were similar for all participants. However for bladder cancer patients, wall displacements were larger (up to 58 mm), less symmetrical, and more variable compared with nondiseased control bladders. CONCLUSIONS: Significant and individualized intrafraction bladder wall displacements may occur during bladder RT delivery. This important source of inaccuracy should be incorporated into treatment planning and verification.
    • A novel imaging technique for fusion of high-quality immobilised MR images of the head and neck with CT scans for radiotherapy target delineation.

      Webster, Gareth J; Kilgallon, J E; Ho, Kean F; Rowbottom, Carl G; Slevin, Nicholas J; Mackay, Ranald I; North Western Medical Physics, Christie Hospital NHS Foundation Trust, Manchester, UK. gareth.webster@physics.cr.man.ac.uk (2009-06)
      Uncertainty and inconsistency are observed in target volume delineation in the head and neck for radiotherapy treatment planning based only on CT imaging. Alternative modalities such as MRI have previously been incorporated into the delineation process to provide additional anatomical information. This work aims to improve on previous studies by combining good image quality with precise patient immobilisation in order to maintain patient position between scans. MR images were acquired using quadrature coils placed over the head and neck while the patient was immobilised in the treatment position using a five-point thermoplastic shell. The MR image and CT images were automatically fused in the Pinnacle treatment planning system using Syntegra software. Image quality, distortion and accuracy of the image registration using patient anatomy were evaluated. Image quality was found to be superior to that acquired using the body coil, while distortion was < 1.0 mm to a radius of 8.7 cm from the scan centre. Image registration accuracy was found to be 2.2 mm (+/- 0.9 mm) and < 3.0 degrees (n = 6). A novel MRI technique that combines good image quality with patient immobilization has been developed and is now in clinical use. The scan duration of approximately 15 min has been well tolerated by all patients.
    • Electron beam quality control using an amorphous silicon EPID

      Beck, James A; Budgell, Geoff J; Roberts, D A; Evans, P M; North Western Medical Physics, Christie Hospital NHS Foundation Trust, Withington, Manchester M20 4BX, United Kingdom. (2009-04)
    • The cost effectiveness of in vivo dosimetry is not proven.

      Mackay, Ranald I; Williams, Peter C; North Western Medical Physics, Christie Hospital NHS Trust, Wilmslow Road, Manchester M20 4BX, UK. ranald.mackay@physics.cr.man.ac.uk (2009-04)
      In vivo dosimetry is a check of the radiotherapy treatment process. Recently, it has been argued that in vivo dosimetry at the start of every patient's radiotherapy is cost effective. We have examined and extended the cost effectiveness argument and show that the model does not deliver the stated benefits.
    • Procedure guideline for planar radionuclide cardiac ventriculogram for the assessment of left ventricular systolic function.

      Nicol, Alice; Avison, Mike; Harbinson, Mark; Jeans, Steve; Waddington, Wendy; Woldman, Simon; Southern General Hospital, NHS Greater Glasgow and Clyde, Glasgow, UK. alice.nicol@ggc.scot.nhs.uk (2009-03)
    • Comparison of IPSM 1990 photon dosimetry code of practice with IAEA TRS-398 and AAPM TG-51.

      Vargas-Castrillón, Silvia T; Cutanda Henriquez, Francisco; NW Medical Physics, Christie Hospital NHS Foundation Trust, Manchester, UK. stvcastrillon@hotmail.com (2009)
      Several codes of practice for photon dosimetry are currently used around the world, supported by different organizations. A comparison of IPSM 1990 with both IAEA TRS-398 and AAPM TG-51 has been performed. All three protocols are based on the calibration of ionization chambers in terms of standards of absorbed dose to water, as it is the case with other modern codes of practice. This comparison has been carried out for photon beams of nominal energies: 4 MV, 6 MV, 8 MV, 10 MV and 18 MV. An NE 2571 graphite ionization chamber was used in this study, cross-calibrated against an NE 2611A Secondary Standard, calibrated in the National Physical Laboratory (NPL). Absolute dose in reference conditions was obtained using each of these three protocols including: beam quality indices, beam quality conversion factors both theoretical and NPL experimental ones, correction factors for influence quantities and absolute dose measurements. Each protocol recommendations have been strictly followed. Uncertainties have been obtained according to the ISO Guide to the Expression of Uncertainty in Measurement. Absorbed dose obtained according to all three protocols agree within experimental uncertainty. The largest difference between absolute dose results for two protocols is obtained for the highest energy: 0.7% between IPSM 1990 and IAEA TRS-398 using theoretical beam quality conversion factors.
    • Accuracy and precision of an IGRT solution.

      Webster, Gareth J; Rowbottom, Carl G; Mackay, Ranald I; North Western Medical Physics, Christie Hospital NHS Trust, Manchester, United Kingdom. Gareth.Webster@physics.cr.man.ac.uk (2009)
      Image-guided radiotherapy (IGRT) can potentially improve the accuracy of delivery of radiotherapy treatments by providing high-quality images of patient anatomy in the treatment position that can be incorporated into the treatment setup. The achievable accuracy and precision of delivery of highly complex head-and-neck intensity modulated radiotherapy (IMRT) plans with an IGRT technique using an Elekta Synergy linear accelerator and the Pinnacle Treatment Planning System (TPS) was investigated. Four head-and-neck IMRT plans were delivered to a semi-anthropomorphic head-and-neck phantom and the dose distribution was measured simultaneously by up to 20 microMOSFET (metal oxide semiconductor field-effect transmitter) detectors. A volumetric kilovoltage (kV) x-ray image was then acquired in the treatment position, fused with the phantom scan within the TPS using Syntegra software, and used to recalculate the dose with the precise delivery isocenter at the actual position of each detector within the phantom. Three repeat measurements were made over a period of 2 months to reduce the effect of random errors in measurement or delivery. To ensure that the noise remained below 1.5% (1 SD), minimum doses of 85 cGy were delivered to each detector. The average measured dose was systematically 1.4% lower than predicted and was consistent between repeats. Over the 4 delivered plans, 10/76 measurements showed a systematic error > 3% (3/76 > 5%), for which several potential sources of error were investigated. The error was ultimately attributable to measurements made in beam penumbrae, where submillimeter positional errors result in large discrepancies in dose. The implementation of an image-guided technique improves the accuracy of dose verification, particularly within high-dose gradients. The achievable accuracy of complex IMRT dose delivery incorporating image-guidance is within +/- 3% in dose over the range of sample points. For some points in high-dose gradients, submillimeter errors in position can lead to errors > 3%. The precision of the delivery system was demonstrated to be within the experimental noise of the detector system of 1.5% (1 SD).
    • Rectal motion can reduce CTV coverage and increase rectal dose during prostate radiotherapy: A daily cone-beam CT study.

      Sripadam, Raj; Stratford, Julia; Henry, Ann M; Jackson, Andrew; Moore, Christopher J; Price, Patricia M; Clatterbridge Centre for Oncology, Bebington, Wirral, UK. (2009-03)
      BACKGROUND AND PURPOSE: Daily on-treatment verification cone-beam CT (CBCT) was used to study the effect of rectal motion on clinical target volume (CTV) coverage during prostate radiotherapy. MATERIAL AND METHODS: CBCT scans were acquired from 15 patients immediately after daily treatment. From these images, the rectum was contoured allowing the analysis of rectal volume cross-sectional area (CSA) and the determination of rectal dose. Rectal wall motion was quantified as a surrogate measure of prostate displacement and CTV coverage was subjectively assessed. RESULTS: Rectal volume decreased over the treatment course in 13 patients (P<0.001). Rectal wall regions corresponding to the prostate base displayed the greatest motion; larger displacements were seen in patients with larger rectal planning volumes. CTV coverage was inadequate, at the prostate base only, in 38% of the fractions delivered to 4/7 patients with a large rectum at planning (>100 cm(3)). In patients with small rectum at planning (<50 cm(3)) up to 25% more rectal volume than predicted was included in the high-dose region. CONCLUSIONS: Rectal motion during treatment in prostate cancer patients has implications for CTV coverage and rectal dose. Measures to ensure consistency in daily rectal volume or image-guided strategies should be considered.
    • Inter-fraction motion and dosimetric consequences during breast intensity-modulated radiotherapy (IMRT).

      Jain, Pooja; Marchant, Thomas E; Green, Melanie M; Watkins, Gillian R; Davies, Julie; McCarthy, Claire; Loncaster, Juliette A; Stewart, Alan L; Magee, Brian; Moore, Christopher J; et al. (2009-01)
      BACKGROUND AND PURPOSE: Intensity-modulated radiotherapy (IMRT) can improve dose homogeneity within the breast planned target volume (PTV), but may be more susceptible to patient/organ motion than standard tangential radiotherapy (RT). We used daily cone-beam CT (CBCT) imaging to assess inter-fraction motion during breast IMRT and its subsequent impact on IMRT and standard RT dose homogeneity. MATERIALS AND METHODS: Ten breast cancer patients selected for IMRT were studied. CBCT images were acquired immediately after daily treatment. Automatic image co-registration was used to determine patient positioning variations. Daily PTV contours were used to calculate PTV variations and daily delivered IMRT and theoretically planned tangential RT dose. RESULTS: Group systematic (and random) setup errors detected by CBCT were 5.7 (3.9)mm laterally, 2.8 (3.5)mm vertically and 2.3 (3.2)mm longitudinally. Rotations >2 degrees in any axis occurred on 53/106 (50%) occasions. Daily PTV volume varied up to 23%. IMRT dose homogeneity was superior at planning and throughout the treatment compared with standard RT (1.8% vs. 15.8% PTV received >105% planned mean dose), despite increased motion sensitivity. CONCLUSIONS: CBCT revealed inadequacies of current patient positioning and verification procedures during breast RT and confirmed improved dose homogeneity using IMRT for the patients studied.
    • A computationally efficient method for automatic registration of orthogonal x-ray images with volumetric CT data.

      Chen, Xin; Varley, Martin R; Shark, Lik-Kwan; Shentall, Glyn S; Kirby, Mike C; ADSIP Research Centre, University of Central Lancashire, Preston, UK. xchen2@uclan.ac.uk (2008-02-21)
      The paper presents a computationally efficient 3D-2D image registration algorithm for automatic pre-treatment validation in radiotherapy. The novel aspects of the algorithm include (a) a hybrid cost function based on partial digitally reconstructed radiographs (DRRs) generated along projected anatomical contours and a level set term for similarity measurement; and (b) a fast search method based on parabola fitting and sensitivity-based search order. Using CT and orthogonal x-ray images from a skull and a pelvis phantom, the proposed algorithm is compared with the conventional ray-casting full DRR based registration method. Not only is the algorithm shown to be computationally more efficient with registration time being reduced by a factor of 8, but also the algorithm is shown to offer 50% higher capture range allowing the initial patient displacement up to 15 mm (measured by mean target registration error). For the simulated data, high registration accuracy with average errors of 0.53 mm +/- 0.12 mm for translation and 0.61 +/- 0.29 degrees for rotation within the capture range has been achieved. For the tested phantom data, the algorithm has also shown to be robust without being affected by artificial markers in the image.
    • Chemoradiotherapy for locally advanced pancreatic cancer: a radiotherapy dose escalation and organ motion study.

      Henry, Ann M; Ryder, W David J; Moore, Christopher J; Sherlock, David J; Geh, J I; Dunn, P; Price, Patricia M; Academic Department of Radiation Oncology, The University of Manchester, Department of Medical Statistics, Christie Hospital NHS Trust, Manchester, UK. (2008-09)
      AIMS: To determine the efficacy of radiation dose escalation and to examine organ motion during conformal radiotherapy for locally advanced pancreatic cancer. MATERIALS AND METHODS: Thirty-nine patients who were consecutively treated with chemoradiotherapy were studied. Fifteen patients, treated from 1993 to 1997, received 50 Gy in 20 fractions (group I). Twenty-four patients, treated from 1997 to 2003, received an escalated dose of 55 Gy in 25 fractions (group II). Intra-fraction pancreatic tumour motion was assessed in three patients using megavoltage movies during radiation delivery to track implanted radio-opaque markers. RESULTS: Improved survival rates were seen in latterly treated group II patients (P=0.083), who received escalated radiotherapy to smaller treatment volumes due to advances in verification. Worse toxicity effects (World Health Organization grade 3-4) were reported by some patients (<10%), but treatment compliance was similar in both groups, indicating equivalent tolerance. Substantial intra-fraction tumour displacement due to respiratory motion was observed: this was greatest in the superior/inferior (mean=6.6 mm) and anterior/posterior (mean=4.75 mm) directions. Lateral displacements were small (<2 mm). CONCLUSIONS: Dose escalation is feasible in pancreatic cancer, particularly when combined with a reduction in irradiated volume, and enhanced efficacy is indicated. Large, globally applied margins to compensate for pancreatic tumour motion during radiotherapy may be inappropriate. Strategies to reduce respiratory motion, and/or the application of image-guided techniques that incorporate individual patients' respiratory motion into radiotherapy planning and delivery, will probably improve pancreatic radiotherapy.
    • Auditory cortical activation and speech perception in cochlear implant users.

      Green, Kevin M J; Julyan, Peter J; Hastings, David L; Ramsden, Richard T; Department of Otolaryngology, Manchester Royal Infirmary Manchester, UK. kmjgreen@rcsed.ac.uk (2008-03)
      Cochlear implantation is generally accepted as a successful means of restoring auditory sensation to profoundly deaf individuals. Although most patients can expect a satisfactory outcome following implantation, some have poor speech perception outcomes. This investigation used [18F]-fluorodeoxyglucose positron emission tomography to measure cortical activity resulting from auditory stimulation in seven 'good' and four 'poor' cochlear implant recipients. Activations were significantly greater in both the primary and association cortices in the good compared with the poor implant users. We suggest that the ability to access the more specialised speech processing abilities of the auditory association cortices helps determine outcome following cochlear implantation.
    • Hand function after high dose rate brachytherapy for squamous cell carcinoma of the skin of the hand.

      Somanchi, B V; Stanton, Anthony; Webb, M; Loncaster, Juliette A; Allan, Ernest; Muir, L T S W; Department of Hand Surgery, Salford Royal Hospital, Salford M6 8HD, UK. brindavihari2001@yahoo.com (2008-11)
      AIMS: Current recommendations for the treatment of squamous cell carcinoma of the hand are almost unanimously in favour of ablative surgery. However, many of the patients are frail and elderly, and surgical techniques frequently involve skin grafts or amputation of digits. A non-invasive method of treatment is, therefore, often preferred. Radiotherapy using a brachytherapy technique is a well-established option. This study investigated whether patients found the treatment acceptable and assessed the outcome of treatment in terms of local control, cosmesis and hand function. MATERIALS AND METHODS: Twenty-five patients who underwent mould brachytherapy using a microselectron high dose rate radiotherapy device were available for assessment. We assessed the functional status of the hand and fingers by means of the Disability of Arm, Shoulder and Hand and Michigan Hand Outcomes questionnaires. We examined the hand to assess the severity of post-radiation stigmata. We enquired as to patient acceptability of treatment and outcome. RESULTS: Of 25 patients who agreed to participate, the fingers were affected in 15 and the dorsum of the hand in 10. The mean age at the time of radiotherapy was 69 years (range 50-87). There were no significant differences in parameters, such as range of motion of fingers and wrist, hand/finger grip strength, between the treated and opposite sides. Sensation, including two-point discrimination, was not significantly different from the untreated hand. Seventeen patients had minor skin changes. No patient found the treatment painful or unacceptable. Twenty patients were very satisfied and five patients were moderately satisfied with the cosmetic result. CONCLUSIONS: We conclude that high dose rate brachytherapy is a safe and simple alternative to surgical treatment for squamous cell carcinoma of the hand, as it is not only successful in eradicating tumour, but also preserves hand function.
    • Radical chemoradiotherapy for adenocarcinoma of the distal oesophagus and oesophagogastric junction: what planning margins should we use?

      Whitfield, Gillian A; Jackson, Andrew; Moore, Christopher J; Price, Patricia M; Academic Department of Radiation Oncology, University of Manchester, Manchester, UK. gillian.whitfield@manchester.ac.uk (2008-12)
      Distal oesophageal and Type I-II oesophagogastric junctional adenocarcinomas have a poor prognosis. In radical chemoradiotherapy, consensus is lacking on radiotherapy margins. Here, we review the effect of common imaging modalities on the extent of the gross tumour volume (GTV) and the evidence for margins. To do this, papers were identified from PubMed, and geometric uncertainties were combined using the British Institute of Radiology formula. CT and endoscopic ultrasound were best for GTV delineation, but the role of positron emission tomography is uncertain. Evidence suggests 3 cm proximal and 5 cm distal GTV-CTV (clinical target volume) margins (along the mucosa) for advanced tumours, but is lacking for early tumours and radial margins. Nodal spread, present in most pT2 tumours, is strongly prognostic and is initially to regional nodes (not wholly covered by typical radiotherapy). Calculated CTV-PTV (planning target volume) margins for three-dimensional conformal radiotherapy using literature estimates of tumour motion and set-up errors with bony online set-up correction, ignoring delineation errors, are 2.2 cm superiorly (sup) and inferiorly (inf) and 1.2-1.3 cm radially (1.3 cm sup-inf; 0.8 cm radially if the tumour's mid-position is known). As these margins may risk excessive toxicity, we propose treating microscopic disease for potentially curable tumours (cT2N0, some cT3N0), but gross disease only for advanced tumours. Recommended GTV-CTV margins are a maximum of 3 cm proximally and 5 cm distally up to cT2N0; 3 cm proximally and 5 cm distally for cT3N0 if anticipated toxicity allows; and 0 cm for cT4 and most node-positive tumours. The CTV-PTV margins above must be added to this for all stages. Methods of including elective nodal areas close to the GTV should be researched, e.g. nodal maps and intensity-modulated radiotherapy.
    • Early clinical evaluation of a novel three-dimensional structure delineation software tool (SCULPTER) for radiotherapy treatment planning.

      McBain, Catherine A; Moore, Christopher J; Green, Matthew M L; Price, Gareth J; Sykes, Jonathan R; Amer, Aminah; Khoo, Vincent S; Price, Patricia M; Academic Department of Radiation Oncology, The University of Manchester, Manchester, UK. (2008-08)
      Modern radiotherapy treatment planning (RTP) necessitates increased delineation of target volumes and organs at risk. Conventional manual delineation is a laborious, time-consuming and subjective process. It is prone to inconsistency and variability, but has the potential to be improved using automated segmentation algorithms. We carried out a pilot clinical evaluation of SCULPTER (Structure Creation Using Limited Point Topology Evidence in Radiotherapy) - a novel prototype software tool designed to improve structure delineation for RTP. Anonymized MR and CT image datasets from patients who underwent radiotherapy for bladder or prostate cancer were studied. An experienced radiation oncologist used manual and SCULPTER-assisted methods to create clinically acceptable organ delineations. SCULPTER was also tested by four other RTP professionals. Resulting contours were compared by qualitative inspection and quantitatively by using the volumes of the structures delineated and the time taken for completion. The SCULPTER tool was easy to apply to both MR and CT images and diverse anatomical sites. SCULPTER delineations closely reproduced manual contours with no significant volume differences detected, but SCULPTER delineations were significantly quicker (p<0.05) in most cases. In conclusion, clinical application of SCULPTER resulted in rapid and simple organ delineations with equivalent accuracy to manual methods, demonstrating proof-of-principle of the SCULPTER system and supporting its potential utility in RTP.
    • A novel method for the evaluation of uncertainty in dose-volume histogram computation.

      Henríquez, Francisco Cutanda; Castrillón, Silvia Vargas; NW Medical Physics, Christie Hospital NHS Foundation Trust, Manchester, United Kingdom. francisco.cutanda@hotmail.com (2008-03-15)
      PURPOSE: Dose-volume histograms (DVHs) are a useful tool in state-of-the-art radiotherapy treatment planning, and it is essential to recognize their limitations. Even after a specific dose-calculation model is optimized, dose distributions computed by using treatment-planning systems are affected by several sources of uncertainty, such as algorithm limitations, measurement uncertainty in the data used to model the beam, and residual differences between measured and computed dose. This report presents a novel method to take them into account. METHODS AND MATERIALS: To take into account the effect of associated uncertainties, a probabilistic approach using a new kind of histogram, a dose-expected volume histogram, is introduced. The expected value of the volume in the region of interest receiving an absorbed dose equal to or greater than a certain value is found by using the probability distribution of the dose at each point. A rectangular probability distribution is assumed for this point dose, and a formulation that accounts for uncertainties associated with point dose is presented for practical computations. RESULTS: This method is applied to a set of DVHs for different regions of interest, including 6 brain patients, 8 lung patients, 8 pelvis patients, and 6 prostate patients planned for intensity-modulated radiation therapy. CONCLUSIONS: Results show a greater effect on planning target volume coverage than in organs at risk. In cases of steep DVH gradients, such as planning target volumes, this new method shows the largest differences with the corresponding DVH; thus, the effect of the uncertainty is larger.