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C G Rowbottom

Publications and source records attributed to C G Rowbottom.

8 recordsLinked to original sources
PubMed2001

Beam-orientation optimization of intensity-modulated radiotherapy: clinical application to parotid gland tumours.

BACKGROUND AND PURPOSE: An optimization algorithm has been developed to determine the best beam-arrangement for a small number of intensity-modulated radiotherapy (IMRT) fields. The algorithm is designed to avoid, if possible, beam-orientations that pass through organs-at-risk (OARs) with low radiation tolerance. MATERIALS AND METHODS: An independent, fast IMRT algorithm based on the Bortfeld algorithm was developed to determine the profile of the intensity-modulated beams (IMBs) for each beam-arrangement and a fast-simulated-annealing algorithm finds the 'optimal' beam-arrangement. The final beam-arrangement was transferred to the CORVUS (NOMOS Corporation) treatment planning system, and the IMBs were re-optimized for comparison with a standard nine-field, equi-spaced arrangement. The algorithm has been initially tested on a single example patient, with a parotid gland carcinoma. RESULTS: The nine-field, IMRT plan for an example patient with a parotid gland tumour significantly reduced the dose to the cochlea compared with the conformal radiotherapy plan. In addition, the planning-target-volume (PTV) homogeneity was improved, but the plan produced a higher dose to the contralateral parotid (73% of the OAR received more than 6 Gy). The beam-orientation optimization algorithm produced a three-field plan that greatly reduced the dose to the contralateral parotid (maximum dose of 2 Gy), whilst maintaining the PTV dose homogeneity and the reduced cochlear dose of the nine-field plan. Some changes in the dose to the other OARs, namely the brain and the oral cavity, were seen, but were deemed not to be clinically significant. CONCLUSIONS: In conclusion, IMB-orientation optimization for head and neck treatment sites can produce improvements in treatment plans with only a few fields.

Algorithms↗
PubMed2001

Optimisation of radiotherapy for carcinoma of the parotid gland: a comparison of conventional, three-dimensional conformal, and intensity-modulated techniques.

BACKGROUND AND PURPOSE: To compare external beam radiotherapy techniques for parotid gland tumours using conventional radiotherapy (RT), three-dimensional conformal radiotherapy (3DCRT), and intensity-modulated radiotherapy (IMRT). To optimise the IMRT techniques, and to produce an IMRT class solution. MATERIALS AND METHODS: The planning target volume (PTV), contra-lateral parotid gland, oral cavity, brain-stem, brain and cochlea were outlined on CT planning scans of six patients with parotid gland tumours. Optimised conventional RT and 3DCRT plans were created and compared with inverse-planned IMRT dose distributions using dose-volume histograms. The aim was to reduce the radiation dose to organs at risk and improve the PTV dose distribution. A beam-direction optimisation algorithm was used to improve the dose distribution of the IMRT plans, and a class solution for parotid gland IMRT was investigated. RESULTS: 3DCRT plans produced an equivalent PTV irradiation and reduced the dose to the cochlea, oral cavity, brain, and other normal tissues compared with conventional RT. IMRT further reduced the radiation dose to the cochlea and oral cavity compared with 3DCRT. For nine- and seven-field IMRT techniques, there was an increase in low-dose radiation to non-target tissue and the contra-lateral parotid gland. IMRT plans produced using three to five optimised intensity-modulated beam directions maintained the advantages of the more complex IMRT plans, and reduced the contra-lateral parotid gland dose to acceptable levels. Three- and four-field non-coplanar beam arrangements increased the volume of brain irradiated, and increased PTV dose inhomogeneity. A four-field class solution consisting of paired ipsilateral coplanar anterior and posterior oblique beams (15, 45, 145 and 170 degrees from the anterior plane) was developed which maintained the benefits without the complexity of individual patient optimisation. CONCLUSIONS: For patients with parotid gland tumours, reduction in the radiation dose to critical normal tissues was demonstrated with 3DCRT compared with conventional RT. IMRT produced a further reduction in the dose to the cochlea and oral cavity. With nine and seven fields, the dose to the contra-lateral parotid gland was increased, but this was avoided by optimisation of the beam directions. The benefits of IMRT were maintained with three or four fields when the beam angles were optimised, but were also achieved using a four-field class solution. Clinical trials are required to confirm the clinical benefits of these improved dose distributions.

Humans↗
PubMed2001

Simultaneous optimization of beam orientations and beam weights in conformal radiotherapy.

A methodology for the concurrent optimization of beam orientations and beam weights in conformal radiotherapy treatment planning has been developed and tested on a cohort of five patients. The algorithm is based on a beam-weight optimization scheme with a downhill simplex optimization engine. The use of random voxels in the dose calculation provides much of the required speed up in the optimization process, and allows the simultaneous optimization of beam orientations and beam weights in a reasonable time. In the implementation of the beam-weight optimization algorithm just 10% of the original patient voxels are used for the dose calculation and cost function evaluation. A fast simulated annealing algorithm controls the optimization of the beam arrangement. The optimization algorithm was able to produce clinically acceptable plans for the five patients in the cohort study. The algorithm equalized the dose to the optic nerves compared to the standard plans and reduced the mean dose to the brain stem by an average of 4.4% (+/- 1.9, 1 SD), p value = 0.007. The dose distribution to the PTV was not compromised by developing beam arrangements via the optimization algorithm. In conclusion, the simultaneous optimization of beam orientations and beam weights has been developed to be routinely used in a realistic time. The results of optimization in a small cohort study show that the optimization can reliably produce clinically acceptable dose distributions and may be able to improve dose distributions compared to those from a human planner.

Algorithms↗
PubMed1999

Constrained customization of non-coplanar beam orientations in radiotherapy of brain tumours.

A methodology for the constrained customization of non-coplanar beam orientations in radiotherapy treatment planning has been developed and tested on a cohort of five patients with tumours of the brain. The methodology employed a combination of single and multibeam cost functions to produce customized beam orientations. The single-beam cost function was used to reduce the search space for the multibeam cost function, which was minimized using a fast simulated annealing algorithm. The scheme aims to produce well-spaced, customized beam orientations for each patient that produce low dose to organs at risk (OARs). The customized plans were compared with standard plans containing the number and orientation of beams chosen by a human planner. The beam orientation constraint-customized plans employed the same number of treatment beams as the standard plan but with beam orientations chosen by the constrained-customization scheme. Improvements from beam orientation constraint-customization were studied in isolation by customizing the beam weights of both plans using a dose-based downhill simplex algorithm. The results show that beam orientation constraint-customization reduced the maximum dose to the orbits by an average of 18.8 (+/-3.8, ISD)% and to the optic nerves by 11.4 (+/-4.8, ISD)% with no degradation of the planning target volume (PTV) dose distribution. The mean doses, averaged over the patient cohort, were reduced by 4.2 (+/-1.1, ISD)% and 12.4 (+/-3.1, ISD)% for the orbits and optic nerves respectively. In conclusion, the beam orientation constraint-customization can reduce the dose to OARs, for few-beam treatment plans, when compared with standard treatment plans developed by a human planner.

Adenoma↗
PubMed1999

Beam-orientation customization using an artificial neural network.

A methodology for the constrained customization of coplanar beam orientations in radiotherapy treatment planning using an artificial neural network (ANN) has been developed. The geometry of the patients, with cancer of the prostate, was modelled by reducing the external contour, planning target volume (PTV) and organs at risk (OARs) to a set of cuboids. The coordinates and size of the cuboids were given to the ANN as inputs. A previously developed beam-orientation constrained-customization (BOCC) scheme employing a conventional computer algorithm was used to determine the customized beam orientations in a training set containing 45 patient datasets. Twelve patient datasets not involved in the training of the artificial neural network were used to test whether the ANN was able to map the inputs to customized beam orientations. Improvements from the customized beam orientations were compared with standard treatment plans with fixed gantry angles and plans produced from the BOCC scheme. The ANN produced customized beam orientations within 5 degrees of the BOCC scheme in 62.5% of cases. The average difference in the beam orientations produced by the ANN and the BOCC scheme was 7.7 degrees (+/-1.7, 1 SD). Compared with the standard treatment plans, the BOCC scheme produced plans with an increase in the average tumour control probability (TCP) of 5.7% (+/-1.4, 1 SD) whilst the ANN generated plans increased the average TCP by 3.9% (+/-1.3, 1 SD). Both figures refer to the TCP at a fixed rectal normal tissue complication probability (NTCP) of 1%. In conclusion, even using a very simple model for the geometry of the patient, an ANN was able to produce beam orientations that were similar to those produced by a conventional computer algorithm.

Humans↗
PubMed1998

A case study comparing the relative benefit of optimizing beam weights, wedge angles, beam orientations and tomotherapy in stereotactic radiotherapy of the brain.

A treatment-planning case study has been performed on a patient with a medium-sized, convex brain tumour. The study involved the application of advanced treatment-plan optimization techniques to improve on the dose distribution of the 'standard plan' used to treat the patient. The standard plan was created according to conventional protocol at the Royal Marsden NHS Trust, and consisted of a three-field (one open and two wedged) non-coplanar arrangement, with field shaping to the beam's-eye view of the planning target volume (PTV). Three optimized treatment plans were created corresponding to (i) the optimization of the beam weights and wedge angles of the standard plan, (ii) the optimization of the beam orientations, beam weights and wedge angles of the standard plan, and (iii) a full fluence tomotherapy optimization of 1 cm wide (at isocentre), 270 degree arcs. (i) and (ii) were created on the VOXELPLAN research 3D treatment-planning system, using in-house developed optimization algorithms, and (iii) was created on the PEACOCK tomotherapy planning system. The downhill-simplex optimization algorithm is used, in conjunction with 'threshold-dose' cost-function terms enabling the algorithm to optimize specific regions of the dose-volume histogram (DVH) curve. The 'beam-cost plot' tool is presented as a visual aid to the selection of beneficial beam directions. The methods and pitfalls in the transfer of plans and patient data between the two planning systems are discussed. Each optimization approach was evaluated, relative to the standard plan, on the basis of DVH and dose statistics in the PTV and organs at risk (OARs). All three optimization approaches were able to improve on the dose distribution of the standard plan. The magnitude of the improvement was greater for the optimized beam-orientation and tomotherapy plans (up to 15% and 30% for the maximum and mean OAR doses). A smaller improvement was observed in the beam-weight and wedge-angle optimized plan (up to 5% and 10% in the maximum and mean OAR doses). In the tomotherapy plan, difficulty was encountered achieving an acceptable homogeneity of dose in the PTV. This was improved by treating the gross tumour volume (GTV) and (PTV - GTV) regions as separate targets in the inverse planning, with the latter region prescribed a slightly higher dose to reduce edge under-dosing. In conclusion, for the medium-sized convex tumour studied, the tomotherapy dose distribution showed a significant improvement on the standard plan, but no significant improvement over a conventional three-field plan where the beam orientations, beam weights and wedge angles had been optimized.

Adenoma↗
PubMed1998

Improvements in prostate radiotherapy from the customization of beam directions.

A methodology for optimizing the beam directions in radiotherapy treatment planning has been developed and tested on a cohort of twelve prostate patients. An optimization algorithm employing a an objective cost function was used, based on beam's-eye-view volumetrics but also employing a simple dose model and biological considerations for organs-at-risk (OARs). The cost function embodies information about the volume of OARs in a single field and their position relative to the planning target volume (PTV). The proximity of the PTV to the surface of the patient is also included. Within the algorithm "importance factor" were used to model the clinical importance of different organs-at-risk so that all organs-at-risk were included in a single objective score. "Gantry-angle-windows" were introduced to restrict the available beam directions. The methodology was applied to twelve prostate patients to determine the optimum beam directions for three-field direction plans. Orientation-optimized and standard treatment plans were compared via measures of tumor control probability (TCP) and normal tissue complication probability (NTCP). Standard plans had fixed beam directions whereas orientation-optimized plans contained beam directions chosen by the algorithm. The beam-weights of both the orientation-optimized and standard plans were optimized using a dose-based simulated annealing algorithm to allow the improvements by optimizing the beam directions to be studied in isolation. The results of the comparison show that optimization of the beam directions yielded better plans, in terms of TCP and NTCP, than the standard plans. When the dose to the isocenter was scaled to produce a rectal NTCP of 1%, the average TCP of the orientation-optimized plans was (5.7 +/- 1.4)% greater than that for the standard plans. In conclusion, the customization of beam directions in the treatment planning of prostate patients using and objective cost function and allowed gantry-angle-windows produces superior three-field direction plans compared to standard treatment plans.

Algorithms↗