Opportunity knocked.
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Foreign Professional Personnel↗
Biomedical subjects
M Oldham
Publications and source records attributed to M Oldham.
International recruitment. Learning the hard way.
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Foreign Professional Personnel↗
High resolution gel-dosimetry by optical-CT and MR scanning.
The increased intricacy of Intensity-Modulated-Radiation-Therapy (IMRT) delivery has created the need for a high-resolution 3D-dosimetry (three-dimensional) system capable of measuring and verifying the complex delivery. Present clinical methods are inadequate being restricted to single points (e.g., ion-chambers) or to 2D planes (e.g., film), and are labor intensive. In this paper we show that gel-dosimetry in conjunction with optical-CT scanning can yield maps of dose that are of sufficient accuracy, resolution and precision to allow verification of complex radiosurgery deliveries, and by extension IMRT deliveries. The radiosurgery dose-distribution represents the most challenging case encountered in external beam therapy by virtue of the steep dose-gradients and high resolution of delivery. We characterize the stringent radiosurgery requirements by the RTAP (Resolution-Time-Accuracy-Precision) criteria defined as < or = 1 mm3 spatial resolution, < or = 1 hour imaging time, accurate to within 3%, and within -1% precision. The RTAP criteria is applied to an in-house laser-based optical-CT scanning system presented here, and evaluated using gel-flasks containing BANG3 gel. The same gel flasks were subsequently imaged using the MR imaging protocol recommended by the gel manufacturer, but modified to match as closely as possible the RTAP. The resulting dose-maps demonstrate the high precision (< 1.3% noise at high dose) achievable with optical CT scanning while preserving high spatial resolution (<1 mm3). Using the sequence above, the MR gel-dose maps were found to have poorer precision by a factor of 5, under the strict conditions of the RTAP. The optical CT gel-dosimetry system was further evaluated for the verification of a complex 3-isocenter radiosurgery delivery. In conclusion, this work demonstrates that gel-dosimetry and optical-CT scanning approach an important long-term goal of radiation dosimetry, as specified by the RTAP criteria, and have potential to impact the clinic by improving and facilitating clinical dose verification for the most complex external beam radiation treatments.
Calibration↗
Practical aspects of in situ 16O (gamma,n) 15O activation using a conventional medical accelerator for the purpose of perfusion imaging.
We report investigations into the feasibility of generating radioactive oxygen (15O, a positron emitter, with half-life 2.05 min) using a tuned Elekta SL25 accelerator, for the end purpose of imaging tumor perfusion. 15O is produced by the "gamma, neutron," (gamma,n) reaction between high-energy photons and normal oxygen (16O) in the body. As most in vivo 16O is bound in water molecules the 15O radio-marker is produced in proportion to water content in tissue. Imaging the washout of the 15O distribution using sensitive positron-emission-tomography (PET) technology can yield spatial information about blood perfusion in the tissue. The aim of this article was to determine the amount of 15O activity that could be produced by the tuned medical accelerator. A further aim was to model the activation process using Monte Carlo and to investigate ways to optimize the amount of 15O that could be generated. Increased activation was achieved by (i) tuning the beam to give higher-energy electrons incident on the target of the accelerator, (ii) increasing dose rate by removing the conventional filtration in the beam and reducing the source to object distance, and (iii) reducing low-energy photons by means of a carbon block absorber. The activity per-unit-dose produced by the tuned beam was measured by irradiating spheres of water to known doses and placing the spheres in a calibrated coincidence-counting apparatus. Peak energy of the tuned bremsstrahlung beam was estimated at 29 MeV, and generated activity up to 0.24/microCi/cc/3Gy in water. The measured amount of 15O agreed to within 10% of the prediction from the Monte-Carlo-computed spectrum, indicating reasonable ability to model the activation process. The optimal thickness of the carbon absorber was found to be about 25 cm. The insertion of a carbon absorber improved spectral quality for activation purposes but at the cost of reduced dose rate. In conclusion, the viability of generating 15O with an Elekta SL25 has been demonstrated. In conjunction with recent advances in high-sensitivity portable PET imaging devices, real potential exists for imaging in situ activated 15O washout as a surrogate measurement of macroscopic tumor perfusion.
Calibration↗
Efficacy and safety of paroxetine treatment for chronic PTSD: a fixed-dose, placebo-controlled study.
OBJECTIVE: This study evaluated the efficacy and safety of paroxetine for the treatment of patients with chronic posttraumatic stress disorder (PTSD). METHOD: Outpatients with chronic PTSD according to DSM-IV criteria and a score of 50 or more on the Clinician-Administered PTSD Scale, part 2, were randomly assigned to take placebo (N=186), 20 mg/day of paroxetine (N=183), or 40 mg/day of paroxetine (N=182) for 12 weeks. Efficacy was assessed by examining the change in total score from baseline to endpoint on the Clinician-Administered PTSD Scale, part 2, and rates of response ("very much improved" or "much improved") for global improvement on the Clinical Global Impression scale. RESULTS: Paroxetine-treated patients in both dose groups demonstrated significantly greater improvement on primary outcome measures compared to placebo-treated patients in the intent-to-treat analysis. Moreover, paroxetine treatment resulted in statistically significant improvement compared to placebo on all three PTSD symptom clusters (reexperiencing, avoidance/numbing, and hyperarousal), social and occupational impairment, and comorbid depression. Paroxetine was effective for both men and women. Treatment response did not vary by trauma type, time since trauma, or severity of baseline PTSD or depressive symptoms. Both doses were well tolerated. CONCLUSIONS: Doses of 20 and 40 mg/day of paroxetine are effective and well tolerated in the treatment of adults with chronic PTSD.
Adult↗
Optimized MR imaging for polyacrylamide gel dosimetry.
Polyacrylamide gels are a powerful tool to measure radiation dose by quantifying the NMR T2 relaxation times of the irradiated gel. The exploitation of these radiation sensitive gels in clinical radiotherapy requires accurate mapping of T2 values. This paper describes the optimization strategy used to identify accurate and practical methods of measuring the range of T2 values typical of gel dosimeters (140-700 ms). The MR imaging techniques used to measure T2 values and the choice of image acquisition parameters are described. Four sequences are compared and the results are analysed in terms of accuracy, signal-to-noise ratio and acquisition time. A multiple spin echo sequence was found to yield the most accurate results (98.9%). Single spin echo sequences, such as Hahn spin echo and EPI spin echo, were found to measure gel T2 values with an accuracy of 90.1%. This paper reports the importance of careful selection and optimization of the MR imaging sequences for accurate and reliable polyacrylamide gel dosimetry.
Echo-Planar Imaging↗
Noise in polymer gel measurements using MRI.
With the development of conformal radiotherapy, particularly intensity modulated radiation therapy (IMRT), there is a clear need for multidimensional dosimeters. A commercial polymerizing gel, BANG-2 gel (MGS Research, Inc., Guilford, CT), has recently been developed that shows potential as a multi-dimensional dosimeter. This study investigates and characterizes the noise and magnetic resonance (MR) artifacts from imaging BANG-2 gels. Seven cylindrical vials (4 cm diam, 20 cm length) were irradiated end on in a water bath and read using MRI (B0=1.5 T, TE=20 ms/100 ms, TR=3000 ms). The gel calibration compared the measured depth-dose distributions in water against the change in solvent-proton R2 relaxivity of the gel. A larger vial (13 cm diam, 14 cm length) was also irradiated to test the calibration accuracy in a vial of sufficient volume for dose distribution measurements. The calibration curve proved accurate to within 1.3% in determining the depth dose measured by the larger vial. An investigation of the voxel-to-voxel (IXIX 3 mm3) noise and sensitivity response curve showed that the voxel-to-voxel variation dominated the dose measurement uncertainty. The voxel-to-voxel standard deviation ranged from 0.2 Gy for the unirradiated gel to 0.7 Gy at 20 Gy. Slice-to-slice R2 magnitude deviations were also observed corresponding to 0.2 Gy. These variations limited the overall accuracy of the gel dose measurements and warrant an investigation of more accurate MR readout sequences.
Calibration↗
Radiation dosimetry using polymer gels: methods and applications.
New, complex radiotherapy delivery techniques require dosimeters that are able to measure complex three-dimensional dose distributions accurately and with good spatial resolution. Polymer gel is an emerging new dosimeter being applied to these challenges. The aim of this review is to present a practical overview of polymer gel dosimetry, including gel manufacture, imaging, calibration and application to radiotherapy verification. The dosimeters consist of a gel matrix within which is suspended a solution of acrylic molecules. These molecules polymerize upon exposure to radiation, with the degree of polymerization being proportional to absorbed dose. The polymer distribution can be measured in two or three dimensions using MRI or optical tomography and, after calibration, the images can be converted into radiation dose distributions. Manufacture of the gel is reported to be reproducible, and measured dose in the range 0-10 Gy is accurate to within 3-5%. In-plane image resolution of 1 mm x 1 mm, with image slice thicknesses of between 2-5 mm, is typically achievable using clinical 1.5 T MR scanners and standard T2 weighted imaging sequences. The gels have been used to verify a number of conventional and novel radiotherapy modalities, including brachytherapy, intensity modulated radiotherapy and stereotactic radiosurgery. All the studies have confirmed the value and versatility of the dosimetry technique.
Acrylamide↗
Comparison of intensity-modulated tomotherapy with stereotactically guided conformal radiotherapy for brain tumors.
PURPOSE: Intensity-modulated radiotherapy (IMRT) offers the potential to more closely conform dose distributions to the target, and spare organs at risk (OAR). Its clinical value is still being defined. The present study aims to compare IMRT with stereotactically guided conformal radiotherapy (SCRT) for patients with medium size convex-shaped brain tumors. METHODS AND MATERIALS: Five patients planned with SCRT were replanned with the IMRT-tomotherapy method using the Peacock system (Nomos Corporation). The planning target volume (PTV) and relevant OAR were assessed, and compared relative to SCRT plans using dose statistics, dose-volume histograms (DVH), and the Radiation Therapy Oncology Group (RTOG) stereotactic radiosurgery criteria. RESULTS: The median and mean PTV were 78 cm3 and 85 cm3 respectively (range 62-119 cm3). The differences in PTV doses for the whole group (Peacock-SCRT +/-1 SD) were 2%+/-1.8 (minimum PTV), and 0.1%+/-1.9 (maximum PTV). The PTV homogeneity achieved by Peacock was 12.1%+/-1.7 compared to 13.9%+/-1.3 with SCRT. Using RTOG guidelines, Peacock plans provided acceptable PTV coverage for all 5/5 plans compared to minor coverage deviations in 4/5 SCRT plans; acceptable homogeneity index for both plans (Peacock = 1.1 vs. SCRT = 1.2); and comparable conformity index (1.4 each). As a consequence of the transaxial method of arc delivery, the optic nerves received mean and maximum doses that were 11.1 to 11.6%, and 10.3 to 15.2% higher respectively with Peacock plan. The maximum optic lens, and brainstem dose were 3.1 to 4.8% higher, and 0.6% lower respectively with Peacock plan. However, all doses remained below the tolerance threshold (5 Gy for lens, and 50 Gy for optic nerves) and were clinically acceptable. CONCLUSIONS: The Peacock method provided improved PTV coverage, albeit small, in this group of convex tumors. Although the OAR doses were higher using the Peacock plans, all doses remained within the clinically defined threshold and were clinically acceptable. Further improvements may be expected using other methods of IMRT planning that do not limit the treatment delivery to transaxial arcs. Each IMRT system needs to be individually assessed as the paradigm utilized may provide different outcomes.
Algorithms↗
Is it possible to optimize a radiotherapy treatment plan?
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Algorithms↗
A comparison of coplanar four-field techniques for conformal radiotherapy of the prostate.
BACKGROUND AND PURPOSE: Conformal radiotherapy of the prostate is an increasingly common technique, but the optimal choice of beam configuration remains unclear. This study systematically compares a number of coplanar treatment plans for four-field irradiation of two different clinical treatment volumes: prostate only (PO) and the prostate plus seminal vesicles (PSV). MATERIALS AND METHODS: A variety of four-field coplanar treatment plans were created for PO and PSV volumes in each of ten patients. Plans included a four-field 'box' plan, a symmetric plan having bilateral anterior and posterior oblique fields, a plan with anterior oblique and lateral fields, a series of asymmetric plans, and a three-field plan having anterior and bilateral fields for comparison. Doses of 64 and 74 Gy were prescribed to the isocentre. Plans were compared using the volume of rectum irradiated to greater than 50% (V50), 80% (V80) and 90% (V90) of the prescribed dose. Tumour control probabilities (TCP) and normal tissue complication probabilities (NTCP) for the rectum, bladder and femoral heads were also evaluated. Femoral head dose was limited such that less than 10% of each femoral head received 70% of the prescribed dose. RESULTS: For the PO group, the optimal plan consisted of anterior oblique and lateral fields (Rectal V80 = 23.8+/-5.0% (1 SD)), while the box technique (V80 = 26.0+/-5.8%) was less advantageous in terms of rectal sparing (P = 0.001). Similar results were obtained for the PSV group (Rectal V80 = 43.9+/-5.0% and 47.3+/-5.5% for the two plan types, respectively, P = 0.001). The three-field plan was comparable to the optimal four-field plan but gave higher superficial body dose. With dose escalation from 64 to 74 Gy, the mean TCP for the optimal plan rose from 52.0+/-2.8% to 74.1+/-2.0%. Meanwhile, rectal NTCP for the optimal plan rose by 3.5% (PO) or 8.4% (PSV), compared to 4.7% (PO) or 10.1% (PSV) for the box plan. CONCLUSIONS: For PO volumes, a plan with gantry angles of 35 degrees, 90 degrees, 270 degrees and 325 degrees offers a high level of rectal sparing and acceptable dose to the femoral heads for all patients, while for PSV volumes, the corresponding plan has gantry angles of 20 degrees, 90 degrees , 270 degrees and 340 degrees. Using these plans, the gain in TCP resulting from dose escalation can be achieved with a smaller increase in anticipated rectal NTCP.
Algorithms↗
Experimental 3D dosimetry around a high-dose-rate clinical 192Ir source using a polyacrylamide gel (PAG) dosimeter.
It is well known that the experimental dosimetry of brachytherapy sources presents a challenge. Depending on the particular-dosimeter used, measurements can suffer from poor spatial resolution (ion chambers), lack of 3D information (film) or errors due to the presence of the dosimeter itself distorting the radiation flux. To avoid these problems, we have investigated the dosimetry of a clinical 192Ir source using a polyacrylamide gel (PAG) dosimeter. Experimental measurements of dose versus radial distance from the centre of the source (cross-line plots) were compared with calculations produced with a Nucletron NPS planning system. Good agreement was found between the planning system and gel measurements in planes selected for analysis. Gel dosimeter measurements in a coronal plane through the phantom showed a mean difference between measured absorbed dose and calculated dose of 0.17 Gy with SD = 0.13 Gy. Spatially, the errors at the reference point remain within one image pixel (1.0 mm). The use of polymer gel dosimetry shows promise for brachytherapy applications, offering complete, three-dimensional dose information, good spatial resolution and small measurement errors. Measurements close to the source, however, are difficult, due to some of the limiting properties of the polyacrylamide gel.
Acrylic Resins↗
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↗
Dynamics of polymerization in polyacrylamide gel (PAG) dosimeters: (I) ageing and long-term stability.
Few quantitative data are available on the kinetics of polymerization reactions in polymer gel (PAG) dosimeters and their long-term stability. Post-irradiation polymerization reactions have been found to continue for several weeks, posing questions regarding dosimeter stability and its achievement. In this paper we report an investigation of polymerization kinetics in PAG dosimeters and the effect of diffusing oxygen into the dosimeter, post irradiation, as a potential method of inhibiting further polymerization and stabilizing the dose distribution. Results show continuous post-irradiation changes in transverse relaxation rate R2 with time over the five week study period and that a steady-state may not be reached for a period of months. An assessment is made of the appropriate time to image the dosimeter which shows that after three to four days the polymerization change is slow compared with imaging time. The implications of the time delay between irradiation and imaging are discussed in terms of the resultant sensitivity of the dosimeter and accuracy of the dose measured. In pairs of dosimeters, one sealed the other open to air, oxygen diffusing into the dosimeter arrests polymerization. However, the diffusion rate is too slow to make this method practicable. The slow diffusion means that while in regions near the air/gel interface polymerization is quickly arrested, in deeper regions it may continue for many hours, causing artefacts in the dose distribution. In the companion paper to this from a collaborating team, a study focusing on modelling oxygen diffusion in dosimeter gel will be presented.
Acrylic Resins↗
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↗
Improving calibration accuracy in gel dosimetry.
A new method of calibrating gel dosimeters (applicable to both Fricke and polyacrylamide gels) is presented which has intrinsically higher accuracy than current methods, and requires less gel. Two test-tubes of gel (inner diameter 2.5 cm, length 20 cm) are irradiated separately with a 10 x 10 cm2 field end-on in a water bath, such that the characteristic depth-dose curve is recorded in the gel. The calibration is then determined by fitting the depth-dose measured in water, against the measured change in relaxivity with depth in the gel. Increased accuracy is achieved in this simple depth-dose geometry by averaging the relaxivity at each depth. A large number of calibration data points, each with relatively high accuracy, are obtained. Calibration data over the full range of dose (1.6-10 Gy) is obtained by irradiating one test-tube to 10 Gy at dose maximum (Dmax), and the other to 4.5 Gy at Dmax. The new calibration method is compared with a 'standard method' where five identical test-tubes of gel were irradiated to different known doses between 2 and 10 Gy. The percentage uncertainties in the slope and intercept of the calibration fit are found to be lower with the new method by a factor of about 4 and 10 respectively, when compared with the standard method and with published values. The gel was found to respond linearly within the error bars up to doses of 7 Gy, with a slope of 0.233 +/- 0.001 s(-1) Gy(-1) and an intercept of 1.106 +/- 0.005 Gy. For higher doses, nonlinear behaviour was observed.
Acrylamides↗
An investigation into the dosimetry of a nine-field tomotherapy irradiation using BANG-gel dosimetry.
BANG-gel dosimetry offers the potential for measuring the dose delivered by a radiotherapy treatment technique, in three dimensions, with high spatial resolution and good accuracy. The ability to measure comprehensively a 3D dose distribution is a major advantage of the gel dosimeter over conventional planar and point-based dosimeter devices, particularly when applied to the verification of complex dose distributions characteristic of intensity-modulated radiotherapy (IMRT). In this paper an in-house manufactured BANG-gel dosimeter was applied to study the dose distributions of two irradiation experiments for which the distributions were known: (i) a dosimetrically simple parallel-opposed irradiation, and (ii) a more complex nine-field 'static tomotherapy' intensity-modulated irradiation delivered with the Nomos MIMiC. The uniform distribution in (i) allowed a study of the magnetic resonance (MR) imaging parameters to achieve an optimal trade-off between noise and image resolution (optimum image resolution for the Siemens 1.5T Vision system was determined to be approximately 0.8 mm2 with a slice thickness of 2 mm). The spatial uniformity of gel sensitivity to radiation was found to depend strongly on the presence of oxygen, which must be eliminated for the gel dosimeter to be of use. The gel dosimeter was found to agree well with predicted dose distributions and accurately measured the steep penumbral fall-off of dose, even after many days, proving its potential for the verification of IMRT distributions. In the nine-field IMRT delivery (ii) the predicted dose was computed by both an in-house 'component-delivery' dose algorithm and the Peacock planning-system dose algorithm. Good agreement was found between the two algorithms despite the latter's omission of the change in penumbral characteristics with aperture-size during delivery, lack of inhomogeneity correction and approximate modelling of leaf leakage. These effects were found to be small for the problem studied. The predicted distribution agreed well with the gel-measured distribution at medium and high doses (50-90% isodose lines) although differences of up to 10% were observed at lower doses (30% isodose line). The gel dosimeter was found to have the potential to verify IMRT distributions but required considerable care to achieve accurate results. Attention was required to achieve uniformity of gel sensitivity (to prevent oxygen contamination), and in the calibration process.
Acrylamide↗
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↗