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M Bidmead

Publications and source records attributed to M Bidmead.

9 recordsLinked to original sources
PubMed2006

Movement of the cervix in after-loading brachytherapy: implications for designing external-beam radiotherapy boost fields.

AIMS: Women with invasive carcinoma of the cervix treated by chemo-radiotherapy and brachytherapy may also receive a pelvic sidewall boost using a midline shield (MLS). The purpose of this study was to assess the usefulness of implanted gold grains in detecting the movement of the cervix caused by the insertion of low-dose-rate brachytherapy applicators, and its implications in designing the MLS. MATERIALS AND METHODS: The medical records of 42 women with various stages of cervical carcinoma, who were treated by radical chemo-radiotherapy, were reviewed. All of these women underwent examination under anaesthesia (EUA) and a gold-grain insertion to demarcate the vaginal tumour extent, in the antero-posterior and lateral planes, before starting external-beam radiotherapy. The isocentric orthogonal films (simulator films) of external radiotherapy and brachytherapy were compared to assess the change in position of the gold grains and the consequences for the design of the MLS for parametrial and pelvic sidewall boosts. RESULTS: A significant shift in the position of the gold grains was noted in both the x (lateral) and the y (cranial/caudal) axes. The median shift of the midline, right and left lateral gold grains was 4.5, 5 and 7 mm in the x axis, whereas it was 10, 8 and 9.5 mm in the y axis, respectively. The median shift in the x and y axes was 5.5 and 9 mm, ranging from 1 to 40 mm and 1 to 45 mm, respectively. The gold grains were shifted cranially in 34 (80%) and laterally in 29 (69%) women. Thirty-two women (76.2%) received parametrial boost radiotherapy, of which 25 (59.5%) women had a customised, pear-shaped shield, and the remaining seven (16.7%) had a straight-sided, rectangular MLS. Four women (9.5%) relapsed locally, and three of them had been treated using a customised shield. In two of these four women, there was an absolute under-dosage of the central pelvis at the tip of the intra-uterine tube by 50% of the parametrial boost dose (5.4 Gy/3 fractions/3 days). CONCLUSIONS: Insertion of the gold grains during pre-treatment EUA is a useful technique in detecting the movement of the cervix. A significant shift in the position of the gold grains was noted in both the x (lateral) and the y (cranial/caudal) axes. These shifts in the cervix can result in under-dosage of the central pelvis when delivering parametrial boosts with the MLS in place on the basis of the brachytherapy check films. When designing the individualised MLS, the resulting under-dosage could be avoided by taking account of the shift in the gold grain markers and allow the delivery of a more homogenous dose to the pelvis.

Adult↗
PubMed2005

Head-and-neck IMRT treatments assessed with a Monte Carlo dose calculation engine.

IMRT is frequently used in the head-and-neck region, which contains materials of widely differing densities (soft tissue, bone, air-cavities). Conventional methods of dose computation for these complex, inhomogeneous IMRT cases involve significant approximations. In the present work, a methodology for the development, commissioning and implementation of a Monte Carlo (MC) dose calculation engine for intensity modulated radiotherapy (MC-IMRT) is proposed which can be used by radiotherapy centres interested in developing MC-IMRT capabilities for research or clinical evaluations. The method proposes three levels for developing, commissioning and maintaining a MC-IMRT dose calculation engine: (a) development of a MC model of the linear accelerator, (b) validation of MC model for IMRT and (c) periodic quality assurance (QA) of the MC-IMRT system. The first step, level (a), in developing an MC-IMRT system is to build a model of the linac that correctly predicts standard open field measurements for percentage depth-dose and off-axis ratios. Validation of MC-IMRT, level (b), can be performed in a rando phantom and in a homogeneous water equivalent phantom. Ultimately, periodic quality assurance of the MC-IMRT system is needed to verify the MC-IMRT dose calculation system, level (c). Once the MC-IMRT dose calculation system is commissioned it can be applied to more complex clinical IMRT treatments. The MC-IMRT system implemented at the Royal Marsden Hospital was used for IMRT calculations for a patient undergoing treatment for primary disease with nodal involvement in the head-and-neck region (primary treated to 65 Gy and nodes to 54 Gy), while sparing the spinal cord, brain stem and parotid glands. Preliminary MC results predict a decrease of approximately 1-2 Gy in the median dose of both the primary tumour and nodal volumes (compared with both pencil beam and collapsed cone). This is possibly due to the large air-cavity (the larynx of the patient) situated in the centre of the primary PTV and the approximations present in the dose calculation.

Algorithms↗
PubMed2005

Phase III pilot study of dose escalation using conformal radiotherapy in prostate cancer: PSA control and side effects.

Radical radiotherapy is a standard form of management of localised prostate cancer. Conformal treatment planning spares adjacent normal tissues reducing treatment-related side effects and may permit safe dose escalation. We have tested the effects on tumour control and side effects of escalating radiotherapy dose and investigated the appropriate target volume margin. After an initial 3-6 month period of androgen suppression, 126 men were randomised and treated with radiotherapy using a 2 by 2 factorial trial design. The initial radiotherapy tumour target volume included the prostate and base of seminal vesicles (SV) or complete SV depending on SV involvement risk. Treatments were randomised to deliver a dose of 64 Gy with either a 1.0 or 1.5 cm margin around the tumour volume (1.0 and 1.5 cm margin groups) and also to treat either with or without a 10 Gy boost to the prostate alone with no additional margin (64 and 74 Gy groups). Tumour control was monitored by prostate-specific antigen (PSA) testing and clinical examination with additional tests as appropriate. Acute and late side effects of treatment were measured using the Radiation Treatment and Oncology Groups (RTOG) and LENT SOM systems. The results showed that freedom from PSA failure was higher in the 74 Gy group compared to the 64 Gy group, but this did not reach conventional levels of statistical significance with 5-year actuarial control rates of 71% (95% CI 58-81%) in the 74 Gy group vs 59% (95% CI 45-70%) in the 64 Gy group. There were 23 failures in the 74 Gy group and 33 in the 64 Gy group (Hazard ratio 0.64, 95% CI 0.38-1.10, P=0.10). No difference in disease control was seen between the 1.0 and 1.5 cm margin groups (5-year actuarial control rates 67%, 95% CI 53-77% vs 63%, 95% CI 50-74%) with 28 events in each group (Hazard ratio 0.97, 95% CI 0.50-1.86, P=0.94). Acute side effects were generally mild and 18 weeks after treatment, only four and five of the 126 men had persistent > or =Grade 1 bowel or bladder side effects, respectively. Statistically significant increases in acute bladder side effects were seen after treatment in the men receiving 74 Gy (P=0.006), and increases in both acute bowel side effects during treatment (P=0.05) and acute bladder sequelae (P=0.002) were recorded for men in the 1.5 cm margin group. While statistically significant, these differences were of short duration and of doubtful clinical importance. Late bowel side effects (RTOG> or =2) were seen more commonly in the 74 Gy and 1.5 cm margin groups (P=0.02 and P=0.05, respectively) in the first 2 years after randomisation. Similar results were found using the LENT SOM assessments. No significant differences in late bladder side effects were seen between the randomised groups using the RTOG scoring system. Using the LENT SOM instrument, a higher proportion of men treated in the 74 Gy group had Grade > or =3 urinary frequency at 6 and 12 months. Compared to baseline scores, bladder symptoms improved after 6 months or more follow-up in all groups. Sexual function deteriorated after treatment with the number of men reporting some sexual dysfunction (Grade> or =1) increasing from 38% at baseline to 66% at 6 months and 1 year and 81% by year 5. However, no consistent differences were seen between the randomised groups. In conclusion, dose escalation from 64 to 74 Gy using conformal radiotherapy may improve long-term PSA control, but a treatment margin of 1.5 cm is unnecessary and is associated with increased acute bowel and bladder reactions and more late rectal side effects. Data from this randomised pilot study informed the Data Monitoring Committee of the Medical Research Council RT 01 Trial and the two studies will be combined in subsequent meta-analysis.

Adenocarcinoma↗
PubMed2000

Target volume definition in conformal radiotherapy for prostate cancer: quality assurance in the MRC RT-01 trial.

BACKGROUND AND PURPOSE: Prior to randomization of patients into the UK Medical Research Council multicentre randomized trial (RT-01) of conformal radiotherapy (CFRT) in prostate cancer, clinicians at participating centres were required to complete a quality assurance (QA) clinical planning exercise to enable an investigation of inter-observer variability in gross target volume (GTV) and normal structure outlining. MATERIALS AND METHODS: Thirteen participating centres and two investigators completed the clinical planning exercise of three practice planning cases. Clinicians were asked to draw outlines of the GTV, rectum and bladder on hard-copy computerized tomography (CT) films of the pelvis, which were transferred onto the Cadplan computer planning system by a single investigator. Centre, inferior and superior CT levels of GTV, rectum and bladder were noted, and volume calculations performed. Planning target volumes (PTV) were generated using automatic volume expansion of GTVs by a 1 cm margin. Anterior, right and left lateral beam eye views (BEV) of the PTVs were generated. Using a common central point, the BEV PTVs were superimposed for each beam direction of each case. Radial PTV variation was investigated by measurement of a novel parameter, termed the radial line measurement variation (RLMV). RESULTS: GTV central slice and length were defined with reasonable consistency. The RLMV analysis showed that the main part of the prostate gland, bladder and inferior rectum were outlined with good consistency among clinicians. However, the outlining of the prostatic apex, superior aspect of the prostate projecting into the bladder, seminal vesicles, the base of seminal vesicles and superior rectum were more variable. CONCLUSION: This exercise has demonstrated adequate consistency of GTV definition. The RLMV method of analysis indicates particular regions of clinician uncertainty. Appropriate feedback has been given to all participating clinicians, and the final RT-01 trial protocol has been modified to accommodate these findings.

Humans↗
PubMed1998

Radiotherapy planning techniques for thyroid cancer.

External beam radiotherapy has a role in each histological type of thyroid cancer. For treatment confined to the thyroid bed, an antero--oblique wedged pair of beams is simple to apply. More frequently, however, the volume needs to include both sides of the neck and adequate dose must be given down to the level of the suprasternal notch, precluding use of lateral fields. Thus, anterior and posterior fields are usually necessary, extending from the tips of the mastoid processes or hyoid down to the carina and laterally to include both sides of the neck and supraclavicular fossae. The mandible and infraclavicular portions of both lungs are shielded, but there is no midline lead in the phase one volume. A mid-plane dose of 46 Gy given in 23 daily fractions results in an acceptable early radiation reaction and will avoid late damage to the spinal cord. Because of considerable variation of interplanar distance along the length of the volume, a lateral simulator film should be taken to determine the maximum cord dose. For most patients, a three-dimensional CT planned phase two volume will be required and should be determined prior to completing phase one. The optimum beam arrangement, usually incorporating conformal beam shaping assisted by use of a multileaf collimator, should avoid further dose to the cord. If there is additional dose to the spinal cord, this phase can be introduced before 46 Gy is reached.

Adenocarcinoma, Follicular↗
PubMed1996

Pictorial review: comparison of portal imaging and megavoltage verification films for conformal pelvic irradiation.

This study has evaluated the use of electronic portal imaging (EPI) as a replacement for megavoltage verification films in the treatment of conformal pelvic patients. The two methods of imaging have been compared in 40 patients. Several advantages of EPI were identified, including case of image acquisition. regular assessment of reproducibility of set-up and the possibility of on-line intervention when necessary. The findings suggest that EPI is a suitable replacement for films.

Humans↗
PubMed1990

Radiotherapy of brain tumours: reduced irradiation of normal brain.

We analysed the dose-volume distribution in normal brain in eight patients undergoing localized external beam radiotherapy for brain tumours. The results have been represented as integral dose-volume histograms and show that large volumes of normal brain receive clinically significant doses of radiation. A mean of 43% (range 24%-57%) of normal brain volume received more than 50% and a mean of 22% (range 9%-38%) received more than 85% of the maximum tumour dose. The amount of normal brain irradiated increased with enlarging target volume. With the use of customized shielding blocks the mean volume reduction of normal brain receiving more than 50% and 85% maximum tumour dose was 178 ml (median 183 ml; range 89-244 ml) and 110 ml (median 110 ml; 40-179 ml) respectively. This represents an average reduction of 13% and 8% of normal brain volume. Although clinically important this may not be sufficient for a significant improvement in therapeutic ratio.

Brain Neoplasms↗