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J W Denham

Publications and source records attributed to J W Denham.

At least 19 recordsLinked to original sources
PubMed1992

A practical evaluation of five dose-volume histogram reduction algorithms.

A unifying approach to cumulative dose-volume histogram (CDVH) reduction analysis is presented, utilising two weighted linear interpolation models (VWD, DWV), two weighted probability models (VWP, DWP) and a novel integral probability model (IPM). As a test of their predictive value these algorithms were applied to CDVH data generated from lung doses, measured by TLD arrays in a female anthropomorphic phantom. Three arbitrary configurations of breast size and location of "target volume" within the breast were "treated", using an appropriate electron field (Varian Clinac 1800) or double-plane iridium-192 implant. Calculated effective doses from each of the reduction algorithms showed the iridium implant to be dosimetrically the most favourable in two the three configurations. Likewise, complication probabilities, based on a logistic dose-volume response function showed lung complication probabilities to be lower for the interstitial technique in the same situations. All algorithms tested showed reasonable consistency, with the exception of the VWD. The rationale and value of comparative rather than absolute dose-volume histogram analyses are discussed.

Algorithms↗
PubMed1992

Tangential breast irradiation: simple improvements.

A series of studies using phantom and in vivo dosimetry measurements with diodes and thermoluminescent dosimetry were undertaken to establish whether simple methods are available to obtain improvements in homogeneity of dose in the treated breast, and reductions of dose to tissues outside it, when using tangential 6MV photon fields. These studies confirmed that the use of an appropriate lung density correction factor in the planning process is likely to cause a reduction in the amount of wedge compensation predicted to be necessary to produce reasonable dose homogeneity in the central axis of the beam. This was shown to be of value in eliminating potential areas of overdosage in the chest wall medial and lateral to the breast mound, and also in reducing unwanted doses to the contralateral breast and lung. Further reductions in dose to contralateral breast were confirmed to occur when the majority, or all, of the wedge compensation predicted necessary is placed on the lateral field and when the lateral tangential field is angled anteriorly in such a way as to align the posterior beam edges. Skin does above, below, and over the breast mound were observed to depend critically upon angle of incidence of the beam, with its consequent effect upon electron build-up, and the position of the breast contour in the beam. Skin doses above and below the breast mound were shown to exceed over the mound itself. This differential effect was observed to increase with increasing wedge compensation. In some situations skin doses below the breast mound nearly reached prescribed dose within the breast. The design and use of simple lead attenuators to reduce these areas of high dosage is discussed.

Breast Neoplasms↗
PubMed1992

Treatment and planning decisions in non-small cell carcinoma of the lung: an Australasian patterns of practice study.

Fourteen practising radiation oncologists were surveyed to assess their treatment and planning habits utilizing six sample cases of non-small cell carcinoma of the lung. Respondents were first given a general questionnaire, designed to evaluate their theoretical treatment and planning recommendations based on various tumour and patient related variables. Respondents then undertook a practical planning exercise utilizing planning CT and simulator radiographs for each of the six sample cases. Each case was accompanied by a brief history and report outlining specific tumour stage and non-stage related variables. The practical planning exercise was repeated on the second day of the survey utilizing different non-stage related variables but identical radiology and stage-related information. This design enabled firstly, a comparison of clinicians' intended policy and planning methods with actual policy and planning decisions, and secondly, an assessment of intra-clinician variability in decision making and planning practice. Good agreement was evident among clinicians with respect to general, non-case specific treatment policies; however, very significant variation occurred at an inter- and intra-clinician level and involved the entire treatment and planning process for individual cases. Despite identical treatment intent across identical radiological case pairings, clinicians chose widely differing margins and target volumes in their planning exercise. Treatment intent appeared to be influenced more by non-stage related variables rather than stage related information and radiological appearances per se. We have shown that experienced radiation oncologists do not adhere to stated case selection criteria and show inconsistencies in their treatment planning for non-small cell carcinoma of the lung.

Australia↗
PubMed1992

Dose normalisation and specification: from woe to go.

A questionnaire has been completed by 16 practising Radiation Oncologists from 10 centres in Australia and New Zealand which confirms that considerable variation in dose normalisation and specification practices exists between Australasian centres. The establishment of a working party to determine whether a uniform code of practice (such as ICRU 29 or a modification thereof) is desirable, and can be adopted in Australasia, is recommended.

Australia↗
PubMed1992

Patterns of treatment failure and prognostic factors associated with the treatment of esophageal carcinoma with chemotherapy and radiotherapy either as sole treatment or followed by surgery .

PURPOSE: The records of patients with esophageal cancer who were treated with a combined modality therapy were reviewed to determine the effects of simultaneously administered chemotherapy and radiotherapy (RT) at sites of recurrence and the relationship between treatment outcome and clinicopathologic variables. PATIENTS AND METHODS: One hundred seventeen patients were treated with fluorouracil (800 mg/m2) [corrected] and cisplatin (80 mg/m2) combined with either 36 Gy (36 patients) or 54 to 60 Gy (35 patients) of RT as sole therapy. Forty-six patients underwent surgery after they had received chemotherapy and 36 Gy of RT as initial treatment. Patients with either squamous cell cancer (SCC) or adenocarcinoma were included. RESULTS: Complete endoscopic regression after an initial 36 Gy of RT and chemotherapy occurred in more than 50% of patients and in both tumor types. Relief of dysphagia accompanied tumor regression. Forty-two tumors were resected, and 11 showed a complete histologic response. Significant associations were demonstrated between enhanced survival and a diagnosis of SCC, a complete endoscopic response to initial chemotherapy and RT, and a tumor length of less than 5 cm. Multivariate analyses suggested that tumor length and complete endoscopic response were independent prognostic variables. The survival rate of patients treated by resection or radical-dosage RT was not significantly different. CONCLUSIONS: The relief of dysphagia demonstrates the palliative value of chemotherapy and RT in both tumor types. The similar survival rates of patients with SCC or adenocarcinoma treated either surgically or with high-dose combined therapy (54 to 60 Gy) emphasize the need to evaluate the role of surgery and combined treatment in randomized studies.

Adenocarcinoma↗
PubMed1991

Breast conservation, the problem of treating the excision site effectively: physical criteria for the choice of technique used.

This paper examines how physical factors such as the depth of the excision cavity below the skin surface and its distance from the underlying lung may impact upon the choice between the use of an electron field (from a Varian Clinac 1800) or an implant (using a double plane of iridium-192 wires). Data have been derived from a phantom dosimetry experiment simulating different permutations of breast size and depth of excision cavity. An anthropomorphic female phantom with two different-sized wax breast phantoms has been used to simulate the clinical circumstances envisaged and isodose distributions have been estimated from an array of TLD readings. The biological significance of doses measured in skin and lung have been examined using the linear-quadratic (LQ) model. Both on physical and biological grounds, the results favour the implant under the experimental conditions adopted. The use of the electron beam to definitively treat the excision cavity (omitting breast tangents) to 60 Gy would result in unacceptable late effects in the skin and an observable incidence of pneumonitis if the excision cavity were near the chest wall. Small carcinogenic risks, particularly to the lung, are apparent with each modality, but may be moderated for the iridium-192 implant by a reduced carcinogenic potential associated with low-dose rate radiation. The use of the newer radionuclides iodine-125 and samarium-145, with less penetrating gamma ray emissions, might be preferred to iridium-192 from the point of view of bronchial carcinogenesis if definitive treatment of the excision cavity became widespread practice.

Brachytherapy↗
PubMed1991

Boost dosage to the excision site following conservative surgery for breast cancer: it's easy to miss!

Surgical haemoclips have been left in situ in 27 consecutive patients conservatively operated on for early breast cancer by two surgeons in Newcastle, New South Wales, to demarcate the limits of the excision cavity for accurate postoperative irradiation. As anticipated, the position of these clips varied widely in relation to the patient's recollection of the position of the original lump, the surgical notes, and the surgical scar. In addition the dimensions of the clipped area also varied considerably. So great was the variation in position of the clips that incomplete coverage of the excision cavity in the 'coronal' (en face) plane using an electron field could have occurred in an estimated 10/24 (42%) evaluable cases had surgical clips not been left in situ. Depth of the surgical clips below the skin surface also varied markedly between patients. In 19/26 (73%) evaluable cases the clips were observed to be sited 3 cm or more below the skin surface, while in only 5/26 (19.2%) were the clips found to be 2 cm or less deep to the surface. Had a 9 MeV beam from our Clinac 1800 been used to treat all the cases, a major underdose of the excision cavity would have been likely in 21/26 (81%) evaluable cases. This figure would be improved to 11/26 (42%) had a 12 MeV beam been used--still a very high figure. Neither of these points have received much attention in the literature. This small study sounds a distinct warning and needs to be repeated on a larger scale.

Breast Neoplasms↗
PubMed1991

Clinical utility of high-resolution portal films.

We have evaluated the film quality and overall clinical utility of a unique high-resolution portal film system which utilizes high contrast graphics art film. A total of 127 unselected patients had their conventional portal films and high-resolution films of the same site, compared and graded subjectively for a variety of parameters by an independent panel of radiotherapists and radiographers. Although consistent improvements in most aspects of image quality were noted, improved overall clinical usefulness of the high-resolution portal film system in comparison to the conventional films, when subjected to multiple regression analysis, was confined to lateral neck views only. High-resolution portal film utility was also found to depend significantly on field size with areas less than 110 cm2 having a markedly worse clinical utility score.

Humans↗
PubMed1991

Concurrent cisplatin, infusional fluorouracil, and conventionally fractionated radiation therapy in head and neck cancer: dose-limiting mucosal toxicity.

After a preliminary dose-finding study involving 12 patients with advanced or locally recurrent head and neck cancer, 27 patients were treated on a phase II protocol, using fluorouracil 350 mg/m2/d by continuous intravenous (IV) infusion over 5 days, followed on the sixth day by a 2-hour IV infusion of cisplatin 50 mg/m2, administered during the first and fourth weeks of radiation therapy to total doses between 60 and 64 Gy, using 2 Gy daily fractions. Eight of these 27 patients had American Joint Committee on Cancer Staging (AJCC) stage III disease, and 12 had stage IV disease. Four had recurrent disease after surgery. Three-year follow-up is now available. Twenty-one (77.8%) remitted completely following treatment, and 11 remain free of local and regional relapse at 3 years. Four have developed systemic metastases. Following successful salvage treatment in two cases, estimated determinate survival at 3 years is 64%. Acute toxicity was manageable with this regime. Eleven instances of grade 3 Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer (RTOG/EORTC) mucositis were observed, which caused interruptions to radiotherapy in only four cases. No late sequelae have so far been recorded. It is concluded that the protocol described is tolerable but probably did not cause a greater number of locoregional "cures" than would have been expected following conventional radiotherapy alone in this group of patients. The use of infusional fluorouracil with concurrent conventionally fractionated radiation therapy and cisplatin infusion results in mucositis that limits the dose of fluorouracil to levels that are probably subtherapeutic.

Adult↗
PubMed1990

Low dose rate teletherapy using a telecaesium 137 unit radiobiological, physical and clinical considerations.

Low dose rate teletherapy aims to combine the supposedly superior results obtained with low dose rate implants with the convenience and staff protection characteristics of external beam therapy. Previous investigators have used telecobalt units to produce dose rates of 1.1 to 1.8 Gy/hr to treat in daily sessions lasting 6-10 hours to total doses of 60-70 Gy. These studies have not discounted the possibility that much of the advantage of interstitial implants results from the low dose rates used per se, and from the fact that the total dose is delivered in a short overall time. The relationship between total dose, dose rate and volume giving normal tissue and anit-tumour effects, however, remains ill-defined. At the Newcastle Mater Misericordiae Hospital a Caesium teletherapy unit has been modified to treat at low dose rates and a study has been designed with a view to establish which permutations of total dose and dose rate are isoeffective for acute mucosal and acute skin reactions in the dose rate range between 0.8 and 9.6 Gy/hr (1.3 and 16 cGy/min).

Cesium Radioisotopes↗
PubMed1990

CT scanning for definitive radiotherapy planning of prostate cancer: necessity or nicety? Results from survey of radiation oncologists working at different institutions in Australasia.

Interactive computerised tomographic (CT) planning techniques offer the prospect of better anatomical localisation, more consistent tumour coverage, and limiting normal tissue dose. However, its value in the management of prostate cancer remains undefined. The present study addresses the impact of planning CT on the designated target volumes for localised carcinoma of the prostate at a multi-institution national level. Nine radiation oncologists from different centres in Australia and New Zealand were asked to designate a target volume on five sample patients with different disease stages (A2-C2) using both conventional cystogram films and planning CT scans. Target volumes estimated by CT means in this study differed by more than 10% from those estimated by conventional means in 75.6% of instances, being smaller in 55.6%. Volumes varied widely between individual radiation oncologists, both using conventional planning and CT information. These variations were found to exceed any differences in the volume caused by the planning technique itself. Results from this survey suggest that volumes appear to change more according to the individual radiation oncologist rather than to any other factor. In most or all of the sample cases six of nine radiation oncologists defined the borders of their CT volumes to be either consistently smaller (5 out of 9) or greater (1 out of 9) than their conventionally defined borders. The results of this survey are potentially important and warrant repetition with larger sample numbers in other countries where interactive CT planning facilities exist, both with and without diagnostic radiological input, to exclude similar variation and to define causes for any variations that do become apparent.

Data Collection↗