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J Perks

Publications and source records attributed to J Perks.

17 recordsLinked to original sources
PubMed2005

Glass rod detectors for small field, stereotactic radiosurgery dosimetric audit.

This paper demonstrates the feasibility of using glass rod detectors for quality assurance audit of radiosurgery units. Five radiosurgery units (3 Gamma Knife model C, 1 Gamma Knife model U and 1 Cyberknife) located in California participated in the study. At each center glass rod detectors were used to measure a number of dosimetric parameters including relative collimator output factor and absolute dose rate. The Gamma Knife data obtained is in excellent agreement with the commissioning data generated by the manufacturer for each unit and the Cyberknife data is in general agreement with the data published by other centers. In particular the output factor of the 4 mm Gamma Knife helmet factor, a subject of abundant debate, was measured in the range 0.863-0.872 with an accuracy of better than 1% across the four participating centers. It is hoped that this pilot study will facilitate a nationwide postal audit of stereotactic radiosurgery units.

Calibration↗
PubMed2002

High precision focused irradiation in the form of fractionated stereotactic conformal radiotherapy (SCRT) for benign meningiomas predominantly in the skull base location.

OBJECTIVE: To present early clinical results of stereotactic conformal radiotherapy (SCRT) in patients with benign predominantly skull base meningiomas. MATERIAL AND METHODS: Between August 1994 and August 1999, 41 patients with benign residual or recurrent meningiomas were treated with SCRT. Thirty-three were histologically verified. All patients were immobilized in a GTC stereotactic relocatable frame, and underwent a post-contrast CT localization scan with additional MRI for fusion in 15 patients. Treatment was delivered on a 6 MV linear accelerator using three (12 patients), or 4 (29 patients) non-coplanar conformal fixed fields to doses of 50-55 Gy in 30-33 daily fractions. Tumours were relatively large with a median gross tumour volume (GTV) of 17.9 cm3 (range 2.5-183 cm3). RESULTS: At a median follow-up of 21 months (range 6-62 months) none of 41 patients have recurred. The current imaging tumour control rate is 100% at 1 and 3 years. The actuarial survival at 2 years is 100% and 91% at 3 and 5 years. Following SCRT tumour decreased in size in 9 patients. SCRT was well tolerated. Five patients had improvement in vision, and six patients improvement in cranial nerve function. Two patients whose planning target volume (PTV) included the sella developed hypopituitarism during and at 18 months after SCRT. One patient with pre-existing hydrocephalus due to pineal region meningioma developed cognitive impairment 7 months after treatment. One patient with involvement of the optic nerve had visual deterioration at 18 months. CONCLUSIONS: SCRT is a feasible high precision irradiation technique for residual and recurrent skull base meningiomas including both small and larger tumours with excellent early tumour control and low toxicity. Longer follow-up is necessary to demonstrate sustained tumour control and low morbidity of such high precision localized method of fractionated irradiation.

Adult↗
PubMed2002

Stereotactic radiosurgery XIV: The role of the haemosiderin 'ring' in the development of adverse reactions following radiosurgery for intracranial cavernous malformations: a sustainable hypothesis.

There are strong data supporting the clinical efficacy of ionizing radiation therapy in the treatment of extracranial cavernous angiomas; no unusual complications occur. There is no a priori reason to anticipate a high rate of complications following radiosurgery for brain cavernous angiomas and yet equivalent dose prescriptions (site, size and target volume) to those used for AVM are associated with a considerably higher complication rate. The observed sub-acute reactions sometimes recover with steroid therapy. Previous authors have not sought to define the aetiological basis of this observation. Haemosiderin staining of the fringe of normal brain tissue surrounding the cavernoma is a unique feature of these brain lesions and the potential radiosensitizing properties of this iron based substance, for which there is a considerable experimental and clinical observational basis for radiosensitization, are reviewed. These provide good support for the concept that this characteristic feature of brain cavernomas accounts for the higher post radiation reaction/complication rate. Treatment considerations, stemming from these observations, are suggested.

Brain Neoplasms↗
PubMed2002

Radiosurgery for residual or recurrent nonfunctioning pituitary adenoma.

OBJECT: Nonfunctioning pituitary adenomas comprise approximately 30% of all pituitary tumors. The purpose of this retrospective study is to evaluate the efficacy and role of gamma knife radiosurgery (GKS) in the management of residual or recurrent nonfunctioning pituitary adenomas. METHODS: A review was conducted of the data obtained in 42 patients who underwent adjuvant GKS at the University of Pittsburgh between 1987 and 2001. Prior treatments included transsphenoidal resection, craniotomy and resection, or conventional radiotherapy. Endocrinological, ophthalmological, and radiological responses were evaluated. The duration of follow-up review varied from 6 to 102 months (mean 31.2 months). Fifteen patients were observed for more than 40 months. The mean radiation dose to the tumor margin was 16 Gy. Conformal radiosurgery planning was used to restrict the dose to the optic nerve and chiasm. Tumor control after GKS was achieved in 100% of patients with microadenomas and 97% of patients with macroadenomas. Gamma knife radiosurgery was equally effective in controlling adenomas with cavernous sinus invasion and suprasellar extension. No patient developed a new endocrinological deficiency following GKS. One patient's tumor enlarged with an associated decline in visual function. Another patient experienced a deterioration of visual fields despite a decrease in tumor size. CONCLUSIONS: Gamma knife radiosurgery can achieve tumor control in virtually all residual or recurrent nonfunctioning pituitary adenomas. Dose sparing facilitates tumor management even when the adenoma is close to the optic apparatus or invades the cavernous sinus.

Adenoma↗
PubMed2001

Stereotactic radiotherapy for solitary brain metastases.

PURPOSE: Surgery is considered to be the treatment of choice for patients with solitary brain metastases. We report a single-centre experience of stereotactic radiotherapy (SRT)/radiosurgery as an alternative to surgery and define prognostic parameters that provide for a more rational selection of patients for appropriate treatment. PATIENTS AND METHODS: Between 1990 and 1997, 96 patients with 106 brain metastases received SRT to a dose of 20 Gy in two fractions (range 20-30 Gy in 24 fractions) either alone or in combination with whole brain radiotherapy. RESULTS: After SRT, 51% of patients had improvement in neurological function. The median survival of the 96 patients was 9 months. The Radiation Therapy Oncology Group prognostic grouping for patients with multiple brain metastases (prognostic factors: age, performance status, systemic metastases, status of primary tumour) was applicable to this cohort, with median survivals of 15, 8 and 2 months for favourable, intermediate and poor prognostic groups respectively. CONCLUSION: SRT is a non-invasive method of treatment of solitary brain metastases and the outcome is comparable with the results obtained after surgical excision. Prognosis is determined by factors defined for patients with multiple brain metastases, with performance status being the most important. SRT/radiosurgery should be reserved for patients with favourable prognostic factors, with a Karnofsky performance status >70, who have a reasonable chance of good quality prolonged survival. In future trials, radiosurgery should be compared in terms of survival, quality of life and health economics to whole brain radiotherapy and surgery.

Adult↗
PubMed2001

Is distortion correction necessary for digital subtraction angiography in the Gamma Knife treatment of intra-cranial arteriovenous malformations?

OBJECTIVE: The published literature maintains that distortion correction of digital subtraction angiography is essential for accurate definition of the arteriovenous malformation (AVM) nidus when performing Gamma Knife radiosurgery. However, as Gamma Knife treatments usually involve small volume targets, which are purposely positioned as close to the centre of the frame as possible, we postulated that the angiographic target images should be minimally distorted. Thus, the use of uncorrected images would not significantly compromise the accuracy of the treatment. We investigated this postulate. DESIGN: Patient and phantom images with and without distortion correction were assessed. The errors measured in the angiograms were compared to those of MR and CT images of the same subjects. Any errors less than 0.5 mm in any modality were accepted as intrinsic. RESULTS: All errors measured in the study were sub-millimetre. In the patient group, errors with distortion correction averaged 0.13 mm (range 0-0.3 mm). Without distortion correction, errors averaged 0.34 mm (range 0.1-0.6 mm). By comparison, the average error for intracranial MR imaging was 0.3 mm, with a maximum of 0.6 mm. CONCLUSION: For small, intracranial AVMs distortion correction did not significantly reduce the errors associated with the definition of the stereotactic co-ordinates. We suggest that prior to the purchase of this software, similar in-house testing should be performed.

Angiography, Digital Subtraction↗
PubMed1999

Social awareness of air quality information.

In the UK, air quality information is made available through a range of media. However, limited attention has been paid to ensuring that the information is provided to the public in a format that is understandable and relevant to their needs. This research has begun the task of determining the nature and extent of public air quality requirements by performing a social survey (using a postal questionnaire) to provide a basic snapshot of the public's views and by determining the views of information providers and interested professionals. The paper identifies the main shortcomings in current public air quality information provision. The social survey and workshop results demonstrate that current information provision and dissemination does not match public requirements; the depth and breadth of local information needs to be enhanced. Local authorities need to improve their co-ordination and collaboration, the role of the mass-media needs to be considered carefully, air quality needs to be better described and its implications for individuals spelled out and certain public groups need special consideration. In addition, local authorities need more guidance on communicating air quality, possibly through a best practice guide. Further research is required to identify the best descriptors for air quality, to improve the effectiveness of public advice during episodes of poor air quality and to use public air quality information to effect behavioral changes.

Air Pollution↗
PubMed1999

Stereotactically guided conformal radiotherapy for meningiomas.

PURPOSE: Stereotactically guided conformal radiotherapy, (SCRT) is a high precision technique of conformal radiotherapy (RT) which reduces the volume of normal tissue irradiated compared to conventional RT and may lead to a reduction in long-term toxicity We describe the technique and the preliminary results in patients with inoperable, residual or recurrent meningiomas. MATERIAL AND METHODS: From July 1993 to November 1997, 24 patients (median age: 56 years, range: 28-72) with base of skull (n = 21). falx or upper skull (n = 3) meningiomas were treated with SCRT. The technique employed immobilization in a Gill-Thomas-Cosman (GTC) frame and CT localization with a Brown-Roberts-Wells (BRW) fiducial system for stereotactic space definition. The planning target volume (PTV) was defined as gross tumour volume (GTV) and a 0.5-1 cm margin. Treatment was delivered with three (12 patients) or four non-coplanar conformal fixed fields (12 patients) Conformal blocking was achieved either with lead alloy blocks (n = 11) or with a multi-leaf collimator (MLC) (n = 13). Patients were treated on a 6 MV linear accelerator to doses of 50-55 Gy, in 30-33 daily fractions. The treatments were carried out as part of a routine work of a busy radiotherapy department. RESULTS: Median GTV for 24 meningiomas was 21.7 cm3 (range: 4.4-183 cm3). SCRT was well tolerated with minimal toxicity Three months after the end of radiotherapy, seven of 15 patients with neurological deficit had an improvement and eight remained unchanged. Two patients experienced early side effects (one VII nerve palsy, one Addisonian state). At a median follow-up of 13-months (range: 3-43) the 1 year progression free survival and overall survival are 100%. which is within the range expected for conventional fractionated radiotherapy for meningiomas. CONCLUSIONS: SCRT is a feasible technique of high precision conformal RT for patients with meningiomas. Potential advantages in tumour control, survival and toxicity over conventional RT, require evaluation in long-term prospective studies.

Adult↗
PubMed1999

Dose quality assurance for stereotactic radiotherapy treatments.

A simple Perspex phantom is presented for routine dosimetry checks of stereotactic radiotherapy procedures, along with a procedure for checking the planning process. The phantom is hemispherical and water filled. It can be fitted into the Brown-Robert-Wells fiducial system for CT scanning and attached to the stereotactic frame for treatment. Both arcing and fixed field plans can be carried out on the phantom. We present our results, performed on a Varian 600C linac, which were found to be within 2% of the expected dose.

Humans↗
PubMed1994

Should we stitch the subcutaneous fat layer following saphenous vein excision for coronary revascularization?

We report a prospective trial to establish whether a subcutaneous fat stitch reduces the incidence of haematoma formation, infection and wound dehiscence following saphenous vein excision for coronary revascularization. Two groups of patients undergoing coronary revascularization were studied. In the first group of 100 patients the saphenous vein was harvested from both legs. Legs were randomized to have either a fat stitch or no fat stitch during wound closure. By using both legs of each patient we eliminated the effect of general factors on wound healing, thus the patients acted as their own controls. In the second group of 200 patients, the saphenous vein was harvested from the thigh, and patients randomly allocated to either a fat stitch or no fat stitch during wound closure. The wounds were examined daily for 7 days, and again after 6 weeks at the follow-up. There was no difference in the rate of wound complication in the fat stitch groups (9%) compared with the no fat stitch groups (8%), however, the fat stitch groups required more surgical intervention for skin edge necrosis. It appears that closure of the subcutaneous fat following saphenectomy is unnecessary, and may be detrimental to skin healing.

Adipose Tissue↗
PubMed1993

Plasma aluminium in a reference population: the effects of antacid consumption and its influence on biochemical indices of bone formation.

Aluminium is involved in the etiology of several complications of chronic renal failure and has been firmly established as having toxic effects on bone tissue. We have measured plasma aluminium together with serum osteocalcin, procollagen I C-terminal peptide and total alkaline phosphatase activity in healthy subjects and in a group of subjects who consumed aluminium-containing and non-aluminium containing antacid preparations, with normal renal function. Age-related healthy reference ranges for plasma aluminium are presented and the effects of chronic antacid consumption on plasma aluminium and biochemical markers of bone formation investigated. In 172 healthy subjects the mean plasma aluminium concentration was 4.4 +/- 2.9 micrograms L-1, men having a significantly greater circulating aluminium load than women (5.4 +/- 2.8 micrograms L-1 vs. 4.0 +/- 2.8 micrograms L-1 respectively (P = 0.0039)). Older men were found to have significantly higher plasma aluminium levels than younger men. Increased plasma aluminium was seen in subjects taking antacids although this was not associated with significant changes in most indices of bone formation.

Adult↗
PubMed1993

Anomalous rise of serum osteocalcin following desferrioxamine treatment in aluminium intoxication.

A patient with impaired renal function, severe osteomalacia and aluminium intoxication is described. In response to Desferal (desferrioxamine) treatment, serum osteocalcin rose 8-fold whereas serum alkaline phosphatase and procollagen I peptide levels changed little. Chromatographic separation showed that the measured osteocalcin coeluted with intact osteocalcin. The osteocalcin in the serum probably comes from the liberation of pre-existing osteocalcin from the bone, concomitant with aluminium mobilisation, rather than by stimulation of de novo synthesis.

Aluminum↗