P N Plowman

St. Michael's Hospital, Toronto, Ontario, Canada

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Publications (195)854.94 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Low-grade ocular adnexal lymphoma is a rare disease and often treated with local radiotherapy to varying doses. Most previously reported studies have a very heterogeneous patient population and treatments. We report the outcomes from a 10 year cohort of patients at our institution treated with primary radiation therapy.Materials and methodsWe analysed a retrospective case series of patients with stage IE low-grade ocular adnexal lymphoma including a review of case notes, histological reports and radiotherapy charts. We assessed local and distant tumour control and relapse rates in addition to toxicity. Disease-free survival was estimated using the Kaplan–Meier method.ResultsIn total, 81 patients and 85 orbits were treated with primary radiotherapy to a median dose of 30 Gy in 15 fractions over 3 weeks. Seventy-nine per cent were treated with standard MV external beam radiotherapy to the whole orbit and 21% with a lens-sparing technique. The median follow-up was 4.4 years (range 0.2–10.4). Local control rates were 100%, with 5% of patients experiencing disease relapse elsewhere. No patients died from lymphoma. Cumulative acute toxicity rates were 51% (mainly erythema and conjunctivitis) and late toxicity rates were 8% (mainly cataract). The lens-sparing technique was associated with a significant reduction in cataract rate (P = 0.013) and an increase in acute toxicity (P < 0.001).Conclusions This study has shown excellent local control rates and acceptable toxicity from the treatment of stage IE low-grade ocular adnexal lymphoma with localised radiotherapy to a median dose of 30 Gy in 15 fractions over 3 weeks.
    Clinical Oncology 10/2014; 27(3). DOI:10.1016/j.clon.2014.10.002 · 3.40 Impact Factor
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    ABSTRACT: Background: 131I-meta-iodobenzylguanidine (131I-MIBG) has been in therapeutic use since 1980s. Newer treatment modalities are emerging for neuroendocrine tumours (NETs) and chromaffin cell tumours (CCTs), but many of these do not yet have adequate long-term follow-up to determine their longer term efficacy and sequelae. Methods: Fifty-eight patients with metastatic NETs and CCTs who had received 131I-MIBG therapy between 2000 and 2011 were analysed. Survival and any long-term haematological or renal sequelae were investigated. Results: In the NET group, the overall median survival and median survival following the diagnosis of metastatic disease was 124 months. The median survival following the commencement of 131I-MIBG was 66 months. For the CCT group, median survival had not been reached. The 5-year survival from diagnosis and following the diagnosis of metastatic disease was 67% and 67.5% for NETs and CCTs, respectively. The 5-year survival following the commencement of 131I-MIBG therapy was 68%. Thirty-two patients had long-term haematological sequelae: 5 of these 32 patients developed haematological malignancies. Two patients developed a mild deterioration in renal function. Conclusion: Long follow up of 131I-MIBG therapy reveals a noteable rate of bone marrow toxicities and malignancy and long term review of all patients receiving radionuclide therapies is recommended.
    British Journal of Cancer 07/2013; 109(3). DOI:10.1038/bjc.2013.365 · 4.84 Impact Factor
  • D K Woolf · M Ahmed · P N Plowman
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    ABSTRACT: Lymphomas of the orbit and eye are rare conditions that should be treated as separate entities due to the differences in presumed aetiology, investigations, management and outcomes. Orbital lymphoma is most often of low-grade histology; thyroid eye disease may predispose and chlamydial infection has been suggested as a trigger. Commonly, stage IE, in most cases, can be managed with radiotherapy alone using either a kilovoltage portal for conjunctival disease or a wedged pair of megavoltage beams for more infiltrative disease to a dose of 30 Gy in 15 fractions over 3 weeks. However, medical therapy is being investigated, including a rituximab-only approach for conjunctival-only presentations. The cure rate for stage IE disease is very high. In contrast, primary ocular lymphoma is often of high-grade histology, in particular diffuse large B-cell lymphoma, and can be regarded as one end of primary central nervous system lymphoma - both eyes and brain being at risk. Immunosuppression predisposes to the disease. Management consists of an initial high-dose chemotherapy regimen with methotrexate. In most cases, this should be followed by radiotherapy to the whole brain and globes to a dose of 30-36 Gy with a boost to bulk/presenting disease. Cure rates are rarely above 50%.
    Clinical Oncology 04/2012; 24(5):339-44. DOI:10.1016/j.clon.2012.03.001 · 3.40 Impact Factor
  • D Smith · N MacDougall · J Monk · A Sibtain · M E Powell · P N Plowman
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    ABSTRACT: Intensity-modulated radiotherapy (IMRT) is a relatively new technique of delivering external beam radiotherapy that is becoming increasingly available in the UK. This paper summarises the introduction and initial clinical work in IMRT over the period 2004-2009. Physics aspects of commissioning are described, including the development of a robust method of quality control using a sweeping gap test. Details of the organisational changes necessary to introduce IMRT are given. The clinical selection and practice in head and neck sites are described, together with promising early results on the maintenance of salivary flow after IMRT. A summary of research into optimal planning for pelvic cancer follows. The controversial areas of breast and paediatric IMRT are discussed with recommendations on practice. The potential for concomitant boost therapy is exemplified in the treatment of brain metastatic disease.
    Clinical Oncology 10/2010; 22(8):666-74. DOI:10.1016/j.clon.2010.06.018 · 3.40 Impact Factor
  • European Journal of Endocrinology 08/2010; 163(2):357-8. DOI:10.1530/EJE-10-0498 · 4.07 Impact Factor
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    ABSTRACT: Cushing's disease (CD) in prepubertal children is very rare and presents important diagnostic and therapeutic challenges. We report experience of the management of this subpopulation of CD patients. Retrospective patient case note review. Between 1985 and 2008, 17 prepubertal children (13M, 4F), aged 5.7-14.1 years presented to our centre for diagnosis and management of CD. All children had subnormal linear growth and excessive weight gain at presentation. A high proportion (85% of males, 75% of females) had evidence of excessive virilisation. Striae and hypertension were seen in 41% of patients. The investigation with highest sensitivity (100%) for CD was excessive increase of serum cortisol to i.v. CRH (mean increase 113%). Pituitary imaging performed in all the patients showed poor concordance with findings at surgery (31%). In contrast bilateral simultaneous inferior petrosal sinus sampling (BSIPSS), performed in 11/16 subjects showed a high correlation with surgical findings (91%). In 16 patients, transsphenoidal selective adenomectomy (TSS) achieved a cure rate of 44%. However, in the 11 patients who had pre-operative BSIPSS, the cure rate was 64%. Of the 16 patients, 9 patients who were not cured by TSS received external pituitary radiotherapy. Prepubertal CD had distinctive features with increased frequency in males, abnormal auxology and excessive virilisation. The cortisol response to i.v. CRH administration was particularly exuberant and contributed to diagnosis. BSIPSS was much more helpful than pituitary imaging in localisation of the microadenoma and was associated with improved cure rate by TSS.
    European Journal of Endocrinology 12/2009; 162(3):603-9. DOI:10.1530/EJE-09-0509 · 4.07 Impact Factor
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    AA Edwards · E Keggin · P N Plowman
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    ABSTRACT: Whole brain radiotherapy (WBRT) is the standard non-surgical treatment for brain metastatic disease, but rarely eradicates bulky metastases from most common cancers. Recent literature has demonstrated the safety and efficacy of delivering very high focal doses of radiation (by radiosurgical techniques) to the gross tumour volume of bulky brain metastases, thereby obtaining more certain local control than is achieved by WBRT. In this paper we report a study of 11 patients with bulky brain metastases in whom an intensity-modulated radiation therapy (IMRT) facility has been used to concomitantly boost the gross tumour volume of bulky brain metastatic disease (to 40 Gy) during a standard 30 Gy in 10 fractions WBRT schedule. No acute or subacute morbidity was encountered, and good early control data were noted. We discuss the perceived advantages of such a technique.
    The British journal of radiology 12/2009; 83(986):133-6. DOI:10.1259/bjr/28596848 · 2.03 Impact Factor
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    ABSTRACT: We report the use of 'gamma knife' (GK) radiosurgery in 25 patients with pituitary adenomas not cured despite conventional therapy, including external beam radiotherapy. All patients had previously received conventional radiotherapy for a mean of 11.8 years prior to receiving GK; 23 out of 25 had also undergone pituitary surgery on at least one occasion. Seventeen had hyperfunctioning adenomas that still required medical therapy without an adequate biochemical control--ten somatotroph adenomas, six corticotroph adenomas and one prolactinoma, while eight patients had non-functioning pituitary adenomas (NFPAs). Following GK, mean GH fell by 49% at 1 year in patients with somatotroph tumours. Serum IGF1 fell by 32% at 1 year and by 38% at 2 years. To date, 80% of the patients with acromegaly have achieved normalisation of IGF1, and 30% have also achieved a mean GH level of <1.8 ng/ml correlating with normalised mortality. A total of 75% NFPAs showed disease stabilisation or shrinkage post GK. The patient with a prolactinoma showed a dramatic response: 75% reduction in prolactin at 2 years, with a marked shrinkage on magnetic resonance imaging. The results in corticotroph adenomas were variable. Prior to GK, 72% of the patients were panhypopituitary, and 42% of the remainder have developed new anterior pituitary hormone deficiencies to date. No other adverse events have been detected at a mean follow-up of 36.4 months. These data indicate that GK is a safe and effective adjunctive treatment for patients with NFPAs and acromegaly not satisfactorily controlled with surgery and radiotherapy.
    European Journal of Endocrinology 09/2009; 161(6):819-28. DOI:10.1530/EJE-09-0493 · 4.07 Impact Factor
  • M P Y Chan · J L Hungerford · J E Kingston · P N Plowman
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    ABSTRACT: Radiation is implicated in the induction of second malignancies in children with bilateral retinoblastoma. There is a need to determine whether this risk can be justified by good visual outcome when external beam radiotherapy (EBRT) is used as a salvage treatment. To study the effectiveness of EBRT as a salvage treatment after failed primary chemotherapy and focal treatment in bilateral retinoblastoma. This is a retrospective observational case series. The outcome measures after EBRT are: rate of eye preservation, rate of tumour control, visual potential, visual acuity and radiation-induced side-effects. Thirty-six eyes (22 patients) were included. The median follow-up after EBRT was 40 months (19-165 months). Thirty-two eyes received lens-sparing radiotherapy, and four received whole-eye radiation. The rate of eye preservation was 83.3% (30/36 eyes). Twenty-four eyes (66.7%) were controlled by EBRT and required no further treatment. Of the 30 preserved eyes, 20 eyes (66.7%) had extramacular tumours without retinal detachment and therefore potential for central vision. The final visual acuity was recorded for 19 eyes. Ten eyes (52.6%) read 6/9-6/5, three eyes (15.8%) read 6/18-6/36, and six eyes (31.6%) read 6/60 or worse. Significant radiation- induced side effects were limited to cataracts and dry eyes with whole-eye radiation. There were no second cancers or deaths. Salvage EBRT is highly effective in preserving eyes with useful vision in bilateral retinoblastoma after failed chemotherapy and focal treatments. These results will help the parents and ophthalmologists of such patients to reach an informed decision when weighing up the benefits of EBRT against its potential oncogenic effect.
    The British journal of ophthalmology 04/2009; 93(7):891-4. DOI:10.1136/bjo.2007.129981 · 2.98 Impact Factor
  • H O'Donnell · K Cooke · N Walsh · P N Plowman
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    ABSTRACT: New technology - specifically intensity-modulated radiotherapy (IMRT) - is now being applied to breast radiotherapy and a recent dosimetric analysis confirmed the advantages of IMRT over 'wedge-only' plans. Such application to everyday practice raises new issues and here we present the early experience of IMRT-based breast irradiation in a single centre. We present cases of breast cancer treated by Tomotherapy-based IMRT, where the perceived advantages of IMRT are considerable. Cases presented are bilateral disease, left breast irradiation, pectus excavatum, prominent contralateral prosthesis and internal mammary chain disease. We discuss the practicalities of such treatment and the advantages over standard breast irradiation techniques. Advantages include better conformity of treatment with lowering of dosages to underlying organs at risk, for example ipsilateral lung and heart. There is improved coverage of the planning target volume, including regional nodes, without field junction problems. Planning, quality assurance and treatment delivery are more time consuming than for standard breast irradiation and the low dose 'bath' is increased. The standard radiotherapy tangential technique for breast/chest wall treatments has not significantly changed over many decades, whereas across many other tumour sites there have been great advances in radiotherapy technology. The dosimetric advantages of IMRT are readily apparent from our early experience. The wider spread of the lower dose zone (the low dose 'bath' of radiation) is a potential concern regarding late oncogenesis and methods to minimise such risks should be considered.
    Clinical Oncology 03/2009; 21(4):294-301. DOI:10.1016/j.clon.2009.01.010 · 3.40 Impact Factor
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    Clinical Endocrinology 12/2008; 55(5):575 - 587. DOI:10.1046/j.1365-2265.2001.01396.x · 3.46 Impact Factor
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    ABSTRACT: A 64-year-old woman was previously treated for Cushing's disease with trans-sphenoidal surgery, external beam radiotherapy and bilateral adrenalectomy. Progression of an aggressive corticotroph adenoma was evident 3 years post-adrenalectomy; involvement of the clivus was treated with surgery and gamma knife radiosurgery. Tumour spread through the skull base, occiput and left ear with persistent facial pain and left ear discharge; progression continued despite second gamma knife treatment. ACTH levels peaked at 2472 and 2265 pmol/l pre- and post-hydrocortisone respectively. Treatment with temozolomide resulted in a significant improvement in symptoms, a reduction of plasma ACTH to 389 pmol/l and regression of tumour on magnetic resonance imaging scan after four cycles of treatment. We propose that temozolomide is an effective and well-tolerated therapeutic tool for the treatment of Nelson's syndrome and a useful addition to the range of therapies available to treat this condition.
    European Journal of Endocrinology 12/2008; 160(1):115-9. DOI:10.1530/EJE-08-0557 · 4.07 Impact Factor
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    ABSTRACT: To describe two patients with localized orbital amyloidosis and the response of their condition to surgical debulking followed by external beam radiotherapy. Retrospective noncomparative interventional case series. Stabilization or regression of orbital signs after treatment. Patients with biopsy-proven diagnosis of localized progressive orbital amyloidosis received 34 and 30 Gy fractionated external beam radiotherapy. The clinical case notes and histopathology for the two patients were reviewed. A 69-year-old man with orbital amyloid deposition in association with localized MALT lymphoma had a marked improvement in orbital signs following surgical debulking and radiotherapy, with no recurrence over two years. A 59-year-old woman with localized orbital amyloidosis showed regression of disease after surgical debulking and radiotherapy, with no evidence of recurrence after six years of follow-up. External beam radiotherapy following surgical debulking appears to halt the progression of localized orbital amyloidosis. Radiotherapy may be used in conjunction with surgical debulking of disease.
    Orbit (Amsterdam, Netherlands) 12/2008; 27(6):432-7. DOI:10.1080/01676830802350216
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    P N Plowman · K Cooke · N Walsh
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    ABSTRACT: The potential conformality advantages of intensity-modulated radiation therapy (IMRT; TomoTherapy Hi Art system) over conventional linear accelerator based therapy was assessed in six consecutive children referred for extracranial radiotherapy. IMRT/tomotherapy was considered advantageous for (i) small abdominal tumours, compared with parallel opposed or single portal technology using a conventional linear accelerator, and (ii) re-treatment of an ethmoidal sarcoma, but not for palliation of a small spinal metastasis, or therapy for a whole deep cervical node chain or a pelvic side wall tumour in a young child. Considerations integral to the treatment decision included target volume dose conformality, "low-dose bath" effects (oncogenic and late growth sequelae) and treatment delivery time. IMRT/tomotherapy was the selected modality for therapy when the conformality advantages were perceived to outweigh any disadvantages in three out of the six cases. The dose conformality advantages of IMRT/tomotherapy are sufficient to selectively recommend its availability to the paediatric practice in accordance to the following criteria: (i) where conformality of radiation therapy to the target/tumour is critical and where the margin of safety (from gross/clinical target volume to planning target volume (PTV)) around the tumour is narrow; (ii) where adjacent organs at risk of radiation damage have a low threshold for damage; and (iii) where the "low-dose bath" phenomenon, which occurs between the upper and lower axial limits of the PTV, is not sufficiently disadvantageous (with regard to late oncogenesis or growth retardation) to outweigh the more confined (non-tumour) integral doses received in higher dose corridors through the body when utilizing conventional radiation techniques.
    The British journal of radiology 12/2008; 81(971):872-80. DOI:10.1259/bjr/14878999 · 2.03 Impact Factor
  • M. Elsworthy · P.N. Plowman
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    ABSTRACT: Lymphopaenia is the earliest and the most sensitive routinely assessed biological parameter of corporeal radiation exposure in clinical practice; bone marrow, lymph nodes and peripheral blood lymphocyte populations are also at risk. During radical prostate radiotherapy, in 28 patients, the mean peripheral lymphocyte count fell from 1.76 × 109/l (standard deviation (SD) 0.63, 95% confidence interval (conf.) 0.23) to 1.10 × 109/l (SD 0.38, conf. 0.14), (p < 0.05). The question was asked as to whether intensity-modulated radiation therapy (IMRT) by TomoTherapy would cause more lymphopaenia than three-field conformal radiotherapy, bearing in mind the ‘low dose bath’ effect of IMRT and the long ‘beam-on’ times. Thirteen patients receiving three-field conformal radiotherapy experienced a fall in peripheral lymphocyte counts from 2.02 (SD: 0.62. conf. 0.43) to 1.17 × 109/l (SD: 0.47, conf. 0.26) after 34–38 Gy, as compared to a fall from 1.6 × 109/l (SD: 0.6, conf. 0.35) to 1.04 × 109/l (SD: 0.3, conf. 0.15) for 15 TomoTherapy patients—non-significant differences. We conclude that for this (approximately) standard, small-volume pelvic radiotherapy and to the dose under scrutiny, we cannot detect differences between the two radiotherapy techniques in terms of the lymphopaenia accruing. Neutrophil counts were similarly non-significantly different.
    Journal of Radiotherapy in Practice 11/2008; 7(04):223 - 227. DOI:10.1017/S1460396908006444
  • P N Plowman
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    ABSTRACT: Since the advent of PSA screening, the detection of early (organ confined) prostate cancer has improved. Although some indolent cancers in the elderly may be safely watched, the early diagnosis in younger men requires curative treatment. Two exciting modernized radiation therapy methods provide alternatives to major surgery and lead to cure rates equivalent to surgery. Modern intensity modulated external beam radiotherapy (IMRT) allows high-dose treatment to the prostate (+/- seminal vesicles) while maximally sparing the rectum (due to the extraordinary capability of creating a concavity in a high-dose radiation therapy volume). This has allowed escalation in the therapy dose to the prostate and improved cure rates. We have recently compared two different IMRT methods. Our introduction of "axial limits" rectal definition allows more accurate quantitation of relevant rectal sparing. Prostate radiation seed brachytherapy (Seattle 125-iodine method) provides a sophisticated, single-session radiation therapy method that has become the most popular curative method by busy men who want minimum interruption to their lives. The implant is "tailored" for the individual's gland size and shape, and in the London adaptation of the method there is interoperative monitoring of seed implantation, such that if any seed is slightly misplaced the information of deposition site is relayed back to a computer, which reconfigures the deposition of all subsequent seeds such that an ideal plan is achieved-dynamic, iterative, computer assisted implantation. The popularity of these two radiation techniques is largely due to the lesser rate of morbidity compared to surgery and the usual fast return to everyday life.
    Annals of the New York Academy of Sciences 10/2008; 1138(1):257-66. DOI:10.1196/annals.1414.031 · 4.38 Impact Factor
  • H E O'Donnell · K Finnegan · H Eliades · S Oliveros · P N Plowman
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    ABSTRACT: Improved prostate cancer cure rates have been attributed to higher radiotherapy dose prescriptions delivered more safely by modern conformal/intensity-modulated radiotherapy (IMRT) methods. As the dose becomes more concentrated conformally on the prostate, the volume of the rectum "at risk" for damage becomes smaller and more focal on the anterior rectal wall between the upper and lower axial limits of the planning target volume (PTV). The rectal dose-volume histogram (DVH) traditionally studies the whole volume of the rectum, and such definition for "avoidance" planning presupposes that rectal tolerance depends on "whole organ" radiation tolerance (as might, for example, lung or kidney). However, rectal morbidity with modern prostate radiotherapy is determined by anterior rectal wall tolerance between the superior and inferior limits of the PTV; this, we argue, is not dependent on whole organ tolerance. Recent published studies attempting to improve rectal DVH definition have studied the rectal wall only and concluded that rectal wall DVH is more relevant than whole rectum. In this manuscript, it is first demonstrated that a large and more relevant difference exists when comparing whole rectal DVH to "PTV limits" rectal DVH. Secondly, when considering "PTV limits" rectal DVH, the wall vs whole perimeter comparison differs little. Furthermore, by adopting a "PTV limits" DVH, the inferior right quartile of the DVH accurately reflects the dose distribution to the most vulnerable section of the anterior rectal wall. With improving IMRT technologies, scrutiny of this part of the rectal DVH will most accurately predict rectal sparing - reflected in this manuscript by the less precipitous decline of the TomoTherapy DVH vs the three-dimensional conformal DVH towards the maximum dose point received by the rectum.
    The British journal of radiology 05/2008; 81(964):327-32. DOI:10.1259/bjr/75868623 · 2.03 Impact Factor
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    ABSTRACT: This manuscript describes a direct comparison between radiation treatment plans in terms of dosimetric outcomes created by two different IMRT systems: TomoTherapy HiArt and dynamic linac intensity-modulated radiotherapy (dIMRT). Three patient cases were selected (with disease in different anatomical areas): vertebral metastasis re-treatment, radical prostate therapy and an ethmoid sarcoma re-treatment. Each case presents significant and varying dosimetric difficulties with respect to avoidance of adjacent organs. The patients were each planned and treated at the Cromwell Hospital (London, UK) using the TomoTherapy HiArt system, with planning replicated at St Bartholomew's Hospital (London, UK) using Eclipse Treatment Planning System and a 6EX linac with a 120-leaf multileaf collimator (Varian Medical Systems). For both modalities, all treatment plans conformed to the stringent clinical dose constraints set. For the vertebral body re-treatment, both techniques demonstrated adequate and similar planning target volume (PTV) coverage and sparing of the spinal cord. The critical structure sparing and PTV coverage for the prostate treatment was again similar for both modalities. For re-treatment of the paediatric ethmoid sarcoma, tomotherapy was able to produce slightly better organ sparing whilst producing PTV coverage similar to linac dIMRT. The data presented in this manuscript demonstrate subtle dosimetric differences between the two techniques but no marked advantage with either system. Therefore, other factors may need to be considered when making a decision between tomotherapy and linac dIMRT.
    The British journal of radiology 05/2008; 81(964):333-40. DOI:10.1259/bjr/67084583 · 2.03 Impact Factor
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    ABSTRACT: With the stricter endocrine definitions of cure following conventionally planned and fractionated radiotherapy for functioning pituitary adenomas, together with the move in the profession (since the advent of high quality MRI) to postpone radiation therapy until macroscopic disease appears after surgery, it is now realised that cure rates following conventional radiotherapy approximate three out of four rather than the >90% cited for more than a decade. Patients with persistent active tumours may be successfully further treated by focal radiation therapy by one of the stereotactic focal techniques. We have experience of such re-treatment radiation therapy in 50 patients. With careful case selection, we here demonstrate that in acromegaly, for example, normalisation of both GH and IGF levels may be achieved in 37-58% of these previously irradiated patients with low risk of late morbidity. Unquestionably, growth delay occurs in many cases but the long term tumour control rate has yet to be established.
    Pituitary 04/2008; 12(1):30-4. DOI:10.1007/s11102-008-0115-5 · 3.20 Impact Factor
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    H E O'Donnell · P N Plowman · M K Khaira · G Alusi
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    ABSTRACT: "Gamma Knife radiosurgery" is high-dose conformal radiation therapy used for the treatment of small target lesions in the head. It is a minimally invasive technique of multiple fixed, precisely aimed cobalt beams, and relies upon strict patient immobilization via a pinned stereotactic frame to deliver treatment to a precisely located target within a coordinated mapping system. This technique has been widely validated for the treatment of intra-cranial neoplasms and arteriovenous malformations. In this manuscript, two cases of early diagnosed, locally recurrent (persistent) nasopharyngeal carcinoma, successfully treated by Gamma Knife, are described. In one of these, early diagnosis by PET scanning may have improved the chance of cure.
    The British journal of radiology 02/2008; 81(961):e26-30. DOI:10.1259/bjr/15812414 · 2.03 Impact Factor

Publication Stats

3k Citations
854.94 Total Impact Points


  • 2008
    • St. Michael's Hospital
      Toronto, Ontario, Canada
  • 1986–2008
    • SickKids
      • Division of Hematology/Oncology
      Toronto, Ontario, Canada
  • 1992–2007
    • Great Ormond Street Hospital for Children NHS Foundation Trust
      Londinium, England, United Kingdom
  • 2005
    • University of California, Davis
      • Department of Radiation Oncology
      Davis, CA, United States
  • 2001
    • WWF United Kingdom
      Londinium, England, United Kingdom
  • 1997
    • Cleveland State University
      Cleveland, Ohio, United States
  • 1990
    • Stanford Medicine
      Stanford, California, United States
    • University of Sussex
      • Centre for Genome Damage and Stability
      Brighton, England, United Kingdom
  • 1984–1986
    • Tulane University
      • Department of Medicine
      New Orleans, Louisiana, United States