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Evaluation of MRI Distortion Correction for Use in Radiotherapy Treatment Planning
S38
Abstracts / Clinical Oncology 23 (2011) S1eS58
in weekly fractions of 6 Gy, to the whole breast except in four cases with small low grade lesions who were treated entirely with partial breast irradiation. All tumours were clinically regressing after 30 Gy, and a ‘boost’ to the primary site was given, using the same fractionation, for three to five further treatments. Response and skin reactions were assessed clinically weekly during radiotherapy, and response then reassessed between 4 and 8 weeks after completion of radiotherapy, and at varying intervals thereafter. Results: All showed significant responses, four complete response (CR) and four partial response (PR); no extensive grade 3 skin reactions were seen in healthy skin at sites away from the tumour. During subsequent follow-up, admittedly short, no local progression has been noted, but three patients died of other causes. This gives an actuarial 9-month ‘clinical benefit’ (as used in endocrine response assessment: PR or CR maintained, no progression) of 100%. Patients seemed ostensibly happy with the weekly schedule, with very few missed appointments despite the ardours for such patients of hospital attendance. Conclusions: This is a small series reporting a treatment that is only appropriate for a very small number of patients, but our encouraging preliminary findings, in terms of response, toxicity and social acceptability, confirm other early reports, and suggest that such a schedule merits further evaluation.
P37 VMAT versus IMRT d a Question of Modulation L. Hammond *, K. Brown y, S. Smith y, G. Lamb y * Department of Physics, University of Strathclyde, Glasgow, UK y Beatson West of Scotland Cancer Centre, Department of Clinical Physics and Bio-engineering, Gartnavel General Hospital, Glasgow, UK Aim: Patient specific pre-treatment quality assurance (QA) overhead for volumetric modulated arc therapy (VMAT) may limit patient numbers due to both machine capacity and physicist time. The aim of this study is to determine if QA failures can be predicated. Method: Eight head and neck patients were retrospectively planned using the Eclipse Treatment Planning System (Version 8.6.15) (Varian Medical Systems) with both VMAT and conventional intensity modulated radiotherapy (IMRT). Plans were assessed to determine if there was any correlation between plan properties and results from pre-treatment QA. Pre-treatment QA was performed using MapCHECK and ArcCHECK (Sun Nuclear Corporation) for IMRT and VMAT, respectively. Plan properties investigated were: PTV conformity index; monitor units (MU); distance between and volume of planning target volume (PTV) and critical structures; avoidance sectors; gradient of dose from PTV to spinal cord; and leaf gap. Results: VMAT plans with avoidance sectors and with MUs greater than 600 produced a gamma analysis pass rate (3%, 3 mm) between 88 and 96%. Plans with no avoidance sectors and lower MU produced a pass rate between 96 and 100%. IMRT plans produced a pass rate of 95% and above. PTV volume, distance from critical structures, PTV conformity index and gradient of dose from PTV to spinal cord produced no correlation with gamma analysis pass rate. VMAT plans with an average of 48% of leaf gaps less than 20 mm had gamma analysis pass rates between 88 and 96%. Plans with an average of 29% of leaf gaps less than 20 mm had gamma analysis pass rates above 96%. Conclusion: A requirement for pre-treatment QA can be predicted at the planning stage by assessing the number of MU, presence of avoidance sectors and the proportion of small leaf gaps.
P38 Evaluation of MRI Distortion Correction for Use in Radiotherapy Treatment Planning E.C. Harron *, M.J. Firbank y, J. McKenna z, H.M. McCallum *, R. Mohanraj * * Regional Medical Physics Department, Freeman Hospital, Newcastle upon Tyne, UK y Wolfson Research Centre, Newcastle University, Campus for Ageing and Vitality, Newcastle upon Tyne, UK z Northern Centre for Cancer Care, Freeman Hospital, Newcastle upon Tyne, UK Aims: The aim of this work was to investigate the distortion correction feature of a dedicated Siemens Espree 1.5 T MRI scanner for use in radiotherapy treatment planning. This application of MRI requires a high degree of
spatial accuracy to allow fusion of CT and MRI images to improve tumour delineation. Commercially available phantoms did not satisfy requirements as they did not allow testing over a sufficiently large field of view, and needed repositioning between scans to image different planes. Method: A 30 cm cube was constructed from LegoÔ arranged in a regular pattern in nickel sulphate solution, which permitted imaging in orthogonal planes without repositioning. Clinical sequences were used to acquire images of the phantom, and the Siemens 2D and 3D distortion correction applied. Acquisitions were repeated with a custom-made couch top and coil support to check these did not cause further distortion. Distortion remaining after correction was quantified using the radiotherapy simulation software currently employed for clinical image fusion, comparing distances measured on MRI to known physical dimensions. Results: The 3D distortion correction was found to provide the best spatial accuracy. It was established that the distortion correction was applied symmetrically in the bore, and so clinical images needed to be centred on the magnet isocentre for the distortion correction to be symmetrically applied across the images. The dimensional accuracy for axial, sagittal and coronal images was found to be 3 mm over 240 mm distance, for slices positioned no more than 100 mm longitudinally from the magnet isocentre. The custommade couch top and coil supports were not found to adversely affect the spatial accuracy of the corrected images. Conclusion: Since LegoÔ is manufactured to a high degree of accuracy and can be easily visualised, this enabled the phantom to be used for quantification of the distortion correction feature of the MRI scanner.
P39 Late Onset Bowel Dysfunction Post-pelvic Radiotherapy: a National Survey of Current Practice of Gastroenterologists C. Henson *, S.E. Davidson *, R.P. Symonds y, R. Swindell z, H.J. Andreyev x * Department of Clinical Oncology, The Christie NHS Foundation Trust, Manchester, UK y Department of Clinical Oncology, Leicester Royal Infirmary, Leicester, UK z Department of Statistics, The Christie NHS Foundation Trust, Manchester UK x Department of Gastroenterology, Royal Marsden Hospital, London, UK Background and purpose: About 17 000 patients receive treatment with radical pelvic radiotherapy annually in the UK [1]. Studies suggest that up to 50% develop significant gastrointestinal symptoms after treatment [2e4]. The Department of Health estimates that £40 million is wasted on ineffective treatments annually in this patient group. We aimed to determine the current practice of British gastroenterologists in regards to chronic bowel dysfunction post-pelvic radiotherapy. Materials and methods: A questionnaire was developed and sent to all 866 gastroenterologists in the UK. This was resent up to a maximum of five times. Results: In total, 165 (20%) gastroenterologists responded. Several paradoxes were identified by this survey. Most gastroenterologists surveyed (61%) only see one to four patients annually with bowel dysfunction post-pelvic radiotherapy, with only 3% seeing more than 20 per year. Fifty-eight per cent of gastroenterologists consider themselves either ‘confident with basic cases’ or ‘confident in all cases’. Fifty-nine per cent of those surveyed think a gastroenterologist with a specialist interest should manage these patients, but only 29% think a specific service is required for this patient group. A third (34%) rate the current service as ‘poor’ or ‘fails to meet the needs of patients’. Only 18% rate the treatments currently available as effective ‘often’ or ‘most of the time’, with 58% stating that they are only effective ‘sometimes’. Only 43% receive referrals directly from clinical oncologists. Conclusions: Clinical oncologists recognise chronic bowel dysfunction as a significant problem, yet most gastroenterologists are referred few patients. Both this and the low response rate to this survey may reflect the perception that current services are inadequate and inappropriate widespread therapeutic nihilism. References [1] West CM, Davidson SE. Measurement tools for gastrointestinal symptoms in radiation oncology. Curr Opin Support Palliat Care 2009;3:36e40. [2] Andreyev J. Gastrointestinal symptoms after pelvic radiotherapy: a new understanding to improve management of symptomatic patients. Lancet Oncol 2007;8:1007e1017.
Abstracts / Clinical Oncology 23 (2011) S1eS58
in weekly fractions of 6 Gy, to the whole breast except in four cases with small low grade lesions who were treated entirely with partial breast irradiation. All tumours were clinically regressing after 30 Gy, and a ‘boost’ to the primary site was given, using the same fractionation, for three to five further treatments. Response and skin reactions were assessed clinically weekly during radiotherapy, and response then reassessed between 4 and 8 weeks after completion of radiotherapy, and at varying intervals thereafter. Results: All showed significant responses, four complete response (CR) and four partial response (PR); no extensive grade 3 skin reactions were seen in healthy skin at sites away from the tumour. During subsequent follow-up, admittedly short, no local progression has been noted, but three patients died of other causes. This gives an actuarial 9-month ‘clinical benefit’ (as used in endocrine response assessment: PR or CR maintained, no progression) of 100%. Patients seemed ostensibly happy with the weekly schedule, with very few missed appointments despite the ardours for such patients of hospital attendance. Conclusions: This is a small series reporting a treatment that is only appropriate for a very small number of patients, but our encouraging preliminary findings, in terms of response, toxicity and social acceptability, confirm other early reports, and suggest that such a schedule merits further evaluation.
P37 VMAT versus IMRT d a Question of Modulation L. Hammond *, K. Brown y, S. Smith y, G. Lamb y * Department of Physics, University of Strathclyde, Glasgow, UK y Beatson West of Scotland Cancer Centre, Department of Clinical Physics and Bio-engineering, Gartnavel General Hospital, Glasgow, UK Aim: Patient specific pre-treatment quality assurance (QA) overhead for volumetric modulated arc therapy (VMAT) may limit patient numbers due to both machine capacity and physicist time. The aim of this study is to determine if QA failures can be predicated. Method: Eight head and neck patients were retrospectively planned using the Eclipse Treatment Planning System (Version 8.6.15) (Varian Medical Systems) with both VMAT and conventional intensity modulated radiotherapy (IMRT). Plans were assessed to determine if there was any correlation between plan properties and results from pre-treatment QA. Pre-treatment QA was performed using MapCHECK and ArcCHECK (Sun Nuclear Corporation) for IMRT and VMAT, respectively. Plan properties investigated were: PTV conformity index; monitor units (MU); distance between and volume of planning target volume (PTV) and critical structures; avoidance sectors; gradient of dose from PTV to spinal cord; and leaf gap. Results: VMAT plans with avoidance sectors and with MUs greater than 600 produced a gamma analysis pass rate (3%, 3 mm) between 88 and 96%. Plans with no avoidance sectors and lower MU produced a pass rate between 96 and 100%. IMRT plans produced a pass rate of 95% and above. PTV volume, distance from critical structures, PTV conformity index and gradient of dose from PTV to spinal cord produced no correlation with gamma analysis pass rate. VMAT plans with an average of 48% of leaf gaps less than 20 mm had gamma analysis pass rates between 88 and 96%. Plans with an average of 29% of leaf gaps less than 20 mm had gamma analysis pass rates above 96%. Conclusion: A requirement for pre-treatment QA can be predicted at the planning stage by assessing the number of MU, presence of avoidance sectors and the proportion of small leaf gaps.
P38 Evaluation of MRI Distortion Correction for Use in Radiotherapy Treatment Planning E.C. Harron *, M.J. Firbank y, J. McKenna z, H.M. McCallum *, R. Mohanraj * * Regional Medical Physics Department, Freeman Hospital, Newcastle upon Tyne, UK y Wolfson Research Centre, Newcastle University, Campus for Ageing and Vitality, Newcastle upon Tyne, UK z Northern Centre for Cancer Care, Freeman Hospital, Newcastle upon Tyne, UK Aims: The aim of this work was to investigate the distortion correction feature of a dedicated Siemens Espree 1.5 T MRI scanner for use in radiotherapy treatment planning. This application of MRI requires a high degree of
spatial accuracy to allow fusion of CT and MRI images to improve tumour delineation. Commercially available phantoms did not satisfy requirements as they did not allow testing over a sufficiently large field of view, and needed repositioning between scans to image different planes. Method: A 30 cm cube was constructed from LegoÔ arranged in a regular pattern in nickel sulphate solution, which permitted imaging in orthogonal planes without repositioning. Clinical sequences were used to acquire images of the phantom, and the Siemens 2D and 3D distortion correction applied. Acquisitions were repeated with a custom-made couch top and coil support to check these did not cause further distortion. Distortion remaining after correction was quantified using the radiotherapy simulation software currently employed for clinical image fusion, comparing distances measured on MRI to known physical dimensions. Results: The 3D distortion correction was found to provide the best spatial accuracy. It was established that the distortion correction was applied symmetrically in the bore, and so clinical images needed to be centred on the magnet isocentre for the distortion correction to be symmetrically applied across the images. The dimensional accuracy for axial, sagittal and coronal images was found to be 3 mm over 240 mm distance, for slices positioned no more than 100 mm longitudinally from the magnet isocentre. The custommade couch top and coil supports were not found to adversely affect the spatial accuracy of the corrected images. Conclusion: Since LegoÔ is manufactured to a high degree of accuracy and can be easily visualised, this enabled the phantom to be used for quantification of the distortion correction feature of the MRI scanner.
P39 Late Onset Bowel Dysfunction Post-pelvic Radiotherapy: a National Survey of Current Practice of Gastroenterologists C. Henson *, S.E. Davidson *, R.P. Symonds y, R. Swindell z, H.J. Andreyev x * Department of Clinical Oncology, The Christie NHS Foundation Trust, Manchester, UK y Department of Clinical Oncology, Leicester Royal Infirmary, Leicester, UK z Department of Statistics, The Christie NHS Foundation Trust, Manchester UK x Department of Gastroenterology, Royal Marsden Hospital, London, UK Background and purpose: About 17 000 patients receive treatment with radical pelvic radiotherapy annually in the UK [1]. Studies suggest that up to 50% develop significant gastrointestinal symptoms after treatment [2e4]. The Department of Health estimates that £40 million is wasted on ineffective treatments annually in this patient group. We aimed to determine the current practice of British gastroenterologists in regards to chronic bowel dysfunction post-pelvic radiotherapy. Materials and methods: A questionnaire was developed and sent to all 866 gastroenterologists in the UK. This was resent up to a maximum of five times. Results: In total, 165 (20%) gastroenterologists responded. Several paradoxes were identified by this survey. Most gastroenterologists surveyed (61%) only see one to four patients annually with bowel dysfunction post-pelvic radiotherapy, with only 3% seeing more than 20 per year. Fifty-eight per cent of gastroenterologists consider themselves either ‘confident with basic cases’ or ‘confident in all cases’. Fifty-nine per cent of those surveyed think a gastroenterologist with a specialist interest should manage these patients, but only 29% think a specific service is required for this patient group. A third (34%) rate the current service as ‘poor’ or ‘fails to meet the needs of patients’. Only 18% rate the treatments currently available as effective ‘often’ or ‘most of the time’, with 58% stating that they are only effective ‘sometimes’. Only 43% receive referrals directly from clinical oncologists. Conclusions: Clinical oncologists recognise chronic bowel dysfunction as a significant problem, yet most gastroenterologists are referred few patients. Both this and the low response rate to this survey may reflect the perception that current services are inadequate and inappropriate widespread therapeutic nihilism. References [1] West CM, Davidson SE. Measurement tools for gastrointestinal symptoms in radiation oncology. Curr Opin Support Palliat Care 2009;3:36e40. [2] Andreyev J. Gastrointestinal symptoms after pelvic radiotherapy: a new understanding to improve management of symptomatic patients. Lancet Oncol 2007;8:1007e1017.