Abstract 1381:
Prostate and pelvis radiotherapy using IMRT and ultra small superparamagnetic nano-particles to optimise dose to involved lymph nodes
Citation: European Journal of Cancer Supplements Volume 3, No. 2, October 2005, Page 399
N. van As1, A. Jackson2, S. Sohaib3, C. South4, E. Charles-Edwards4, S. Reinsberg4, M. Leach4, D. Dearnaley2
1Royal Marden Hospital and Institute of Cancer Research, Academic Department of Radiotherapy and Oncology, London, United Kingdom
2Royal Marden Hospital and Institute of Cancer Research, Department of Radiology, London, United Kingdom
3Royal Marden Hospital, Joint Department of Radiotherapy Physics, London, United Kingdom
4Royal Marden Hospital and Institute of Cancer Research, CRUK Clinical MR Research Group, London, United Kingdom
Purpose:
To demonstrate how ferumoxtran (Sinerem) enhanced MRI may help to define the clinical target volume for a lymph node boost with intensity modulated radiotherapy (IMRT) in patients with prostate cancer and pelvic nodal involvement.
Patients and methods: As part of an ongoing phase I dose escalation trial, patients with prostate cancer and either a high risk of, or with overt pelvic nodal involvement are treated with 3 years of androgen deprivation and radiotherapy to the prostate (70 Gy) and pelvic lymph nodes (60 Gy) using an IMRT technique.
Overtly involved lymph nodes are boosted with a further 5 Gy.
Two patients with prior suggestion of pelvic nodal involvement radiologically, underwent MRI before and after administration of the ultrasmall superparamagnetic iron oxide (USPIO) contrast agent ferumoxtran (Sinerem®, Guerbet, Paris, France).
A novel flat top couch insert was used for MRI scanning to give better comparability with the planning CT scan. The MR images were used in conjunction with the planning CT to define the nodal boost volume.
Results:
Pre-treatment imaging had demonstrated suspicious lymph node enlargement in both obturator regions in one patient and the pre-sacral region in the other.
At the time of planning CT and ferumoxtran contrasted MRI, each patient had received androgen deprivation for 12 months. For the first patient, the radiotherapy planning CT scan showed probable lymph nodes at the previously noted sites, with the left obturator node measuring 8 mm in its short axis diameter. MRI following ferumoxtran showed signal retention typical of malignant infiltration at the sites of previously suspected lymphadenopathy, whereas there was the expected signal loss due to uptake of USPIO contrast in other nodal areas. Fig 1a and 1b show the pre and post ferumoxtran MR images respectively for the first patient.
A suspicious lymph node in the left obturator region is arrowed. The MR images facilitated segmentation of the suspicious lymph nodes using co-registration with the radiotherapy planning CT in the first patient, and with reference to bony anatomical landmarks in the second. A radiotherapy boost dose was then delivered to the sites of lymphatic involvement using an IMRT technique. Fig 1c shows the radiotherapy dose distribution for the first patient at the level of the involved lymph node in the left obturator region.
Fig. 1
Discussion: MR scanning pre and post ferumoxtran at the time of the radiotherapy planning scan can provide clarification of pelvic lymph node status in patients with suspicious radiological findings at presentation. Such MRI images can be co-registered with the planning CT in order to achieve more precise target definition.
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