Nuclear Medicine Physics Lecture Notes PDF

Nuclear Medicine Physics Dr Mohammed Saeed Alqahtani Lecture 5 Nuclear Oncology 2 Background ▪ Nuclear medicine has a major role in the management of malignant tumors. ▪ With the developments toward molecular imaging and the advancement of equipment used for imaging particularly after combining the...

Nuclear Medicine Physics Dr Mohammed Saeed Alqahtani Lecture 5 Nuclear Oncology 2 Background ▪ Nuclear medicine has a major role in the management of malignant tumors. ▪ With the developments toward molecular imaging and the advancement of equipment used for imaging particularly after combining the nuclear medicine instruments with morphologic modalities, it has even become a more integral part of management protocols. ▪ This role includes detection of malignant tumors, staging and restaging of the disease, early detection of recurrence, evaluation of the response to therapy, and prediction of the prognosis. ▪ Additionally sentinel node identification and localization for biopsy is another important use of nuclear medicine to help plan the most suitable management for several tumors. 3 Background → The main tumor imaging radiopharmaceuticals can be summarized as shown in the following table: Nonspecific agents Specific agents 67Ga 131I /123I 201TI 111In / 99mTc - Octreotide 99mTc - Sestamibi Monoclonal antibodies 99mTc - MDP 131I /123I 18F MIBG - FDG 4 Clinical Uses ▪ Diagnosis of Tumors ▪ Pretreatment staging of malignant disease ▪ Detection of residual or recurrent disease ▪ Evaluating response to therapy ▪ Radiotherapy planning ▪ Sentinel lymph node localization 5 Diagnosis of Tumors ▪ Nuclear medicine helps in the detection and characterization of certain tumors. Examples include evaluation of nodular thyroid disease as nodules that may be malignant. ▪ Scintimamography is another example used in selected patients when mammography is not conclusive. It is a simple procedure using intravenous injection of 99mTc MIBI followed by early and delayed imaging of the breasts and can indicate the nature of visualized lesions. ▪ Positron emission mammography (PEM) is recent being used in such cases. 6 Diagnosis of Tumors Negative radionuclide mammography study 7 Diagnosis of Tumors Focal accumulation of 99mTc MIBI in the right breast (arrow) proven to be cancer 8 Diagnosis of Tumors ▪PET/CT is also increasingly used for managing many types of cancer including detection. ▪Evaluation of the nature of solitary lung nodule and, in certain cases, of suspected breast cancer and tumor detection in cases with unknown primary are examples. 9 Diagnosis of Tumors Solitary lung nodule with high FDG activity (arrow) indicating malignancy 10 Diagnosis of Tumors 18F FDG-PET/CT study showing primary tumor in the right breast (solid arrow) and foci of lymph node involvement (open arrow) 11 Staging of Malignant Disease ▪ Staging of cancer depends on the size of the primary neoplasm, its extent to regional lymph nodes, and the presence or absence of metastasis. ▪ Accurate staging of malignant lesions at the time of initial presentation is of utmost importance to provide appropriate management for a particular patient. 12 Staging of Malignant Disease ▪ Overstaging can inappropriately deprive a patient from receiving curative treatment such as surgery. ▪ On the other hand understaging can subject a patient to undergo futile but drastic treatments that can even increase the morbidity and mortality (e.g. pneumonectomy in lung cancer) without any increase in the chance of cure. ▪ Imaging plays a significant role in staging. Bone imaging using 99mTc MDP and 18F has established value in detecting metastatic bone disease. ▪ Similarly, several radiopharmaceuticals are used in staging and follow-up of neuroendocrine tumors. 13 Staging of Malignant Disease ▪ Although the ideal staging is a microscopic process, many times it is not possible to biopsy each and every lesion to find out whether they are malignant or not. ▪ Nuclear medicine procedures, especially 18F FDG-PET, have a higher degree of accuracy compared with CT or MRI alone in staging tumors particularly lymph node involvement. ▪ The accuracy of CT in staging mediastinal disease in lung cancer as an example is approximately 70 %; MRI is slightly higher at around 80 %, while 18F FDG accuracy is better than 90 %. 14 Detection of Residual or Recurrent Disease ▪ The role of identifying viable tumors by imaging is increasing because of the problems encountered by MRI and CT, especially after surgical, radiation, or chemotherapy treatment in differentiating post-therapy changes from residual viable tumor tissue, local recurrence, or necrosis. ▪ As a result different radiopharmaceuticals play an important role in different malignancies and for detecting recurrence. ▪ PET, and if not thalium-201, helps in detecting tumor recurrence and in differentiating tumor recurrence f necrosis as post-therapy changes that is difficult to differentiate based on CT or MRI. 15 Detection of Residual or Recurrent Disease Baseline (a) and follow-up (b) F-18-FDG-PET/CT studies of a 21-year-old man with Hodgkin’s lymphoma. The follow-up shows recurrent tumor at multiple lymph nodes and spleen 16 Evaluating Response to Therapy ▪ The role of identifying viable tumors by imaging is increasing because of the problems encountered by MRI and CT, especially after surgical, radiation, or chemotherapy treatment in differentiating post-therapy changes from residual viable tumor tissue, local recurrence, or necrosis. ▪ As a result different radiopharmaceuticals play an important role in different malignancies and for detecting recurrence. ▪ PET, and if not thalium-201, helps in detecting tumor recurrence and in differentiating tumor recurrence f necrosis as post-therapy changes that is difficult to differentiate based on CT or MRI. 17 Evaluating Response to Therapy ▪ Patients can respond differently to the same treatment protocol and accordingly individualization of therapy should be more appropriate. ▪ However, as tumors and their hosts are heterogeneous, there are many crucial secondary problems related to the individualization of therapy. ▪ The most important element in individualization of therapy is to be able to rapidly assess whether a chosen treatment strategy is effective. 18 Evaluating Response to Therapy ▪ Tumor volume changes observed during follow-up CT or MRI studies in principle can be used for evaluation of response to antitumor therapy. However, it is not early enough before the patient develops considerable toxicity and side effects from the prescribed chemotherapy. ▪ Radiopharmaceutical agents like Gallium in lymphoma and FDG in many tumors such as Lymphoma, lung, head and neck cancer, breast cancer and others have shown good results to predict response to a treatment regimen as early as after 1–3 cycles of chemotherapy. 19 Evaluating Response to Therapy Ga-67 study (a) in a patient with non-Hodgkin’s lymphoma. Follow-up study (b) shows clearly an excellent response to chemotherapy evidenced by clearing of the foci of uptake noted in the first pretherapy study 20 Radiotherapy Planning ▪ CT has a high diagnostic ability by visualizing lesion morphology and by providing the exact localization of sites but lacks the information of the functional status. Whereas, PET with 18F-FDG provides information about the metabolism and viability of the lesions but fails to provide precise topographic localization. 21 Radiotherapy Planning ▪ Fused images from FDG-PET and CT provides valuable information resulting in more accurate delineation of normal tissues from tumor-bearing areas at high risk for recurrence compared with CT alone and PET/CT can improve the therapeutic window for radiation therapy. ▪ Image fusion is also reported to increase the confidence of the radiation oncologist while drawing target volumes and thereby, reduces the interobserver variation. 22 Sentinel Lymph Node Localization ▪ This is relatively a recent trend for identifying the sentinel node(s) which represents the first drain for the primary tumor and is particularly used in breast Cancer, Cutaneous Melanoma, Squamous Cell Carcinoma of Head and Neck, and colorectal cancer. ▪ Tracer (99mTc radiolabeled particles) is injected into a specific location based on tumor type, and they are retained in the lymph nodes. ▪ Radioactive sentinel nodes can be detected using imaging with a gamma camera and/or a gamma probe at surgery. 23 Sentinel Lymph Node Localization a b (a) FDG-PET pretherapy study of a patient with non-Hodgkin’s lymphoma (b) Follow-up study showing favorable response to therapy with clearing of the uptake in multiple foci in the chest and abdomen 24 Sentinel Lymph Node Localization Initial (a) and follow-up (b) F-18 FDG of a patient with osteogenic sarcoma in the right distal femur (arrow) showing decreasing uptake in the follow-up study after chemotherapy indicating favourable response to therapy 25 Sentinel Lymph Node Localization Initial (a) and follow-up (b) F-18 FDG of a patient with osteogenic sarcoma in the right distal femur (arrow) showing decreasing uptake in the follow-up study after chemotherapy indicating favourable response to therapy 26 Sentinel Lymph Node Localization (a) Sentinel node visualization (arrow) in a patient with breast cancer. (b) an example of a gamma probe which is used during surgery for localization with no need for imaging 27 Sentinel Lymph Node Localization ▪ Although sentinel node imaging does not image the cancer, it can identify the lymph node/nodes where the primary tumor drains. Excision followed by immunohistological staining of the sentinel node can identify micrometastases. ▪ At the present time, sentinel lymph node localization technique is the most acceptable alternative to routine total node dissection, such as axillary dissection in breast cancer. 28 29 Further Reading 1. Bahl S, Alavi A, Basu S, Czerniecki BJ (2009) The role of PET and PET/CT in the surgical management of breast cancer: a review. PET Clin 4:277–287 2. Eubank WB, Lee JH, Mankoff DA (2009) Disease restaging and diagnosis of recurrent and metastatic disease following primary therapy with FDG-PET imaging. PET Clin 4:299–312 3. Francis IR, Brown RKJ, Avram AM (2005) The clinical role of CT/PET in oncology: an update. Cancer Imaging 5:S68–S75 4. Jana S, Abdel-Dayem HM (2006) Basis of tumor imaging; scintigraphic and pathophysiologic correlation. In: Elgazzar AH (ed) Pathophysiologic basis of nuclear medicine, 2nd edition. Springer, Berlin-New York 30