PET Applications in Oncology 2015/2016 الدكتور قصي المقبل أخصائي الطب النووي- أستاذ مشارك كلية الطب-جامعة العلوم والتكنولوجيا الأردنية

Types of Radiation Particulate: Emission of beta particles (electrons) Negative electrons (regular electrons) Positive electrons (positrons) Photonic (electromagnetic) : gamma ray and x-ray Emission of photons (gamma ray or x-ray)

Positron emission 18 18 e + F O v + + 9 8

Beta particles Negatron: Negatively charged electron (beta -). It is a regular electron. Positron: Positively charged electron (beta +). Positron interacts with an electron in a process called annihilation. This results in the total destruction of positron and electron and release of two photons in opposite directions (co-incidence event).

Positron interaction: annihilation reaction The important and recognizable feature of positron decay is annihilation radiation. A positron will lose its kinetic energy through ionization and excitations by collision with electrons a similar fashion to a beta particle. A positron cannot exist at rest, and therefore when it has expended all its kinetic energy it combines with an electron and their mass is converted into energy in the form of two 0.511 MeV gamma-rays 1800 apart. For this form of decay to occur, a minimum energy of 1.022 MeV is required, any excess energy being given to the positron.

Coincidence Detection g1 Simultaneous detection of the two photons in opposite directions is the basis of “coincidence detection and coincidence imaging. Although most of the annihiliation photons will not be detected, some will remain in the plane of the detecotr ring, and 2 detectors hit, yeild electronic signals. Simultaneous pulses from 2 detectors indicate that the event occurred somewhere along the path between them. The path is referred to as the line of response (LOR) The number of coinidence events between two detectors indicates how much activity there was along the LOR. g2 Coincidence event detected in ring PET scanner

Coincidence Detection To detect the co-incidence (two gamma rays), a special scanner is needed. The scanner is designed in away that several detectors are arranged around the gantry. Each detector is linked electronically with other detectors as shown.

Radio-labeling of Glucose with radioactive Flourine-18

FDG The main application of PET scanning is in staging of cancer. Theoretically, cancer and its metastatic lesions have high metabolic rate. This means that glucose consumption is high. Glucose is labelled with F18 (positron emitter). O is removed and F18 is inserted instead resulting in FDG (Flourodexyglucose).

PET defined: Positron Radionuclide imaging using “unconventional” positron emitting radiopharmaceuticals Emission Detection of radiation energy emitted from the patient rather than transmitted through the patient Tomography Computer generated 3 dimensional images of the radionuclidic distribution within the patient

PET/CT Scanner

PET/CT scanner PET scanner is combined with CT scanner CT image is obtained first followed by PET image. CT image is obtained with low dose x-ray and no contrast. CT image is fused with PET image for anatomical correlation (lesion localization). CT image in PET/CT is a non-diagnostic image.

Normal PET Scan The following structures takes-up or accumulate FDG (physiologic uptake): brain, salivary glands, heart, liver, spleen, bowel, kidneys, urinary bladder and bone skeleton. Brain cortex takes significant amount of FDG which makes it difficult to see abnormally hot lesions. Hence, MRI is better than PET in detecting brain metastasis.

Normal PET scan

Normal PET/CT Scan PET scan CT scan PET/CT scan

Abnormal Patterns Hot lesions due to malignancy. Hot lesions due to inflammatory process. Hot lesions due to acute infection.

Abnormal PET scan

PET Indications in Oncology Up-staging or down-staging of cancer when clinically indicated. Differentiation of scar from residual disease. ? recurrent cancers (restaging). Follow-up of therapy (radio-chemotherapy). Radiotherapy mapping.

Overview Typically, the threshold for lesion detection by PET scan is approximately 6 mm and bigger. Use of PET imaging in tumor staging results in a change of therapy in as many as 25% to 50% of patients Small lung metastases are best identified by CT scan.

Radiotherapy Planning PET imaging can be of considerable value in planning radiation therapy, especially when tumor anatomy and metabolism are mapped by using PET/CT.

Tumor Mapping

Solitary Lung Nodule The sensitivity and specificity of PET for differentiating benign from malignant causes for solitary pulmonary parenchymal nodules that are greater than 1 cm is about 95% and 80%, respectively.

SPN

SPN False-positive studies may occur in sarcoidosis, tuberculosis, and fungal infections. False-negative studies may be seen in carcinoid tumor, a bronchioalveolar cancer, or a well-differentiated adenocarcinoma.

Small Lung Nodule Follow by CT

Lung Cancer Staging of non-small cell lung cancer. Assessment of recurrence. Monitoring therapy. Assessment of pleural malignancy.

Pleural Effusion PET can be helpful in evaluating patients presenting with pleural effusions by distinguishing malignant from benign effusions with an accuracy of 90%.

Malignant Pleural Effusion

Lymph Nodes PET scan is superior to CT scan for evaluation of hilar and mediastinal lymph nodes. Surgical resection of a primary lesion is often possible with ipsilateral, hilar, and mediastinal lymph node involvement. But disease in the contralateral, hilar, and mediastinal nodes usually dictates nonsurgical treatment.

Ipsilateral LNs

Distant Metastasis PET is better than CT scan and bone scan for detecting distant metastases.

Mets: mediastinum, liver and bone

Local Recurrence In the postsurgical patient, PET can reliably differentiate postsurgical scarring from metabolically active recurrent tumor.

Recurrent NSCLC

Colorectal cancer PET is superior to CT in detecting distant metastases, both nodals and extranodal including liver metastases. PET plays an important role in the selection of patients for curative resection of isolated hepatic metastases by determining the presence or absence of coexisting extrahepatic metastases.

Metastatic Pelvic LN

Multiple Liver metastases

Colorectal Cancer Recurrence PET is useful for differentiating postsurgical and radiation change from recurrent disease, especially in the pelvis and presacral space. PET is valuable in cases in which there is a rising CEA titer and no obvious abnormality on CT.

Recurrent rectal cancer (presacral)

Lymphoma Impact on staging: 44% of the patients Impact on management: >60% of the patients. PET is accurate in nodal and extra-nodal disease. PET assesses response to treatment. PET can detect residual disease.

Lymphoma-nodal and extra-nodal disaese (spleen)

Positive Pre-chemotherapy and negative post-chemotherapy (cervical lymphoma)

Residual Disease Post-Chemotherapy

Esophageal Cancer Distant metastasis: PET is the single most accurate noninvasive imaging tool for detecting metastasis. PET is the best imaging tool for local recurrence.

Metastatic esophageal cancer

Head and Neck Cancer PET is more accurate for cervical nodal disease and distant mets than is diagnostic CT. PET is the best imaging tool in local recurrence vs scar.

Metastatic LN in Head and Neck Ca.

Breast Cancer Staging and re-staging of locally advanced disease including inflammatory breast cancer. Staging of young patients. Post-chemotherapy evaluation of metastatic disease.

Breast ca bone mets

Pre-chemotherapy PET Post-chemotherapy PET