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Slackers Radiation Oncology Fact Stack Mike Ori Disclaimer • These represent my understanding of the subject and have not been vetted or reviewed by faculty. Use at your own peril. • I can’t type so below are common missing letters you may need to supply • erl • I didn’t use greek letters because they are a pain to cut and paste in. • What are the five stages of cancer diagnosis and therapy • • • • • Screening Diagnosis Staging Therapy Follow-up • What is the most successful use of radiology for screening • Mammography • What is one area where radiology techniques have not been successful in screening • Ultrasound screening of the prostate • Explain the role of contrast kinetics in MRI • Wash-in and wash-out times help differentiate benign and malignant • Normal tissue tends to have slower wash-in and wash-out kinetics than tumor. • What is a sestamibi scan • Use of 99mTc-sestamibi to identify areas of angiogenesis and tumor. • Compare sestamibi scans to MRI • • • • Uses ionizing radiation Not as available as MR Faster Cheaper • What is octreotide scanning • A somatostatin-like compound that can interact wit somatostatin receptors on the surface of cells. Some types of cancer (neuroendocrine mostly) are notable for such receptors. • Compare octreotide scanning to MRI/CT • Sometimes shows mets when other modalities don’t • Poorer anatomic localization than other modalities • Can be used to indicate treatment with yttrium 90-octrotide • What is MRI spectroscopy • The use of the MRI machine to perform spectroscopic analysis of tissue to look for marker compounds that indicate growth or abnormal metabolism. • Rarely used capability due to reimbursement • What radiographic techniques can be used to stage cancer • CT – The workhorse • PET – Especially when combine with CT • MRI – Increasing in use. Dominant in some areas • Radionucleotide bone scans – For skeletal mets • Ultrasound – Rarely • How does PET scanning work • Fluoro-D-Glucose is injected into the body. Hot spots appear in any tissue actively metabolizing glucose. This includes tumors but also inflammed and regnerating areas. • For what cancers is PET scanning approved • • • • • • • • • Non-small cell lung cancer Colorectal cancer Melanoma Lymphoma Head and neck cancer (not thyroid or CNS) Esophageal Cervical Breast monitoring and restaging Thyroid restaging • Explain radionucleotide bone scans • 99mTC-methylene diphosphonate is injected into the body and incorporated into hydroxyapatite in the bone by osteoblasts. Thus areas of bone growth are visible. • Needs follow-up anatomic imaging • What is the role of radioactive iodine in the treatment of thyroid neoplasia • RAI is used post surgery to destroy remaining thyroid tissue. • What is image guided therapy • The use of radiology techniques in the performance of treatment • Intra arterial chemo catheter • Embolization – Simple – Chemo • Alcohol ablation/cryotherapy • RF ablation • Focused ultrasound • What is RECIST • Response evaluation criteria in solid tumors is an heuristic used to quantify the change in a solid tumor over time. – CR = complete response – PR = partial response, 30% decrease – PD = progressive disease, 20% increase – SD = stable disease • What type of radiation is used in radiotherapy • Ionizing radiation such as x-rays, gamma rays, electrons, protons • What device produces the radiation used most predominantly in the US • The linear accelerator or linac • How many linacs can fit on the head of a pin? • None. • Differentiate teletherapy from brachytherapy • Teletherapy uses a radiation beam generated by source remote to the patient. This is your classic sci-fi death ray. • Brachytherapy places an intrinsically radioactive substance in close approximation to the target tissue. • What is linear energy transfer • The amount of energy transferred per unit length of track • What is the bragg peak • The point of maximum energy release along a track. • Differentiate directly ionizing from indirectly ionizing radiation • Directly ionizing radiation has sufficient energy to directly disrupt the atomic structure of DNA. Protons. • Indirectly ionizing radiation creates free radicals that damage DNA. X-rays. • What is the primary method of cell killing caused by radiation • Double stand DNA breaks that are improperly repaired. • Why are oxygenated cells more susceptible to radiation than are hypoxic cells • The ionizing process generates free electrons which are taken up by oxygen to generate oxygen radicals which attack DNA. In hypoxic conditions, less oxygen is available to generate free radicals. • Which phase of the cell cycle is sensitive to radiation? Which is resistant? • G1/M are sensitive • S is resistant • What factors influence the survival of a radiated cell? • • • • Position in the mitotic cycle Molecular checkpoint activation Hypoxia Repopulation • Describe how a 50Gy dose of radiation is delivered to patients • The dose is usually fractionated into multiple doses of ~2Gy. These are then delivered over the course of many days until the total prescription is delivered. • Describe image modulated radiation therapy • IMRT uses a multi-leaf collimator shape a radiation beam to limit exposure of adjacent structures. • List several benign diseases for which radiotherapy can be prescribed • Omas of the CNS – – – – • • • • • Schwanoma Chordoma Meningioma Pituitary adenoma AVM Trigeminal neuralgia Pterygium Heterotopic ossification Trigeminal neuralgia