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Principles of Radiaton Oncology. Diane Severin 2011. Radiation oncology is the specialty which uses various forms of radiation to treat cancer patients. 5 year program. Knowledge base includes CT and MRI based anatomy, clinical oncology, medical physics and radiobiology. Overview. History
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Principles of Radiaton Oncology • Diane Severin • 2011
Radiation oncology is the specialty which uses various forms of radiation to treat cancer patients. • 5 year program. • Knowledge base includes CT and MRI based anatomy, clinical oncology, medical physics and radiobiology.
Overview • History • Biology of Radiotherapy • Physics of Radiotherapy • Clinical Radiation Oncology
History of Radiotherapy • 1895 Wilhelm Roentgen described X-rays • 1898 Marie and Pierre Curie discovered radium. • 1901 first therapeutic use of radium for skin brachytherapy • 1903 first description of the effect of radiation on a lymphoma nodes • 1905 first description of sensitivity of seminoma to radiation
History of Radiotherapy • 1915 The atomic model by Ernest Rutherford and development of Xray tubes • 1951 first Cobalt unit in London, Ontario • 1952 first linear accelerator in Stanford, California • 1973 CT scanner invented by Hounsfield • 1990 first use of scanners and computers for IMRT
History of Radiotherapy • The early radiotherapy machines would deposit dose superficially and were limited by skin toxicity. • The development of linear accelerators that deposit dose deeper into tissues as well as three dimensional treatment planning systems has improved the ability to deliver dose while sparing normal tissues. • More than 1/2 of cancer patients receive radiotherapy at some point in their care.
Biology of Radiation • Radiation can be thought of as packets of energy in the form of photons (eg: Xrays) or particles (eg: protons, neutrons, electrons, alpha particles). • As they penetrate tissue they can cause ionization directly or indirectly. • Dose deposited is measured in gray(Gy) 1 Joule/kg. Older unit was rad 1/100 Gy or 1 cGy
Biology of Radiation Most damage is caused by hydroxyl
Biology of Radiation • Cell death from radiation is thought to be primarily due to DNA damage in the form of single strand and double strand breaks. • Particulate radiation such as alpha particles, neutrons, protons cause more ionizations and more double strand breaks than Xrays. • Normal tissue can repair damage better than cancer tissue.
Biology of Radiation • Biologic modifiers of the effect of radiation include: • Oxygen - If tumors are hypoxic there is less cell kill with radiation. Important to correct anemia. • Chemotherapy - can sensitize cells to radiation eg: cisplatin, 5fluorouracil, etoposide etc. • Radioprotectors - sulfhydryl compounds (amifostine) can protect cells from radiation. • Hyperthermia
Physics of Radiation • 1. External Beam Radiotherapy (sometimes called Teletherapy) • 2. Brachytherapy • 3. Radioisotope therapy eg: radioactive iodine
External Beam RT • 60Co delivers mega-voltage radiation (1.25 MeV) using radioactive material as the source of the gamma rays. • Linear accelerators produce x-rays and electrons which have high energies. They are mounted as gantries which can rotate 360 degrees in space around a treatment table. This is what is used now.
External Beam RT Linear accelerator
External Beam RT The spike ones are only in the states and Vancouver
External Beam RT • Stereotactic radiosurgery/radiotherapy is a technique that gives a highly conformal treatment with very small margins. Large often single doses are given. • Initially used for brain lesions it’s use is expanding to other parts of the body.
Brachytherapy • Brachytherapy is radiation treatment delivered from close range to tumors that can be accessed by interstitial, intracavitary or surface applicators. • Inside the applicators are radioactive materials that are encapsulated in cylinder or seed form. • The radioactive material decays with time releasing low energy particles or photons. • Must be on isolation because these people are radioactive
Brachytherapy • Dose drops off via the inverse square law which helps protect normal tissues. • Cesium 137, Iridium 192, iodine 125 are examples of isotopes used. • Cervix cancer, prostate cancer, uterine cancer are treated with brachytherapy.
Radioisotope Therapy • Iodine 131 is used in treatment of thyroid cancer. • Radiation safety precautions necessary as patients are radioactive. • Other radioisotope therapies include MIBG, octreotide, strontium etc.
Clinical Radiation Oncology (RO) • The ultimate goal of radiation therapy is to deliver a high dose to the target volume (tumor) while minimizing dose to the normal tissue.
Clinical RO • Multidisciplinary interactions are important ie: medical oncology, surgery, internal medicine, physics, nurses, rehabilitation, psychology and therapists. • Treatment given with curative intent for many sites: H&N, CNS, Lung, GI, breast, prostate, bladder, lymphoma, sarcoma, skin, gynecologic tumors. • Palliative treatment important for pain, bleeding, brain mets and obstructive symptoms.
Clinical RO • Process of Radiation Therapy • 1. Consultation with the radiation oncologist. • History and examination of the patient, education regarding type and stage of cancer, discussion of benefits and risks of therapy, consent for therapy.
Clinical RO • 2. Immobilization and CT simulation • Aquaplast shells, vac fix bags, tatoos • CT simulation is a scan obtained in the position the patient will be in for their treatment.
Clinical RO • 3. Treatment Planning • The gross tumor volume (GTV) is contoured by the radiation oncologist. • Meshing of CT sim scans with MRI scans or PET scans can help in volume definition.
Clinical RO • CTV is a margin around the GTV to account for potential locoregional subclinical extension of cancer cells. • It can include microscopic spread to lymph nodes. • Eg: the mesorectum, internal iliac, presacral and lower common iliac nodes are included in the CTV for rectal cancers
Clinical RO • PTV is the planning target volume. It is a volumetric expansion which accounts for organ motion as well as set up uncertainty. • ITV (internal target volume) is used in tumors in which a significant amount of variation in tumor position occurs eg: due to respiration. • 4D CT simulation is required for ITV definition
Clinical RO • Field Definition – The radiation oncologist can define fields to be treated. • If normal tissue constraints require it, more complex treatment planning can occur using intensity modulated radiotherapy (IMRT) or tomotherapy.
Clinical RO • 4. Therapy • Patients have daily treatments. They are in the radiation room 15 minutes or less and in the cancer institute 30 – 45 minutes total • In curative therapies, treatments are often fractionated ie: small doses per day for many days eg: 36 fractions/ 5days per week/ 7 weeks • They are assessed weekly by the radiation oncologist to ensure they are tolerating therapy
Clinical RO • Fractionation occurs to prevent late side-effects. • If treated palliatively for pain or other symptoms they are often given fewer fractions eg: 8 Gy in 1 fx, 20 Gy in 5 fx or 30 Gy in 10 fx. • Late side-effects are less of a concern due to survival time in these patients. Also the doses are lower and are tolerated by normal tissues.
Clinical RO • 5. Follow up • Following therapy follow up is arranged 6 – 8 weeks later for most patients. • Long term follow up depends on tumor type and chance of curative salvage if recurrence detected early. • Eg: colorectal cancer vs breast cancer
Clinical RO • Side-Effects of Therapy • Early side-effects occur within weeks of radiation therapy. (ONLY in radiated area.) • They occur in tissues with rapid cell turnover and are thought to occur due to depletion of the stem cells within that tissue. • Eg: tumor shrinkage, skin irritation/blistering, diarrhea
Clinical RO • Late side-effects of radiation occur months to years after radiation. • The incidence of late effects depends on the volume irradiated, the structure irradiated, total dose and most importantly fraction size. Ie: bigger doses per fraction lead to increased long term side-effects.
