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Flashcards in Introduction to Radiation Oncology Deck (14):

What is the role of radiation oncology and cancer treatment?

  • At a multidisciplinary tumor board, the patient’s case, diagnostic and staging procedures, and pathology is discussed, and in coordination with the other oncologist the best treatment strategy chosen
  • The role of the radiation oncologist (RO) is to:
    • provide an oncologic opinion at tumor board
    • discuss with the patient the rationale for treatment
    • the time frame of therapy
    • the potential acute and late side effects of treatment
    • assess the patient weekly during their treatments to manage acute side effects
    • follow them over the long-term to assess outcomes and address potential late side effects
  • The goal of radiation therapy is to precisely deliver a measured dose of radiation to the target volume while minimizing damage to adjacent healthy tissue
  • The aims are to:
    • eradicate tumor
    • minimize side effects
    • provide the patient with a high quality of life
    • prolong survival (depending on site and tumor)
    • and provide effective palliation from symptoms of cancer (in patients with metastatic and/or incurable disease)


Whats the difference between definitive, adjuvant, curative, and pallative uses of radiation in cancer treatment?

  • Definitive: RT may be the sole or major treatment modality
    • It can be given concurrently with chemotherapy therapy or alone
  • Adjuvant: RT may precede or follow surgical intervention (multi-modality therapy)
    • The goal of therapy is determined at the onset of treatment
  • Treatment is given with either curative or palliative intent.
  • Curative: There is loco-regionally confined disease with a probability of long-term survival after adequate therapy
    • Some side effects of therapy, although undesirable, are accepted in light of a chance of cure
    • Examples include:
      • A patient will early stage localized prostate cancer treated with radioactive seeds (Low Dose Rate (LDR) brachytherapy)
      • A patient with locally-advanced lung cancer that is un-resectable and treated with concurrent chemo-radiation
      • A patient with a large oral tongue cancer undergoes surgical resection of his tumor and neck nodes followed by concurrent chemo-radiation
  • Palliation: Disease is considered incurable and patients have symptoms that are causing discomfort or an impending condition that could lead to symptoms and affect quality of life
    • Lower tolerance for toxicity in this setting
    • Examples include:
      • Bone metastases that is causing pain in a patient with breast cancer
      • Invasion of the bladder by a prostate tumor that is causing hematuria
      • An asymptomatic patient with epidural disease in the spinal canal that could lead to spinal cord compression and cause paralysis


What are the major steps of radiotherapy?

  • Consultation:
    • The patient is seen by a radiation oncologist; a history is taken, a physical examination is performed, and laboratory and imaging studies are reviewed
    • The radiation oncologist and patient have a discussion about treatment options, radiotherapy, its process, benefits and toxicities
  • CT Simulation:
    • An immobilization device is crafted and patient positioning is optimized
    • Sometimes, radio-opaque markers or contrast are used
    • A CT scan is obtained
    • Motion management or 4D simulation may be added
    • Tattoos are placed
  • Planning and quality assurance:
    • The radiation oncologist delineates both target structures and normal tissues for avoidance
    • Constraints are set concerning optimal target coverage and normal tissue sparing
    • A radiation plan is created
    • This plan then undergoes a series of quality assurance checks by the physics team
  • Initiation of treatment:
    • The patient begins radiation therapy
    • The radiation oncologist checks all details before initiation
  • Monitoring on treatment:
    • Each patient is seen at least weekly in order to monitor and manage acute toxicity
  • Follow-up:
    • The patient is followed at regular intervals for years in order to monitor for recurrence and/or treatment-related toxicity
    • Surveillance imaging may be ordered


Describe the radiation physics employed in cancer treatment.

  • When radiation interacts with biologic material, the absorption of energy can lead to excitation (raising of an electron in at atom or molecule to a higher energy level without ejection of the electron) or ionization (sufficient energy is present to eject an electron)
    • Ionizing radiation releases enough energy to break strong chemical bonds, alter DNA and cause a biologic event
  • Radiation is administered to cells either in the form of photons (x-rays and gamma rays) or particles (protons, neutrons, and electrons).
  • X-rays (produced artificially by a machine and most commonly used for treatments) and gamma rays (produced by decay of radioactive isotopes) are ionizing radiation that have short wavelengths and thus higher frequency or large photon energy and are able to break chemical bonds and cause biologic effects
  • Radiation can be classified as directly or indirectly ionizing
    • Charged particles in general are directly ionizing
    • There is direct interaction with subcellular structures to produce chemical and biologic changes
    • Electromagnetic radiation is indirectly ionizing - radiation interacts with H20 and generates free radicals that then interact with subcellular structures


How does radiation kill cancer cells?

  • DNA is the principal target for the biologic effects of radiation
  • Ionizing radiation results in events such as:
    • base and sugar damage
    • single strand (SSB) breaks
    • double strand (DSB) breaks
  • Single strand breaks are repaired easily by using the opposite strand as a template
  • The generation of DSB causes important biologic endpoints such as cell death


How is radiation dose quantified and determined for cancer treatment?

  • The amount of radiation given is measured in gray (Gy)
    • One Gy is defined as the absorption of one joule of energy in the form of ionizing radiation, per kg of matter
  • The amount of radiation given depends on the intent of treatment and type and stage of cancer.
    • Generally doses in conventional fractionation are given at 1.8Gy to 2Gy per day
    • For curative cases of epithelial tumors, doses range from 60 to 80 Gy over 7 to 9 weeks
    • For radiosensitive tumors like seminomas and lymphomas, doses of 20 to 45Gy are given over 3 to 5 weeks
    • Palliative doses vary widely but in general are delivered over 1 to 4 weeks (20 to 40Gy) and can be given in conventional fractionation of 1.8Gy to 2Gy or larger fractions of 3Gy to 5Gy or in a single fraction
    • Some common palliative doses are 30Gy in 10 fractions over 2 weeks, 20Gy 5 fractions over 1 week, and 8Gy in a single fraction


What is fractionation, and why is it necessary?

  • Sparing of normal tissue:
    • Both malignant and normal cells are subject to the effects of ionizing radiation
    • Normal cells have the intact mechanism to detect and repair DNA breaks and mutations (repair of sublethal damage) between fractions and repopulate if sufficient time between fractions is present
    • Many malignant cells lack these molecular mechanisms and are preferentially targeted by the radiation
    • There is a tolerance to the dose that normal tissue can tolerate and this determines the maximum dose that be given during a course of treatment
  • Better efficacy of cell kill:
    • Dividing the dose into small fractions allows for tumors that are in a relatively radio-resistant phase of the cell cycle during treatment to cycle into a sensitive phase prior to delivery of the next fraction (reassortment)
    • Tumor cells that are acutely or chronically hypoxic (which renders them more radioresistant) may reoxygenate between fractions allowing for better cell kill


What are the pros and cons of extending treatment time with radiation in cancer treatment?

  • The advantages of prolonging treatment time are to spare early reactions for normal tissue and to allow for reoxygenation of tumors
  • Prolonging treatment time, however, can allow surviving tumor cells to proliferate during treatment
    • It is preferred to finish the RT course as prescribed within a set time frame once treatment has commenced


What is external beam radiotherapy (EBRT)? What is its clinical use?

  • The most common RT approach is to deliver RT from a source outside the patient (external beam RT).
  • Radiation is generated by Linear accelerators (LINACS), which, are found in all RT centers, or Cobalt-60 machines (via radioactive decay of Cobalt), which, are mostly obsolete in the US
    • In LINACS, electrons are accelerated and can exit the machine as an electron beam or strike a target to produce x-rays (photons), which are then directed at the target volume
    • The energies generated by LINACS range from 4 MV to 20 MV (megavolts)
      • Photons are most commonly used to treat cancers as they can penetrate deep into tissue
  • Electrons are used in the treatment of superficial lesions (ie. skin cancers) as they have a limited range
  • Examples of EBRT include:
    • 3D CRT (Three dimensional conformal RT):
      • allows for simple 2 field plans to more complex 5 to 6 field plans
    • IMRT (Intensity Modulated RT):
      • used in more complex scenarios such as treatment of brain tumors, head and neck cancers, prostate cancer
      • Allows for dose escalation and better sparing of adjacent critical structure than 3D-CRT
    • SRS/SBRT (Stereotactic Radiosurgery/Stereotactic Body Radiotherapy)
      • used to treat small well defined lesions
      • genrally delivered in large fractions and given in a single fraction and up to 5 fractions
    • Particle therapy (proton therapy and neutron therapy)
      • requires special equipment to generate high-energy particles and have limited availability


What is brachytherapy and what are its clinical applications?

  • The radiation source is placed inside the patient or next to the area of interest
    • Emission is active over a relatively short distance (deliver high doses to target volume while minimizing dose to adjacent tissue)
    • It can be given alone or after EBRT to increase dose to target volume.
  • Can be delivered with a low-dose-rate system (LDR) or a high-dose-rate system (HDR)
    • LDR: dose is generally 0.4 to 2Gy per hour, common sources used are Iodine-125 and Palladium-103 in prostate cancer and Cesium-137 in the treatment of cervical cancer
      • Sources may be placed in tumor permanently (prostate) or temporarily (cervix) until desired dose is reached
    • HDR: dose is delivered at >12Gy per hour, common source used is Iridium-192 in the treatment of prostate cancers and gynecological malignancies
      • Sources are placed in the tumors temporarily and radiation is delivered over several fractions


What is intraoperative radiation therapy?

  • Radiation is given at the time of surgery in a single fraction
  • Decision to give RT is made at time of surgery based on presence of adverse features (example: + margin)
  • Can be delivered with linac or brachytherapy
  • Used in breast, pelvic, and abdominal malignancies
  • May precede or follow EBRT


What is targeted radionucleotide therapy/unsealed sources?

  • Targeted therapy with the use of radionuclides that decay in the body in specific locations
  • Some examples include:
    • Strontium, Samarium, and Radium 223 for metastatic prostate cancer: Radioisotopes can accumulate in bone and can be used in treatment of extensive metastatic bone disease
    • Iodine-131: thyroid cells selectively accumulate 1-131 – the release of radiation can be used to treat thyroid malignancies


What are some acute side effects of radiotherapy?

  • Side effects can be divided into acute (occur during treatment) and late (occur after 90 days)
    • Side effects depend on:
      • the anatomic site
      • proximity of critical organs to target volume
      • dose per fraction
      • cumulative dose and concurrent treatment
  • Acute Side Effects are generally temporary and start during the 2nd week of RT and can persist for weeks to months after RT is completed
    • Most acute side effects are predictable
    • They can be exacerbated by:
      • previous surgeries
      • concurrent treatments (chemotherapy)
      • patient’s underlying symptoms prior to starting treatment
      • use of irritants during treatment (smoking)
      • noncompliance with recommended symptom management therapies during treatment
    • Typically related to:
      • denuding of epithelial surfaces
      • inflammatory cascade
      • hematocytopenia


What are som eof the late side effects of radiation therapy?

  • Late Side Effects can be permanent and can manifest months to decades after completion of treatment
    • Examples include:
      • cardiac toxicity in young patients treated for lymphoma
      • xerostomia in patient’s treated for head and neck cancers
      • radiation induced secondary malignancy in a pediatric patient that occurs when they are an adult
    • Typically related to vascular structures, fibrosis and parenchymal cell death
  • Close follow up with the oncology team to address potential late side effects and serial imaging as indicated are important aspects of patient care after treatment