RADIATION Flashcards
Q: Name two types of ionizing radiation; which one is used in H&N Ca [?]
- Photons (Xrays / Gamma rays) → H&N Use
- Particle Radiation (electrons, protons, neutrons, etc)
Q: Characteristics of Photon Radiation; which one used in H&N [?]
- Low (5MeV; H&N) or high (20MeV) energy
- Skin-sparing properties
- Depth-dose properties (Penetration)
- Isodose distribution (Beam Uniformity)
Q: Characteristics of Electron Beam XRT [?]
- Good for Superficial lesions, deep tissue sparing.
- Range of Penetration (cm) = MeV/3.
Q: Three Advantages of Brachytherapy [?]
- Better dose Localization
- Continuous Fractionation.
- Decreased dose to Adjacent normal tissue.
- Radioactive source placed in proximity to lesion.
Q: Brachytherapy source placement (3 types) [?]
1- Interstitial: radiation source directly on target tissue (i.e. prostate or breast).
2- Intracavitary: vagina, cervix.
3- Intraluminal: trachea, esophagus.
4- Surface mold: skin.
** #2-4 → “Contact brachytherapy” = radiation source in adjacent target tissue
Q: Brachytherapy time frames of use [?]
- Temporary – long-lived isotopes used (RIC = Radium, Iridium, Cesium). -Permanent – short-lived isotopes used (PIG = Palladium, Iodine, Gold).
Q: (TK) IMRT: What is it? Disadvantages [?]
- Intensity-modulated RT.
- Use of CT & Software to use multiple beams of varying intensity from different directions for accurate delivery based on tumour size & location; conformal therapy (dose distribution around tumour)
PROS:
(i)Localized radiation, (ii) high dose radiation to tumour site, (iii)sparing of normal structures (reduced toxicity).
Disadvantages:
(i) expensive, (ii) time-consuming, (iii) special immobilization required, (iv)steep
radiation falloff (limit of rads depends on tumour mapping marks by physician), (v)steep learning curve
Q: Radiotherapy Pearls [?]
- Cell Death = Inability to Proliferate; both DNA strands must be knocked out.
- Log cell kill = particular radiation Dose will kill the same Proportion of cells.
- Therapeutic Window = Dose Response curves between Tumor cell & Tissue damage; relative positions of curves determine safety of tumor control.
- Shrinking Field technique; now replaced by concomitant boost?
Q: Radiotherapy: Mechanisms of cell injury(2) & percentages of each [?]
- Direct injury – Electron from x-ray absorption causes DNA Damage (1/3)
- Indirect injury – Electron from x-ray creates an Oxygen Free Radical which then damages the DNA
(2/3)
Q: What are the 4 R’s of radiotherapy injury mechanisms [?]
- Repair – Sublethal injury will be repaired by the cell if it takes no further hits, increased fractionation = increased repair (by normal tissue, since cancer cells are worse at repair).
- Reoxygenation – Presence of oxygen increases the effects of Ionizing Radiation, radiosensitivity stays the same down to 20mmHg oxygen, below this sensitivity decreases. With fractionation hypoxic tumours reoxygenate and become more RT-sensitive.
- Redistribution – Max. radioresistance = Late S phase; max. radiosensitivity = Early M phase (late G2 also very radiosensitive); fractionation allows increased radiosensitivity, as surviving cells redistribute themselves to other phases in cycle).
- Repopulation – Tumors accelerate repopulation after cell reduction from surgery or radiation (this is one disadvantage of hyperfractionation, addressed by accelerated Fx’n).
Q: (DO): What is radiosensitivity [?]
What are the key components that make cells more sensitive [?]
Radiosensitiviy: the ability of radiation to lead to cell death via DNA damage without
adequate DNA repair.
Components:
- High cell division rate: rapidly dividing cell = increased susceptibility to DNA damage (M phase = radiosensitive vs. S phase = radioresistant)
- Low capacity for DNA repair
- High oxygen content
Q: (DO): List examples of radiosensitive (2) and radioresistant tumours [?]
- Radiosensitive: lymphoma, oral mucosa ca (SCC)
- Radioresistant: sarcomas, melanomas
Q: Definition of a Gray and Rad [?]
- Gray (Gy) = Joule/kg =The absorption of one joule of radiation energy by one kilogram of tissue
- Rad = Radiation absorbed dose; 100 rad = 1 Gy
Q: Describe Standard [?]
Standard: single dose/fraction (1.8-2.0Gy) of radiation per day, MON-FRI. (i.e 2Gy OD 5d/wk for 7 weeks (35F) = 70Gy)
Q: Describe Hyperfractionation [?]
Multiple fractions per day, lower doses per fraction, increased total dosing, increased duration of treatment (i.e. 1.2Gy BID 5d/wk for 7wks for 68F = 81.6Gy) Improved radiosensitivity of tumour cells via “Repair, reoxygenate, redistribute”
Q: Describe Accelerated fractionation [?]
Accelerated: increases amount of dose per fraction, same total dosing, decreased duration of treatment (i.e 1.6Gy/fractions/BID 5d/wk 67.2Gy/42 fractions/6wks).
- Allows decreased time for tumour “Repopulation”
- Intense: 1.5Gy TID 7d/wk x 36F = 54Gy
- Split: 1.6Gy BID 5d/wk x42F (split with 2 week gap in between) = 67.2Gy
- Concomittant Boost: 1.8Gy OD 5d/wk (30F) +1.5Gy dose BID on last 12F = 72Gy
Q: Describe Standard, Hyperfractionation, Accelerated fractionation [?]
Q: Adv / DisAdv of Hyperfractionation and Accelerated Fractionation [?]
Q Discuss “BOOST” radiation [?]
- Form of accelerated radiation
- Increase the number of fractions per day at a given time of radiation treatment (usually the end)
- Indicated for locally advanced disease → better LRC not OS
- Allows more rads to tumour due to “shrinking field”
Q: Discuss “SPLIT-COURSE” radiation [?]
- Form of accelerated radiation
- Gap midway between radiation course to allow healing of surrounding tissue
- Decide during the gap whether or not to continue with palliative or curative intent
Q: Dose limiting factors for Intensity and Total dose [?]
- Intensity (Increased # of daily fractions OR reduced duration of overall treatment → Acute toxicity = Mucositis → accelerated rads and hyperfractionated rads
- Total dose – Late toxicity = Soft tissue Fibrosis → hyperfractionated rads
Q: Time required post-XRT to call biopsy reliable [?]
- 3 months .
- Cell lysis occurs at mitosis, 4-5 divisions occur before Lysis .
- Lethally injured cells and Surviving cells are morphologically identical .
Q: (DO): Options for administration of radiations [?]
- Preoperative (neoadjuvant)
- Postoperative (adjuvant)
- Concurrent (with chemotherapy)
- Palliative (unresectable disease; stage IVb)
Q: PROS/CONS of Preoperative Radiotherapy for SCC [?]
Q: PROS/CONs of Postoperative Radiation therapy for SCC [?]
Q: Best Postoperative Time interval for Adjuvant XRT [?]
- Within 6 weeks
Q: General Indications for Post-operative Radiotherapy [?]
- T3 or T4 lesion
- Perineural invasion
- Lymphovascular invasion
- Extracapsular spread
- > N1
- Positive resection margins (considered gross residual disease, >106 cells)
Q: Distance of tumor to resection Margin that is considered Close [?]
- ≤5 mm .
- Found to have Same Prognostic significance for Recurrence as Positive Margins .
Q: Six beneficial mechanisms of Chemoradiotherapy [?]
- Can act on Different subsets of tumor cells
- Recruit cells from G0 into radiation sensitive phases
- Chemo Inhibits Repair of sublethal radiation injury
- Tumor shrinkage decreases Interstitial pressure, thus increases drug and O2 delivery - Prevents Radiation Resistance
- Cell-cycle Synchronization increases the effectiveness of both therapies
Q: Indications for postoperative Chemo with XRT [?]
- ECS
- Positive margins
Q: Toxic CNS doses [?] - Somnolence syndrome
- Myelopathy – 50 Gy in 25 fractions - Transverse Myelitis – 50 Gy
- Brain Necrosis – 70Gy
Q: Nine Late Complications of Radiotherapy for NPC in 6 different sites [?]
SKIN
- Skin necrosis
- Second Primary
ORAL/MANDIBLE
- Osteoradionecrosis
- Xerostomia (35Gy)
EYES
- Cataracts – 6Gy
EAR
- Middle ear effusion secondary to ET dysfunction
- ?Osteromyelitis of temporal bone
NASOPHARYNX
- Nasopharyngeal stenosis
CNS
- Transverse myelitis (50 Gy)
- Somnolence syndrome,
- Brain necrosis (65 Gy)
Q: Seven Complications of Radiotherapy for Neck disease [?]
- Xerostomia – 5-6 Gy in 5-6 weeks?
- Mucositis
- Dental caries
- ORN – In up to 5% of patients, rare <60 Gy, increased if chemo-XRT
- Soft tissue fibrosis
- Hypothyroidism – 1% clinically overt, 10% occult after 50 Gy in 4 weeks - Immunosuppresion
- Spinal cord Necrosis – Limit to 45-50 Gy in 5 weeks
- 2nd primary
Q: (TK) How is Radiation Toxicity graded [?]
- RTOG Scale: Separate Acute & Late morbidity scales for each body/tissue site
- Graded 1-5 based on severity (0= no symptoms, 5 = death directly related to XRT)
- i.e. mucous membrane (acute): 1 = injection / mild pain; 4 = ulceration / necrosis
Q: Osteoradionecrosis, 4 treatment modalities [?]
- CONSERVATIVE/MEDICAL
- Topical Care
- Biopsy + culture of site
- IV antibiotics
- HBO
- SURGICAL
- Sequestration
- Mandibulectomy with reconstruction (plates/soft tissue/ osseocutaneous free flap)
Q: (LK) What are the different grades of ORN [?]
- Grade I = exposed alveolar bone + HBO responsive (most common)
- Grade II = exposed alveolar bone + HBO unresponsive → sequestrectomy/saucerization
- Grade III =
(i) full-thickness bone involvement,
(ii) resorption of inferior mandibular border,
(iii) orocutaneous fistula, and/or
(iv) pathologic fracture
Q: What is the Marx protocol: [?]
Q: Three typical osseous findings of mandibular ORN on CT scans [?]
“LORDS of the Cort”
- Loss of trabeculation
- Osseous fragmentation - Radiolucency
- Demineralization
- Sequestration
- Cortical thinning
Q: Four Intraorbital Complications of Radiotherapy, Maximum Doses where applicable [?]
- Cataracts – as little as 6 Gy
- Lacrimal gland injury – ~35 Gy in 3.5 weeks - Radiation Retinopathy – 50 Gy
- Optic Nerve injury – 50 Gy
Q: What Spinal Cord Complication can occur Post-Radiotherapy? Sign/Dose of radiation is associated [?]
- Radiation Myelopathy
- L’Hermitte’s Sign – Electric shock sensations triggered by Flexing the Cervical Spine
- Transverse myelitis
- Spinal cord necrosis
- Doses of 50 Gy in 5-6 weeks
Q: Criteria (and name of) for diagnosis of Post-Radiation Sarcoma (PRS) [?]
Cahan’s criteria
- Different Histology
- PRS is located within the field of irradiation
- Patients with cancer syndromes such as Li-Fraumeni (p53 mutation) and Rothmund-Thomson are excluded
- Must be biopsy-proven
- Latent period (period between initiation of radiotherapy and histologic diagnosis of second neoplasm) is >4yrs
Q: Dose of XRT for Micropscopic disease and N0 neck [?]
See NCCN guidelines pg. 102
- Microscopic disease = 65 Gy
- N0 neck = 55 Gy
Q: When and for which levels to do an Elective Neck Dissection (or Irradiate) according to Primary
Tumors [?]
