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48 Cards in this Set
- Front
- Back
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HDR Advantages |
-No/reduced exposure to medical personnel -Permits treatments on an outpatient basis using multiple fractions -Suited for large patient populations -Can optimize dose distribution vs. manual afterloading techniques -Techniques more consistent/reproduceable -Can be sole procedure or w/external beam |
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HDR Disadvantages |
-Remote afterloaders are EXPENSIVE and require BIG shielding -Can share HDR within other treatment rooms... scheduling conflicts -HDR quality assurance requirements are MUCH higher due to complexity of equipment and frequent source exchange -Involves much more staff time |
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HDR Remote Afterloader |
-Several channels and indexing system -Directs source to each channel/position -Applicators or catheters in patients connected to channels by transfer tubes -Rotating turret used to align source -Dummy wire -Precision positioning accuracy: +/- 1mm |
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HDR Characteristics |
Single source of high activity (~10 Ci = 370 GBq) Usually Ir-192 (HL = ?) but Co-60 (HL = ?) and Cs-137 (HL = ?) have been used Why Ir-192? Higher specific activity (smaller sources), low photon energy (low shielding req.), but short half-life (replace source 3-4 months) |
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Source Dimensions |
Vary from 0.3-0.6mm in diameter and 3.5-10mm in length. UMN = 0.9 x 4.5mm |
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HDR Safety Systems |
-Door Interlocks -Catheter Interlocks -Backup power (batteries) -Manual source retraction mechanism -System to detect blockage or excessive friction during source transit |
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Rotte Applicator - Endometrial |
Separations of 2, 3.2, 4, 5 cm (distance between ends of applicators) |
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Biologically Effective Dose |
n=fractions, d=dose per fraction EBRT and HDR: BED = n*d*(1+d/(alpha/beta)) LDR, MDR, Pulse Dose Rate: BED = n*d*(1+g(t,T1/2,mu)*d/(alpha/beta)) g depends on total irradiation time, kinetics of repair half time, mu = ln(2/T1/2*) |
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Dose Specification Points on CT |
Point A = 2 cm up, 2 cm over Point B = 5 cm up, 5 cm over Rectum Blader Cervical Tumor, Point (T) Vaginal Surface Sigmoid |
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EQD2 |
EQD2 = equivalent dose in 2 Gy fractions EQD2 = BED normalized to a conventional EBRT scheme of 2 Gy per fraction |
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Bladder Point Dose Defn |
-Dilute contrast in catheter bulb (wtf?) -ICRU 38 bladder point < 80% Point A dose (2cm up, 2cm over) -Bladder bulb may underestimate bladder wall dose |
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Rectal Dose Defn |
-Interectal barium or Gastrograffin -Multiple points on AP/lateral fields closest to applicator -ICRU 38 rectal points < 80% of Point A dose -Same criteria for Sigmoid |
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Point A Dose Specification |
-2cm up from cervical os (Smit sleeve), 2cm lateral to tandem -Tapered dose distribution along tandem: Dose points placed 12 mm from tandem tip and progressively extend to 14, 16, 18, and 20 mm to level of Point A, across from each dwell. -Decrease sigmoid +/- bladder dose -Decrease small bowel dose |
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Point T |
-Cervical Tumor Point: 1cm above cervical marker and 1cm lateral to tandem -Defines dose within cervix -Should be 2-2.5x Point A dose -This is an HDR point ONLY. NOT AN LDR POINT. |
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Vaginal Surface Dose |
140-200% of Point A |
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HDR Shielding |
Based on NRC from 10 CFR 20.1301 and 10 CFR 20.1201 In unrestricted room, dose cannot exceed 2 mrem (0.02 mSv) in any 1 hour Workload and Use Factor applied, dose received in unrestricted area not to exceed 2 mrem/hour |
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Shielding Calculation (Universally Applicable to ALL exams...) |
B = P*d^2/WUT |
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Licensing Requirements |
Must apply for license or license amendment with appropriate regulatory agency: NRC or the state if in an Agreement State a) applicants qualifications and desc. of personnel training program b) administrative requirements: ALARA program, RSO, rad safety committee, written quality management program c) technical requirements: calibration and survey, leak testing, inventory sources, etc. |
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License Application |
1) Source description 2) Manufacturer's name and model of HDR 3) Intended use 4) Authorized users (physicians) and authorized physicist(s) ensuring they meet experienced/educational req. in 10 CFR 35.940 and 10 CFR 35.961 5) Outline of initial training of users and device operators 8 hours of "hands on" |
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Written Directive |
By authorized user, must include: -name and hospital number of patient -HDR source material -dose per fraction -total dose -site of adminisration |
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Patient Identification |
Must be verified by TWO independent methods as the individual named in the written directive: -Ask them their name -Confirming name by comparison with ID bracelet |
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Treatment Delivery |
Prior to initiating treatment, "authorized operator" must verify the NAME of the patient, the DOSE, the SITE of administration, and the TIMES for each dwell location are in agreement with written directive. |
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Post-Treatment Survey |
Always, immediately following each treatment, survey the AFTERLOADING DEVICE and the PATIENT (ensure source returned to shielded position) |
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Source Replacement |
Vendor will conduct source replacement, and perform checks following installation. ENSURE THE NEW SOURCE ACTIVITY IS ENTERED INTO THE TREATMENT PLANNING COMPUTER |
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Supervision |
Both the "authorized physician user" and the "authorized medical physicist" MUST BE PHYSICALLY PRESENT. |
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Medical Event |
-Wrong Drug -Wrong Route of Administration -Wrong Patient -Wrong Site -Dose different by >20% from that prescribed -Use of a leaking source to treat patient. |
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HDR Source Calibration |
AAPM recommends AIR KERMA STRENGTH (Sk) -Exposure rate measured in free air at a distance 1m from the source -Units if uGy-m^2/hr |
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Cooperative Ocular Melanoma Study |
COMS - Used a Ru-106 eye applicators. eMax = 39.4 keV, 100% electrons. T1/2 of 373.6d. 85 Gy to tumor apex. Max dose of 800 Gy to sclera. |
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Proton Beam Therapy |
Reduced energy in particles due to slowing down in tissue causes an increased interaction with electrons. Maximum interaction at the end of the range is called the Bragg Peak. |
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Spread Out Bragg Peak (SOBP) |
Employing a mono-energetic beam of sufficiently high energy and range to cover distal end of target volume and adding beams of decreasing energy and intensity to cover the proximal portion... though you cause a marked increase to the entrance dose! |
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Energy-Range Straggling |
Simply the uncertainty in the actual range of each particle which smears out the maximum treatment depth. Quantum mechanically, even a single collision to a particular scattering angle may have a range of inelastic energy loss. |
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Stopping Power |
Rate of energy loss due to ionization and excitation caused by a charged particle travelling in a medium is proportional to the square of the particle charge and inversely proportional to the square of its velocity Impact Theory has been used to approximate relationship between Coloumb force and energy xfer of moving, charged particles |
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Average rate of energy transfer (Stopping Power) |
dE/dX ~ 4*Pi*z*z*e^4/(m2*v1^2) (MeV/cm) |
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Linear Energy Transfer |
LET = dE/dl Either Track Average or Energy Average. TA: tracks divided into equal segments and deposited energy is averaged EA: particle tracks divided into equal energy increments and averaged over entire tracks length |
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Microdosimetry |
Using a spherical proportional counter to directly measure average energy deposited in the counter gas (tissue-equivalent) for fixed track length. Nucleas diameter (~1 micron) @ 5-10 torr of pressure. "Event spectra" measured to allow separated contributions to dose according to recoil particle mass.
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RBE and OER |
As energy increases, LET decreases. RBE = LD50(High LET)/LD50(Co-60) |
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Typical LET ranges |
Photons = 1-5 keV/micron Neutrons and Heavy Ions = 500-600 keV/micron LET Maximum is about 100 keV/micron. No more gain in cell killing above that. Threshhold for doublestrand breaks is 10-12 keV/micron |
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OER |
OER is the ratio of doses that produce the same biological effect between a well-oxygenated system and an anoxic system. Low LET = large OER. High LET = low OER. |
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Quality Index |
The RBE radiosensitivity for a given particle type. |
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Proton Dosimetry |
Same as all the rest. Absorbed dose to water with quality factors (chamber-specific quality factor included!) |
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Beam Quality Index |
Res = Rp - zref Residual range => Rp = practical range (10% intersection of tail drop off), zref = middle of SOBP |
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Passive Beam Spreading |
Use of a plastic compensator. First developed and still most commonly used. Interdependent upon range and field size. Scattering foil thickness has to be increased, resulting in a degradation of beam energy or loss of treatment range. |
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Active Beam Spreading |
Pencil beam scanning or active-beam shaping. 2 magnetic dipoles allow the scanning of the beam over the treatment field. |
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Novel Particle Accelerators |
Laser plasma generated proton beams: terawatt-laser pulse... Dielectric Wall Proton Accelerator... |
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Quality Assurance |
1) Automatic procedures ensure correct beam energy and correct modulation for SOBP. 2) QA for pencil beam scanning monitors scanning patterns. 3) Functionality of interlocks for safety 4) Daily check of monitor unit calibration 5) Verification of treatment portal and MU 6) Verification of correct installation of aux equipment and patient-specific treatment aids |
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IGRT Doses to Know |
MV Portal ~ 6.0 cGy kV Portal ~ 0.1 cGy MVCBCT ~ 2-17 cGy kVCBCT ~0.1-4 cGy (3x to bone) MVCT ~ 1-3 cGy MVTomo ~ 2.5cGy (4mm couch travel/fine pitch) ~ 1.25 (8mm couch travel/normal pitch) ~0.83 cGy (12mm couch travel/coarse pitch) |
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IGRT Dose Considerations |
MV Imaging: dose to bone ~ dose to soft tissue Exit dose = 50% of entrance dose kV Imaging: dose to bone ~ 2.4x dose to tissue Exit Dose = 5% of entrance dose |
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Stuff |
More Stuff.
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