Intracavitary Brachy Dose Specifications + HDR Intracavitary Brachy
what are two fractionation schemes for HDR cylinder treatments with EBRT and what is one without external beam
- 3 x 600 to the surface of the cylinder - 1 x 700 to 5 mm from the surface of the cylinder - 4 x 880 to the surface of the cylinder (no external beam)
ABS recommendation for dose fractionation options to point A
- 4 x 7 Gy - 5 x 6 Gy - 6 x 5 Gy - 5 x 5.5 Gy
where are dose optimization points placed with cylinder applicators
- along the surface and dome of the cylinder - or at some specified depth (usually 0.5 cm)
minimum information required to be recorded with ICRU 38 treatment with tandem and ovoids
- applicator types - source type - loadings - orthogonal radiographs of the application - height, width, and thickness of pear-shaped reference volume
ICRU 38
- bladder & rectal points - nodal points - pelvic sidewall points
list all the "systems"
- historical - Manchester - ICRU 38 - ABS
how does the ICRU clarify dose specification location
- isodose surface of 60 Gy just surrounds the target volume (based on Paris experience) - point A is too uncertain, they don't recommend using it - defines height, width, and thickness of the pear-shaped reference volume
what ICRU 38 points are to monitor pelvic dose
- lymphatic trapezoid - pelvic wall points
pelvic wall points correspond to what structures
- parametrium - obturator nodes
dose per insertion constraints
- point A?: 17-20 Gy - Bladder <15 Gy - Rectum <15 Gy
historical "systems"
- stockholm - paris
according to RTOG for ICRU 38 methods of dose determination of the rectum and bladder, each of these structures should be limited to _____ of the prescribed dose
70%
according to ABS consensus guidelines, HDR brachy + EBRT the course of the treatment should be complete in how many weeks
8 or less
tandem and ring is HDR or LDR
HDR
what is the down side of HDR heyman capsules/applicators compared to LDR
LDR is less rigid - HDR is rigid so the source doesn't get stuck
stockholm system and paris system used what radioisotope
Ra226
ICRU dose is based on what
TRAK total reference air kerma - uGym^2h^-1
ABS guidelines for volumetric imaging for DVH values for HR-CTV and Organs at risk are: a. 90% & 2 cc b. 95% & 0.2 cc c. 97% & 2 cc d. 97% & 0.2 cc
a. 90% & 2 cc
manchester system
aka paterson-parker system Points A & B
The ABS guidelines recommend that the GEC-ESTRO guidelines for contouring be followed. For CT, the HR-CTV should include the folloiwng: A. Cervix B. Parametrial Extension C. Pelvic Sidewall Disease D. Nodal Disease a. A, B, & C b. A & B c. A & C d. All of the above
b. A& B
ICRU 38 recommends a system of dose specification that relates the dose distibution to a: a. point b. target volume c. both
b. target volume
true or false: you need heterogeneity corrections for brachytherapy planning
false
true or false: he exclusive use of DVH based parameters to select a source is recommended
false: it is not recommended. You must also consider spatial dose distribution
true or false: when using vaginal dome HDR, you cannot put cylinders behind the dome
false: you can put cylinders behind the dome
name of HDR tandem and ovoid applicator
fletcher-williamson
what is HR-CTV
high risk CTV - contoured 3 cm superior above the ovoids along the tandem
what makes MR compatible applicators compatible with MR
lack of shields
the pear-shaped isodose distribution helps limit dose to what, and increase dose to what
limits dose to bladder and rectum increase dose to cervical and paracervical tissues
what is the most extensively used dose specification system
manchester - aka paterson-parker
why is the tip often loaded with longer dwell times
ovoids contribute dose by the cervix
what dose the lymphatic trapezoid correspond to
para-aortic nodes, common iliac nodes, and external iliac nodes
where is point A and where is point B in the original manchester system and revised
point A: 2 cm superior to ovoids: 2 cm lateral of the center of the uterine canal point B: 3 cm lateral to point A (obturator nodes) Point A: 2 cm superior to ovoids: 2 cm sup to the lower end of the tandem along the tandem and 2 cm lateral to the central canal Point B: 2 cm sup to the external cervical os and 5 cm lateral along the body plane
what is the alternative to mini ovoids (and is also unshielded)
ring applicators - same pear-shape dose distribution as tandem and ovoids
what is the consequence of HDR heyman capusules being more rigid
the top of the uterus will be the low dose region because of anisotropy of the sources
what length of the tandem is activated
tip to 1/4 to 1/2 cm above the ovoids
why is it so important to check the tandem placement before planning
to make sure the tandem is not perforating the uterus - and that it is centered within the uterus - and that ovoids are at vaginal cuff - and uterus is packed away from OAR
true or false: the larger the cylinder, the lower the vaginal surface dose
true
which stepping source has the greatest weight in the tandem
usually in the first 2 cm of the tandem
