Hand Calc Flashcards
How does MU change when TMR change
as TMR decreases, MU increases
How does TMR change when calc point depth changes
as depth increases, TMR decreases
Whole brain irradiation- patient selection
metastatic diseases: frequent breast, lungs, melanoma, sarcoma, CNS
Goal of treatment (whole brain)
palliation of symptoms
quality of life
prolonging survival
could be prophylactically (PCI)
what us treating prophylactically
PCI given to small cell lung cancer a head of time because patients have brain cancer frequently. when treating prophylactically, we treat the areas that we think will develop cancer later on, so we treat in advance with lower dose (24 Gy in 12 fx)
whole brain immobilization
supine, exact bar, reg.h. “B”, pad on table, mask, arms across chest holding A-bar, knee wedge
where is the isocenter placed for whole brain
mid- separation
why is isocenter placed at mid separation
for homogeneous dose distribution, if the isocenter is off, we will have a hot and cold plan
Conventional Whole brain sim
- Fluoroscopic x-ray will be taken of treatment field
- Doctor draw field (wax pencil in scan or digitally)
- Blocking created (cerrobend or MLC)
Virtual whole brain sim (more realistic)
- Pt receives CT scan
- Axial slices imported into treatment planning computer
- Dr draws field on TPS
- MLCs for blocking
Whole Brain Fields gantry angles
Opposed laterals
tilted anterior
why do we set beam angles tilted anterior and opposed laterals (obliged) for whole brain
TO LIMIT DIVERGENCES TO THE LENSES
How to change gantry angles to limit divergence for whole brain
ex: if beam 1 is at 278 (270+8), beam 2 will be at 82 (90-8)
where is interior border usually placed for whole brain
below C1, or could be below C2 as well but rare
why is the interior border always placed at C1 or C2
patients are usually here for metastatic cancer, chances are they will come back for more treatment. When that happens, we want to know where we stopped at the previous irradiation so that we can avoid overlapping and overtreating that area
Superior and lateral borders incorporate flash for whole brain, why?
patient’s set up can be different each day. flash ensures we have the whole skull covered every treatment. Also, if the field borders are against the head, we do not have adequate dmax to tissue
critical structures to consider when treating whole brain
face
lenses
what happens if we dont consider face and lenses for whole brain irradiation
radiation induced cataract that can develop in 20 years
block position for whole brain
“one thumb length” away from target
Whole brain palliative prescription
30 Gy for 10 fx
Whole Brain PCI fractionation
24 Gy in 12 fx
whole brain calculation
heterogeneous calculation if imported into TPS
what is the normalization of whole brain
100% to iso, no further optimization needed
what happens when you normalize down
plan gets hotter
what happens when you normalize up
plan gets cooler
what do you do when you want to increase coverage
normalize down (hotter)
what is MDACC normalization percentage allowed
95-105%
whole number or 0.5
no simulation?
- pt could be seen on weekend by physician
- therapist turns collimator to block critical structures or hand block
- homogeneous calculation done
- calc verified by dosimetrist/physics on monday
MU tolerance
3% or 2 MUs
what does homogeneous calculation mean
not considering different materials, treating as if were treating water
heterogeneous
considering different kinds of materials such as tissues bones, etc…
purpose of wedge
wedges are designed for breasts
they compensate for missing tissue/ manipulate the iso line to make it look like it pushes dose heel to toe (they dont actually push dose)
why do we have MLC on superior part of field border
to make the superior border nondivergent, if not, the border would diverse out
what is displacement
how far the calc point is from central axis in y-direction
why should electron be at 90 degree (appositional) to skin surface in breast
if at an oblique angle, can have hot spots and cold spots
4 calc point rules
- inside the field
- at least 2 cm from jaw edge
- must be tissue equivalent material
- cannot be in build up region (really close to surface)
why does the calc point have to be inside the field
if not, TPS will push MU to that point
why does calc point have to be at least 2cm from jaw edge
oe else, we dont have full buildup, dose is not accurately reflected
why must calc point be in tissue equivalent material
cant be in bone or air, or else we dont have adequate buildup
why cant calc point be in buildup region
cant have dmax
pinnacle doesnt model the buildup region well
4 rad onc emergencies
- spinal cord compression
- uncontrolled bleeding
- extreme cases of pain due to bone mets
- Superior vena cava syndrome (if tumor compressses on SVC, pt can die)
Palliative Spine irradiation goal of treatment
- palliation of symptoms
- quality of life
- could be one of the rad onc emerg
Palliative Spine irradiation patient selection
metastatic diseases (breast, lung, melanoma, CNS)
when would a patient receive no sim for palliative spine treatment
if they come on the weekend
can you use MLCs without sim
yes, you can digitize in Mosaiq
Vertebral column anatomy
C1-C7
T1-T12
L1-L5
S1-S5
where is T12
floating rib
palliative spine single PA field benefits
reproducible
efficient to calc, set up, and treat
cost efficient for palliative care
palliative spine single PA field negatives
high surface dose
not optimized dose distribution
palliative spine AP/PA fields benefits
reproducible
efficient to calc, set up, and treat
cost efficient for palliative care
palliative spine AP/PA field negatives
not fully optimized dose distribution
possible excessive dose from entrance from AP beam
palliative spine AP/PA field energy choice
AP/Pa- both 6X
AP/PA- both 18X
PA-6X and AP-18X- very prevalent
why is PA-6X and AP-18X the optimal energy choice for AP/PA spine treatment
higher energy, higher penetration
palliative spine Rt and Lt Laterals benefits
reproducible
efficient to calc, set up, and treat
palliative spine Rt and Lt Laterals negatives
suboptimal dose distribution
possibly added complication and cost of wedges
where in the body would you treat the spine with opposed laterals instead of AP/PA
cervical spine- spare mandible
palliative spine wedge pair benefits
reproducible
efficient to calc, set up, and treat
slightly optimized dose distribution
palliative spine wedge pair negatives
added complications of wedges in calc and treatment
added cost of wedges
Palliative Spine prescription
usually 30 Gy in 10 fx
Palliative spine that deliver one large dose to a bone met that is causing extreme pain (8 Gy or 12 Gy)
“rapid” or “one shot”
what is the difference between heterogeneous and homogeneous calc
heterogeneous: looks at effective depth
homogeneous: looks at reference depth (physical/ geometric depth)
Palliative Spin optimization
based on doctor reference
