External Beam Radiation
Therapy Special
Procedures
Kent A. Gifford, Ph.D., Acknowledgements to :
Karl L. Prado, Ph.D., Charles Bloch, Ph.D.,
Peter Balter, Ph.D., Gurpreet Arora, B.S.
Department of Radiation Physics
Total Body Irradiation
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Indications
Techniques
Dosimetry Data
Examples
TBI: Clinical Indications
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Preparation for marrow or stem-cell
implantation
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Suppress immune system to prevent rejection
Rid body of tumor cells not reached by
chemotherapeutic agents (e.g. CNS)
TBI Techniques
AAPM Report 17, figure 1.
source moves horizontally
single source,
long SSD
half body, direct
and oblique fields
patient moves horizontally
half body, adjacent
direct fields
TBI Techniques
AAPM Report 17, figure 1.
two vertical beams
four sources
single source, short SSD
two horizontal beams
head rotation
MDACC “Classic” TBI
MDACC TBI Techniques:
Mick-Radio Nuclear Stand
Total Skin Irradiation
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High Dose-Rate Total Skin Electron
(HDTSE-) Treatment: Technique
Description
Indications
Methodology
Data / Calculation
Dose Verification (TLD)
MDACC TSEI technique
(modified Stanford technique)
2 angled beams (90°±23°) for
uniform coverage and reduced total
body dose
 patient is 25 cm behind lucite plate
improved dose uniformity
(6 fields w/plate 8 fields w/o
plate, Holt JG, Perry DJ. Med.
Phys. 9:769-776(1982))
increased dose to self shielded
areas by diffusion
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6 positions, every 60°
MDACC TSEI technique
(modified Stanford technique)
1st day of cycle
2nd day of cycle
laser
ANT
RPO
POST
LPO
LAO
RAO
Stanford dual beam technique
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feet straight ahead or pointed slightly outwards
for better balance
elbows at or above shoulder level
arms parallel to the scatter plate
QA - Patient TLD’s
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TLD’s are taped to the patient’s skin and
irradiated for one cycle (12 beams)
reference TLD’s are irradiated using a
10x10 cm2 field of 9 MeV electrons at
2.0 cm depth (100 cm SSD) in an
acrylic phantom
SRS: Available Systems
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Gamma Knife
Radionics Xknife/Xplan
Brainlab
Cyberknife
Others (many “homemade”)
Delivery techniques
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201 intersecting beams (Gamma Knife)
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Arcs with circular collimators (1-4 cm)
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spherical dose distributions
ellipsoid dose distributions
Multiple fields, shaped with miniature MLC
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arbitrary dose distributions
IMRT
Stereotactic Radiosurgery
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Elimination of motion
& setup errors means
smaller field size can
be used
Reduction in field size
allows higher dose per
fraction, and reduction
in number of fractions
(1 to 5)
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Large dose to small
lesions with minimal
dose to surrounding
tissue.
Single fraction
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“Out-of-town” patients
Patients in poor health
Other patients who
might be burdened by
protracted treatment.
Bloch, Ph.D.
SRS QA
Treatment
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Typically 5 arcs, about 60 degree each.
5-10 MU/degree  300 - 600 MU/arc.
300 MU/min  1-2 minutes per arc.
Total treatment is 5-10 min of beam time.
Room entries between arcs to move couch
and re-check patient alignment.
Gating Study-Left Breast
By Gurpreet Arora, B.S.
PROBLEM: Thoracic tumors
move
Planning on the three CT sets
CT at Inspiration
CT at Expiration
CT during Free Breathing
Combined to form ITVs
By Peter Balter, Ph.D. and
Lei Dong, Ph.D.
The GE system for 4D
scanning
GE PET/CT
(can be used on any GE CT scanner)
Uses Varian RPMto
monitor respiration
By Peter Balter, Ph.D.