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Contents
Abstract Introduction
Equipment requirement
Physical requirement
Single scattered electron beam therapy
Other techniques of skin therapy Stanford technique
Dose rates
Setup problems
Dose prescription
Dosimetric setup Dosimetric problems
Clinically acceptance objectives
Conclusion
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Abstract:
Total skin electron beam therapy has been in medical service since
the middle of the last century in order to confront rare skin
malignancies. Since then various techniques have been developed,
all aiming at better clinical results in conjunction with less post-
irradiation complications. In this article every available technique is
presented in addition to physical parameters of technique
establishment and common dose fractionation. This study also
revealed the preference of the majority of institutes the last 20
years in sixdual field techniqueat a high dose rate, which is a safeand effective treatment.
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IntroductionTotal skin electron beam is treatment modality for
T-cell lymphoma
Mycosis
Fungoides
Kaposi sarcoma
Low penetration electron beam
Linear accelerator capable of producing large 200 cm 80
cm uniform fields with extended SSD.
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Equipment Requirement
Linear accelerator that can be modified in order to
deliver a homogeneous electron field at a large
distance from its source (2-7 m).
Beam degrader which ensures superficial beam
penetration into tissue. Large treatment room for large SSD.
ventilation that removes O3produced by electron
air interactions .
Auxiliary equipment for the proper and repeatablepositioning.
Dosimetry equipments.
Shielding to avoid sensitivity (eyes & nails)
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Physical requirements
3steps of dosimetric checks1. Physical specification of field dimensions, nominal
SSD, electron beam energies, field at treatment plane
and dose distributions, dose rate and photon
contamination.
2. Dose distribution and rate fordose from electrons
and photons.
3. Clinical aspects that arises dose prescription, dosefractionation, boost fields for underdosed areas,
shielding design
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Requires a linear accelerator that can provide a
homogenous electron field at an SSD of 700 cm.
Energy degrader for beam flattening patient is
irradiated in standing position.
Requires a large treatment room
Single scattered horizontal beam
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Other techniques of skin therapy
Static largeelectronfields withpatient instanding
position.
Static electronfield, rotatedthe standingpatient over
360.
Staticelectron fieldwith patienttranslated inlying position
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Stanford technique
Developed in 1973 at Stanford university
Patient rotates in 60 steps standing at
treatment positions
Beam energy and shape modulators are used. Easily achievable in small treatment rooms.
2 central axes of beam pointing outward
patients body ,so x-ray contamination can be
avoided
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Stanford technique
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Stanford technique
Six dual field techniques or Stanford technique
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Stanford technique
Six dual field technique
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Dose rates
High dose rate 2500-3000 cGy/min at dmax.
Daily treatment time reduced to 9.5min to
15min.
HDR is a treatment modality in mycosis
fungodis with good results and less time
consuming
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Setup problems
Room size
Ventilation of ozone
Skin sensitivity
Eye nail shielding
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Dose prescription
27Gy40Gy(mean dose 35-36Gy) at HDR in an
average of 9weeks,4 days per week.
HDR provides low toxicity ,better tolerance &
reduces treatment time.
For under dosed areas boost fields of 4-26Gy
are prescribed.
For vertex of scalp angled lead reflector isprovided.
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Dosimetric setup
Dosimeter (TLDs, ionization chambers,
gafchromic films)
Solid water phantom or anthromorphic
phantom.
Scanning and evaluation of gafchromic
by Epson10000xl
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Dosimetric problems
On extended SSD;
Combination of partial beams in order to
create a large field that cover patient
dimensions.Beam energy degrdading, because lowest
energy provided in electron mode is 6MeV.
Thickness of degrader can vary from 3mm
to 18mm.
If air volume is not sufficient use acraylic
sheet for secondary scattering.
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Conclusion
Total skin electron beam irradiation is an effectivetreatment for various skin malignancies.
Toxicity can be reduced by HDR & appropriate shielding.
All techniques require linear accelerator with electron
mode & large SSD.
Dosimetric technique should be carried out to ensure
treatment quality.
Prescribed doses differ according to personalized
patient needs and treatment schedules.
36-40 Gy dose delivered in 4 days per week for 9
weeks at HDR.
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