total skin electron boost;treatment modality for acute lymphoblastic lymphoma (mycosis fungodies)

8/12/2019 Total skin electron boost;treatment modality for Acute lymphoblastic lymphoma (Mycosis Fungodies)

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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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total skin electron boost;treatment modality for acute lymphoblastic lymphoma (mycosis fungodies)

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