technical issues in breast radiotherapy
DESCRIPTION
TRANSCRIPT
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TECHNICAL ISSUES IN BREAST RADIOTHERAPY Dr Bharti Devnani
Moderator:- Dr Manoj Kumar Sharma
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RADIOTHERAPY BY CONVENTIONAL METHOD
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IMMOBILIZATION METHODS FOR IMPLEMENTATION
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BREAST BOARD
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Several adjustable features to allow for the manipulation of patients arms, wrists, head and shoulders.
To make chest wall surface horizontal, brings arms out of the way of lateral beams.
Arm abducted at 90 & hand holds handle of arm rest.⁰
Face turned towards opposite side.
Thermoplastic breast support can be added.
Constructed of carbon fiber which has lower attenuation levels
permitting maximum beam penetration.
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VAC-LOCK
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Breast ring with valecro Alpha cradle
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FIELD BORDERS
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FOR TANGENTIAL FIELDS Upper border – 2nd ICS (angle of Louis) when
supra clavicular field used. When SCF not irradiated – head of clavicle
Medial border – at or 1cm away from midline
Lateral border – 2-3cm beyond all palpable breast tissue – mid axillary line
Lower border – 2cm below inframammary fold
Anterior -2cm margin of light, above the highest point of breast.
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A pectoralis major muscle
B axillary lymph nodes: levels I
C axillary lymph nodes: levels II
D axillary lymph nodes: levels III
E supraclavicular lymph nodes
F internal mammary lymph nodes
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HOW TO IMPLEMENT IT?
Deciding angle of rotation of gantry for tangential fields:
Lead wire placed on lateral border Field opened at 0⁰ rotation on chest wall and
central axis placed along medial border of marked field
Gantry rotated , until on fluoroscopy, central axis & lead wire intersect – angle of gantry at that pt. noted – medial tangent angle
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CENTRAL LUNG DISTANCE
Perpendicular distance from post. tangential field edge to post part of ant. chest wall at centre of field
Best predictor of %age of ipsilateral lung vol. treated by tangential fields
CLD (cm) % of lung irradiated
1.5 cm 6%
2.5 cm 16%
3.5 cm 26%
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IMPORTANCE OF BEAM MODIFICATION DEVICES (WEDGES)
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Higher dose to
the apex without wedges
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BOLUS
Increases dose to skin & scar after
mastectomy
Cosmetic results may be inferior
Universal wax bolus used
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IRRADIATION OF REGIONAL LYMPHATICS
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SCF IRRADIATION
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SCF
Single anterior field is used.Field borders – Upper border : thyrocricoid groove
Medial border : at or 1cm across midline extending upward following medial border of SCM ms to thyrocricoid groove
Lateral border: insertion of deltoid muscle
Lower border : matched with upper order of tangential fields
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A pectoralis major muscle
B axillary lymph nodes: levels I
C axillary lymph nodes: levels II
D axillary lymph nodes: levels III
E supraclavicular lymph nodes
F internal mammary lymph nodes
SUPRACLAVICULAR-AXILLARY FIELD
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Humeral head shielding:–
• If arm angled >90⁰: Ax nodes overlap head
of humerus anteriorly.
• Larger the angle – less the head of humerus
spared in s.c port
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MATCHING SUPRACLAV & CHEST WALL FIELDS
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AngulationBy inferior angulation of the tangential fields.
Half beam block technique Blocking the supraclav field’s inferior half, eliminating its divergence inferiorly .
Hanging block technique
Superior edge of tangential beam
made vertical by vertical
hanging block.
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Single isocentre technique:
• Isocentre placed at the
junction
of tangential and
supraclavicular field
• Inferior portion of field
blocked for supraclavicular
treatment and superior
portion blocked for tangential
field
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IMN IRRADIATION
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1. Extension of tangential fields– by extending medial border – 3cm across midline or by using imaging techniques
2. Separate field – • Medial border – midline , matching with
tangential field border• Lateral border – 5-6cm from midline• Superior border – abuts inferior border of
supraclav field or at 1st ICS (superior border of head of clavicle) if only IMNs are to be treated
• Inferior border – at xiphoid or higher if 1st three ICS covered
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More normal tissue is being irradaited. (lung, heart and contralateral breast)
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Anterior field Oblique field
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MATCHING THE TANGENTIAL BEAMS WITH INTERNAL MAMMARY FIELD
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ISSUES WITH DIRECT ANTERIOR FIELD (LARGE BREASTED WOMEN)
Cold region:- large amount of breast tissue over the
matchline
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POSTERIOR AXILLARY BOOST
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Medial border – To allow 1.5-2cm of lung on the portal film
Inferior border – at same level of inferior border of s.c field
Lateral border – just blocks fall off across post axillary fold
Superior border – splits the clavicle
Superolaterally – shields or splits humeral head
Centre – at acromial process of scapula
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ELECTRON BOOST
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BOOST-ELECTRONS
Appropriate energy selected to allow 85 -90% isodose line to encompass target volume & decrease dose to the lung.
Clinical set up - post lumpectomy volume or scar on skin +3 cm in all directions.
Energy – 9-16 MeV
Dose – 10-20Gy
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TREATMENT IN PRONE POSITION
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Plexiglas plateform with
rounded opening
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TREATMENT IN LATERAL DECUBITUS POSITION
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Carbon epoxy disposer
Opposite breast retracted upwards & outwards from the
field by elastic straps
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• Useful for voluminous breast• For patients who are heavy smoker and previous history of lung or cardiac disease
• For deep seated tumor
Disadvantage – For nodal RT treatment position has to be changed
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TREATMENT OF BILATERAL BREAST CANCER WITH CONVENTIONAL TECHNIQUE
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ROLE OF IMRT IN BREAST CANCER
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Reduces the hotspots specially in the superior and inframammary portions of the breast.
Increases homogenity
Manifests clinically into decrease in moist desqumation in these areas.
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IMRT BREAST: WHY?
(1) Better dose homogeneity for whole breast RT
(2) Better coverage of tumor cavity(3) Feasibility of SIB(4) Decrease dose to the critical organs(5) Left sided tumors- decrease heart dose
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FORWARD PLAN IMRT
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ROLE OF 4D-CRT
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RTOG GUIDELINES
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DURING CT SIMULATION
Post-BCS
Post-Mastectomy
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REGIONAL NODAL CONTOURING
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Breast-superior
Breast-inferior
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SCF begins
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Axillary level III begins
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Axillary level II begins
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Axillary level I begins
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Axillary level I ends
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IMC begins
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IMC ends
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THANK YOU
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INTERSTICIAL BOOST
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When the CTV extends
deeper than 28 mm under the
epidermal surface, implants
have a higher ballistic
selectivity in terms of the
volume of the irradiated
breast tissue and dose to the
skin blood vessels than
electron beam boosts.
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LOCALIZATION OF LUMPECTOMY CAVITY
Pre-op clinical finding , pictures Imaging- mammogram,usg,MRI Per-op finding HPR Surgical clips Post op imaging with USG,CT or MRI
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Use of marker clips to localise the
boost target volume and
simulate entrance points of guide
needle at the skin of the
breast
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Use of mammography in defining the boost target localisation in breast conserving treatment
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A. Defining the implantation isocentre and definitive needle entrance and exit points at the skin for a breast implant. Reconstruction boost target isocentre from mammography, by simulator, or CT. The indicated entrance points are too close to the target volume (A)
B. Inclination of the implantation equator plane away from the target to avoid an overlap of the boost PTV and needle exit points at the skin
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(C). Indication of new entrance and exit points, further away from the boost CTV, to avoid skin teleangiectases .
(D)Occurrence of severe teleangiectasic ‘stars’ at skin entrance or exit points if rules for implementation are not followed
Why this planning so important.With a delivered dose of 50 Gy , chances of late teleangiectases may occur in 30% of cases Vessels may have already received 20–40 Gy from the breastirradiation.Therefore, there is usually only a small dose amount left in skin vessel tolerance for teleangiectases
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ANAESTHESIA Breast implants can easily be carried out under
L.A. and premedication with 2.5–5 mg midazolam given 15–30 min before the implantation.(GA, <0.5%)
The patient is placed in supine position with the homolateral arm in 90° abduction.
After the design of implant geometry and localisation of entrance and exit points of the needles, the skin is infiltrated at each point with 0.5–1 ml 1% lidocaine.
Retroareolar region is painful (1-5 ml extra infiltrate in that area)
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DESIGN OF THE IMPLANT GEOMETRY
Needles are implanted parallel and equidistance from each other (Paris system).
In most cases inserted in a mediolateral direction.
In very medially or laterally located tumor sites, needles should be implanted in a craniocaudal direction .to enable separate target area from skin points.
In some rare cases, the upper outer quadrant has to be implanted with needles orientated in a 45° angle to avoid overlap of source positions and skin
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2 planes of needles are usually needed to cover the PTV.
A single plane may be sufficient in case of a target thickness of less than 12 mm.
Three planes are required in a large breast where the targeted breast tissue between pectoral fascia and skin is thicker than 30 mm.
Five to nine needles spaced 15–20 mm are usually required.
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Reference needle is first implanted at the posterior (deepest) side into the centre of the PTV.
For definitive positioning, the needle should pass about 5 mm behind the internal scar.
The other needles of the posterior plane are then implanted parallel to the first one.
For definitive positioning, the needle should pass about 5 mm behind the internal scar.
The other needles of the posterior plane are then implanted parallel to the first one.