Total body irradiation

TOTAL BODY IRRADIATION

BASIL PAUL SUNNYRADIOTHERAPIST

INTRODUCTION• TBI started using in 1956 by Dr. Donnall

Thomas to treat patients with end stage leukemia

• He was awarded Nobel prize for medicine in 1990

• Rationale for use of TBI not changed

• Tremendous change in Delivery of TBI

Radiation sources used – Co^60 / LINAC

Dose measure techniques- more reliable and accurate rather than erythema dose for determination of dose delivered

INTRODUCTION

• One of main component in interdisciplinary treatment of hematological malignancies-leukemia, lymphoma, rarely solid tumors

• Enables myeloablative high dose therapy (HDT) & immunoablative conditioning therapy prior to stem cell transplantation

TASKS OF TBI• Eradicating diseased marrow

• Reducing tumor burden

• Immunosuppression- lymphocyte elimination to allow grafting of donor bone marrow

• Deplete the BM to allow physical space for engraftment of healthy donor marrow

• Eradication of cells with genetic disorders-Fanconi’s anemia, thalassemia major, Wiskott- Aldrich syndrome

TBI IN CONDITIONING REGIMENS

MALIGNANT

1. LUKEMIAS,

ACUTE MYELOID LUKEMIA (AML)

ACUTE LYMPHOBLASTIC LUKEMIA (ALL)

CHRONIC MYELOID LUKEMIA (CML)

HAIRY CELL LUKEMIA

2. LYMPHOMAS/ MYELOPROLIFERATIVE DISORDERS

NON HODGKINS LYMPHOMAS

REFRACTORY HODGKINS DISEASES

MYELODYSPLASIA

MULTIPLE MYELOMA

TBI IN CONDITIONING REGIMENS

• PEDIATRIC SOLID TUMORS

NEUROBLASTOMA

EWINGS SARCOMA

• ADULT SOLID TUMORS

SMALL CELL OF LUNG

TESTICULAR CARCINOMA

TBI IN CONDITIONING REGIMENS

• NON MALIGNANT CONDITIONS

IMMUNE DISORDERS

APLASTIC ANEMIA

GENETIC DISORDERS

WISKOTT AIDRICH SYNDROME

OSTEOPETEROSIS

TAR SYD

FANCONI ANEMIA

CURRENT INDICATIONS

• HIGH RISK AML/CML IN FIRST REMISSION

• SECOND REMISSION AML

• SECOND REMISSION ALL IF THERE IS HLA COMPATIBLE SIBLING DONOR

• FIRST REMISSION ALL WITH CNS INVOLVEMENT / PH CHROMOSOME POSTIVITY

• LOW GRADE LYMPHOMA AFTER CHEMO FAILURE

• CHILDHOOD AML/ ALL IN SECOND / SUBSEQUENT REMISSIONS

ADVANTAGES

• No sparing of sanctuary sites (testis, brain)

• Dose homogeneity regardless of blood supply

• Independent of hepatic & renal functions

• No problems with excretion or detoxification

• Ability to tailor the dose distribution by shielding specific organs or by boosting sites

DISADVANTAGES

• Potential late side effects

Sterility

Cataract

Growth retardation

Neurological toxicity

• Patient body contour irregularities causes adding of compensators

PRE- REQUISITES FOR TBI

• Medical history and evaluation

• Interdisciplinary approach from doctors and health professionals

• RT & BM transplantation facility must be in same center

• Conditions with a low risk of infections is recommended

PHYSICAL EXAMINATION

• Evaluation of oral cavity and dentition

• Neurological evaluation

• PS

• Organ function analysis

CCT> 60 ml/min

AST / ALT < twice the upper level of normal

PFT

EF> 40%

• Infectious disease evaluation

• Sperm banking

TECHNIQUES OF TBI

• Patient comfort and Reproducibility

• Position of patient and stability

• The common factor in the different techniques of TBI is to deliver the prescribed dose of radiation to the entire body in uniformity of +/-10% of the prescription dose. +/-5% considered as the best.

IMPORTANT CRITERIAS

BILATERAL TBI

BILATERAL TBI

• Designed by Khan et al

• Patient sitting or lying down on a couch

Good Patient comfort

Less homogeneous dose distribution due to variable body thickness, needs compensating blocks.

AP-PA TBI

AP-PA TBI

• Irradiated anteroposteriorly by parallel opposed fields while positioned upright several meters from the source

• More homogeneous dose distribution

• The principle of the technique is that the standing TBI allows shielding of certain critical organs from photons and boosting of superficial tissues in the shadow of the blocks with electrons

OTHER TBI TECHNIQUES

MODIFIED CONVENTIONAL MACHINES

• Large stationary Beam , stationary patient

Extended SSD technique

Collimator removal method

• Moving techniques

Translational beam method

Sweeping beam method

McGill UNIVERSITYSWEEPING BEAM TECHNIQUE

TBI: McGill TECHNIQUE

TBI-IRRADIATION METHODS

TRANSLATIONAL COUCH

Computer controlled

POSITION

• Patient lies supine

Length of patient - not more than 140 cm

If length greater than 140 cm – legs folded with pillow tucked b/n both legs

• Arms flexed and placed near to chestwall

• Knees adjoined together, wrapped

• Positioned at extended SSD of 300 cm

40 x 40 cm FieldSize, Gantry 90, Collimation 45

MeasurementsSkullNeck

Shoulder

Chest

Abdomen

Thigh

Knee

Calf

Ankle

TARGET VOLUME

• All malignant cells including those circulating

• whole cellular immune system

• The Whole Body, including Skin

DOSE PRESCRIPTION

• High Dose TBI – 13.2 Gy in 6 fractions over 3 days

• Standard dose TBI – 12 Gy in 6 fractions over 3 days

• Low dose TBI – 2 Gy in single fraction

• Lung is the dose-limiting organ (maximum 10 Gy).

DOSE REFERENCE POINTS

• The dose reference point is defined

at mid abdomen at the height of the umbilicus

according to an international consensus

TREATMENT DELIVERY

• Delivered in the position which measurements are taken

• Under sterile conditions

OPTIMIZATION OF DOSE

• The homogeneity of dose in the target volume

• The effective sparing the lungs

DOSE VERIFICATION

• In vivo dosimetry is done with Semiconductor diodes, mosfet, LiF TLD chips

• It is placed for skull, H&N , mediastinal regions

1. COMPENSATORS

• Influences of irregular body contours have

to be compensated.

• Tissue compensators are used in

Head and neck region

Lower extremities and

Lungs (Not required usually as effective thickness at

mid mediastinum is greater than at umbilicals. Arms positioned inline with lungs and increase total thickness)

TBI AAPM Report 17

2. BEAM SPOILER

Skin/ surface doses in Megavoltage beams is less than D max

Beam spoiler has to be positioned close to the patient, For build-up the surface dose up to at least 90% of the prescribed dose

1-2 cm thick acrylic is sufficient to meet these requirements

.

3. DOSE HOMOGENIZATION in parts of the target volume with reduced dose :

• Thoracic wall receives a lower dose due to lung shielding.

• Additional irradiation however is not used

• Electron boost can be given if necessary

ACUTE COMPLICATIONS

• Nausea& Vomiting• Headache• Fatigue• Ocular dryness• Esophagitis• Loss of apetite• Erythema/hyperpigmentation• Mucositis• Diarrhea• Fever

CHRONIC COMPLICATIONS

• Ocular – Cataract, dryness, keratitis

• Salivary glands – Xerostomia, dental caries, tooth abnormalities

• Pneumonitis or pulmonary fibrosis

• Hepatotoxicity

• Radiation nephropathy

• Growth abnomalities in children

• Sterility and endocrine abnormalities

• Secondary mets

Targeted TBI – TMI and TMLI

• Total marrow irradiation - skeletal bone. Conditioning regimen for multiple myeloma

• Total marrow and lymphoid irradiation (TMLI) - bone, major lymph node chains, liver, spleen, and sanctuary sites, such as brain. Conditioning regimen for myeloid and lymphoid leukemia

TOMOTHERAPY

• Desirable to deliver radiation only to immune organs and bone marrow spaces sparing sensitive structures like brain, lens, lungs, kidneys

• IMRT planning could accomplish this, but most systems are limited by field size issues

• Accurate IMRT depends on reproducible patient position, which is complicated when considering treating the entire marrow spaces

TOMOTHERAPY

• Tomotherapy - linear accelerator mounted in head of a spiral CT unit

• IMRT delivered as beams spiral down axis of patient supine on treatment couch

• The beams can be planned to deliver dose to bones and bone marrow, liver and spleen as well as major nodal groups and to relatively spare the lungs and kidneys

TOMOTHERAPY ISODOSE DISTRIBUTION

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