SAMIR LAOUI, PH.D 08/15/2016

DEFINITION

Taken from the Greek word “brachys,” meaning

“near”, Brachytherapy (brak-e-THER-uh-pee) is

a procedure that involves placing radioactive

material inside your body

“……. there is no reason why

a tiny fragment of radium

sealed up in a glass tube

should not be inserted into

the very heart of the cancer;

thus acting directly upon the

diseased material.”

Alexander Graham Bell Letter to Science, 1903

IN 1903 GYNECOLOGICAL BRACHYTHERAPY

WAS FIRST INTRODUCED BY…….

On 15 September 1903, she treated an

inoperable cancer of the cervix uteri with 700

milligrams of radium bromide sealed

in a glass tube.

Margaret Abigail Cleaves

Two applications of 10 minutes each were made with an interval of 3 days between.

O'Brien, F. w. (1947): Amer. J. Roentgenol., 57, 281.

1920S : RADIUM SURFACE THERAPY

Radium surface brachytherapy

treatment of skin cancer at the

Institut Curie, Paris, 1922

1920S : USE OF SEEDS

Implantation of radon seeds

for a carcinoma of the rectum,

1929, at London Hospital

INTRODUCTION

ICRU 38 classification

Low dose rate (LDR): 0.4 – 2 Gy/hr

Medium dose rate (MDR): 1-12 Gy/hr

High dose rate (HDR): > 12 Gy/hr

Intracavitary brachytherapy

Intraluminal brachytherapy

Interstitial brachytherapy

BRACHYTHERAPY SOURCE STRENGTH

Milligram radium equivalent

The air Kerma strength is defined as the air

kerma rate (µGy/hr) at a specified distance (1m)

Unit of uGym2/hr

CALIBRATION OF BRACHYTHERAPY SOURCE

Air kerma strength

22)( lXlKS

e

W

lk

air kerma rate at

distance l U

-12hGym

-1Gyh

Distance l

2m

air kerma strength.

-1mRh

Exposure rate

AIR KERMA STRENGTH

Sk(U) = air Kerma source strength (U)

Conversion factors from mCi:

Ir-192 1 mCi : 0.238 U

I-125 1 mCi : 0.787 U

Pd-103 1 mCi : 0.773 U

U-12

hGym

TRACEABILITY

The AAPM Task Group No. 40 had

recommended traceability of brachytherapy

sources in 1994

Direct traceability

Secondary traceability

Secondary traceability by statistical inference

TRACEABILITY

The NIST standard

ADCLs standards

A customer’s source is calibrated at an ADCL or

NIST by placing it in the well chamber

A customer’s well chamber is calibrated at an

ADCL or NIST against a national standard at an

ADCL or NIST.

TRACEABILITY

SOURCE DOSIMETRY: ICWG

Current standard is to follow the dose

calculation formalism of ICWG and TG-43 –

Specification of dose at a point is given by

Interstitial Collaborative Working Group

GOAL OF QA PROGRAM

The QA program consists of a set of mandated

redundant performance checks, physical

measurements, documentation standards,

training and experience standards, and

guidelines

GOAL OF QA PROGRAM

QA program endpoints

Safety of the patient, the public, and the institution

Positional accuracy +/-2mm is reasonable (+/-

1mm, NRC)

Temporal accuracy 2%

Source calibration +/-3%, relative to existing air

kerma strength standards seems reasonable.

dose calculation +/-2%

PHYSICIST’S ROLE

Applicator insertion process

Implant design and evaluation process

Treatment delivery process

PERFORMANCE OF BRACHYTHERAPY

PROCEDURE

The physician–physicist interaction is a critical

link in promoting safe and accurate

Brachytherapy practices

Ordering sources (RML)

Receiving sources

Treatment planning goal, according to

prescription

TREATMENT QA

It is recommended that standard patterns of

dwell times for similar applications be used

whenever possible

Physicist should check the applicator position

and the connections between applicator and

afterloader head before treatment to be sure

that they agree with the treatment plan.

DOSE SPECIFICATION AND REPORTING

Lack of universal system for dose specification and reporting

Many quantities have been used to quantify, prescribe, and to constrain intracavitary therapy at gynecologic malignancies

Dose to point A

Vaginal surface dose

Treatment time

Curie seconds

DOSE SPECIFICATION AND REPORTING:

INTRACAVITARY BRACHYTHERAPY

ICRU attempted to address this issue in report N 38

In addition to reporting source strengths, treatment time, and standard isodose contours

the dimensions of the 60-Gy isodose (EBT + HDR)

the dose at a bladder point

Rectal dose

Doses at points representing lower para-aortic

Dose at points representing distal parametrium and lymph nodes

BACKGROUND

Prompted by:

A death related to personnel errors in HDR

Greater use of HDR brachytherapy units

NRC proposal to rewrite 10 CFR 35

The need for education on comprehensive HDR

safe-treatment-delivery procedures

None of old reports addresses the details and

issues related to the safe delivery of HDR

treatments.

EGREGIOUS INCIDENT

Death related to personnel errors

Source left in the patient

Radiation alarm ignored

Survey meter was not used

OVERVIEW

To examine the current high dose-rate (HDR)

treatment delivery practices and to prepare a

document to assure safe delivery of HDR

treatments

The document provides an extensive quality

assurance (QA) check list

HDR PROS

Dose optimization capability

Outpatient treatment

More stable positioning

Smaller applicators

Sources do not need to be shipped

Better documentation

Reduced exposure to personnel

HDR CONS

More complex

Errors can lead to severe consequences

Radiobiological disadvantages (normal tissue

toxicity)

Need for accurate dosimetry

Potential of very high dose to patient and

personnel if source fails to retract

DESIGN OF AN HDR BRACHYTHERAPY

PROGRAM

HDR brachytherapy is prone to errors

The physicist’s role is to define the organization

and responsibilities of the treatment delivery

team members

PRINCIPLES OF GOOD HDR PROGRAM DESIGN

Use written documentation whenever possible

Develop a formal procedure for each type of expected case Roles, applicators, emergency situation, QA list

Exploit redundancy Independent verification

Exploit quality improvement techniques: Comprehensive QA program

DOCUMENTATION AND CHECKLIST

I. Written prescription and daily treatment

record

II. Treatment day remote afterloader QA protocol

III. QA procedure flow checkoff list

IV. Physicist’s treatment plan/documentation

review

V. Implant geometry, Dwell time calculations

VI. Dose verification

STAFFING AND TRAINING

Physicians, department heads, and

administrators must realize that development and

maintenance of a safe and effective HDR program

requires a significant time commitment for all

staff involved, especially the medical physicist on

whom the burden of acceptance testing the

equipment, developing procedures, and training

other staff falls

STAFFING AND TRAINING

For an average load of 10 fractions per week,

including periodic QA, staff training and

treatment record audits, 1 FTE of a qualified

medical physicist should be allocated

TREATMENT SPECIFIC QA - DAILY

DAILY QA

PRESCRIPTION

TREATMENT SPECIFIC QA

Applicator preparation & insertion

Reviewed for correct operation and configuration

Implant localization and simulation

A correctly labeled sketch of implant should be drawn

Make use of template forms which help describe implant geometry

DOSE DISTRIBUTION

DOSE DOCUMENTATION

DOSE DOCUMENTATION

DOSE INDEPENDENT VERIFICATION

Final Treatment

checklist

TREATMENT SPECIFIC QA

Whenever treatment is interrupted, it is essential to

check the area monitor to confirm that the source has

been retracted

Again, after treatment is complete, it is again essential

check the area monitor to confirm that the source has

been retracted

EMERGENCY PROCEDURES

The best strategy is to be prepared for all scenarios by

developing emergency procedures for the following

categories:

Physical emergencies (fire, earthquake, floods, etc.)

Minor emergencies (loose source guide tube, vault

door not closing completely)

Major emergencies

Failure of source to retract, patient medical emergency,

computer failure etc.

Dose rates at the periphery of the volume of tissue irradiated by

a static 10 Ci source. The dose rate is about 400 cGy/min at the

periphery of a sphere of 10 cm3

Speed is of the essence in removing the source from the patient

in order to limit the dose to small volumes of local tissue

THANKS AAPM 2016 annual meeting