CARE MEDICINE SURGERY
as Day Care Treatment
Bhargava, SS Dagaonkar
Brachytherapy (Brachy: Greek,
for short distance) consist of placing Radioactive sources very close to or
in contact with the target tissue. In most of the cases Brachytherapy is complimentary
to teletherapy or external beam irradiation, sometimes only Brachytherapy is
required. Because the absorbed dose falls of so rapidly with increasing distance
from the sources, high doses (up to 70 Gy) may be safely given to a localized
target region over a short time.
In today perspective of day care treatment, with reducing cost of treatment
and complications related to long stay in the bed, High Dose Rate (HDR) brachytherapy
has become an important tool of radiotherapy, as curative as well as complimentary
treatment to External beam Irradiation. Now with the availability of micro -
HDR brachytherapy machines with a three dimensional treatment planning system
and networking with radio diagnostic facilities, e.g. CT scan, MRI and scanning
of X-ray films, three dimensional treatment planning has become a standard in
all good cancer hospitals.
Brachytherapy may be classified in different terms:
1. Surgical approach to the target volume : -
(A) Interstitial, (B) Intracavitary,
(C) Transluminal, (D) Mould technique.
2. Implant procedure : - (A) Preloaded,
(B) Manually after loaded, (C) Remotely after loaded.
3. Dose Rate : - (A) Low dose rate, (B) Medium dose rate, (C) High dose rate.
4. Type of Implants: - (A) Temporary Implants,
(B) Permanent Implants.
Physics of brachytherapy : The clinically utility of any radionuclide depends
on physical properties such as Half life, Radiation output per unit activity
(Ci / gr.), and photon energy. Other factors such as cost effectiveness, safety
and toxicity also influence its uses.
The single sources dose distribution is of central importance to treatment planning
because given the implant geometry in the patient the dose distribution can
be derived using the principle of superimposition with the use of digital computer
containing the co-ordinates of each source to each point of interest is calculated
from the single source array. These contributions are added together to obtain
estimates of total dose rate of each point, represented by isodose rate curve.
Four factors in general, influence the single source dose distribution:-
1. Distance (inverse square law).
2. Absorption and scattering in the source core.
4. Photon attenuation and scattering in the surrounding tissue.
A. Isotopes used : The need for high specific activity sources limits the no.
of radioisotopes suitable for HDR remote after-loaders. The majority of HDR
units use Ir 192. The smaller Ir 192 source permits access to more body site
via interstitial or intraluminal applications.
B. Applicators : Virtually any applicator designed for low dose rate (LDR) manual
after loading has been, or could be adopted for HDR system. One attractive feature
of HDR remote after loaders, especially the stepping source type, where a single
small source with high activity, moves into the whole length of the applicator,
as pre-planned by the computer, at each place for a specified time; this possibility
of manipulating the dose distribution by controlling the dwell time, which is
used at each dwell position.
C. Pulsed brachytherapy (PB) : PB provides all the advantages of single stepping
source technology available with HDR, such as optimisation of dwell times, but
at a low dose rate. The Ir 192 source is about 1/10 the activity of an HDR source
and therefore provides treatment at an intermediate dose rate (1.5 to 5 Gy /
D. Clinical application : Micro - HDR brachytherapy can be used for treating
very precisely and conformally, any part of the body, e.g. Brain, Head and Neck
cancers, Lung, Oesophagus, Breast, GI Tract, Pancreas, Biliary system, Renal
bed, Rectum, anal canal, Prostate, Uterus, Cervix and Prostate as well as penile
Advantages of remote after loading
1. Radiation exposure to staff virtually eliminated.
2. Improved control of isodose distribution.
3. Low probability of misplacing or losing sources.
4. No source preparation work.
5. Source Loading, unloading and recording performed automatically.
Some additional advantages of HDR
1. Patient immobilization time is short; hence complications resulting from
prolonged bed rest, e.g. pulmonary emboli are eliminated.
2. Use of external applicator fixation devices allows more constant and reproducible
geometry of source positioning.
3. Treatment planning and dosimetry are more exact and optimisation is possible
using varying source dwelling time.
How HDR brachytherapy is practised as day care treatment Whenever a patient
is planned for brachytherapy he /she is advised to come overnight fasting. The
anaesthetist is called and applicators are placed inside the patient under anaesthesia.
The patient is shifted to Simulator for localization of applicators and taking
simulation films. Once films are ready these are digitised and the points of
interest are marked. Then with the help of physicist planning is done. One attractive
feature of HDR remote after loaders, especially the stepping source type, where
a single small source with high activity moves into whole length of applicator
as pre-planned by computer at each place for a specified time, is the possibility
of manipulating the dose distribution by controlling the dwell time used at
each dwell position. Once planning is finalized patient is taken on treatment
table and transfer tubes are connected to applicators which are placed in the
target within patients and treatment is started. Once treatment is over, applicators
are removed and patient is kept for recovery in the department. The patient
can go back home on the same day.
Important organs with cancers treated more frequently:-
1. Cervix and uterus 5. Prostate
2. Breast 6. Buccal Mucosa
3. Soft tissue sarcomas 7. Tongue
A potential new application of brachytherapy is to prevent re-stenosis after
coronary angioplasty, stenting, peripheral vascular bypass surgery or access
procedures for renal dialysis.
Re-stenosis after coronary angioplasty or stenting has been reported in well
over 30% to 40% cases. Coronary brachytherapy, started with coating of stents
with Radioactive p32. Then, Ir192, Sr90 were also used by applicators.
(Consultant Radiation Oncologist, Dept. of Radiation Oncology, Bombay Hospital
Institute of Medical Sciences, Mumbai)