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Brachytherapy as Day Care Treatment
Sudhir K 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.
3. Encapsulation.
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 / hr.).

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 interstitial.

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
4. Oesophagus

Endovascular brachytherapy
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)

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