Brachytherapy

Basics of brachytherapy

1. Brachytherapy DR/Saeed Albehairy Lecturer of clinical oncology, BNS University , Egypt MD of clinical oncology, Cairo University

2. Definition Giving radiotherapy 1- from short distance 2- using radioactive sources It is also named internal radiotherapy

3. Advantages of brachytherapy High dose of radiation is delivered to tumor in short time, So biologically very effective Normal tissue spared due to rapid dose fall off Better tumor control Radiation morbidity minimal R adiation reactions localized &manageable Treatment time short – reduces risk of tumor repopulation Therapeutic ratio high

4. D isadvantages of brachytherapy Invasive Need anesthesia Limited availability Any small error leads to high normal tissue dose and treatment failure Radiation hazards exposure

5. Types of brachytherapy Depends on Duration of implant Source position Source loading pattern Dose rate

6. D uration of implant Temporary - Dose is delivered over a short period of time and the sources are removed after the prescribed dose has been reached. It may be LDR or HDR. The specific treatment duration will depend on many different factors, including the required rate of dose delivery and the type, size and location of the cancer . Ex :- Cs(Cesium)137 , Ir (Iridium)192 Permanent - also known as seed implantation, involves placing small LDR radioactive seeds (about the size of a grain of rice) in the tumor or treatment site and leaving them there permanently to gradually decay. Ex :- I(Iodine)125 , Pd ( P allidium )103 , Au(Gold)198

7. Source position Interstitial - the sources are placed directly in the target tissue of the affected site, such as the prostate or breast . Contact - involves placement of the radiation source in a space next to the target tissue. Intracavitary – Consists of positioning applicators bearing radioactive sources into the body cavity in close proximity to target tissue eg :- Cervix Intraluminal – Consists of inserting single line source into a body lumen to treat its surface &adjacent tissue . Eg . esophagus Surface ( Mould therapy) Consists of an applicator containing array of radioactive sources designed to deliver a uniform dose distribution to skin/mucosal surface . Intravascular – Inserting a single line source to Blood vessels to treat the layers of blood vessel

8. Source loading pattern Pre-loading :- Inserting needles/tubes containing radioactive material directly into the tumor After-loading :- First, the non-radioactive tubes inserted into tumor Manual After Loading :- Ir192 wires, sources manipulated into applicator by means of forceps & hand-held tools Remote After Loading :- consists of pneumatically or motor-driven source transport system

9. Dose rate Low-dose rate(LDR)- Emit radiation at a rate of 0.4–2 Gy/hour. Medium-dose rate (MDR)- characterized by a medium rate of dose delivery , ranging between 2-12 Gy/hour. High-dose rate (HDR)-when the rate of dose delivery exceeds 12 Gy/h. Pulsed-dose rate (PDR) - involves short pulses of radiation, typically once an hour, to simulate the overall rate and effectiveness of LDR treatment. Ultra low dose rate - Dose range 0.03 to 0.3 Gy/ Hr

10. HDR V/S LDR Advantages :- Radiation protection Allows shorter treatments times HDR sources are of smaller diameter than the cesium sources that are used for intracavitary LDR ,hence reduced need of Anaesthesia HDR makes treatment dose distribution optimization possible Disadvantage Radiobiological Limited experience The economic disadvantage Greater potential risks

11. IDEAL ISOTOPE Easily available & Cost effective Gamma ray energy high enough to avoid increased energy deposition in bone & low enough to minimise radiation protection requirements Preferably monoenergetic : Optimum 300 KeV to 400 KeV (max=600 kev ) Half life: – Moderate (few years) half life removable implants – Shorter half life for permanent implants

12. Interstitial permanent implant for prostate

13. Interstitial temporary breast implant Intraluminal esophageal brachytherapy

14. Remote Afterloading machine Manual A fterloading