BrachytherapyLDR and HDR:

A PrimerDr Santam Chakraborty

Radiation Oncology

Brachytherapy

● Derived from: Brachys (Gr.) - short range/ distance

● Involves:o Sealed radioactive

sourceso Intra / peri-tumor

placemento Geometrical Arrangement Image: wired.com

Primer on Sources

● Radioactive sources:o Naturalo Man-made

● Sealed.● Most Common:

o Iridium 192o Cobalt 60o Cesium 137o Radium 226

What is dose

● Dose : Amount of energy absorbed per unit mass of tissue.

● Energy deposition : Ionization● Unit : Gy

What is Dose Rate

● Amount of Dose per unit time. ● Earlier : Exposure per unit time● Depends upon:

o Amount of Radioactive source implantedo Point of measurement.

Size does matter ..

High specific activity of Iridium makes miniaturization possible.

Types of Dose Rate

1. Ultralow dose rate: 0.01 - 0.03 Gy / hr2. Low dose rate (LDR): 0.4 - 2 Gy / hr3. Medium dose rate (MDR): 2 - 12 Gy /hr4. High dose rate (HDR): > 12 Gy / hr

LDR vs HDR : Sources

● Low specific activity● Various forms:

o Wireso Needles o Tubes

● Inventory required● Personnel protection

: distance and time

● High specific activity● Single form:

o Tubular source● Inventory not

required● Personnel

protection: NA (cannot be handled)

Equipment...

L Bench Selectron Microselectron

LDR vs HDR : Biology

● Biological implications - related to how well cells repair radiation induced damage.

● Radiation induced damage:o Lethal o Sub - lethal

● Sublethal damage can be repaired o Provided we give time to the cell !!

LDR vs HDR : Biology

● In LDR treatment times are in the range of 60 - 144 hours.

● Repair half times: o Normal cells: 2 - 4 hours. o Tumor cells: 0.5 - 1 hour.

● So during LDR treatment - repair of damage also occurs.

LDR vs HDR : Biology

● In HDR treatments:o Sublethal damage is not repaired. o As a result cell kill is more.

● As a result normal cells are damaged MORE with HDR as compared to LDR if the SAME dose is used.

LDR vs HDR : Biology

LDR vs HDR : Biology

● To circumvent this problems:o HDR is given in lower total dose o Correction factor of 0.6 used.

Implies for a LDR dose of 70 Gy, HDR dose will be 42 Gy

o Also dose is fractionated Typical fraction sizes :3.5 - 7 Gy. Interfraction gap: 6 hours.

LDR vs HDR : Nursing

Several nursing implications for LDR brachytherapy:● Prolonged treatment time:

o DVTo Pressure Ulcerso Low residue dieto Paino Applicator displacement

LDR vs HDR : Nursing

Several nursing implications for LDR brachytherapy:● Prolonged treatment time:

o DVTo Pressure Ulcerso Low residue dieto Paino Applicator displacement

LDR vs HDR : Nursing

● Radioactive source placed inside patient for a long time:o Barrier nursingo Isolation of patiento Personnel dosimetry

LDR vs HDR : Cervical Cancer

http://www.jeccr.com/content/28/1/47

LDR vs HDR : Oral Cancer

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0065423

Summary

● Though potentially radiobiologically superior LDR superseded by HDR:o Logistical advantageso Dosimetric advantageso Radiation Protection advantages

Thank You