Lecture 5

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Which of the following is an operational classification of radiation damage?

Lethal Damage

Potentially Lethal Damage (PLD)

Sublethal Damage (SLD)

All of the above (correct)

What is the characteristic of Lethal Damage?

It causes cell death under ordinary circumstances

It is Irreversible and leads to cell death (correct)

It is repairable under normal circumstances

It is modifiable by postirradiation conditions

What is the potential outcome of Potentially Lethal Damage (PLD) repair?

Enhanced cell survival (correct)

Cell death under ordinary circumstances

Formation of lethal damage with additional exposure

None of the above

Which type of radiation damage can be repaired under normal circumstances?

Sublethal Damage (SLD) Signup and view all the answers

Where was PLD repair studied in vitro?

In density-inhibited stationary-phase cell cultures Signup and view all the answers

How can PLD repair in vitro be enhanced?

By remaining in a density-inhibited state for 6 or 12 hours after irradiation Signup and view all the answers

What is the relevance of PLD repair in radiotherapy?

It influences the fraction of surviving cells after irradiation Signup and view all the answers

Which of the following is true about sublethal damage repair (SLD)?

SLD involves three simultaneous processes: prompt repair, reassortment, and repopulation. Signup and view all the answers

What is the effect of dividing the total dose into two equal fractions with a time gap of 1 to 4 hours for X-rays?

It leads to a significant increase in cell survival due to prompt repair of SLD. Signup and view all the answers

What is the effect of dividing the dose into two fractions with a time gap for neutrons?

It has little effect on SLD repair and does not significantly impact cell survival. Signup and view all the answers

What is the dose-rate effect?

Dose rate is a critical factor influencing the biological consequences of absorbed doses from x- or γ-rays. Signup and view all the answers

What is the importance of understanding the dose-rate effect in radiotherapy planning?

It maximizes tumor control while minimizing damage to healthy tissues. Signup and view all the answers

What does the survival curve demonstrate in the dose-rate effect?

The survival curve shows a shoulder due to repeated shoulders in each fraction. Signup and view all the answers

What is the impact of repair times on survival curves at low dose rates?

Repair times can vary among different cell types. Signup and view all the answers

Which type of brachytherapy involves implanting sources directly into tumors and adjacent tissues?

Interstitial Brachytherapy Signup and view all the answers

Which type of brachytherapy is a temporary procedure lasting 1 to 4 days?

LDR Intracavitary Brachytherapy Signup and view all the answers

What is the advantage of Permanent Interstitial Implants?

An operation to remove the implant is not needed. Signup and view all the answers

What is the common use of iodine-125 in brachytherapy?

Delivering a total prescribed dose of 160 Gy. Signup and view all the answers

What is the dose rate of LDR Intracavitary Brachytherapy?

About 50 cGy per hour Signup and view all the answers

What is the potential advantage of HDR techniques in brachytherapy?

Reduced normal tissue exposure for specific cases like cervical carcinoma. Signup and view all the answers

What is the definition of Potentially Lethal Damage Repair (PLD)?

Radiation damage modification post-irradiation. Signup and view all the answers

What is the definition of Sublethal Damage Repair (SLD)?

Increase in survival if radiation dose is split into two fractions separated in time. Signup and view all the answers

What is the effect of reducing the dose rate in radiation therapy?

Reduction in cell killing due to Sublethal Damage Repair (SLD) during prolonged exposure. Signup and view all the answers

Which of the following best describes the dose-rate effect in mouse jejunum crypt cells?

The dose-rate effect in mouse jejunum crypt cells is characterized by a dramatic decrease in cell survival as the dose rate decreases. Signup and view all the answers

Which of the following is true about the repair of sublethal radiation damage (SLD)?

The dose-rate effect is caused by the repair of SLD. Signup and view all the answers

What is the importance of apoptosis in the dose-rate effect?

Apoptosis plays a significant role in the dose-rate effect, with different cell types showing variations in the importance of apoptosis. Signup and view all the answers

What is the inverse dose-rate effect in HeLa cells?

The inverse dose-rate effect in HeLa cells refers to an increase in the efficiency of cell killing with decreasing dose rate. Signup and view all the answers

What is the significance of the G2 phase in the inverse dose-rate effect?

The G2 phase is a radiosensitive phase where cells become arrested at low dose rates, contributing to the inverse dose-rate effect. Signup and view all the answers

What is brachytherapy also known as?

Brachytherapy is also known as intracavitary therapy. Signup and view all the answers

What is the transition in brachytherapy from low dose rate (LDR) to high dose rate (HDR) therapy?

The transition from LDR to HDR therapy in brachytherapy is for specific cases, with a focus on cervical carcinoma. Signup and view all the answers