Radiation Therapy and Fractionation

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What is the main advantage of dividing the high dose of radiation into many fractions in radiation therapy?

To deliver the radiation dose more quickly

To increase the overall radiation dose

To allow healthy cells to recover and repopulate between fractions (correct)

To target tumor cells more precisely

What is the primary reason why radiation therapy is especially effective for superficial skin cancers?

The skin is more accessible to radiation (correct)

The healthy cells have better DNA repair mechanisms

The cancer cells are more sensitive to radiation

The tumor cells are more easily targeted

What is the main factor that determines the effectiveness of radiation therapy in individual cases?

The dose of radiation delivered

The frequency of radiation sessions

The cancer type and specifics of individual cases (correct)

The type of radiation used

What is the purpose of the 'Repopulation' phase in the 4 R's of fractionation?

To allow healthy and malignant cells to repopulate after irradiation Signup and view all the answers

What is the typical dose per fraction in a conventional fractionation scheme?

1.8-2.2 Gy Signup and view all the answers

What is the total dose range for conventional fractionation?

45.0 - 50.4 Gy Signup and view all the answers

Which type of fractionation scheme is used to avoid late normal tissue complications?

Hyper-fractionation Signup and view all the answers

What is the dose per fraction range for accelerated fractionation?

1.4 - 2.5 Gy Signup and view all the answers

What is the main issue with hyper-fractionation?

No clear benefit has been demonstrated Signup and view all the answers

Which of the following factors can be controlled in radiotherapy?

Means of delivering the radiation, radiation type, total dose, fractions, and time between fractions Signup and view all the answers

Why are alpha particles not commonly used in radiotherapy?

Because they have a very short range Signup and view all the answers

What is the main advantage of beam sources in radiotherapy?

They deliver a uniform, well-defined, and stable beam Signup and view all the answers

What has become important in the last 25 years of radiotherapy development?

Computerization and intensity modulated beam delivery Signup and view all the answers

What type of radiation therapy involves sealed radioactive sources placed in proximity to the tumor?

Brachytherapy Signup and view all the answers

What was the goal of radiotherapy development in the first 50 years?

To produce ever higher photon and electron beam energies and intensities Signup and view all the answers

What is the primary purpose of a teletherapy machine?

To contain and control the radiation source Signup and view all the answers

What is the typical diameter of a teletherapy source?

Between 1 and 2 cm Signup and view all the answers

What is the effect of decreasing the source diameter?

Smaller physical penumbra and higher cost Signup and view all the answers

What is the typical dose rate at 80 cm from the teletherapy source?

1-2 Gy/min Signup and view all the answers

Why is a standard source capsule design used?

To enable swapping of sources between machines Signup and view all the answers

What is the term used to describe treatment machines that incorporate gamma ray sources for external beam radiotherapy?

Teletherapy machines Signup and view all the answers

Which of the following is a consideration when selecting a suitable source for teletherapy devices?

Half-life Signup and view all the answers

What is the most widely used teletherapy source?

60Co radionuclides Signup and view all the answers

What is the primary factor that determines the effectiveness of a teletherapy source?

Photon energy Signup and view all the answers

What is the purpose of considering the decay into a more stable daughter nucleus in teletherapy sources?

To ensure the source is stable during treatment Signup and view all the answers