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Evaluation of rectal shielding in a Henschke system applicator
S J Howlett1, J W Denham, T Kron
1Department of Radiation Oncology Newcastle Mater Misericordiac Hospital, Waratah, Australia.
Summary
Ovoid shielding in the Henschke applicator can reduce rectal dose by 5-15%, particularly with iridium-192 sources. This technique offers a worthwhile option for gynecologic brachytherapy, improving treatment accuracy.
Area of Science:
- Gynecologic oncology
- Radiation oncology
- Medical physics
Background:
- Brachytherapy is a key treatment for gynecologic cancers.
- The Henschke applicator is commonly used for intracavitary brachytherapy.
- Ovoid shielding is a technique to reduce radiation dose to surrounding tissues.
Purpose of the Study:
- To evaluate the effectiveness of ovoid shielding in the Henschke intracavitary gynecologic 3-channel applicator.
- To quantify the reduction in rectal dose achieved with ovoid shielding.
- To compare measured doses with treatment planning computer calculations.
Main Methods:
- Utilized an acrylic phantom and a modified Henschke applicator to simulate standard treatments.
- Employed thermoluminescent dosimeters (TLDs) to measure point A and rectal doses.
- Calibrated TLDs against a caesium teletherapy unit and estimated shielding effects for iridium-192 wire.
Main Results:
- Ovoid shielding reduced rectal doses by 5-15% in the measured area.
- The shielding effect was more pronounced when using iridium-192 sources compared to caesium-137.
- Good agreement was observed between computed and measured point A doses, considering steep dose gradients.
Conclusions:
- Ovoid shielding is a valuable option for the Henschke applicator, offering dose reduction benefits.
- While not providing a large rectal dose reduction with caesium-137, it is a worthwhile consideration.
- The study confirms the accuracy of treatment planning calculations for point A doses.