Measuring foetal dose from tomotherapy treatments

TL;DR

This study investigates foetal radiation doses during helical tomotherapy treatments, finding doses generally below risky levels and comparable or lower than other radiotherapy methods, with implications for treatment planning in pregnant patients.

Contribution

First assessment of foetal doses in tomotherapy treatments, providing measurement data and dose estimation guidelines for pregnant patients.

Findings

All measured doses were below 100 mGy, the high-risk threshold.

Largest dose measured was 75 mGy, about 0.125% of prescription.

Doses beyond 30 cm from treatment site were consistently low (<50 mGy).

Abstract

Introduction: Treating pregnant women in the radiotherapy clinic is a rare occurrence. When it does occur, it is vital that the dose received by the developing embryo or foetus is understood as fully as possible. This study presents the first investigation of foetal doses delivered during helical tomotherapy treatments. Materials & Methods: Six treatment plans were delivered to an anthropomorphic phantom using a tomotherapy machine. These included treatments of the brain, unilateral and bilateral head-and-neck, chest wall, and upper lung. Measurements of foetal dose were made with an ionisation chamber positioned at various locations longitudinally within the phantom to simulate a variety of patient anatomies. Results: All measurements were below the established limit of 100 mGy for a high risk of damage during the first trimester. The largest dose encountered was 75 mGy (0.125% of prescription dose). The majority of treatments with measurement positions less than 30 cm fell into the range of uncertain risk (50 - 100 mGy). All treatments with measurement positions beyond 30 cm fell into the low risk category (< 50 mGy). Conclusions: For the cases in this study, tomotherapy resulted in foetal doses that are at least on par with, if not significantly lower than, similar 3D conformal or intensity-modulated treatments delivered with other devices. Recommendations were also provided for estimating foetal doses from tomotherapy plans.