Abstract
To create a comprehensive dataset of peripheral dose (PD) measurements from a new generation of linear accelerators with and without the presence of a newly designed fetal shield, PD measurements were performed to evaluate the effects of depth, field size, distance from the field edge, collimator angle, and beam modifiers for common treatment protocols and modalities. A custom fetal lead shield was designed and made for our department that allows external beam treatments from multiple angles while minimizing the need to adjust the shield during patient treatments. PD measurements were acquired for a comprehensive series of static fields on a stack of Solid Water. Additionally, PDs from various clinically relevant treatment scenarios for pregnant patients were measured using an anthropomorphic phantom that was abutted to a stack of Solid Water. As expected, the PD decreased as the distance from the field edge increased and the field size decreased. On average, a PD reduction was observed when a 90° collimator rotation was applied and/or when the tertiary MLCs and jaws defined the field aperture. However, the effect of the collimator rotation (90° versus 0°) in PD reduction was not found to be clinically significant when the tertiary MLCs were used to define the field aperture. In the presence of both the MLCs and the fetal shield, the PD was reduced by 58% at a distance of 10 cm from the field edge. The newly designed fetal shield may effectively reduce fetal dose and is relatively easy to setup. Due to its design, we are able to use a broad range of treatment techniques and beam angles. We believe the acquired comprehensive PD dataset collected with and without the fetal shield will be useful for treatment teams to estimate fetal dose and help guide decisions on treatment techniques without the need to perform pretreatment phantom measurements.PACS number(s): 87.53.Bn, 87.55.D‐, 87.55.N
Highlights
Owrangi et al.: Revisiting fetal dose during radiation therapy and behavioral disorders.[1,2,3,4] these risks can be minimized with careful planning and precautions to ensure the dose to the fetus is as low as reasonably achievable.The goal of radiotherapy is to deliver a high dose to the defined treatment target in an attempt to control the growth of the tumor while minimizing dose to normal structures
All peripheral dose (PD) measurements were normalized to the central axis dose (CAX) dose at the depth of 1.5 cm, for the same field sizes
In the presence of the fetal shield, the PD for the 6 × 6 cm2 field size decreases from 0.30% to 0.26% and 0.01% to 0.005% at distances of 10 and 40 cm from the field edge
Summary
Owrangi et al.: Revisiting fetal dose during radiation therapy and behavioral disorders.[1,2,3,4] these risks can be minimized with careful planning and precautions to ensure the dose to the fetus is as low as reasonably achievable.The goal of radiotherapy is to deliver a high dose to the defined treatment target in an attempt to control the growth of the tumor while minimizing dose to normal structures. Owrangi et al.: Revisiting fetal dose during radiation therapy and behavioral disorders.[1,2,3,4] these risks can be minimized with careful planning and precautions to ensure the dose to the fetus is as low as reasonably achievable. To achieve the optimum treatment plan that balances the risks and benefits of radiotherapy, deliberate treatment strategies should be used in an attempt to minimize fetal dose, and prior to initiating treatment, fetal dose should be evaluated. The abdominal region should not be defined as part of the treatment volume[1] and the fetus will only be exposed to out-of-field/ peripheral dose. Peripheral dose (PD) is the absorbed dose received outside of the radiation treatment field. The principal components of PD are: 1) leakage radiation through the head of the treatment machine, 2) radiation scattered from the collimators and beam modifiers, and 3) radiation scattered within the patient from the irradiated volume (internal scatter).(1)
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