Radiation simulation for breast cancer is a critical component of planning and optimizing radiation therapy (RT) to ensure the tumor receives the prescribed dose while minimizing exposure to healthy tissue, particularly the heart and lungs. The purpose of this session is to customize the treatment to your particular anatomy and ensure accurate targeting. Consistent positioning is crucial for reproducibility.
As you will see in the pictures that follow, a high-resolution CT scan is taken in the treatment position. I like to refer to this as the Superman position. You lie face down with the targeted breast hanging down through an opening in the board with your arms above your head to expose your chest wall. The radiation therapist will then slide you into the CT Scanner for a scan that takes approximately 5 minutes. During the scan, the therapist will use laser beams to place markers on your body for treatment cycles. These are not specific to the target area but are used as anatomy markets to line your body up in the machine.
This image is imported into a Treatment Planning System (TPS) where the radiation oncologist will contour the Gross Tumor Volume (GTV), Clinical Target Volume (CTV) and Planned Target Volume (PTV) in order to calculate a specific radiation plan. This can be done through a variety of techniques as seen below:
| Technique | Description | Use Case |
|---|---|---|
| 3D Conformal RT (3D-CRT) | Static beams shaped to the breast | Early-stage breast cancer |
| IMRT | Modulated beams with more dose shaping | Complex anatomy, close to heart |
| VMAT | Arc-based IMRT | Faster delivery, dose conformality |
| DIBH (Deep Inspiration Breath Hold) | Technique to reduce heart dose | Left-sided breast cancers |
| Proton Therapy | Uses protons for precise dose delivery | Re-irradiation, pediatric, cardiac-sparing cases |
Dosage calculation and optimization are completed via Monte Carlo or collapsed cone convolution algorithms. Constraints are applied to PTV and Organs at Risk (OARs) and they will visualize Dose-Volume Histograms (DVHs) to evaluate plan quality. I am going to just assume that really smart people have developed these methods and that none of us need more detail than this.
Once the scan is complete, the therapist will place waterproof tape over your anatomy marker and schedule your treatment plan which will begin about a week after your simulation. This gives the radiology oncologist and physicist time to review the plan and make sure dose meets prescription and OAR limits. At your first session, phantom testing will be completed, beam delivery verified, and dosage measurements performed.
In my particular case, I will be receiving 20 treatments over the course of four weeks. Three of these will be covering the entire breast area with one week targeted at the tumor cavity. Remember, radiation, unlike chemotherapy, is a very targeted treatment. Side effects typically will show around 2-3 weeks in and should resolve after treatments cease. These are typically skin side effects, such as burning and tightness, and overall fatigue. Be sure to stay well hydrated and consume high amounts of protein during the treatment cycles. Treatment for me begins June 4th. Let the countdown begin!
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