Radiotherapy: The Next Chapter
First radiotherapy clinic, 19 June. Adjuvant radiotherapy planned to the right breast, undissected axilla, and internal mammary chain, with a tumour bed boost (15 fractions over 3 weeks, starting mid-July). The team are being thorough given the extent of initial lymph node involvement.
Radiotherapy: The Next Chapter
Surgery is done. Pathology is confirmed. And now, less than three weeks after the immunostaining came back clear, we were sitting in a clinic on Harley Street talking about the next treatment.
19 June 2026. First appointment with the clinical oncologist for radiotherapy planning.
Why radiotherapy, after a pCR?
This is the question worth answering first. If the histology showed no residual cancer (complete pathological response, every node clear) - why does radiotherapy still follow?
The answer comes down to what the cancer looked like at the start, not the end.
At diagnosis, there were 5-7 abnormal lymph nodes on ultrasound, multiple level 1/2 nodes on PET, a high-level node up near the axillary vessels, and possibly some lower right cervical nodes too. That is extensive regional disease. Chemotherapy shrunk all of it to nothing (which is extraordinary), but radiotherapyâs job is to reduce the risk of it ever coming back in the chest wall, the axilla, or the lymph node regions.
The surgery removed the breast tissue and the axillary nodes, but some nodal regions (the internal mammary chain along the breastbone, the undissected axilla, and potentially the lower neck) are not surgically accessible in the same way. Radiotherapy covers those areas.
The clinical oncologist was also clear that a tumour bed boost is recommended even with pCR. The boost is an extra dose of radiation precisely targeted to where the tumour used to sit. The rationale: the treatment worked, so finish the job properly.
What the radiotherapy involves
The fields
Radiation will be directed at:
- The right breast (the conserved breast)
- The undissected axilla (the parts of the armpit not surgically removed)
- The internal mammary chain (IMC) - lymph node territory along the inside of the chest
- Possibly the lower neck - depending on what the baseline PET scan shows when it is retrieved and reviewed at the MDT on 25 June
The dose
| What | Dose |
|---|---|
| Breast + regional nodes | 40.05 Gy in 15 fractions (3 weeks) |
| Tumour bed boost | Combined plan to 48 Gy total |
A âfractionâ is simply one session of radiotherapy - one visit, one dose. So 5 fractions means 5 daily sessions over one week, and 15 fractions means 15 sessions over 3 weeks. The 5-fraction approach has become more common in recent years as a quicker option, but the surgeon recommended the longer course specifically to reduce the risk of breast oedema - fluid build-up in the breast tissue that causes swelling, heaviness, and lasting firmness. After axillary clearance, the lymphatic drainage of the breast is already disrupted (the nodes that help drain fluid have been removed), and the higher dose-per-session of a 5-fraction course carries a greater risk of triggering that fluid build-up in already-affected tissue. Delivering the dose across 15 smaller sessions is gentler on the tissue and less likely to cause lasting swelling.
This is described as highly complex radiotherapy, not a simple breast-only course. The extent of the initial disease means the fields are larger and require more precision in planning.
The technique: DIBH
A deep inspiratory breath hold technique will be used. In plain terms: during each treatment, the patient takes a deep breath and holds it, which lifts and expands the lungs and naturally moves the heart further away from the radiation field. It is a standard approach to protect the heart, especially relevant here given the coronary artery calcification already noted by cardiology.
The timeline
| Date | What |
|---|---|
| 25 June 2026 | Womenâs Health Centre MDT (case discussion and PET review) |
| 29 June 2026 | Planning CT scan |
| 13 July 2026 (provisional) | Radiotherapy starts |
| ~early August 2026 | Treatment ends (15 fractions, 3 weeks) |
| On completion | Follow-up with clinical oncologist |
Phesgo continues
The clinical oncologist confirmed that Phesgo can continue during radiotherapy, provided travel logistics allow. The antibody treatment does not stop for radiotherapy, which means the HER2-targeted therapy that has been running since the start of chemotherapy keeps going through this phase too.
Consented
Acute and long-term side effects were discussed in clinic, and Sarah consented for treatment at this appointment. The team are booked; the planning scan is in the diary.
This is not the end. But it is the last active treatment phase, and the beginning of the end.
What comes next
After radiotherapy completes, the plan is:
- Ongoing Phesgo to finish the full antibody course
- Breast ultrasound arranged for shortly before the surgical follow-up
- Surgical review with the breast surgeon, 20 November 2026
- Continued oversight from the medical oncology team
The road through treatment has been long. First appointment with the surgeon was November 2025. From diagnosis, through the cardiac pause, through EC and Taxol and Phesgo, through surgery and pathology and the wait for immunostaining, to here.
Three weeks of radiotherapy, and then recovery.