10/08/2026
This explains why each of us may have had different treatment. I had 35, but also still had positive pathology after chemo and node involvement.
Never heard it explained this was before.
5, 8, 10 OR 15 FRACTIONS?
WHY DOESN’T EVERY BREAST CANCER PATIENT GET THE SAME NUMBER OF SESSIONS?
When patients hear that one woman received 5 radiotherapy sessions, another received 15, and someone else received 8 or 10, it is natural to ask: “Why? Isn’t the treatment supposed to be the same?” The answer is that fractionation is not simply a matter of counting treatment visits. In radiotherapy, we are constantly balancing total dose, dose per fraction, treatment volume, tumor biology, normal-tissue tolerance, and the patient's individual clinical situation.
The classic approach to breast radiotherapy used 50 Gy in 25 fractions, delivering 2 Gy per fraction over approximately 5 weeks. Modern evidence demonstrated that breast cancer can be safely treated with larger doses per fraction, leading to moderate hypofractionation, such as 40 Gy in 15 fractions over 3 weeks or 42.5 Gy in 16 fractions. ASTRO guidelines have recognized 40 Gy/15 fractions and 42.5 Gy/16 fractions as established hypofractionated whole-breast schedules.
Then came a major change: ultrahypofractionation. The FAST-Forward trial compared 26 Gy in 5 fractions over 1 week with 40 Gy in 15 fractions and demonstrated that the 5-fraction schedule was non-inferior for local control at 5 years, with comparable normal-tissue effects in the studied population. This is why 5-fraction breast radiotherapy has become an important option for appropriately selected patients.
But here's the key physics concept: 26 Gy in 5 fractions is not simply “40 Gy divided into fewer days.” Each fraction is larger—5.2 Gy per fraction—and the biological effect depends on both total dose and fraction size. This is where radiobiology and the linear-quadratic model become important. We have to consider how tumor cells and late-responding normal tissues respond to different fraction sizes, rather than comparing total physical dose alone.
So why might one patient receive 5 fractions while another receives 15? The decision can depend on the treatment volume and clinical situation. Whole-breast or chest-wall treatment, regional nodal irradiation, partial-breast irradiation, reconstruction, tumor characteristics, age, anatomy, previous treatment and institutional protocols can all influence the appropriate fractionation. For example, ASTRO's partial-breast guideline includes 30 Gy in 5 fractions and 40.05 Gy in 15 fractions as external-beam partial-breast options for appropriately selected early-stage patients.
And yes—8 fractions can appear in breast radiotherapy too, but the context matters. Eight fractions are commonly encountered in some tumor-bed boost or partial-breast brachytherapy approaches rather than representing a universal whole-breast schedule. For example, a sequential boost of 16 Gy in 8 fractions has been used after whole-breast treatment, while GEC-ESTRO partial-breast brachytherapy schedules have included 32 Gy in 8 fractions.
The same principle explains why 10 fractions can appear in breast treatment. Depending on the technique and target, partial-breast irradiation may use regimens such as 38.5 Gy in 10 fractions, while other clinical protocols have investigated schedules such as 34 Gy in 10 fractions. These are not interchangeable with 10 fractions of whole-breast irradiation—the target volume and dose per fraction matter just as much as the number of fractions.
So when someone says, “She only received five sessions—does that mean her treatment was weaker?” the answer is no. Five fractions can represent a carefully designed, evidence-based radiotherapy regimen in the appropriate patient. Conversely, choosing 15 fractions is not necessarily “older” or “less advanced.” Sometimes the larger number of fractions is the more appropriate choice because of the patient's target volumes, nodal treatment, anatomy, reconstruction, risk factors, or the evidence supporting that particular clinical situation.
Fractionation is not about giving radiation for more days or fewer days.
It is about finding the right relationship between dose, fraction size, biology, tumor control and normal-tissue protection.
5 fractions.
8 fractions.
10 fractions.
15 fractions.
Different numbers—but behind every number, there is radiobiology, clinical evidence and a reason.
References
Brunt AM, et al. FAST-Forward Trial: 26 Gy or 27 Gy in 5 fractions vs 40 Gy in 15 fractions. Lancet Oncology / Health Technology Assessment.
Smith BD, et al. ASTRO Guideline on Radiation Therapy for the Whole Breast. Practical Radiation Oncology.
Meattini I, et al. ESTRO-ACROP consensus recommendations on dose and fractionation for early breast cancer. Lancet Oncology. 2022.
ASTRO. Clinical Practice Guideline: Partial Breast Irradiation. 2023/2024.