How Many Radiotherapy Sessions for Breast Cancer? From 25 Sessions Down to One
- รศ.พญ.เยาวนุช คงด่าน
- 11 hours ago
- 9 min read
How Many Radiotherapy Sessions for Breast Cancer? From 25 Sessions Down to One
Breast cancer radiotherapy no longer means one fixed number of sessions. Depending on the schedule your radiation oncologist selects, treatment may run 25–33 sessions (the conventional schedule, about 5–6 weeks), 15–16 sessions (the current international standard, about 3 weeks), 5 sessions in a single week, or a single session delivered during surgery with IORT in carefully selected patients. This article, prepared by the breast specialist team at Namarak Hospital in Bangkok, explains how these schedules differ and what determines the right number for each patient.
More sessions is not automatically better, and fewer is not automatically safer. What matters is the total biological dose and the schedule that fits the individual's disease — a decision made by the treating team.
In this article
Why radiotherapy is given after breast cancer surgery
All schedules compared at a glance
Conventional schedule: 25–33 sessions
Current standard: 15–16 sessions
One week, 5 sessions
Accelerated partial breast irradiation (APBI): 5–10 sessions
IORT: a single session in the operating room
The tumour bed boost — and using IORT as the boost
What determines your number of sessions
Are side effects different with shorter schedules?
Frequently asked questions
Planning treatment from abroad
Why radiotherapy is given after breast cancer surgery
Radiotherapy after surgery targets any cancer cells that may remain in tissue that cannot be seen. It substantially reduces the risk of local recurrence, and in certain groups it also improves long-term survival.
Radiotherapy is usually indicated for:
Patients who have breast-conserving surgery — nearly all require radiotherapy, because breast conservation matches mastectomy in outcome only when radiotherapy is given.
Patients who have a mastectomy but carry risk factors such as a large tumour, lymph node involvement, or close surgical margins.
Some patients may reasonably omit radiotherapy — for example, selected older patients with small, hormone-receptor-positive tumours and no nodal involvement, where endocrine therapy alone may be appropriate. This is an individualised decision.
All schedules compared at a glance
Schedule | Sessions | Duration | Approximate dose |
Conventional | 25 (+ boost 5–8) | 5–6 weeks | 50 Gy |
Moderate hypofractionation | 15–16 | ~3 weeks | 40–42.5 Gy |
Ultra-hypofractionation | 5 | 1 week | 26 Gy |
APBI | 5–10 | 1–2 weeks | ~30–38.5 Gy by technique |
IORT (in the operating room) | 1 | Day of surgery | 20 Gy at applicator surface (50 kV) |
Who each schedule is for
Conventional — specific clinical situations, such as certain nodal irradiation scenarios
Moderate hypofractionation — the current standard for most patients with early breast cancer
Ultra-hypofractionation — patients meeting FAST-Forward criteria, especially those facing travel constraints
APBI — selected low-risk patients meeting specific eligibility criteria
IORT — selected early-stage patients, or as a boost in higher-risk patients
Important note on comparing doses: the IORT dose is prescribed at the applicator surface and falls off rapidly with depth. It is therefore not directly comparable to external beam figures — 20 Gy with IORT does not mean "weaker" or "stronger" than 26 Gy in five fractions, because the two are measured at different points and cover different tissue volumes.
Conventional schedule: 25–33 sessions
Treatment is given once daily, five days a week, for about five weeks (25 sessions), plus a tumour bed boost of 5–8 sessions where indicated — roughly 30–33 in total.
The practical drawback is the travel burden: attending hospital almost every working day for over a month is a genuine obstacle for patients living outside the city, still working, or dependent on someone to bring them. This schedule is used less often today, though it retains a role in specific clinical situations.
Current standard: 15–16 sessions
This schedule gives a slightly higher dose per session over fewer visits — around 15–16 sessions in about three weeks. Large randomised trials (including the UK START trials and a Canadian trial), together following more than 7,000 patients for up to ten years, confirmed that disease control matches the conventional schedule with no increase in long-term side effects.
International guidelines therefore treat 15–16 sessions as the standard for most patients with early breast cancer. Patients who remember a relative being treated over six weeks some years ago are often surprised at how much shorter their own plan is.
One week, 5 sessions
The UK FAST-Forward trial, involving about 4,000 patients, compared 26 Gy in five fractions over one week against the standard 40 Gy in 15 fractions over three weeks. At five years the five-fraction schedule was non-inferior for local control, and longer follow-up out to ten years has continued to support this, with acceptable long-term side effects.
Many centres worldwide have adopted this schedule, particularly for patients facing travel constraints. Selection still depends on disease features, breast size and shape, and whether regional lymph nodes need to be treated.
Accelerated partial breast irradiation (APBI): 5–10 sessions
For selected low-risk patients, radiotherapy may be directed only to the tissue around the surgical cavity rather than the whole breast, in roughly 5–10 sessions.
The rationale is that most local recurrences arise close to the original tumour site, so concentrating the dose there may give comparable results while sparing normal tissue. APBI covers several techniques, each with specific eligibility criteria.
IORT: a single session in the operating room
IORT (Intraoperative Radiation Therapy) delivers radiotherapy once, during surgery, immediately after the tumour is removed. An applicator is placed into the surgical cavity and low-energy radiation is delivered directly to the surrounding tissue over roughly 20–50 minutes, while the patient is still under anaesthesia — so nothing is felt during treatment.
IORT is used in two distinct roles: (1) replacing whole-breast radiotherapy in selected early-stage patients, and (2) as a boost alongside whole-breast radiotherapy in higher-risk patients.
For eligible patients, treatment is completed on the day of surgery, with no repeat hospital visits over subsequent weeks, and the rapid fall-off of low-energy radiation with distance limits the dose reaching the heart and lungs.
Selection criteria used at Namarak Hospital, based on the TARGIT-A trial, generally include: age 45 or above, cancer suitable for breast-conserving surgery, a unifocal tumour no larger than 3 cm, and no extensive nodal involvement.
Limitations that must be understood clearly
At the time IORT is delivered, the full pathology report is not yet available. If higher-risk features emerge afterwards, whole-breast radiotherapy may still be recommended — a risk-adapted approach.
The ELIOT trial, using a different IORT technique, found higher recurrence rates when patient selection was less strict — underlining that selection is the single most important factor.
The American Society for Radiation Oncology (ASTRO) has stated that long-term follow-up data for some IORT techniques remain limited and that the technique is not incorporated as a primary recommendation in standard practice guidelines.
Namarak Hospital therefore offers IORT only to carefully selected patients, with both benefits and limitations explained in full so that the decision is made jointly with the medical team. It is not appropriate for everyone.
The tumour bed boost — and using IORT as the boost
Some patients receive an additional 5–8 sessions directed at the original tumour site after whole-breast radiotherapy. This boost reduces the risk of recurrence at that site and is typically given to younger patients, those with higher-risk pathology, or where margins were close. So the full answer to "how many sessions" must include it: 15 sessions + a 5-session boost = 20.
IORT delivered as the boost
IORT can also be used as the boost itself: a single intraoperative dose to the tumour cavity, followed by conventional whole-breast radiotherapy afterwards. This applies to patients at higher risk of local recurrence who already have an indication for a boost — for example premenopausal patients, tumours larger than 2 cm, grade 3 tumours, HER2-positive or triple-negative disease, or an extensive intraductal component.
Practical advantages over an external boost include direct visualisation of the cavity during surgery, and removing 5–8 additional hospital visits. Importantly, the patient still receives standard whole-breast radiotherapy, so this is not a reduction in treatment.
Current evidence: the prospective TARGIT BQR registry, covering more than 1,000 patients across ten German centres, reports that an IORT boost combined with whole-breast irradiation is safe and feasible, with good oncological outcomes at five years. The randomised TARGIT-B trial, testing whether an IORT boost is superior to an external boost, has completed recruitment and final results are awaited. For now this remains an individualised option rather than a standard recommendation replacing external boost for all patients.
At Namarak Hospital, the Intrabeam 600 delivers the boost at 20 Gy at the applicator surface in a single intraoperative session, followed by whole-breast radiotherapy according to the treatment plan.
What determines your number of sessions
Type of surgery — breast conservation or mastectomy
Stage and tumour features — size, focality, nodal involvement, subtype, hormone receptor and HER2 status
Post-operative pathology — whether margins are adequately clear
Whether regional lymph nodes require treatment
Anatomical factors — breast size and shape, cardiac position in left-sided disease
Comorbidities and personal circumstances, including travel constraints
Other treatments given, such as chemotherapy before or after surgery
Are side effects different with shorter schedules?
A common concern is whether fewer, larger doses are more damaging. Long-term trial data show that the established shorter schedules (15–16 sessions, and 5 sessions per FAST-Forward criteria) carry overall long-term side effects comparable to conventional treatment in appropriately selected patients.
Common effects across all schedules include skin darkening or dryness in the treated area, fatigue, and temporary breast swelling — most of which settle after treatment ends. Longer-term changes such as tissue firmness or altered breast shape occur in a minority.
Modern technique also reduces cardiac dose — for example deep inspiration breath hold for selected patients with left-sided disease.
Frequently asked questions
How many radiotherapy sessions are needed for breast cancer?
It depends on the schedule chosen: 25–33 sessions over 5–6 weeks (conventional), 15–16 sessions over about 3 weeks (current standard), 5 sessions in one week, or a single session with IORT for selected early-stage patients. The radiation oncologist determines the appropriate number based on each patient's disease.
How long does each session take, and is it painful?
Each session takes roughly 10–20 minutes in the treatment room, with only a few minutes of actual radiation delivery. It is not painful — similar to having an X-ray. Most of the time is spent positioning the patient accurately.
Do fewer sessions mean a worse outcome?
No. The shorter schedules in current use have been compared against conventional treatment in trials involving thousands of patients followed for up to a decade, and give equivalent disease control in eligible patients, because the dose per session is calculated to produce a comparable biological effect. Not every patient, however, is suitable for a shorter schedule.
Can radiotherapy be omitted after breast-conserving surgery?
Most patients require it, because breast conservation matches mastectomy in outcome only when radiotherapy is given. Only specific groups — such as older patients with small, hormone-sensitive tumours and no nodal involvement — may be considered for alternatives, assessed individually.
Is IORT really a single session, and might more be needed?
In appropriately selected patients IORT is a single intraoperative treatment with no further radiotherapy. Because it is given before the final pathology is available, however, whole-breast radiotherapy may still be recommended afterwards if higher-risk features are identified.
Is IORT only used instead of whole-breast radiotherapy?
No. IORT has two roles: replacing whole-breast radiotherapy in selected early-stage patients, and serving as the tumour bed boost — a single intraoperative dose followed by conventional whole-breast radiotherapy — in higher-risk patients who already require a boost. The medical team determines which role applies.
Is there residual radiation that could harm people nearby?
No. Neither external beam radiotherapy nor IORT leaves residual radiation in the patient. Normal close contact with family, children and elderly relatives is safe.
Planning treatment from abroad
For international patients, the number of sessions has a direct effect on how long you need to stay in Thailand. A five-session schedule can often be completed within a single week, while conventional treatment requires a stay of more than a month. Where IORT is appropriate, radiotherapy may be completed during the operation itself.
Namarak Hospital delivers IORT with the Intrabeam 600 in its own operating theatre, while external beam radiotherapy is delivered in partnership with collaborating hospitals, with the Namarak team planning treatment and coordinating care throughout.
About Namarak Hospital
Namarak Hospital is a breast-specialised hospital in Bangkok providing complete care — from 3D mammography screening and diagnosis through surgery, treatment and long-term follow-up — delivered by a multidisciplinary team of breast surgeons, radiation oncologists and medical oncologists, led by Assoc. Prof. Youwanush Kongdan, President of the Thai Breast Disease Society.
If you are planning treatment and want to know which radiotherapy schedule fits your situation, or would like a Second Opinion before deciding, our team is available for consultation — book an appointment online or call +66 2 059 0245.
Written and medically reviewed by: Assoc. Prof. Youwanush Kongdan — President of the Thai Breast Disease Society, and the medical team at Namarak Hospital
Key references: START trials (UK), FAST-Forward (5-year and 10-year results), TARGIT-A, TARGIT BQR, ELIOT, and the ASTRO statement on IORT
This article is for general information only and is not individual medical advice. Please consult a qualified specialist for diagnosis and treatment appropriate to your situation.
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