Accelerated Partial Breast Irradiation for Early Breast Cancer

Inclusion Criteria:

Patients must fulfill all of the following criteria for admission to study:

* Women aged \>= 50 years.
* Histologically confirmed diagnosis of invasive breast carcinoma of non-lobular histology.
* Bilateral mammograms performed within 6 months prior to registration.
* Treated with breast conserving surgery (primary excision or re-excision) with negative radial resection margins of \>= 2 mm\* for both the invasive and if present, associated intraductal tumour.

  \*Patients with superficial or deep resection margin of \< 2 mm are eligible if surgery has removed all of the intervening breast tissue from the subcutaneous tissue to the pectoralis fascia.
* Unifocal tumour measuring ≤ 20 mm in maximum microscopic dimension.
* Negative nodal status determined by sentinel node biopsy, axillary dissection, or for women \> 70 years of age, clinical examination.
* No evidence of distant metastasis.
* Assessed by surgeon and radiation oncologist to be suitable for breast conserving therapy.
* Ability to tolerate protocol therapy.
* Protocol therapy must commence no later than 12 weeks from the last surgical procedure or 8 weeks from the last dose of chemotherapy.
* Availability for long-term follow-up.
* Women of child-bearing potential must use adequate contraception during RT.
* Written informed consent.

Exclusion Criteria:

Patients who fulfill any of the following criteria are not eligible for admission to study:

* Multifocal or multicentric tumours.
* Clinical or pathologic evidence of any of the following tumour features: extension to chest wall (excluding pectoralis muscle); oedema (including peau d'orange) or ulceration of skin; satellite skin nodules confined to the same breast; and inflammatory carcinoma.
* Presence of extensive intraductal component (ductal carcinoma in situ occupying \> 25% of the primary invasive tumour and present adjacent to the primary tumour).
* Node-positive breast cancer determined by sentinel node biopsy, axillary dissection, or in women \> 70 years of age, clinical examination.
* Inability to localise surgical cavity on CT scans with no evidence of a surgical cavity, seroma or surgical clips delineating the tumour bed.
* Treatment target volume estimated to occupy \> 25% of the ipsilateral whole breast volume.
* Synchronous or metachronous bilateral invasive or intraductal breast cancer.
* Locally recurrent breast cancer.
* Ipsilateral breast implant.
* Serious non-malignant disease that precludes definitive surgical or radiation treatment (e.g. scleroderma, systemic lupus erythematosus, cardiovascular/pulmonary/renal disease).
* Previous or concomitant malignancies except non-melanoma skin cancer, carcinoma in situ of the cervix, and invasive carcinoma of the colon, thyroid, cervix, or endometrium treated five years prior to study entry.
* Women who are pregnant or lactating.
* Psychiatric or addictive disorders that preclude obtaining informed consent or adherence to protocol