Partial Breast Irradiation Using Interstitial Permanent Palladium-103 Seed Implant

Inclusion Criteria:

* Patient consent and signature of approved consent form.

  * Age greater than 55 years and postmenopausal.
  * Life expectancy of at least ten years
  * Stage 0 or I breast cancer. Tumour size \< 2 cm.
  * Invasive cancer must be pathologic grade 1 or 2
  * Histology must be either Ductal Carcinoma In Situ or invasive ductal adenocarcinoma of the breast.
  * Tumour removed by lumpectomy with clear margins (DCIS and invasive).
  * Unifocal disease
  * For invasive breast cancer, axillary staging by either sentinel node biopsy or axillary dissection (minimum of 6 axillary nodes). Not required for DCIS.
  * Brachytherapy generally should be performed within 16 weeks of the last surgery (lumpectomy, re-excision of margins, or axillary staging procedure). If \> 16 weeks, will be assessed on case-by-case basis, based on seroma visibility and the presence of surgical clips in the tumour bed.
  * Tumour must be Estrogen Receptor positive.
  * The lumpectomy cavity (seroma) must be clearly delineated by ultrasound and CT and should be \< 3 cm diameter (equivalent sphere) resulting in a maximum of 125 cc planning target volume (PTV).
  * Breast seed implant must be considered technically deliverable by interstitial brachytherapy by the attending radiation oncologist and must be a minimum 2-plane implant.
  * If prior non-breast malignancies, must have been disease-free for 5 or more years. Time limit waived for carcinoma in-situ of the cervix or colon, melanoma in-situ, and basal or squamous cell carcinoma of the skin.

Exclusion Criteria:

* Stage T2 or higher breast cancer

  * Histologically positive axillary nodes.
  * High grade (grade 3) invasive ductal carcinoma
  * Extensive DCIS
  * Lymphatic or Vascular Invasion positive
  * Significant persistent post surgical complications
  * Palpable or radiographically suspicious ipsilateral or contralateral axillary, or regional nodes, unless histologically confirmed negative.
  * Suspicious microcalcifications, densities, or palpable abnormalities in the ipsilateral or contralateral breast unless confirmed benign.
  * Proven multi-centric carcinoma (invasive cancer or DCIS)
  * Paget's disease of the nipple.
  * Synchronous bilateral invasive or non-invasive breast cancer.
  * History of previous ipsilateral invasive breast cancer or DCIS.
  * Surgical margins that are positive or cannot be microscopically assessed.
  * Clear delineation of the target lumpectomy cavity not possible.
  * Breast implants.
  * Prior ipsilateral breast or thoracic radiotherapy.
  * Known genetic mutation in Breast Cancer Associated (BRCA 1 or 2)
  * Collagen vascular disease,