Multiple randomized studies have shown that adding adjuvant radiation therapy after breast conservation surgery significantly decreases the risk of local recurrence. These studies established adjuvant whole breast radiation therapy in the setting of breast conservation as standard of care for the management of early stage breast.
A course of adjuvant whole breast radiation typically comprises 25 -30 treatments over 5-6.5 weeks (total dose of 50-66 Gy). Most women find this schedule quite cumbersome especially when their place of residence or work is not in close proximity to the radiation center.
Several treatment techniques and fractionation schemes have been developed which provide a more convenient schedule to patients. One such approach is accelerated hypofractionated whole breast radiotherapy where by a larger dose of radiation is given each day allowing for a shorter total treatment course. The most commonly used schedule, pioneered in Canada, delivers 16 treatments over 3 weeks (total dose of 42.5 Gy). Whelan and colleagues at Princess Margaret Hospital conducted a randomized study trial comparing this Canadian schedule to the standard regimen and found no statistically difference in local recurrence or cosmetic outcomes between the two regimens. Canadian fraction is now being offered more frequently in select centers around the United States.
For a very select group of patient with early stage breast cancer and low risk features, an even shorter course of one week of radiation therapy has emerged This is called accelerated partial breast irradiation (APBI). With this technique, radiation is not delivered to the entire breast but is directed at the area at highest risk for local recurrence – the tumor bed i.e. the lumpectomy cavity.
Partial breast irradiation can be performed using different modalities, external beam therapy and interstitial or intracavitary brachtherapy. While brachytherapy requires the insertion, in the tumor bed, of catheters or a balloon device (Mammosite) harboring a radioactive source; external beam radiation is a non-invasive procedure. Radiation is typically delivered twice daily over 5 days after which the device is removed.
APBI is being compared to standard whole breast irradiation in the ongoing RTOG 0413/ NSABP 39 trial.
An even shorter course of partial breast radiation is called IORT (Intraoperative radiation therapy). As the name suggests, this modality delivers radiation therapy during surgery. This can be accomplished either with brachytherapy or external beam radiation as described above is directed to surgical bed. This is quite an attractive option because radiation is delivered in a single day.
A novel method to deliver intraoperative partial breast radiation therapy utilizes a device called Intrabeam. The apparatus delivers low energy x -rays using a spherical applicator modeled to conform to the lumpectomy cavity. This device was utilized in the TARGIT trial, a phase III trial which randomized patients with early stage breast cancer to conventional whole breast radiation therapy over 5-6.5 weeks or single dose rendered intraoperatively using this novel technique.
All the aforementioned techniques and regimens, provides physicians with an array of approaches in their armamentarium from which to offer patients new and appealing options of adjuvant radiation therapy in the setting of breast conservation.
These abbreviated treatment courses are much more convenient for patients and should translate into improved compliance with radiation.
In addition, treatment directed at the tumor bed without treating the entire breast minimizes dose to normal tissue such as contralateral breast, lung, and heart in the case of left-sided breast cancers.
It is therefore not surprising that these options are highly sought after, and are being more frequently employed by radiation oncologists across the country. Armed with this knowledge, I conclude with a statement of precaution. Because long-term follow up is limited on the PBI frontier, strict guidelines and selection criteria must be enforced to determine which patients are eligible for these novel and promising techniques.
