Radiation oncology (London, England) 2012-09-24
Is there an advantage to delivering breast boost in the lateral decubitus position?   
ABSTRACT
BACKGROUND
The purpose of this study was to compare the change in depth of target volume and dosimetric parameters between the supine and lateral decubitus positions for breast boost treatment with electron beam therapy.
METHODS
We analyzed 45 patients who were treated, between 2009-2010, with whole breast radiation (WBRT) followed by a tumor bed boost in the lateral decubitius position. Tumor bed volume, distance from skin to the maximal depth of the tumor bed, D90 (dose covering 90% of the tumor bed volume), maximal dose, electron energy and doses to heart and lungs were compared. Additional variables of body mass index (BMI) and tumor bed location were also analyzed to see if there was a benefit limited to any subgroup.
RESULTS
Median BMI for the 45 patients treated was 30.6 (20.6-42.4). When comparing the supine scan to the lateral decubitus scan, there was no significant difference in the tumor bed volume (p = 0.116). There was a significant difference between depth to the tumor bed in the supine scan and lateral decubitus scan (p < 0.001). The mean maximum doses and D90 between the two scans were 110.7 (100.0-133.0)% vs 106.1 (95.1-116.9)% (p < 0.05) and 93.9 (81.3-01.0-101.0)% vs. 98.2 (89.1-108.0)% (p = 0.004) respectively. There was no difference in dose delivered to the lungs or heart between the two scans (p = 0.848 and p = 0.992 respectively). On subset analysis, there was a difference in depth to tumor that was seen across all BMI classes, including normal (p ≤ 0.001, overweight (p ≤ 0.001) and obese (p ≤ 0.001). The majority of patients had a tumor in the upper outer quadrant (77.8%) and on subset analysis, there was a significant difference in tumor bed volume (p < 0.01), depth to tumor (p < 0.01), tumor bed coverage [D90] (p < 0.05), maximum dose (p < 0.05) and energy (p < 0.001) for this location.
CONCLUSIONS
Delivering a tumor bed boost in the lateral decubitus position reduces the distance to the tumor bed allowing for a lower energy treatment to be used to treat breast cancer. It improves coverage and decreases maximal dose to the target volume, all of which would help reduce skin morbidities and should be considered for patients with upper outer quadrant disease, irrespective of BMI status.

Related Questions

 At what energy of electrons would it be better to use photons?  How many fields and what field angles should be used for photon boosts?&nbs...

Are there any quantitative measures that you use to help select patients such as  breast size or heart dose? Or do you use a case-by-case qualita...

Mini-tangents only? 3-4 fields including lightly weighed perpendicular to chest with some exit dose to lung?

If using boost, how would you define the tumor bed? Would you consider resimulation for target localization? If so, what is the maximum interval of t...

Is there a certain energy beyond which you feel the acute or late toxicity to the skin/breast warrants a switch to photon techniques?