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
What is the maximum electron energy you would consider using for a breast lumpectomy boost?
I don’t go higher than 12 MeV (normalized typically to 80-85%) and usually am more in the 9 MeV range nowadays if using pure electrons. I have moved to doing most lumpectomy boosts with photons as we can be pretty conformal and more homogeneous (although sometimes we end up treating more breast tiss...
Would you omit a boost in a patient with an indication if a very large (>200cc) post-op seroma obscures the actual tumor bed?
Generally for these patients with seroma > 100 cc, prefer aspiration and settling of seroma before starting RT. Also in general, we tend to rescan for boost most of the time as favor lateral decubitus position and also account for change in size of seroma. Kannan et al., PMID 23006598
What techniques do you typically use for a photon breast boost?
Depends on the location of the cavity and depth, and breast anatomy. Mini tangents work well but can have a lot of doses beyond boost volumes. I sometimes will use a 3 field approach with a lightly waited anterior electron/photon field depending on the depth of the cavity.
When do you recommend prone breast radiation?
If the plan is for whole breast radiotherapy without nodal treatment, I treat almost all women prone. The only women that are treated supine are those that have lump cavities that preclude the benefit of a prone plan (positioned posteriorly along chest wall, so tangents cut through lung/heart) or th...
When giving a breast boost, what are indications for a photon breast boost?
In general, once the surgical cavity depth approaches 5 cm then it is harder to cover with electrons. That being said, for these patients with disease in the outer quadrant, the lateral decubitus position helps significantly to bring the cavity close to the surface. We published this data: http://ww...