Women treated with accelerated partial breast irradiation (PBI) may avoid extra radiation dose when treated in the prone position, according to research published August 13 in Clinical Oncology.
While prone positioning is linked to lower heart and lung doses and lower rates of acute dermatitis, doses were minimal regardless of whether women are treated in the prone or supine position, wrote a team led by Andrew Wanna, MD, from New York University.
“Both treatment positions were safe, and there were no differences in target coverage or ipsilateral breast dosimetry between the two groups,” the Wanna team wrote.
Researchers continue to explore strategies to reduce radiation exposure to the heart and lungs during breast irradiation. Prone positioning may help by displacing the treated breast away from the chest wall by gravity. However, the researchers noted that evidence for prone positioning for partial breast irradiation is limited, including for accelerated PBI, which uses smaller treatment volumes.
Wanna and colleagues compared dosimetry and acute toxicities between women treated in the prone and supine positions. They noted that their institution offers accelerated PBI at 3,000 cGy in five fractions.
The study included 168 women were treated in 2022 and 2023, with 134 treated in the prone position and 34 treated in the supine position. Of the supine patients, 23 were treated with photon-only plans and 11 with mixed photon-electron plans.
The researchers observed no statistically significant differences in age, body mass index, tumor size, or breast laterality between the two groups. They also noted that planned target volume was larger for prone patients (p = 0.002), target coverage was similar in both positions, and ipsilateral breast dosimetry did not significantly differ.
Women treated in the prone position had significantly lower average heart dose compared to women treated in the supine position, with the difference being clearer in right-sided patients. The average heart dose was also significantly higher in mixed photon-electron plans compared to supine photon-only plans. Prone women also experienced lower ipsilateral lung dose.
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Comparison of heart, lung dose between women treated in prone, supine positions |
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Measure |
Supine |
Prone |
P value |
|
Average heart dose |
14.9 cGy |
9.6 cGy |
0.03 |
|
Average heart dose (right side) |
8.6 cGy |
6.9 cGy |
0.04 |
|
Average heart dose (left side) |
16.5 cGy |
17.6 cGy |
0.71 |
|
Average ipsilateral lung dose (V10Gy) |
1.44% |
0.28% |
|
The supine cohort experienced grade 1 and grade 2 dermatitis more often (p = 0.03) and women with a BMI of 30 or higher had significantly higher fatigue (p = 0.03). Finally, the study authors highlighted that target coverage was “excellent and equivalent” in both cohorts.
The results point to “marginal dosimetric and toxicity advantages” for treatment in the prone position for women who can tolerate both positions.
“Nevertheless, for patients who are unable to tolerate prone positioning due to factors such as limited shoulder mobility, body habitus, respiratory difficulty, or general discomfort, these data demonstrate that supine positioning with a tangential beam arrangement remains a safe and effective alternative, achieving excellent dosimetric and clinical outcomes,” the authors wrote.
The authors called for prospective studies to confirm the dosimetric advantages of prone positioning and tangential beam geometry with accelerated PBI.
Read the full study here.