A dosimetric comparison between the supine and prone positions for three-field intact breast radiotherapy.
OBJECTIVE
Supine tangential radiotherapy for the intact breast is a standard component of breast conservation management; a supraclavicular (SCV) field can be added for patients at high risk for nodal failure. Treatment in the prone position has demonstrated improvements in lung sparing, but has been limited to early-stage patients in whom radiation to only the breast was indicated. We sought to investigate the dosimetric feasibility of treating women in the prone position, using a 3-field monoisocentric technique.


METHODS
A total of 10 patients previously simulated supine and prone were selected for replanning. The heart, ipsilateral breast, contralateral breast, and axillary/SCV lymph node regions were contoured in accordance with Radiation Therapy Oncology Group guidelines. The 3-field monoisocentric plans were created for both the supine and prone scans. Target coverage, homogeneity, and organ at risk sparing were examined.


RESULTS
Both plans achieved acceptable coverage of the breast. The mean percentage of the breast receiving at least 95% of the prescription dose (V95%) were similar in the prone and supine positions, 89.3% versus 90.7% (P = 0.29). Mean V95% of the level 3 axilla and SCV were 93.8% versus 97.0% prone versus supine (P = 0.16). The percentage of ipsilateral lung receiving >20 Gy was substantially reduced from 21.2% supine to 9.3% prone (P = 0.001).


CONCLUSIONS
Three-field radiotherapy in the prone position appears to be dosimetrically equivalent to supine treatment with respect to target coverage, but the prone position decreases lung dose.
Gielda
Benjamin T
BT
Department of Radiation Oncology, Rush University Medical Center, Chicago, IL 60612, USA. Benjamin_gielda@rush.edu
Strauss
Jonathan B
JB
Marsh
James C
JC
Turian
Julius V
JV
Griem
Katherine L
KL
D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000532:radiotherapy*; D019583:Dose Fractionation, Radiation; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008168:Lung / Q000528:radiation effects; D008198:Lymph Nodes / Q000528:radiation effects*; D008875:Middle Aged; D016684:Prone Position; D011832:Radiation Injuries / Q000209:etiology / Q000517:prevention & control*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D018714:Radiotherapy, Adjuvant / Q000009:adverse effects / Q000379:methods; D020266:Radiotherapy, Conformal / Q000009:adverse effects / Q000379:methods*; D012189:Retrospective Studies; D016683:Supine Position