Dosimetric comparison of proton and photon three-dimensional, conformal, external beam accelerated partial breast irradiation techniques.
OBJECTIVE
To compare the dosimetry of proton and photon-electron three-dimensional, conformal, external beam accelerated partial breast irradiation (3D-CPBI).


METHODS
Twenty-four patients with fully excised, Stage I breast cancer treated with adjuvant proton 3D-CPBI had treatment plans generated using the mixed-modality, photon-electron 3D-CPBI technique. To facilitate dosimetric comparisons, planning target volumes (PTVs; lumpectomy site plus 1.5-2.0 cm margin) and prescribed dose (32 Gy) were held constant. Plans were optimized for PTV coverage and normal tissue sparing.


RESULTS
Proton and mixed-modality plans both provided acceptable PTV coverage with 95% of the PTV receiving 90% of the prescribed dose in all cases. Both techniques also provided excellent dose homogeneity with a dose maximum exceeding 110% of the prescribed dose in only one case. Proton 3D-CPBI reduced the volume of nontarget breast tissue receiving 50% of the prescribed dose by an average of 36%. Statistically significant reductions in the volume of total ipsilateral breast receiving 100%, 75%, 50%, and 25% of the prescribed dose were also observed. The use of protons resulted in small, but statistically significant, reductions in the radiation dose delivered to 5%, 10%, and 20% of ipsilateral and contralateral lung and heart. The nontarget breast tissue dosimetric advantages of proton 3D-CPBI were not dependent on tumor location, breast size, PTV size, or the ratio of PTV to breast volume.


CONCLUSIONS
Compared to photon-electron 3D-CPBI, proton 3D-CPBI significantly reduces the volume of irradiated nontarget breast tissue. Both approaches to accelerated partial breast irradiation offer exceptional lung and heart sparing.
Kozak
Kevin R
KR
Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
Katz
Angela
A
Adams
Judith
J
Crowley
Elizabeth M
EM
Nyamwanda
Jacqueline A
JA
Feng
Jennifer K
JK
Doppke
Karen P
KP
Delaney
Thomas F
TF
Taghian
Alphonse G
AG
D000368:Aged; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D018270:Carcinoma, Ductal, Breast / Q000532:radiotherapy; D018275:Carcinoma, Lobular / Q000532:radiotherapy; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D015412:Mastectomy, Segmental; D008875:Middle Aged; D017785:Photons / Q000627:therapeutic use*; D061766:Proton Therapy; D011859:Radiography; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal; D011522:Protons
D011522:Protons