Does three-dimensional external beam partial breast irradiation spare lung tissue compared with standard whole breast irradiation?
OBJECTIVE
To determine whether three-dimensional conformal partial breast irradiation (3D-PBI) spares lung tissue compared with whole breast irradiation (WBI) and to include the biologically equivalent dose (BED) to account for differences in fractionation.


METHODS
Radiotherapy treatment plans were devised for WBI and 3D-PBI for 25 consecutive patients randomized on the NSABP B-39/RTOG 0413 protocol at Mayo Clinic in Jacksonville, Florida. WBI plans were for 50 Gy in 25 fractions, and 3D-PBI plans were for 38.5 Gy in 10 fractions. Volume of ipsilateral lung receiving 2.5, 5, 10, and 20 Gy was recorded for each plan. The linear quadratic equation was used to calculate the corresponding dose delivered in 10 fractions and volume of ipsilateral lung receiving these doses was recorded for PBI plans. Ipsilateral mean lung dose was recorded for each plan and converted to BED.


RESULTS
There was a significant decrease in volume of lung receiving 20 Gy with PBI (median, 4.4% vs. 7.5%; p < 0.001), which remained after correction for fractionation (median, 5.6% vs. 7.5%; p = 0.02). Mean lung dose was lower for PBI (median, 3.46 Gy vs. 4.57 Gy; p = 0.005), although this difference lost significance after conversion to BED (median, 3.86 Gy(3) vs 4.85 Gy(3), p = 0.07). PBI plans exposed more lung to 2.5 and 5 Gy.


CONCLUSIONS
3D-PBI exposes greater volumes of lung tissue to low doses of radiation and spares the amount of lung receiving higher doses when compared with WBI.
Jain
Anudh K
AK
Department of Radiation Oncology, Mayo Clinic, Jacksonville, Florida, USA.
Vallow
Laura A
LA
Gale
Ashley A
AA
Buskirk
Steven J
SJ
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D016014:Linear Models; D008168:Lung / Q000528:radiation effects*; D008875:Middle Aged; D011832:Radiation Injuries / Q000517:prevention & control*; D011859:Radiography; D020266:Radiotherapy, Conformal / Q000379:methods*; D012062:Relative Biological Effectiveness