Room: AAPM ePoster Library
Purpose: evaluate the dosimetric effects of DIBH for left-sided breast electron boost.
Methods: patients with left-sided breast cancer were divided into four 10-patient groups based on tumor location in the four quadrants of the breast. All patients received radiotherapy of 42.4 Gy in 16 fractions to the whole breast under DIBH, followed by free breathing (FB) electron boost of 10 Gy in 4 fractions to the lumpectomy cavity. Each patient had one FB and one DIBH CT scan during simulation. The cavity contour on the FB scan was transferred to the DIBH scan after fusing the two CTs with a region of interest in the treated breast. Comparison of FB versus DIBH treatment was performed by replicating the original electron field from the FB scan to the DIBH scan. The replicated electron field in the DIBH scan was confirmed to be appropriate with minor modification of the alignment to the cavity. Dose calculation was performed for both treatments using electron Monte Carlo with the same monitor units in the original FB plan.
Results: with FB, DIBH reduced the heart mean dose (Dmean), maximum dose (Dmax), V1Gy, and V2Gy by an average of 34.2%, 30.9%, 41.1% and 59.8%, respectively, for tumors in upper inner quadrant (UIQ).The average reductions in these metrics were 29.7%, 33.6%, 35% and 57.8% for upper outer quadrant (UOQ) tumors, and were 20.3%, 21.9%, 20.6% and 35.7% for lower inner quadrant (LIQ) tumors. For lower outer quadrant (LOQ) tumors however, the average decrease in Dmax and V2Gy were 22.4% and 14.8%, but an average increase in the heart Dmean and V1Gy by 13.7% and 12.4% was observed.
Conclusion: for electron boost would further reduce radiation dose to heart in left- sided breast cancer patients, especially for tumors located at UIQ, UOQ and LIQ.
Funding Support, Disclosures, and Conflict of Interest: This research was funded in part through the NIH/NCI Cancer Center Support Grant P30 CA008748.