Volumetric modulated arc therapy improves dosimetry and reduces treatment time compared to conventional intensity-modulated radiotherapy for locoregional radiotherapy of left-sided breast cancer and internal mammary nodes.
OBJECTIVE
Volumetric modulated arc therapy (VMAT) is a novel extension of conventional intensity-modulated radiotherapy (cIMRT), in which an optimized three-dimensional dose distribution may be delivered in a single gantry rotation. VMAT is the predecessor to RapidArc (Varian Medical System). This study compared VMAT with cIMRT and with conventional modified wide-tangent (MWT) techniques for locoregional radiotherapy for left-sided breast cancer, including internal mammary nodes.


METHODS
Therapy for 5 patients previously treated with 50 Gy/25 fractions using nine-field cIMRT was replanned with VMAT and MWT. Comparative endpoints were planning target volume (PTV) dose homogeneity, doses to surrounding structures, number of monitor units, and treatment delivery time.


RESULTS
For VMAT, two 190 degrees arcs with 2-cm overlapping jaws were required to optimize over the large treatment volumes. Treatment plans generated using VMAT optimization resulted in PTV homogeneity similar to that of cIMRT and MWT. The average heart volumes receiving >30 Gy for VMAT, cIMRT, and MWT were 2.6% +/- 0.7%, 3.5% +/- 0.8%, and 16.4% +/- 4.3%, respectively, and the average ipsilateral lung volumes receiving >20 Gy were 16.9% +/- 1.1%, 17.3% +/- 0.9%, and 37.3% +/- 7.2%, respectively. The average mean dose to the contralateral medial breast was 3.2 +/- 0.6 Gy for VMAT, 4.3 +/- 0.4 Gy for cIMRT, and 4.4 +/- 4.7 Gy for MWT. The healthy tissue volume percentages receiving 5 Gy were significantly larger with VMAT (33.1% +/- 2.1%) and IMRT (45.3% +/- 3.1%) than with MWT (19.4% +/- 3.7%). VMAT reduced the number of monitor units by 30% and the treatment time by 55% compared with cIMRT.


CONCLUSIONS
VMAT achieved similar PTV coverage and sparing of organs at risk, with fewer monitor units and shorter delivery time than cIMRT.
Radiation Therapy Program, British Columbia Cancer Agency-Vancouver Island Centre, Victoria, British Columbia, Canada. cpopescu@bccancer.bc.ca
Carmen C
CC
Popescu
Ivo A
IA
Olivotto
Wayne A
WA
Beckham
Will
W
Ansbacher
Sergei
S
Zavgorodni
Richard
R
Shaffer
Elaine S
ES
Wai
Karl
K
Otto
D000328:Adult; D000368:Aged; D000465:Algorithms; D001940:Breast; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D001955:British Columbia; D005260:Female; D006321:Heart / Q000528:radiation effects; D006801:Humans; D008168:Lung / Q000528:radiation effects; D015182:Lymphatic Irradiation / Q000379:methods; D008875:Middle Aged; D011832:Radiation Injuries / Q000517:prevention & control; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013679:Technology, Radiologic; D035441:Thoracic Wall; D013997:Time Factors; D047368:Tumor Burden