The influence of respiratory motion on dose distribution in accelerated partial breast irradiation using volumetric modulated arc therapy.

Abstract

Accelerated partial breast irradiation (APBI) is alternative treatment option for patients with early stage breast cancer. The interplay effect on volumetric modulated arc therapy APBI (VMAT-APBI) has not been clarified. This study aimed to evaluate the feasibility of VMAT-APBI for patients with small breasts and investigate the amplitude of respiratory motion during VMAT-APBI delivery that significantly affects dose distribution. The VMAT-APBI plans were generated with 28.5Gy in five fractions. We performed patient-specific quality assurance using Delta4 phantom under static conditions. We also measured point dose and dose distribution using the ionization chamber and radiochromic film under static and moving conditions of 2, 3 and 5mm. We compared the measured and calculated point doses and dose distributions by dose difference and gamma passing rates. A total of 20 plans were generated; the dose distributions were consistent with those of previous reports. For all measurements under static conditions, the measured and calculated point doses and dose distributions showed good agreement. The dose differences for chamber measurement were within 3%, regardless of moving conditions. The mean gamma passing rates with 3%/2mm criteria in the film measurement under static conditions and with 2mm, 3mm, and 5mm of amplitude were 95.0±2.0%, 93.3±3.3%, 92.1±6.2% and 84.8±7.8%, respectively. The difference between 5mm amplitude and other conditions was statistically significant. Respiratory management should be considered for the risk of unintended dose distribution if the respiratory amplitude is >5mm.