Room: Exhibit Hall | Forum 4
Purpose: Traditionally, the SOC for adjuvant breast radiation therapy with conservation surgery utilizes 3D conformal tangents with a sequentially delivered electron boost. Recently, the use of a hypofractionated simultaneous integrated boost(SIB) to the lumpectomy cavity has begun to be implemented due to its ability compress the treatment schedule. To date, the optimal technique for delivering a surgical cavity boost in the setting of a Deep Inspiration Breath Hold(DIBH) has yet to be determined. The purpose of this study is to dosimetrically compare DIBH Volumetric Modulated Arc Therapy(VMAT) using a simultaneous integrated boost vs. a sequential boost to determine the most effective treatment delivery technique.
Methods: Fifteen (n=15) patients with left sided breast cancer and varying lumpectomy cavity sites were retrospectively planned using the Pinnacle3 TPS. Two DIBH VMAT plans were generated for each patient, one with a sequential electron boost and the other with a simultaneous integrated boost. Plans were optimized with identical beam parameters and plan geometries and normalized such that 95% of the PTV received 95% of the prescription dose following the recommendation of RTOG 1005. Plans were evaluated using the mean biologically effective dose(BED), volumetric data at fixed BEDs, and the target volume conformity(CI, D95/V100) in Velocity for PTV and organs at risk(OAR).
Results: For the PTV, there was no statistically significant differences in the conformity index, but statistically significant differences (p<0.05) were observed in the mean BEDs for the breast PTV and lumpectomy PTV. Regarding the OARs, statistically significant differences in the lungs and heart were found for the following metrics: V20GyBED, VmeanBED, and V5GyBED.
Conclusion: This study evaluated the dosimetric differences between DIBH VMAT sequential boost and DIBH VMAT SIB plans. VMATSIB provides a potential alternative to a sequential delivery due to the better OAR sparing, comparable PTV coverage, and compressed treatment schedule.
TH- External beam- photons: treatment planning/virtual clinical studies