The following is a summary of “Effect of simultaneous integrated boost concepts on photoneutron and distant out-of-field doses in VMAT for prostate cancer,” published in the September 2023 issue of Oncology by Gauter-Fleckenstein et al.
Simultaneous integrated boost (SIB) in volumetric modulated arc therapy (VMAT) for prostate cancer (PCA) may increase out-of-field (DOOF) and photoneutron(HPN) doses.
Researchers performed a retrospective study comparing the DOOF and HPN in flattened (FLAT) and flattening filter-free(FFF) 6-MV and 10-MV volumetric modulated arc therapy(VMAT) treatment plan with and without SIB.
The study included 8 groups of 30 VMAT plans for PCA with 6 MV or 10 MV, with or without FF, and with uniform (2 Gy) or SIB target dose (2.5/3.0 Gy) prescriptions (CONV, SIB) were generated. All 240 plans were delivered on a slab-phantom and compared with respect to measured DOOF and HPN at 61.8 cm distance from the isocenter. The 6‑ and 10-MV flattened VMAT plans with conventional fractionation (6- and 10-MV FLAT CONV) served as standard reference groups. Doses were analyzed as a function of delivered monitor units (MU) and weighted equivalent square field size Aeq.. Pearson’s correlation coefficients between the presented quantities were determined.
The SIB plan led to reduced HPN throughout the entire prostate radiation treatment (10-MV SIB vs. CONV -38.2%). Removing the flattening filter resulted in lower HPN (10-MV CONV -17.2%; 10-MV SIB -22.5%). SIB also reduced DOOF by 39% in all scenarios, while flattening FFF mode reduced DOOF by an average of 60%. Strong Pearson correlations were observed between monitor units (MU) and HPN (r > 0.9) and between MU and DOOF (0.7 < r < 0.9).
The study recommended SIB with FFF-VMAT for moderately hypofractionated 6-MV treatment to reduce photoneutron and OOF doses.