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  (D_OOF) and photoneutron(H_PN) doses. 

Researchers performed a retrospective study comparing the D_OOF and H_PN 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 D_OOF and H_PN 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 A_eq.. Pearson’s correlation coefficients between the presented quantities were determined.

The SIB plan led to reduced H_PN 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 D_OOF  by 39% in all scenarios, while flattening FFF mode reduced D_OOF by an average of 60%. Strong Pearson correlations were observed between monitor units (MU) and H_PN (r > 0.9) and between MU and D_OOF (0.7 < r < 0.9).

The study recommended  SIB with FFF-VMAT for moderately hypofractionated 6-MV treatment to reduce photoneutron and OOF doses.

Source: pubmed.ncbi.nlm.nih.gov/37707518/