1.5T MR-guided RT versus linac-based VMAT SBRT in localized prostate cancer: a toxicity comparison
PD-0574
Abstract
1.5T MR-guided RT versus linac-based VMAT SBRT in localized prostate cancer: a toxicity comparison
Authors: Luca Nicosia1, Claudio Vitale1, Francesco Cuccia1, Michele Rigo1, Vanessa Figlia1, Rosario Mazzola1, Niccolò Giaj-Levra1, Francesco Ricchetti1, Ruggiero Ruggeri1, Filippo Alongi1
1IRCCS Sacro Cuore Don Calabria Hospital, Advanced Radiation Oncology Department, Negrar, Italy
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Purpose or Objective
to compare acute toxicity of prostate cancer
(PCa) stereotactic body radiotherapy (SBRT) delivered by MR-guided radiotherapy
(MRgRT) with 1.5T MR-linac (MRgRT) or by volumetric modulated arc (VMAT) with
linac.
Material and Methods
patients with histologically diagnosed
low-to-intermediate risk class PCa were treated with exclusive SBRT. The
schedule in 5 fractions were 35 Gy and 36.25 Gy for low and intermediate risk
class, respectively. Patients treated with MRgRT were enrolled in an
ongoing Ethical Committee (EC) approved trial (n° 23748), while patients
treated with CBCT-IGRT linac-based SBRT were enrolled in an EC approved PCa
SBRT phase II trial (n° SBRT PROG112CESC). The primary end-point was acute toxicity. Patients
were included in the analysis if they had at least 6 months of follow-up for
the acute toxicity end-point evaluation. Toxicity assessment was performed
according to CTCAE v5.0 scale. International Prostatic Symptoms Score (IPSS)
was also performed.
Results
137 patients were included in the analysis. 57
(41.6%) were treated with MRgRT, and 80 with conventional linac. The median
initial PSA before RT was 6.5 ng/ml (range 1-19). Globally, acute G1, G2, and
G3 toxicity occurred in 32 (23.3%) 20 (14.5%), and 4 (2.8%) patients. At the
univariate analysis acute G1 did not differs significantly between MRgRT and CBCT-IGRT
linac (23.75% versus 21%; p=n.s.), while G2
toxicity was significantly lower in the MRgRT group (4.5% versus 10%; p=0.032).
Acute G2 gastrointestinal (GI) toxicity occurred in 7% and 7.5% of MRgRT and CBCT-IGRT
linac group (p=0.61), while acute G2
genitourinary (GU) toxicity occurred in 10.5% and 15% of MRgRT and CBCT-IGRT
linac group (p=0.004). The median IPSS before
and after SBRT was 3 (1-16) and 5 (1-18). Acute G3 toxicity occurred in 2 in
the MRgRT and 2 in the linac group (p=n.s.).
Conclusion
prostate SBRT with 1.5TMR-linac is feasible and
safe. Compared to linac-based SBRT, MRgRT seems characterized by a reduced
incidence of grade 2 toxicity. A longer follow-up and a larger population is
needed to confirm these preliminary data.