Treatment planning parameters in intensity modulated radiotherapy for prostate cancer and their dosimetric impact: a study using Monaco TPS.

This study aimed to determine the most appropriate treatment planning solution for prostate cancer radiotherapy by analyzing the effect of planning parameters on dosimetric outcome. Four volumetric modulated arc therapy (VMAT) / intensity modulated radiation therapy (IMRT) plans were created for each of the 20 patients included in the study, using minimum segment width (MSW) of 0.5, 1.0, 1.5, and 2.0 cm. All prostate plans underwent "Fluence Smoothing" on "High", while plans using MSW = 1.0 were reoptimized with both "Low" and "Medium" settings. All plans met the planning objectives. MSW = 0.5 resulted in better tumour coverage (by over 0.3 Gy), enhanced conformity and better sparing for the majority of organs at risk (OARs). However, this small MSW was associated with a notable increase in monitor units (MUs) (by over 300), control points (CPs) (by over 83) and delivery time (DT) (by over 0.88 min). The most significant impact of reduced fluence smoothing was observed in parameters such as MUs (reduced by over 53) and DT (reduced by over 0.15 min), which improved gamma passing rate (GPR). In the context of dosimetric outcomes, variations in fluence smoothing had minimal effect on the dose distribution to the planning target volume and most OARs. It is concluded that clinically acceptable dose distributions were achieved across all segment widths and fluence smoothing levels. However, using a 1.0 cm MSW with medium-to-high fluence smoothing provided a favourable balance between plan quality, delivery accuracy and efficiency in prostate cancer, without compromising dosimetric outcomes.