For postprostatectomy patients at higher risk of nodal involvement the irradiation of pelvic lymph nodes may improve the therapeutic ratio. However, whole pelvic radiotherapy results in increased doses delivered to the pelvic bones’ marrow and other OARs. The aim of this study was to compare IMRT and VMAT techniques in terms of sparing of pelvic bones. The VMAT and IMRT plans were created for ten patients. Treatment plans were generated for prostate bed (PTV1) and pelvic lymph nodes (PTV2). The delivered mean dose to the sum of PTV1 and PTV2 was 46Gy in 23 fractions and additionally a mean dose of 18Gy in 9 fractions was prescribed to PTV1. The target coverage and the OARs sparing were compared across techniques. The following OARs were delineated: pelvic bones, bowel bag, rectum and bladder. The following dose volume parameters were compared using the Wilcoxon test: pelvic bones V30Gy[%], V40Gy[%], the bowel bag V30Gy[cc], V45Gy[cc], rectum V40Gy[%], V50Gy[%], V60Gy[%] and bladder V40Gy[%], V50Gy[%], V60Gy[%]. The target coverage in VMAT and IMRT plans was comparable. The value of PTV1 V95% and PTV2 V95% were both >99%. The VMAT plans result in decrease of pelvic bones V30Gy[%] and significant increase of the following parameters: rectum V60Gy[%], bladder V60Gy[%] and bowel bag V30Gy[cc]. Differences between values of V40Gy[%] and V50Gy[%] for bladder and rectum across mentioned techniques were statistically not significant. A comparison between VMAT and IMRT techniques showed, that the VMAT technique reduces the delivered dose to pelvic bones and thus also to red marrow. However, IMRT provided better sparing at higher doses for rectum, bladder and bowel bag. These results should be taken into consideration when VMAT and IMRT techniques being used in the whole pelvic radiotherapy of patients after radical prostatectomy.

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Maria Poncyljusz, Wojciech Bulski, "Assessing the role of VMAT relative to IMRT for patients after prostatectomy in terms of sparing pelvic bones," RAD Conf. Proc, vol. 4, 2020, pp. 72–75, http://doi.org/10.21175/RadProc.2020.15