Normal tissue sparing using different techniques for prostate irradiation.

Abstract

The aim of this study was to investigate normal tissue sparing through dosimetric parameters of normal tissue volumes using different irradiation techniques for conventional (CFRT) and simultaneously integrated boost (SIB) schedules. Several dose-escalation studies for localized prostate cancer (PCa) have shown advanced biochemical relapse-free (bRFS) rates and also better local control for higher total doses using either CFRT or SIB schedules. Besides the most important organs-at-risk, absorbed dose reduction of other surrounding normal tissues are also preferable. In order to analyse the normal tissue sparing, dosimetric parameters of different normal tissue volumes were examined. Treatment plans for 15 high risk prostate cancer patients were created using RapidArc (RA), Sliding Window (SW) IMRT and 4-field box (3D-CRT) technique. In order to evaluate normal tissue sparing, the volume of pelvic region was divided into six normal tissue cylinders with 1cm wall thickness, located in each other. All plans met the criteria of target coverage (V95%>95%). All techniques provided the same results for OARs except 3D-CRT for rectum and bilateral femoral heads. The values of V5, V10 and V15 increased in cases which included RapidArc technique and decreased for V20 and V30. The dosimetric parameters for the cylindrical normal tissue volumes show that using RapidArc technique gives equal or slightly better normal tissue sparing and SIB provided the same normal tissue sparing as CFRT planned with RapidArc.