Peripheral photon doses from different techniques delivered in prostate radiotherapy : experimental measurements and TPS calculations

Abstract EN

Advanced techniques and modalities in delivering radiotherapy improved the ability of delivering higher tumor doses while minimizing dose to the critical organs.

The aim of this work is to determine experimentally out-of-field doses associated with these modern radiotherapy techniques for actual clinical case of prostate carcinoma and intercompare it with the treatment planning system (TPS) calculations.

Three prostate treatment plans of the intensity-modulated radiation therapy (IMRT), RapidArc, and the Three-Dimensional Conformal Radiotherapy (3D-CRT) techniques were delivered to an anthropomorphic phantom using 6 MV photons beams produced from a UNIQUE linear accelerator.

The out-of-field surface doses at various distances from the isocenter and peripheral doses to organs at risk (OARs) were measured using the thermoluminescent detectors (TLD-700) then compared to the calculated doses from the used commercial Eclipse TPS version 11.

The two implemented algorithms in the Eclipse TPS (analytical anisotropic algorithm, AAA and the Acuros XB algorithm, AXB) underestimated the surface out-of-field doses by a maximum average deviation of 49% till the distance of 15 cm from the isocenter reported to the 3D-CRT technique.

IMRT and RA techniques were more precise than 3D-CRT in tumor coverage and sparing of OARs but resulted in larger peripheral photon doses.

RA technique has the advantage of less treatment time than IMRT technique and also produce less peripheral photon doses because it uses fewer monitor units.

Our results show that although AXB algorithm is significantly faster in dose calculations than AAA algorithm especially in modern techniques, but less accurate in estimating the out-of-field doses.