Comparison of conventional radiotherapy and intensity-modulated radiotherapy for post-operative radiotherapy for primary extremity soft tissue sarcoma.

Abstract

Doses in conventional radiotherapy for extremity soft tissue sarcoma (STS) potentially exceed normal tissue tolerances. This study compares 3D-conformal radiotherapy (3D-CRT) with intensity-modulated radiotherapy (IMRT) in optimising target volume coverage and minimising integral dose to organs-at-risk (OAR). Ten patients undergoing post-operative radiotherapy for extremity STS were assessed. PTV(1) was defined as tumour bed plus 5cm superiorly/inferiorly and 3cm circumferentially, PTV(2) was defined as 2cm isotropically. OAR were defined as whole femur, neurovascular bundle, tissue corridor and normal tissue outside PTV(1). For each patient 2-phase 3D-CRT was compared to 2/3 field (2/3f) and 4/5 field (4/5f) IMRT with simultaneous integrated boost (SIB). The primary planning objective was to minimise femur and skin corridor dose. Volumetric analysis and conformity and heterogeneity indices were used for plan comparison. A planning protocol containing dose/volume constraints for target and OAR was defined. 4/5f IMRT showed greatest conformity and homogeneity. IMRT resulted in significantly lower femur V45 using 2/3f (p=0.01) and 4/5f (p=0.0009) than 3D-CRT. 4/5f IMRT resulted in significantly lower normal tissue V55 (p=0.004) and maximum dose (p=0.04) than 3D-CRT. A reproducible set of planning guidelines and dose-volume constraints for 3D-CRT and IMRT planning for extremity sarcomas was devised. 4/5f IMRT with SIB resulted in better target coverage and significantly decreased OAR dose. Further evaluation of this technique within a clinical trial is recommended to demonstrate that the technical benefit of the more complex technique translates into patient-derived benefit by reducing late toxicity.