3d Conformal Radiotherapy Versus Imrt In The Adjuvant Treatment Of Soft Tissue Sarcoma Of The Adductor Compartment Of The Thigh

Post-operative radiotherapy in patients with extremity sarcomas traditionally employs conventional or 3D planned fields to large volumes of the limb. Doses delivered in conventional fractionation potentially exceed tolerance doses of surrounding normal tissue. This study compares the ability of conformal radiotherapy plans versus IMRT plans to minimise the integral dose to surrounding organs at risk (OAR). A planning protocol was defined for target volume, OAR definition and dose/volume constraints. CTV was defined as tumor bed. A 5 cm margin was added superiorly and inferiorly and 3 cm circumferentially to form PTV1. PTV2 was 2 cm isotropic expansion of the CTV. The protocol defined modifications of the PTV for scar coverage, skin, femur and pelvic extension. OAR were defined as whole femur, neurovascular bundle, a tissue corridor and normal tissue outside the PTV. Pelvic organs were contoured for 4 patients whose disease involved the insertion of the muscle group. Three types of treatment plan were created in 7 patients designated for postoperative radiotherapy of primary adductor compartment sarcomas. The primary planning objective was to minimise the dose to femur and skin corridor. Volumetric dosimetry analysis was performed for all defined OAR to a conventional 3D conformal plan, which was forward-planned using wedges and MLCs, a 2/3 field inverse planned IMRT solution using the same gantry angles and an iteratively developed 4/5 field inverse planned IMRT for each patient. The mean dose (Dmean) and volume receiving greater than organ tolerance for each OAR were defined, eg V45 (%volume receiving 45 Gy or more). A dose equivalent to 66 Gy to PTV1 and 50 Gy to PTV2 in 2 Gy per fraction was modelled using a concomitant boost for the conformal and a simultaneous boost for the IMRT plans. The median volume of PTV1 was 1499 cc (range 597–3919 cc). The median volume of PTV2 was 902 cc (range 284–2629 cc). IMRT resulted in a greater decrease in dose to OAR than the conformal plans. 4/5 field IMRT resulted in a significantly lower V45 than conformal radiotherapy (p = 0.03). A greater decrease in dose was seen using IMRT in patients with large PTVs (volume of the central PTV slice greater than 50% of the central thigh slice) and/or whose PTV covered greater than 50% of the transverse diameter of the femur. For the first time a reproducible set of planning guidelines and dose volume constraints for 3D conformal planning and IMRT inverse planning for sarcomas of the extremity was devised. 4/5 field IMRT resulted in a decreased dose to OAR in patients with large or wide PTVs but less so for smaller and superficially located PTVs.Tabled 1OAR median dose/volume results from the three plans3D Conformal2/3 field IMRT4/5 field IMRTFemur V4528.6%22.7%20.4%Neurovascular bundle V4527.6%25.6%26.9%Tissue corridor Dmean13.9 Gy9.7 Gy10.3 GyNormal tissue V558.7%5.0%1.1% Open table in a new tab