Anatomy driven optimization strategy for total marrow irradiation with a volumetric modulated arc therapy technique

Abstract

The purpose of this study was to evaluate the possibility of dose distribution optimization for total marrow irradiation (TMI) employing volumetric‐modulated arc therapy (VMAT) with RapidArc (RA) technology setting isocenter's positions and jaw's apertures according to patient's anatomical features. Plans for five patients were generated with the RA engine (PROIII): eight arcs were distributed along four isocenters and simultaneously optimized with collimator set to 90°. Two models were investigated for geometrical settings of arcs: (1) in the “symmetric” model, isocenters were equispaced and field apertures were set the same for all arcs to uniformly cover the entire target length; (2) in the “anatomy driven” model, both field sizes and isocenter positions were optimized in order to minimize the target volume near the field edges (i.e., to maximize the freedom of motion of MLC leaves inside the field aperture (for example, avoiding arcs with ribs and iliac wings in the same BEV)). All body bones from the cranium to mid of the femurs were defined as PTV; the maximum length achieved in this study was 130 cm. Twelve (12) Gy in 2 Gy/fractions were prescribed in order to obtain the covering of 85% of the PTV by 100% of the prescribed dose. For all organs at risk (including brain, optical structures, oral and neck structures, lungs, heart, liver, kidneys, spleen, bowels, bladder, rectum, genitals), planning strategy aimed to maximize sparing according to ALARA principles, looking to reach a mean dose lower than 6 Gy (i.e., 50% of the prescribed dose). Mean MU/fraction resulted 3184±354 and 2939±264 for the two strategies, corresponding to a reduction of 7% (range −2% to 13%) for (1) and (2). Target homogeneity, defined as normalD2%−normalD98% was 18% better for (2). Mean dose to the healthy tissue, defined as body minus PTV, had 10% better reduction with (2). The isocenter's position and the jaw's apertures are significant parameters in the optimization of the TMI with RA technique, giving the medical physicist a crucial role in driving the optimization and thus obtaining the best plan. A clinical protocol started in our department in October 2010.PACS numbers: 87.55.de, 87.55.dk, 87.56.nk, 87.57.uq

Plan robustness in field junction region from arcs with different patient orientation in total marrow irradiation with VMAT

“…A first plan on "Body CT" was optimized ("Body plan"): according to ALARA (as low as reasonable achievable) principle [7] the isocenters positions and jaws sizes were chosen following the anatomy driven strategy proposed in our previous work, based on the personal anatomy [8]. In brief, 10 full arcs (360 ) of 6 MV were optimized simultaneously with 5 isocenters using asymmetric jaw settings to cover the entire PTV Body length.…”

The accuracy of the Acuros XB algorithm in external beam radiotherapy – a comprehensive review

“…In the study the AXB10 was the only dose calculation algorithm for VMAT treatment plans. Fogliata et al 61 and Mancosu et al 62 have studied the application of VMAT technique in total marrow irradiation and in the studies, the AXB10 was the only algorithm that was used. For the radiotherapy of the breast, another group has produced two papers, by Essers et al 63 and Osman et al 64 , in which the application of VMAT and breath-hold techniques is assessed applying the AXB10.…”

Interplay effects between dose distribution quality and positioning accuracy in total marrow irradiation with volumetric modulated arc therapy

“…1,2 The feasibility and early clinical data of TMI-TMLI were reported both by conventional Linac using intensity modulated RT (IMRT), 3,4 helical tomotherapy (HT) based approaches, 5,6 and more recently, volumetric modulated arc therapy (VMAT) using RapidArc (RA) approach (Varian Medical Systems, Palo Alto, CA). [7][8][9][10][11] In particular, the RA technique allows to simultaneously optimize the multileaf collimator (MLC) positions, the dose rate, and the gantry rotation speed to achieve the desired dose distribution.…”