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 D2%−D98% 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
Highlights
Total marrow irradiation (TMI) is a new potential approach for conditioning regimen in patients scheduled for hematopoietic cell transplantation in multiple myeloma, leukemia, and lymphomas
The study showed, on an anthropomorphic phantom, that intensity-modulated techniques might reduce the dose to organs at risk (OAR) by 29%–65% compared to conventional total body irradiation
A similar approach was followed by Aydogan et al[2] Other analogue investigations were performed by means of helical tomotherapy (HT)-based approaches.[3,4] The City of Hope group in Duarte (USA) reported on both simulation studies and treatment of 21 patients.[4]. For a group of 13 patients treated for multiple myeloma on a dose escalation protocol, the authors demonstrated that median organ doses were 15%–65% of that received from the gross target volume
Summary
Total marrow irradiation (TMI) is a new potential approach for conditioning regimen in patients scheduled for hematopoietic cell transplantation in multiple myeloma, leukemia, and lymphomas. The aim of this innovative technique is to improve the coverage of target hematopoietic or lymphoid tissues while reducing the involvement of the remaining healthy tissues in the body, and reducing toxicities with respect to the standard total body irradiation (TBI) where all the body is irradiated homogenously. The study showed, on an anthropomorphic phantom, that intensity-modulated techniques might reduce the dose to organs at risk (OAR) by 29%–65% compared to conventional total body irradiation. Primarily grade 1-2 acute effects were observed, and no patient showed grade 4 toxicity
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
