Abstract
Treatment planning of radiotherapy for skull base involvement of multiple myeloma presenting with visual impairment should be optimized to alleviate symptoms immediately and sufficiently while minimizing toxicities. Two such patients were treated with fractionated stereotactic radiotherapy by using Dynamic Conformal Arcs (DCA) under image guidance based on bony anatomy alignment. DCA planning was optimized after considering the possibility for amendment of visual organ displacement resulting from early tumor shrinkage during treatment through 1) the use of a target volume with modified geometry as a surrogate for leaf adaptation in order to improve target coverage, and 2) manual adjustment of a subset of leaf positions to reduce the dose gradient immediately inside the target boundary facing the visual organs and to eliminate an undesirable dose hotspot. In both cases, anticipated geometric changes in the target volume associated with improvement of visual organ displacement toward the target centroid were observed before the completion of treatment. Favorable visual functional outcomes as well as local tumor control were achieved during 14 months and 4 months follow-up periods. Notably, inexorable visual loss in one patient was fully reversed within one month after radiotherapy. We described the modification techniques for DCA planning in detail.
Highlights
Skull base involvement is an unusual clinical manifestation of symptomatic multiple myeloma (MM), and it can be the predominant site of either relapsed or initial disease [1] [2]
We describe two cases in which patients harboring skull base involvement of MM presented with visual impairment, and were treated by using image-guided fractionated stereotactic radiotherapy (SRT) based on modified dynamic conformal arcs (DCA) planning, with special consideration given to the possibility of visual organ displacement resulting from early tumor shrinkage during treatment
Image guidance was implemented via 6 degree-of-freedom (6D) verification and correction on the basis of paired orthogonal kV radiographic images obtained by using the ExacTrac Robotics® (BrainLAB AG) equipped with the NovalisTx platform [5]
Summary
Skull base involvement is an unusual clinical manifestation of symptomatic multiple myeloma (MM), and it can be the predominant site of either relapsed or initial disease [1] [2]. We describe two cases in which patients harboring skull base involvement of MM presented with visual impairment, and were treated by using image-guided fractionated stereotactic radiotherapy (SRT) based on modified dynamic conformal arcs (DCA) planning, with special consideration given to the possibility of visual organ displacement resulting from early tumor shrinkage during treatment. Magnetic resonance (MR) images obtained 2 months after the initial study showed a slight enlargement of the sellar tumor, associated with increased compression of the optic chiasm (Figure 1(a) and Figure 2(d)) Her visual symptoms were not progressive, early radiotherapy was considered in order to preserve visual function before the occurrence of tumor progression refractory to pharmacotherapy. Systemic control of MM was still maintained 18 months after initial treatment through the continued administration of lanalidomide and dexamethasone
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