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Particle beam radiotherapy with a surgical spacer placement for advanced abdominal leiomyosarcoma results in a significant clinical benefit

Leiomysarcoma is a rare malignant tumor originating from smoothmuscle cells. Because of the limited number of cases, the naturalhistory and optimal treatment have not been clariﬁed. In particular,prognosis of leiomyosarcoma originating from large vessels includingthe inferior vena cava (IVC) and aorta is extremely poor. Recent datasupport an aggressive surgical resection combined with adjuvantchemotherapy as the best treatment option for a leiomyosarcoma fromthe IVC [1,2]. However, the long-term outcome of curative resectionsfor leiomyosarcoma from large vessels has been disappointing. The5-year survival rates obtained with absolute curative resections wereobserved to range from 34.8% to 53.3% [1,2]. Hines et al. [2]suggested that radiation therapy after a surgical resection may prolongsurvival. It should be noted, however, that an absolute curativeresection was performed in all of their cases and the effectiveness ofchemotherapy and radiotherapy were assessed in the framework ofadjuvant therapy. There is no report about the treatment of anunresectable leiomyosarcoma and the overall survival rate.Particle beam radiotherapy is a new mode of radiotherapy that hasan inherent advantage over photon radiotherapy. Particle beams, suchas proton and carbon ion beams, show an increase in energy depositionwith penetration depth up to a sharp maximum at the end of their rangeto form the so-called Bragg peak. It thus permits delivery of higherdoses of radiation to the tumor, which may lead to profoundlyimproved tumor eradication. Recent results from major centers haveshown the therapeutic superiority of particle radiotherapy for variouskinds of malignant tumors [3,4]. However, the application of particlebeam radiotherapy for abdominal malignant tumors is restrictedbecause most of them come in contact with the intestine that cannottolerate the radical dose of particle beams. Several studies haveinvestigated the risk factors related to late gastrointestinal tractdisturbance after radiotherapy. Ishikawa et al. [5] assessed that thedosimetric parameter was a very important factor in the occurrence ofgastrointestinal bleeding after particle radiotherapy. Gastrointestinaldisturbances, such as ulcer formation and colitis, generally occurwithin several months after the completion of particle radiotherapy.However, the irradiated volume of a marginal tumor is normallylimited to make it lower than the maximum dose in order to prevent anytoxicity to the nearby gastrointestinal tract. To overcome thislimitation, we developed a novel two-step treatment with a surgicalspacer placement and subsequent proton beam radiotherapy andachieved a signiﬁcant clinical beneﬁt for three patients.