Initial Clinical Experience with Uni-Directional LDR Brachytherapy in the Treatment of Retroperitoneal Sarcoma

Abstract

Retroperitoneal sarcomas (RPS)s constitute 10%-15% of patients diagnosed with soft tissue sarcomas. Despite advances in cancer care and aggressive management, the 5-year overall survival rate is 47%-67%. The crude cumulative incidence of local recurrence (LR) is 26%. A previous trial combining preoperative external beam radiation therapy with post-operative brachytherapy found substantial toxicity and treatment related death. This report demonstrates the utility of unidirectional LDR brachytherapy for treatment of RPS. In this study, the unidirectional device employed is a permanent, Pd-103 brachytherapy device designed to be implanted during surgical resection for the treatment of anticipated positive or close surgical margins. The device consists of a plane of sources with an unidirectional gold shield backing to protect normal tissues yet direct radiation to the target margin(s). The sources are embedded in a bio-absorbable matrix membrane that may be cut to size to allow for conformal targeting of the surgical tumor bed. At surgery, patients were assessed and determined to have close or positive margins. The prescribed LDR brachytherapy dose averaged 34.7 Gy (range: 20 – 60 Gy) and covered an average area of 6060 mm2 (∼58 sources). Pd-103 has a half-life of 16.99 days and delivers therapeutic radiation dose over several weeks. The device was attached with sutures and tacks. Seven RPS patients have been implanted with the CivaSheet at 4 medical centers. Six patients had recurrent sarcoma in the retroperitoneum or pelvic side wall. One patient had locally advanced leiomyosarcoma with no previous treatment. Three patients had prior EBRT at first diagnosis (45 – 57.5 Gy). Five patients received neoadjuvant EBRT (35 – 57.5 Gy) prior to surgery plus brachytherapy. The patients tolerated the implant well with no complications following surgery. There have been 0 reports of source movement in RPS patients. At median 15 months (8-24 months) follow-up, 0/7 patients have demonstrated local recurrence as defined as the targeted field of brachytherapy radiation. One patient (1/7) recurred outside of the surgical field and subsequent brachytherapy radiation. There were 0 reported incidences of acute or late radiation toxicity despite the surrounding organs at risk, inclusive of the small intestine, ureter and kidneys. Unidirectional, planar Pd-103 LDR brachytherapy has demonstrated a 100% local recurrence free survival with no acute or late-term toxicities at a median of 15 months in our patient cohort. Application of uni-directional, planar Pd-103 LDR brachytherapy technology is very safe and easy, and should be considered to escalate dose or retreat to the high risk margins of RPS after resection.