Rectal dose-sparing effect with bioabsorbable spacer placement in carbon ion radiotherapy for sacral chordoma: dosimetric comparison of a simulation study

Abstract

It is difficult to treat patients with an inoperable sarcoma adjacent to the gastrointestinal (GI) tract using carbon ion radiotherapy (C-ion RT), owing to the possible development of serious GI toxicities. In such cases, spacer placement may be useful in physically separating the tumor and the GI tract. We aimed to evaluate the usefulness of spacer placement by conducting a simulation study of dosimetric comparison in a patient with sacral chordoma adjacent to the rectum treated with C-ion RT. The sacral chordoma was located in the third to fourth sacral spinal segments, in extensive contact with and compressing the rectum. Conventional C-ion RT was not indicated because the rectal dose would exceed the tolerance dose. Because we chose spacer placement surgery to physically separate the tumor and the rectum before C-ion RT, bioabsorbable spacer sheets were inserted by open surgery. After spacer placement, 67.2 Gy [relative biological effectiveness (RBE)] of C-ion RT was administered. The thickness of the spacer was stable at 13–14 mm during C-ion RT. Comparing the dose–volume histogram (DVH) parameters, Dmax for the rectum was reduced from 67 Gy (RBE) in the no spacer plan (simulation plan) to 45 Gy (RBE) in the spacer placement plan (actual plan) when a prescribed dose was administered to the tumor. Spacer placement was advantageous for irradiating the tumor and the rectum, demonstrated using the DVH parameter analysis.

Safety and Efficacy of Re-irradiation With Carbon-ion Radiotherapy for Pelvic Recurrence of Rectal Cancer After Preoperative Chemoradiotherapy: A Retrospective Analysis

“…In these cases, a spacer that physically separates the tumor from the GI tract or other OARs may be useful (23,24). Using Gore-Tex sheets is one option in spacer placement but, recently, another option has emerged, use of a bioabsorbable polyglycolic acid (PGA) spacer which was developed in Japan (25,26). Using a Gore-Tex sheet as a spacer enables higher dose administration of C-ion RT for tumor control, even in cases of re-irradiation.…”

Visualizing Bioabsorbable Spacer Effectiveness by Confirming the Distal-Tail of Carbon-Ion Beams: First-In-Human Report

“…The safety of the PGA spacer has been reported [ 8 ], and another report of dosimetric comparison in a simulation study revealed that the PGA spacer improves dose distribution [ 10 ]. In this case, the tumor was close to the GI tract, and the PGA spacer was inserted, resulting in a reduced C-ion RT dose for the GI tract, and the treatment was safely performed.…”

“…However, C-ion RT cannot be performed for tumors close to or attached to the gastrointestinal (GI) tract due to the high risk of severe toxicity except with the surgical insertion of a spacer that physically separates the tumor from the GI tract. The spacer stops the C-ion beams at the distal end or reduces the radiation dose to the lateral penumbra by keeping a distance from the GI tract [ 8 , 9 , 10 , 11 ]. Previously, Gore-Tex sheets were used as spacers, and a favorable clinical result for C-ion RT patients was reported [ 12 ].…”

“…However, there were infection risks and adverse effects on the GI tract due to using Gore-Tex sheets for an extended period after C-ion RT. Recently, bioabsorbable polyglycolic acid (PGA) spacer (Alfresa Pharma Corporation, Osaka, Japan) was developed in Japan, and the mainstream of spacer-placement options shifted from Gore-Tex sheets to the PGA spacer [ 8 , 10 , 11 ]. This is due to the PGA spacer’s safety compared to Gore-Tex sheets owing to the PGA spacer absorption 32 weeks after the placement.…”

Carbon Ion Radiation Therapy for Postoperative Pelvic Recurrence of Rectal Cancer With a Large Tumor Infiltrating and Compressing the Rectum: A Case Report

“…Additionally, patients with tumors infiltrating the rectum or tumors located with little-to-no space for inserting a spacer (eg, pelvic floor) were not suitable for insertion of a spacer that physically separates the tumor and the rectum to avoid severe rectal toxicities. 8 , 9 Therefore, to treat pelvic recurrences of rectal cancer without causing severe toxicities in cases where the tumor infiltrates or compresses the rectum, lowering the administration dose, rectal dose adjustment, and colostomy before C-ion RT might be necessary.…”