Spatial and volumetric changes of retroperitoneal sarcomas during pre-operative radiotherapy

Treatment Guidelines for Preoperative Radiation Therapy for Retroperitoneal Sarcoma: Preliminary Consensus of an International Expert Panel

“…As stated previously, based on documented interfractional RPS tumor movement, we recommend daily IGRT in the form of volumetric soft tissue imaging (eg cone beam CT, megavoltage CT, or MRI) at least 2 to 5 times per week and orthogonal kV imaging on days that volumetric imaging is not performed (56). If significant changes in tumor size are detected on soft tissue volumetric imaging, it is appropriate to replan the patient treatment to ensure adequate dosimetric coverage of the volumes at risk.…”

“…Investigators from Princess Margaret Cancer Centre assessed interfractional changes of RPS during preoperative RT by using analysis of weekly cone beam CT imaging coregistered with simulation CT scans. They found RPS tumor displacement of 8.6 mm laterally, 15 mm anteroposteriorly, and 15 mm superoinferiorly (56). Growth of the tumor during radiation therapy may require replanning, particularly if the growth displaces the adjacent kidney or liver as the consensus guidelines do not advocate an expansion from iGTV to ITV along these surfaces.…”

Volumetric‐modulated arc therapy versus intensity‐modulated radiotherapy for large volume retroperitoneal sarcomas: A comparative analysis of dosimetric and treatment delivery parameters

“…Zhuang has modeled dose uncertainty in relation to organ motion and field size and concluded that there is higher dose uncertainty with increasing field size and motion amplitude . The treatment of RPS generally requires large field sizes, and previous literature has documented significant motion of these tumors and adjacent organs, particularly in the upper abdomen . IMRT plans that require a higher number of MUs and take longer to deliver, therefore, would be more vulnerable to the increased dose uncertainty from intra‐fraction tumor and organ motion.…”

Radiation therapy in retroperitoneal sarcoma management

“…For upper abdominal targets, the use of these to minimize or account for target motion is highly desirable, whereas for lower abdominal or pelvic targets, respiration has less significant effect on target motion and thus the use of these techniques may be omitted. 23 The design of PTV margins may be affected, with larger margin expansions-typically 9-12 mm as practiced in the recently completed EORTC-STBSG 62092-22092 trial-usually required for the management of target motion particularly for upper abdominal targets. When target motion management is undertaken together with frequent volumetric imaging during the course of radiation (eg, cone-beam CT), PTV margin expansion may be reduced substantially.…”

“…Similarly, the use of 4DCT reconstructions or respiratory gating apparatus are dependent on the position of the target. For upper abdominal targets, the use of these to minimize or account for target motion is highly desirable, whereas for lower abdominal or pelvic targets, respiration has less significant effect on target motion and thus the use of these techniques may be omitted . The design of PTV margins may be affected, with larger margin expansions—typically 9‐12 mm as practiced in the recently completed EORTC‐STBSG 62092‐22092 trial—usually required for the management of target motion particularly for upper abdominal targets.…”