Inverse treatment planning for spinal robotic radiosurgery: an international multi‐institutional benchmark trial

Abstract

Stereotactic radiosurgery (SRS) is the accurate, conformal delivery of high‐dose radiation to well‐defined targets while minimizing normal structure doses via steep dose gradients. While inverse treatment planning (ITP) with computerized optimization algorithms are routine, many aspects of the planning process remain user‐dependent. We performed an international, multi‐institutional benchmark trial to study planning variability and to analyze preferable ITP practice for spinal robotic radiosurgery. 10 SRS treatment plans were generated for a complex‐shaped spinal metastasis with 21 Gy in 3 fractions and tight constraints for spinal cord (normalV14Gy<2 cc, normalV18Gy<0.1 cc) and target (coverage >95%). The resulting plans were rated on a scale from 1 to 4 (excellent‐poor) in five categories (constraint compliance, optimization goals, low‐dose regions, ITP complexity, and clinical acceptability) by a blinded review panel. Additionally, the plans were mathematically rated based on plan indices (critical structure and target doses, conformity, monitor units, normal tissue complication probability, and treatment time) and compared to the human rankings. The treatment plans and the reviewers' rankings varied substantially among the participating centers. The average mean overall rank was 2.4 (1.2‐4.0) and 8/10 plans were rated excellent in at least one category by at least one reviewer. The mathematical rankings agreed with the mean overall human rankings in 9/10 cases pointing toward the possibility for sole mathematical plan quality comparison. The final rankings revealed that a plan with a well‐balanced trade‐off among all planning objectives was preferred for treatment by most participants, reviewers, and the mathematical ranking system. Furthermore, this plan was generated with simple planning techniques. Our multi‐institutional planning study found wide variability in ITP approaches for spinal robotic radiosurgery. The participants', reviewers', and mathematical match on preferable treatment plans and ITP techniques indicate that agreement on treatment planning and plan quality can be reached for spinal robotic radiosurgery.PACS number(s): 87.55.de

Treatment Planning Considerations for Robotic Guided Cardiac Radiosurgery for Atrial Fibrillation

“…Random effects in treatment planning and subsequent plan comparison may be small [38-40], but cannot be disregarded in this sample size. 4D planning comes with all its known problems [49-51] and 5D dose calculation [54] or phantom studies [36] may be more appropriate when investigating dosimetric effects from cardiac motion.…”

“…Sequential Multi-Objective Optimization (SMOO®) [38] was performed using the Iris® collimator [39] according to the best practice guidelines for robotic radiosurgery treatment planning [40]. Prescription dose was 25 Gy in a single fraction to the LPTV and RPTV according to results known prior to this study [5, 6].…”

Performance assessment of a new optimization system for robotic SBRT MLC-based plans

“…Additional steps to improve delivery efficiency optimization may also be necessary [12]. As a result, complex treatment plans requiring many objectives and/or targeted to large lesions may necessitate extremely long optimization times which can extend up to four hours [12][13][14][15]. The VOLO optimization system was implemented to overcome the limitations of the Sequential algorithm.…”

Second infield re‐irradiation with a resulting cumulative equivalent dose (EQD2max) of >180 Gy for patients with recurrent head and neck cancer

“…Safety concerns for re‐RT/SBRT especially focus on possible carotid rupture and increased doses to organs at risk (OAR), that is, brain or spinal cord. As there are no data regarding OAR doses for re‐RTs, inverse treatment planning usually is guided by the as‐low‐as‐reasonably‐achievable principle . The mechanisms underlying radiation‐induced carotid rupture, in the worst case leading to carotid artery blow‐out syndrome (CBOS) and death, were not yet conclusively revealed.…”

“…As there are no data regarding OAR doses for re-RTs, inverse treatment planning usually is guided by the as-low-as-reasonably-achievable principle. 22 The mechanisms underlying radiation-induced carotid rupture, in the worst case leading to carotid artery blow-out syndrome (CBOS) and death, were not yet conclusively revealed. A major risk factor is atherosclerosis, accompanied by insufficient vasa vasorum, adventitia fibrosis, and subendothelial edema due to RT.…”