Purpose: MR-guided adaptive radiotherapy (MRgART) has a potential to treat kidney lesions with less toxicity. This study performed a retrospective analysis to determine the percentage of patients who may not require the adaptive procedure.
Methods: A retrospective study was performed on twenty patients, who have been treated with stereotactic MRgART for a kidney tumor with 40Gy in 5 fractions on a 0.35T MR-Linac. Prior to each treatment, the target and organs-at-risk (OARs) were recontoured on a pretreatment MRI scan for adaptive planning. The recontoured OARs included gastrointestinal organs (GI: stomach, duodenum, small bowel, and large bowel) and kidneys. The dose metrics of the planning target volume (PTV) and OARs were extracted for initial plans, predicted plans and re-optimization plans for all fractions delivered to the twenty patients.
Results: A total of 98 fractions were delivered. Plan adaptation was required when the predicted plan violated GI-OAR constraints (V33Gy>0.5cc) or PTV coverage was low (V40Gy<95%). Thirty-seven fractions (38%) failed to meet GI-OAR metrics in the predicted plans. Fifty-four fractions (55%) met GI-OAR metrics while improving PTV coverage in the re-optimization plans. When comparing plans among the patients, 15% of patient cases violated GI-OAR metrics in the predicted plan and met the metrics in the re-optimization plan with >5% improvement in PTV coverage; 45% of patient cases violated GI-OAR metrics and met the metrics with <5% coverage improvement in the re-optimization plan; 5% of patient cases met GI-OAR metrics but re-optimization improved target coverage (>5%); 35% of patient cases had no GI-OAR violations and insignificant coverage improvement (<5%).
Conclusion: Our study indicated that two-thirds of patients would benefit by adaptive planning and one-third of patients may be appropriate for non-adaptive MR-guided therapy. Further study will investigate how to identify patients who may not require the adaptive procedure to improve treatment efficiency.
Not Applicable / None Entered.
IM/TH- MRI in Radiation Therapy: MRI/Linear accelerator combined (general)