1. Isotoxic dose prescription level strategies for stereotactic liver radiotherapy: the price of dose uniformity
- Author
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Morten Høyer, Per Rugaard Poulsen, Anders Traberg Hansen, and Esben S. Worm
- Subjects
BODY RADIATION-THERAPY ,MOTION ,Movement ,medicine.medical_treatment ,LUNG-TUMORS ,Radiosurgery ,NSCLC ,030218 nuclear medicine & medical imaging ,Dose uniformity ,03 medical and health sciences ,0302 clinical medicine ,TARGETS ,Humans ,ESCALATION ,Medicine ,Computer Simulation ,RECONSTRUCTION ,Radiology, Nuclear Medicine and imaging ,SBRT ,business.industry ,Radiotherapy Planning, Computer-Assisted ,Liver Neoplasms ,Radiotherapy Dosage ,Hematology ,General Medicine ,Dose prescription ,Target dose ,Radiation therapy ,METASTASES ,Liver ,Oncology ,030220 oncology & carcinogenesis ,Radiotherapy, Intensity-Modulated ,business ,Nuclear medicine - Abstract
Introduction: To find the optimal dose prescription strategy for liver SBRT, this study investigated the tradeoffs between achievable target dose and healthy liver dose for a range of isotoxic uniform and non-uniform prescription level strategies. Material and methods: Nine patients received ten liver SBRT courses with intrafraction motion monitoring during treatment. After treatment, five VMAT treatment plans were made for each treatment course. The PTV margin was 5 mm (left-right, anterior-posterior) and 10 mm (cranio-caudal). All plans had a mean CTV dose of 56.25 Gy in three fractions, while the PTV was covered by 50%, 67%, 67 s% (steep dose gradient outside CTV), 80%, and 95% of this dose, respectively. The 50%, 67 s%, 80%, and 95% plans were then renormalized to be isotoxic with the standard 67% plan according to a Lyman-Kutcher-Burman normal tissue complication probability model for radiation induced liver disease. The CTV D98 and mean dose of the iso-toxic plans were calculated both without and with the observed intrafraction motion, using a validated method for motion-including dose reconstruction. Results: Under isotoxic conditions, the average [range] mean CTV dose per fraction decreased gradually from 21.2 [20.5-22.7] Gy to 15.5 [15.0-16.6] Gy and the D98 dose per fraction decreased from 20.4 [19.7-21.7] Gy to 15.0 [14.5-15.5] Gy, as the prescription level to the PTV rim was increased from 50% to 95%. With inclusion of target motion the mean CTV dose was 20.5 [16.5-22.5] Gy (50% PTV rim dose) and 15.4 [13.9-16.7] Gy (95% rim dose) while D98 was 17.8 [7.4-20.6] Gy (50% rim dose) and 14.6 [8.8-15.7] Gy (95% rim dose). Conclusion: Requirements of a uniform PTV dose come at the price of excess normal tissue dose. A non-uniform PTV dose allows increased CTV mean dose at the cost of robustness toward intrafraction motion. The increase in planned CTV dose by non-uniform prescription outbalanced the dose deterioration caused by motion.
- Published
- 2019