Is Real-Time Inverse Planning Optimizing Dose to the Normal Brain? A Prospective Comparative Trial in a Series of Brain Metastases Treated by Stereotactic Radiosurgery

<b><i>Background:</i></b> Radiosurgery has demonstrated good safety and efficacy in the treatment of multiple brain metastases (BMs). However, multi-target dose planning can be challenging and time-consuming. A recently developed real-time inverse treatment planning (IP) by convex optimization has been demonstrated to produce high-quality treatment plans with good conformity and selectivity in single-target plans. We intended to test the capacity of this IP to rapidly generate efficient plans while optimizing the preservation of normal tissue in multiple BM. <b><i>Methods:</i></b> Seventy-nine patients (mean age 62.4, age range 22–85) with a total of 272 BMs were treated by Gamma Knife Radiosurgery. All subjects were treated using a forward planning (FP) technique by an expert neurosurgeon. The new Intuitive Plan was applied and able to automatically generate an alternative plan for each patient. All planning variables were collected from the IP to be compared with the corresponding measurements obtained from the FP. A paired sample <i>t</i> test was applied to compare the 2 plans for the following variables: brain volumes receiving 10 Gy (V10) (primary endpoint), and 12 Gy (V12), planning indices (selectivity, coverage, gradient, and Paddick Conformity Index [PCI]), beam-on time (BOT), and integral doses. Additionally, the noninferiority margin for each item was calculated, and the 2 plans were compared for noninferiority using a paired <i>t</i> test. <b><i>Results:</i></b> The mean age of patients was 62.4 years old (age range 22–85), with a sex ratio of 1.02. The average number of lesions per patient was 3.4 (range 1–12). The mean prescription dose was 21.46 Gy (range 14–24 Gy). Noninferiority of the IP was concluded for V10, V12, prescription isodose volume, BOT, PCI, and selectivity. The V10 (and V12) was significantly lower with the IP (<i>p</i> &#x3c; 0.001). These volumes were 8.69 cm³ ± 11.39 and 5.47 cm³ ± 7.03, respectively, for the FP and 7.57 cm³ ± 9.44 and 4.78 cm³ ± 5.86 for the IP. Only the coverage was significantly lower with the IP (−2.3%, <i>p</i> &#x3c; 0.001), but both selectivity (+17%) and PCI (+15%) were significantly higher with the IP than FP (<i>p</i> &#x3c; 0.001). <b><i>Conclusion:</i></b> This IP demonstrated its capacity to generate multi-target plans rapidly, with a dose to the brain (V10) and BOT noninferior to the one of a human expert planner. These results would benefit from confirmation in a larger prospective series.

A Novel Fuzzy Logic Guided Method for Automatic gEUD-based Inverse Treatment Planning

Generalized equivalent uniform dose (gEUD) -based hybrid objective functions are widely used in intensity modulated radiotherapy (IMRT). To improve its efficiency, a novel fuzzy logic guided inverse planning method was developed for the automatic parameters optimization of the gEUD-based radiotherapy optimization. Simple inference rules were formulated according to the knowledge of the treatment planner. Then they automatically and iteratively guide the parameters modification according to the percentage of deviation between the current dose and the prescribed dose. weighting factors and prescribed dose were automatically adjusted by developed fuzzy inference system (FIS). The performance of the FIS was tested on ten prostate cancer cases. Experimental results indicate that proposed automatic method can yield comparable or better plans than manual method. The fuzzy logic guided automatic inverse planning method of parameters optimization can significantly improve the efficiency of the method of manually adjusting parameters, and contributes to the development of fully automated planning.

Hippocampal Dosimetric Evaluation in Locally Advanced Nasopharyngeal Carcinoma Patients Treated with Intensity Modulated Radiotherapy

Introduction: Treatment of locally advanced nasopharyngeal (Npx) cancer usually requires the inclusion of the sphenoid body or higher in intermediate risk CTV dose regions. This makes the avoidance of intracranial OAR such as temporal lobes, optic apparatus and cochlea challenging. There are different accumulating data confirming the impact of hippocampus (HC) irradiation on neurocognitive functions after whole brain radiotherapy & Npx cases were specifically addressed in several publications. The specified dose constrain in RTOG 0933 was Dmax <9 Gy. Our aim is to retrospectively evaluate the doses delivered to the HC in patients with locally advanced Npx carcinoma. Methods: Our study included twelve patients with locally advanced nasopharyngeal carcinoma (Stage III-IVA) previously treated at NEMROCK by either IMRT or VMAT. The HC was retrospectively delineated without being accounted for in the inverse treatment planning. Bilateral HC were delineated as a single OAR, and a margin of 3 mm was added to create the HC zone. We evaluated the doses delivered to the hippocampus by conducting a dosiemtric analysis on the treatment plan already used. Results: DVH Analysis: The mean volumes (std) for PTV70 primary, PTV70 LN and PTV59.4 were 83.62 cm3 (±33.51), 119.5 cm3 (±122.66) and 1017.58 cm3 (±140.28) respectively. The mean HC volume (std) was 4.17 cm3 (±1.66). The mean HC Dmin, Dmean, Dmedian and Dmax were 6.57 Gy, 25.05 Gy, 24.18 Gy and 52.95 Gy respectively. The mean HC V5, V10, V20, V40, V50 and V60 were 92.83%, 78.95%, 55.91%, 20.37%, 9.9% and 3.38% respectively. There was no difference between IMRT and VMAT in terms of HC volumetric and dosimetric parameters. Conclusion: In locally advanced Npx carcinoma, HC is exposed to significant doses, particularly with T4 disease (intracranial extension). In view of the low radiation tolerance of HC and its close proximity to CTV54-60 Gy in Npx cases, HC contouring and avoidance should be considered.