Treatment planning for spinal radiosurgery : A competitive multiplatform benchmark challenge.

PURPOSE: To investigate the quality of treatment plans of spinal radiosurgery derived from different planning and delivery systems. The comparisons include robotic delivery and intensity modulated arc therapy (IMAT) approaches. Multiple centers with equal systems were used to reduce a bias based on individual's planning abilities. The study used a series of three complex spine lesions to maximize the difference in plan quality among the various approaches. METHODS: Internationally recognized experts in the field of treatment planning and spinal radiosurgery from 12 centers with various treatment planning systems participated. For a complex spinal lesion, the results were compared against a previously published benchmark plan derived for CyberKnife radiosurgery (CKRS) using circular cones only. For two additional cases, one with multiple small lesions infiltrating three vertebrae and a single vertebra lesion treated with integrated boost, the results were compared against a benchmark plan generated using a best practice guideline for CKRS. All plans were rated based on a previously established ranking system. RESULTS: All 12 centers could reach equality (n = 4) or outperform (n = 8) the benchmark plan. For the multiple lesions and the single vertebra lesion plan only 5 and 3 of the 12 centers, respectively, reached equality or outperformed the best practice benchmark plan. However, the absolute differences in target and critical structure dosimetry were small and strongly planner-dependent rather than system-dependent. Overall, gantry-based IMAT with simple planning techniques (two coplanar arcs) produced faster treatments and significantly outperformed static gantry intensity modulated radiation therapy (IMRT) and multileaf collimator (MLC) or non-MLC CKRS treatment plan quality regardless of the system (mean rank out of 4 was 1.2 vs. 3.1, p = 0.002). CONCLUSIONS: High plan quality for complex spinal radiosurgery was achieved among all systems and all participating centers in this planning challenge. This study concludes that simple IMAT techniques can generate significantly better plan quality compared to previous established CKRS benchmarks.

Single fraction radiosurgery/stereotactic body radiation therapy (SBRT) for spine metastasis: A dosimetric comparison of multiple delivery platforms.

There are numerous commercial radiotherapy systems capable of delivering single fraction spine radiosurgery/SBRT. We aim to compare the capabilities of several of these systems to deliver this treatment when following standardized criteria from a national protocol. Four distinct target lesions representing various case presentations of spine metastases were contoured in both the thoracic and lumbar spine of an anthropomorphic SBRT phantom. Single fraction radiosurgery/SBRT plans were designed for each target with each of our treatment platforms. Plans were prescribed to 16 Gy in one fraction to cover 90% of the target volume using normal tissue and target constraints from RTOG 0631. We analyzed these plans with priority on the dose to 10% of the partial spinal cord and dose to 0.03 cc of the spinal cord. Each system was able to maintain 90% target coverage while meeting all the constraints of RTOG 0631. On average, CyberKnife was able to achieve the lowest spinal cord doses overall and also generated the sharpest dose falloff as indicated by the Paddick gradient index. Treatment times varied widely depending on the modality utilized. On average, treatment can be delivered faster with Flattening Filter Free RapidArc and Tomotherapy, compared to Vero and Cyberknife. While all systems analyzed were able to meet the dose constraints of RTOG 0631, unique characteristics of individual treatment modalities may guide modality selection. Specifically, certain modalities performed better than the others for specific target shapes and locations, and delivery time varied significantly among the different modalities. These findings could provide guidance in determining which of the available modalities would be preferable for the treatment of spine metastases based on individualized treatment goals.

Evaluation of Dose Accuracy in the Near-Surface Region for Whole Breast Irradiation Techniques in a Multi-institutional Consortium.

PURPOSE: To assess the accuracy of dose calculations in the near-surface region for different treatment planning systems (TPSs), treatment techniques, and energies to improve clinical decisions for patients receiving whole breast irradiation (WBI). METHODS AND MATERIALS: A portable custom breast phantom was designed for dose measurements in the near-surface regions. Treatment plans of varying complexities were created at 8 institutions using 4 different TPSs on an anonymized patient data set (50 Gy in 25 fractions) and peer reviewed by participants. The plans were recalculated on the phantom data set. The phantom was aligned with predetermined shifts and laser marks or cone beam computed tomography, and the irradiation was performed using a variety of linear accelerators at the participating institutions. Dose was measured with radiochromic film placed at 0.5 and 1.0 cm depth and 3 locations per depth within the phantom. The film was scanned and analyzed >24 hours postirradiation. RESULTS: The percentage difference between the mean of the measured and calculated dose across the participating centers was -0.2 % ± 2.9%, with 95% of measurements within 6% agreement. No significant differences were found between the mean of the calculated and measured dose for all TPSs, treatment techniques, and energies at all depths and laterality investigated. Furthermore, no significant differences were observed between the mean of measured dose and the prescription dose of 2 Gy per fraction. CONCLUSION: These results demonstrate that dose calculations for clinically relevant WBI plans are accurate to within 6% of measurements in the near-surface region for various complexities, TPSs, linear accelerators, and beam energies. This work lays the necessary foundation for future studies investigating the correlation between near-surface dose and acute skin toxicities.

The Continuous Assessment of Cranial Motion in Thermoplastic Masks During CyberKnife Radiosurgery for Trigeminal Neuralgia.

Stereotactic radiosurgery (SRS) treatment is characterized by high doses per fraction and extremely steep dose gradients. This requires a great degree of accurate localization to the appropriate treatment position, and continuous immobilization during the treatment session. In the case of Trigeminal Neuralgia (TGN) treatment this is especially true as the very small target volume makes positional accuracy critical. In this study we carried out a quantitative analysis of patient motion during the full treatment fraction within a radiosurgery immobilization mask system. Patient cranial movement was assessed by using the image guidance stereo x-ray cameras on a CyberKnife (CK) M6 robotic radiosurgery system (Accuray, Sunnyvale, CA). A total of five patients received treatments for either right or left TGN. The duration of treatment varied from 24-64 minutes. Orthogonal images were taken every 15 seconds during the treatment to assess patient movement. Approximately 60 stereo images were taken per patient and a total of 560 images were analyzed in this study. The mean absolute movement in each of longitudinal, lateral or vertical directions was approximately 0.3 mm for the duration of the treatment; however, on occasion much greater movement was observed during a fraction. The maximum displacement was in the longitudinal direction and reached 2.4 mm compared to the initial setup. Images taken at the end of the treatment session showed that the patients typically return to a position closer to the original setup position than the maximum excursion that occurred. This data suggests that although this mask system appears stable during much of the treatment session; for some patients there may be momentary patient movements that take place. Frequent imaging and correction can help mitigate the effect of this movement. It is important to understand the limitations of non-invasive mask systems when used for very high precision treatment.