Multi-institutional investigation into the robustness of intra-cranial multi-target stereotactic radiosurgery plans to patient setup errors.

This study aimed to analyse correlations between planning factors including plan geometry and plan complexity with robustness to patient setup errors. Multiple-target brain stereotactic radiosurgery (SRS) plans were obtained through the Trans-Tasman Radiation Oncology Group (TROG) international treatment planning challenge (2018). The challenge dataset consisted of five intra-cranial targets with a 20 Gy prescription. Setup error was simulated using an in-house tool. Dose to targets was assessed via dose covering 99 % (D99 %) of gross tumour volume (GTV) and 98 % of planning target volume (PTV). Dose to organs at risk was assessed using volume of normal brain receiving 12 Gy and maximum dose covering 0.03 cc of brainstem. Plan complexity was assessed via edge metric, modulation complexity score, mean multi-leaf collimator (MLC) gap, mean MLC speed and plan modulation. Even for small (0.5 mm/°) errors, GTV D99 % was reduced by up to 20 %. The strongest correlation was found between lower complexity plans (larger mean MLC gap and lower edge metric) and higher robustness to setup error. Lower complexity plans had 1 %-20 % fewer targets/scenarios with GTV D99 % falling below the specified tolerance threshold. These complexity metrics correlated with 100 % isodose volume sphericity and dose conformity, though similar conformity was achievable with a range of complexities. A higher level of importance should be directed towards plan complexity when considering plan robustness. It is recommended when planning multi-target SRS, larger MLC gaps and lower MLC aperture irregularity be considered during plan optimisation due to higher robustness should patient positioning errors occur.

May L ，Barnes M ，Hardcastle N ，Hernandez V ，Saez J ，Rosenfeld A ，Poder J ... -  《-》

Multi-institutional investigation into the robustness of intra-cranial multi-target stereotactic radiosurgery plans to delivery errors.

May L ，Hardcastle N ，Hernandez V ，Saez J ，Rosenfeld A ，Poder J ... -  《-》

Dosimetric effect of rotational setup errors in stereotactic radiosurgery with HyperArc for single and multiple brain metastases.

In stereotactic radiosurgery (SRS) with single-isocentric treatments for brain metastases, rotational setup errors may cause considerable dosimetric effects. We assessed the dosimetric effects on HyperArc plans for single and multiple metastases. For 29 patients (1-8 brain metastases), HyperArc plans with a prescription dose of 20-24 Gy for a dose that covers 95% (D95% ) of the planning target volume (PTV) were retrospectively generated (Ref-plan). Subsequently, the computed tomography (CT) used for the Ref-plan and cone-beam CT acquired during treatments (Rot-CT) were registered. The HyperArc plans involving rotational setup errors (Rot-plan) were generated by re-calculating doses based on the Rot-CT. The dosimetric parameters between the two plans were compared. The dosimetric parameters [D99% , D95% , D1% , homogeneity index, and conformity index (CI)] for the single-metastasis cases were comparable (P > 0.05), whereas the D95% for each PTV of the Rot-plan decreased 10.8% on average, and the CI of the Rot-plan was also significantly lower than that of the Ref-plan (Ref-plan vs Rot-plan, 0.93 ± 0.02 vs 0.75 ± 0.14, P < 0.01) for the multiple-metastases cases. In addition, for the multiple-metastases cases, the Rot-plan resulted in significantly higher V10Gy (P = 0.01), V12Gy (P = 0.02), V14Gy (P = 0.02), and V16Gy (P < 0.01) than those in the Ref-plan. The rotational setup errors for multiple brain metastases cases caused non-negligible underdosage for PTV and significant increases of V10Gy to V16Gy in SRS with HyperArc.

Sagawa T ，Ohira S ，Ueda Y ，Akino Y ，Mizuno H ，Matsumoto M ，Miyazaki M ，Koizumi M ，Teshima T ... -  《Journal of Applied Clinical Medical Physics》

A hybrid planning strategy for stereotactic body radiation therapy of early stage non-small-cell lung cancer.

Currently dynamic conformal arcs (DCA) and volumetric modulated arc therapy (VMAT) are two popular planning techniques to treat lung stereotactic body radiation therapy (SBRT) patients. Of the two, DCA has advantages in terms of multi-leaf collimator (MLC) motion, positioning error, and delivery efficiency. However, VMAT is often the choice when critical organ sparing becomes important. We developed a hybrid strategy to incorporate DCA component into VMAT planning, results were compared with DCA and VMAT plans. Four planning techniques were retrospectively simulated for 10 lung SBRT patients: DCA, Hybrid-DCA (2/3 of the doses from DCA beams), Hybrid-VMAT (2/3 of the doses from VMAT beams) and VMAT. Plan complexity was accessed by modulation complexity score (MCS). Conformity index (CI) for the planning target volume (PTV), V20 and V5 for the lung, V30 for the chestwall, and maximum dose to all other critical organs were calculated. Plans were compared with regard to these metrics and measured agreement between the planned and delivered doses. DCA technique did not result in acceptable plan quality due to target location for five patients. Hybrid-DCA produced one unacceptable plan, and Hybrid-VMAT and VMAT produced no unacceptable plans. The CI improved with increasing VMAT usage, as did the dose sparing to critical structures. Compared to the VMAT technique, a total MU reduction of 14%, 25% and 37% were found for Hybrid-VMAT, Hybrid-DCA and DCA techniques for 54 Gy patient group, and 9%, 23% and 34% for 50 Gy patient group, suggesting improvement in delivery efficiency with increasing DCA usage. No significant variations of plan complexity were observed between Hybrid-DCA and Hybrid-VMAT (P = 0.46 from Mann-Whitney U-test), but significant differences were found among DCA, Hybrid and VMAT (P < 0.05). Better agreements between the planned and delivered doses were found with more DCA contributions. By adding DCA components to VMAT planning, hybrid technique offers comparable dosimetry to full VMAT, while increasing delivery efficiency and minimizing MLC complexity.

Liu H ，Sintay B ，Pearman K ，Shang Q ，Hayes L ，Maurer J ，Vanderstraeten C ，Wiant D ... -  《Journal of Applied Clinical Medical Physics》

Robust Optimization of SBRT Planning for Patients With Early Stage Non-Small Cell Lung Cancer.

Shang H ，Pu Y ，Wang Y 《-》