Feasibility of radical cardiac-sparing, treatment planning strategies for patients with locally advanced, non-small cell lung cancer.

PURPOSE: A set of treatment planning strategies were designed and retrospectively implemented for locally advanced, non-small cell lung cancer (NSCLC) patients in order to minimize cardiac dose without compromising target coverage goals. METHODS: Retrospective analysis was performed for 20 NSCLC patients prescribed to 60-66 Gy that received a mean heart dose (MHD) ≥10 Gy. Three planning approaches were designed and implemented. The first was a multi-isocentric (MI) volume-modulated arc therapy (VMAT) approach (HEART_MI) with one isocenter located within the tumor and the second chosen up to 10 cm away longitudinally. The second was a noncoplanar (NCP) VMAT approach (HEART_NCP) utilizing up to three large couch angles and a standard arc at couch 0. The final planning strategy took a mixed approach (HEART_HYBRID) utilizing the HEART_NCP strategy for two thirds of the treatment combined with a plan utilizing a pair of opposite-opposed gantry angles for the remaining treatments. Investigational plans were compared to original plans using dose-volume histogram metrics such as organ volume receiving greater than x Gy (Vx) or mean dose (Dmean). RESULTS: Although there was a small but statistically significant decrease in internal target volume coverage for HEART_MI plans and, conversely, a statistically significant increase for HEART_NCP plans, all generated plans met physician-prescribed target constraints. For heart dose, there were statistically significant decreases in all heart metrics and particularly MHD for the HEART_MI (9.8 vs. 15.4 Gy [p < 0.001], respectively), HEART_NCP (9.2 vs. 15.4 Gy [p < 0.001]), respectively), and HEART_HYBRID (7.9 vs. 15.4 Gy [p < 0.001], respectively) strategies. CONCLUSIONS: The strategy providing the best compromise between plan quality and cardiac dose reduction was HEART_NCP, which produced MHD reductions of 37.6% ± 12.9% (6.2 ± 3.4 Gy) relative to original plans. This strategy could potentially reduce adverse cardiac events, leading to improved quality of life for these patients.

MRI-guided Radiotherapy (MRgRT) for Treatment of Oligometastases: Review of Clinical Applications and Challenges.

PURPOSE: Early clinical results on the application of magnetic resonance imaging (MRI) coupled with a linear accelerator to deliver Magnetic Resonance-guided Radiation Therapy (MRgRT) have demonstrated feasibility for safe delivery of stereotactic body radiation therapy in treatment of oligometastatic disease. Here, we set out to review the clinical evidence and challenges associated with MRgRT in this setting. METHODS AND MATERIALS: We performed a systematic review of the literature pertaining to clinical experiences and trials on the use of MRgRT primarily for the treatment of oligometastatic cancers. We reviewed the opportunities and challenges associated with the use of MRgRT. RESULTS: Benefits of MRgRT pertaining to superior soft-tissue contrast, real-time imaging and gating, and online adaptive radiation therapy facilitate safe and effective dose escalation to oligometastatic tumors while simultaneously sparing surrounding healthy tissues. Challenges concerning further need for clinical evidence and technical considerations related to planning, delivery, quality assurance of hypofractionated doses, and safety in the MRI environment must be considered. CONCLUSIONS: The promising early indications of safety and effectiveness of MRgRT for stereotactic body radiation therapy-based treatment of oligometastatic disease in multiple treatment locations should lead to further clinical evidence to demonstrate the benefit of this technology.

Anisotropic Bladder Planning Target Volume in Bladder Radiation Therapy.

PURPOSE: This study aimed to investigate 3 planning target volume (PTV) margin expansions and determine the most appropriate volume to be used in bladder preservation therapy when using daily cone beam computed tomography (CBCT). We aimed to establish whether a smaller PTV expansion is feasible without risking geographical miss. METHODS AND MATERIALS: The study included patients with bladder cancer who were treated with a hypofractionated course of radiation therapy delivered with intensity modulated radiation therapy. The clinical target volume (CTV) was the whole empty bladder, and the PTV consisted of a 1.5-cm margin around the bladder (PTV1.5 cm). Patients underwent daily CBCT imaging before treatment to assess the bladder volume and ensure accurate positioning. We investigated 2 additional smaller PTV margin expansions to determine the most appropriate volume to be used with CBCT as a daily image guided radiation therapy modality. These margins were created retrospectively on every CBCT. The first additional volume was a uniform PTV margin of the surrounding 1 cm (PTV1 cm). When considering that the majority of the internal bladder movement was due to the variation in filling that occurs in the superior and anterior directions, a second volume of an anisotropic PTV margin with a 1.5-cm superior/anterior and 1 cm in other directions (PTV1/1.5 cm) was created. We recorded the frequency and measured the volume of bladder falling out of each PTV based on the daily CBCT. RESULTS: For the purpose of this study, we considered an arbitrary 5 cm3 of CTV falling out of the designated PTV as a clinically significant volumetric miss. The frequency of such a miss when applying the uniform PTV1 cm was 1%. However, when applying the uniform PTV1.5 cm and anisotropic PTV1/1.5 cm margins, the frequency was 0.5% and 0.5%, respectively. CONCLUSIONS: The anisotropic PTV expansion of 1.5 cm superiorly and anteriorly and 1 cm in all other directions around the bladder (CTV) provides a safe PTV approach when daily CBCT imaging is used to localize an empty bladder.