The OSI system is capable of detecting 0.1 +/- 0.1 mm 1D spatial displacement of a phantom in near real time and useful in head-motion monitoring. This new frameless SRS procedure using the mask-less head-fixation system provides immobilization similar to that of conventional frame-based SRS. Head-motion monitoring using near-real-time surface imaging provides adequate accuracy and is necessary for frameless SRS in case of unexpected head motion that exceeds a set tolerance.

Background and PurposeThis study summarizes the cranial stereotactic radiosurgery (SRS) volumetric modulated arc therapy (VMAT) procedure at our institution.Materials and MethodsVolumetric modulated arc therapy plans were generated for 40 patients with 188 lesions (range 2–8, median 5) in Eclipse and treated on a TrueBeam STx. Limitations of the custom beam model outside the central 2.5 mm leaves necessitated more than one isocenter pending the spatial distribution of lesions. Two to nine arcs were used per isocenter. Conformity index (CI), gradient index (GI) and target dose heterogeneity index (HI) were determined for each lesion. Dose to critical structures and treatment times are reported.ResultsLesion size ranged 0.05–17.74 cm3 (median 0.77 cm3), and total tumor volume per case ranged 1.09–26.95 cm3 (median 7.11 cm3). For each lesion, HI ranged 1.2–1.5 (median 1.3), CI ranged 1.0–2.9 (median 1.2), and GI ranged 2.5–8.4 (median 4.4). By correlating GI to PTV volume a predicted GI = 4/PTV0.2 was determined and implemented in a script in Eclipse and used for plan evaluation. Brain volume receiving 7 Gy (V 7 Gy) ranged 10–136 cm3 (median 42 cm3). Total treatment time ranged 24–138 min (median 61 min).ConclusionsVolumetric modulated arc therapy provide plans with steep dose gradients around the targets and low dose to critical structures, and VMAT treatment is delivered in a shorter time than conventional methods using one isocenter per lesion. To further improve VMAT planning for multiple cranial metastases, better tools to shorten planning time are needed. The most significant improvement would come from better dose modeling in Eclipse, possibly by allowing for customizing the dynamic leaf gap (DLG) for a special SRS model and not limit to one DLG per energy per treatment machine and thereby remove the limitation on the Y‐jaw and allow planning with a single isocenter.

Background and purpose: Minimizing acute esophagitis (AE) in locally advanced non-small cell lung cancer (LA-NSCLC) is critical given the proximity between the esophagus and the tumor. In this pilot study, we developed a clinical platform for quantification of accumulated doses and volumetric changes of esophagus via weekly Magnetic Resonance Imaging (MRI) for adaptive radiotherapy (RT). Material and methods: Eleven patients treated via intensity-modulated RT to 60-70 Gy in 2-3 Gy-fractions with concurrent chemotherapy underwent weekly MRIs. Eight patients developed AE grade 2 (AE2), 3-6 weeks after RT started. First, weekly MRI esophagus contours were rigidly propagated to planning CT and the distances between the medial esophageal axes were calculated as positional uncertainties. Then, the weekly MRI were deformably registered to the planning CT and the total dose delivered to esophagus was accumulated. Weekly Maximum Esophagus Expansion (MEex) was calculated using the Jacobian map. Eventually, esophageal dose parameters (Mean Esophagus Dose (MED), V 90% and D 5cc) between the planned and accumulated dose were compared. Results: Positional esophagus uncertainties were 6.8 ± 1.8 mm across patients. For the entire cohort at the end of RT: the median accumulated MED was significantly higher than the planned dose (24 Gy vs. 21 Gy p = 0.006). The median V 90% and D 5cc were 12.5 cm 3 vs. 11.5 cm 3 (p = 0.05) and 61 Gy vs. 60 Gy (p = 0.01), for accumulated and planned dose, respectively. The median MEex was 24% and was significantly associated with AE2 (p = 0.008). Conclusions: MRI is well suited for tracking esophagus volumetric changes and accumulating doses. Longitudinal esophagus expansion could reflect radiation-induced inflammation that may link to AE.

Purpose/Objective To determine clinically helpful dose-volume and clinical metrics correlating with symptomatic radiation pneumonitis (RP) in malignant pleural mesothelioma (MPM) patients with two lungs treated with hemithoracic intensity modulated pleural radiation therapy (IMPRINT). Methods and Materials Treatment plans and resulting normal organ dose-volume histograms of 103 consecutive MPM patients treated with IMPRINT (2/2005–1/2015) to the highest dose ≤50.4 Gy satisfying departmental normal tissue constraints were uniformly recalculated. Patient records provided maximum RP grade (CTCAE v4.0), clinical and demographic information. Correlations analyzed with the Cox model were: ≥ Grade 2 RP (RP2+) and ≥ Grade 3 RP (RP3+) with clinical variables, with volumes of PTV and PTV-Lung overlap and with mean dose, percent volume receiving dose D, (VD), highest dose encompassing % volume V, (DV), and heart, total, ipsilateral, and contralateral lungs volumes. Results Twenty-seven patients had RP2+ (14 with RP3+). Median prescription dose was 46.8 Gy (39.6 to 50.4 Gy, 1.8Gy/fraction). Median age was 67.6 years (42 to 83 years). There were 79 males, 40 never-smokers, 44 with left-sided MPM. There were no significant (p≤0.05) correlations with clinical variables, prescription dose, total lung dose-volume metrics and PTV-Lung overlap volume. Dose-volume correlations for heart were RP2+ with VD (35≤D≤47 Gy, V43 strongest at p=0.003), RP3+ with VD (31 ≤D≤ 45 Gy), RP2+ with DV (5 ≤V≤ 30%), RP3+ with DV (15 ≤V≤ 35%) and mean dose. Significant for ipsilateral lung were RP2+ with VD (38 ≤D≤44 Gy), RP3+ with V41, RP2+ and RP3+ with minimum dose; for contralateral lung, RP2+ with maximum dose. Correlation of PTV with RP2+ was strong (p<0.001) and also significant with RP3+. Conclusions Heart dose correlates strongly with symptomatic RP in this large cohort of MPM patients with two lungs treated with IMPRINT. Planning constraints to reduce future heart doses are suggested.

Dose distributions of 192Ir HDR brachytherapy in phantoms simulating water, bone, lung tissue, water-lung and bone-lung interfaces using the Monte Carlo codes EGS4, FLUKA and MCNP4C are reported. Experiments were designed to gather point dose measurements to verify the Monte Carlo results using Gafchromic film, radiophotoluminescent glass dosimeter, solid water, bone, and lung phantom. The results for radial dose functions and anisotropy functions in solid water phantom were consistent with previously reported data (Williamson and Li). The radial dose functions in bone were affected more by depth than those in water. Dose differences between homogeneous solid water phantoms and solid water-lung interfaces ranged from 0.6% to 14.4%. The range between homogeneous bone phantoms and bone-lung interfaces was 4.1% to 15.7%. These results support the understanding in dose distribution differences in water, bone, lung, and their interfaces. Our conclusion is that clinical parameters did not provide dose calculation accuracy for different materials, thus suggesting that dose calculation of HDR treatment planning systems should take into account material density to improve overall treatment quality.