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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), V90% and D5cc) 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 V90% and D5cc were 12.5 cm3 vs. 11.5 cm3 (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. Keywords: MRI, Esophagus, Adaptive radiotherapy, Lung cancer, Dose accumulation

Purpose To evaluate the dosimetric effects of the AeroFormTM (AirXanpders®, Palo Alto, CA) tissue expander in‐situ for breast cancer patients receiving post‐mastectomy radiation therapy. Methods and Materials A film phantom (P1) was constructed by placing the metallic canister of the AeroForm on a solid water phantom with EBT3 films at five depths ranging from 2.6 mm to 66.2 mm. A breast phantom (P2), a three‐dimensional printed tissue‐equivalent breast with fully expanded AeroForm in‐situ, was placed on a thorax phantom. A total of 21 optical luminescent dosimeters (OLSDs) were placed on the anterior skin–gas interface and the posterior chest wall–metal interface of the AeroForm. Both phantoms were imaged with a 16‐bit computed tomography scanner with orthopedic metal artifact reduction. P1 was irradiated with an open field utilizing 6 MV and 15 MV photon beams at 0°, 90°, and 270°. P2 was irradiated using a volumetric modulated arc therapy plan with a 6 MV photon beam and a tangential plan with a 15 MV photon beam. All doses were calculated using Eclipse (Varian, Palo Alto, CA) with AAA and AcurosXB (AXB) algorithms. Results The average dose differences between film measurements and AXB in the region adjacent to the canister in P1 were within 3.1% for 15 MV and 0.9% for 6 MV. Local dose differences over 10% were also observed. In the chest wall region of P2, the median dose of OLSDs in percentage of prescription dose were 108.4% (range 95.4%–113.0%) for the 15MV tangential plan and 110.4% (range 99.1%–113.8%) for the 6MV volumetric modulated arc therapy plan. In the skin–gas interface, the median dose of the OLSDs were 102.3% (range 92.7%–107.7%) for the 15 MV plan and 108.2% (range 97.8–113.5%) for the 6 MV plan. Measured doses were, in general, higher than calculated doses with AXB calculations. The AAA dose algorithms produced results with slightly larger discrepancies between measurements compared with AXB. Conclusions The AeroForm creates significant dose uncertainties in the chest wall–metal interface. The AcurosXB dose calculation algorithm is recommended for more accurate calculations. If possible, post‐mastectomy radiation therapy should be delivered after the permanent implant is in place.

Background and Purpose This study summarizes the cranial stereotactic radiosurgery (SRS) volumetric modulated arc therapy (VMAT) procedure at our institution. Materials and Methods Volumetric 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. Results Lesion 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). Conclusions Volumetric 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.

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, (V D ), highest dose encompassing % volume V, (D V ), 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 V D (35≤D≤47 Gy, V 43 strongest at p=0.003), RP3+ with V D (31 ≤D≤ 45 Gy), RP2+ with D V (5 ≤V≤ 30%), RP3+ with D V (15 ≤V≤ 35%) and mean dose. Significant for ipsilateral lung were RP2+ with V D (38 ≤D≤44 Gy), RP3+ with V 41 , RP2+ and RP3+ with minimum dose; for contralateral lung, RP2+ with maximum dose. Correlation of PTV with RP2+ was strong (p 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.

PURPOSE To establish a new clinical procedure in frameless stereotactic radiosurgery (SRS) for patient setup verification at treatment couch angles as well as for head-motion monitoring during treatment using video-based optical surface imaging (OSI). METHODS A video-based three-dimensional (3D) OSI system with three ceiling-mounted camera pods was employed to verify setup at treatment couch angles as well as to monitor head motion during treatment. A noninvasive head immobilization device was utilized, which includes an alpha head mold and a dental mouthpiece with vacuum suction; both were locked to the treatment couch. Cone beam computed tomography (CBCT) was used as the standard for image-guided setup. Orthogonal 2D-kV imaging was applied for setup verification before treatment, between couch rotations, and after treatment at zero couch angle. At various treatment couch angles, OSI setup verification was performed, relative to initial OSI setup verification at zero couch angle after CBCT setup through a coordinate transformation. For motion monitoring, the setup uncertainty was decoupled by taking an on-site surface image as new reference to detect motion-induced misalignment in near real-time (1-2 frames per second). Initial thermal instability baseline of the real-time monitoring was corrected. An anthropomorphous head phantom and a 1D positioning platform were used to assess the OSI accuracy in motion detection in longitudinal and lateral directions. Two hypofractionated (9 Gy x 3 and 6 Gy x 5) frameless stereotactic radiotherapy (SRT) patients as well as two single-fraction (21 and 18 Gy) frameless SRS patients were treated using this frameless procedure. For comparison, 11 conventional frame-based SRS patients were monitored using the OSI to serve as clinical standards. Multiple noncoplanar conformal beams were used for planning both frameless and frame-based SRS with a micromultileaf collimator. RESULTS The accuracy of the OSI in 1D motion detection was found to be 0.1 mm with uncertainty of +/- 0.1 mm using the head phantom. The OSI registration against simulation computed tomography (CT) external contour was found to be dependent on the CT skin definition with -0.4 mm variation. For frame-based SRS patients, head-motion magnitude was detected to be

Dose distributions of (192)Ir 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.

To establish a new clinical procedure in frameless stereotactic radiosurgery (SRS) for patient setup verification at treatment couch angles as well as for head-motion monitoring during treatment using video-based optical surface imaging (OSI).A video-based three-dimensional (3D) OSI system with three ceiling-mounted camera pods was employed to verify setup at treatment couch angles as well as to monitor head motion during treatment. A noninvasive head immobilization device was utilized, which includes an alpha head mold and a dental mouthpiece with vacuum suction; both were locked to the treatment couch. Cone beam computed tomography (CBCT) was used as the standard for image-guided setup. Orthogonal 2D-kV imaging was applied for setup verification before treatment, between couch rotations, and after treatment at zero couch angle. At various treatment couch angles, OSI setup verification was performed, relative to initial OSI setup verification at zero couch angle after CBCT setup through a coordinate transformation. For motion monitoring, the setup uncertainty was decoupled by taking an on-site surface image as new reference to detect motion-induced misalignment in near real-time (1-2 frames per second). Initial thermal instability baseline of the real-time monitoring was corrected. An anthropomorphous head phantom and a 1D positioning platform were used to assess the OSI accuracy in motion detection in longitudinal and lateral directions. Two hypofractionated (9 Gy x 3 and 6 Gy x 5) frameless stereotactic radiotherapy (SRT) patients as well as two single-fraction (21 and 18 Gy) frameless SRS patients were treated using this frameless procedure. For comparison, 11 conventional frame-based SRS patients were monitored using the OSI to serve as clinical standards. Multiple noncoplanar conformal beams were used for planning both frameless and frame-based SRS with a micromultileaf collimator.The accuracy of the OSI in 1D motion detection was found to be 0.1 mm with uncertainty of +/- 0.1 mm using the head phantom. The OSI registration against simulation computed tomography (CT) external contour was found to be dependent on the CT skin definition with -0.4 mm variation. For frame-based SRS patients, head-motion magnitude was detected to be1.0 mm (0.3 +/- 0.2 mm) and1.0 degree (0.2 degrees +/- 0.2 degrees) for 98% of treatment time, with exception of one patient with head rotation1.5 degrees for 98% of the time. For frameless SRT/SRS patients, similar motion magnitudes were observed with an average of 0.3 +/- 0.2 mm and 0.2 degrees +/- 0.1 degree in ten treatments. For 98% of the time, the motion magnitude was1.1 mm and 1.0 degree. Complex head-motion patterns within 1.0 mm were observed for frameless SRT/SRS patients. The OSI setup verification at treatment couch angles was found to be within 1.0 mm.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.

Purpose: To analyze the setup accuracy of a thermoplastic mask system using two‐dimensional (2D) on‐board imager (OBI) and compare the results with the relocatable Gill‐Thomas‐Cosman (GTC) frame for fractionated stereotactic radiotherapy (FSRT). Method and Materials: Residual setup accuracy of 9 patients with brain lesions undergoing image‐guided hypo‐fractionated FSRT immobilized using a thermoplastic mask system were retrospectively studied. For each patient, image‐guided setup was performed for each treatment using orthogonal pairs of 2D OBI radiographs registered with reference digitally reconstructedradiography(DRR). Residual errors in the anterial‐posterior (A/P), right‐left (R/L) and superior‐inferior (S/I) directions were measured using in‐house software by contouring and comparing the location of bony anatomy on the DRRs and the orthogonal pairs of OBI radiographs taken immediately before the radiation treatment. The PTV margins required to ensure minimum dose to CTV is 95% for 90% of patients as proposed by Van Herk were also calculated for each direction. Results: Totally, setup accuracy was successfully analyzed for 45 fractions (5 fractions for each patient). The mean and standard deviation (SD) of the residual errors in the A/P, R/L, and S/I directions were 0.04±0.79 (mean ± 1 SD) mm, 0.3±1.32 mm, and −0.39±0.51mm respectively. The required margin to guarantee adequate PTV coverage were 2.57 mm, 3.98 mm and 1.86 mm in respectively the AP, R/L, and S/I direction. These margins were comparable to the 3mm PTV margin currently used for the hypo‐fractionated treatment using the GTC frame at our institution. Conclusion: The setup accuracy of 2D image‐guided FSRT immobilized with the thermoplastic mask system is compatible to the GTC frame for patients with brain lesions.