Cancers arising on nasal skin or in the nasal cavity being treated high energy photons or electrons may require bolus to ensure adequate superficial dose deposition. Creating a conformal bolus material on this irregular surface can pose a challenge. In this study, we evaluated the clinical feasibility, benefits and workflow of using 3D-printed bolus that is made of water-equivalent soft polymer materials and customized to patient anatomy by a 3D printer for nasal radiotherapy. We compared 3D-printed bolus with a conventional flat bolus or multi-layer thermoplastic bolus in 9 patients undergoing radiotherapy for nasal cancer. The 3D-printed polymer bolus was soft and had water-equivalency, which was measured dosimetrically by printing a 10x10x1 cm3 flab using a 3D printer and compared with the conventional flat bolus. Using a planning system, a bolus contour conformal to the skin was converted to a mesh structure using a plug-in script and exported as a STL file to the 3D printer. The treatment isocenter was either printed on the bolus with a creation of 5 dots, or identified by unique bolus edges using the planning system and marked in black. During treatment, a conventional bolus or the 3D-printed bolus was used and skin dose was measured using two optically stimulated luminescence (OSL: 10x10x1 mm3) dosimeters taped under the boluses. The skin-bolus airgap was visualized with cone-beam computed tomography (CBCT), while the pictures of bolus conditions were taken in each case. To quantify the mean airgap distance in mm, the airgap was contoured and its volume was calculated. Then the skin was evenly expanded with 1mm interval and the expansion volume under the bolus was calculated. The match between the volume of the airgap and the expanded region defines the mean airgap distance. The mean airgap distance, surface dose, and clinical efforts and time were compared. The bolus-to-skin conformality of a 3D-printed bolus is much improved with the mean (<2mm) and maximum (5-8mm) gap distances, reduced by 50%-150% from the conventional boluses based on CBCT. The conformality is reduced when two OSL dosimeters were placed underneath the bolus due to the chip size, yielding a similar airgap and similar skin dose (p=0.7) near the prescription dose (100%) in all cases (104%±11% for 3D-printed bolus and 105%±7% for other boluses). The 3D-printed bolus provides (1) minimal nasal alteration without forcing the bolus to retain conformal using adhesive tape; (2) minimal efforts at setup with only gentle waggling to fit patient facial surface; and (3) minimal time spending in bolus preparation and at patient setup. The bolus printing is streamlined in parallel to treatment planning. The 3D-printed bolus is dosimetrically equivalent to the conventional bolus, providing a safe, highly conformal, and convenient option for clinical use. With modification, similar procedure and clinical workflow may be applied to other anatomic sites. More clinical evaluations are on-going.
Purpose: This study is designed to analyze the properties of beam path length at different brain locations and the effect of Inhomogeneity orrection (IC) on isocenter dose of cranial Stereotactic Radiosurgery (SRS) treatment planning. Method: Fifty five clinical cranial SRS plans, with total 63 lesions were analyzed in this study. Lesions were grouped as frontal (16 lesions), parietal (10 lesions), temporal (10 lesions), occipital (10 lesions), cerebellum (10 lesions), and acoustic neuroma (7 lesions). All plans were planned on Brainlab iPlan RT Dose 3.0.2. Pencil beam convolution dose calculation algorithm was used both with and without IC with identical beam parameters. Nine to 11 beams were used for each lesion. Average beam path length, and differences in isocenter dose for each lesion with and without IC were analyzed. Result: The mean and standard deviation (SD) of average beam path length for frontal, parietal, temporal, occipital, cerebellum and acoustic neuroma lesions without IC were 47.54±16.03mm, 45.33±8.69mm, 64.15±12.33mm, 51.27±9.73mm, 78.70±10.89mm and 79.92±7.46mm, respectively. The corresponding results with IC were 56.08±14.86mm, 52.80±8.79mm, 71.85±12.27mm, 59.97±10.20mm, 86.57±11.26mm and 90.07±7.57mm, respectively. The differences in average beam path length between with and without IC were 8.54±1.62mm, 7.47±1.04mm, 7.70±1.66mm, 8.71±1.56mm, 7.87±1.39mm and 10.15±3.52mm respectively. The mean and SD of isocenter dose for frontal, parietal, temporal, occipital, cerebellum, acoustic neuroma and all lesions combined without IC were 3.83±0.72%, 3.35±0.61%, 3.47±0.88%, 3.99±0.76%, 3.69±0.69%, 4.83 ±1.77% and 3.81±0.96% higher then the isocenter dose with IC, respectively. The maximum dose difference was 7.05% for an acoustic neuroma case and minimum dose difference was 1.59% for a frontal lobe lesion. Conclusion: In conclusion, an isodose difference between dose calculation with and without IC of about 4% was found for cranial SRS case. The effect of planning cranial SRS with or without IC increases with the average path length differences.
Purpose: To investigate an alternative approach to VMAT optimization for hypofractionation lung treatment which increases average aperture opening and results in lower total Monitor Units (MU) without significantly sacrificing plan quality. Methods: Benchmark Volumetric Modulated Arc Therapy (bVMAT) plans were generated for 10 lung Stereotactic Body radiotherapy (SBRT) cases using Eclipse Version 11.0.42 (Varian Medical Systems) without a maximum MU constraint. Prescriptions ranged from 40 to 54Gy in 3 to 5 fractions. AAA dose calculation and PRO fluence based optimization was utilized. Two comparison VMAT plans were generated for each case, one that forced an initial “open” mlc aperture conformal to the tumor as a starting condition (oVMAT) with similar optimization parameters and arc geometries, and one that repeated the bVMAT optimization but added a maximum MU constraint (muVMAT). All plans used two arcs with lengths between 168 to 230 degrees. PTV D 95% and Dmean, lung V20 Gy, chest wall V30 Gy, average aperture opening and MU's were compared. Statistical significance was evaluated using Wilcoxon signed rank test. Results: Average PTV D(95), PTV mean and lung V20Gy over all plans was 99.2 ± 1.7%, 103.3 ± 0.6% and 7.8 ± 2.4% respectively. The average chest wall V30Gy was 61 ± 61 cc and ranged between 0 to 166 cc. There were no significant differences between the three techniques for the dosimetric quantities. MUs were reduced by 11 ±11% (p<0.01) and 25 ± 5% (p<0.01) and the average aperture size was increased by 13.7 ± 14% (p=0.02) and 35.8 ± 10% (p<0.01) with muVMAT and oVMAT, respectively, compared to bVMAT. Conclusion: oVMAT and muVMAT techniques were both able to increase average aperture size and reduce total MU compared to the benchmark VMAT plan, but the magnitude of the changes observed for oVMAT was larger.
Purpose: To develop a biological modeling strategy which incorporates the response observed on the mid‐treatment PET/CT into a dose escalation design for adaptive radiotherapy of non‐small‐cell lung cancer. Method: FDG‐PET/CT was acquired midway through standard fractionated treatment and registered to pre‐treatment planning PET/CT to evaluate radiation response of lung cancer. Each mid‐treatment PET voxel was assigned the median SUV inside a concentric 1cm‐diameter sphere to account for registration and imaging uncertainties. For each voxel, the planned radiation dose, pre‐ and mid‐treatment SUVs were used to parameterize the linear‐quadratic model, which was then utilized to predict the SUV distribution after the full prescribed dose. Voxels with predicted post‐treatment SUV≥2 were identified as the resistant target (response arm). An adaptive simultaneous integrated boost was designed to escalate dose to the resistant target as high as possible, while keeping prescription dose to the original target and lung toxicity intact. In contrast, an adaptive target volume was delineated based only on the intensity of mid‐treatment PET/CT (intensity arm), and a similar adaptive boost plan was optimized. The dose escalation capability of the two approaches was compared. Result: Images of three patients were used in this planning study. For one patient, SUV prediction indicated complete response and no necessary dose escalation. For the other two, resistant targets defined in the response arm were multifocal, and on average accounted for 25% of the pre‐treatment target, compared to 67% in the intensity arm. The smaller response arm targets led to a 6Gy higher mean target dose in the adaptive escalation design. Conclusion: This pilot study suggests that adaptive dose escalation to a biologically resistant target predicted from a pre‐ and mid‐treatment PET/CT may be more effective than escalation based on the mid‐treatment PET/CT alone. More plans and ultimately clinical protocols are needed to validate this approach. MSKCC has a research agreement with Varian Medical System
This study summarizes the cranial stereotactic radiosurgery (SRS) volumetric modulated arc therapy (VMAT) procedure at our institution.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.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 (V7 Gy ) ranged 10-136 cm3 (median 42 cm3 ). Total treatment time ranged 24-138 min (median 61 min).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.
Background and purposeMinimizing 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 methodsEleven 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.ResultsPositional 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).ConclusionsMRI 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: To develop an image‐guided procedure for online head‐rotation correction and real‐time motion monitoring with threshold gating for clinical frameless stereotactic radiosurgery (SRS) using video‐based optical 3D surface imaging (AlignRT) to ensure accurate tumor localization and clinically‐acceptable head motion at all treatment couch angles during treatment. Methods: Eight patients, immobilized with a deep‐head mold and a mouth‐piece fixed to the couch, were treated with single‐fraction frameless SRS. The planning target volume was defined by a 3.0mm‐margin around the gross tumor volume for these patients with brain metastasis. A ceiling‐mounted AlignRT system with three camera pods was used to correct residual head rotation before cone‐beam computed tomography (CBCT) setup, verify setup at all treatment couch angles, and monitor the head motion with 1.0mm gating threshold for beam hold. The external contour of the planing CT and on‐site surface reference images were used for setup verification and motion monitoring, respectively, using the maximum visible skin surface within the entire mid‐to‐upper face as the region of interest. An anthropomorphous head phantom and an adjustable platform (accuracy of 0.1 mm) were used to determine the geometric accuracy of frameless setup procedure and AlignRT motion detection. Results: The phantom experiment shows that the motion detection accuracy was less than 0.1 mm. For these patients, <1 degree head rotation was achieved at the setup by using surface‐image‐guided head repositioning. The patient head motion was found to be <1.0mm for 98% of the time after CBCT setup, while the beam‐hold gating was used for <1% of beam‐on time. The required workload and machine time of this procedure are similar to those of conventional frame‐based SRS. Conclusions: This non‐invasive frameless SRS procedure provides accurate and reliable means to perform clinical SRS. The image‐guided setup and motion control provides adequate accuracy, yet more convenient to the patients, comparing with frame‐based SRS. This research is in part supported by VisionRT through a clinical research agreement.
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