Abstract
PurposeTo demonstrate fast treatment planning feasibility of stereotactic body radiation therapy (SBRT) for centrally located lung tumors on Halcyon Linac via a previously validated knowledge‐based planning (KBP) model to support offline adaptive radiotherapy.Materials/methodsTwenty previously treated non‐coplanar volumetric‐modulated arc therapy (VMAT) lung SBRT plans (c‐Truebeam) on SBRT‐dedicated C‐arm Truebeam Linac were selected. Patients received 50 Gy in five fractions. c‐Truebeam plans were re‐optimized for Halcyon manually (m‐Halcyon) and with KBP model (k‐Halcyon). Both m‐Halcyon and k‐Halcyon plans were normalized for identical or better target coverage than clinical c‐Truebeam plans and compared for target conformity, dose heterogeneity, dose fall‐off, and dose tolerances to the organs‐at‐risk (OAR). Treatment delivery parameters and planning times were evaluated.Results k‐Halcyon plans were dosimetrically similar or better than m‐Halcyon and c‐Truebeam plans. k‐Halcyon and m‐Halcyon plan comparisons are presented with respect to c‐Truebeam. Differences in conformity index were statistically insignificant in k‐Halcyon and on average 0.02 higher (p = 0.04) in m‐Halcyon plans. Gradient index was on average 0.43 (p = 0.006) lower and 0.27 (p = 0.02) higher for k‐Halcyon and m‐Halcyon, respectively. Maximal dose 2 cm away in any direction from target was statistically insignificant. k‐Halcyon increased maximal target dose on average by 2.9 Gy (p < 0.001). Mean lung dose was on average reduced by 0.10 Gy (p = 0.004) in k‐Halcyon and increased by 0.14 Gy (p < 0.001) in m‐Halcyon plans. k‐Halcyon plans lowered bronchial tree dose on average by 1.2 Gy. Beam‐on‐time (BOT) was increased by 2.85 and 1.67 min, on average for k‐Halcyon and m‐Halcyon, respectively. k‐Halcyon plans were generated in under 30 min compared to estimated dedicated 180 ± 30 min for m‐Halcyon or c‐Truebeam plan.Conclusion k‐Halcyon plans were generated in under 30 min with excellent plan quality. This adaptable KBP model supports high‐volume clinics in the expansion or transfer of lung SBRT patients to Halcyon.
Highlights
Surgical resection is an important treatment for earlystage nonsmall-cell lung cancer (NSCLC) patients.many patients are inoperable due to comorbidities, refuse surgical resection, or present with a high chance of post-operative morbidity.[1,2] For these NSCLC patients, stereotactic body radiation therapy (SBRT) has become an extremely effective curative treatment modality.[2]
Maximum intensity projection (MIP) images were derived from the 4DCT scan, and the images were co-registered to the free-breathing 3DCT images to delineate an internal target volume (ITV), the gross target volume (GTV) = ITV
This study reports on the plausibility of generating lung SBRT plans for centrally located early-stage NSCLC patients on ring-mounted Halcyon Linac using a previously trained and validated Truebeam knowledge-based planning (KBP) model
Summary
Surgical resection is an important treatment for earlystage nonsmall-cell lung cancer (NSCLC) patients.many patients are inoperable due to comorbidities, refuse surgical resection, or present with a high chance of post-operative morbidity.[1,2] For these NSCLC patients, stereotactic body radiation therapy (SBRT) has become an extremely effective curative treatment modality.[2] Compared to poor tumor local-control rates from conventional lung radiotherapy (60%–70% local failure rates), lung SBRT has provided very high localcontrol rates up to 97% (median, 3 years actuarial) with less treatment-related toxicity compared to surgery.[1,2,3,4] To deliver high-quality lung SBRT treatments, a precise delivered dose must be highly conformal around the tumor with a steep dose gradient to limit intermediate dose spillage.[5] This can be accomplished using traditional 3D conformal radiation therapy (3D-CRT), intensity-modulated radiation therapy (IMRT), or more recently via manually generated volumetric-modulated arc therapy (VMAT) plans.[6,7,8] Delivering lung SBRT with VMAT provides enhanced dosimetric benefits and faster treatments that may aid in patient compliance.[7,8] Currently, VMAT lung SBRT treatment is being delivered with flattening filter-free (FFF) beams using an SBRT-dedicated C-arm linac.[2,9,10,11] FFF beams provide significantly higher dose rates, less out-of -field scatter dose, less electron contamination, and better target coverage at the tumor–lung interface in comparison to flattened beams.[11] These additional benefits translate to superior treatment in a shorter overall treatment time
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