An Automated knowledge-based planning routine for stereotactic body radiotherapy of peripheral lung tumors via DCA-based volumetric modulated arc therapy.

To develop a knowledge-based planning (KBP) routine for stereotactic body radiotherapy (SBRT) of peripherally located early-stage non-small-cell lung cancer (NSCLC) tumors via dynamic conformal arc (DCA)-based volumetric modulated arc therapy (VMAT) using the commercially available RapidPlanTM software. This proposed technique potentially improves plan quality, reduces complexity, and minimizes interplay effect and small-field dosimetry errors associated with treatment delivery. KBP model was developed and validated using 70 clinically treated high quality non-coplanar VMAT lung SBRT plans for training and 20 independent plans for validation. All patients were treated with 54 Gy in three treatments. Additionally, a novel k-DCA planning routine was deployed to create plans incorporating historical three-dimensional-conformal SBRT planning practices via DCA-based approach prior to VMAT optimization in an automated planning engine. Conventional KBPs and k-DCA plans were compared with clinically treated plans per RTOG-0618 requirements for target conformity, tumor dose heterogeneity, intermediate dose fall-off and organs-at-risk (OAR) sparing. Treatment planning time, treatment delivery efficiency, and accuracy were recorded. KBPs and k-DCA plans were similar or better than clinical plans. Average planning target volume for validation was 22.4 ± 14.1 cc (7.1-62.3 cc). KBPs and k-DCA plans provided similar conformity to clinical plans with average absolute differences of 0.01 and 0.01, respectively. Maximal doses to OAR were lowered in both KBPs and k-DCA plans. KBPs increased monitor units (MU) on average 1316 (P < 0.001) while k-DCA reduced total MU on average by 1114 (P < 0.001). This routine can create k-DCA plan in less than 30 min. Independent Monte Carlo calculation demonstrated that k-DCA plans showed better agreement with planned dose distribution. A k-DCA planning routine was developed in concurrence with a knowledge-based approach for the treatment of peripherally located lung tumors. This method minimizes plan complexity associated with model-based KBP techniques and improve plan quality and treatment planning efficiency.

Visak J ，Ge GY ，McGarry RC ，Randall M ，Pokhrel D ... -  《Journal of Applied Clinical Medical Physics》

Development and clinical validation of a robust knowledge-based planning model for stereotactic body radiotherapy treatment of centrally located lung tumors.

To develop a robust and adaptable knowledge-based planning (KBP) model with commercially available RapidPlanTM for early stage, centrally located non-small-cell lung tumors (NSCLC) treated with stereotactic body radiotherapy (SBRT) and improve a patient's"simulation to treatment" time. The KBP model was trained using 86 clinically treated high-quality non-coplanar volumetric modulated arc therapy (n-VMAT) lung SBRT plans with delivered prescriptions of 50 or 55 Gy in 5 fractions. Another 20 independent clinical n-VMAT plans were used for validation of the model. KBP and n-VMAT plans were compared via Radiation Therapy Oncology Group (RTOG)-0813 protocol compliance criteria for conformity (CI), gradient index (GI), maximal dose 2 cm away from the target in any direction (D2cm), dose to organs-at-risk (OAR), treatment delivery efficiency, and accuracy. KBP plans were re-optimized with larger calculation grid size (CGS) of 2.5 mm to assess feasibility of rapid adaptive re-planning. Knowledge-based plans were similar or better than n-VMAT plans based on a range of target coverage and OAR metrics. Planning target volume (PTV) for validation cases was 30.5 ± 19.1 cc (range 7.0-71.7 cc). KBPs provided an average CI of 1.04 ± 0.04 (0.97-1.11) vs. n-VMAT plan'saverage CI of 1.01 ± 0.04 (0.97-1.17) (P < 0.05) with slightly improved GI with KBPs (P < 0.05). D2cm was similar between the KBPs and n-VMAT plans. KBPs provided lower lung V10Gy (P = 0.003), V20Gy (P = 0.007), and mean lung dose (P < 0.001). KBPs had overall better sparing of OAR at the minimal increased of average total monitor units and beam-on time by 460 (P < 0.05) and 19.2 s, respectively. Quality assurance phantom measurement showed similar treatment delivery accuracy. Utilizing a CGS of 2.5 mm in the final optimization improved planning time (mean, 5 min) with minimal or no cost to the plan quality. The RTOG-compliant adaptable RapidPlan model for early stage SBRT treatment of centrally located lung tumors was developed. All plans met RTOG dosimetric requirements in less than 30 min of planning time, potentially offering shorter "simulation to treatment" times. OAR sparing via KBPs may permit tumorcidal dose escalation with minimal penalties. Same day adaptive re-planning is plausible with a 2.5-mm CGS optimizer setting.

Visak J ，McGarry RC ，Randall ME ，Pokhrel D ... -  《Journal of Applied Clinical Medical Physics》

A novel and clinically useful dynamic conformal arc (DCA)-based VMAT planning technique for lung SBRT.

Volumetric modulated arc therapy (VMAT) is gaining popularity for stereotactic treatment of lung lesions for medically inoperable patients. Due to multiple beamlets in delivery of highly modulated VMAT plans, there are dose delivery uncertainties associated with small-field dosimetry error and interplay effects with small lesions. We describe and compare a clinically useful dynamic conformal arc (DCA)-based VMAT (d-VMAT) technique for lung SBRT using flattening filter free (FFF) beams to minimize these effects. Ten solitary early-stage I-II non-small-cell lung cancer (NSCLC) patients were treated with a single dose of 30 Gy using 3-6 non-coplanar VMAT arcs (clinical VMAT) with 6X-FFF beams in our clinic. These clinically treated plans were re-optimized using a novel d-VMAT planning technique. For comparison, d-VMAT plans were recalculated using DCA with user-controlled field aperture shape before VMAT optimization. Identical beam geometry, dose calculation algorithm, grid size, and planning objectives were used. The clinical VMAT and d-VMAT plans were compared via RTOG-0915 protocol compliances for conformity, gradient indices, and dose to organs at risk (OAR). Additionally, treatment delivery efficiency and accuracy were recorded. All plans met RTOG-0915 requirements. Comparing with clinical VMAT, d-VMAT plans gave similar target coverage with better target conformity, tighter radiosurgical dose distribution with lower gradient indices, and dose to OAR. Lower total number of monitor units and small beam modulation factor reduced beam-on time by 1.75 min (P < 0.001), on average (maximum up to 2.52 min). Beam delivery accuracy was improved by 2%, on average (P < 0.05) and maximum up to 6% in some cases for d-VMAT plans. This simple d-VMAT technique provided excellent plan quality, reduced intermediate dose-spillage, and dose to OAR while providing faster treatment delivery by significantly reducing beam-on time. This novel treatment planning approach will improve patient compliance along with potentially reducing intrafraction motion error. Moreover, with less MLC modulation through the target, d-VMAT could potentially minimize small-field dosimetry errors and MLC interplay effects. If available, d-VMAT planning approach is recommended for future clinical lung SBRT plan optimization.

Pokhrel D ，Visak J ，Sanford L 《Journal of Applied Clinical Medical Physics》

A simple, yet novel hybrid-dynamic conformal arc therapy planning via flattening filter-free beam for lung stereotactic body radiotherapy.

Due to multiple beamlets in the delivery of highly modulated volumetric arc therapy (VMAT) plans, dose delivery uncertainties associated with small-field dosimetry and interplay effects can be concerns in the treatment of mobile lung lesions using a single-dose of stereotactic body radiotherapy (SBRT). Herein, we describe and compare a simple, yet clinically useful, hybrid 3D-dynamic conformal arc (h-DCA) planning technique using flattening filter-free (FFF) beams to minimize these effects. Fifteen consecutive solitary early-stage I-II non-small-cell lung cancer (NSCLC) patients who underwent a single-dose of 30 Gy using 3-6 non-coplanar VMAT arcs with 6X-FFF beams in our clinic. These patients' plans were re-planned using a non-coplanar hybrid technique with 2-3 differentially-weighted partial dynamic conformal arcs (DCA) plus 4-6 static beams. About 60-70% of the total beam weight was given to the DCA and the rest was distributed among the static beams to maximize the tumor coverage and spare the organs-at-risk (OAR). The clinical VMAT and h-DCA plans were compared via RTOG-0915 protocol for conformity and dose to OAR. Additionally, delivery efficiency, accuracy, and overall h-DCA planning time were recorded. All plans met RTOG-0915 requirements. Comparison with clinical VMAT plans h-DAC gave better target coverage with a higher dose to the tumor and exhibited statistically insignificance differences in gradient index, D2cm , gradient distance and OAR doses with the exception of maximal dose to skin (P = 0.015). For h-DCA plans, higher values of tumor heterogeneity and tumor maximum, minimum and mean doses were observed and were 10%, 2.8, 1.0, and 2.0 Gy, on average, respectively, compared to the clinical VMAT plans. Average beam on time was reduced by a factor of 1.51. Overall treatment planning time for h-DCA was about an hour. Due to no beam modulation through the target, h-DCA plans avoid small-field dosimetry and MLC interplay effects and resulting in enhanced target coverage by improving tumor dose (characteristic of FFF-beam). The h-DCA simplifies treatment planning and beam on time significantly compared to clinical VMAT plans. Additionally, h-DCA allows for the real time target verification and eliminates patient-specific VMAT quality assurance; potentially offering cost-effective, same or next day SBRT treatments. Moreover, this technique can be easily adopted to other disease sites and small clinics with less extensive physics or machine support.

Pokhrel D ，Halfman M ，Sanford L 《Journal of Applied Clinical Medical Physics》

Improvement of conformal arc plans by using deformable margin delineation method for stereotactic lung radiotherapy.

Stereotactic body radiotherapy (SBRT) is an established treatment technique in the management of medically inoperable early stage non-small cell lung cancer (NSCLC). Different techniques such as volumetric modulated arc (VMAT) and three-dimensional conformal arc (DCA) can be used in SBRT. Previously, it has been shown that VMAT is superior to DCA technique in terms of plan evaluation parameters. However, DCA technique has several advantages such as ease of use and considerable shortening of the treatment time. DCA technique usually results in worse conformity which is not possible to ameliorate by inverse optimization. In this study, we aimed to analyze whether a simple method - deformable margin delineation (DMD) - improves the quality of the DCA technique, reaching similar results to VMAT in terms of plan evaluation parameters. Twenty stage I-II (T1-2, N0, M0) NSCLC patients were included in this retrospective dosimetric study. Noncoplanar VMAT and conventional DCA plans were generated using 6 MV and 10 MV with flattening filter free (FFF) photon energies. The DCA plan with 6FFF was calculated and 95% of the PTV was covered by the prescription isodose line. Hot dose regions (receiving dose over 100% of prescription dose) outside PTV and cold dose regions (receiving dose under 100% of prescription dose) inside PTV were identified. A new PTV (PTV-DMD) was delineated by deforming PTV margin with respect to hot and cold spot regions obtained from conventional DCA plans. Dynamic multileaf collimators (MLC) were set to PTV-DMD beam eye view (BEV) positions and the new DCA plans (DCA-DMD) with 6FFF were generated. Three-dimensional (3D) dose calculations were computed for PTV-DMD volume. However, the prescription isodose was specified and normalized to cover 95% volume of original PTV. Several conformity indices and lung doses were compared for different treatment techniques. DCA-DMD method significantly achieved a superior conformity index (CI), conformity number (CIPaddick ), gradient index (R50% ), isodose at 2 cm (D2 cm ) and external index (CΔ) with respect to VMAT and conventional DCA plans (P < 0.05 for all comparisons). CI ranged between 1.00-1.07 (Mean: 1.02); 1.00-1.18 (Mean: 1.06); 1.01-1.23 (Mean 1.08); 1.03-1.29 (Mean: 1.15); 1.04-1.29 (Mean: 1.18) for DCA-DMD-6FFF, VMAT-6FFF, VMAT-10FFF DCA-6FFF and DCA-10FFF respectively. DCA-DMD-6FFF technique resulted significantly better CI compared to others (P = 0.002; < 0.001; < 0.001; < 0.001). R50% ranged between 3.22-4.74 (Mean: 3.99); 3.24-5.92 (Mean: 4.15) for DCA-DMD-6FFF, VMAT-6FFF, respectively. DCA-DMD-6FFF technique resulted lower intermediate dose spillage compared to VMAT-6FFF, though the difference was statistically insignificant (P = 0.32). D2 cm ranged between 35.7% and 67.0% (Mean: 53.2%); 42.1%-79.2% (Mean: 57.8%) for DCA-DMD-6FFF, VMAT-6FFF respectively. DCA-DMD-6FFF have significantly better and sharp falloff gradient 2 cm away from PTV compared to VMAT-6FFF (P = 0.009). CΔ ranged between 0.052 and 0.140 (Mean: 0.085); 0,056-0,311 (Mean: 0.120) for DCA-DMD, VMAT-6FFF, respectively. DCA-DMD-6FFF have significantly improved CΔ (P = 0.002). VMAT- V20 Gy , V2.5 Gy and mean lung dose (MLD) indices are calculated to be 4.03%, 23.83%, 3.42 Gy and 4.19%, 27.88%,3.72 Gy, for DCA-DMD-6FFF and DCA techniques, respectively. DCA-DMD-6FFF achieved superior lung sparing compared to DCA technique. DCA-DMD-6FFF method reduced MUs 44% and 33% with respect to VMAT-6FFF and 10FFF, respectively, without sacrificing dose conformity (P < 0.001; P < 0.001). Our results demonstrated that DCA plan evaluation parameters can be ameliorated by using the DMD method. This new method improves DCA plan quality and reaches similar results with VMAT in terms of dosimetric parameters. We believe that DCA-DMD is a simple and effective technique for SBRT and can be preferred due to shorter treatment and planning time.

Güngör G ，Demir M ，Aydın G ，Yapıcı B ，Atalar B ，Özyar E ... -  《Journal of Applied Clinical Medical Physics》