1
|
Shaw M, Lye J, Alves A, Lehmann J, Sanagou M, Geso M, Brown R. Measuring dose in lung identifies peripheral tumour dose inaccuracy in SBRT audit. Phys Med 2023; 112:102632. [PMID: 37406592 DOI: 10.1016/j.ejmp.2023.102632] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/25/2023] [Revised: 04/25/2023] [Accepted: 06/21/2023] [Indexed: 07/07/2023] Open
Abstract
PURPOSE Stereotactic Body Radiotherapy (SBRT) for lung tumours has become a mainstay of clinical practice worldwide. Measurements in anthropomorphic phantoms enable verification of patient dose in clinically realistic scenarios. Correction factors for reporting dose to the tissue equivalent materials in a lung phantom are presented in the context of a national dosimetry audit for SBRT. Analysis of dosimetry audit results is performed showing inaccuracies of common dose calculation algorithms in soft tissue lung target, inhale lung material and at tissue interfaces. METHODS Monte Carlo based simulation of correction factors for detectors in non-water tissue was performed for the soft tissue lung target and inhale lung materials of a modified CIRS SBRT thorax phantom. The corrections were determined for Gafchromic EBT3 Film and PTW 60019 microDiamond detectors used for measurements of 168 SBRT lung plans in an end-to-end dosimetry audit. Corrections were derived for dose to medium (Dm,m) and dose to water (Dw,w) scenarios. RESULTS Correction factors were up to -3.4% and 9.2% for in field and out of field lung respectively. Overall, application of the correction factors improved the measurement-to-plan dose discrepancy. For the soft tissue lung target, agreement between planned and measured dose was within average of 3% for both film and microDiamond measurements. CONCLUSIONS The correction factors developed for this work are provided for clinical users to apply to commissioning measurements using a commercially available thorax phantom where inhomogeneity is present. The end-to-end dosimetry audit demonstrates dose calculation algorithms can underestimate dose at lung tumour/lung tissue interfaces by an average of 2-5%.
Collapse
Affiliation(s)
- Maddison Shaw
- Australian Clinical Dosimetry Service, Australian Radiation Protection and Nuclear Safety Agency, Melbourne, Australia; School of Health and Biomedical Sciences, RMIT University, Melbourne, Australia.
| | - Jessica Lye
- Australian Clinical Dosimetry Service, Australian Radiation Protection and Nuclear Safety Agency, Melbourne, Australia; Olivia Newton John Cancer Wellness and Research Centre, Austin Health, Australia
| | - Andrew Alves
- Australian Clinical Dosimetry Service, Australian Radiation Protection and Nuclear Safety Agency, Melbourne, Australia
| | - Joerg Lehmann
- Department of Radiation Oncology, Calvary Mater Newcastle, Newcastle, Australia; School of Science, RMIT University, Melbourne, Australia; School of Mathematical and Physical Sciences, University of Newcastle, Australia; Institute of Medical Physics, University of Sydney, Australia
| | - Masoumeh Sanagou
- Australian Radiation Protection and Nuclear Safety Agency, Melbourne, Australia
| | - Moshi Geso
- School of Health and Biomedical Sciences, RMIT University, Melbourne, Australia
| | - Rhonda Brown
- Australian Clinical Dosimetry Service, Australian Radiation Protection and Nuclear Safety Agency, Melbourne, Australia
| |
Collapse
|
2
|
Vassiliev ON, Peterson CB, Chang JY, Mohan R. Monte Carlo evaluation of target dose coverage in lung stereotactic body radiation therapy with flattening filter-free beams. JOURNAL OF RADIOTHERAPY IN PRACTICE 2022; 21:81-87. [PMID: 35401050 PMCID: PMC8992779 DOI: 10.1017/s1460396920000886] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Aim Previous studies showed that replacing conventional flattened beams (FF) with flattening filter-free (FFF) beams improves the therapeutic ratio in lung stereotactic body radiation therapy (SBRT), but these findings could have been impacted by dose calculation uncertainties caused by the heterogeneity of the thoracic anatomy and by respiratory motion, which were particularly high for target coverage. In this study, we minimized such uncertainties by calculating doses using high-spatial-resolution Monte Carlo and four-dimensional computed tomography (4DCT) images. We aimed to evaluate more reliably the benefits of using FFF beams for lung SBRT. Materials and methods For a cohort of 15 patients with early stage lung cancer that we investigated in a previous treatment planning study, we recalculated dose distributions with Monte Carlo using 4DCT images. This included fifteen FF and fifteen FFF treatment plans. Results Compared to Monte Carlo, the treatment planning system (TPS) over-predicted doses in low-dose regions of the planning target volume. For most patients, replacing FF beams with FFF beams improved target coverage, tumor control, and uncomplicated tumor control probabilities. Conclusions Monte Carlo tends to reveal deficiencies in target coverage compared to coverage predicted by the TPS. Our data support previously reported benefits of using FFF beams for lung SBRT.
Collapse
Affiliation(s)
- Oleg N Vassiliev
- Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Christine B Peterson
- Department of Biostatistics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Joe Y Chang
- Division of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| | - Radhe Mohan
- Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
| |
Collapse
|
3
|
Dwivedi S, Kansal S, Shukla J, Bharati A, Dangwal VK. Dosimetric evaluation of different planning techniques based on flattening filter-free beams for central and peripheral lung stereotactic body radiotherapy. Biomed Phys Eng Express 2021; 7. [PMID: 34638107 DOI: 10.1088/2057-1976/ac2f0d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2021] [Accepted: 10/12/2021] [Indexed: 11/11/2022]
Abstract
This study aimed to dosimetrically compare and evaluate the flattening filter-free (FFF) photon beam-based three-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT) for lung stereotactic body radiotherapy (SBRT). RANDO phantom computed tomography (CT) images were used for treatment planning. Gross tumor volumes (GTVs) were delineated in the central and peripheral lung locations. Planning target volumes (PTVs) was determined by adding a 5 mm margin to the GTV. 3DCRT, IMRT, and VMAT plans were generated using a 6-MV FFF photon beam. Dose calculations for all plans were performed using the anisotropic analytical algorithm (AAA) and Acuros XB algorithms. The accuracy of the algorithms was validated using the dose measured in a CIRS thorax phantom. The conformity index (CI), high dose volume (HDV), low dose location (D2cm), and homogeneity index (HI) improved with FFF-VMAT compared to FFF-IMRT and FFF-3DCRT, while low dose volume (R50%) and gradient index (GI) showed improvement with FFF-3DCRT. Compared with FFF-3DCRT, a drastic decrease in the mean treatment time (TT) value was observed with FFF-VMAT for different lung sites between 57.09% and 60.39%, while with FFF-IMRT it increased between 10.78% and 17.49%. The dose calculation with Acuros XB was found to be superior to that of AAA. Based on the comparison of dosimetric indices in this study, FFF-VMAT provides a superior treatment plan to FFF-IMRT and FFF-3DCRT in the treatment of peripheral and central lung PTVs. This study suggests that Acuros XB is a more accurate algorithm than AAA in the lung region.
Collapse
Affiliation(s)
- Shekhar Dwivedi
- Department of Medical Physics, Tata Memorial Centre, Homi Bhabha Cancer Hospital and Research Centre, Mullanpur & Sangrur, India.,Department of Physics, Maharaja Ranjit Singh Punjab Technical University, Bathinda, India
| | - Sandeep Kansal
- Department of Physics, Maharaja Ranjit Singh Punjab Technical University, Bathinda, India
| | - Jooli Shukla
- Department of Physics, Dr Bhimrao Ambedkar University, Agra, India
| | - Avinav Bharati
- Department of Radiation Oncology, Dr Ram Manohar Lohia Institute of Medical Sciences, Lucknow, India
| | | |
Collapse
|
4
|
Ji T, Sun L, Cai F, Li G. Comparison between flattening filter-free (FFF) and flattened photon beam VMAT plans for the whole brain radiotherapy (WBRT) with hippocampus sparing. Asia Pac J Clin Oncol 2021; 18:e263-e267. [PMID: 34333848 PMCID: PMC9540553 DOI: 10.1111/ajco.13624] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Accepted: 05/30/2021] [Indexed: 11/30/2022]
Abstract
Purpose To evaluate and investigate the feasibility of flattening filter‐free (FFF) beam for the whole‐brain radiotherapy (WBRT) with hippocampus sparing. Methods Eighteen patients with volumetric‐modulated arc therapy (VMAT) plans in FFF and conventional beam modes were included in this study. The prescribed dose was 30 Gy in 10 fractions. The conformity index (CI), heterogeneity index reported by TPS (HI‐M), and homogeneity index (HI) for planning target volume (PTV) were evaluated. Subsequently, the following parameters for PTV were calculated and compared: D2%, D98%; the mean dose, maximum dose, and minimal dose for OARs. Plan modulation index, total MUs, and the gamma index were used to evaluate the plan quality. Results HI‐M results were similar for the two techniques (1.239 vs. 1.247, respectively, p = 0.048); FFF beam plans yielded lower D2% compared to FF beam plans (3,416.3 cGy vs. 3,437.2 cGy, p = 0.22), mean dose (3,177.5 cGy vs. 3,195.2 cGy, p = 0.009), and CI (0.884 vs. 0.876, p = 0.001) for PTV. Significant differences were observed between the two beam modes (FF model vs. FFF model) for the maximum dose (1,612.9 cGy vs. 1,470.2 cGy, respectively, p < 0.001), minimum dose (987.6 cGy vs. 898.8 cGy, respectively, p < 0.001), and the mean dose (1144.4 cGy vs. 1047.3 cGy, respectively, p < 0.001) to the hippocampus, and the maximum dose to the eyes (2,792.6 cGy vs. 2,751.3 cGy, respectively, p < 0.001). The average total MUs for FFF‐VMAT plans was significantly greater than FF‐VMAT plans. However, differences for the plan modulation index and the gamma index were negligible. Conclusion In comparison with FF beam, the FFF beam mode offers a clear benefit with respect to WBRT with hippocampal sparing.
Collapse
Affiliation(s)
- Tianlong Ji
- Department of Radiation oncology, The First Hospital of China Medical University, Shenyang, China
| | - Lu Sun
- Department of Radiation oncology, The First Hospital of China Medical University, Shenyang, China
| | - Feng Cai
- Department of Radiation oncology, The First Hospital of China Medical University, Shenyang, China
| | - Guang Li
- Department of Radiation oncology, The First Hospital of China Medical University, Shenyang, China
| |
Collapse
|
5
|
Agarwal P, Kinhikar R. In regard to the article 'Effectiveness of robust optimization in volumetric modulation arc therapy using 6 and 10 MV flattening filter-free beam therapy planning for lung stereotactic body radiation therapy with a breath-hold technique,' Vol. 61, No. 4, 2020. JOURNAL OF RADIATION RESEARCH 2021; 62:740-742. [PMID: 34156471 PMCID: PMC8273789 DOI: 10.1093/jrr/rrab019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2020] [Revised: 02/06/2021] [Indexed: 06/13/2023]
Affiliation(s)
- Priyanka Agarwal
- Medical Physicist, Homi Bhabha Cancer hospital, Varanasi, UP 221005, India
| | - Rajesh Kinhikar
- Medical Physicist, Tata Tata Memorial Hospital, Mumbai, Maharashtra 400012, India
| |
Collapse
|
6
|
Pokhrel D, Visak J, Critchfield LC, Stephen J, Bernard ME, Randall M, Kudrimoti M. Clinical validation of ring-mounted halcyon linac for lung SBRT: comparison to SBRT-dedicated C-arm linac treatments. J Appl Clin Med Phys 2020; 22:261-270. [PMID: 33342070 PMCID: PMC7856490 DOI: 10.1002/acm2.13146] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Revised: 11/19/2020] [Accepted: 12/04/2020] [Indexed: 12/31/2022] Open
Abstract
Stereotactic body radiotherapy (SBRT) of lung tumors via the ring‐mounted Halcyon Linac, a fast kilovoltage cone beam CT‐guided treatment with coplanar geometry, a single energy 6MV flattening filter free (FFF) beam and volumetric modulated arc therapy (VMAT) is a fast, safe, and feasible treatment modality for selected lung cancer patients. Four‐dimensional (4D) CT‐based treatment plans were generated using advanced AcurosXB algorithm with heterogeneity corrections using an SBRT board and Halcyon couch insert. Halcyon VMAT‐SBRT plans with stacked and staggered multileaf collimators produced highly conformal radiosurgical dose distribution to the target, lower intermediate dose spillage, and similar dose to adjacent organs at risks (OARs) compared to SBRT‐dedicated highly conformal clinical noncoplanar Truebeam VMAT plans following the RTOG‐0813 requirements. Due to low monitor units per fraction and less multileaf collimator (MLC) modulation, the Halcyon VMAT plan can deliver lung SBRT fractions with an overall treatment time of less than 15 min (for 50 Gy in five fractions), significantly improving patient comfort and clinic workflow. Higher pass rates of quality assurance results demonstrate a more accurate treatment delivery on Halcyon. We have implemented Halcyon for lung SBRT treatment in our clinic. We suggest others use Halcyon for lung SBRT treatments using abdominal compression or 4D CT‐based treatment planning, thus expanding the access of curative ultra‐hypofractionated treatments to other centers with only a Halcyon Linac. Clinical follow‐up results for patients treated on Halcyon Linac with lung SBRT is ongoing.
Collapse
Affiliation(s)
- Damodar Pokhrel
- Medical Physics Graduate Program, Department of Radiation Medicine, University of Kentucky, Lexington, KY, USA
| | - Justin Visak
- Medical Physics Graduate Program, Department of Radiation Medicine, University of Kentucky, Lexington, KY, USA
| | - Lana C Critchfield
- Medical Physics Graduate Program, Department of Radiation Medicine, University of Kentucky, Lexington, KY, USA
| | - Joseph Stephen
- Medical Physics Graduate Program, Department of Radiation Medicine, University of Kentucky, Lexington, KY, USA
| | - Mark E Bernard
- Medical Physics Graduate Program, Department of Radiation Medicine, University of Kentucky, Lexington, KY, USA
| | - Marcus Randall
- Medical Physics Graduate Program, Department of Radiation Medicine, University of Kentucky, Lexington, KY, USA
| | - Mahesh Kudrimoti
- Medical Physics Graduate Program, Department of Radiation Medicine, University of Kentucky, Lexington, KY, USA
| |
Collapse
|
7
|
Using FFF beams to improve the therapeutic ratio of lung SBRT. JOURNAL OF RADIOTHERAPY IN PRACTICE 2020; 20:419-425. [DOI: 10.1017/s1460396920000576] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
AbstractAim:The aim of this study was to investigate the extent to which lung stereotactic body radiotherapy (SBRT) treatment plans can be improved by replacing conventional flattening filter (FF) beams with flattening filter-free (FFF) beams.Materials and methods:We selected 15 patients who had received SBRT with conventional 6-MV photon beams for early-stage lung cancer. We imported the patients’ treatment plans into the Eclipse 13·6 treatment planning system, in which we configured the AAA dose calculation model using representative beam data for a TrueBeam accelerator operated in 6-MV FFF mode. We then created new treatment plans by replacing the conventional FF beams in the original plans with FFF beams.Results:The FFF plans had better target coverage than the original FF plans did. For the planning target volume, FFF plans significantly improved the D98, D95, D90, homogeneity index and uncomplicated tumour control probability. In most cases, the doses to organs at risk were lower in FFF plans. FFF plans significantly reduced the mean lung dose, V10, V20, V30, and normal tissue complication probability for the total lung and improved the dosimetric indices for the ipsilateral lung. For most patients, FFF beams achieved lower maximum doses to the oesophagus, heart and the spinal cord, and a lower chest wall V30.Conclusions:Compared with FF beams, FFF beams achieved lower doses to organs at risk, especially the lung, without compromising tumour coverage; in fact, FFF beams improved coverage in most cases. Thus, replacing FF beams with FFF beams can achieve a better therapeutic ratio.
Collapse
|
8
|
Pokhrel D, Sanford L, Larkin S, Dhanireddy B, Bernard ME, Randall M, McGarry RC. On the use of single‐isocenter VMAT plans for SBRT treatment of synchronous multiple lung lesions: Plan quality, treatment efficiency, and early clinical outcomes. J Appl Clin Med Phys 2020. [PMCID: PMC7484875 DOI: 10.1002/acm2.12938] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Cone‐beam computed tomography (CT)‐guided volumetric‐modulated arc therapy (VMAT) plans for stereotactic body radiotherapy (SBRT) treatment of synchronous multiple lung lesions with a flattening filter‐free (FFF) beam is a safe and highly effective treatment option for oligometastases lung cancer patients. Fourteen patients with metastatic non–small‐cell lung cancer (NSCLC) lesions (two to five) received a single‐isocenter VMAT SBRT treatment in our clinic. Four‐dimensional (4D) CT‐based treatment plans were generated using advanced AcurosXB‐based dose calculation algorithm using heterogeneity corrections with a single isocenter placed between/among the lesions. Compared to 10X‐FFF and traditional flattened 6X (6X‐FF) beams, 6X‐FFF beam produced highly conformal radiosurgical dose distribution to each target volume, reduced dose to adjacent organs at risk (OAR), and significantly reduced the lung SBRT fraction duration to < 3.5 min/fraction for 54/50 Gy treatments in 3/5 fractions — significantly improving patient convenience and clinic workflow. Early follow‐up CT imaging (mean, 9 months) results show high local control rates (100%) with no acute lung or rib toxicity. Longer clinical follow up in a larger patient cohort is ongoing to further validate the outcomes of this treatment approach.
Collapse
Affiliation(s)
- Damodar Pokhrel
- Department of Radiation Medicine Medical Physics Graduate Program University of Kentucky Lexington KY USA
| | - Lana Sanford
- Department of Radiation Medicine Medical Physics Graduate Program University of Kentucky Lexington KY USA
| | - Shilpa Larkin
- Department of Radiation Medicine Medical Physics Graduate Program University of Kentucky Lexington KY USA
| | - Bhaswanth Dhanireddy
- Department of Radiation Medicine Medical Physics Graduate Program University of Kentucky Lexington KY USA
| | - Mark E. Bernard
- Department of Radiation Medicine Medical Physics Graduate Program University of Kentucky Lexington KY USA
| | - Marcus Randall
- Department of Radiation Medicine Medical Physics Graduate Program University of Kentucky Lexington KY USA
| | - Ronald C. McGarry
- Department of Radiation Medicine Medical Physics Graduate Program University of Kentucky Lexington KY USA
| |
Collapse
|
9
|
Pokhrel D, Visak J, Sanford L. A novel and clinically useful dynamic conformal arc (DCA)-based VMAT planning technique for lung SBRT. J Appl Clin Med Phys 2020; 21:29-38. [PMID: 32306530 PMCID: PMC7386176 DOI: 10.1002/acm2.12878] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Revised: 03/12/2020] [Accepted: 03/15/2020] [Indexed: 12/26/2022] Open
Abstract
Purpose 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. Materials and Methods 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. Results 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. Conclusion 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.
Collapse
Affiliation(s)
- Damodar Pokhrel
- Department of Radiation Medicine, Medical Physics Graduate Program, University of Kentucky, Lexington, KY, USA.,Department of Radiation Medicine, University of Kentucky, Markey Cancer Center, Lexington, KY, USA
| | - Justin Visak
- Department of Radiation Medicine, Medical Physics Graduate Program, University of Kentucky, Lexington, KY, USA
| | - Lana Sanford
- Department of Radiation Medicine, Medical Physics Graduate Program, University of Kentucky, Lexington, KY, USA
| |
Collapse
|
10
|
Pokhrel D, Halfman M, Sanford L. A simple, yet novel hybrid-dynamic conformal arc therapy planning via flattening filter-free beam for lung stereotactic body radiotherapy. J Appl Clin Med Phys 2020; 21:83-92. [PMID: 32243704 PMCID: PMC7324700 DOI: 10.1002/acm2.12868] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Revised: 02/23/2020] [Accepted: 03/09/2020] [Indexed: 12/25/2022] Open
Abstract
Purpose 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. Materials and Methods 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. Results 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. Conclusion 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.
Collapse
Affiliation(s)
- Damodar Pokhrel
- Department of Radiation Medicine, Medical Physics Graduate Program, University of Kentucky, Lexington, KY, USA
| | - Matthew Halfman
- Department of Radiation Medicine, Medical Physics Graduate Program, University of Kentucky, Lexington, KY, USA
| | - Lana Sanford
- Department of Radiation Medicine, Medical Physics Graduate Program, University of Kentucky, Lexington, KY, USA
| |
Collapse
|
11
|
Pokhrel D, Halfman M, Sanford L. FFF-VMAT for SBRT of lung lesions: Improves dose coverage at tumor-lung interface compared to flattened beams. J Appl Clin Med Phys 2019; 21:26-35. [PMID: 31859456 PMCID: PMC6964748 DOI: 10.1002/acm2.12764] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Revised: 08/09/2019] [Accepted: 10/07/2019] [Indexed: 12/14/2022] Open
Abstract
Purpose To quantify the differences in dosimetry as a function of ipsilateral lung density and treatment delivery parameters for stereotactic, single dose of volumetric modulated arc therapy (VMAT) lung stereotactic body radiation therapy (SBRT) delivered with 6X flattening filter free (6X‐FFF) beams compared to traditional flattened 6X (6X‐FF) beams. Materials/methods Thirteen consecutive early stage I–II non‐small‐cell‐lung cancer (NSCLC) patients were treated with highly conformal noncoplanar VMAT SBRT plans (3–6 partial arcs) using 6X‐FFF beam and advanced Acuros‐based dose calculations to a prescription dose of 30 Gy in one fraction to the tumor margin. These clinical cases included relatively smaller tumor (island tumors) sizes (2.0–4.2 cm diameters) and varying average ipsilateral lung densities between 0.14 g/cc and 0.34 g/cc. Treatment plans were reoptimized with 6X‐FF beams for identical beam/arc geometries and planning objectives. For same target coverage, the organs‐at‐risk (OAR) dose metrics as a function of ipsilateral lung density were compared between 6X‐FFF and 6X‐FF plans. Moreover, monitor units (MU), beam modulation factor (MF) and beam‐on time (BOT) were evaluated. Results Both plans met the RTOG‐0915 protocol compliance. The ipsilateral lung density and the tumor location heavily influenced the treatment plans with 6X‐FFF and 6X‐FF beams, showing differences up to 12% for the gradient indices. For similar target coverage, 6X‐FFF beams showed better target conformity, lower intermediate dose‐spillage, and lower dose to the OAR. Additionally, BOT was reduced by a factor of 2.3 with 6X‐FFF beams compared to 6X‐FF beams. Conclusion While prescribing dose to the tumor periphery, 6X‐FFF VMAT plans for stereotactic single‐dose lung SBRT provided similar target coverage with better dose conformity, superior intermediate dose‐spillage (improved dose coverage at tumor interface), and improved OAR sparing compared to traditional 6X‐FF beams and significantly reduced treatment time. The ipsilateral lung density and tumor location considerably affected dose distributions requiring special attention for clinical SBRT plan optimization on a per‐patient basis. Clinical follow up of these patients for tumor local‐control rate and treatment‐related toxicities is in progress.
Collapse
Affiliation(s)
- Damodar Pokhrel
- Department of Radiation Medicine, Medical Physics Graduate Program, University of Kentucky, Lexington, KY, USA
| | - Matthew Halfman
- Department of Radiation Medicine, Medical Physics Graduate Program, University of Kentucky, Lexington, KY, USA
| | - Lana Sanford
- Department of Radiation Medicine, Medical Physics Graduate Program, University of Kentucky, Lexington, KY, USA
| |
Collapse
|