Comprehensive dosimetric planning comparison for early-stage, non-small cell lung cancer with SABR: fixed-beam IMRT versus VMAT versus TomoTherapy

Helical tomotherapy and two types of volumetric modulated arc therapy: dosimetric and clinical comparison for several cancer sites

Radiotherapy accelerators have undergone continuous technological developments. We investigated the differences between Radixact™ and VMAT treatment plans. Sixty patients were included in this study. Dosimetric comparison between the Radixact™ and VMAT plans was performed for six cancer sites: whole-brain, head and neck, lymphoma, lung, prostate, and rectum. The VMAT plans were generated with two Elekta linear accelerators (Synergy^® and Versa HD™). The planning target volume (PTV) coverage, organs-at-risk dose constraints, and four dosimetric indexes were considered. The deliverability of the plans was assessed using quality assurance (gamma index evaluation) measurements; clinical judgment was included in the assessment. The mean AAPM TG218 (3%-2 mm, global normalization) gamma index values were 99.4%, 97.8%, and 96.6% for Radixact™, Versa HD™, and Synergy®, respectively. Radixact™ performed better than Versa HD™ in terms of dosimetric indexes, hippocampi D_100%, spinal cord D_max, rectum V_{38.4  Gy}, bladder V_{30 Gy}, and V_{40 Gy}. Versa HD™ saved more of the (lungs-PTV) V_{5 Gy} and (lungs-PTV) D_mean, heart D_mean, breasts V_{4 Gy}, and bowel V_{45 Gy}. Regarding Synergy^®, the head and neck Radixact™ plan saved more of the parotid gland, oral cavity, and supraglottic larynx. From a clinical point of view, for the head and neck, prostate, and rectal sites, the Radixact™ and Versa HD™ plans were similar; Radixact™ plans were preferable for the head and neck and rectum to Synergy^® plans. The quality of linac plans has improved, and differences with tomotherapy have decreased. However, tomotherapy continues to be an essential add-on in multi-machine departments.

Real-time B0 compensation during gantry rotation in a 0.35 T MRI-Linac

BACKGROUND

Rotation of the ferromagnetic gantry of a low magnetic field MRI-Linac was previously demonstrated to cause large center frequency offsets of ±400 Hz. The B₀ off-resonances cause image artifacts and imaging isocenter shifts that would preclude MRI-guided arc therapy.

PURPOSE

The purpose of this study was to measure and compensate for center frequency offsets in real-time during gantry rotation on a 0.35 T MRI-Linac using a free induction decay (FID) navigator.

METHODS

A nonselective FID navigator was added before each 2D balanced steady-state free precession (bSSFP) cine image acquisition on a 0.35 T MRI-Linac. Images were acquired at 7.3 frames per second. Phase data from the initial FID navigator (while the gantry was stationary) was used as a reference. The phase data from each subsequent FID navigator was used to calculate the real-time B₀ off-resonance. The transmitter/receiver phase and the phase accrual over the adjacent image acquisition were adjusted to correct for the center frequency offset. Measurements were performed using a MRI-Linac dynamic phantom prior to and while the gantry rotated clockwise and counterclockwise. Image quality and signal-to-noise ratio were compared between uncorrected and B₀ corrected MRIs using a reference image acquired while the gantry was stationary. Four targets in the phantom were manually contoured on the first image frame and an active contouring algorithm was used retrospectively on each subsequent frame to assess image variations and calculate Dice coefficients. Additionally, three healthy volunteers were imaged using the same pulse sequences with and without real-time B₀ compensation during gantry rotation. Normalized root mean square errors (nRMSEs) were calculated for the phantom and in vivo to assess the efficacy of the B₀ compensation on image quality. The measured center frequency offsets from the volunteer and MRI dynamic phantom navigator data were also compared. The sinusoidal behavior of the center frequency offsets was modeled based on the gantry layout and long time constant eddy currents resulting from gantry rotation.

RESULTS

The duration of the FID navigator and processing was 4.5 ms. The FID navigator resulted in a ≤11% drop in signal-to-noise ratio (SNR) in the phantom and in vivo (liver). Dice coefficients from the MR-IGRT phantom contour measurements remained above 0.8 with B₀ compensation. Without B₀ compensation, the Dice coefficients dropped below 0.8 for up to 21% of the time depending on the contour. Real-time B₀ compensation resulted in mean reductions in nRMSE of 51% and 16% for the MR-IGRT phantom and in vivo, respectively. Peak-to-peak center frequency offsets ranged from 757 to 773 Hz in the phantom and 670 to 871 Hz in vivo.

CONCLUSION

Dynamic real-time B₀ compensation significantly improved image quality and reduced artifacts during gantry rotation in the phantom and in vivo. However, the FID navigator resulted in a small drop in the imaging duty cycle and SNR. This article is protected by copyright. All rights reserved.

Exposure of the heart in lung cancer radiation therapy: A systematic review of heart doses published during 2013 to 2020

BACKGROUND AND PURPOSE

Lung cancer radiotherapy increases the risk of cardiotoxicity and heart radiation dose is an independent predictor of poor survival. This study describes heart doses and strategies aiming to reduce exposure.

MATERIALS AND METHODS

A systematic review of lung cancer dosimetry studies reporting heart doses published 2013-2020 was undertaken. Doses were compared according to laterality, region irradiated, treatment modality (stereotactic ablative body radiotherapy (SABR) and non-SABR), planning technique, and respiratory motion management.

RESULTS

For 392 non-SABR regimens in 105 studies, the average MHD was 10.3 Gy (0.0-48.4) and was not significantly different between left and right-sided tumours. It was similar between IMRT and 3DCRT (10.9 Gy versus 10.6 Gy) and lower with particle beam therapy (proton 7.0 Gy; carbon-ion 1.9 Gy). Active respiratory motion management reduced exposure (7.4 Gy versus 9.3 Gy). For 168 SABR regimens in 35 studies, MHD was 4.0 Gy (0.0-32.4). Exposure was higher in central and lower lobe lesions (6.3 and 5.8 Gy respectively). MHD was lowest for carbon ions (0.5 Gy) compared to other techniques. Active respiratory motion management reduced exposure (2.4 Gy versus 5.0 Gy). Delineation guidelines and Dose Volume Constraints for the heart varied substantially.

CONCLUSIONS

There is scope to reduce heart radiation dose in lung cancer radiotherapy. Consensus on planning objectives, contouring and DVCs for the heart may lead to reduced heart doses in the future. For IMRT, more stringent optimisation objectives may reduce heart dose. Active respiratory motion management or particle therapy may be considered in situations where cardiac dose is high.

Shortened Radiation Time Promotes Recovery From Radiation-induced Lymphopenia in Early-Stage Non-small Cell Lung Cancer Patients Treated With Stereotactic Body Radiation Therapy

Background: To evaluate the potential impact of radiation time on radiation-induced lymphopenia (RIL) and subsequently recovery after stereotactic body radiation therapy (SBRT) and to examine the associations between radiation time and with patient outcomes in early-stage non-small cell lung cancer (NSCLC). Methods: Clinical and laboratory records of subjects consisted of 115 patients who had received SBRT for early-stage NSCLC. Clinical and laboratory records were retrospective reviewed to assess the changes in total lymphocyte counts (TLCs) following SBRT. Associations of TLCs kinetics with the clinical and treatment features, and outcomes were analyzed. Results: Most patients (100/115, 86.96%) experienced significantly decreased median TLCs following SBRT (1700 vs 1100 cells/µL; P < .001), and 52 patients (45.21%) met the criteria for lymphopenia. Six months after SBRT, 44 patients (38.26%) had recovered. A negative correlation between TLCs reduction and radiation time was observed (r = −0.381, P < .001). According to the receiver-operating characteristic curve analysis, the optimal cut-off value for radiation time to was 3950 s to predict lymphocyte count recovery (LR) following RIL was 3950 s (P < .001). Multivariate analyses demonstrated that radiation time was significantly associated with LR (odds ratio [OR], 0.113; 95% confidence interval [CI], 0.029-0.432; P = .001) but not TLCs reduction (P = .575). LR within 6 months after SBRT was associated with improved progression-free survival in patients without non-lymphopenia (P = .034), but had little effect in patients with lymphopenia (P = .405). Conclusion: A longer radiation time was associated with a lower rate of LR within 6 months after SBRT in patients with early-stage NSCLC. Given the association of severe and persistent RIL with survival in NSCLC, further study of the effect of radiation time on immune status is warranted.

Dosimetric Comparisons between Proton Beam Therapy and Modern Photon Radiation Techniques for Stage I Non-Small Cell Lung Cancer According to Tumor Location

Simple Summary

Stereotactic ablative radiotherapy (SABR) is a well-established technique used to treat stage I non-small cell lung cancer (NSCLC). Proton beam therapy (PBT) offers dosimetric advantages over photon SABR techniques by reducing doses to normal organs. Hence, it is believed that PBT is helpful for patients with tumors located centrally in stage I NSCLC. However, the benefits of PBT for other locations, such as peripherally located tumors, have not been well-described. We investigated dosimetric benefits for PBT over modern photon radiation techniques for stage I NSCLC according to tumor locations. A total of 42 patients’ (including tumors that were central (11), peripheral (nine), and close to the chest wall (22)) PBT plans were compared with those of modern photon radiation techniques. In all locations, PBT significantly reduced radiation exposure to the lung and heart. To reduce potential lung and heart toxicities, PBT is ideal, even in the peripherally located stage I NSCLC.

Abstract

Herein, we investigated the dosimetric benefits for proton beam therapy (PBT) over modern photon radiation techniques according to tumor location (central, peripheral, and close to the chest wall) for stage I non-small cell lung cancer (NSCLC) patients. A total of 42 patients with stage I NSCLC were treated with PBT with a total dose of 50–70 Gy in four or 10 fractions considering the risk of treatment-related toxicities. Simulation plans for three-dimensional conformal radiation therapy (3D-CRT), static-field intensity-modulated radiotherapy (IMRT), and volumetric-modulated arc therapy (VMAT) were retrospectively generated using the same treatment volumes as implemented in the PBT plans for these patients. Dosimetric improvements were observed with PBT as compared with all the photon-based radiation techniques with regards to the mean lung dose, lung V5 and V10, mean heart dose, and heart V5 and V10 in all locations. Moreover, lower radiation exposure to the chest wall was observed within PBT for peripherally located and close to the chest wall tumors. All radiotherapy modalities achieved clinically satisfactory treatment plans in the current study. Notably, the usage of PBT resulted in significant dosimetric improvements in the lung and heart over photon-based techniques at all tumor locations, including the periphery, for stage I NSCLC.

Cost-Effectiveness Analysis of Stereotactic Ablative Body Radiotherapy for the Treatment of Oligometastatic Tumors versus Standard of Care

BACKGROUND

Recent clinical trial results reported that stereotactic radiotherapy (SABR) may improve survival for patients with oligometastatic (OM) cancer. Given that these results come from a phase II trial, there remains considerable uncertainty about this finding, and about the cost-effectiveness of SABR for patients with OM cancer. In this analysis, we estimate the cost-effectiveness of SABR for oligometastatic cancer patients.

METHODS

A probabilistic time-dependent Markov model was constructed to simulate treatment of oligometastatic cancer patients over five- and ten-year time horizons. The primary data source was the phase II, Stereotactic Ablative Radiotherapy for the Comprehensive Treatment of Oligometastases (SABR-COMET )trial and supplemented with data from the literature. We estimated the effect of SABR and the standard of care (SoC) using quality-adjusted life-years (QALYs). Costs were measured from a provincial payer perspective (2018 Canadian dollars).

RESULTS

In the reference case analysis (five-year time horizon), SABR was associated with additional incremental costs of CAD 38,487 and an incremental QALY gain of 0.84. This resulted in an incremental cost-effectiveness ratio (ICER) of CAD 45,726 per QALY gained. Over a ten-year time horizon, the increased uncertainty in the long-term effectiveness of SABR resulted in an ICER of CAD 291,544 per QALY gained. Estimates from the probabilistic analysis indicated that at a willingness-to-pay (WTP) threshold of CAD 50,000 and CAD 100,000 per QALY gained, there is 54% and 78% probability (respectively) that SABR would be cost-effective using the five-year time horizon.

CONCLUSIONS

The adoption of SABR therapy requires a considerable upfront capital investment. Our results suggest that the cost-effectiveness of SABR is contingent on the uncertainty in the evidence base. Further clinical trials to confirm the effectiveness of SABR and research into the real-world costs associated with this treatment could reduce the uncertainty around implementation of the technology.

A Special Report on 2019 International Planning Competition and a Comprehensive Analysis of Its Results

Purpose

The aim of this work is to introduce the 2019 International Planning Competition and to analyze its results.

Methods and materials

A locally advanced non-small cell lung cancer (LA-NSCLC) case using the simultaneous integrated boost approach was selected. The plan quality was evaluated by using a ranking system in accordance with practice guidelines. Planners used their clinical Treatment Planning System (TPS) to generate the best possible plan along with a survey, designed to obtain medical physics aspects information. We investigated the quality of the large population of plans designed by worldwide planners using different planning and delivery systems. The correlations of plan quality with relevant planner characteristics (work experience, department scale, and competition experience) and with technological parameters (TPS and modality) were examined.

Results

The number of the qualified plans was 287 with a wide range of scores (38.61–97.99). The scores showed statistically significant differences by the following factors: 1) department scale: the mean score (89.76 ± 8.36) for planners from the departments treating >2,000 patients annually was the highest of all; 2) competition experience: the mean score for the 107 planners with previous competition experience was 88.92 ± 9.59, statistically significantly from first-time participants (p = .001); 3) techniques: the mean scores for planners using VMAT (89.18 ± 6.43) and TOMO (90.62 ± 7.60) were higher than those using IMRT (82.28 ± 12.47), with statistical differences (p <.001). The plan scores were negligibly correlated with the planner’s years of work experience or the type of TPS used. Regression analysis demonstrated that plan score was associated with dosimetric objectives that were difficult to achieve, which is generally consistent with a clinical practice evaluation. However, 51.2% of the planners abandoned the difficult component of total lung receiving a dose of 5 Gy in their plan design to achieve the optimal plan.

Conclusion

The 2019 international planning competition was carried out successfully, and its results were analyzed. Plan quality was not correlated with work experiences or the TPS used, but it was correlated with department scale, modality, and competition experience. These findings differed from those reported in previous studies.

Evaluation of cine imaging during multileaf collimator and gantry motion for real-time magnetic resonance guided radiation therapy

Purpose

Real‐time magnetic resonance guided radiation therapy (MRgRT) uses 2D cine imaging for target tracking. This work evaluates the percent image uniformity (PIU) and spatial integrity of cine images in the presence of multileaf collimator (MLC) and gantry motion in order to simulate sliding window and volumetric modulated arc therapy (VMAT) conditions.

Methods

Percent image uniformity and spatial integrity of cine images were measured (1) during MLC motion, (2) as a function of static gantry position, and (3) during gantry rotation. PIU was calculated according to the ACR MRI Quality Control Manual. Spatial integrity was evaluated by measuring the geometric distortion of 16 measured marker positions (10 cm or 15.225 cm from isocenter).

Results

The PIU of cine images did not vary by more than 1% from static linac conditions during MLC motion and did not vary by more than 3% during gantry rotation. Banding artifacts were present during gantry rotation. The geometric distortion in the cine images was less than 0.88 mm for all points measured throughout MLC motion. For all static gantry positions, the geometric distortion was less than 0.88 mm at 10 cm from isocenter and less than 1.4 mm at 15.225 cm from isocenter. During gantry rotation, the geometric distortion remained less than 0.92 mm at 10 cm from isocenter and less than 1.60 mm at 15.225 cm from isocenter.

Conclusion

During MLC motion, cine images maintained adequate PIU, and the geometric distortion of points within 15.225 cm from isocenter was less than the 1 mm threshold necessary for real‐time target tracking and gating. During gantry rotation, PIU was negatively affected by banding artifacts, and spatial integrity was only maintained within 10 cm from isocenter. Future work should investigate the effects imaging artifacts have on real‐time target tracking during MRgRT.

Sparing Organs at Risk with Simultaneous Integrated Boost Volumetric Modulated Arc Therapy for Locally Advanced Non-Small Cell Lung Cancer: An Automatic Treatment Planning Study

Background

The technique of simultaneous integrated boost volumetric modulated arc therapy (SIB-VMAT) has been widely used in locally advanced non-small cell lung cancer; however, its dosimetric advantages are seldom reported. This study aimed to quantify dosimetric advantages of SIB-VMAT.

Methods

Forty patients with stage III non-small cell lung cancer in our hospital were retrospectively included. SIB-VMAT and conventional VMAT (C-VMAT) plans were generated for every patient using the automatic treatment planning system. A reduced dose was delivered to PTV in SIB-VAMT plans compared to C-VMAT plans (50.4Gy vs 60Gy). The prescribed dose was 50.4 Gy in 28 fractions to PTV and 59.92 Gy in 28 fractions to PGTV in SIB-VMAT plans, while 60 Gy in 30 fractions to PTV in C-VMAT plans. Dose-volume metrics of PTV, total lung, heart, esophagus and spinal cord were recorded. The quality score was used to evaluate organs at risk (OAR) protection for two type prescription plans.

Results

Conformal coverage of the targets (PGTV/PTV) by 95% of the prescription dose was well achieved in radiation plans. SIB-VMAT plans achieved significantly higher quality score than C-VMAT plans (Mean: 68.15±13.32 vs 49.15±13.35, P<0.001). More plans scored above sixty in SIB-VMAT group compared to C-VMAT group (72.5% vs 20%, P<0.001). Notable reductions in mean dose, V₃₀, V₄₀ and V₅₀ of total lung were observed in SIB-VMAT plans compared to C-VMAT plans, with median decreased proportions of 6.5%, 8.7%, 19.6% and 32.1%, respectively. Statistically significant decrease in heart V₃₀ and V₄₀ was also achieved in SIB-VMAT plans, with median decreased proportions of 26.1% and 38.8%. SIB-VMAT plans achieved significant reductions in the maximum doses to both esophagus and spinal cord. Patients with CTV/(GTV+GTVnd) ≥8.6 showed more notable decrease in total lung V₅₀ (median, 33.6% vs 28.8%, P=0.001) in SIB-VMAT plans compared to those with the ratio being less than 8.6.

Conclusion

SIB-VMAT technique could lead to a substantial sparing of normal organs, including lung, heart, esophagus and cord, mainly through reducing high and inter-median dose exposure. Patients with CTV/(GTV+GTVnd) ≥8.6 might benefit more from SIB-VMAT.

Helical tomotherapy: Comparison of Hi-ART and Radixact clinical patient treatments at the Technical University of Munich

The helical tomotherapy (HT) Hi-ART system was installed at our department in April 2007. In July 2018 the first Radixact system in Germany has been launched for clinical use. We present differences, advantages and disadvantages and show future perspectives in patient treatment using two HT devices. We investigate patient characteristics, image quality, radiotherapy treatment specifications and analyze the time effort for treatments with the Hi-ART system from April 2010 until May 2017 and compare it to the data acquired in the first nine months of usage of the Radixact system. Comparing the Hi-ART and Radixact system, the unique option of integrated MVCT image acquisition has experienced distinct improvement in image quality. Time effort for irradiation treatment could be improved resulting in a mean beam on time for craniospinal axis treatment of 636.2 s for the Radixact system compared to 915.9 s for the Hi-ART system. The beneficial use of tomotherapy for complex target volumes is demonstrated by a head and neck tumor case and craniospinal axis treatment. With the Radixact system MVCT image quality has been improved allowing for fast and precise interfraction dose adaptation. The improved time effort for patient treatment could increase the accessibility for clinical usage.

Stereotactic ablative radiotherapy of 60 Gy in eight fractions is safe for ultracentral non-small cell lung cancer

Background

There is no consensus on the definition or recommended radiotherapy treatment of ultracentral non‐small cell lung cancer (NSCLC). Here, we report our institution's experience in treating ultracentral lung cancer patients with stereotactic ablative radiotherapy (SABR) of 60 Gy in eight fractions.

Methods

We retrospectively reviewed the outcomes of 21 ultracentral NSCLC patients treated with 60 Gy SABR in eight fractions. We defined ultracentral lung cancer as the planning target volume (PTV) directly abutting or overlapping central structures, including the proximal bronchial tree, heart, and great vessels but not the esophagus. The Kaplan‐Meier method was used to estimate overall survival (OS), progression‐free survival (PFS) and local control (LC). Toxicity was scored per the CTCAE v4.03.

Results

The median follow‐up time was 15 months, and the median OS was 15 months. The one‐ and two‐year OS rates were 87.5% and 76.6%, respectively. The one‐ and two‐year PFS rates were 71.1% and 64.0%, respectively. The one‐ and two‐year LC rates were 92.9% and 92.9%, respectively. The rate of grade 2 treatment‐related toxicities was 19.1%. There was no grade ≥ 3 treatment‐related toxicity.

Conclusion

SABR of 60 Gy in eight fractions is feasible for ultracentral NSCLC.

Do SABR-related toxicities for lung cancer depend on treatment delivery?

Stereotactic ablative radiation therapy for lung cancer is an advanced technique where tumours are ablated with hypofractionated radiation doses, with a high degree of accuracy. The aim of this paper is to review the available literature and to discuss the SABR-induced toxicities for lung malignancies as a function of radiation delivery technique. A Medline search was conducted to identify the appropriate literature to fulfil the aim of this review and data from all applicable papers were collated and analysed. The most common techniques of SABR delivery employ linear accelerators, CyberKnife robotic radiosurgery system, TomoTherapy and the Novalis beam surgery system. Linear accelerator-based treatments give rise to a variety of toxicities that are strongly dependent on both patient-related factors and planning/dosimetry-related factors. The limited number of studies using CyberKnife reported low grade toxicities. Grade three toxicities mainly include fatigue and chest pain, usually in less than 10% of patients. All treatment techniques presented show efficiency in SABR delivery with various toxicities which, at this stage, cannot render one technique better than the other. For more conclusive results, well-designed phase three randomised clinical trials are required with better patient selection criteria, including dose and fractionation, treatment machine and technique, along with the consistent selection of a common toxicity grading criterion.

Dosimetric comparison of the helical tomotherapy, volumetric-modulated arc therapy and fixed-field intensity-modulated radiotherapy for stage IIB-IIIB non-small cell lung cancer

The study aimed to compare the dosimetric parameters to target dose coverage and the critical structures in the treatment planning of helical tomotherapy (TOMO), volumetric-modulated arc therapy (VMAT), and fixed-field intensity-modulated radiotherapy (IMRT) for NSCLC delivering conventionally fractionated radiotherapy. Thirty patients with pathologically confirmed NSCLC were included. Three radiation treatment plans were designed for each patient. All patients received the uniform prescription dose of 60 Gy to the planning target volume. The conformity index (CI), heterogeneity index (HI), and parameters of critical structures were calculated. A significantly superior mean CI was observed in VMAT than in TOMO or IMRT (P = 0.013, 0.001). Mean HI was also better using VAMT or IMRT than TOMO (P = 0.002, 0.003). Mean lung V₂₀ and V₃₀ were significantly reduced by TOMO compared to IMRT (P = 0.019, 0.029). The heart was spared by IMRT compared to TOMO in terms of mean heart dose, V₅, V₁₀, and V₂₀ (P < 0.05). In larger tumor, VMAT provided the optimal dose distribution and sparing to heart. Compared to TOMO and IMRT, VMAT achieved better target dose distribution and similar sparing of critical structures. VMAT seemed to be the optimal technique for NSCLC.