A Randomized Phase 2 Study Comparing 2 Stereotactic Body Radiation Therapy Schedules for Medically Inoperable Patients With Stage I Peripheral Non-Small Cell Lung Cancer: NRG Oncology RTOG 0915 (NCCTG N0927)

Dosimetric comparison of two linear accelerators for lung cancer SBRT using IMRT dose delivery technique: VenusX vs. Edge

BACKGROUND

The VenusX and Edge accelerators are two commercially available systems used for lung stereotactic body radiation therapy (SBRT) with Intensity-Modulated Radiation Therapy (IMRT) techniques.

METHODS

A retrospective analysis was conducted on 40 lung cancer patients treated with the Edge accelerator. Treatment plans using both the Edge (PlanEdge) and VenusX (PlanVX) accelerators were generated and evaluated using various dosimetric metrics, employing statistical analyses to identify significant differences.

RESULTS

For planned target volume (PTV), Plan VX outperformed PlanEdge across the entire cohort, achieving a higher D2 dose (76.84 vs 75.56 Gy, p = 0.005), and showing significant improvements in conformity index (0.84 vs 0.80), homogeneity index (0.50 vs 0.47), and gradient index (5.12 vs 5.62), all with p < 0.001. Plan VX also recorded a lower D2 cm (27.27 vs 27.87 Gy, p = 0.004). Subgroup analyses revealed significant enhancements in conformity index (CI), homogeneity index (HI), and gradient index (GI) for both single and multi-target lesion patients, with multi-target also seeing a notably lower D2 cm. regarding organs at risk (OARs), Plan VX significantly reduced lung mean dose (Dmean) (3.85 to 3.60 Gy), V5 (16.88% to 15.61%), and V20 (5.04% to 4.63%), along with improvements in the great vessels' Dmean and max dose (Dmax), and esophagus' Dmax across all patients. Single-lesion patients saw consistent lung improvements, while multi-lesion patients experienced significant lung reductions and enhancements in great vessels' and esophagus' metrics.

CONCLUSIONS

In conclusion, both PlanVX and PlanEdge achieved treatment plans that met the dosimetric criteria defined by the RTOG guidelines. While Plan VX exhibited improved values in CI, HI, and GI, these findings reflect observed dosimetric differences rather than definitive evidence of clinical superiority. Further prospective studies are warranted to evaluate the clinical relevance of these differences.

Revisiting VEGF/VEGFR-2 signalling as an anticancer target and its inhibitor discovery: where are we and where should we go?

Angiogenesis plays an important role in tumour growth and metastasis. Targeting tumour vascular endothelial cells to inhibit tumour angiogenesis and thus block tumour blood and nutrition supply is the current research focus on anti-tumour growth and metastasis. Vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptor 2 (VEGFR-2) signal pathway regulates the proliferation, migration, survival and angiogenesis of vascular endothelial cells, which is abnormally activated in different tumours. Studies have confirmed that inhibiting VEGF/VEGFR-2 signalling pathway can produce anti-tumour effect. Nowadays, anti-angiogenesis therapy targeting VEGF/VEGFR-2 inhibition has become the most effective clinical strategy for cancer treatment. Therefore, a variety of VEGF/VEGFR-2 inhibitors with different structures have been developed. A few selectively inhibit VEGF to block the activation of VEGFR-2 pathway, while the majority selectively inhibit VEGFR-2 as multi-target inhibitors. Based on the classification of dominant skeletons, this paper briefly analyzes the biological activity, clinical research process and structure-activity relationship of the representative small molecule inhibitors of VEGF/VEGFR-2.

The effect of kV imaging dose on PTV and OAR planning constraints in lung SBRT using stereoscopic/monoscopic real-time tumor-monitoring system

PURPOSE

Quantify the impact of additional imaging doses on clinical dose constraints during lung stereotactic body radiotherapy (SBRT) treatment utilizing stereoscopic/monoscopic real-time tumor monitoring.

MATERIALS AND METHODS

Thirty lung SBRT patients treated with the volumetric arc therapy technique were randomly selected from the institutional clinical database. Contours of patients' and computed tomography data were extracted from the Eclipse treatment planning system, along with information regarding the treatment dose. Subsequently, patient-specific three-dimensional real-time imaging dose distributions were computed using a validated Monte Carlo simulation of the ExacTrac imaging. The 3D imaging dose was added to the treatment dose, and the influence of the imaging dose on clinical dose constraints was analyzed for planning target volume (PTV) and various organs at risk (OARs).

RESULTS

Among the 30 patients, 14 patients exhibited one or more failed OAR constraints based solely on the treatment dose, resulting in a total of 24 constraint failures. The addition of the real-time imaging dose altered the pass/fail criteria for one OAR constraint and two PTV constraints. The change in constraint due to additional imaging dose relative to the prescription dose was less than 1% for all patients, except for one case, where it reached 1.9%, which had remained below the threshold of 5% recommended by AAPM TG-180 guidelines. Furthermore, the additional imaging dose relative to the treatment dose resulted in an increase in OAR constraints ranging from 0 to 27% (mean of 0.8%), with nine cases exceeding 5%.

CONCLUSION

The current study represents the first attempt to investigate the impact of additional imaging doses on clinical planning constraints in real-time tumor monitoring during lung SBRT utilizing ExacTrac imaging system. The addition of an imaging dose will likely have minimal clinical impact.

Reported Early Clinical Outcomes of Forward-Planned Multileaf Collimator-Based 3-Dimensional Conformal Spatially Fractionated Radiation Therapy Technique for Large and Bulky Tumors

PURPOSE

Conventionally fractionated radiation therapy for large, bulky (≥8 cm), unresectable tumors has been hampered by radiation-induced morbidity, but application of spatially fractionated radiation therapy (SFRT) for both palliative and curative intent has been increasingly accepted. We report our clinical use of novel 3-dimensional conformal multileaf collimator (MLC)-based SFRT with same-day computed tomography simulation and forward-planning method, providing a safe, rapidly efficacious reduction in disease burden and pain, with minimal normal-tissue toxicity.

METHODS AND MATERIALS

Patients with large, unresectable bulky tumors received 15 Gy in 1 fraction to the gross tumor volume (GTV) within an hour of computed tomography simulation, using a forward-planned MLC-based SFRT technique. All patients subsequently received either 30 Gy in 10 fractions, generally 2 days after SFRT for palliative intent, or site-specific, full-prescription doses starting 2 to 3 days after SFRT for curative intent. Patients underwent follow-up examinations and imaging in 3-month intervals to assess tumor response, pain control, and radiation-associated toxicity.

RESULTS

Between November 2019 and January 2024, 24 large tumors in 23 patients were analyzed. Median follow-up was 6 months (range 3-36 months). After SFRT, 16 patients (69.5%) proceeded with palliative-intent radiation therapy, 6 patients (26.0%) underwent curative-intent radiation therapy, and 1 patient (4.3%) declined further radiation therapy. Seven patients (30.4%) reported acute radiation-associated toxicities. A total of 3 acute grade ≥3 toxicities (13.0%) were reported, but no grade 5 toxicities occurred. Complete or partial response was seen in 14 of 24 (58%) tumors; clinical benefit rate was 79.2%. Twenty of 23 patients (86.9%) reported pain relief from tumor burden.

CONCLUSIONS

Same-day 3-dimensional MLC-based SFRT method provides fast, safe, and effective management of large, bulky, unresectable tumors for both palliative and therapeutic intents across a wide range of tumor sites and histologies, reducing tumor burden and improving patient comfort and compliance. This method could be useful for rapid SFRT including adaptive treatment. We recommend commissioning and validating this method at other institutions, including community cancer centers, to expand the access of efficient, high-quality SFRT treatment to underserved patient cohorts.

Investigation of factors related to treatment planning of x-ray SBRT and scanning carbon-ion radiation therapy for early-stage lung cancer patients

This study aimed to compare the treatment plans of x-ray SBRT and scanning carbon ion radiation therapy (CIRT) for localized lung tumors, and to evaluate the dose dependence of tumor size tumor-to-heart distance. For phantom verification, we used a chest phantom with a spherical simulated tumor. Treatment plans for 3-dimensional conformal radiation therapy (3D-CRT), volumetric modulated arc therapy (VMAT), and CIRT were created. GTVs were created in sizes ranging from 0.5 to 5 cm in diameter, and the dependence of the lung dose on GTV diameter was evaluated for each treatment plan. For patient validation, 30 cases of localized lung tumors were analyzed. 3D-CRT, VMAT, and CIRT treatment plans were developed, and DVH parameters were evaluated for each GTV size and GTV-to-heart distance. In both phantom and patient validations, the OAR doses were the lowest for CIRT. The lung dose increased with increasing GTV diameter for all three treatment plans. CIRT had the smallest ratio of lung dose increase to GTV diameter increase among the three treatment plans. Heart dose in CIRT was independent of GTV size and GTV-to-heart distance Conclusions: The results of the present study suggested that the use of scanning CIRT can reduce the OAR dose while guaranteeing the tumor dose compared to x-ray SBRT. In addition, it was suggested that CIRT can treat patients with large GTV sizes while maintaining low lung and heart dose.

Artificial Intelligence, Machine Learning and Big Data in Radiation Oncology

This review explores the applications of artificial intelligence and machine learning (AI/ML) in radiation oncology, focusing on computer vision (CV) and natural language processing (NLP) techniques. We examined CV-based AI/ML in digital pathology and radiomics, highlighting the prospective clinical studies demonstrating their utility. We also reviewed NLP-based AI/ML applications in clinical documentation analysis, knowledge assessment, and quality assurance. While acknowledging the challenges for clinical adoption, this review underscores the transformative potential of AI/ML in enhancing precision, efficiency, and quality of care in radiation oncology.

A Dosimetric Comparison of HyperArc Therapy Planning and Volumetric Modulated Arc Therapy Planning in Treating Patients With Glioblastoma Multiforme

BACKGROUND/AIM

This study aimed at evaluating the potential benefit of automatic non-coplanar volumetric arc therapy (VMAT) (hyperarc, HA) technique in treating glioblastoma multiforme (GBM).

PATIENTS AND METHODS

Twenty-seven patients with GBM who received coplanar VMAT (C-VMAT) were selected in this study. HA and non-coplanar VMAT (NC-VMAT) plans were generated with the same prescriptions and constraints. The Target coverage, organs at risk (OARs) dose, and dosimetric indexes were compared among three plans.

RESULTS

The HA plan demonstrated a reduction in dose to normal tissues while maintaining target coverage, compared to C-VMAT and NC-VMAT. Additionally, HA plans demonstrated higher coverage of the GTV and PTV60 as well as improved CI from PTV60 and PTV46 compared to the other plans. Regarding the dose gradient, HA plans showed a greater dose fall-off, resulting in reduced high-dose and intermediate-dose spillage at PTV46 The HA also demonstrated a tighter gradient radius at PTV60 and PTV46 The HA plan requires fewer MUs than both C-VMAT and NC-VMAT.

CONCLUSION

The HA plan had better dosimetric results compared to C-VMAT and NC-VMAT. The HA with automatic planning module and auto-delivery treatment also provided high-quality planning and delivery efficacy. These advantages suggest that HA could potentially escalate tumor doses while minimizing toxicity, thereby improving outcomes in GBM patients.

Comparative Dosimetry and Biological Risk Assessment of Lung Oligometastasis SBRT: VMAT, Helical Tomotherapy, and CyberKnife

PurposeTo compare the dosimetry and biological risk of volumetric modulated arc therapy (VMAT), helical tomotherapy (HT) and cyberKnife (CK) in the treatment of lung oligometastases.Methods and materialsThis retrospective study included a cohort of 21 lung oligometastasis patients, each with 2 or 3 lesions, who had previously undergone stereotactic body radiation therapy (SBRT). VMAT, HT and CK plans were made for each patient. The dose distribution of planning target volume (PTV) and organs at risk (OARs) were evaluated. Three biological risks were evaluated, namely radiation pneumonitis (RP), coronary artery disease (CAD) and congestive heart failure (CHF). Monitor Units (MUs) and beam-on-time were also recorded.ResultsAll techniques were able to produce clinically deliverable plans. The expected biological risks for VMAT plans, CK plans, and HT plans were 6.69%, 5.05%, 5.88% for RP, 1.20%, 1.15%, and 1.17% for CAD, 1.26%, 1.19%, and 1.22% for CHF. The expected risks of RP were slightly lower in CK plans compared to VMAT and HT plans (p < 0.001), with VMAT plans showing the highest expected risks. For central lung cancer, the expected CAD risks of CK and HT plans were lower than those of VMAT plans (p < 0.05). The delivery efficiency of VMAT plans was significantly higher than that of CK plans and HT plans.ConclusionsAll three techniques, VMAT, HT, and CK, meet the therapeutic requirements for target coverage and dose constraints for OARs. Although there are statistical differences, the difference between the expected risk values of RP and CAD is very small, so the clinical manifestations may not show differences.

The Treatment of Patients with Early-Stage Non-Small Cell Lung Cancer Who Are Not Candidates or Decline Surgical Resection: The Role of Radiation and Image-Guided Thermal Ablation

The standard of care for early-stage NSCLC has historically been surgical resection. Given the association of lung cancer with smoking, a large number of early-stage patients also have active smoking-related medical comorbidities such as COPD precluding surgery. The current approach for treating such inoperable patients is frequently considered to be stereotactic body radiation therapy (SBRT). SBRT (also known as stereotactic ablative radiation therapy or SABR) is a curative modality that precisely delivers very high dose radiation in few (typically <5) sessions. That said, because of their minimal invasiveness and repeatable nature, image-guided thermal ablation therapies such as radiofrequency ablation (RFA), microwave ablation (MWA), and cryoablation (CA) have also been used to treat early-stage lung tumors. For those patients deemed to have "high operative risk" (i.e., those who cannot tolerate lobectomy, but are candidates for sublobar resection), the appropriateness of potential alternatives [e.g., SBRT; ablation] to surgery is an active area of investigation. In the absence of completed randomized phase III trials, the approach to comparing outcomes between surgery, SBRT, or ablative therapies by their efficacy or equivalence is complex. An overview of the role of SBRT and other non-surgical modalities in the management of early-stage lung cancer is the subject of the present review.

Treating early-stage centrally-located non-small cell lung cancer with DCAT-SBRT in centers lacking the VMAT technique: a comprehensive study

Background

Volumetric-modulated arc therapy (VMAT) may have the highest overall performance for stereotactic body radiotherapy (SBRT) treatment of inoperable early-stage NSCLC. However, in centers lacking the VMAT technique, the dynamic conformal arc therapy (DCAT) technique is potentially the best option for small and rounded NSCLC-SBRT. Therefore, we will comprehensively analyze the advantages of the DCAT versus the other techniques except VMAT in terms of dosimetry, plan complexity, delivery time, γ-passing rates and the interplay effect.

Methods

36 patients with early-stage centrally located NSCLC with PTV volumes < 65 cc were enrolled. All patients were redesigned with 50Gy/5f, and 100% of the prescribed dose was normalized to cover 95% of the PTV. The other two delivery techniques compared to the DCAT technique include 3-dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT), which use the same parameters for all three techniques.

Results

The dosimetric parameters of the 3-group plans all met the RTOG 0813 protocol. Unsurprisingly, plan complexity parameters such as segments and MUs were significantly reduced in the DCAT plans by 159.56 and 925.90 compared to the IMRT plans, respectively (all P < 0.001). The delivery time of the DCAT plans was the least of 164.51 s (all P < 0.05). Compared to the IMRT plans, the γ-passing rates were higher in the DCAT plans (P < 0.001), with the most significant difference of 6.01% in the (2%, 1 mm) criteria. As for the interplay effect, the mean dose difference (MDD) in the DCAT plans was as good as the 3DCRT plans at different respiratory amplitudes but better than the IMRT plans (all P < 0.05), and the MDD of DCAT plans did not exceed 3% in all respiratory amplitude.

Conclusion

In centers lacking the VMAT technique, implementing SBRT treatment based on the DCAT technique for inoperable early-stage centrally-located NSCLC patients with PTV volumes < 65 cc achieves better treatment efficiency and delivery accuracy while maintaining the plan quality.

RTOG 0915-compliant patient specific QA for lung stereotactic body radiotherapy using the new PTW 1600SRS detector array

PURPOSE

An area of focus in radiotherapy is the treatment of oligometastatic lung cancer using highly conformal techniques such as SBRT, performed using VMAT that involves flattening filter free (FFF) beams. This study proposes a new calibration procedure for PTW Octavius 1600SRS detector array and was designed to also evaluate clinical and dosimetric aspects of a patient-specific quality assurance (PSQA) for lung SBRT patients.

METHODS

The cohort consists of 20 patients, treated for lung metastases using SBRT with 50 Gy dose in 5 fractions (10 Gy/fr). The proposed calibration method uses only one calibration factor determined at maximum dose rate of 6MV FFF photon beam. The dosimetric accuracy of achieving a high dose gradient was analyzed using the RTOG 0915 protocol and was confirmed by PSQA procedures using the PTW Octavius 1600SRS detector.

RESULTS

Conformity index, gradient index, maximum dose at 2 cm and V20 parameters were evaluated with clinical favorable results, with only two plans with lesions situated in the inferior lobe exceeding the deviation allowed for the gradient index. Gamma passing rates using the new calibration method were 98.93% and 99.38% for different gamma criteria of 2 mm/2% and 1 mm/3%, respectively.

CONCLUSIONS

The proposed method for calibration using one calibration factor at maximum dose rate for the involved photon beam shows clinically acceptable gamma passing rates. Employing the RTOG 0915 protocol for lung SBRT treatment plan evaluation brings important dosimetric information about treatment plan quality and dose gradient fall-off which can be correlated with the results achieved during the pretreatment verification procedures.

Dose-Effect Relationship of Kidney Function After SABR for Primary Renal Cell Carcinoma: TROG 15.03 FASTRACK II

PURPOSE

Stereotactic ablative body radiotherapy (SABR) is a novel option to treat primary renal cell carcinoma. However, a high radiation dose may be received by the treated kidney, which may affect its function posttreatment. This study investigates the dose-effect relationship of kidney SABR with posttreatment renal function.

METHODS AND MATERIALS

This was a prespecified secondary endpoint of the multicenter FASTRACK II (Focal Ablative STereotactic RAdiotherapy for Cancers of the Kidney phase II) clinical trial (National Clinical Trial 02613819). Patients received either 26 Gy in a single fraction (SF) for tumors with a maximal diameter of 4 cm or less or 42 Gy in 3 fractions (multifraction [MF]) for larger tumors. To determine renal function change, 99mTc-dimercaptosuccinic acid (DMSA) single-photon emission computed tomography/computed tomography (SPECT/CT) scans were acquired, and the glomerular filtration rate was estimated at baseline, 12, and 24 months posttreatment. Imaging data sets were rigidly registered to the planning CT where kidneys were segmented to calculate dose-response curves.

RESULTS

From 71 enrolled patients, 36 (51%) and 26 (37%) patients were included in this study based on availability of posttreatment data at 12 and 24 months, respectively. The ipsilateral kidney glomerular filtration rate decreased from baseline by 42% and 39% in the SF cohort and by 45% and 62% in the MF cohort, at 12 and 24 months, respectively (P < .03). The loss in renal function was 3.6%/Gy ± 0.8%/Gy and 4.5%/Gy ± 1.0%/Gy in the SF cohort and 1.7%/Gy ± 0.1%/Gy and 1.7%/Gy ± 0.2%/Gy in the MF cohort at 12 and 24 months, respectively. The major loss in renal function occurred in high-dose regions, where dose-response curves converged to a plateau.

CONCLUSIONS

For the first time in a multicenter study, the dose-effect relationship at 12 and 24 months post-SABR treatment for primary renal cell carcinoma was quantified. Kidney function reduces linearly with dose up to 100 Gy BED3.

Technical note: Dosimetry and FLASH potential of UHDR proton PBS for small lung tumors: Bragg-peak-based delivery versus transmission beam and IMPT

BACKGROUND

High-energy transmission beams (TBs) are currently the main delivery method for proton pencil beam scanning ultrahigh dose-rate (UHDR) FLASH radiotherapy. TBs place the Bragg-peaks behind the target, outside the patient, making delivery practical and achievement of high dose-rates more likely. However, they lead to higher integral dose compared to conventional intensity-modulated proton therapy (IMPT), in which Bragg-peaks are placed within the tumor. It is hypothesized that, when energy changes are not required and high beam currents are possible, Bragg-peak-based beams can not only achieve more conformal dose distributions than TBs, but also have more FLASH-potential.

PURPOSE

This works aims to verify this hypothesis by taking three different Bragg-peak-based delivery techniques and comparing them with TB and IMPT-plans in terms of dosimetry and FLASH-potential for single-fraction lung stereotactic body radiotherapy (SBRT).

METHODS

For a peripherally located lung target of various sizes, five different proton plans were made using "matRad" and inhouse-developed algorithms for spot/energy-layer/beam reduction and minimum monitor unit maximization: (1) IMPT-plan, reference for dosimetry, (2) TB-plan, reference for FLASH-amount, (3) pristine Bragg-peak plan (non-depth-modulated Bragg-peaks), (4) Bragg-peak plan using generic ridge filter, and (5) Bragg-peak plan using 3D range-modulated ridge filter.

RESULTS

Bragg-peak-based plans are able to achieve sufficient plan quality and high dose-rates. IMPT-plans resulted in lowest OAR-dose and integral dose (also after a FLASH sparing-effect of 30%) compared to both TB-plans and Bragg-peak-based plans. Bragg-peak-based plans vary only slightly between themselves and generally achieve lower integral dose than TB-plans. However, TB-plans nearly always resulted in lower mean lung dose than Bragg-peak-based plans and due to a higher amount of FLASH-dose for TB-plans, this difference increased after including a FLASH sparing-effect.

CONCLUSION

This work indicates that there is no benefit in using Bragg-peak-based beams instead of TBs for peripherally located, UHDR stereotactic lung radiotherapy, if lung dose is the priority.

Optimal combination of collimator angles for dual-arc volumetric modulated arc therapy planning in stereotactic body radiotherapy for spinal metastases

In planning the treatment of spinal metastases using stereotactic body radiotherapy (SBRT), the optimal blocking of the spinal cord to match the leaf travel can be achieved with a first-arc collimator angle of approximately 90°. We aim to clarify the optimal second-arc collimator angles when the first-arc collimator angle is fixed to 90° in dual-arc volumetric modulated arc therapy (VMAT). For this retrospective study, we considered 37 spinal segments with spinal metastases and created dual-arc VMAT plans. In the plans, 24 Gy in 2 fractions were prescribed, and the first-arc collimator angle was fixed to 90° while varying the second-arc collimator angle in increments of 15° from 0° to 90°. All the plans were normalized such that the planning organ-at-risk volume for the spinal cord D0.035 cc = 17 Gy and satisfied other dose constraints. D95% for the planning target volume (PTV), V100% for the overlap between the PTV and 10 mm expansion of the spinal cord, modified gradient index, monitor unit, and 3%/1 mm gamma passing rates were compared between different second-arc collimator angles using the Wilcoxon signed-rank test and Bonferroni correction. PTV D95% and overlap V100% were the highest for a second-arc collimator angle of 45° and decreased as the angle approached either 0° or 90°. The maximum mean differences of PTV D95% and overlap V100% were -2.66% (90° vs 45°, p < 0.0024) and -5.49% (90° vs 45°, p < 0.0024), respectively. Moreover, the second-arc collimator angle of 45° was the least suitable in terms of the modified gradient index. The required monitor unit increased from the second-arc collimator angle of 15° to 45°, and the 3%/1 mm gamma passing rates reached over 95% for the evaluated second-arc collimator angles of 15°, 30°, and 45°. We found that in the dual-arc VMAT plan for spine SBRT, second-arc collimator angles other than 90° were suitable, and 45° was the optimal angle in terms of target coverage including the area around the spinal cord.

Dosimetric impact of intrafraction patient motion on MLC-based 3D-conformal spatially fractionated radiation therapy treatment of large and bulky tumors

PURPOSE

To evaluate the dosimetric impact on spatially fractionated radiation therapy (SFRT) plan quality due to intrafraction patient motion via multi-field MLC-based method for treating large and bulky (≥8 cm) unresectable tumors.

METHODS

For large tumors, a cone beam CT-guided 3D conformal MLC-based SFRT method was utilized with 15 Gy prescription. An MLC GTV-fitting algorithm provided 1 cm diameter apertures with a 2 cm center-to-center distance at the isocenter. This generated a highly heterogeneous sieve-like dose distribution within an hour, enabling same-day SFRT treatment. Fifteen previously treated SFRT patients were analyzed (5 head & neck [H&N], 5 chest and lungs, and 5 abdominal and pelvis masses). For each plan, intrafraction motion errors were simulated by incrementally shifting original isocenters of each field in different x-, y-, and z-directions from 1 to 5 mm. The dosimetric metrics analyzed were: peak-to-valley-dose-ratio (PVDR), percentage of GTV receiving 7.5 Gy, GTV mean dose, and maximum dose to organs-at-risk (OARs).

RESULTS

For ±1, ±2, ±3, ±4, and ±5 mm isocenter shifts: PVDR dropped by 3.9%, 3.8%, 4.0%, 4.1%, and 5.5% on average respectively. The GTV(V7.5) remained within 0.2%, and the GTV mean dose remained within 3.3% on average, compared to the original plans. The average PVDR drop for 5 mm shifts was 4.2% for H&N cases, 10% for chest and lung, and 2.2% for abdominal and pelvis cases. OAR doses also increased. The maximum dose to the spinal cord increased by up to 17 cGy in H&N plans, mean lung dose (MLD) changed was small for chest/lung, but the bowel dose varied up to 100 cGy for abdominal and pelvis cases.

CONCLUSION

Due to tumor size, location, and characteristics of MLC-based SFRT, isocenter shifts of up to ±5 mm in different directions had moderate effects on PVDR for H&N and pelvic tumors and a larger effect on chest tumors. The dosimetric impact on OAR doses depended on the treatment site. Site-specific patient masks, Vac-Lok bags, and proper immobilization devices similar to SBRT/SRT setups should be used to minimize these effects.

Beyond conventional bounds: Surpassing system limits for stereotactic ablative (SAbR) lung radiotherapy using CBCT-based adaptive planning system

PURPOSE

Online adaptive radiotherapy relies on a high degree of automation to enable rapid planning procedures. The Varian Ethos intelligent optimization engine (IOE) was originally designed for conventional treatments so it is crucial to provide clear guidance for lung SAbR plans. This study investigates using the Ethos IOE together with adaptive-specific optimization tuning structures we designed and templated within Ethos to mitigate inter-planner variability in meeting RTOG metrics for both online-adaptive and offline SAbR plans.

METHODS

We developed a planning strategy to automate the generation of tuning structures and optimization. This was validated by retrospective analysis of 35 lung SAbR cases (total 105 fractions) treated on Ethos. The effectiveness of our planning strategy was evaluated by comparing plan quality with-and-without auto-generated tuning structures. Internal target volume (ITV) contour was compared between that drawn from CT simulation and from cone-beam CT (CBCT) at time of treatment to verify CBCT image quality and treatment effectiveness. Planning strategy robustness for lung SAbR was quantified by frequency of plans meeting reference plan RTOG constraints.

RESULTS

Our planning strategy creates a gradient within the ITV with maximum dose in the core and improves intermediate dose conformality on average by 2%. ITV size showed no significant difference between those contoured from CT simulation and first fraction, and also trended towards decreasing over course of treatment. Compared to non-adaptive plans, adaptive plans better meet reference plan goals (37% vs. 100% PTV coverage compliance, for scheduled and adapted plans) while improving plan quality (improved GI (gradient index) by 3.8%, CI (conformity index) by 1.7%).

CONCLUSION

We developed a robust and readily shareable planning strategy for the treatment of adaptive lung SAbR on the Ethos system. We validated that automatic online plan re-optimization along with the formulated adaptive tuning structures can ensure consistent plan quality. With the proposed planning strategy, highly ablative treatments are feasible on Ethos.

Curcumin and Baicalin Co-Loaded Nanoliposomes for Synergistic Treatment of Non-Small Cell Lung Cancer

Currently, the treatment of patients with advanced non-small cell lung cancer (NSCLC) mainly relies on traditional chemotherapeutic drugs; however, most of them have limited therapeutic effects and high toxicity. Some natural products with good therapeutic efficacy and low toxicity and side effects are limited in clinical application due to their low solubility and bioavailability. In this study, a nanoliposome drug-carrying system (Lip-Cur/Ba) was developed for the co-delivery of curcumin (Cur) and baicalin (Ba) using the thin-film hydration method. In vitro experiments demonstrated that Lip-Cur/Ba had a strong killing effect on A549 cells, and the inhibitory effect of Lip-Cur/Ba on A549 cells was enhanced by 67.8% and 51.9% relative to that of the single-carrier system, which could reduce the use of a single-drug dose (Lip-Cur and Lip-Ba), delay the release rate of the drug and improve the bioavailability. In vivo experiments demonstrated the antitumor activity of Lip-Cur/Ba by intravitreal injection in BALB/c mice, and there were no obvious toxic side effects. This study provides a new idea for curcumin and baicalin to be used in the co-treatment of NSCLC by constructing a new vector.

Moving towards single fraction peripheral lung stereotactic body radiation therapy: patient care during and after the global COVID-19 pandemic

Aim/objectives: Single-fraction stereotactic body radiation therapy (SF-SBRT) for peripheral lung tumors was reviewed. Materials & methods: Medically inoperable peripheral lung tumors eligible for SF-SBRT 34 Gray were treated. Patient characteristics, treatment and toxicity parameters were retrospectively collected, and toxicities were evaluated. Results: A total of 26 patients were assessed with median age of 74 years. Ninety-six percent had early-stage cancer and 35% were treated as per the SABR-BRIDGE protocol. Twenty-six peripheral lesions were treated (median maximal dimension 1.7 cm). Sixty-five percent had grade ≤2 toxicities with radiation pneumonitis (42.3%) and chest wall pain (35%). Radiation pneumonitis and chest wall pain rates were higher in patients with tumor diameters more than 1.5 cm. Conclusion: SF-SBRT is practical and effective treatment technique.

Stereotactic Body Radiation Therapy for Stage IIA to IIIA Inoperable Non-Small Cell Lung Cancer: A Phase 1 Dose-Escalation Trial

PURPOSE

Larger tumors are underrepresented in most prospective trials on stereotactic body radiation therapy (SBRT) for inoperable non-small cell lung cancer (NSCLC). We performed this phase 1 trial to specifically study the maximum tolerated dose (MTD) of SBRT for NSCLC >3 cm.

METHODS AND MATERIALS

A 3 + 3 dose-escalation design (cohort A) with an expansion cohort at the MTD (cohort B) was used. Patients with inoperable NSCLC >3 cm (T2-4) were eligible. Select ipsilateral hilar and single-station mediastinal nodes were permitted. The initial SBRT dose was 40 Gy in 5 fractions, with planned escalation to 50 and 60 Gy in 5 fractions. Adjuvant chemotherapy was mandatory for cohort A and optional for cohort B, but no patients in cohort B received chemotherapy. The primary endpoint was SBRT-related acute grade (G) 4+ or persistent G3 toxicities (Common Terminology Criteria for Adverse Events version 4.03). Secondary endpoints included local failure (LF), distant metastases, disease progression, and overall survival.

RESULTS

The median age was 80 years; tumor size was >3 cm and ≤5 cm in 20 (59%) and >5 cm in 14 patients (41%). In cohort A (n = 9), 3 patients treated to 50 Gy experienced G3 radiation pneumonitis (RP), thus defining the MTD. In the larger dose-expansion cohort B (n = 25), no radiation therapy-related G4+ toxicities and no G3 RP occurred; only 2 patients experienced G2 RP. The 2-year cumulative incidence of LF was 20.2%, distant failure was 34.7%, and disease progression was 54.4%. Two-year overall survival was 53%. A biologically effective dose (BED) <100 Gy was associated with higher LF (P = .006); advanced stage and higher neutrophil/lymphocyte ratio were associated with greater disease progression (both P = .004).

CONCLUSIONS

Fifty Gy in 5 fractions is the MTD for SBRT to tumors >3 cm. A higher BED is associated with fewer LFs even in larger tumors. Cohort B appears to have had less toxicity, possibly due to the omission of chemotherapy.

Utilizing collimated aperture with proton pencil beam scanning (PBS) for stereotactic radiotherapy

PURPOSE

Proton stereotactic radiosurgery (PSRS) has emerged as an innovative proton therapy modality aimed at achieving precise dose delivery with minimal impact on healthy tissues. This study explores the dosimetric outcomes of PSRS in comparison to traditional intensity-modulated proton therapy (IMPT) by focusing on cases with small target volumes. A custom-made aperture system designed for proton therapy, specifically tailored to small target volumes, was developed and implemented for this investigation.

METHODS

A prerequisite mechanical validation through an isocentricity test precedes dosimetric assessments, ensuring the seamless integration of mechanical and dosimetry analyses. Five patients were enrolled in the study, including two with choroid melanoma and three with arteriovenous malformations (AVM). Two treatment plans were meticulously executed for each patient, one utilizing a collimated aperture and the other without. Both plans were subjected to robust optimization, maintaining identical beam arrangements and consistent optimization parameters to account for setup errors of 2 mm and range uncertainties of 3.5%. Plan evaluation metrics encompassing the Heterogeneity Index (HI), Paddick Conformity Index (CIPaddick), Gradient Index (GI), and the R50% index to evaluate alterations in low-dose volume distribution.

RESULTS

The comparative analysis between PSRS and traditional PBS treatment revealed no significant differences in plan outcomes, with both modalities demonstrating comparable target coverage. However, collimated apertures resulted in discernible improvements in dose conformity, dose fall-off, and reduced low-dose volume.

CONCLUSIONS

This study underscores the advantageous impact of the aperture system on proton therapy, particularly in cases involving small target volumes.

Clinical association between plan complexity and the local-recurrence-free-survival of non-small-cell lung cancer patients receiving stereotactic body radiation therapy

PURPOSE

To investigate the clinical impact of plan complexity on the local recurrence-free survival (LRFS) of non-small cell lung cancer (NSCLC) patients treated with stereotactic body radiation therapy (SBRT).

METHODS

Data from 123 treatment plans for 113 NSCLC patients were analyzed. Plan-averaged beam modulation (PM), plan beam irregularity (PI), monitor unit/Gy (MU/Gy) and spherical disproportion (SD) were calculated. The γ passing rates (GPR) were measured using ArcCHECK 3D phantom with 2 %/2mm criteria. High complexity (HC) and low complexity (LC) groups were statistically stratified based on the aforementioned metrics, using cutoffs determined by their significance in correlation with survival time, as calculated using the R-3.6.1 packages. Kaplan-Meier analysis, Cox regression, and Random Survival Forest (RSF) models were employed for the analysis of local recurrence-free survival (LRFS). Propensity-score-matched pairs were generated to minimize bias in the analysis.

RESULTS

The median follow-up time for all patients was 25.5 months (interquartile range 13.4-41.2). The prognostic capacity of PM was suggested using RSF, based on Variable Importance and Minimal Depth methods. The 1-, 2-, and 3-year LRFS rates in the HC group were significantly lower than those in the LC group (p = 0.023), when plan complexity was defined by PM. However, no significant difference was observed between the HC and LC groups when defined by other metrics (p > 0.05). All γ passing rates exceeded 90.5 %.

CONCLUSIONS

This study revealed a significant association between higher PM and worse LRFS in NSCLC patients treated with SBRT. This finding offers additional clinical evidence supporting the potential optimization of pre-treatment quality assurance protocols.

Dose Prescription to Isodose Lines in Static Multi-Beam Stereotactic Body Radiotherapy for Lung Tumors: Which Line Is Optimal?

This study investigated the appropriate dose prescription method in static multi-beam stereotactic body radiotherapy for lung tumors. Static multi-beam stereotactic body radiotherapy is a mainstream treatment in Japan. Based on the hypothesis that dose prescription to lower isodose lines may improve planning target volume dose coverage and decrease doses to organs at risk, we investigated changes in dose-volume histograms with prescription to various isodose lines for planning target volume in static multi-beam stereotactic body radiotherapy. In all treatment plans, 45 Gy in 4 fractions were prescribed to 95% of the planning target volume. By adjusting the leaf margins of each beam, various prescription isodose lines encompassing 95% volume of the planning target volume were generated. The prescription isodose lines investigated were 40, 50, 60, 70, 80 and 90% lines relative to the maximum dose of each planning target volume. The conformity index, homogeneity index, mean lung dose, and V5-V40 of the lung were evaluated. The dose was calculated by the adaptive convolve algorithm. The conformity index was lowest in the 70% or 80% isodose plan. The mean lung doses and V10-V40 of the lung decreased steeply from the 90% to the 70% isodose plan, and was lowest in the 60% and 70% isodose plans. These indices increased in the 40% and 50% isodose plans. The optimal stereotactic body radiotherapy plans appeared to be dose prescription to the 60% or 70% isodose line. Further investigation is warranted to clarify the advantage of using this method clinically.

Current status and breakthroughs in treating advanced non-small cell lung cancer with EGFR exon 20 insertion mutations

Recently, targeted therapy and immunotherapy have emerged as effective treatment options for non-small cell lung cancer (NSCLC). This progress has been facilitated by the rapid development of diagnostic and therapeutic technologies and the continuous research and development of new drugs, leading to a new era in precision medicine for NSCLC. This is a breakthrough for patients with common mutations in the human epidermal growth factor receptor (EGFR) gene in NSCLC. Consequently, the use of targeted drugs has significantly improved survival. Nevertheless, certain rare genetic mutations are referred to as EGFR exon 20 insertion (ex20ins) mutations, which differ in structure from conventional EGFR gene mutations, namely, exon 19 deletion mutations (19-Del) and exon 21 point mutations. Owing to their distinct structural characteristics, patients harboring these EGFR ex20ins mutations are unresponsive to traditional tyrosine kinase inhibitor (TKI) therapy. This particular group of patients did not fall within the scope of their applicability. However, the activating A763_Y764insFQEA mutation elicits a more pronounced response than mutations in the near and far regions of the C-helix immediately following it and should, therefore, be treated differently. Currently, there is a lack of effective treatments for EGFR ex20ins mutations NSCLC. The efficacy of chemotherapy has been relatively favorable, whereas the effectiveness of immunotherapy remains ambiguous owing to inadequate clinical data. In addition, the efficacy of the first- and second-generation targeted drugs remains limited. However, third-generation and novel targeted drugs have proven to be effective. Although novel EGFR-TKIs are expected to treat EGFR ex20ins mutations in patients with NSCLC, they face many challenges. The main focus of this review is on emerging therapies that target NSCLC with EGFR ex20ins and highlight major ongoing clinical trials while also providing an overview of the associated challenges and research advancements in this area.

Feasibility of a Single-Fraction Stereotactic Dose of 30 Gy to Solitary Lung Lesions on Halcyon

Purpose We sought to explore the feasibility of using the current co-planar Halcyon ring delivery system (RDS) with a novel multileaf collimator (MLC) aperture shape controller in delivering a single high dose of 30 Gy to solitary lung lesions via stereotactic body radiotherapy (SBRT). Materials and methods Thirteen non-small-cell lung cancer (NSCLC) patients previously treated with a single dose of 30 Gy to lung lesions via SBRT on the TrueBeam (6MV-FFF) using non-coplanar volumetric modulated arc therapy (VMAT) arcs were anonymized and replanned onto the Halcyon RDS (6MV-FFF) following RTOG-0915 single-fraction criteria. The Halcyon plans utilized a novel dynamic conformal arc (DCA)-based MLC-fitting approach before VMAT optimization with a user-defined aperture shape controller option. The clinical TrueBeam and Halcyon plans were compared via their protocol compliance, target conformity, gradient index, and dose to organs-at-risk (OAR). Treatment delivery efficacy and accuracy were assessed through end-to-end quality assurance (QA) tests on Halcyon and independent dose verification via in-house Monte Carlo (MC) second-check validation. Results All Halcyon lung SBRT plans met RTOG-0915 protocol's requirements for target coverage, conformity, and gradient indices, and maximum dose 2 cm away from the target (D2cm) while being statistically insignificant (p > 0.05) when compared to clinical TrueBeam plans. Additionally, Halcyon provided a similar dose to OAR except for the ribs, where Halcyon demonstrated a lower maximum dose (15.22 Gy vs 17.01 Gy, p < 0.001). However, Halcyon plans required a higher total monitor unit (8892 MU vs 7413 MU, p < 0.001), resulting in a higher beam modulation factor (2.96 MU/cGy vs 2.47 MU/cGy, p < 0.001) and an increase in beam-on time by a factor of 2.1 (11.11 min vs 5.3 min, p < 0.005). End-to-end QA measurements demonstrate that Halcyon plans were clinically acceptable with an average gamma passing rate of 99.8% for 2%/2mm criteria and independent MC 2nd checks within ±2.86%. Conclusion Our end-to-end testing and validation study demonstrates that by utilizing a DCA-based MLC aperture shape controller before VMAT optimization, Halcyon can be used for delivering a single dose of lung SBRT treatment. However, future improvements of Halcyon RDS are recommended to allow higher output rates, rotational couch corrections, and an integrated intrafraction motion management system that will further enhance Halcyon's capability for site-specific single dosage of SBRT.

Impact of Maximum Point Dose Within the Planning Target Volume on Local Control of Nonsmall Cell Lung Cancer Treated With Stereotactic Body Radiotherapy

BACKGROUND

No consensus exists on the maximum dose delivered to the planning target volume (PTV) in the delivery of stereotactic body radiotherapy (SBRT) for primary lung cancer. We investigated whether higher biologically effective doses (BED) within the PTV were associated with improved tumor control.

METHODS

We reviewed patients with early-stage, node-negative nonsmall cell lung cancer who received curative-intent SBRT between 2005 and 2018. We calculated the maximum BED (maxBED) within the PTV for all patients, analyzing outcomes using the cumulative incidence method and Fine-Gray test statistics to assess prognostic impact.

RESULTS

We analyzed 171 patients (median age, 70.2; range, 43 to 90 y) with 181 lung nodules. Median follow-up was 2.7 years (range, 0.1 to 12 y) for all patients and 4.2 years (range, 0.2 to 8.4 y) for living patients. Median maximum tumor diameter was 1.9 cm (range, 0.7 to 5.6 cm). Patients received a prescription of 48 or 50 Gy in 4 or 5 fractions, respectively, except for one who received 60 Gy in 5 fractions. Median maxBED was 120 Gy (range, 101 to 171 Gy). There was no difference in the 3-year local control (LC) rate among patients treated with a maxBED<120 Gy versus ≥120 Gy ( P =0.83).

CONCLUSIONS

No significant differences in LC were observed between patients with early-stage nonsmall cell lung cancer treated with SBRT in 4 or 5 fractions with a maxBED≥120 Gy. However, a higher maxBED trended toward improved LC rates, suggesting a maxBED threshold greater than 120 Gy may be needed to improve LC rates.

Stereotactic body radiotherapy with volumetric intensity-modulated arc therapy and flattening filter-free beams: dosimetric considerations

PURPOSE

The present study comparatively evaluates the impact of energy-matched flattening filter-free (FFF) photon beams with different energy levels on the physical-dosimetric quality of lung and liver stereotactic body radiotherapy (SBRT) treatment plans.

METHODS

For this purpose, 54 different lung and liver lesions from 44 patients who had already received SBRT combined with volumetric modulated arc therapy (VMAT) were included in this retrospective planning study. Planning computed tomography scans already available were used for the renewed planning with 6 MV, 6 MV-FFF, 10 MV, and 10 MV-FFF under constant planning objectives. The treatment delivery data, dosimetric distributions, and dose-volume histograms as well as parameters such as the conformity index and gradient indices were the basis for the evaluation and comparison of treatment plans.

RESULTS

A significant reduction of beam-on time (BOT) was achieved due to the high dose rates of FFF beams. In addition, we showed that for FFF beams compared to flattened beams of the same energy level, smaller planning target volumes (PTV) require fewer monitor units (MU) than larger PTVs. An equal to slightly superior target volume coverage and sparing of healthy tissue as well as organs at risk in both lung and liver lesions were found. Significant differences were seen mainly in the medium to lower dose range.

CONCLUSION

We found that FFF beams together with VMAT represent an excellent combination for SBRT of lung or liver lesions with shortest BOT for 10 MV-FFF but significant dose savings for 6 MV-FFF in lung lesions.

Dosimetric comparison of four-dimensional computed tomography based internal target volume against variations in respiratory motion during treatment between volumetric modulated arc therapy and three-dimensional conformal radiotherapy in lung stereotactic body radiotherapy

This study focused on the dosimetric impact of variations in respiratory motion during lung stereotactic body radiotherapy (SBRT). Dosimetric comparisons between volumetric modulated arc therapy (VMAT) and three-dimensional conformal radiotherapy (3DCRT) were performed using four-dimensional computed tomography (4DCT)-based internal target volumes (ITV). We created retrospective plans for ten patients with lung cancer who underwent SBRT using 3DCRT and VMAT techniques. A Delta4 Phantom + (ScandiDos, Uppsala, Sweden) was used to evaluate the dosimetric robustness of 4DCT-based ITV against variations in respiratory motion during treatment. We analyzed respiratory motion during treatment. Dose-volume histogram parameters were evaluated for the 95% dose (D95%) to the planning target volume (PTV) contoured on CT images obtained under free breathing. The correlations between patient respiratory parameters and dosimetric errors were also evaluated. In the phantom study, the average PTV D95% dose differences for all fractions were - 2.9 ± 4.4% (- 16.0 - 1.2%) and - 2.0 ± 2.8% (- 11.2 - 0.7%) for 3DCRT and VMAT, respectively. The average dose difference was < 3% for both 3DCRT and VMAT; however, in 5 out of 42 fractions in 3DCRT, the difference in PTV D95% was > 10%. Dosimetric errors were correlated with respiratory amplitude and velocity, and differences in respiratory amplitude between 4DCT and treatment days were the main factors causing dosimetric errors. The overall average dose error of the PTV D95% was small; however, both 3DCRT and VMAT cases exceeding 10% error were observed. Larger errors occurred with amplitude variation or baseline drift, indicating limited robustness of 4DCT-based ITV.

Toward an improved assessment of dose conformity in radiotherapy

BACKGROUND

Evaluation of dose conformity is important to ensure minimum dose to normal tissue and sufficient dose coverage of the planning target volume (PTV). The existing conformity indices depend on the PTV volume and do not differentiate between two different scenarios: overdosing normal tissue and underdosing PTV.

PURPOSE

In this study, we introduce a novel index to assess conformity of dose distributions in radiotherapy.

METHODS

The suggested conformity indexC I d e x p $C{I_{{d_{exp}}}}$ is defined by the ratio of the volume representing actual "non-conformity" of the planned dose and the volume representing acceptable "non-conformity." The latter volume is produced by expanding the PTV. If both the average distance (d ¯ $\overline d $ ) between the reference isodose surface and planning target volume and arbitrarily selected PTV expansion margin (d e x p ${d_{exp}}$ ) are much smaller than the size of the PTV,C I d e x p $C{I_{{d_{exp}}}}$ approximately equals the ratiod ¯ d e x p $\dfrac{{\bar d}}{{{d_{exp}}}}$ . In this work,C I d e x p $C{I_{{d_{exp}}}}$ was utilized to analyze 90 cases of brain metastases treated with stereotactic radiation therapy (SRS) and 102 cases of lung cancer treated with stereotactic body radiation therapy (SBRT).

RESULTS

Ford e x p ${d_{exp}}$  = 0.1 cm, all considered SRS treatment plans were characterized byC I d e x p < 1 $C{I_{{d_{exp}}}} < 1$ while 2 out of 102 SBRT plans hadC I d e x p > 1 $C{I_{{d_{exp}}}} > 1$ . The average values ofC I d e x p $C{I_{{d_{exp}}}}$ for SRS and SBRT plans were 0.31 and 0.43, respectively. Ford e x p ${d_{exp}}$  = 0.2 cm, all studied treatment plans hadC I d e x p < 1 $C{I_{{d_{exp}}}} < 1$ , and the average values ofC I d e x p $C{I_{{d_{exp}}}}$ for SRS and SBRT plans were 0.15 and 0.25, respectively.

CONCLUSIONS

The suggested conformity indexC I d e x p $C{I_{{d_{exp}}}}$ varies less with PTV volume than the RTOG and Riet-Paddick indices frequently used for evaluation of dose conformity. In addition,C I d e x p $C{I_{{d_{exp}}}}$ can be expressed as a sum of two terms which describe "over-coverage" and "under-coverage" of the treatment target. The results confirm thatC I d e x p $C{I_{{d_{exp}}}}$ can be used for evaluation of dose conformity in SRS and SBRT.

Stereotactic body radiotherapy in lung cancer: a contemporary review

The treatment of early stage non-small cell lung cancer (NSCLC) has improved enormously in the last two decades. Although surgery is not the only choice, lobectomy is still the gold standard treatment type for operable patients. For inoperable patients stereotactic body radiotherapy (SBRT) should be offered, reaching very high local control and overall survival rates. With SBRT we can precisely irradiate small, well-defined lesions with high doses. To select the appropriate fractionation schedule it is important to determine the size, localization and extent of the lung tumor. The introduction of novel and further developed planning (contouring guidelines, diagnostic image application, planning systems) and delivery techniques (motion management, image guided radiotherapy) led to lower rates of side effects and more conformal target volume coverage. The purpose of this study is to summarize the current developments, randomised studies, guidelines about lung SBRT, with emphasis on the possibility of increasing local control and overall rates in "fit," operable patients as well, so SBRT would be eligible in place of surgery.

Radiotherapy in the management of lung oligometastases

In recent years, the development of both medical imaging and new systemic agents (targeted therapy and immunotherapy) have revolutionized the field of oncology, leading to a new entity: oligometastatic disease. Adding local treatment of oligometastases to systemic treatment could lead to prolonged survival with no significant impact on quality of life. Given the high prevalence of lung oligometastases and the new systemic agents coming with increased pulmonary toxicity, this article provides a comprehensive review of the current state-of-art for radiotherapy of lung oligometastases. After reviewing pretreatment workup, the authors define several radiotherapy regimen based on the localization and size of the oligometastases. A comment on the synergistic combination of medical treatment and radiotherapy is also made, projecting on future steps in this specific clinical setting.

Pulmonary interstitial lymphography: A prospective trial with potential impact on stereotactic ablative radiotherapy planning for early-stage lung cancer

This prospective feasibility trial investigated pulmonary interstitial lymphography to identify thoracic primary nodal drainage (PND). A post-hoc analysis of nodal recurrences was compared with PND for patients with early-stage lung cancer; larger studies are needed to establish correlation. Exploratory PND-inclusive stereotactic ablative radiotherapy plans were assessed for dosimetric feasibility.

Optimizing Clinical Implementation of Hypofractionation: Comprehensive Evidence Synthesis and Practical Guidelines for Low- and Middle-Income Settings

The global cancer burden, especially in low- and middle-income countries (LMICs), worsens existing disparities, amplified by the rising costs of advanced treatments. The shortage of radiation therapy (RT) services is a significant issue in LMICs. Extended conventional treatment regimens pose significant challenges, especially in resource-limited settings. Hypofractionated radiotherapy (HRT) and ultra-hypofractionated/stereotactic body radiation therapy (SBRT) offer promising alternatives by shortening treatment durations. This approach optimizes the utilization of radiotherapy machines, making them more effective in meeting the growing demand for cancer care. Adopting HRT/SBRT holds significant potential, especially in LMICs. This review provides the latest clinical evidence and guideline recommendations for the application of HRT/SBRT in the treatment of breast, prostate, and lung cancers. It emphasizes the critical importance of rigorous training, technology, stringent quality assurance, and safety protocols to ensure precise and secure treatments. Additionally, it addresses practical considerations for implementing these treatments in LMICs, highlighting the need for comprehensive support and collaboration to enhance patient access to advanced cancer care.

Dosimetry and treatment efficiency of SBRT using TaiChiB radiotherapy system for two-lung lesions with one overlapping organs at risk

Purpose

This study aims to assess the dosimetry and treatment efficiency of TaiChiB-based Stereotactic Body Radiotherapy (SBRT) plans applying to treat two-lung lesions with one overlapping organs at risk.

Methods

For four retrospective patients diagnosed with two-lung lesions each patient, four treatment plans were designed including Plan Edge, TaiChiB linac-based, RGS-based, and a linac-RGS hybrid (Plan TCLinac, Plan TCRGS, and Plan TCHybrid). Dosimetric metrics and beam-on time were employed to evaluate and compare the TaiChiB-based plans against Plan Edge.

Results

For Conformity Index (CI), Plan TCRGS outperformed all other plans with an average CI of 1.06, as opposed to Plan Edge's 1.33. Similarly, for R50 %, Plan TCRGS was superior with an average R50 % of 3.79, better than Plan Edge's 4.28. In terms of D2 cm, Plan TCRGS also led with an average of 48.48%, compared to Plan Edge's 56.25%. For organ at risk (OAR) sparing, Plan TCRGS often displayed the lowest dosimetric values, notably for the spinal cord (Dmax 5.92 Gy) and lungs (D1500cc 1.00 Gy, D1000cc 2.61 Gy, V10 Gy 15.14%). However, its high Dmax values for the heart and great vessels sometimes exceeded safety thresholds. Plan TCHybrid presented a balanced approach, showing doses comparable to or better than Plan Edge without crossing safety limits. In terms of beam-on time, Plan TCLinac emerged as the most efficient treatment option in three out of four cases, followed closely by Plan Edge in one case. Plan TCRGS, despite its dosimetric advantages, was the least efficient, recording notably longer beam-on times, with a peak at 33.28 minutes in Case 2.

Conclusion

For patients with two-lung lesions treated by SBRT whose one lesion overlaps with OARs, the Plan TCHybrid delivered by TaiChiB digital radiotherapy system can be recommended as a clinical option.

Narrative Review: Cardiotoxicities and Cardiac-Sparing Techniques in Radiotherapy

This review article aims to synthesize existing data on radiation-induced heart diseases in patients undergoing chest radiation therapy and also explores cardiac-sparing techniques to mitigate cardiotoxic effects. We conducted a comprehensive database search to review and consolidate data regarding chest radiotherapy and effects on the heart as well as techniques to minimize exposure to the heart. The research findings demonstrate associations between radiation exposure to cardiac substructures and subsequent cardiotoxicity. This review also stresses the importance of identifying patients at high-risk for cardiotoxicity as well as advocates for the adoption of stringent cardiac dose constraints in these patients. Advanced cardiac-sparing techniques, notably respiratory motion management, have emerged as pivotal strategies to minimize the likelihood of cardiac events. This narrative review emphasizes the critical role of these innovations in optimizing cardiac health during radiation treatment.

What is the predictive value of RECIST criteria following stereotactic lung radiation?

PURPOSE

Response EvaluationCriteriain Solid Tumors (RECIST) is commonly used to assess response to anti-cancer therapies. However, its application after lung stereotactic ablative radiotherapy (SABR) is complicated by radiation-induced lung changes. This study assesses the frequency of progressive disease (PD) by RECIST following lung SABR and correlates this with actual treatment outcomes as determined by longitudinal follow-up.

METHODS AND MATERIALS

We reviewed patients treated with lung SABR for primary lung tumors or oligometastases between 2010 and 2015. Patients were treated with SABR doses of 54-60 Gy in 3-8 fractions. All follow-up scans were assessed and the treated lesion was serially measured over time, with the maximum diameter on axial CT slices used for RECIST calculations. Lesions demonstrating PD by RECIST criteria were identified and subsequently followed for long-term outcomes. The final 'gold-standard' assessment of response was based on size changes after PD and, as available, positron emission tomography scan and/or biopsy.

RESULTS

Eighty-eight lesions met inclusion criteria. Seventy-five were lung primaries and thirteen were lung metastases. Median follow-up was 52 months (interquartile range: 33-68). Two-thirds (66 %, 58/88) of treated lesions met RECIST criteria for PD; however, local recurrence was only confirmed in 16 % (9/58) of cases. Most lesions that triggered PD by RECIST (47/58, 81 %) were ultimately found not to represent recurrence, while a minority (2/58, 3 %) had an uncertain response. The positive predictive value [PPV] of a RECIST defined PD event was 0.16. If PD was triggered within 12-months post-treatment, PPV was 0.08, compared to 0.21 for lesions triggering PD after 12-months.

CONCLUSION

Using RECIST criteria, two-thirds of patients treated with lung SABR met criteria for PD. However, only a minority had recurrence, leading to a poor PPV of RECIST. This highlights the limitations of RECIST in this setting and provides context for physicians when interpreting post-lung SABR imaging.

Single-Fraction Stereotactic Ablative Body Radiotherapy for Primary and Extracranial Oligometastatic Cancers

Stereotactic ablative body radiotherapy (SABR) consists of delivering high doses of ionising radiation, typically across three to eight fractions with high precision and conformity. SABR has become increasingly commonplace throughout the last quarter of a century and is offered for the treatment of various primary and metastatic tumour types. Delivering SABR in a single fraction has arisen as an appealing possibility for several reasons. These include fewer hospital visits, greater patient convenience, improved sustainability and lower costs. However, these factors must be balanced against considerations such as toxicity, side-effects and, most importantly, progression-free and overall survival. In this review we seek to analyse the results of studies looking at the efficacy of single-fraction SABR for lung, prostate, renal and pancreas primary tumours, as well as oligometastases. The tumour type to be most widely treated with single-fraction SABR is lung, but its remit continues to expand. We also look at the biological rationale underpinning SABR and how this can be extended to single-fraction regimens. Finally, we turn our attention towards the future directions of SABR and specifically single-fraction regimens. These include the possibility of combining SABR with immunotherapy and technological advances in the field, which could serve to expand the scope of SABR. We conclude by summarising the current clinical studies of single-fraction SABR.

Long-Term Survival and Failure Outcomes of Single-Fraction Stereotactic Body Radiation Therapy in Early Stage NSCLC

INTRODUCTION

This study aims to report our 13-year institutional experience with single-fraction stereotactic body radiation therapy (SF-SBRT) for early stage NSCLC.

METHODS

A single-institutional retrospective review of patients with biopsy-proven peripheral cT1-2N0M0 NSCLC undergoing definitive SF-SBRT between September 2008 and May 2022 was performed. All patients were treated to 27 Gy with heterogeneity corrections or 30 Gy without. Primary outcomes were overall survival and progression-free survival. Secondary outcomes included local failure, nodal failure, distant failure, and second primary lung cancer.

RESULTS

Among 263 eligible patients, the median age was 76 years (interquartile range [IQR]: 70-81 y) and median follow-up time was 27.2 months (IQR: 14.25-44.9 mo). Median tumor size was 1.9 cm (IQR: 1.4-2.6 cm), and 224 (85%) tumors were T1. There were 92 patients (35%) alive at the time of analysis with a median follow-up of 34.0 months (IQR: 16.6-50.0 mo). Two- and five-year overall survival was 65% and 26%, respectively. A total of 74 patients (28%) developed disease progression. Rates of five-year local failure, nodal failure, distant failure, and second primary lung cancer were 12.7%, 14.7%, 23.5%, and 12.0%, respectively.

CONCLUSIONS

Consistent with multiple prospective randomized trials, in a large real-world retrospective cohort, SF-SBRT for peripheral early stage NSCLC was an effective treatment approach.

Automated treatment planning for liver cancer stereotactic body radiotherapy

PURPOSE

To evaluate the quality of fully automated stereotactic body radiation therapy (SBRT) planning based on volumetric modulated arc therapy, which can reduce the reliance on historical plans and the experience of dosimetrists.

METHODS

Fully automated re-planning was performed on twenty liver cancer patients, automated plans based on automated SBRT planning (ASP) program and manual plans were conducted and compared. One patient was randomly selected and evaluate the repeatability of ASP, ten automated and ten manual SBRT plans were generated based on the same initial optimization objectives. Then, ten SBRT plans were generated for another selected randomly patient with different initial optimization objectives to assess the reproducibility. All plans were clinically evaluated in a double-blinded manner by five experienced radiation oncologists.

RESULTS

Fully automated plans provided similar planning target volume dose coverage and statistically better organ at risk sparing compared to the manual plans. Notably, automated plans achieved significant dose reduction in spinal cord, stomach, kidney, duodenum, and colon, with a median dose of D2% reduction ranging from 0.64 to 2.85 Gy. R50% and Dmean of ten rings for automated plans were significantly lower than those of manual plans. The average planning time for automated and manual plans was 59.8 ± 7.9 min vs. 127.1 ± 16.8 min (- 67.3 min).

CONCLUSION

Automated planning for SBRT, without relying on historical data, can generate comparable or even better plan quality for liver cancer compared with manual planning, along with better reproducibility, and less clinically planning time.

Extracting the gradient component of the gamma index using the Lie derivative method

Objective. The gamma index (γ) has been extensively investigated in the medical physics and applied in clinical practice. However,γhas a significant limitation when used to evaluate the dose-gradient region, leading to inconveniences, particularly in stereotactic radiotherapy (SRT). This study proposes a novel evaluation method combined withγto extract clinically problematic dose-gradient regions caused by irradiation including certain errors.Approach. A flow-vector field in the dose distribution is obtained when the dose is considered a scalar potential. Using the Lie derivative from differential geometry, we definedL,S, andUto evaluate the intensity, vorticity, and flow amount of deviation between two dose distributions, respectively. These metrics multiplied byγ(γL,γS,γU), along with the threshold valueσ, were verified in the ideal SRT case and in a clinical case of irradiation near the brainstem region using radiochromic films. Moreover, Moran's gradient index (MGI), Bakai's χ factor, and the structural similarity index (SSIM) were investigated for comparisons.Main results. A highL-metric value mainly extracted high-dose-gradient induced deviations, which was supported by highSandUmetrics observed as a robust deviation and an influence of the dose-gradient, respectively. TheS-metric also denotes the measured similarity between the compared dose distributions. In theγdistribution,γLsensitively detected the dose-gradient region in the film measurement, despite the presence of noise. The thresholdσsuccessfully extracted the gradient-error region whereγ> 1 analysis underestimated, andσ= 0.1 (plan) andσ= 0.001 (film measurement) were obtained according to the compared resolutions. However, the MGI, χ, and SSIM failed to detect the clinically interested region.Significance. Although further studies are required to clarify the error details, this study demonstrated that the Lie derivative method provided a novel perspective for the identifying gradient-induced error regions and enabled enhanced and clinically significant evaluations ofγ.

An optimal dose-fractionation for stereotactic body radiotherapy in peripherally, centrally and ultracentrally located early-stage non-small lung cancer

Stereotactic body radiotherapy (SBRT), also known as stereotactic ablative radiotherapy (SABR), is commonly used in inoperable patients with early-stage non-small lung cancer (NSCLC). This treatment has good outcomes and low toxicity in peripherally located tumors. However, in lesions which are located close to structures such as the bronchial tree or mediastinum the risk of severe toxicity increases. This review summarizes the evidence of dose-fractionation in SBRT of NSCLC patients in various locations.

Overcoming Problems Caused by Offset Distance of Multiple Targets in Single-isocenter Volumetric Modulated Arc Therapy Planning for Stereotactic Radiosurgery

Purpose

The purpose of the study is to investigate the impact of large target offset distances on the dose distribution and gamma passing rate (GPR) in single-isocenter multiple-target stereotactic radiosurgery (SIMT SRS) using volumetric modulated arc therapy (VMAT) with a flattening filter-free (FFF) beam from a linear accelerator.

Methods

Two targets with a diameter of 1 cm were offset by "±2, ±4, and ±6 cm from the isocenter in a verification phantom for head SRS (20 Gy/fr). The VMAT plans were created using collimator angles that ensured the two targets did not share a leaf pair from the multi-leaf collimator. To evaluate the low-dose spread intermediate dose spill (R50%), GPRs were measured with a criterion of 3%/2 mm using an electronic portal imaging device and evaluated using monitor unit (MU), modulation complexity score for VMAT (MCSv), and leaf travel (LT) parameters.

Results

For offsets of 2, 4, and 6 cm, the respective parameters were: R50%, 4.75 ± 0.36, 5.13 ± 0.36, and 5.11 ± 0.33; GPR, 95.01%, 93.82%, and 90.67%; MU, 5893 ± 186, 5825 ± 286, and 5810 ± 396; MCSv, 0.24, 0.16, and 0.13; and LT, 189.21 ± 36.04, 327.69 ± 67.01, and 430.39 ± 114.34 mm. There was a spread in the low-dose region from offsets of ≥4 cm and the GPR negatively correlated with LT (r = -0.762). There was minimal correlation between GPR and MU or MCSv.

Conclusions

In SIMT SRS VMAT plans with an FFF beam from a linear accelerator, target offsets of <4 cm from the isocenter can minimize the volume of the low-dose region receiving 10 Gy or more. During treatment planning, it is important to choose gantry, couch, and collimator angles that minimize LT and thereby improve the GPR.

Local control and toxicity after magnetic resonance imaging (MR)-guided single fraction lung stereotactic ablative radiotherapy

PURPOSE

Magnetic resonance imaging (MR)-guided radiotherapy permits continuous intrafraction visualization and use of automatic triggered beam delivery, with use of smaller planning target volumes (PTV). We report on long-term clinical outcomes following MR-guided single fraction (SF) lung SABR on a 0.35 T linac.

MATERIALS AND METHODS

Details of patients treated with SF-SABR for lung tumors were accessed from an ethics approved institutional database. A breath-hold 3D MR simulation scan was performed using a true FISP sequence, followed by a breath-hold 3D CT scan. The gross tumor volume (GTV) was first contoured on the breath-hold CT scan, which was then compared with contours on the 3D MR scan, before the GTV was finalized. SABR plans used step-and-shoot IMRT beams to a PTV derived by adding a 5 mm margin to the breath-hold GTV, and a 3 mm gating window was used. SABR was delivered during repeated breath-holds, using automatic beam gating with continuous visualization of the GTV in a sagittal MR plane.

RESULTS

Between 2018-2022, 50 consecutive patients were treated, and 69% had a primary non-small cell lung cancer. Median PTV was 11.2 cc (range 3.9-53.5); 80% of GTV's were located ≤2.5 cm from the chest wall. Prescribed doses were 34 Gy (in 58%), 30 Gy (32%), or between 20-28 Gy (10%). After a median follow-up of 18.1 months (95% CI 12.8-23.5), the 2-year survival was 82% (89% for primary NSCLC and 62% for metastases). After a median follow-up of 16.1 months (95% CI 11.2-21.1), local recurrences developed in 2 patients (4%). The 3-year local control rate was 97%, and just 1 patient developed grade ≥3 toxicity (chest wall pain).

CONCLUSION

MR-guided SF-SABR delivery to lung tumors on a 0.35 T linac, using repeated breath-holds with automatic beam gating, achieves good tumor control and low toxicity.

Dosimetric performance evaluation of the Halcyon treatment platform for stereotactic radiotherapy: A pooled study

With the advancement of radiotherapy equipment, stereotactic radiotherapy (SRT) has been increasingly used. Among the many radiotherapy devices, Halcyon shows promising applications. This article reviews the dosimetric performance such as plan quality, plan complexity, and gamma passing rates of SRT plans with Halcyon to determine the effectiveness and safety of Halcyon SRT plans. This article retrieved the last 5 years of PubMed studies on the effectiveness and safety of the Halcyon SRT plans. Two authors independently reviewed the titles and abstracts to decide whether to include the studies. A search was conducted to identify publications relevant to evaluating the dosimetric performance of SRT plans on Halcyon using the key strings Halcyon, stereotactic radiosurgery, SRT, stereotactic body radiotherapy, and stereotactic ablative radiotherapy. A total of 18 eligible publications were retrieved. Compared to SRT plans on the TrueBeam, the Halcyon has advantages in terms of plan quality, plan complexity, and gamma passing rates. The high treatment speed of SRT plans on the Halcyon is impressive, while the results of its plan evaluation are also encouraging. As a result, Halcyon offers a new option for busy radiotherapy units while significantly improving patient comfort in treatment. For more accurate results, additional relevant publications will need to be followed up in subsequent studies.

Local control and survival after stereotactic body radiation therapy of early-stage lung cancer patients in Slovenia

BACKGROUND

Stereotactic body radiation therapy (SBRT) precisely and non-invasively delivers ablative radiation dose to tumors in early-stage lung cancer patients who are not candidates for surgery or refuse it. The aim of research was to evaluate local control, overall survival (OS), local progression free survival (LPFS), distant metastases free survival (DMFS), disease free survival (DFS) and toxicity in early-stage lung cancer patients treated with SBRT in a single tertiary cancer centre.

PATIENTS AND METHODS

We retrospectively evaluated medical records and radiation treatment plan parameters of 228 tumors irradiated in 206 early-stage lung cancer patients between 2016 and 2021 at the Institute of Oncology Ljubljana.

RESULTS

After 25 months of median follow up, 68 of 206 (33%) patients died. Median OS was 46 months (CI 36-56), 1-year, 2-year and 3-year OS were 87%, 74% and 62% and 5-year OS was 31%. A total of 45 disease progressions have been identified in 41 patients. Local progress only was noticed in 5 (2%) patients, systemic progress in 32 (16%) and combined systemic and local in 4 (2%) patients. Local control rate (LCR) at 1 year was 98%, at 2 and 3 years 96% and 95% at 5 years. The 1-, 2- and 3-year LPFS were 98%, 96% and 94%, respectively and 5-year LPFS was 82%. One, 2-, 3- and 5-year DFS were 89%, 81%, 72% and 49%, respectively. Among 28 toxicities recorded only one was Grade 4 (pneumonitis), all others were Grade 1 or 2. No differences in LCR, LPFS, DFS were found in univariate analysis comparing patient, tumor, and treatment characteristics. For OS the only statistically significant difference was found in patients with more than 3 comorbidities compared to those with less comorbidities.

CONCLUSIONS

Early lung cancer treated with SBRT at single tertiary cancer centre showed that LCR, LPFS, DFS, DMFS and OS were comparable to published studies. Patients with many comorbidities had significantly worse overall survival compared to those with less comorbidities. No other significant differences by patient, tumor, or treatment characteristics were found for DMFS, LPFS, and DFS. Toxicity data confirmed that treatment was well tolerated.

Consensus Quality Measures and Dose Constraints for Lung Cancer From the Veterans Affairs Radiation Oncology Quality Surveillance Program and ASTRO Expert Panel

PURPOSE

For patients with lung cancer, it is critical to provide evidence-based radiation therapy to ensure high-quality care. The US Department of Veterans Affairs (VA) National Radiation Oncology Program partnered with the American Society for Radiation Oncology (ASTRO) as part of the VA Radiation Oncology Quality Surveillance to develop lung cancer quality metrics and assess quality of care as a pilot program in 2016. This article presents recently updated consensus quality measures and dose-volume histogram (DVH) constraints.

METHODS AND MATERIALS

A series of measures and performance standards were reviewed and developed by a Blue-Ribbon Panel of lung cancer experts in conjunction with ASTRO in 2022. As part of this initiative, quality, surveillance, and aspirational metrics were developed for (1) initial consultation and workup; (2) simulation, treatment planning, and treatment delivery; and (3) follow-up. The DVH metrics for target and organ-at-risk treatment planning dose constraints were also reviewed and defined.

RESULTS

Altogether, a total of 19 lung cancer quality metrics were developed. There were 121 DVH constraints developed for various fractionation regimens, including ultrahypofractionated (1, 3, 4, or 5 fractions), hypofractionated (10 and 15 fractionations), and conventional fractionation (30-35 fractions).

CONCLUSIONS

The devised measures will be implemented for quality surveillance for veterans both inside and outside of the VA system and will provide a resource for lung cancer-specific quality metrics. The recommended DVH constraints serve as a unique, comprehensive resource for evidence- and expert consensus-based constraints across multiple fractionation schemas.

[Limits of dose constraint definition for organs at risk specific to stereotactic radiotherapy]

Stereotactic radiotherapy is a very hypofractionated radiotherapy (>7.5Gy per fraction), and therefore is more likely to induce late toxicities than conventional normofractionated irradiations. The present study examines four frequent and potentially serious late toxicities: brain radionecrosis, radiation pneumonitis, radiation myelitis, and radiation-induced pelvic toxicities. The critical review focuses on the toxicity scales, the definition of the dose constrained volume, the dosimetric parameters, and the non-dosimetric risk factors. The most commonly used toxicity scales remain: RTOG/EORTC or common terminology criteria for adverse events (CTCAE). The definition of organ-at-risk volume requiring protection is often controversial, which limits the comparability of studies and the possibility of accurate dose constraints. Nevertheless, for the brain, whatever the indication (arteriovenous malformation, benign tumor, metastasis of solid tumors...), the association between the volume of brain receiving 12Gy (V12Gy) and the risk of cerebral radionecrosis is well established for both single and multi-fraction stereotactic irradiation. For the lung, the average dose received by both lungs and the V20 seem to correlate well with the risk of radiation-induced pneumonitis. For the spinal cord, the maximum dose is the most consensual parameter. Clinical trial protocols are useful for nonconsensual dose constraints. Non-dosimetric risk factors should be considered when validating the treatment plan.

Assessing the impact of intrafraction motion correction on PTV margins and target and OAR dosimetry for single-fraction free-breathing lung stereotactic body radiation therapy

The objective of this research is to investigate intrafraction motion correction on planning target volume (PTV) margin requirements and target and organ-at-risk (OAR) dosimetry in single-fraction lung stereotactic body radiation therapy (SBRT). Sixteen patients (15 with upper lobe lesions, 1 with a middle lobe lesion) were treated with single-fraction lung SBRT. Cone-beam computed tomography (CBCT) images were acquired before the treatment, between the arcs, and after the delivery of the treatment fraction. Shifts from the reference images were recorded in anterior-posterior (AP), superior-inferior (SI), and lateral (LAT) dimensions. The deviations from the reference image were calculated for 3 clinical scenarios: not applying intratreatment couch shifts and not correcting for pretreatment deviations < 3 mm ( scenario 1), not applying intratreatment couch shifts and correcting for pretreatment deviations < 3 mm ( scenario 2), and applying all pre- and intratreatment couch shifts (scenario 3). PTV margins were determined using the van Herk formalism for each scenario and maximum and average deviations were assessed. The clinical scenarios were modelled in the treatment planning system based on each patient dataset to assess target and OAR dosimetry. Calculated lower-bound PTV margins in the AP, SI, and LAT dimensions were [4.6, 3.5, 2.3] mm in scenario 1, [4.6, 2.4, 2.2] mm in scenario 2, and [1.7, 1.2, 1.0] mm in scenario 3. The margins are lower bounds because they do not include contributions from nonmotion related errors. Average and maximum intrafraction deviations were larger in the AP dimension compared to the SI and LAT dimensions for all scenarios. A unidimensional movement (several mm) in the negative AP dimension was observed in clinical scenarios 1 and 2 but not scenario 3. Average intrafraction deviation vectors were 1.2, 1.1, and 0.3 mm for scenarios 1, 2, and 3, respectively. Modelled clinical scenarios revealed that using scenario 3 yields significantly fewer treatment plan objective failures compared to scenarios 1 and 2 using a Wilcoxon signed-rank test. Intratreatment motion correction between each arc may enable reductions PTV margin requirements. It may also compensate for unidimensional negative AP movement, and improve target and OAR dosimetry.

Cleaning the dose falloff with low modulation in SBRT lung plans

Purpose.This dosimetric study is intended to lower the modulation factor in lung SBRT plans generated in the Eclipse TPS that could replace highly modulated plans that are prone to the interplay effect.Materials and methods.Twenty clinical lung SBRT plans with high modulation factors (≥4) were replanned in Varian Eclipse TPS version 15.5 utilizing 2 mm craniocaudal and 1 mm axial block margins followed by light optimization in order to reduce modulation. A unique plan optimization methodology, which utilizes a novel shell structure (OptiForR₅₀) for R_50%optimization in addition to five consecutive concentric 5 mm shells, was utilized to control dose falloff according to RTOG 0813 and 0915 recommendations. The prescription varied from 34-54 Gy in 1-4 fractions, and the dose objectives were PTV D_95%= Rx, PTV D_max< 140% of Rx, and minimizing the modulation factor. Plan evaluation metrics included modulation factor, CI_RTOG, homogeneity index (HI), R_50%, D_2cm, V_105%, and lung V_8-12.8Gy(Timmerman Constraint). A random-intercept linear mixed effects model was used with a p ≤ 0.05 threshold to test for statistical significance.Results.The retrospectively generated plans had significantly lower modulation factors (3.65 ± 0.35 versus 4.59 ± 0.54; p < 0.001), lower CI_RTOG(0.97 ± 0.02 versus 1.02 ± 0.06; p = 0.001), higher HI (1.35 ± 0.06 versus 1.14 ± 0.04; p < 0.001), lower R_50%(4.09 ± 0.45 versus 4.56 ± 0.56; p < 0.001), and lower lungs V_8-12.8Gy(Timmerman) (4.61% ± 3.18% versus 4.92% ± 3.37%; p < 0.001). The high dose spillage V_105%was borderline significantly lower (0.44% ± 0.49% versus 1.10% ± 1.64%; p = 0.051). The D_2cmwas not statistically different (46.06% ± 4.01% versus 46.19% ± 2.80%; p = 0.835).Conclusion.Lung SBRT plans with significantly lower modulation factors can be generated that meet the RTOG constraints, using our planning strategy.