Dosimetric evaluation of 4 different treatment modalities for curative-intent stereotactic body radiation therapy for isolated thoracic spinal metastases

Time Dependence of Intra-fractional Motion in Spinal Stereotactic Body Radiotherapy

BACKGROUND/AIM

Positional uncertainty in spinal stereotactic body radiotherapy (SBRT) may cause fatal error, therefore, we investigated the intra-fractional spinal motion during SBRT and its time dependency.

PATIENTS AND METHODS

Thirty-one patients who received SBRT using CyberKnife were enrolled in the study. 2D kV X-ray spine images in two directions were taken before and during treatment. Image acquisition intervals during treatment were set at 35-60 sec. Automatic image matchings were performed between the reference digital reconstructed radiography (DRR) and live images, and the spinal position displacements were logged in six translational and rotational directions. If the displacements exceeded 2 mm or 1 degree, the treatment beam delivery was interrupted and the patient position was corrected by moving couch, and the couch adjustments were also logged. Based on the information, the time-dependent accumulated translational and rotational displacements without any couch adjustments were calculated.

RESULTS

Spinal position displacements in all translational and rotational directions were correlated with elapsed treatment time. Especially, Right-Left displacements of >1 mm and >2 mm were observed at 4-6 and 8-10 min after treatment initiation, respectively. Rotational displacements in the Yaw direction >1° were observed at 10-15 min after treatment initiation.

CONCLUSION

The translational and rotational displacements systematically increased with elapsed treatment time. It is suggested that the spine position should be checked at least every 4-6 min or the treatment time should be limited within 4-6 minutes to ensure the irradiation accuracy within the millimeter or submillimeter range.

Dosimetric study for spine stereotactic body radiation therapy: magnetic resonance guided linear accelerator versus volumetric modulated arc therapy

Background Stereotactic body radiation therapy (SBRT) given in 1-5 fractions is an effective treatment for vertebral metastases. Real-time magnetic resonance-guided radiotherapy (MRgRT) improves soft tissue contrast, which translates into accurate delivery of spine SBRT. Here we report on clinical implementation of MRgRT for spine SBRT, the quality of MRgRT plans compared to TrueBeam based volumetric modulated arc therapy (VMAT) plans in the treatment of spine metastases and benefits of MRgRT MR scan. Patients and methods Ten metastatic lesions were included in this study for plan comparison. Lesions were spread across thoracic spine and lumbosacral spine. Three fraction spine SBRT plans: 27Gy to planning target volume (PTV) and 30Gy to gross tumor volume (GTV) were generated on the ViewRay MRIdian Linac system and compared to TrueBeamTM STx based VMAT plans. Plans were compared using metrics such as minimum dose, maximum dose, mean dose, ratio of the dose to 50% of the volume (R50), conformity index, homogeneity index and dose to the spinal cord. Results MRIdian plans achieved equivalent target coverage and spinal cord dose compared to VMAT plans. The maximum and minimum PTV doses and homogeneity index were equivalent for both planning systems. R50 was lower for MRIdian plans compared to VMAT plans, indicating a lower spread of intermediate doses with MRIdian system (5.16 vs. 6.11, p = 0.03). Conclusions MRgRT can deliver high-quality spine SBRT plans comparable to TrueBeam volumetric modulated arc therapy (VMAT) plans.

SBRT planning for spinal metastasis: indications from a large multicentric study

BACKGROUND

The dosimetric variability in spine stereotactic body radiation therapy (SBRT) planning was investigated in a large number of centres to identify crowd knowledge-based solutions.

METHODS

Two spinal cases were planned by 48 planners (38 centres). The required prescription dose (PD) was 3 × 10 Gy and the planning target volume (PTV) coverage request was: V_PD > 90% (minimum request: V_PD > 80%). The dose constraints were: planning risk volume (PRV) spinal cord: V_18Gy < 0.35 cm³, V_{21.9 Gy} < 0.03 cm³; oesophagus: V_{17.7 Gy} < 5 cm³, V_{25.2 Gy} < 0.03 cm³. Planners who did not fulfil the protocol requirements were asked to re-optimize the plans, using the results of planners with the same technology. Statistical analysis was performed to assess correlations between dosimetric results and planning parameters. A quality index (QI) was defined for scoring plans.

RESULTS

In all, 12.5% of plans did not meet the protocol requirements. After re-optimization, 98% of plans fulfilled the constraints, showing the positive impact of knowledge sharing. Statistical analysis showed a significant correlation (p < 0.05) between the homogeneity index (HI) and PTV coverage for both cases, while the correlation between HI and spinal cord sparing was significant only for the single dorsal PTV case. Moreover, the multileaf collimator leaf thickness correlated with the spinal cord sparing. Planners using comparable delivery/planning system techniques produced different QI, highlighting the impact of the planner's skills in the optimization process.

CONCLUSION

Both the technology and the planner's skills are fundamentally important in spine SBRT planning optimization. Knowledge sharing helped to follow the plan objectives.

Treatment planning for spinal radiosurgery : A competitive multiplatform benchmark challenge

PURPOSE

To investigate the quality of treatment plans of spinal radiosurgery derived from different planning and delivery systems. The comparisons include robotic delivery and intensity modulated arc therapy (IMAT) approaches. Multiple centers with equal systems were used to reduce a bias based on individual's planning abilities. The study used a series of three complex spine lesions to maximize the difference in plan quality among the various approaches.

METHODS

Internationally recognized experts in the field of treatment planning and spinal radiosurgery from 12 centers with various treatment planning systems participated. For a complex spinal lesion, the results were compared against a previously published benchmark plan derived for CyberKnife radiosurgery (CKRS) using circular cones only. For two additional cases, one with multiple small lesions infiltrating three vertebrae and a single vertebra lesion treated with integrated boost, the results were compared against a benchmark plan generated using a best practice guideline for CKRS. All plans were rated based on a previously established ranking system.

RESULTS

All 12 centers could reach equality (n = 4) or outperform (n = 8) the benchmark plan. For the multiple lesions and the single vertebra lesion plan only 5 and 3 of the 12 centers, respectively, reached equality or outperformed the best practice benchmark plan. However, the absolute differences in target and critical structure dosimetry were small and strongly planner-dependent rather than system-dependent. Overall, gantry-based IMAT with simple planning techniques (two coplanar arcs) produced faster treatments and significantly outperformed static gantry intensity modulated radiation therapy (IMRT) and multileaf collimator (MLC) or non-MLC CKRS treatment plan quality regardless of the system (mean rank out of 4 was 1.2 vs. 3.1, p = 0.002).

CONCLUSIONS

High plan quality for complex spinal radiosurgery was achieved among all systems and all participating centers in this planning challenge. This study concludes that simple IMAT techniques can generate significantly better plan quality compared to previous established CKRS benchmarks.

In silico assessment of the dosimetric quality of a novel, automated radiation treatment planning strategy for linac-based radiosurgery of multiple brain metastases and a comparison with robotic methods

Background

To appraise the dosimetric features and the quality of the treatment plan for radiosurgery of multiple brain metastases optimized with a novel automated engine and to compare with plans optimized for robotic-based delivery.

Methods

A set of 15 patients with multiple brain metastases was selected for this in silico study. The technique under investigation is the recently introduced HyperArc. For all patients, three treatment plans were computed and compared: i: a HyperArc; ii: a standard VMAT; iii) a CyberKnife. Dosimetric features were computed for the clinical target volumes as well as for the healthy brain tissue and the organs at risk.

Results

The data showed that the best dose homogeneity was achieved with the VMAT technique. HyperArc allowed to minimize the volume of brain receiving 4Gy (as well as for the mean dose and the volume receiving 12Gy, although not statistically significant). The smallest dose on 1 cm³ volume for all organs at risk is for CK techniques, and the biggest for VMAT (p < 0.05). The Radiation Planning Index coefficient indicates that, there are no significant differences among the techniques investigated, suggesting an equivalence among these.

Conclusion

At treatment planning level, the study demonstrates that the use of HyperArc technique can significantly improve the sparing of the healthy brain while maintaining a full coverage of the target volumes.

Treatment plan quality and delivery accuracy assessments on 3 IMRT delivery methods of stereotactic body radiotherapy for spine tumors

Stereotactic body radiotherapy (SBRT) for spine tumors has demonstrated clinical effectiveness. The treatment planning and delivery techniques have evolved from dynamic conformal arc therapy, to fixed gantry angle intensity modulated radiotherapy (IMRT), and most recently to volumetric modulated arc therapy (VMAT). A hybrid-arc (HARC) planning and delivery method combining dynamic conformal arc therapy delivery with a number of equally spaced IMRT beams is proposed. In this study we investigated plan quality, delivery accuracy, and efficiency of 3 delivery techniques: IMRT, HARC, and VMAT. Patients who underwent spine SBRT treatments were randomly selected from an Institutional Review Board-approved registry. For each patient, the prescription dose was 14 to 16 Gy in a single fraction to cover >90% of the tumor (without planning margin) while constraining V_10Gy ≤ 10% of the spinal cord and the maximum point dose (MPD) of the spinal cord ≤ 14 Gy. All cases were clinically treated with fixed gantry step-shoot IMRT plans and then re-planned with VMAT using Pinnacle 9.0 and with HARC using Brainlab iPlan 4.5. Student t-test was used to compare the dosimetric end points, including V_16Gy to the planning target volume, homogeneity index, MPD_PTV, the conformity index, V_10Gy of the spinal cord, and MPD_cord. To compare the accuracy of delivery, we delivered all plans on a phantom and conducted gamma index (GI) comparisons with 3 mm/3% and 2 mm/2% criteria. All plans met our clinical requirements. Among 3 techniques, there were no differences on dose coverage to the tumor volume, maximum dose to the spinal cord, and plan homogeneity index (p > 0.05). The average V_10Gy of the spinal cord was 6.66 ± 0.03%, 5.49 ± 0.03%, and 4.76 ± 0.02% for IMRT, HARC, and VMAT plans, respectively. Accordingly, the conformity indices were 1.30 ± 0.11 and 1.29 ± 0.20, 1.53 ± 0.29, respectively. VMAT plans were significantly (p < 0.05) less conformal but significantly (p < 0.05) lower V_10Gy of the spinal cord than those from HARC and IMRT plans. With delivery accuracy measured by GIs, the average GIs of 3%/3 mm were 92.6 ± 1.1%, 96.5 ± 2.7%, 99.0 ± 1.1% for IMRT, HARC, and VMAT plans, respectively. The differences were significant (p < 0.05). Accordingly, the average monitor units were 9238 ± 2242, 9853 ± 2548 and 5091 ± 910. The plan quality created from the 3 planning techniques can meet the clinical requirement. Adding arc beams in delivery such as in HARC and VMAT plans improves the delivery accuracy. VMAT is the most efficient delivery method.

Comparison of four techniques for spine stereotactic body radiotherapy: Dosimetric and efficiency analysis

PURPOSE

The aim of this study is to compare the dosimetric differences between four techniques for spine stereotactic body radiotherapy (SBRT): CyberKnife (CK), volumetric modulated arc therapy (VMAT), and helical tomotherapy (HT) with dynamic jaws (HT-D) and fixed jaws (HT-F).

MATERIALS/METHODS

Data from 10 patients were utilized. All patients were planned for 24 Gy in two fractions, with the primary objectives being: (a) restricting the maximum dose to the cord to ≤ 17 Gy and/or cauda equina to ≤ 20 Gy, and (b) to maximize the clinical target volume (CTV) to receive the prescribed dose. Treatment plans were generated by separate dosimetrists and then compared using velocity AI. Parameters of comparison include target volume coverage, conformity index (CI), gradient index (GI), homogeneity index (HI), treatment time (TT) per fraction, and monitor units (MU) per fraction.

RESULTS

PTV D2 and D5 were significantly higher for CK compared to VMAT, HT-F, and HT-D (P < 0.001). The average volume of CTV receiving the prescription dose (CTV D95) was significantly less for VMAT compared to CK, HT-F and HT-D (P = 0.036). CI improved for CK (0.69), HT-F (0.66), and HT-D (0.67) compared to VMAT (0.52) (P = 0.013). CK (41.86) had the largest HI compared to VMAT (26.99), HT-F (20.69), and HT-D (21.17) (P < 0.001). GI was significantly less for CK (3.96) compared to VMAT (6.76) (P = 0.001). Likewise, CK (62.4 min, 14059 MU) had the longest treatment time and MU per fraction compared to VMAT (8.5 min, 9764 MU), HT-F (13 min, 10822 MU), and HT-D (13.5 min, 11418 MU) (P < 0.001).

CONCLUSION

Both CK and HT plans achieved conformal target coverage while respecting cord tolerance. Dose heterogeneity was significantly larger in CK. VMAT required the least treatment time and MU output, but had the least steep GI, CI, and target coverage.

Spinal Metastatic Disease: A Review of the Role of the Multidisciplinary Team

Historically, a simple approach centered on palliation was applicable to the majority of patients with metastatic spinal disease. With advances in diagnosis and treatment, a more complicated algorithm has devolved requiring a multidisciplinary approach with institutional commitment and support. We performed a database review including pertinent articles exploring the multidisciplinary management of spinal metastatic disease. The wide variation in clinical presentation and tumor response to treatment necessitates a multidisciplinary approach that integrates the diagnosis and treatment of the cancer, symptom management, and rehabilitation for optimal care of patients with spinal metastases. Advances in the field of radiology have led to earlier and more focused diagnosis of spinal metastasis and acts to guide therapy. Advances in surgical techniques, neurophysiologic monitoring, and anesthetic expertise have allowed surgeons to perform more extensive procedures leading to improved outcomes and reduced morbidity. Radiation oncology input that is essential as external beam radiation therapy can provide significant pain relief. Non-operative measures may include bisphosphonate infusions, management of complications (e.g. hypercalcemia of malignancy), monoclonal antibody infusions, and chemotherapy if indicated in the treatment of the primary malignancy. Input from psychology services is necessary to address the biopsychosocial ramifications of spinal metastasis. Allied health professionals in the form of physiotherapists, social workers, and dieticians also contribute in maximizing patients' quality of life and well-being.