Premature Termination of a Randomized Controlled Trial on Image-Guided Stereotactic Body Radiotherapy of Metastatic Spinal Cord Compression

LESSONS LEARNED

It is possible to plan and treat some patients with stereotactic body radiotherapy (SBRT) in a timely fashion in an acute setting. Advanced and, in some indications, already implemented technologies such as SBRT are difficult to test in a randomized trial.

BACKGROUND

Stereotactic body radiotherapy (SBRT) in metastatic spinal cord compression (MSCC) could be an alternative to decompressive surgery followed by fractionated radiotherapy.

METHODS

In a randomized, single-institution, noninferiority trial, patients with MSCC were assigned to stereotactic body radiotherapy of 16 Gy in 1 fraction or decompression surgery followed by fractionated radiotherapy of 30 Gy in 10 fractions. Primary endpoint was ability to walk by EQ5D-5L questionnaire. Based on power calculations, 130 patients had to be included to be 89% sure that a 15% difference between the treatment arm and the experimental arm could be detected.

RESULTS

Ten patients were accrued in 23 months, with six patients allocated to surgery and four patients to stereotactic body radiotherapy. The trial was closed prematurely because of poor accrual. One patient undergoing surgery and one patient undergoing stereotactic body radiotherapy were unable to walk at 6 weeks. Two patients were not evaluable at 6 weeks.

CONCLUSION

A randomized, phase II, clinical trial comparing surgery followed by fractionated radiotherapy or image-guided SBRT of MSCC was initiated. SBRT was shown to be feasible, with three out of four patients retaining walking function. The trial was determined futile as a result of low accrual.

Image-guided radiotherapy reduces the risk of under-dosing high-risk prostate cancer extra-capsular disease and improves biochemical control

BACKGROUND

To determine if reduced dose delivery uncertainty is associated with daily image-guidance (IG) and Prostate Specific Antigen Relapse Free Survival (PRFS) in intensity-modulated radiotherapy (IMRT) of high-risk prostate cancer (PCa).

METHODS

Planning data for consecutive PCa patients treated with IMRT (n = 67) and IG-IMRT (n = 35) was retrieved. Using computer simulations of setup errors, we estimated the patient-specific uncertainty in accumulated treatment dose distributions for the prostate and for posterolateral aspects of the gland that are at highest risk for extra-capsular disease. Multivariate Cox regression for PRFS considering Gleason score, T-stage, pre-treatment PSA, number of elevated clinical risk factors (T2c+, GS7+ and PSA10+), nomogram-predicted risk of extra-capsular disease (ECD), and dose metrics was performed.

RESULTS

For IMRT vs. IG-IMRT, plan dosimetry values were similar, but simulations revealed uncertainty in delivered dose external to the prostate was significantly different, due to positioning uncertainties. A patient-specific interaction term of the risk of ECD and risk of low dose to the ECD (p = 0.005), and the number of elevated clinical risk factors (p = 0.008), correlate with reduced PRFS.

CONCLUSIONS

Improvements in PSA outcomes for high-risk PCa using IG-IMRT vs. IMRT without IG may be due to improved dosimetry for ECD.

Patterns of failure for patients with glioblastoma following O-(2-[18F]fluoroethyl)-L-tyrosine PET- and MRI-guided radiotherapy

BACKGROUND AND PURPOSE

To evaluate the patterns of failure following clinical introduction of amino-acid O-(2-[¹⁸F]fluoroethyl)-L-tyrosine (FET)-PET-guided target definition for radiotherapy (RT) of glioblastoma patients.

MATERIALS AND METHODS

The first 66 consecutive patients with confirmed histology, scanned using FET-PET/CT and MRI were selected for evaluation. Chemo-radiotherapy was delivered to a volume based on both MRI and FET-PET (PET_vol). The volume of recurrence (RV) was defined on MRI data collected at the time of progression according to RANO criteria.

RESULTS

Fifty patients were evaluable, with median follow-up of 45months. Central, in-field, marginal and distant recurrences were observed for 82%, 10%, 2%, and 6% of the patients, respectively. We found a volumetric overlap of 26%, 31% and 39% of the RV with the contrast-enhancing MR volume, PET_vol and the composite MRPET_vol, respectively. MGMT-methylation (p=0.03), larger PET_vol (p<0.001), and less extensive surgery (p<0.001), were associated with larger PET_vol overlap.

CONCLUSION

The combined MRPET_vol had a stronger association with the recurrence volume than either of the modalities alone. Larger overlap of PET_vol and RV was observed for patients with MGMT-methylation, less extensive surgery, and large PET_vol on the RT-planning scans.

Liquid fiducial marker applicability in proton therapy of locally advanced lung cancer

BACKGROUND AND PURPOSE

We investigated the clinical applicability of a novel liquid fiducial marker (LFM) for image-guided pencil beam scanned (PBS) proton therapy (PBSPT) of locally advanced lung cancer (LALC).

MATERIALS AND METHODS

The relative proton stopping power (RSP) of the LFM was calculated and measured. Dose perturbations of the LFM and three solid markers, in a phantom, were measured. PBSPT treatment planning on computer tomography scans of five patients with LALC with the LFM implanted was performed with 1-3 fields.

RESULTS

The RSP was experimentally determined to be 1.164 for the LFM. Phantom measurements revealed a maximum relative deviation in dose of 4.8% for the LFM in the spread-out Bragg Peak, compared to 12-67% for the solid markers. Using the experimentally determined RSP, the maximum proton range error introduced by the LFM is about 1mm. If the marker was displaced at PBSPT, the maximum dosimetric error was limited to 2 percentage points for 3-field plans.

CONCLUSION

The dose perturbations introduced by the LFM were considerably smaller than the solid markers investigated. The RSP of the fiducial marker should be corrected in the treatment planning system to avoid errors. The investigated LFM introduced clinically acceptable dose perturbations for image-guided PBSPT of LALC.

A dosimetric comparison of real-time adaptive and non-adaptive radiotherapy: A multi-institutional study encompassing robotic, gimbaled, multileaf collimator and couch tracking

PURPOSE

A study of real-time adaptive radiotherapy systems was performed to test the hypothesis that, across delivery systems and institutions, the dosimetric accuracy is improved with adaptive treatments over non-adaptive radiotherapy in the presence of patient-measured tumor motion.

METHODS AND MATERIALS

Ten institutions with robotic(2), gimbaled(2), MLC(4) or couch tracking(2) used common materials including CT and structure sets, motion traces and planning protocols to create a lung and a prostate plan. For each motion trace, the plan was delivered twice to a moving dosimeter; with and without real-time adaptation. Each measurement was compared to a static measurement and the percentage of failed points for γ-tests recorded.

RESULTS

For all lung traces all measurement sets show improved dose accuracy with a mean 2%/2mm γ-fail rate of 1.6% with adaptation and 15.2% without adaptation (p<0.001). For all prostate the mean 2%/2mm γ-fail rate was 1.4% with adaptation and 17.3% without adaptation (p<0.001). The difference between the four systems was small with an average 2%/2mm γ-fail rate of <3% for all systems with adaptation for lung and prostate.

CONCLUSIONS

The investigated systems all accounted for realistic tumor motion accurately and performed to a similar high standard, with real-time adaptation significantly outperforming non-adaptive delivery methods.

Stereotactic radiosurgery versus decompressive surgery followed by postoperative radiotherapy for metastatic spinal cord compression (STEREOCORD): Study protocol of a randomized non-inferiority trial

Current treatment standard for patients with metastatic spinal cord compression (MSCC) is decompressive surgery followed by radiotherapy. Stereotactic radiosurgery (SRS) could be considered a treatment option for MSCC for patients with minor neurologic deficits. If SRS is safely and effectively delivered with equivalent functional outcome, the patients would avoid the risks associated with an invasive procedure. This paper presents the design of a non-inferiority clinical trial evaluating the safety, tolerability and feasibility of SRS vs. current standard treatment for patients with MSCC. Patients fulfilling inclusion criteria will be randomized 1:1 to each arm. The primary endpoint is ability to walk six weeks after treatment. Secondary endpoints are levels of pain, bladder control, quality of life, response rate, toxicity and number of treatment days. 65 patients in each arm are required for the power of 89% to detect a clinically relevant inferior outcome.

Impact of [18F]-fluoro-ethyl-tyrosine PET imaging on target definition for radiation therapy of high-grade glioma

BACKGROUND

We sought to assess the impact of amino-acid (18)F-fluoro-ethyl-tyrosine (FET) positron emission tomography (PET) on the volumetric target definition for radiation therapy of high-grade glioma versus the current standard using MRI alone. Specifically, we investigated the influence of tumor grade, MR-defined tumor volume, and the extent of surgical resection on PET positivity.

METHODS

Fifty-four consecutive high-grade glioma patients (World Health Organization grades III-IV) with confirmed histology were scanned using FET-PET/CT and T1 and T2/fluid attenuated inversion recovery MRI. Gross tumor volume and clinical target volumes (CTVs) were defined in a blinded fashion based on MRI and subsequently PET, and volumetric analysis was performed. The extent of the surgical resection was reviewed using postoperative MRI.

RESULTS

Overall, for ∼ 90% of the patients, the PET-positive volumes were encompassed by T1 MRI with contrast-defined tumor plus a 20-mm margin. The tumor volume defined by PET was larger for glioma grade IV (P < .001) and smaller for patients with more extensive surgical resection (P = .004). The margin required to be added to the MRI-defined tumor in order to fully encompass the FET-PET positive volume tended to be larger for grade IV tumors (P = .018).

CONCLUSION

With an unchanged CTV margin and by including FET-PET for gross tumor volume definition, the CTV will increase moderately for most patients, and quite substantially for a minority of patients. Patients with grade IV glioma were found to be the primary candidates for PET-guided radiation therapy planning.

The dosimetric impact of inversely optimized arc radiotherapy plan modulation for real-time dynamic MLC tracking delivery

PURPOSE

Real-time dynamic multileaf collimator (MLC) tracking for management of intrafraction tumor motion can be challenging for highly modulated beams, as the leaves need to travel far to adjust for target motion perpendicular to the leaf travel direction. The plan modulation can be reduced by using a leaf position constraint (LPC) that reduces the difference in the position of adjacent MLC leaves in the plan. The purpose of this study was to investigate the impact of the LPC on the quality of inversely optimized arc radiotherapy plans and the effect of the MLC motion pattern on the dosimetric accuracy of MLC tracking delivery. Specifically, the possibility of predicting the accuracy of MLC tracking delivery based on the plan modulation was investigated.

METHODS

Inversely optimized arc radiotherapy plans were created on CT-data of three lung cancer patients. For each case, five plans with a single 358° arc were generated with LPC priorities of 0 (no LPC), 0.25, 0.5, 0.75, and 1 (highest possible LPC), respectively. All the plans had a prescribed dose of 2 Gy × 30, used 6 MV, a maximum dose rate of 600 MU/min and a collimator angle of 45° or 315°. To quantify the plan modulation, an average adjacent leaf distance (ALD) was calculated by averaging the mean adjacent leaf distance for each control point. The linear relationship between the plan quality [i.e., the calculated dose distributions and the number of monitor units (MU)] and the LPC was investigated, and the linear regression coefficient as well as a two tailed confidence level of 95% was used in the evaluation. The effect of the plan modulation on the performance of MLC tracking was tested by delivering the plans to a cylindrical diode array phantom moving with sinusoidal motion in the superior-inferior direction with a peak-to-peak displacement of 2 cm and a cycle time of 6 s. The delivery was adjusted to the target motion using MLC tracking, guided in real-time by an infrared optical system. The dosimetric results were evaluated using gamma index evaluation with static target measurements as reference.

RESULTS

The plan quality parameters did not depend significantly on the LPC (p ≥ 0.066), whereas the ALD depended significantly on the LPC (p < 0.001). The gamma index failure rate depended significantly on the ALD, weighted to the percentage of the beam delivered in each control point of the plan (ALD(w)) when MLC tracking was used (p < 0.001), but not for delivery without MLC tracking (p ≥ 0.342). The gamma index failure rate with the criteria of 2% and 2 mm was decreased from > 33.9% without MLC tracking to <31.4% (LPC 0) and <2.2% (LPC 1) with MLC tracking.

CONCLUSIONS

The results indicate that the dosimetric robustness of MLC tracking delivery of an inversely optimized arc radiotherapy plan can be improved by incorporating leaf position constraints in the objective function without otherwise affecting the plan quality. The dosimetric robustness may be estimated prior to delivery by evaluating the ALD(w) of the plan.