Less Time Is Less Motion: Analysis of Practical Efficiencies Gained With a Modified Workflow Integrating Planar kV Midimaging With CBCT for Spine Stereotactic Body Radiation Therapy.

Purpose: Our purpose was to optimize an image guided radiation therapy (IGRT) workflow to achieve practical setup accuracy in spine stereotactic body radiation therapy (SBRT). We assessed the time-saving efficiencies gained from incorporating planar kV midimaging as a surrogate for cone beam computed tomography (CBCT) for intrafraction motion monitoring. Methods and Materials: We selected 5 thoracic spine SBRT patients treated in 5 fractions and analyzed patient shifts captured by a modified IGRT workflow using planar kV midimaging integrated with CBCT to maintain a tolerance of 1 mm and 1°. We determined the frequency at which kV midimaging captured intrafraction motion as validated on repeat CBCT and assessed the potential time and dosimetric advantages of our modified IGRT workflow. Results: Patient motion, detected as out-of-tolerance shifts on planar kV midimaging, occurred during 6 of 25 fractions (24%) and were validated on repeat CBCT 100% of the time. Observed intrafraction absolute shifts (mean ± standard deviation) for the 25 fractions were 0.39 ± 0.21, 0.56 ± 0.22, and 0.45 ± 0.21 mm for lateral-longitude-vertical translations and 0.38 ± 0.12°, 0.32 ± 0.09°, and 0.47 ± 0.14° for pitch-roll-yaw rotation, which if uncorrected, could have significantly affected target coverage and increased spinal cord dose. The average times for pretreatment imaging, midtreatment verification, and total treatment time were 8.94, 2.81, and 16.21 minutes. Our modified IGRT workflow reduced the total number of CBCTs required from 120 to 35 (70%) and imaging dose from 126.2 to 43.4 cGy (65.6%) while maintaining high fidelity for our patient population. Conclusions: Accurate patient positioning was effectively achieved with use of multiple 2-dimensional-3-dimensional kV images and an average of 1 verification CBCT scan per fraction. Integration of planar kV midimaging can effectively reduce treatment time associated with spine SBRT delivery and minimize the potential dosimetric effect of intrafraction motion on target coverage and spinal cord dose.

Clinical Outcomes After Lung Stereotactic Body Radiation Therapy in Patients With or Without a Prior Lung Resection.

OBJECTIVES: Tumor control (TC), toxicity and survival, following stereotactic body radiation therapy (SBRT) were compared between patients with and without a prior lung resection (PLR). MATERIALS AND METHODS: The study is comprised of 130 patients with 141 peripheral tumors treated with SBRT at our institution from 2009 to 2013. Primary TC and lobar control (LC) were defined per RTOG 0236. Toxicity was scored using Common Terminology Criteria for Adverse Events version 4.0. Survival/TC and toxicity were compared between patients with and without PLR using the Kaplan-Meier method and cumulative incidence, respectively. Fine and Gray regression was used for univariable/multivariable analysis for radiation pneumonitis (RP). RESULTS: Of the 130 patients with median age 70 years (range, 42 to 93 y), 50 had undergone PLR (median time between PLR and SBRT: 33 mo; range, 1 to 206), including pneumonectomy (12%), lobectomy (46%), wedge resection (42%). With a median follow-up of 21 months in survivors, the PLR group had better TC (1-y 100% vs. 93%; P<0.01) and increased grade ≥2 (RP; 1-y 12% vs. 1%; P<0.01). OS was not significantly different between the 2 groups (1-y 91% vs. 85%; P=0.24). On univariable/multivariable analyses, biologically effective dose was associated with TC (hazard ratios, 0.97; 95% confidence interval, 0.94-0.999; P=0.04). Chemotherapy use was associated with grade ≥2 RP for all patients (hazard ratios, 14.92; 95% confidence interval, 5.68-39.21; P<0.0001) in multivariable analysis. PLR was not associated with increased RP in multivariable analysis. CONCLUSIONS: Patients with PLR who receive lung SBRT for lung tumors have high local control and relatively low toxicity. SBRT is an excellent option to treat second lung tumors or pulmonary metastases in patients with PLR.

Inter-scan and inter-observer tumour volume delineation variability on cone beam computed tomography in patients treated with stereotactic body radiation therapy for early-stage non-small cell lung cancer.

INTRODUCTION: Quantification of volume changes on cone beam computed tomography (CBCT) during lung stereotactic body radiation therapy (SBRT) for non-small cell lung cancer (NSCLC) may provide a useful radiological marker for radiation response and for adaptive treatment planning. This study quantifies inter-scan and inter-observer variability in tumour volume delineation on CBCT. METHODS: Three clinicians independently contoured the primary gross tumour volume (GTV) manually on CBCTs taken immediately before SBRT treatment (pre) and after the same SBRT treatment (post) for 19 NSCLC patients. Relative volume differences (RVD) were calculated between the pre- and post-CBCTs for a given treatment and between any two of three observers for a given CBCT. Coefficient of variation (CV) was used to quantitatively measure and compare the extent of variability. RESULTS: Inter-observer variability had a significantly higher CV of 0.15 ± 0.13 compared to inter-scan CV of 0.03 ± 0.04 with P < 0.0001. The greatest variability was observed with tumours (<2 cm in diameter) versus larger tumours with 95% limit of agreement (LOA) (Mean ± Standard Deviation) of 1.90% ± 19.55% vs. -0.97% ± 12.26% for inter-scan RVD and 29.99% ± 73.84% vs. 9.37% ± 29.95% for inter-observer RVD respectively. CONCLUSIONS: Inter-observer variability was greater than inter-scan variability for tumour volume delineation on CBCT with greatest variability for small tumours (<2 cm in diameter). LOA for inter-scan variability (~12%) helps defines a threshold for clinically meaningful tumour volume change during SBRT treatment for tumours with diameter greater than 2 cm, with larger thresholds needed for smaller tumours.

Evaluation of initial setup accuracy and intrafraction motion for spine stereotactic body radiation therapy using stereotactic body frames.

PURPOSE: The purposes of this study were (1) to evaluate the initial setup accuracy and intrafraction motion for spine stereotactic body radiation therapy (SBRT) using stereotactic body frames (SBFs) and (2) to validate an in-house-developed SBF using a commercial SBF as a benchmark. METHODS AND MATERIALS: Thirty-two spine SBRT patients (34 sites, 118 fractions) were immobilized with the Elekta and in-house (BHS) SBFs. All patients were set up with the Brainlab ExacTrac system, which includes infrared and stereoscopic kilovoltage x-ray-based positioning. Patients were initially positioned in the frame with the use of skin tattoos and then shifted to the treatment isocenter based on infrared markers affixed to the frame with known geometry relative to the isocenter. ExacTrac kV imaging was acquired, and automatic 6D (6 degrees of freedom) bony fusion was performed. The resulting translations and rotations gave the initial setup accuracy. These translations and rotations were corrected for by use of a robotic couch, and verification imaging was acquired that yielded residual setup error. The imaging/fusion process was repeated multiple times during treatment to provide intrafraction motion data. RESULTS: The BHS SBF had greater initial setup errors (mean±SD): -3.9±5.5mm (0.2±0.9°), -1.6±6.0mm (0.5±1.4°), and 0.0±5.3mm (0.8±1.0°), respectively, in the vertical (VRT), longitudinal (LNG), and lateral (LAT) directions. The corresponding values were 0.6±2.7mm (0.2±0.6°), 0.9±5.3mm (-0.2±0.9°), and -0.9±3.0mm (0.3±0.9°) for the Elekta SBF. The residual setup errors were essentially the same for both frames and were -0.1±0.4mm (0.1±0.5°), -0.2±0.4mm (0.0±0.4°), and 0.0±0.4mm (0.0±0.4°), respectively, in VRT, LNG, and LAT. The intrafraction shifts in VRT, LNG, and LAT were 0.0±0.4mm (0.0±0.3°), 0.0±0.5mm (0.0±0.4°), and 0.0±0.4mm (0.0±0.3°), with no significant difference observed between the 2 frames. CONCLUSIONS: These results showed that the combination of the ExacTrac system with either SBF was highly effective in achieving both setup accuracy and intrafraction stability, which were on par with that of mask-based cranial radiosurgery.

Salvage whole brain radiotherapy or stereotactic radiosurgery after initial stereotactic radiosurgery for 1-4 brain metastases.

Patients with limited brain metastases are often candidates for stereotactic radiosurgery (SRS) or whole brain radiotherapy (WBRT). Among patients who receive SRS, the likelihood and timing of salvage WBRT or SRS remains unclear. We examined rates of salvage WBRT or SRS among 180 patients with 1-4 newly diagnosed brain metastases who received index SRS from 2008-2013. Competing risks multivariable analysis was used to examine factors associated with time to WBRT. Patients had non-small cell lung (53 %), melanoma (23 %), breast (10 %), renal (6 %), or other (8 %) cancers. Median age was 62 years. Patients received index SRS to 1 (60 %), 2 (21 %), 3 (13 %), or 4 (7 %) brain metastases. Median survival after SRS was 9.7 months (range, 0.3-67.6 months). No further brain-directed radiotherapy was delivered after index SRS in 55 % of patients. Twenty-seven percent of patients ever received salvage WBRT, and 30 % ever received salvage SRS; 12 % of patients received both salvage WBRT and salvage SRS. Median time to salvage WBRT or salvage SRS were 5.6 and 6.1 months, respectively. Age ≤60 years (adjusted hazard ratio [AHR] = 2.80; 95 % CI 1.05-7.51; P = 0.04) and controlled/absent extracranial disease (AHR = 6.76; 95 % CI 1.60-28.7; P = 0.01) were associated with shorter time to salvage WBRT. Isolated brain progression caused death in only 11 % of decedents. In summary, most patients with 1-4 brain metastases receiving SRS never require salvage WBRT or SRS, and the remainder do not require salvage treatment for a median of 6 months.

Local control after fractionated stereotactic radiation therapy for brain metastases.

Stereotactic radiosurgery (SRS) is frequently used in the management of brain metastases, but concerns over potential toxicity limit applications for larger lesions or those in eloquent areas. Fractionated stereotactic radiation therapy (SRT) is often substituted for SRS in these cases. We retrospectively analyzed the efficacy and toxicity outcomes of patients who received SRT at our institution. Seventy patients with brain metastases treated with SRT from 2006-2012 were analyzed. The rates of local and distant intracranial progression, overall survival, acute toxicity, and radionecrosis were determined. The SRT regimen was 25 Gy in 5 fractions among 87 % of patients. The most common tumor histologies were non-small cell lung cancer (37 %), breast cancer (20 %) and melanoma (20 %), and the median tumor diameter was 1.7 cm (range 0.4-6.4 cm). Median survival after SRT was 10.7 months. Median time to local progression was 17 months, with a local control rate of 68 % at 6 months and 56 % at 1 year. Acute toxicity was seen in 11 patients (16 %), mostly grade 1 or 2 with the most common symptom being mild headache. Symptomatic radiation-induced treatment change was seen on follow-up MRIs in three patients (4.3 %). SRT appears to be a safe and reasonably effective technique to treat brain metastases deemed less suitable for SRS, though dose intensification strategies may further improve local control.

Low incidence of chest wall pain with a risk-adapted lung stereotactic body radiation therapy approach using three or five fractions based on chest wall dosimetry.

PURPOSE: To examine the frequency and potential of dose-volume predictors for chest wall (CW) toxicity (pain and/or rib fracture) for patients receiving lung stereotactic body radiotherapy (SBRT) using treatment planning methods to minimize CW dose and a risk-adapted fractionation scheme. METHODS: We reviewed data from 72 treatment plans, from 69 lung SBRT patients with at least one year of follow-up or CW toxicity, who were treated at our center between 2010 and 2013. Treatment plans were optimized to reduce CW dose and patients received a risk-adapted fractionation of 18 Gy×3 fractions (54 Gy total) if the CW V30 was less than 30 mL or 10-12 Gy×5 fractions (50-60 Gy total) otherwise. The association between CW toxicity and patient characteristics, treatment parameters and dose metrics, including biologically equivalent dose, were analyzed using logistic regression. RESULTS: With a median follow-up of 20 months, 6 (8.3%) patients developed CW pain including three (4.2%) grade 1, two (2.8%) grade 2 and one (1.4%) grade 3. Five (6.9%) patients developed rib fractures, one of which was symptomatic. No significant associations between CW toxicity and patient and dosimetric variables were identified on univariate nor multivariate analysis. CONCLUSIONS: Optimization of treatment plans to reduce CW dose and a risk-adapted fractionation strategy of three or five fractions based on the CW V30 resulted in a low incidence of CW toxicity. Under these conditions, none of the patient characteristics or dose metrics we examined appeared to be predictive of CW pain.

Total dural irradiation: RapidArc versus static-field IMRT: a case study.

The purpose of this study was to compare conventional fixed-gantry angle intensity-modulated radiation therapy (IMRT) with RapidArc for total dural irradiation. We also hypothesize that target volume-individualized collimator angles may produce substantial normal tissue sparing when planning with RapidArc. Five-, 7-, and 9-field fixed-gantry angle sliding-window IMRT plans were generated for comparison with RapidArc plans. Optimization and normal tissue constraints were constant for all plans. All plans were normalized so that 95% of the planning target volume (PTV) received at least 100% of the dose. RapidArc was delivered using 350° clockwise and counterclockwise arcs. Conventional collimator angles of 45° and 315° were compared with 90° on both arcs. Dose prescription was 59.4 Gy in 33 fractions. PTV metrics used for comparison were coverage, V(107)%, D1%, conformality index (CI(95)%), and heterogeneity index (D(5)%-D(95)%). Brain dose, the main challenge of this case, was compared using D(1)%, Dmean, and V(5) Gy. Dose to optic chiasm, optic nerves, globes, and lenses was also compared. The use of unconventional collimator angles (90° on both arcs) substantially reduced dose to normal brain. All plans achieved acceptable target coverage. Homogeneity was similar for RapidArc and 9-field IMRT plans. However, heterogeneity increased with decreasing number of IMRT fields, resulting in unacceptable hotspots within the brain. Conformality was marginally better with RapidArc relative to IMRT. Low dose to brain, as indicated by V5Gy, was comparable in all plans. Doses to organs at risk (OARs) showed no clinically meaningful differences. The number of monitor units was lower and delivery time was reduced with RapidArc. The case-individualized RapidArc plan compared favorably with the 9-field conventional IMRT plan. In view of lower monitor unit requirements and shorter delivery time, RapidArc was selected as the optimal solution. Individualized collimator angle solutions should be considered by RapidArc dosimetrists for OARs dose reduction. RapidArc should be considered as a treatment modality for tumors that extensively involve in the skull, dura, or scalp.

Linear accelerator-based stereotactic radiosurgery for brainstem metastases: the Dana-Farber/Brigham and Women's Cancer Center experience.

To review the safety and efficacy of linear accelerator-based stereotactic radiosurgery (SRS) for brainstem metastases. We reviewed all patients with brain metastases treated with SRS at DF/BWCC from 2001 to 2009 to identify patients who had SRS to a single brainstem metastasis. Overall survival and freedom-from-local failure rates were calculated from the date of SRS using the Kaplan-Meier method. Prognostic factors were evaluated using the log-rank test and Cox proportional hazards model. A total of 24 consecutive patients with brainstem metastases had SRS. At the time of SRS, 21/24 had metastatic lesions elsewhere within the brain. 23/24 had undergone prior WBRT. Primary diagnoses included eight NSCLC, eight breast cancer, three melanoma, three renal cell carcinoma and two others. Median dose was 13 Gy (range, 8-16). One patient had fractionated SRS 5 Gy ×5. Median target volume was 0.2 cc (range, 0.02-2.39). The median age was 57 years (range, 42-92). Follow-up information was available in 22/24 cases. At the time of analysis, 18/22 patients (82%) had died. The median overall survival time was 5.3 months (range, 0.8-21.1 months). The only prognostic factor that trended toward statistical significance for overall survival was the absence of synchronous brain metastasis at the time of SRS; 1-year overall survival was 31% with versus 67% without synchronous brain metastasis (log rank P = 0.11). Non-significant factors included primary tumor histology and status of extracranial disease (progressing vs. stable/absent). Local failure occurred in 4/22 cases (18%). Actuarial freedom from local failure for all cases was 78.6% at 1 year. RTOG grade 3 toxicities were recorded in two patients (ataxia, confusion). Linac-based SRS for small volume brainstem metastases using a median dose of 13 Gy is associated with acceptable local control and low morbidity.

An MLC-based linac QA procedure for the characterization of radiation isocenter and room lasers' position.

We have designed and implemented a new stereotactic linac QA test with stereotactic precision. The test is used to characterize gantry sag, couch wobble, cone placement, MLC offsets, and room lasers' positions relative to the radiation isocenter. Two MLC star patterns, a cone pattern, and the laser line patterns are recorded on the same imaging medium. Phosphor plates are used as imaging medium due to their sensitivity to red light. The red light of room lasers erases some of the irradiation information stored on the phosphor plates enabling accurate and direct measurements for the position of room lasers and radiation isocenter. Using film instead of the phosphor plate as imaging medium is possible, however, it is less practical. The QA method consists of irradiating four phosphor plates that record the gantry sag between the 0 degrees and 180 degrees gantry angles, the position and stability of couch rotational axis, the sag between the 90 degrees and 270 degrees gantry angles, the accuracy of cone placement on the collimator, the MLC offsets from the collimator rotational axis, and the position of laser lines relative to the radiation isocenter. The estimated accuracy of the method is +/- 0.2 mm. The observed reproducibility of the method is about +/- 0.1 mm. The total irradiation/ illumination time is about 10 min per image. Data analysis, including the phosphor plate scanning, takes less than 5 min for each image. The method characterizes the radiation isocenter geometry with the high accuracy required for the stereotactic radiosurgery. In this respect, it is similar to the standard ball test for stereotactic machines. However, due to the usage of the MLC instead of the cross-hair/ball, it does not depend on the cross-hair/ball placement errors with respect to the lasers and it provides more information on the mechanical integrity of the linac/couch/laser system. Alternatively, it can be used as a highly accurate QA procedure for the nonstereotactic machines. Noteworthy is its ability to characterize the MLC position accuracy, which is an important factor in IMRT delivery.