Radiotherapy for Atypical Teratoid/=Rhabdoid Tumor (ATRT) on the Pediatric Proton/Photon Consortium Registry (PPCR)

PURPOSE

Atypical teratoid/rhabdoid tumors (ATRT) of the central nervous system (CNS) are rare tumors with a poor prognosis and variable use of either focal or craniospinal (CSI) radiotherapy (RT). Outcomes on the prospective Pediatric Proton/Photon Consortium Registry (PPCR) were evaluated according to RT delivered.

METHODS

Pediatric patients receiving RT were prospectively enrolled on PPCR to collect initial patient, disease, and treatment factors as well as provide follow-up for patient outcomes. All ATRT patients with evaluable data were included. Kaplan-Meier analyses with log-rank p-values and cox proportional hazards regression were performed.

RESULTS

The PPCR ATRT cohort includes 68 evaluable ATRT patients (median age 2.6 years, range 0.71-15.40) from 2012 to 2021. Median follow-up was 40.8 months (range 3.4-107.7). Treatment included surgery (65% initial gross total resection or GTR), chemotherapy (60% with myeloablative therapy including stem cell rescue) and RT. For patients with M0 stage (n = 60), 50 (83%) had focal RT and 10 (17%) had CSI. Among patients with M + stage (n = 8), 3 had focal RT and 5 had CSI. Four-year overall survival (OS, n = 68) was 56% with no differences observed between M0 and M + stage patients (p = 0.848). Local Control (LC) at 4 years did not show a difference for lower primary dose (50-53.9 Gy) compared to ≥ 54 Gy (73.3% vs 74.7%, p = 0.83). For patients with M0 disease, four-year OS for focal RT was 54.6% and for CSI was 60% (Hazard Ratio 1.04, p = 0.95. Four-year event free survival (EFS) among M0 patients for focal RT was 45.6% and for CSI was 60% (Hazard Ratio 0.71, p = 0.519). For all patients, the 4-year OS comparing focal RT with CSI was 54.4% vs 60% respectively (p = 0.944), and the 4-year EFS for focal RT or CSI was 42.8% vs 51.4% respectively (p = 0.610).

CONCLUSION

The PPCR ATRT cohort found no differences in outcomes according to receipt of either higher primary dose or larger RT field (CSI). However, most patients were M0 and received focal RT. A lower primary dose (50.4 Gy), regardless of patient age, is appealing for further study as part of multi-modality therapy.

RADT-21. PATTERNS OF CARE AND OUTCOMES IN PEDIATRIC HIGH-GRADE GLIOMA PATIENTS ENROLLED IN THE PEDIATRIC PROTON/PHOTON CONSORTIUM REGISTRY

BACKGROUND

Proton therapy (PRT) is increasingly utilized for pediatric brain tumors to reduce radiation associated treatment effects, but there is a lack of data evaluating PRT in pediatric high-grade glioma (pHGG). The purpose of this analysis is to report patterns of care and clinical outcomes for pHGG patients treated with PRT and enrolled in the prospective Pediatric Proton/Photon Consortium Registry (PPCR).

METHODS

Fifty-five pHGG participants treated with PRT were enrolled in the PPCR between Jan 2013 and Aug 2020. Progression free (PFS) and overall survival (OS) rates were calculated according to the Kaplan-Meier method. Univariate analyses were performed using Cox proportional hazards model with Firth’s penalization.

RESULTS

Among 49 patients with complete data, the median age was 12, the majority of patients were male (29), white (35), and non-Hispanic/Latino (41). Histology was grade IV (37), grade III (10) or HGG not specified (8). Resection was gross-total (24), near-total (4), or sub-total/biopsy (17). Six patients received prior RT. The median RT dose was 57.6 Gy (RBE) starting a median of 33.5 days after surgery. 39 patients received chemotherapy. The most common acute treatment toxicities were alopecia (36), fatigue (34), radiation dermatitis (22), nausea/vomiting (19), and headache (19). Median follow-up was 3.14 years (95% CI 1.62-3.97). At 3 years, PFS (95% CI) was 35.5% (20.8-50.6%) and OS was 55.6% (38-70%). Median PFS and OS are 1.6 (1.2-3.1) and 3.6 (1.6-NA) years, respectively. Higher radiation dose was associated with greater PFS (HR 0.97 (0.94-1.01), p=0.059) and OS (HR 0.95 (0.93-0.99), p=0.006). Patients ≤ 3 years at diagnosis (n=8) had 3-year PFS/OS of 72.9%/87.5% vs. 27.8%/49.4% for older patients (p=0.068/0.089, respectively).

CONCLUSION

These are the first published data with PRT for pHGG. Clinical outcomes are comparable to historical data with photon therapy. Additional analysis of treatment associated toxicity and patient quality-of-life are warranted.

Proton pencil beam scanning treatment with feedback based voluntary moderate breath hold

Introduction The aim of this article is to introduce a novel protocol for proton pencil beam scanning treatment with moderate deep inspiration breath hold (mDIBH) and report on our clinical implementation results. Methods Three computed tomography (CT) scannings to build the patient's anatomy model were performed during the patient's voluntary mDIBH. All 3 CT scans were used in the optimization during the treatment planning process. Both orthogonal kV imaging and cone-beam computed tomography (CBCT) were implemented for patient alignment with BH prior to the treatment. The BH CBCT images were analyzed for BH reproducibility and the virtual total dose (VTD) retrospectively. To find the VTD, a series of deformable image registrations (DIR) were performed between CBCT and pCT. The effect of the variation of lung density on the dose distribution was also analyzed in the study. Results The values of the mean, standard deviation, maximum, and minimum of the tumor location difference between the CBCT and pCT were 1.9, 1.6, 4.7, and 0.0 mm, respectively. The percentage difference in D99% of CTVs between VTD and the nominal plan was within 1.5%. Conclusions The feedback-based voluntary moderate BH proton PBS treatment was successfully performed in our clinic. This study shows that there is a potential to implement the BH treatment widely in proton centers.

Predictors and Patterns of Regional Recurrence Following Lung SBRT: A Report From the Elekta Lung Research Group

INTRODUCTION

The objective of this study was to determine the predictors and patterns of regional recurrence (RR) following stereotactic body radiotherapy (SBRT) for primary lung cancers.

MATERIAL AND METHODS

Details of patient factors, treatment, and outcome factors were extracted from a multi-institutional (5) database. All events were calculated from the end of radiotherapy. Estimates of local recurrence, RR, and distant metastases (DM) were calculated using the competing risk method. Cause-specific and overall survival were calculated using the Kaplan-Meier method. Details of locations and number of simultaneous RRs were categorized by lymph node anatomic station.

RESULTS

A total of 734 patients were analyzed. The median follow-up was 3.0 years in surviving patients. Four hundred seventy-six (65%) patients had pathologic proof of disease. There were 64 patients with RR. The 2-year local recurrence, RR, and distant metastases rates were 5.6%, 9.0%, and 14.6% respectively. The 2-year cause-specific and overall survival were 89.9% and 63.7%, respectively. There were 136 simultaneous sites of RR. There were 21 recurrences in stations 4R (15.4%), 9 (6.6%) in 4L, 30 (22%) in 7, 19 (13.9%) in 10R, and 14 (10.3%) in 10L. The most common stations for isolated recurrence (n = 19) were station 7 (n = 5; 26.3%) and station 10R (n = 6; 31.6%). The most common RR levels were stations 4 and 7 for right and left upper lobe, stations 5, 7, and 10 for left lower lobe tumors, and stations 7 and 10 for right lower lobe tumors.

CONCLUSION

Stations 4, 7, and 10 were the most common stations for RR. These patterns of recurrence may guide nodal staging procedures prior to SBRT.

Evaluation of image guided motion management methods in lung cancer radiotherapy

PURPOSE

To evaluate the accuracy and reliability of three target localization methods for image guided motion management in lung cancer radiotherapy.

METHODS

Three online image localization methods, including (1) 2D method based on 2D cone beam (CB) projection images, (2) 3D method using 3D cone beam CT (CBCT) imaging, and (3) 4D method using 4D CBCT imaging, have been evaluated using a moving phantom controlled by (a) 1D theoretical breathing motion curves and (b) 3D target motion patterns obtained from daily treatment of 3 lung cancer patients. While all methods are able to provide target mean position (MP), the 2D and 4D methods can also provide target motion standard deviation (SD) and excursion (EX). For each method, the detected MP/SD/EX values are compared to the analytically calculated actual values to calculate the errors. The MP errors are compared among three methods and the SD/EX errors are compared between the 2D and 4D methods. In the theoretical motion study (a), the dependency of MP/SD/EX error on EX is investigated with EX varying from 2.0 cm to 3.0 cm with an increment step of 0.2 cm. In the patient motion study (b), the dependency of MP error on target sizes (2.0 cm and 3.0 cm), motion patterns (four motions per patient) and EX variations is investigated using multivariant linear regression analysis.

RESULTS

In the theoretical motion study (a), the MP detection errors are -0.2 ± 0.2, -1.5 ± 1.1, and -0.2 ± 0.2 mm for 2D, 3D, and 4D methods, respectively. Both the 2D and 4D methods could accurately detect motion pattern EX (error < 1.2 mm) and SD (error < 1.0 mm). In the patient motion study (b), MP detection error vector (mm) with the 2D method (0.7 ± 0.4) is found to be significantly less than with the 3D method (1.7 ± 0.8,p < 0.001) and the 4D method (1.4 ± 1.0, p < 0.001) using paired t-test. However, no significant difference is found between the 4D method and the 3D method. Based on multivariant linear regression analysis, the variances of MP error in SI direction explained by target sizes, motion patterns, and EX variations are 9% with the 2D method, 74.4% with the 3D method, and 27% with the 4D method. The EX/SD detection errors are both < 1.0 mm for the 2D method and < 2.0 mm for the 4D method.

CONCLUSIONS

The 2D method provides the most accurate MP detection regardless of the motion pattern variations, while its performance is limited by the accuracy of target identification in the projection images. The 3D method causes the largest error in MP determination, and its accuracy significantly depends on target sizes, motion patterns, and EX variations. The 4D method provides moderate MP detection results, while its accuracy relies on a regular motion pattern. In addition, the 2D and 4D methods both provide accurate measurement of the motion SD/EX, providing extra information for motion management.

Real-time catheter tracking for high-dose-rate prostate brachytherapy using an electromagnetic 3D-guidance device: a preliminary performance study

PURPOSE

In order to increase the accuracy and speed of catheter reconstruction in a high-dose-rate (HDR) prostate implant procedure, an automatic tracking system has been developed using an electromagnetic (EM) device (trakSTAR, Ascension Technology, VT). The performance of the system, including the accuracy and noise level with various tracking parameters and conditions, were investigated.

METHODS

A direct current (dc) EM transmitter (midrange model) and a sensor with diameter of 1.3 mm (Model 130) were used in the trakSTAR system for tracking catheter position during HDR prostate brachytherapy. Localization accuracy was assessed under both static and dynamic analyses conditions. For the static analysis, a calibration phantom was used to investigate error dependency on operating room (OR) table height (bottom vs midposition vs top), sensor position (distal tip of catheter vs connector end of catheter), direction [left-right (LR) vs anterior-posterior (AP) vs superior-inferior (SI)], sampling frequency (40 vs 80 vs 120 Hz), and interference from OR equipment (present vs absent). The mean and standard deviation of the localization offset in each direction and the corresponding error vectors were calculated. For dynamic analysis, the paths of five straight catheters were tracked to study the effects of directions, sampling frequency, and interference of EM field. Statistical analysis was conducted to compare the results in different configurations.

RESULTS

When interference was present in the static analysis, the error vectors were significantly higher at the top table position (3.3 ± 1.3 vs 1.8 ± 0.9 mm at bottom and 1.7 ± 1.0 mm at middle, p < 0.001), at catheter end position (3.1 ± 1.1 vs 1.4 ± 0.7 mm at the tip position, p < 0.001), and at 40 Hz sampling frequency (2.6 ± 1.1 vs 2.4 ± 1.5 mm at 80 Hz and 1.8 ± 1.1 at 160 Hz, p < 0.001). So did the mean offset errors in the LR direction (-1.7 ± 1.4 vs 0.4 ± 0.5 mm in AP and 0.8 ± 0.8 mm in SI directions, p < 0.001). The error vectors were significantly higher with surrounding interference (2.2 ± 1.3 mm) vs without interference (1.0 ± 0.7 mm, p < 0.001). An accuracy of 1.6 ± 0.2 mm can be reached when using optimum configuration (160 Hz at middle table position). When interference was present in the dynamic tracking, the mean tracking errors in LR direction (1.4 ± 0.5 mm) was significantly higher than that in AP direction (0.3 ± 0.2 mm, p < 0.001). So did the mean vector errors at 40 Hz (2.1 ± 0.2 mm vs 1.3 ± 0.2 mm at 80 Hz and 0.9 ± 0.2 mm at 160 Hz, p < 0.05). However, when interference was absent, they were comparable in the both directions and at all sampling frequencies. An accuracy of 0.9 ± 0.2 mm was obtained for the dynamic tracking when using optimum configuration.

CONCLUSIONS

The performance of an EM tracking system depends highly on the system configuration and surrounding environment. The accuracy of EM tracking for catheter reconstruction in a prostate HDR brachytherapy procedure can be improved by reducing interference from surrounding equipment, decreasing distance from transmitter to tracking area, and choosing appropriated sampling frequency. A calibration scheme is needed to further reduce the tracking error when the interference is high.

Outcomes after stereotactic lung radiotherapy or wedge resection for stage I non-small cell lung cancer (NSCLC)

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Background: To compare clinical outcomes between lung stereotactic radiotherapy (SBRT) and wedge resection for stage I NSCLC. Methods: 112 cases of T1–2N0 NSCLC were treated with wedge resection (n=69) or image-guided lung SBRT (n=43) from 2/2003–8/2008. SBRT patients were treated on a phase II trial. All patients were ineligible for anatomic lobectomy; 93% undergoing SBRT were medically inoperable; 7% refused surgery. Mean FEV1 and DLCO were 1.58L and 13.9ml/min/mmHg for wedge cases vs 1.29L and 10.1ml for SBRT (p<0.01, p<0.01). Mean Charlson Co-morbidity Index and median age were 3 and 74y for wedge vs 4 and 77y for SBRT (p<0.01, p=0.04). Patients were staged using CT, 18FDG PET-CT, pulmonary function testing, and chemistries. SBRT patients had bone scan and brain MRI. Mediastinoscopies were performed for 28% of wedge cases vs.16% for SBRT (p=NS). SBRT was prescribed as 48 (T1) or 60 (T2) Gy in 4–5 fractions to the edge of the target volume. Adjuvant chemotherapy was given to 22% of SBRT vs12% of wedge patients (p=NS). Results: Median potential follow-up=2.3y. No significant differences were identified in local (LR), regional (RR), or locoregional recurrence (LRR), distant metastasis (DM), freedom from any failure (FFF), overall survival, or cause-specific survival between the two groups (Table); however, trends toward reduced LR and improved FFF were found with SBRT. Results excluding cases of synchronous primary tumors or pathologicalT4 (satellite lesion at wedge) are also shown, with FFF significantly better for SBRT. Multivariate analysis showed tumor grade to predict LR; LR to predict DM; LR and angiolymphatic invasion to predict RR and RR, (+)margin, FEV1, and pathologic diameter OS (p=0.06, p=0.08, p=0.01, p=0.04) in wedge cases. Conclusions: Both lung SBRT and wedge resection are reasonable treatment options for Stage I NSCLC patients ineligible for anatomic lobectomy. SBRT showed trends toward reduced LR and failure. Additional follow-up will be needed to verify durability of these findings.

[Table: see text]

No significant financial relationships to disclose.