Journal of radiosurgery and SBRT最新文献

Purpose: Competing radiosurgery plans are compared based on their conformity and gradient of dose distribution to the target volume (TV). Most widely used quality metrics such as new conformity index (NCI) and gradient index (GI) are known to have strong volume dependency on the TV of interest. A simple quality measure without the volume dependency is presented for evaluating stereotactic radiosurgery plans, expressed in distance dimension compared to the unit-less volume ratio used in NCI and GI.

Methods and materials: The conformity distance measure (CDM) is defined as the effective radius of the union volume subtracted by that of the intersection volume, where volume operations are on TV and prescription isodose volume (PIV). Gradient distance measure (GDM) is defined as the effective radius of 50% PIV (low dose volume of the plan) subtracted by that of corresponding ideal low dose volume (iLDV). Volume independency and consistent sensitivity of CDM and GDM on PIV displacement and dose spillage are analyzed using a simple two-sphere model. 2429 cases of Gamma Knife and 76 cases of Linac based radiosurgery plans for brain metastasis were retrospectively studied to demonstrate volume independency of the new measures and their implication on target coverage.

Results: The sensitivity of NCI on PIV displacement and dose spillage was inversely proportional to the effective radius of the target volume, while the sensitivity of CDM on target motion and dose spillage was constant regardless the target volume. The iLDV for 50% PIV was approximately 2.4 times of PIV based on previous Linac based radiosurgery/IMRT/VMAT plans and single shot analysis from Gamma Knife (GK), ICON. Although NCI ranged from 1 to 14.7 for GK plans and from 1.2 to 20.8 for VMAT plans showing strong volume dependency, CDM showed negligible volume dependency of less than 2.1 mm for more than 90% cases and peak frequency was at 0.8 mm. CDM was correlated well with target coverage as a function of PIV displacement regardless of target volume. Target coverage, V100, was larger than 95% when PIV displacement is less than CDM.

Conclusions: The new conformity and gradient measure, CDM and GDM are proposed in this paper. The new measures are volume independent which is preferred for reliable evaluation of the radiosurgery plan quality over wide range of radiosurgery targets. As represented by distance dimension similar to PTV margin, the new measures may be more adequate for image guided radiosurgery applications.

Purpose: The epidural space is a frequent site of cancer recurrence after spine stereotactic radiosurgery (SSRS). This may be due to microscopic disease in the epidural space which is underdosed to obey strict spinal cord dose constraints. We hypothesized that the epidural space could be purposefully irradiated to prescription dose levels, potentially reducing the risk of recurrence in the epidural space without increasing toxicity.

Methods and materials: SSRS clinical treatment plans with spinal cord contours, spinal planning target volumes (PTV_spine), and delivered dose distributions were retrospectively identified. An epidural space PTV (PTV_epidural) was contoured to avoid the spinal cord and focus on regions near the PTV_spine. Clinical plan constraints included PTV_spine constraints (D_95% and D_5%, based on prescription dose) and spinal cord constraints (D_max < 1300 cGy, D10% < 1000 cGy). Plans were revised with three prescriptions of 1800, 2000 and 2400 cGy in two sets, with one set of revisions (supplemented plans) designed to additionally target the PTV_epidural by optimizing PTV_epidural D_95% in addition to meeting every clinical plan constraint. Clinical and revised plans were compared according to their PTV_epidural DVH distributions, and D_95% distributions.

Results: Seventeen SSRS plans meeting the above criteria were identified. Supplemented plans had higher doses to the epidural low-dose regions at all prescription levels. Epidural PTV D_95% values for the supplemented plans were all statistically significantly different from the values of the base plans (p < 10^-4). The epidural PTV D_95% increases depended on the initial prescription, increasing from 11.52 to 16.90 Gy, 12.23 to 18.85 Gy, and 13.87 to 19.54 Gy for target prescriptions of 1800, 2000 and 2400 cGy, respectively.

Conclusions: Purposefully targeting the epidural space in SSRS may increase control in the epidural space without significantly increasing the risk of spinal cord toxicity. A clinical trial of this approach should be considered.

Purpose: Rib fractures are a well-described complication following thoracic stereotactic body radiation therapy (SBRT). However, there are limited data in the setting of liver-directed SBRT.

Methods: Patients who underwent liver SBRT from 2014 to 2019 were analyzed. Logistic regression models were used to identify the demographic, clinical, and dosimetric factors associated with the development of rib fractures.

Results: Three hundred and forty-three consecutive patients were reviewed with median follow-up of 9.3 months (interquartile range [IQR]: 4.7-17.4 months); 81% of patients had primary liver tumors and 19% had liver metastases. Twenty-one patients (6.2%) developed rib fractures with a median time to diagnosis of 7 months following SBRT (IQR: 5-19 months). Of those patients, 11 experienced concomitant chest wall pain, while 10 patients had an incidental finding of a rib fracture on imaging. On univariate analysis, female gender (odds ratio [OR]: 2.29; p = 0.05), V30 Gy (OR: 1.02; p < 0.001), V40 Gy (OR: 1.08; p < 0.001), maximum chest wall dose (OR: 1.1; p < 0.001), and chest wall D30 cm³ (OR: 1.09; p < 0.001) were associated with an increased probability of developing a rib fracture. On multivariate analysis, maximum chest wall dose (OR: 1.1; p < 0.001) was associated with developing a rib fracture. Receipt of more than one course of SBRT (p = 0.34), left versus right sided lesion (p = 0.69), osteoporosis (p = 0.54), age (p = 0.82), and PTV volume (p = 0.55) were not significant.

Conclusions: Rib fractures following liver SBRT were observed in 6.2% of patients with the majority being asymptomatic. To mitigate this risk, clinicians should minimize dose delivery to the chest wall. Female patients may be at increased risk.

Purpose: To investigate the impact of tumor position displacements (TPDs) on tumor dose coverage in photon and proton stereotactic body radiation therapy (SBRT) treatments for lung cancer patients.

Methods: From our institutional database of 2877 fractions from 770 lung cancer patients treated with photon SBRT in 2017-2021, 163 fractions from 88 patients with recorded iso-center shifts of >1.5 cm in any direction under kV-cone-beam CT guidance were identified. By double registrations with bony and tumor alignments, the difference between the iso-center shifts of these two alignments was categorized as TPDs. One fraction from each of 15 patients who had TPD magnitudes >3 mm were selected for this study. For each patient, one proton plan using intensity modulated proton therapy (IMPT) with robust optimization was generated retrospectively. All photon plans had V_100%RX>99% of GTVs and V_100%RX>98% of ITVs. Proton plans were evaluated with two worse-case scenario (voxelwise worst and worst scenario) using 5mm and 3.5% uncertainty to achieve the same planning goals as the corresponding photon plans. These two evaluation proton plans were named proton-1st and proton-2nd plans. The dosimetric effect of TPD was simulated by shifting tumor contours with the corresponding shift on patient specific planning CT and by recalculating the dose of the original plan.

Results: The range of magnitude of TPDs was 3.58-28.71 mm. In photon plans, TPDs did not impact tumor dose coverage, still achieving V_100%RX of the GTV≥99% and V_100%RX of the ITV≥98%. In proton plans for patients with TPDs>10 mm, inadequate target dose coverage was observed. More specifically, 8 fractions of proton-1st plans and 4 fractions of proton-2nd had V_100%RX of the GTV<99% and V_100%RX of the ITV<98%.

Conclusions: Adequate tumor dose coverage was achieved in photon SBRT for magnitude of TPDs up to 20 mm. TPDs had greater impact in proton SBRT and adaptive planning was needed when the magnitude of TPDs>10 mm to provide adequate tumor dose coverage.

Background: There is limited data on clinical outcomes following SBRT for patients with metastatic head and neck squamous cell carcinoma (mHNC).

Method: An international SBRT registry was utilized to identify patients. LC and OS were evaluated with the Kaplan-Meier method and a Cox-proportional hazards model for multivariate analysis (MVA) to assess potential prognostic factors.

Results: We identified 81 patients with 98 lesions treated with SBRT. Areas treated included the lung (53.0%), non-regional lymph nodes (16.0%), and spine (12.3%). OS rates at 1 year and 2 years were 66.4% and 43.1%, respectively. Utilizing KPS, spinal disease, and GTV, 1-year OS estimates were 90.9%, 70.4%, 54.5%, and 25% for patients with 0-3 of these factors, respectively (p = 0.002). One-year and 2-year LC rates were both 93.3%. Roughly 17% of patients reported toxicities (none Grade 3+).

Conclusions: SBRT resulted in promising LC for mHNC patients. Spinal disease, GTV, and KPS should be considered in selecting patients with mHNC that may benefit from SBRT.

We present the case of a 65-year-old male with tumor-induced osteomalacia (TIO) caused by an FGF23-secreting phosphaturic tumor of C2 treated definitively with stereotactic body radiation therapy (SBRT) and kyphoplasty. The patient exhibited notable reduction in FGF23 6 weeks following radiotherapy. He also received a dose of the FGF23 monoclonal antibody, burosumab. We discuss the case with emphasis on radiation in the management of TIO. This case demonstrates SBRT as a well-tolerated local treatment option for the management of unresectable FGF23-producing tumors.

Purpose/objectives: Frameless Gamma Knife stereotactic radiosurgery (GKSRS) has become an effective supplement to frame-based, which is however sensitive to patient's involuntary motions and prone to prolonged treatment duration. Such delays during treatment inevitably result in patient discomfort and the inability to complete intended treatment. The purpose of this study is to investigate whether active coaching during frameless GKSRS can reduce actual treatment duration.

Materials/methods: Patients treated at a single institution with frameless GKSRS from 2017 to 2020 were retrospectively identified. Beginning in 2019, all patients treated with frameless GKSRS were actively coached to prevent treatment interruptions. Patient characteristics and treatment plans were compared between the cohorts of patients treated with and without active coaching. Linear regressions between the planned and actual treatment duration of treatment sessions were performed on either cohort. ANOVA and Wilcoxon tests were used for statistical analyses with a p-value less than 0.05 considered as significant.

Results: Of the total 43 patients and 105 treatment sessions identified, 27 patients underwent 51 treatment sessions of frameless GKSRS with active coaching. There was no significant difference in patient characteristics and treatment plans between the two cohorts. Patients treated with active coaching underwent significantly fewer CBCTs during treatment. The median planned and actual treatment durations were 31.4 and 51.7 min for the non-coached cohort, and 38.6 and 49.8 min for the coached cohort. The results of linear regressions showed that the actual treatment duration was 1.29 and 1.56 times longer with and without active coaching, respectively, which indicated a significant reduction in the actual treatment duration with active coaching.

Conclusion: Our results suggest that active coaching was associated with significant reductions of actual treatment duration. This simple intervention can be clinically implemented to prevent unnecessary treatment interruptions, improve patient comfort and ensure completion of treatment as prescribed during frameless GKSRS.