Linac-based stereotactic radiosurgery (SRS) in the treatment of refractory trigeminal neuralgia: Detailed description of SRS procedure and reported clinical outcomes.

PURPOSE/OBJECTIVES: To present our linac-based SRS procedural technique for medically and/or surgically refractory trigeminal neuralgia (TN) treatment and simultaneously report our clinical outcomes. MATERIALS AND METHODS: Twenty-seven refractory TN patients who were treated with a single fraction of 80 Gy to TN. Treatment delivery was performed with a 4 mm cone size using 7-arc arrangement with differential-weighting for Novalis-TX with six MV-SRS (1000 MU/min) beam and minimized dose to the brainstem. Before each treatment, Winston-Lutz quality assurance (QA) with submillimeter accuracy was performed. Clinical treatment response was evaluated using Barrow Neurological Institute (BNI) pain intensity score, rated from I to V. RESULTS: Out of 27 patients, 22 (81%) and 5 (19%) suffered from typical and atypical TN, respectively, and had median follow-up interval of 12.5 months (ranged: 1-53 months). For 80 Gy prescriptions, delivered total average MU was 19440 ± 611. Average beam-on-time was 19.4 ± 0.6 min. Maximum dose and dose to 0.5 cc of brainstem were 13.4 ± 2.1 Gy (ranged: 8.4-15.9 Gy) and 3.6 ± 0.4 Gy (ranged: 3.0-4.9 Gy), respectively. With a median follow-up of 12.5 months (ranged: 1-45 months) in typical TN patients, the proportion of patients achieving overall pain relief was 82%, of which half achieved a complete pain relief with BNI score of I-II and half demonstrated partial pain reduction with BNI score of IIIA-IIIB. Four typical TN patients (18%) had no response to radiosurgery treatment. Of the patients who responded to treatment, actuarial pain recurrence free survival rates were approximately 100%, 75%, and 50% at 12 months, 15 months, and 24 months, respectively. Five atypical TN patients were included, who did not respond to treatment (BNI score: IV-V). However, no radiation-induced cranial-toxicity was observed in all patients treated. CONCLUSION: Linac-based SRS for medically and/or surgically refractory TN is a fast, effective, and safe treatment option for patients with typical TN who had excellent response rates. Patients, who achieve response to treatment, often have durable response rates with moderate actuarial pain recurrence free survival. Longer follow-up interval is anticipated to confirm our clinical observations.

Monte Carlo evaluation of tissue heterogeneities corrections in the treatment of head and neck cancer patients using stereotactic radiotherapy.

The purpose of this study was to generate Monte Carlo computed dose distributions with the X-ray voxel Monte Carlo (XVMC) algorithm in the treatment of head and neck cancer patients using stereotactic radiotherapy (SRT) and compare to heterogeneity corrected pencil-beam (PB-hete) algorithm. This study includes 10 head and neck cancer patients who underwent SRT re-irradiation using heterogeneity corrected pencil-beam (PB-hete) algorithm for dose calculation. Prescription dose was 24-40 Gy in 3-5 fractions (treated 3-5 fractions per week) with at least 95% of the PTV volume receiving 100% of the prescription dose. A stereotactic head and neck localization box was attached to the base of the thermoplastic mask fixation for target localization. The gross tumor volume (GTV) and organs-at-risk (OARs) were contoured on the 3D CT images. The planning target volume (PTV) was generated from the GTV with 0 to 5 mm uniform expansion; PTV ranged from 10.2 to 64.3 cc (average = 35.0±17.5 cc). OARs were contoured on the 3D planning CT and consisted of spinal cord, brainstem, optic structures, parotids, and skin. In the BrainLab treatment planning system (TPS), clinically optimal SRT plans were generated using hybrid planning technique (combination of 3D conformal nonco-planar arcs and nonopposing static beams) for the Novalis-Tx linear accelerator consisting of high-definition multileaf collimators (HD-MLCs: 2.5 mm leaf width at isocenter) and 6 MV-SRS (1000 MU/min) beam. For the purposes of this study, treatment plans were recomputed using XVMC algorithm utilizing identical beam geometry, multileaf positions, and monitor units and compared to the corresponding clinical PB-hete plans. The Monte Carlo calculated dose distributions show small decreases (< 1.5%) in calculated dose for D99, Dmean, and Dmax of the PTV coverage between the two algorithms. However, the average target volume encompassed by the prescribed percent dose (Vp) was about 2.5% less with XVMC vs. PB-hete and ranged between -0.1 and 7.8%. The averages for D100 and D10 of the GTV were lower by about 2% and ranged between -0.8 and 3.1%. For the spinal cord, both the maximal dose difference and the dose to 0.35 cc of the structure were higher by an average of 4.2% (ranged 1.2 to -13.6%) and 1.4% (ranged 7.5 to -11.3%), respectively, with XVMC calculation. For the brainstem, the maximal dose dif-ferences and the dose to 0.5 cc of the structure were, on average, higher by 2.4% (ranged 6.4 to -8.0%) and 3.6% (ranged 6.4 to -9.0%), respectively. For the parotids, both the mean dose and the dose to 20 cc of parotids were higher by an average of 3% (ranged -0.2 to -5.9%) and 4% (ranged -0.2 to -8%), respectively, with XVMC calculation. For the optic apparatus, results from both algorithms were similar. However, the mean dose to skin was 3% higher (ranged 0 to -6%), on average, with XVMC compared to PB-hete, although the maximum dose to skin was 2% lower (ranged -5% to 15.5%). The results from our XVMC dose calculations for head and neck SRT patients indicate small to moderate underdosing of the tumor volume when compared to PB-hete calculation. However, Vp was up to 7.8% less for the lower-neck patient with XVMC. Critical structures, such as spinal cord, brainstem, or parotids, could potentially receive higher doses when using XVMC algorithm. Given the proximity to critical structures and the smaller volumes treated with SRT in the region of the head and neck, the differences between XVMC and PB-hete calculation methods may be of clinical interest.

Comparisons of multiple automated anatomy-based image-guidance methods for patient setup before head/neck external beam radiotherapy.

The purpose was to assess the variability in automated translational head/neck setup corrections computed from several different imaging modalities and rigid registration methods using patient anatomy. Shifts were calculated using three commercial and one in-house automated rigid registration methods for nine head/neck patients who were imaged with three different image-guidance systems. The mean difference between the daily isocenter shifts determined by the four methods ranged from 2.8 to 12.5 mm for all of the test cases.These differences are much greater than the variability observed for a rigid imaging phantom. Image-guided setup procedures have an uncertainty that depends on the imaging modality, the registration algorithm, the image resolution and the image content. In the absence of an absolute ground truth, the variation in the shifts calculated by several different methods provides a useful estimate of that uncertainty.

Comparison of daily couch shifts using MVCT (TomoTherapy) and B-mode ultrasound (BAT System) during prostate radiotherapy.

The purpose of this study was to compare daily couch shifts after prostate localization between megavoltage CT (MVCT, Hi-ART TomoTherapy) and b-mode ultrasound (BAT system). Nine hundred and thirteen couch shifts from 22 consecutive patients treated using MVCT localization were compared to 853 shifts from 23 randomly selected patients treated using b-mode ultrasound prostate localization. Shifts were made in three principal axes based on prostate position after comparing daily images to the initial planning CT. Mean shift for each axis and the shift variability both between and within individual subjects were calculated. Variability was higher for BAT compared to MVCT for vertical and cranial-caudal (CC) shifts (p=0.0084 and 0.01037, respectively), while lateral shifts were significantly greater for MVCT. For each individual, the pairwise correlations between shifts in different axes were calculated. Among all the groups and pairings, only the pairing of vertical and cranial/caudal adjustments in BAT-localized patients showed significant evidence of correlation after adjustment for multiple pairwise comparisons (p=0.0006). When compared to MVCT, the use of BAT for prostate localization results in greater variability of positional adjustments in vertical and CC directions. This likely reflects differences in the ability to precisely align b-mode ultrasound contours to KVCT images, as well as prostate excursion in vertical and CC direction caused by the ultrasound probe. These considerations need to be made when defining treatment volumes, and argue for the use of less disruptive techniques for daily prostate localization.

Treatment planning strategy for whole-brain radiotherapy with hippocampal sparing and simultaneous integrated boost for multiple brain metastases using intensity-modulated arc therapy.

PURPOSE: To retrospectively evaluate the accuracy, plan quality and efficiency of intensity-modulated arc therapy (IMAT) for hippocampal sparing whole-brain radiotherapy (HS-WBRT) with simultaneous integrated boost (SIB) in patients with multiple brain metastases (m-BM). MATERIALS AND METHODS: A total of 5 patients with m-BM were retrospectively replanned for HS-WBRT with SIB using IMAT treatment planning. The hippocampus was contoured on diagnostic T1-weighted magnetic resonance imaging (MRI) which had been fused with the planning CT image set. The hippocampal avoidance zone (HAZ) was generated using a 5-mm uniform margin around the paired hippocampi. The m-BM planning target volumes (PTVs) were contoured on T1/T2-weighted MRI registered with the 3D planning computed tomography (CT). The whole-brain planning target volume (WB-PTV) was defined as the whole-brain tissue volume minus HAZ and m-BM PTVs. Highly conformal IMAT plans were generated in the Eclipse treatment planning system for Novalis-TX linear accelerator consisting of high-definition multileaf collimators (HD-MLCs: 2.5-mm leaf width at isocenter) and 6-MV beam. Prescription dose was 30Gy for WB-PTV and 45Gy for each m-BM in 10 fractions. Three full coplanar arcs with orbit avoidance sectors were used. Treatment plans were evaluated using homogeneity (HI) and conformity indices (CI) for target coverage and dose to organs at risk (OAR). Dose delivery efficiency and accuracy of each IMAT plan was assessed via quality assurance (QA) with a MapCHECK device. Actual beam-on time was recorded and a gamma index was used to compare dose agreement between the planned and measured doses. RESULTS: All 5 HS-WBRT with SIB plans met WB-PTV D2%, D98%, and V30Gy NRG-CC001 requirements. The plans demonstrated highly conformal and homogenous coverage of the WB-PTV with mean HI and CI values of 0.33 ± 0.04 (range: 0.27 to 0.36), and 0.96 ± 0.01 (range: 0.95 to 0.97), respectively. All 5 hippocampal sparing patients met protocol guidelines with maximum dose and dose to 100% of hippocampus (D100%) less than 16 and 9Gy, respectively. The dose to the optic apparatus was kept below protocol guidelines for all 5 patients. Highly conformal and homogenous radiosurgical dose distributions were achieved for all 5 patients with a total of 33 brain metastases. The m-BM PTVs had a mean HI = 0.09 ± 0.02 (range: 0.07 to 0.19) and a mean CI = 1.02 ± 0.06 (range: 0.93 to 1.2). The total number of monitor units (MU) was, on average, 1677 ± 166. The average beam-on time was 4.1 ± 0.4 minute . The IMAT plans demonstrated accurate dose delivery of 95.2 ± 0.6%, on average, for clinical gamma passing rate with 2%/2-mm criteria and 98.5 ± 0.9%, on average, with 3%/3-mm criteria. CONCLUSIONS: All hippocampal sparing plans were considered clinically acceptable per NRG-CC001 dosimetric compliance criteria. IMAT planning provided highly conformal and homogenous dose distributions for the WB-PTV and m-BM PTVs with lower doses to OAR such as the hippocampus. These results suggest that HS-WBRT with SIB is a clinically feasible, fast, and effective treatment option for patients with a relatively large numbers of m-BM lesions.

Regulatory evaluation of prostate volume implants: pitfalls of a retrospective assessment.

PURPOSE: Evaluate for regulatory compliance the prostate implants from the Philadelphia Veterans Medical Center applying both an activity-based and volume-corrected D(90) (the maximum dose delivered to 90% of the prostate volume) metrics. METHODS AND MATERIALS: Dosimetry from 107 prostate implants performed at the Philadelphia Veterans Medical Center used immediate postprocedural CT image sets. D(90) values were adjusted for volume differences from planning volumes. Medical events (MEs) determined from the volume-corrected data were compared with an activity-based metric. RESULTS: Examination of images using original and third-party reviewed prostate contours revealed 56 and 62 cases with D(90) values <80% of the prescription dose, respectively. Because postprocedural prostate volumes were on average 55.7% larger than the planned volume, clinical nomogram-based doses using the implanted activity and actual volumes found 34-47 implants failing to achieve doses greater than 80% of the prescription dose. Volume correction identified 20 MEs, 9 cases with D(90) values within 4% of the ME threshold and 11 significantly inferior cases with median D(90) values <52% of the prescribed dose. Eleven implants also had 20% or more seeds beyond the treatment site according to an activity metric recommended by the VHA Blue Ribbon Panel. Ten of these 11 cases were also identified by volume-corrected D(90) metric. The remaining 96 cases, however, had 95% (±6%) of seeds placed within the treatment site. CONCLUSIONS: Of the cases reported to the United States Nuclear Regulatory Commission (NRC) on the basis of Day-1 D(90) values, many appear to have been acceptable implants relative to standard-of-practice clinical criteria. The activity-based dose metric, endorsed by the NRC Advisory Committee on the Medical Uses of Isotopes in 2005 and recommended by the VHA Blue Ribbon Panel for Prostate Brachytherapy yields a more robust determination of ME for this population of implants.