Intensity-modulated Stereotactic Radiotherapy Research Articles

Fractionated Stereotactic Intensity-Modulated Radiotherapy for Large Brain Metastases: Comprehensive Analyses of Dose–Volume Predictors of Radiation-Induced Brain Necrosis

Background: The objective was to explore dosimetric predictors of brain necrosis (BN) in fractionated stereotactic radiotherapy (SRT). Methods: After excluding collinearities carefully, multivariate logistic models were developed for comprehensive analyses of dosimetric predictors in patients who received first-line fractionated SRT for brain metastases (BMs). The normal brain volume receiving an xx Gy biological dose in 2 Gy fractions (VxxEQD2) was calculated from the retrieved dose–volume parameters. Results: Thirty Gy/3 fractions (fr) SRT was delivered to 34 patients with 75 BMs (median target volume, 3.2 cc), 35 Gy/5 fr to 30 patients with 57 BMs (6.4 cc), 37.5 Gy/5 fr to 28 patients with 47 BMs (20.2 cc), and 40 Gy/10 fr to 20 patients with 37 BMs (24.3 cc), according to protocols, depending on the total target volume (p < 0.001). After excluding the three-fraction groups, the incidence of symptomatic BN was significantly higher in patients with a larger V50EQD2 (adjusted odds ratio: 1.07, p < 0.02), V55EQD2 (1.08, p < 0.01), or V60EQD2 (1.09, p < 0.01) in the remaining five- and ten-fraction groups. The incidence of BN was also significantly higher in cases with V55EQD2 > 30 cc or V60EQD2 > 20 cc (p < 0.05). These doses correspond to 28 or 30 Gy/5 fr and 37 or 40 Gy/10 fr, respectively. Conclusions: In five- or ten-fraction SRT, larger V55EQD2 or V60EQD2 are BN risk predictors. These biologically high doses may affect BN incidence. Thus, the planning target volume margin should be minimized as much as possible.

Stereotactic intensity-modulated radiotherapy for skull base meningioma using the HybridArc with Novalis STx system.

Skull base meningiomas are often difficult to remove completely with preserved nerve function and may require radiation therapy. However, the Gamma Knife is unsuitable for large tumor volume or the optic nerve, which is difficult to identify on imaging. We report the results of stereotactic radiotherapy with HybridArc using Novalis STx for skull base meningiomas. We retrospectively examined 28 patients with skull base meningioma who underwent stereotactic radiotherapy (54 Gy/30 fractions) with HybridArc. The 28 patients, nine males and 19 females, were aged 31-83 years (mean 58.4 years), and the tumor volume was 2.6-97.1 mL (mean 29.7 mL). HybridArc irradiation was performed with D95 54 Gy/30 fractions for all patients with a median follow-up period of 36.0 months (range: 12-78 months). Tumor control rates at 1, 2, and 5 years after radiotherapy were 92.6%, 89.1%, and 82.8%, respectively. Only one non-atypical meningioma remained uncontrolled; thus, the tumor control rate for non-atypical meningioma at 1, 2, and 5 years was 94.1%. Tumor control rates for atypical meningioma at 1, 2, and 5 years were 85.7%, 71.4%, and 53.6%, respectively, significantly worse than for non-atypical meningiomas (P = 0.0395). Radiation injury was observed in two cases (7.1%). Visual field defects were observed in 16 patients, and diplopia in 6. Visual field and diplopia improvements were achieved in 5 and 2 patients, respectively (with overlap). Stereotactic radiotherapy (54 Gy/30 fractions) with HybridArc using Novalis STx is a safe and effective approach for relatively large skull base meningiomas.

Changes in target volume during irradiation of canine intranasal tumors can significantly impact radiation dosimetry.

Nasal tumor size can change during radiation therapy (RT). The amount of peritumoral fluid (eg, mucohemorrhagic effusions) can also fluctuate. How often this occurs and the magnitude of change are unknown. Likewise, there are no data which describe dosimetric effects of these changing volumes during a course of RT in veterinary medicine. This study addresses that gap in knowledge. Using pet dogs with nasal tumors, three CT image sets were created. Different Hounsfield units were applied to the gross tumor volume (GTV) of each image set: unchanged, -1000 (AIR), -1000 (to the portion of the GTV that actually underwent volume reduction during clinical RT; REAL). Two plans were created: 18-fraction three-dimensional conformal RT (3DCRT) and three-fraction intensity-modulated stereotactic RT (IM-SRT). For nearby normal tissues and GTV, near-maximum doses (D2% and D5% ) and volumes receiving clinically significant doses were recorded. To verify "AIR" results, thermoluminescent dosimeters recorded dose in cadavers that were irradiated using both 3DCRT and IM-SRT plans. "AIR" scenario had ≤1.5Gray (Gy) increases in D2% and ≤3.2 cc increases of volume. "REAL" scenario had ≤0.97Gy increases in D5% and ≤0.55 cc increases of volume at clinically relevant doses. Both were statistical significant. Results suggest that near-complete resolution of GTV warrants plan revision.

Fractionated stereotactic radiotherapy for the treatment of optic nerve sheath meningiomas

Radiosurgery has become an important treatment alternative to surgery for a variety of intracranial lesions. As currently practiced, it has in fact replaced surgery as a standard of care in some instances, compliments surgery as a post-operative adjunct in others, and most commonly represents an alternative to surgery or the only treatment option. Radiosurgery techniques have evolved quickly with the development of new technologies enabling more complex yet more efficient treatment plans. As a consequence, these technologies have broadened radiosurgery applications and improved radiosurgery outcomes. Among these newer techniques, treatments involving fractionated stereotactic radiation referred to as fractionated stereotactic radiotherapy, or FSR, have emerged as a consequence of linear accelerators designed for and dedicated to stereotactic techniques. Without the logistical constraints of retrofitted general purpose linear accelerators used in radiation oncology, often available only once or twice a week, dedicated units have enabled the design of treatment paradigms that strive for an ideal treatment based on the radiobiology of the target and dose-limiting contiguous tissues.This chapter will summarize our fifteen year experience with the Varian 600SR, initially with the Radionics software more recently modified to a Novalis shaped beam radiosurgery unit, and our practice of FSR for a variety of intracranial lesions. Special attention will be devoted to tumors involving or near the special sensory cranial nerves. Given the versatility of the Novalis treatment planning platform, one has the option of comparing different treatment planning solutions at once, including stereotactic intensity-modulated radiation therapy (IMRT). For selected skull base lesions, we have found that stereotactic IMRT yields greater conformality than FSR and we will therefore include its application among fractionation strategies.

Helical image-guided stereotactic body radiotherapy (SBRT) for the treatment of early-stage lung cancer: a single-institution experience at the Willis-Knighton Cancer Center.

Our aim is to report on the clinical methods and outcomes of helical intensity-modulated stereotactic body radiotherapy (SBRT) for the treatment of early-stage non-small cell lung cancer (NSCLC). Seventy-nine patients with stage I NSCLC underwent helical SBRT with 48 Gy in 4 fractions or 60 Gy in 5 fractions. All patients underwent 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) or FDG-PET/computed tomography (CT) scanning in the immobilized treatment position for planned fusion with a separate kilovoltage (KV) CT simulation prior to treatment. Megavoltage CT images were obtained on the treatment unit prior to therapy and repeated at mid-fraction with comparison and fusion to the KV CT simulation planning images to assure setup accuracy. Serial follow-up with FDG-PET or FDG-PET/CT was performed at 3-4 months and every 6 months thereafter. Median follow-up was 27 months (range, 4-82 months). Overall local control rate (LCR) was 93.6% (95% confidence interval [CI], 86.0-97.3%) and 3-year overall survival (OS) was 58.4% (95% CI, 47.2-69.5%). For patients with T1N0M0 disease (n = 59) the LCR was 94.9% (95% CI, 86.1-98.3%) and the 3-year OS was 62.8% (95% CI, 49.9-73.9%). Patients treated with 60 Gy had longer 3-year OS than patients treated with 48 Gy (65.2% vs 37.5%; P = 0.044). SBRT-related toxicity was modest, with 10 patients developing grade 1/2 chest wall toxicity based on the Common Terminology Criteria for Adverse Events (CTCAE). Image-guided SBRT with helical IMRT delivered in 4 or 5 fractions of 12 Gy with rigid immobilization, FDG-PET-assisted targeting, and repeat mid-fraction CT scan is an effective treatment for early NSCLC.

Can a commercially available EPID dosimetry system detect small daily patient setup errors for cranial IMRT/SRS?

PurposeThe purpose of this study was to determine if the Sun Nuclear PerFRACTION electronic portal imager device dosimetry software would be able to detect setup errors in a clinical setting and would be able to correctly identify the direction in which the setup error was introduced. Methods and materialsA 7-field intensity modulated radiation therapy (IMRT) treatment plan for a centrally located tumor was developed for 1 phantom and 5 canine cadaver heads. Systematic setup errors were introduced by manually moving the treatment couch by 1, 3, and 5 mm in each translational direction to assess stereotactic radiation surgery (SRS), IMRT, and 3-dimensional (3D) treatment tolerances after the initial alignment was performed. An angular setup error of 5° yaw was also assessed. The delivered treatment fluence was automatically imported in the PerFRACTION software and compared with the baseline fluence. ResultsIn the canine phantom, a 5-mm shift was undetected by gamma analysis, and up to a 2-cm shift had to be introduced for the gamma pass rate of 3%/3 mm to fall below a 95% pass rate criterion. The same 5-mm shift using 3% difference caused the pass rates for 2 fields to drop below the 95% tolerance. For each respective translational shift, the affected beam angles were consistent across the cadaver heads and correlated with the direction of translational shift. The best field pass rate, worst field pass rate, and average pass rate across all 7 fields was analyzed to develop clinical guidance on parameter settings for SRS, IMRT, and 3D tolerances. ConclusionsPerFRACTION 2-dimensional mode successfully detected setup errors outside the systematic error tolerance for SRS, IMRT, and 3D when an appropriate analysis metric and pass/fail criteria was implemented. Our data confirm that percent difference may be more sensitive in detecting plan failure than gamma analysis.

Comparison of Single and Multiple Isocenter Stereotactic Intensity Modulated Radiation Therapy Plans With at Least 4 Brain Tumors

Comparison of Single and Multiple Isocenter Stereotactic Intensity Modulated Radiation Therapy Plans With at Least 4 Brain Tumors

DOSIMETRIC CONSEQUENCES OF USING CONTRAST-ENHANCED COMPUTED TOMOGRAPHIC IMAGES FOR INTENSITY-MODULATED STEREOTACTIC BODY RADIOTHERAPY PLANNING.

Veterinary Radiology & UltrasoundVolume 57, Issue 3 p. 352-352 CORRIGENDUMFree Access DOSIMETRIC CONSEQUENCES OF USING CONTRAST-ENHANCED COMPUTED TOMOGRAPHIC IMAGES FOR INTENSITY-MODULATED STEREOTACTIC BODY RADIOTHERAPY PLANNING This article corrects the following: DOSIMETRIC CONSEQUENCES OF USING CONTRAST-ENHANCED COMPUTED TOMOGRAPHIC IMAGES FOR INTENSITY-MODULATED STEREOTACTIC BODY RADIOTHERAPY PLANNING Hiroto Yoshikawa, Donald M. Roback, Susan M. Larue, Michael W. Nolan, Volume 56Issue 6Veterinary Radiology & Ultrasound pages: 687-695 First Published online: August 4, 2015 First published: 27 April 2016 https://doi.org/10.1111/vru.12364AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat In Yoshikawa et al.1 errors were published in the tables and in the equation on page 689. Page 689: The calculation of X is missing the multiplier of 100 (x 100) to make the fraction into a percentage. Here is the correct equation: Tables 1 – 6: The word “gray” in the footnote labelled with an asterisk should have been published with a capital “G” as it is a proper noun. Here is the correct footnote: *All doses are reported in Gray. Table 6: In the “Downstream tissues” columns, the right column under “Pelvic” should have been “Post” instead of “Pelvic” while the columns under “Nasal” should have been “Pre” and “Post” instead of “Nasal” and “Pelvic”, respectively. Correct Table 6 is shown below. Table 6. Statistical Comparison of Mean Doses in Tissues (Upstream and Downstream of, and Within a Contrast-enhancing Tissue) Along the Axis of a Single Nonuniform Treatment Field Enhancing region Downstream tissues Upstream tissues Pelvic Nasal Pelvic Nasal Pelvic Nasal Pre Post Pre Post Pre Post Pre Post Pre Post Pre Post Mean 4.34 4.36 3.95 3.94 4.13 4.10 3.81 3.79 4.47 4.48 3.98 3.96 Std Dev 3.17 3.21 1.89 1.89 2.95 2.92 1.86 1.86 3.39 3.40 2.05 2.03 Lower 95% CI 2.07 2.07 2.59 2.59 2.03 2.02 2.48 2.46 2.04 2.05 2.51 2.51 Upper 95% CI 6.60 6.66 5.31 5.29 6.24 6.19 5.134 5.12 6.89 6.91 5.44 5.41 P-value* 0.11 0.32 0.0059 0.50 0.48 0.45 *All doses are reported in Gray. Two-tailed Wilcoxon matched-pairs signed-rank test, comparing doses calculated on pre- and postcontrast CT scans. We apologize for these errors. REFERENCE 1Yoshikawa H, Roback DM, Larue SM, Nolan MW. Dosimetric consequences of using contrast-enhanced computed tomographic images for intensity-modulated stereotactic body radiotherapy planning. Vet Radiol Ultrasound 2015; 56: 687– 695. Volume57, Issue3May/June 2016Pages 352-352 ReferencesRelatedInformation

DOSIMETRIC CONSEQUENCES OF USING CONTRAST-ENHANCED COMPUTED TOMOGRAPHIC IMAGES FOR INTENSITY-MODULATED STEREOTACTIC BODY RADIOTHERAPY PLANNING.

Potential benefits of planning radiation therapy on a contrast-enhanced computed tomography scan (ceCT) should be weighed against the possibility that this practice may be associated with an inadvertent risk of overdosing nearby normal tissues. This study investigated the influence of ceCT on intensity-modulated stereotactic body radiotherapy (IM-SBRT) planning. Dogs with head and neck, pelvic, or appendicular tumors were included in this retrospective cross-sectional study. All IM-SBRT plans were constructed on a pre- or ceCT. Contours for tumor and organs at risk (OAR) were manually constructed and copied onto both CT's; IM-SBRT plans were calculated on each CT in a manner that resulted in equal radiation fluence. The maximum and mean doses for OAR, and minimum, maximum, and mean doses for targets were compared. Data were collected from 40 dogs per anatomic site (head and neck, pelvis, and limbs). The average dose difference between minimum, maximum, and mean doses as calculated on pre- and ceCT plans for the gross tumor volume was less than 1% for all anatomic sites. Similarly, the differences between mean and maximum doses for OAR were less than 1%. The difference in dose distribution between plans made on CTs with and without contrast enhancement was tolerable at all treatment sites. Therefore, although caution would be recommended when planning IM-SBRT for tumors near "reservoirs" for contrast media (such as the heart and urinary bladder), findings supported the use of ceCT with this dose calculation algorithm for both target delineation and IM-SBRT treatment planning.

Comparison of doses received by the hippocampus in patients treated with single isocenter– vs multiple isocenter–based stereotactic radiation therapy to the brain for multiple brain metastases

To investigate the doses received by the hippocampus and normal brain tissue during a course of stereotactic radiation therapy using a single isocenter (SI)–based or multiple isocenter (MI)–based treatment planning in patients with less than 4 brain metastases. In total, 10 patients with magnetic resonance imaging (MRI) demonstrating 2-3 brain metastases were included in this retrospective study, and 2 sets of stereotactic intensity-modulated radiation therapy (IMRT) treatment plans (SI vs MI) were generated. The hippocampus was contoured on SPGR sequences, and doses received by the hippocampus and the brain were calculated and compared between the 2 treatment techniques. A total of 23 lesions in 10 patients were evaluated. The median tumor volume, the right hippocampus volume, and the left hippocampus volume were 3.15, 3.24, and 2.63mL, respectively. In comparing the 2 treatment plans, there was no difference in the planning target volume (PTV) coverage except in the tail for the dose-volume histogram (DVH) curve. The only statistically significant dosimetric parameter was the V100. All of the other measured dosimetric parameters including the V95, V99, and D100 were not significantly different between the 2 treatment planning techniques. None of the dosimetric parameters evaluated for the hippocampus revealed any statistically significant difference between the MI and SI plans. The total brain doses were slightly higher in the SI plans, especially in the lower dose region, although this difference was not statistically different. The use of SI-based treatment plan resulted in a 35% reduction in beam-on time. The use of SI treatments for patients with up to 3 brain metastases produces similar PTV coverage and similar normal tissue doses to the hippocampus and the brain when compared with MI plans. SI treatment planning should be considered in patients with multiple brain metastases undergoing stereotactic treatment.

Proof of principle: Applicator-guided stereotactic IMRT boost in combination with 3D MRI-based brachytherapy in locally advanced cervical cancer

To describe a new technique involving high-precision stereotactic intensity-modulated radiation therapy (IMRT) boost in combination with intracavitary-interstitial (IC-IS) brachytherapy (BT) in cervical tumors that cannot be sufficiently covered by IC-IS-BT due to extensive residual disease and/or difficult topography at the time of BT. Three patients with stage IIIB-IVA cervical cancer had significant residual disease at the time of BT. MRI-guided IC-IS-BT (pulsed-dose rate) was combined with a stereotactic IMRT boost guided according to the BT applicator in situ, using cone beam CT. The planning aim dose (total external beam radiotherapy and BT) for the high-risk clinical target volume (HR-CTV) was D90 >70-85Gy, whereas constraints for organs at risk were D2cm3 <70Gy for rectum, sigmoid, and bowel and <90Gy for bladder in terms of equivalent total dose in 2Gy fractions. An IMRT boost adapted to the BT dose distribution was optimized to target the regions poorly covered by BT. HR-CTV doses of D90 >81Gy were obtained in the central HR-CTV and D90 >69Gy in the distal regions of HR-CTV. Image-guided set up of the IMRT boost with the applicator in situ was feasible. The dose plans were robust to intra-fraction uncertainties of 3mm. Local control with acceptable morbidity was obtained at a followup of 3, 2.5, and 1 year, respectively. The combination of MRI-guided BT with an applicator-guided stereotactic IMRT boost is feasible. This technique seems to be useful in the few cases where HR-CTV coverage cannot be obtained even with IS-IC-BT.

Safety and efficacy of intensity-modulated stereotactic body radiotherapy using helical tomotherapy for lung cancer and lung metastasis.

Stereotactic body radiotherapy (SBRT) proved to be an effective treatment with acceptable toxicity for lung tumors. However, the use of helical intensity-modulated (IM) SBRT is controversial. We investigated the outcome of lung tumor patients treated by IMSBRT using helical tomotherapy with a Japanese standard fractionation schedule of 48 Gy in 4 fractions (n = 37) or modified protocols of 50–60 Gy in 5–8 fractions (n = 35). Median patient's age was 76 years and median follow-up period for living patients was 20 months (range, 6–46). The median PTV was 6.9 cc in the 4-fraction group and 14 cc in the 5- to 8-fraction group (P = 0.001). Grade 2 radiation pneumonitis was seen in 2 of 37 patients in the 4-fraction group and in 2 of 35 patients in the 5- to 8-fraction group (log-rank P = 0.92). Other major complications were not observed. The LC rates at 2 years were 87% in the 4-fraction group and 83% in the 5- to 8-fraction group. Helical IMSBRT for lung tumors is safe and effective. Patients with a high risk of developing severe complications may also be safely treated using 5–8 fractions. The results of the current study warrant further studies of helical IMSBRT.

Neural stem cell sparing by linac based intensity modulated stereotactic radiotherapy in intracranial tumors

BackgroundNeurocognitive decline observed after radiotherapy (RT) for brain tumors in long time survivors is attributed to radiation exposure of the hippocampus and the subventricular zone (SVZ). The potential of sparing capabilities for both structures by optimized intensity modulated stereotactic radiotherapy (IMSRT) is investigated.MethodsBrain tumors were irradiated by stereotactic 3D conformal RT or IMSRT using m3 collimator optimized for PTV and for sparing of the conventional OARs (lens, retina, optic nerve, chiasm, cochlea, brain stem and the medulla oblongata). Retrospectively both hippocampi and SVZ were added to the list of OAR and their dose volume histograms were compared to those from two newly generated IMSRT plans using 7 or 14 beamlets (IMSRT-7, IMSRT-14) dedicated for optimized additional sparing of these structures. Conventional OAR constraints were kept constant. Impact of plan complexity and planning target volume (PTV) topography on sparing of both hippocampi and SVZ, conformity index (CI), the homogeneity index (HI) and quality of coverage (QoC) were analyzed. Limits of agreement were used to compare sparing of stem cell niches with either IMSRT-7 or IMSRT-14. The influence of treatment technique related to the topography ratio between PTV and OARs, realized in group A-D, was assessed by a mixed model.ResultsIn 47 patients CI (p ≤ 0.003) and HI (p < 0.001) improved by IMSRT-7, IMSRT-14, QoC remained stable (p ≥ 0.50) indicating no compromise in radiotherapy. 90% of normal brain was exposed to a significantly higher dose using IMSRT. IMSRT-7 plans resulted in significantly lower biologically effective doses at all four neural stem cell structures, while contralateral neural stem cells are better spared compared to ipsilateral. A further increase of the number of beamlets (IMSRT-14) did not improve sparing significantly, so IMSRT-7 and IMSRT-14 can be used interchangeable. Patients with tumors contacting neither the subventricular zone nor the cortex benefit most from IMSRT (p < 0.001).ConclusionThe feasibility of neural stem cell niches sparing with sophisticated linac based inverse IMSRT with 7 beamlets in an unselected cohort of intracranial tumors in relation to topographic situation has been demonstrated. Clinical relevance testing neurotoxicity remains to be demonstrated.

Intensity-modulated stereotactic body radiotherapy for stage I non-small cell lung cancer

This study aimed to investigate the clinical outcomes of intensity-modulated radiotherapy (IMRT)-based stereotactic body radiotherapy (SBRT) for patients with stage I non-small cell lung cancer (NSCLC). A prospective database of 16 consecutive patients receiving SBRT for pathologically-proven and peripherally-located stage I NSCLC was reviewed. Fifteen patients were medically inoperable and one patient refused to undergo surgery. The median age of the patients was 76 years (range, 69–86). Treatment planning used four-dimensional computed tomography and fixed-field IMRT (n=11) or volumetric-modulated arc therapy (VMAT; n=5). The SBRT scheme was 48 Gy in four fractions (n=9) or 55 Gy in five fractions (n=7), delivered on consecutive days. The overall response rate at 6 months was 78.6%, including a complete response in three (21.4%) patients and a partial response in eight (57.1%). Three patients (21.4%) demonstrated a stable disease status. The median follow-up time was 14 months (range, 6–20) for the surviving patients. One patient developed local failure at 11 months, while another suffered from regional failure in a subcarinal lymph node at 4 months. Two patients did not survive within the first 6 months; one patient died during salvage chemotherapy for mediastinal lymph node metastasis and the other succumbed to a cause unrelated to lung cancer. The Kaplan-Meier estimates of local failure-free, progression-free and overall survival rates at 18 months were 91.0, 85.2 and 87.5%, respectively. The toxicity was mild; no severe (grade ≥3) toxicity was identified. IMRT-based (including VMAT) delivery of SBRT for patients with stage I NSCLC demonstrated favorable responses and local control without severe toxicity.

Intensity-modulated stereotactic radiotherapy for the treatment of medically inoperable patients with NSCLC stage I

The standard treatment for stage I non-small cell lung cancer (NSCLC) is lobectomy. However, a considerable number of patients are not eligible for standard lung surgery due to poor pulmonary function or comorbidities. We evaluated the efficacy and tolerability of intensity-modulated stereotactic radiotherapy (IMSRT) with moderate hypofractionation for these patients. Twelve patients were selected for IMSRT. 4D-CT planning was performed by gating CT-scanning positioning. The applied doses ranged between 10x4.5Gy (80% ID) (N=1), 12x4.5Gy (95% ID) (N=1) and 10x5.5Gy (95% ID) (N=10). Long-term follow-up was performed including spirometry and CT for evaluation of local, locoregional and distant control. Even in patients with poor pulmonary function IMRST was safe and well tolerated. No severe acute adverse effects were observed. Estimated local control at 2years was 90%. Moreover, IMSRT does not induce a significant deterioration of pulmonary function. IMRST is safe and feasible even for patients with very poor pulmonary function. The applied dose provides a high local control rate, although the biological equivalent dose (BED) is lower compared to the average of other SRT regimens. Therefore, IMRST may be an efficient alternative for all NSCLC stage I patients with contraindications to standard lobectomy especially in patients with small tumors in high-risk localisations.

Verification and dosimetric impact of Acuros XB algorithm on intensity modulated stereotactic radiotherapy for locally persistent nasopharyngeal carcinoma

The main aim of the current study was to assess the dosimetric impact on intensity modulated stereotactic radiotherapy (IMSRT) for locally persistent nasopharyngeal carcinoma (NPC) due to the recalculation from the Anisotropic Analytical Algorithm (AAA) to the recently released Acuros XB (AXB) algorithm. The dosimetric accuracy of using AXB in predicting air∕tissue interface doses from an open single small field in a simple geometric phantom and intensity modulated small fields in an anthropomorphic phantom was also investigated. The central axis percentage depth doses (PDD) of a rectangular phantom containing an air cavity were calculated by both AAA and AXB from 6 MV beam with small field sizes (2 × 2 to 5 × 5 cm(2)). These data were compared to PDD measured by thin thermoluminescent dosimeters (TLDs) and Monte Carlo simulations. The doses predicted by AAA and AXB near air∕tissue interfaces from five different IMSRT plans were compared to the TLD measured doses in an anthropomorphic phantom. The PTV coverage, conformity and doses to organs at risk (OARs) calculated by AAA and AXB were compared for 12 patients, using identical beam setup, leaves movement and monitor units. Testing using the simple rectangular phantom demonstrated that AAA and AXB overestimated the PDD at the air∕tissue interfaces by up to 41% and 6%, respectively, from a 2 × 2 cm(2) field. The secondary build-up curves predicted by AXB caught up well with the measured data at around 2 mm beyond the air cavity. Testing using the anthropomorphic phantom showed that AAA overestimated the doses by up to 10%, while the measured doses matched those of the AXB to within 3%. Using AAA, the planning target coverage represented by 100% of the reference dose was estimated to be 4% higher than using AXB. The averaged minimum dose to the PTV predicted by AAA was about 4% higher and OARs doses 3% to 6% higher compared to AXB. AXB should be used whenever possible as the standard reference for IMSRT boost of NPC cases. The more accurate AXB indicating lower target coverage and lower minimum target dose compared to AAA should be noted.

OC-0466 VIRTUAL SOURCE MODELLING OF PHOTON BEAMS FOR MONTE CARLO BASED RADIATION THERAPY TREATMENT PLANNING

OC-0466 VIRTUAL SOURCE MODELLING OF PHOTON BEAMS FOR MONTE CARLO BASED RADIATION THERAPY TREATMENT PLANNING

Hypofractionated frameless stereotactic intensity-modulated radiotherapy with whole brain radiotherapy for the treatment of 1–3 brain metastases

The aim of the study is to evaluate the efficacy and toxicity of hypofractionated frameless stereotactic radiotherapy (HSRT) with whole brain radiotherapy (WBRT) for the treatment of 1-3 brain metastases. 38 patients with a total of 58 brain metastases were treated at Ghent University Hospital with WBRT (10 × 3 Gy) followed by HSRT (5 × 6 Gy). Patients with RPA class I (n = 8) and II (n = 30) were eligible for HSRT. Acute toxicity was scored with the RTOG toxicity criteria. Response rates were scored every 3 months using the McDonald criteria. Overall survival (OS), brain-specific survival, local and distant brain control were calculated using the Kaplan-Meier method. Patient (age, Karnofsky performance score, KPS, RPA class) and tumor characteristics (number of lesions, extracranial metastases, brain tumor volume, primary cancer status, histology) were tested in univariate and multivariate analysis. Survival at 6 and 12 months was 65 and 35 %, respectively. On univariate analysis KPS < 90, number of lesions, a histologic diagnosis of adenocarcinoma and uncontrolled primary cancer status were statistic significant predictors for poor OS. Four patients (11 %) developed a grade 3 toxicity. Rates of complete remission, partial remission, no change and progressive disease were 30, 40, 23 and 5 %, respectively. Median survival was 7.6 months. The actuarial brain-specific survival was 97 % at 6 months and 91 % at 1 year of follow-up. The 1-year actuarial local and distant brain control was 66 and 75 %, respectively. WBRT + HSRT is an effective treatment for patients with up to three brain metastases.

The accuracy of dose calculations by anisotropic analytical algorithms for stereotactic radiotherapy in nasopharyngeal carcinoma

Nasopharyngeal tumors are commonly treated with intensity-modulated radiotherapy techniques. For photon dose calculations, problems related to loss of lateral electronic equilibrium exist when small fields are used. The anisotropic analytical algorithm (AAA) implemented in Varian Eclipse was developed to replace the pencil beam convolution (PBC) algorithm for more accurate dose prediction in an inhomogeneous medium. The purpose of this study was to investigate the accuracy of the AAA for predicting interface doses for intensity-modulated stereotactic radiotherapy boost of nasopharyngeal tumors. The central axis depth dose data and dose profiles of phantoms with rectangular air cavities for small fields were measured using a 6 MV beam. In addition, the air–tissue interface doses from six different intensity-modulated stereotactic radiotherapy plans were measured in an anthropomorphic phantom. The nasopharyngeal region of the phantom was especially modified to simulate the air cavities of a typical patient. The measured data were compared to the data calculated by both the AAA and the PBC algorithm. When using single small fields in rectangular air cavity phantoms, both AAA and PBC overestimated the central axis dose at and beyond the first few millimeters of the air–water interface. Although the AAA performs better than the PBC algorithm, its calculated interface dose could still be more than three times that of the measured dose when a 2 × 2 cm2 field was used. Testing of the algorithms using the anthropomorphic phantom showed that the maximum overestimation by the PBC algorithm was 20.7%, while that by the AAA was 8.3%. When multiple fields were used in a patient geometry, the dose prediction errors of the AAA would be substantially reduced compared with those from a single field. However, overestimation of more than 3% could still be found at some points at the air–tissue interface.

Dosimetric Comparison of Intensity-Modulated Stereotactic Radiotherapy With Other Stereotactic Techniques for Locally Recurrent Nasopharyngeal Carcinoma

Locally recurrent nasopharyngeal carcinoma (NPC) patients can be salvaged by reirradiation with a substantial degree of radiation-related complications. Stereotactic radiotherapy (SRT) is widely used in this regard because of its rapid dose falloff and high geometric precision. The aim of this study was to examine whether the newly developed intensity-modulated stereotactic radiotherapy (IMSRT) has any dosimetric advantages over three other stereotactic techniques, including circular arc (CARC), static conformal beam (SmMLC), and dynamic conformal arc (mARC), in treating locally recurrent NPC. Computed tomography images of 32 patients with locally recurrent NPC, previously treated with SRT, were retrieved from the stereotactic planning system for contouring and computing treatment plans. Treatment planning of each patient was performed for the four treatment techniques: CARC, SmMLC, mARC, and IMSRT. The conformity index (CI) and homogeneity index (HI) of the planning target volume (PTV) and doses to the organs at risk (OARs) and normal tissue were compared. All four techniques delivered adequate doses to the PTV. IMSRT, SmMLC, and mARC delivered reasonably conformal and homogenous dose to the PTV (CI <1.47, HI <0.53), but not for CARC (p < 0.05). IMSRT presented with the smallest CI (1.37) and HI (0.40). Among the four techniques, IMSRT spared the greatest number of OARs, namely brainstem, temporal lobes, optic chiasm, and optic nerve, and had the smallest normal tissue volume in the low-dose region. Based on the dosimetric comparison, IMSRT was optimal for locally recurrent NPC by delivering a conformal and homogenous dose to the PTV while sparing OARs.