Slav Yartsev

Simultaneous Infield Boost With Helical Tomotherapy for Patients With 1 to 3 Brain Metastases

Objective:We sought to model the feasibility of a simultaneous in field boost (SIB) to individual brain metastases during a course of whole brain radiotherapy (WBXRT) using helical tomotherapy (HT) intensity-modulated radiation therapy. Patients and Methods:Planning computed tomography data from 14 patients with 1 to 3 brain metastases were used to model an intralesional SIB delivery that yielded a total intralesional dose of 60 Gy with a surrounding whole brain dose of 30 Gy (designed to be isoeffective to WBXRT of 30 Gy with an 18 Gy in 1 fraction radiosurgery boost). Accuracy of treatment of a phantom on the HT unit was measured. Comparisons of HT delivery versus a conventional stereotactic radiotherapy technique for a particularly challenging simulated anatomy were made. Results:In all cases, SIB to 60 Gy with WBXRT to 30 Gy was possible while maintaining critical structures below assigned dose limits. Estimated radiation delivery time for the SIB treatment was approximately 10 minutes per fraction. Planning and treatment of the head phantom was associated with an overall accuracy of 2 mm. Comparison to conventional noncoplanar arc fractionated stereotactic radiotherapy plan demonstrated similar target coverage and improved critical tissue sparing even for a challenging anatomy with multiple lesions in the same plane as the optic apparatus. Conclusions:Based on this study, use of an image guided SIB using HT seemed feasible and a phase I trial initiated at our institution is described. Potential advantages of this approach include frameless stereotaxis through daily megavoltage computed tomography localization, more efficient use of resources and exploitation of radiobiologic advantages of fractionation.

Dosimetric comparison of helical tomotherapy, RapidArc, and a novel IMRT & Arc technique for esophageal carcinoma

PURPOSE To compare radiotherapy treatment plans for mid- and distal-esophageal cancer with primary involvement of the gastroesophageal (GE) junction using a novel IMRT & Arc technique (IMRT & Arc), helical tomotherapy (HT), and RapidArc (RA1 and RA2). METHODS AND MATERIALS Eight patients treated on HT for locally advanced esophageal cancer with radical intent were re-planned for RA and IMRT&Arc. RA plans employed single and double arcs (RA1 and RA2, respectively), while IMRT&Arc plans had four fixed-gantry IMRT fields and a conformal arc. Dose-volume histogram statistics, dose uniformity, and dose homogeneity were analyzed to compare treatment plans. RESULTS RA2 plans showed significant improvement over RA1 plans in terms of OAR dose and PTV dose uniformity and homogeneity. HT plan provided best dose uniformity (p=0.001) and dose homogeneity (p=0.002) to planning target volume (PTV), while IMRT&Arc and RA2 plans gave lowest dose to lungs among four radiotherapy techniques with acceptable PTV dose coverage. Mean V(10) of the lungs was significantly reduced by the RA2 plans compared to IMRT&Arc (40.3%, p=0.001) and HT (66.2%, p<0.001) techniques. Mean V(15) of the lungs for the RA2 plans also showed significant improvement over the IMRT&Arc (25.2%, p=0.042) and HT (34.8%, p=0.027) techniques. These improvements came at the cost of higher doses to the heart volume compared to HT and IMRT&Arc techniques. Mean lung dose (MLD) for the IMRT&Arc technique (21.2 ± 5.0% of prescription dose) was significantly reduced compared to HT (26.3%, p=0.004), RA1 (23.3%, p=0.028), and RA2 (23.2%, p=0.017) techniques. CONCLUSION The IMRT&Arc technique is a good option for treating esophageal cancer with thoracic involvement. It achieved optimal low dose to the lungs and heart with acceptable PTV coverage. HT is a good option for treating esophageal cancer with little thoracic involvement as it achieves superior dose conformality and uniformity. The RA2 technique provided for improved treatment plans using additional arcs with low doses to the lungs at the cost of increased heart dose. Plan quality could still be improved through the use of additional arcs.

On the performances of Intensity Modulated Protons, RapidArc and Helical Tomotherapy for selected paediatric cases

BackgroundTo evaluate the performance of three different advanced treatment techniques on a group of complex paediatric cancer cases.MethodsCT images and volumes of interest of five patients were used to design plans for Helical Tomotherapy (HT), RapidArc (RA) and Intensity Modulated Proton therapy (IMP). The tumour types were: extraosseous, intrathoracic Ewing Sarcoma; mediastinal Rhabdomyosarcoma; metastastis of base of skull with bone, para-nasal and left eye infiltration from Nephroblastoma of right kidney; metastatic Rhabdomyosarcoma of the anus; Wilms tumour of the left kidney with multiple liver metastases. Cases were selected for their complexity regardless the treatment intent and stage. Prescribed doses ranged from 18 to 53.2 Gy, with four cases planned using a Simultaneous Integrated Boost strategy. Results were analysed in terms of dose distributions and dose volume histograms.ResultsFor all patients, IMP plans lead to superior sparing of organs at risk and normal healthy tissue, where in particular the integral dose is halved with respect to photon techniques. In terms of conformity and of spillage of high doses outside targets (external index (EI)), all three techniques were comparable; CI90% ranged from 1.0 to 2.3 and EI from 0 to 5%. Concerning target homogeneity, IMP showed a variance (D5%–D95%) measured on the inner target volume (highest dose prescription) ranging from 5.9 to 13.3%, RA from 5.3 to 11.8%, and HT from 4.0 to 12.2%. The range of minimum significant dose to the same target was: (72.2%, 89.9%) for IMP, (86.7%, 94.1%) for RA, and (79.4%, 94.8%) for HT. Similarly, for maximum significant doses: (103.8%, 109.4%) for IMP, (103.2%, 107.4%) for RA, and (102.4%, 117.2%) for HT. Treatment times (beam-on time) ranged from 123 to 129 s for RA and from 146 to 387 s for HT.ConclusionFive complex pediatric cases were selected as representative examples to compare three advanced radiation delivery techniques. While differences were noted in the metrics examined, all three techniques provided satisfactory conformal avoidance and conformation.

Comparing two strategies of dynamic intensity modulated radiation therapy (dIMRT) with 3-dimensional conformal radiation therapy (3DCRT) in the hypofractionated treatment of high-risk prostate cancer

BackgroundTo compare two strategies of dynamic intensity modulated radiation therapy (dIMRT) with 3-dimensional conformal radiation therapy (3DCRT) in the setting of hypofractionated high-risk prostate cancer treatment.Methods3DCRT and dIMRT/Helical Tomotherapy(HT) planning with 10 CT datasets was undertaken to deliver 68 Gy in 25 fractions (prostate) and simultaneously delivering 45 Gy in 25 fractions (pelvic lymph node targets) in a single phase. The paradigms of pelvic vessel targeting (iliac vessels with margin are used to target pelvic nodes) and conformal normal tissue avoidance (treated soft tissues of the pelvis while limiting dose to identified pelvic critical structures) were assessed compared to 3DCRT controls. Both dIMRT/HT and 3DCRT solutions were compared to each other using repeated measures ANOVA and post-hoc paired t-tests.ResultsWhen compared to conformal pelvic vessel targeting, conformal normal tissue avoidance delivered more homogenous PTV delivery (2/2 t-test comparisons; p < 0.001), similar nodal coverage (8/8 t-test comparisons; p = ns), higher and more homogenous pelvic tissue dose (6/6 t-test comparisons; p < 0.03), at the cost of slightly higher critical structure dose (Ddose, 1–3 Gy over 5/10 dose points; p < 0.03). The dIMRT/HT approaches were superior to 3DCRT in sparing organs at risk (22/24 t-test comparisons; p < 0.05).ConclusiondIMRT/HT nodal and pelvic targeting is superior to 3DCRT in dose delivery and critical structure sparing in the setting of hypofractionation for high-risk prostate cancer. The pelvic targeting paradigm is a potential solution to deliver highly conformal pelvic radiation treatment in the setting of nodal location uncertainty in prostate cancer and other pelvic malignancies.

Inter and Intrafraction Uncertainty in Prostate Bed Image-Guided Radiotherapy

PURPOSE The goals of this study were to measure inter- and intrafraction setup error and prostate bed motion (PBM) in patients undergoing post-prostatectomy image-guided radiotherapy (IGRT) and to propose appropriate population-based three-dimensional clinical target volume to planning target volume (CTV-PTV) margins in both non-IGRT and IGRT scenarios. METHODS AND MATERIALS In this prospective study, 14 patients underwent adjuvant or salvage radiotherapy to the prostate bed under image guidance using linac-based kilovoltage cone-beam CT (kV-CBCT). Inter- and intrafraction uncertainty/motion was assessed by offline analysis of three consecutive daily kV-CBCT images of each patient: (1) after initial setup to skin marks, (2) after correction for positional error/immediately before radiation treatment, and (3) immediately after treatment. RESULTS The magnitude of interfraction PBM was 2.1 mm, and intrafraction PBM was 0.4 mm. The maximum inter- and intrafraction prostate bed motion was primarily in the anterior-posterior direction. Margins of at least 3-5 mm with IGRT and 4-7 mm without IGRT (aligning to skin marks) will ensure 95% of the prescribed dose to the clinical target volume in 90% of patients. CONCLUSIONS PBM is a predominant source of intrafraction error compared with setup error and has implications for appropriate PTV margins. Based on inter- and estimated intrafraction motion of the prostate bed using pre- and post-kV-CBCT images, CBCT IGRT to correct for day-to-day variances can potentially reduce CTV-PTV margins by 1-2 mm. CTV-PTV margins for prostate bed treatment in the IGRT and non-IGRT scenarios are proposed; however, in cases with more uncertainty of target delineation and image guidance accuracy, larger margins are recommended.

Phase I Trial of Simultaneous In-Field Boost With Helical Tomotherapy for Patients With One to Three Brain Metastases

PURPOSE Stereotactic radiosurgery is an alternative to surgical resection for selected intracranial lesions. Integrated image-guided intensity-modulated-capable radiotherapy platforms such as helical tomotherapy (HT) could potentially replace traditional radiosurgery apparatus. The present studys objective was to determine the maximally tolerated dose of a simultaneous in-field boost integrated with whole brain radiotherapy for palliative treatment of patients with one to three brain metastases using HT. METHODS AND MATERIALS The inclusion/exclusion criteria and endpoints were consistent with the Radiation Therapy Oncology Group 9508 radiosurgery trial. The cohorts were constructed with a 3 + 3 design; however, additional patients were enrolled in the lower dose tolerable cohorts during the toxicity assessment periods. Whole brain radiotherapy (30 Gy in 10 fractions) was delivered with a 5-30-Gy (total lesion dose of 35-60 Gy in 10 fractions) simultaneous in-field boost delivered to the brain metastases. The maximally tolerated dose was determined by the frequency of neurologic Grade 3-5 National Cancer Institute Common Toxicity Criteria, version 3.0, dose-limiting toxicity events within each Phase I cohort. RESULTS A total of 48 patients received treatment in the 35-Gy (n = 3), 40-Gy (n = 16), 50-Gy (n = 15), 55-Gy (n = 8), and 60-Gy (n = 6) cohorts. No patients experienced dose-limiting toxicity events in any of the trial cohorts. The 3-month RECIST assessments available for 32 of the 48 patients demonstrated a complete response in 2, a partial response in 16, stable disease in 6, and progressive disease in 8 patients. CONCLUSION The delivery of 60 Gy in 10 fractions to one to three brain metastases synchronously with 30 Gy whole brain radiotherapy was achieved without dose-limiting central nervous system toxicity as assessed 3 months after treatment. This approach is being tested in a Phase II efficacy trial.

Optimization of megavoltage CT scan registration settings for thoracic cases on helical tomotherapy.

This study aims to investigate the settings that provide optimum registration accuracy when registering megavoltage CT (MVCT) studies acquired on tomotherapy with planning kilovoltage CT (kVCT) studies of patients with lung cancer. For each experiment, the systematic difference between the actual and planned positions of the thorax phantom was determined by setting the phantom up at the planning isocenter, generating and registering an MVCT study. The phantom was translated by 5 or 10 mm, MVCT scanned, and registration was performed again. A root-mean-square equation that calculated the residual error of the registration based on the known shift and systematic difference was used to assess the accuracy of the registration process. The phantom study results for 18 combinations of different MVCT/kVCT registration options are presented and compared to clinical registration data from 17 lung cancer patients. MVCT studies acquired with coarse (6 mm), normal (4 mm) and fine (2 mm) slice spacings could all be registered with similar residual errors. No specific combination of resolution and fusion selection technique resulted in a lower residual error. A scan length of 6 cm with any slice spacing registered with the full image fusion selection technique and fine resolution will result in a low residual error most of the time. On average, large corrections made manually by clinicians to the automatic registration values are infrequent. Small manual corrections within the residual error averages of the registration process occur, but their impact on the average patient position is small. Registrations using the full image fusion selection technique and fine resolution of 6 cm MVCT scans with coarse slices have a low residual error, and this strategy can be clinically used for lung cancer patients treated on tomotherapy. Automatic registration values are accurate on average, and a quick verification on a sagittal MVCT slice should be enough to detect registration outliers.

Optimization of megavoltage CT scan registration settings for brain cancer treatments on tomotherapy.

This study aims to determine the settings that provide the optimal clinical accuracy and consistency for the registration of megavoltage CT (MVCT) with planning kilovoltage CT image sets on the Hi-ART tomotherapy system. The systematic offset between the MVCT and the planning kVCT was determined by registration of multiple MVCT scans of a head phantom aligned with the planning isocentre. Residual error vector lengths and components were used to quantify the alignment quality for the phantom shifted by 5 mm in different directions obtained by all 27 possible combinations of MVCT inter-slice spacing, registration techniques and resolution. MVCT scans with normal slices are superior to coarse slices for registration of shifts in the superior-inferior, lateral and anterior-posterior directions. Decreasing the scan length has no detrimental effect on registration accuracy as long as the scan lengths are larger than 24 mm. In the case of bone technique and fine resolution, normal and fine MVCT scan slice spacing options give similar accuracy, so normal mode is preferable due to shorter procedure and less delivered dose required for patient set-up. A superior-inferior field length of 24-30 mm, normal slice spacing, bone technique, and fine resolution is the optimum set of registration settings for MVCT scans of a Rando head phantom acquired with the Hi-ART tomotherapy system, provided the registration shifts are less than 5 mm.

Evaluation of inter-fraction prostate motion using kilovoltage cone beam computed tomography during radiotherapy.

AIMS The success of delivering the prescribed radiation dose to the prostate while sparing adjacent sensitive tissues is largely dependent on the ability to accurately target the prostate during treatment. Kilovoltage cone beam computed tomography (CBCT) imaging can be used to monitor and compensate for inter-fraction prostate motion, but this procedure increases treatment session time and adds incidental radiation dose to the patient. We carried out a retrospective study of CBCT data to evaluate the systematic and random correction shifts of the prostate with respect to bones and external marks. MATERIALS AND METHODS A total of 449 daily CBCT studies from 17 patients undergoing intensity-modulated radiotherapy (IMRT) for localised prostate cancer were analysed. The difference between patient set-up correction shifts applied by radiation therapists (via matching prostate position in CBCT and planning computed tomography) and shifts obtained by matching bony anatomy in the same studies was used as a measure of the daily inter-fraction internal prostate motion. RESULTS The average systematic and random shifts in prostate positions, calculated over all fractions versus only 10 fractions, were not found to be significantly different. DISCUSSION The measured prostate shifts with respect to bony anatomy and external marks after the first 10 imaging sessions were shown to provide adequate predictive power for defining patient-specific margins in future fractions without a need for ongoing computed tomography imaging. Different options for CBCT imaging schedule are proposed that will reduce the treatment session time and imaging dose to radiotherapy patients while ensuring appropriate prostate cover and normal tissue sparing.

The effects of field-of-view and patient size on CT numbers from cone-beam computed tomography.

Cone-beam computed tomography (CBCT) is used for patient alignment before treatment and is ideal for use in adaptive radiotherapy to account for tumor shrinkage, organ deformation and weight loss. However, CBCT images are prone to artifacts such as streaking and cupping effects, reducing image quality and CT number accuracy. Our goal was to determine the optimum combination of cone-beam imaging options to increase the accuracy of image CT numbers. Several phantoms with and without inserts of known relative electron densities were imaged using the Varian on-board imaging system. It was found that CT numbers are most influenced by the selection of field-of-view and are dependent on object size and filter type. Image acquisition in half-fan mode consistently produced more accurate CT numbers, regardless of phantom size. Values measured using full-fan mode can differ by up to 7% from planning CT values. No differences were found between CT numbers of all phantom images with low and standard dose modes.