Three-dimensional patient setup errors at different treatment sites measured by the Tomotherapy megavoltage CT

Accuracy Evaluation Trial of Mixed Reality-Guided Spinal Puncture Technology

Purpose

To evaluate the accuracy of mixed reality (MR)-guided visualization technology for spinal puncture (MRsp).

Methods

MRsp involved the following three steps: 1. Lumbar spine computed tomography (CT) data were obtained to reconstruct virtual 3D images, which were imported into a HoloLens (2nd gen). 2. The patented MR system quickly recognized the spatial orientation and superimposed the virtual image over the real spine in the HoloLens. 3. The operator performed the spinal puncture with structural information provided by the virtual image. A posture fixation cushion was used to keep the subjects' lateral decubitus position consistent. 12 subjects were recruited to verify the setup error and the registration error. The setup error was calculated using the first two CT scans and measuring the displacement of two location markers. The projection points of the upper edge of the L3 spinous process (L3↑), the lower edge of the L3 spinous process (L3↓), and the lower edge of the L4 spinous process (L4↓) in the virtual image were positioned and marked on the skin as the registration markers. A third CT scan was performed to determine the registration error by measuring the displacement between the three registration markers and the corresponding real spinous process edges.

Results

The setup errors in the position of the cranial location marker between CT scans along the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) axes of the CT bed measured 0.09 ± 0.06 cm, 0.30 ± 0.28 cm, and 0.22 ± 0.12 cm, respectively, while those of the position of the caudal location marker measured 0.08 ± 0.06 cm, 0.29 ± 0.18 cm, and 0.18 ± 0.10 cm, respectively. The registration errors between the three registration markers and the subject's real L3↑, L3↓, and L4↓ were 0.11 ± 0.09 cm, 0.15 ± 0.13 cm, and 0.13 ± 0.10 cm, respectively, in the SI direction.

Conclusion

This MR-guided visualization technology for spinal puncture can accurately and quickly superimpose the reconstructed 3D CT images over a real human spine.

Treatment planning of total marrow irradiation with intensity-modulated spot-scanning proton therapy

Purpose

The goal of this study is to investigate treatment planning of total marrow irradiation (TMI) using intensity-modulated spot-scanning proton therapy (IMPT). The dosimetric parameters of the intensity-modulated proton plans were evaluated and compared with the corresponding TMI plans generated with volumetric modulated arc therapy (VMAT) using photon beams.

Methods

Intensity-modulated proton plans for TMI were created using the Monte Carlo dose-calculation algorithm in the Raystation 11A treatment planning system with spot-scanning proton beams from the MEVION S250i Hyperscan system. Treatment plans were generated with four isocenters placed along the longitudinal direction, each with a set of five beams for a total of 20 beams. VMAT-TMI plans were generated with the Eclipse-V15 analytical anisotropic algorithm (AAA) using a Varian Trilogy machine. Three planning target volumes (PTVs) for the bones, ribs, and spleen were covered by 12 Gy. The dose conformity index, D80, D50, and D10, for PTVs and organs at risk (OARs) for the IMPT plans were quantified and compared with the corresponding VMAT plans.

Results

The mean dose for most of the OARs was reduced substantially (5% and more) in the IMPT plans for TMI in comparison with VMAT plans except for the esophagus and thyroid, which experienced an increase in dose. This dose reduction is due to the fast dose falloff of the distal Bragg peak in the proton plans. The conformity index was found to be similar (0.78 vs 0.75) for the photon and proton plans. IMPT plans provided superior superficial dose coverage for the skull and ribs in comparison with VMAT because of increased entrance dose deposition by the proton beams.

Conclusion

Treatment plans for TMI generated with IMPT were superior to VMAT plans mainly due to a large reduction in the OAR dose. Although the current IMPT-TMI technique is not clinically practical due to the long overall treatment time, this study presents an enticing alternative to conventional TMI with photons by providing superior dose coverage of the targets, increased sparing of the OARs, and enhanced radiobiological effects associated with proton therapy.

Multi-institutional evaluation of MVCT guided patient registration and dosimetric precision in total marrow irradiation: A global health initiative by the international consortium of total marrow irradiation

PURPOSE

Total marrow irradiation (TMI) is a highly conformal treatment of the human skeleton structure requiring a high degree of precision and accuracy for treatment delivery. Although many centers worldwide initiated clinical studies using TMI, currently there is no standard for pretreatment patient setup. To this end, the accuracy of different patient setups was measured using pretreatment imaging. Their impact on dose delivery was assessed for multiple institutions.

METHODS AND MATERIALS

Whole body imaging (WBI) or partial body imaging (PBI) was performed using pretreatment megavoltage computed tomography (MVCT) in a helical Tomotherapy machine. Rigid registration of MVCT and planning kilovoltage computed tomography images were performed to measure setup error and its effect on dose distribution. The entire skeleton was considered the planning target volume (PTV) with five sub regions: head/neck (HN), spine, shoulder and clavicle (SC), and one avoidance structure, the lungs. Sixty-eight total patients (>300 images) across six institutions were analyzed.

RESULTS

Patient setup techniques differed between centers, creating variations in dose delivery. Registration accuracy varied by anatomical region and by imaging technique, with the lowest to the highest degree of pretreatment rigid shifts in the following order: spine, pelvis, HN, SC, and lungs. Mean fractional dose was affected in regions of high registration mismatch, in particular the lungs.

CONCLUSIONS

MVCT imaging and whole body patient immobilization was essential for assessing treatment setup, allowing for the complete analysis of 3D dose distribution in the PTV and lungs (or avoidance structures).

Cone-beam CT-based inter-fraction localization errors for tumors in the pelvic region

PURPOSE

To evaluate inter-fraction tumor localization errors (TE) in the RapidArc® treatment of pelvic cancers based on CBCT. Appropriate CTV-to PTV margins in a non-IGRT scenario have been proposed.

METHODS

Data of 928 patients with prostate, gynecological, and rectum/anal canal cancers were retrospectively analyzed to determine systematic and random localization errors. Two protocols were used: daily online IGRT (d-IGRT) and weekly IGRT. The latter consisted in acquiring a CBCT for the first 3 fractions and subsequently once a week. TE for patients who underwent d-IGRT protocol were calculated using either all CBCTs or the first 3.

RESULTS

The systematic (and random) TE in the AP, LL, and SI direction were: for prostate bed 2.7(3.2), 2.3(2.8) and 1.9(2.2) mm; for prostate 4.2(3.1), 2.9(2.8) and 2.3(2.2) mm; for gynecological 3.0(3.6), 2.4(2.7) and 2.3(2.5) mm; for rectum 2.8(2.8), 2.4(2.8) and 2.3(2.5) mm; for anal canal 3.1(3.3), 2.1(2.5) and 2.2(2.7) mm. CTV-to-PTV margins determined from all CBCTs were 14 mm in the AP, 10 mm in the LL and 9-9.5 mm in the SI directions for the prostate and the gynecological groups and 9.5-10.5 mm in AP, 9 mm in LL and 8-10 mm in the SI direction for the prostate bed and the rectum/anal canal groups. If assessed on the basis of the first 3 CBCTs, the calculated CTV-to-PTV margins were slightly larger.

CONCLUSIONS

without IGRT, large CTV-to-PTV margins up to 15 mm are required to account for inter-fraction tumor localization errors. Daily IGRT should be used for all hypo-fractionated treatments to reduce margins and avoid increased toxicity to critical organs.

Dose Escalation of Total Marrow Irradiation in High-Risk Patients Undergoing Allogeneic Hematopoietic Stem Cell Transplantation

Patients with refractory leukemia or minimal residual disease (MRD) at transplantation are at increased risk of relapse. Augmentation of irradiation, especially to sites of disease (ie, bone marrow) is one potential strategy for overcoming this risk. We studied the feasibility of radiation dose escalation in high-risk patients using total marrow irradiation (TMI) in a phase I dose-escalation trial. Four pediatric and 8 adult patients received conditioning with cyclophosphamide and fludarabine in conjunction with image-guided radiation to the bone marrow at 15 Gy and 18 Gy (in 3-Gy fractions), while maintaining the total body irradiation (TBI) dose to the vital organs (lungs, hearts, eyes, liver, and kidneys) at <13.2 Gy. The biologically effective dose of TMI delivered to the bone marrow was increased by 62% at 15 Gy and by 96% at 18 Gy compared with standard TBI. Although excessive dose-limiting toxicity, defined by graft failure or excessive specific organ toxicity, was not encountered, 3 of 6 patients experienced treatment-related mortality at 18 Gy. Thus, we halted enrollment at this dose level and treated an additional 4 patients at 15 Gy. The 1- year overall survival was 42% (95% confidence interval [CI], 15%-67%) and disease-free survival was 22% (95% CI, 4%-49%). The rate of relapse was 36% (95% CI, 10%-62%), and nonrelapse mortality was 42% (95% CI, 14%-70%). This study shows that TMI dose escalation to 15 Gy is feasible with acceptable toxicity in pediatric and adult patients with high-risk leukemia undergoing umbilical cord blood and sibling donor transplantation.

A retrospective tomotherapy image-guidance study: analysis of more than 9,000 MVCT scans for ten different tumor sites

The purpose of this study was to quantify the systematic and random errors for various disease sites when daily MVCT scans are acquired, and to analyze alterna- tive off-line verification protocols (OVP) with respect to the patient setup accuracy achieved. Alignment data from 389 patients (9,418 fractions) treated at ten differ- ent anatomic sites with daily image-guidance (IG) on a helical tomotherapy unit were analyzed. Moreover, six OVP were retrospectively evaluated. For each OVP, the frequency of the residual setup errors and additional margins required were calculated for the treatment sessions without image guidance. The magnitude of the three-dimensional vector displacement and its frequency were evaluated for all OVP. From daily IG, the main global systematic error was in the vertical direction (4.4-9.4 mm), and all rotations were negligible (less than 0.5°) for all anatomic sites. The lowest systematic and random errors were found for H&amp;N and brain patients. All OVP were effective in reducing the mean systematic error to less than 1 mm and 0.2° in all directions and roll corrections for almost all treatment sites. The treatment margins needed to adapt the residual errors should be increased by 2-5 mm for brain and H&amp;N, around 8 mm in the vertical direction for the other anatomic sites, and up to 19 mm in the longitudinal direction for abdomen patients. Almost 70% of the sessions presented a setup error of 3 mm for OVPs with an imaging frequency above 50%. Only for brain patients it would be feasible to apply an OVP because the residual setup error could be compensated for with a slight margin increase. However, daily imaging should be used for anatomic sites of difficult immobilization and/or large interfraction movement. 

Multi-institutional feasibility study of a fast patient localization method in total marrow irradiation with helical tomotherapy: a global health initiative by the international consortium of total marrow irradiation

PURPOSE

To develop, characterize, and implement a fast patient localization method for total marrow irradiation.

METHODS AND MATERIALS

Topographic images were acquired using megavoltage computed tomography (MVCT) detector data by delivering static orthogonal beams while the couch traversed through the gantry. Geometric and detector response corrections were performed to generate a megavoltage topogram (MVtopo). We also generated kilovoltage topograms (kVtopo) from the projection data of 3-dimensional CT images to reproduce the same geometry as helical tomotherapy. The MVtopo imaging dose and the optimal image acquisition parameters were investigated. A multi-institutional phantom study was performed to verify the image registration uncertainty. Forty-five MVtopo images were acquired and analyzed with in-house image registration software.

RESULTS

The smallest jaw size (front and backup jaws of 0) provided the best image contrast and longitudinal resolution. Couch velocity did not affect the image quality or geometric accuracy. The MVtopo dose was less than the MVCT dose. The image registration uncertainty from the multi-institutional study was within 2.8 mm. In patient localization, the differences in calculated couch shift between the registration with MVtopo-kVtopo and MVCT-kVCT images in lateral, cranial-caudal, and vertical directions were 2.2 ± 1.7 mm, 2.6 ± 1.4 mm, and 2.7 ± 1.1 mm, respectively. The imaging time in MVtopo acquisition at the couch speed of 3 cm/s was <1 minute, compared with ≥15 minutes in MVCT for all patients.

CONCLUSION

Whole-body MVtopo imaging could be an effective alternative to time-consuming MVCT for total marrow irradiation patient localization.

Optimizing image guidance frequency and implications on margins for gynecologic malignancies

Background

To analyze setup deviations using daily megavoltage computed tomography (MVCT) and to evaluate three MVCT frequency reducing protocols for gynecologic cancer patients treated with helical tomotherapy.

Methods

We recorded the setup errors of 56 patients with gynecological cancer observed throughout their whole course by matching their daily MVCT with the planning CT. Systematic and random errors were calculated on a patient and population basis. We defined three different protocols corresponding to MVCTs from the first five fractions (FFF), the first ten fractions (FTF) or from the first and third weeks (505). We compared theoretical. setup errors calculated using these 5 or 10 early MVCT scans with the actual errors found with the remaining fractions to to analyze the residual deviations.

Results

The total systematic (random) deviations had means of −2.0 (3.8)mm, 0.5 (3.4)mm, 0.5 (6.1)mm and −0.5° (0.9°) in vertical (V), longitudinal (LO), lateral (LA), and roll (R) directions, respectively. The proposed three MVCT protocols resulted in minor residual deviations. In all three protocols, 95% of all calculated residual deviations were less than or equal to 5 mm in all 3 directions. When examining the additional minimal CTV-PTV setup margins that were calculated based on these residual deviations, the 505 protocol would have allowed smaller margins than the FFF and FTF protocol, particularly in the V direction.

Conclusions

For patients with gynecologic cancer, the 505-protocol led to the lowest residual deviations and therefore might offer the best approach in reducing the frequency of pre-treatment MVCTs.

Total Body Irradiation (TBI) using Helical Tomotherapy in children and young adults undergoing stem cell transplantation

Background

Establishing Total Body Irradiation (TBI) using Helical Tomotherapy (HT) to gain better control over dose distribution and homogeneity and to individually spare organs at risk. Because of their limited body length the technique seems especially eligible in juvenile patients.

Patients and methods

The cohort consisted of 10 patients, 6 female and 4 male, aged 4 - 22 y with acute lymphoblastic- (ALL) or acute myeloic leukemia (AML). All patients presented with high risk disease features. Body length in treatment position ranged from 110–180 cm. Two Gy single dose was applied BID to a total dose of 12 Gy. Dose volume constraint for the PTV was 95% dose coverage for 95% of the volume. The lungs were spared to a mean dose of [less than or equal to] 10 Gy. Patients were positioned in a vac-loc bag in supine position with a 3-point head mask.

Results

Average D95 to the PTV was 11.7 Gy corresponding to a mean coverage of the PTV of 97.5%. Dmean for the lungs was 9.14 Gy. Grade 3–4 side effects were not observed.

Conclusions

TBI using HT is feasible and well tolerated. A benefit could be demonstrated with regard to dose distribution and homogeneity and the selective dose-reduction to organs at risk.

Is helical tomotherapy accurate and safe enough for spine stereotactic body radiotherapy?

PURPOSE

We assessed the accuracy and safety of spine stereotactic body radiation therapy (SBRT) using helical tomotherapy (HT) via evaluating intrafractional patient movement.

METHODS

From July 2009 to April 2011, 22 patients with spine lesions received SBRT using HT, with a total of 61 fractions. To evaluate intrafractional movement, we compared post-treatment megavoltage CT scans with planning CT images and obtained translational [lateral (X), craniocaudal (Y), anterioposterior (Z)] offsets and total displacements (R). We analyzed the correlation of intrafractional motion with patient and treatment characteristics. We also analyzed dosimetric change to the target and spinal cord, resulting from intrafractional movement, in the three patients that showed the greatest R values.

RESULTS

Intrafractional movements were 0.7 ± 0.6 mm (X), 1.1 ± 0.7 mm (Y), 0.9 ± 0.6 mm (Z), and 1.8 ± 0.6 mm (R). This movement did not correlate with age, pain score, treatment time, or treatment site. Only patients with lower BMIs have a tendency to move more during treatment. Patient immobilization using wrapping form (thermoplastic mask and BodyFIX(®) system) resulted in less lateral movement and total displacement than others (0.498 ± 0.409 vs. 1.138 ± 0.637 mm, P < 0.001 for X; and 1.638 ± 0.691 vs. 1.976 ± 0.495 mm, P = 0.032 for R). However, this intrafractional motion did not affect the dose delivery to the target and spinal cord.

CONCLUSION

SBRT using HT can be a safe treatment modality for spine metastasis with enhanced targeting accuracy.