Automatic end-to-end VMAT treatment planning for rectal cancers.

BACKGROUND: The treatment planning process from segmentation to producing a deliverable plan is time-consuming and labor-intensive. Existing solutions automate the segmentation and planning processes individually. The feasibility of combining auto-segmentation and auto-planning for volumetric modulated arc therapy (VMAT) for rectal cancers in an end-to-end process is not clear. PURPOSE: To create and clinically evaluate a complete end-to-end process for auto-segmentation and auto-planning of VMAT for rectal cancer requiring only the gross tumor volume contour and a CT scan as inputs. METHODS: Patient scans and data were retrospectively selected from our institutional records for patients treated for malignant neoplasm of the rectum. We trained, validated, and tested deep learning auto-segmentation models using nnU-Net architecture for clinical target volume (CTV), bowel bag, large bowel, small bowel, total bowel, femurs, bladder, bone marrow, and female and male genitalia. For the CTV, we identified 174 patients with clinically drawn CTVs. We used data for 18 patients for all structures other than the CTV. The structures were contoured under the guidance of and reviewed by a gastrointestinal (GI) radiation oncologist. The predicted results for CTV in 35 patients and organs at risk (OAR) in six patients were scored by the GI radiation oncologist using a five-point Likert scale. For auto-planning, a RapidPlan knowledge-based planning solution was modeled for VMAT delivery with a prescription of 25 Gy in five fractions. The model was trained and tested on 20 and 34 patients, respectively. The resulting plans were scored by two GI radiation oncologists using a five-point Likert scale. Finally, the end-to-end pipeline was evaluated on 16 patients, and the resulting plans were scored by two GI radiation oncologists. RESULTS: In 31 of 35 patients, CTV contours were clinically acceptable without necessary modifications. The CTV achieved a Dice similarity coefficient of 0.85 (±0.05) and 95% Hausdorff distance of 15.25 (±5.59) mm. All OAR contours were clinically acceptable without edits, except for large and small bowel which were challenging to differentiate. However, contours for total, large, and small bowel were clinically acceptable. The two physicians accepted 100% and 91% of the auto-plans. For the end-to-end pipeline, the two physicians accepted 88% and 62% of the auto-plans. CONCLUSIONS: This study demonstrated that the VMAT treatment planning technique for rectal cancer can be automated to generate clinically acceptable and safe plans with minimal human interventions.

Definitive single fraction spine stereotactic radiosurgery for metastatic sarcoma: Simultaneous integrated boost is associated with high tumor control and low vertebral fracture risk.

INTRODUCTION: Sarcoma spinal metastases (SSM) are particularly difficult to manage given their poor response rates to chemotherapy and inherent radioresistance. We evaluated outcomes in a cohort of patients with SSM uniformly treated using single-fraction simultaneous-integrated-boost (SIB) spine stereotactic radiosurgery (SSRS). MATERIALS AND METHODS: A retrospective review was conducted at a single tertiary institution treated with SSRS for SSM between April 2007-April 2023. 16-24 Gy was delivered to the GTV and 16 Gy uniformly to the CTV. Kaplan-Meier analysis was conducted to assess time to progression of disease (PD) with proportionate hazards modelling used to determine hazard ratios (HR) and respective 95 % confidence intervals (CI). RESULTS: 70 patients with 100 lesions underwent SSRS for SSM. Median follow-up was 19.3 months (IQR 7.7-27.8). Median age was 55 years (IQR42-63). Median GTV and CTVs were 14.5 cm3 (IQR 5-32) and 52.7 cm3 (IQR 29.5-87.5) respectively. Median GTV prescription dose and biologically equivalent dose (BED) [α/ß = 10] was 24 Gy and 81.6 Gy respectively. 85 lesions received 24 Gy to the GTV. 27 % of patients had Bilsky 1b or greater disease. 16 of 100 lesions recurred representing a crude local failure rate of 16 % with a median time to failure of 10.4 months (IQR 5.7-18) in cases which failed locally. 1-year actuarial local control (LC) was 89 %. Median overall survival (OS) was 15.3 months (IQR 7.7-25) from SSRS. Every 1 Gy increase in GTV absolute minimum dose (DMin) across the range (5.8-25 Gy) was associated with a reduced risk of local failure (HR = 0.871 [95 % CI 0.782-0.97], p = 0.009). 9 % of patients developed vertebral compression fractures at a median of 13 months post SSRS (IQR 7-25). CONCLUSION: This study represents one of the most homogenously treated and the largest cohorts of patients with SSM treated with single-fraction SSRS. Despite inherent radioresistance, SSRS confers durable and high rates of local control in SSM without unexpected long-term toxicity rates.

Automated field-in-field whole brain radiotherapy planning.

PURPOSE: We developed and tested an automatic field-in-field (FIF) solution for whole-brain radiotherapy (WBRT) planning that creates a homogeneous dose distribution by minimizing hotspots, resulting in clinically acceptable plans. METHODS: A configurable auto-planning algorithm was developed to automatically generate FIF WBRT plans independent of the treatment planning system. Configurable parameters include the definition of hotspots, target volume, maximum number of subfields, and minimum number of monitor units per field. This algorithm iteratively identifies a hotspot, creates two opposing subfields, calculates the dose, and optimizes the beam weight based on user-configured constraints of dose-volume histogram coverage and least-squared cost functions. The algorithm was retrospectively tested on 17 whole-brain patients. First, an in-house landmark-based automated beam aperture technique was used to generate the treatment fields and initial plans. Second, the FIF algorithm was employed to optimize the plans using physician-defined goals of 99.9% of the brain volume receiving 100% of the prescription dose (30 Gy in 10 fractions) and a target hotspot definition of 107% of the prescription dose. The final auto-optimized plans were assessed for clinical acceptability by an experienced radiation oncologist using a five-point scale. RESULTS: The FIF algorithm reduced the mean (± SD) plan hotspot percentage dose from 35.0 Gy (116.6%) ± 0.6 Gy (2.0%) to 32.6 Gy (108.8%) ± 0.4 Gy (1.2%). Also, it decreased the mean (± SD) hotspot V107% [cm3 ] from 959 ± 498 cm3 to 145 ± 224 cm3 . On average, plans were produced in 16 min without any user intervention. Furthermore, 76.5% of the auto-plans were clinically acceptable (needing no or minor stylistic edits), and all of them were clinically acceptable after minor clinically necessary edits. CONCLUSIONS: This algorithm successfully produced high-quality WBRT plans and can improve treatment planning efficiency when incorporated into an automatic planning workflow.

Acute and Late Pulmonary Effects After Radiation Therapy in Childhood Cancer Survivors: A PENTEC Comprehensive Review.

OBJECTIVES: The Pediatric Normal Tissue Effects in the Clinic (PENTEC) pulmonary task force reviewed dosimetric and clinical factors associated with radiation therapy (RT)-associated pulmonary toxicity in children. METHODS: Comprehensive search of PubMed (1965-2020) was conducted to assess available evidence and predictive models of RT-induced lung injury in pediatric cancer patients (<21 years old). Lung dose for radiation pneumonitis (RP) was obtained from dose-volume histogram (DVH) data. RP grade was obtained from standard criteria. Clinical pulmonary outcomes were evaluated using pulmonary function tests (PFTs), clinical assessment, and questionnaires. RESULTS: More than 2,400 abstracts were identified; 460 articles had detailed treatment and toxicity data; and 11 articles with both detailed DVH and toxicity data were formally reviewed. Pooled cohorts treated during 1999 to 2016 included 277 and 507 patients age 0.04 to 22.7 years who were evaluable for acute and late RP analysis, respectively. After partial lung RT, there were 0.4% acute and 2.8% late grade 2, 0.4% acute and 0.8% late grade 3, and no grade 4 to 5 RP. RP risk after partial thoracic RT with mean lung dose (MLD) <14 Gy and total lung V20Gy <30% is low. Clinical and self-reported pulmonary outcomes data included 8,628 patients treated during 1970 to 2013, age 0 to 21.9 years. At a median 2.9- to 21.9-year follow-up, patients were often asymptomatic; abnormal PFTs were common and severity correlated with lung dose. At ≥10-year follow-up, multi-institutional studies suggested associations between total or ipsilateral lung doses >10 Gy and pulmonary complications and deaths. After whole lung irradiation (WLI), pulmonary toxicity is higher; no dose response relationship was identified. Bleomycin and other chemotherapeutics at current dose regimens do not contribute substantially to adverse pulmonary outcomes after partial lung irradiation but increase risk with WLI. CONCLUSIONS: After partial lung RT, acute pulmonary toxicity is uncommon; grade 2 to 3 RP incidences are <1%. Late toxicities, including subclinical/asymptomatic impaired pulmonary function, are more common (<4%). Incidence and severity appear to increase over time. Upon review of available literature, there appears to be low risk of pulmonary complications in children with MLD < 14 Gy and V20Gy <30% using standard fractionated RT to partial lung volumes. A lack of robust data limit guidance on lung dose/volume constraints, highlighting the need for additional work to define factors associated with RT-induced lung injury.

Brain stereotactic radiosurgery using MR-guided online adaptive planning for daily setup variation: An end-to-end test.

Online magnetic resonance (MR)-guided radiotherapy is expected to benefit brain stereotactic radiosurgery (SRS) due to superior soft tissue contrast and capability of daily adaptive planning. The purpose of this study was to investigate daily adaptive plan quality with setup variations and to perform an end-to-end test for brain SRS with multiple metastases treated with a 1.5-Tesla MR-Linac (MRL). The RTsafe PseudoPatient Prime brain phantom was used with a delineation insert that includes two predefined structures mimicking gadolinium contrast-enhanced brain lesions. Daily adaptive plans were generated using six preset and six random setup variations. Two adaptive plans per daily MR image were generated using the adapt-to-position (ATP) and adapt-to-shape (ATS) workflows. An adaptive patient plan was generated on a diagnostic MR image with simulated translational and rotational daily setup variation and was compared with the reference plan. All adaptive plans were compared with the reference plan using the target coverage, Paddick conformity index, gradient index (GI), Brain V12 or V20, optimization time and total monitor units. Target doses were measured as an end-to-end test with two ionization chambers inserted into the phantom. With preset translational variations, V12 from the ATS plan was 17% lower than that of the ATP plan. With a larger daily setup variation, GI and V12 of the ATS plan were 10% and 16% lower than those of the ATP plan, respectively. Compared to the ATP plans, the plan quality index of the ATS plans was more consistent with the reference plan, and within 5% in both phantom and patient plans. The differences between the measured and planned target doses were within 1% for both treatment workflows. Treating brain SRS using an MRL is feasible and could achieve satisfactory dosimetric goals. Setup uncertainties could be accounted for using online plan adaptation. The ATS workflow achieved better dosimetric results than the ATP workflow at the cost of longer optimization time.

Validation of PTV margin for Gamma Knife Icon frameless treatment using a PseudoPatient® Prime anthropomorphic phantom.

The Gamma Knife Icon allows the treatment of brain tumors mask-based single-fraction or fractionated treatment schemes. In clinic, uniform axial expansion of 1 mm around the gross tumor volume (GTV) and a 1.5 mm expansion in the superior and inferior directions are used to generate the planning target volume (PTV). The purpose of the study was to validate this margin scheme with two clinical scenarios: (a) the patient's head remaining right below the high-definition motion management (HDMM) threshold, and (b) frequent treatment interruptions followed by plan adaptation induced by large pitch head motion. A remote-controlled head assembly was used to control the motion of a PseudoPatient® Prime head phantom; for dosimetric evaluations, an ionization chamber, EBT3 films, and polymer gels were used. These measurements were compared with those from the Gamma Knife plan. For the absolute dose measurements using an ionization chamber, the percentage differences for both targets were less than 3.0% for all scenarios, which was within the expected tolerance. For the film measurements, the two-dimensional (2D) gamma index with a 2%/2 mm criterion showed the passing rates of ≥87% in all scenarios except the scenario 1. The results of Gel measurements showed that GTV (D100 ) was covered by the prescription dose and PTV (D95 ) was well above the planned dose by up to 5.6% and the largest geometric PTV offset was 0.8 mm for all scenarios. In conclusion, the current margin scheme with HDMM setting is adequate for a typical patient's intrafractional motion.

Spine stereotactic radiosurgery for metastases from hepatobiliary malignancies: patient selection using PRISM scoring.

OBJECTIVE: Dose escalation via stereotactic radiation therapy techniques has been necessary for hepatobiliary malignancies in the primary and oligometastatic setting, but such dose escalation is challenging for spine metastases due to spinal cord proximity. Here, we investigate the role of spine stereotactic radiosurgery (SSRS) in the management of such metastases. METHODS: We retrospectively reviewed patients treated with SSRS to spinal metastases from hepatobiliary malignancies between 2004 and 2017 at our Institution. We used the Kaplan-Meier method to calculate overall survival (OS) and local control (LC) and Cox regression analysis to identify factors associated with disease-related outcomes. RESULTS: We identified 28 patients treated to 43 spinal metastases with SSRS for either HCC or cholangiocarcinoma. The 1-year LC and OS were 85% and 23%, respectively. The median time to death was 6.2 months, while median time to local failure was not reached. Tumor volume > 60 cc (SHR 6.65, p = 0.03) and Bilsky ≥ 1c (SHR 4.73, p = 0.05) predicted for poorer LC, while BED10 > 81 Gy trended towards better local control (SHR 4.35, p = 0.08). Child-Pugh Class (HR 3.02, p = 0.003), higher PRISM Group (HR 3.49, p = 0.001), and systemic disease progression (HR 3.65, p = 0.001) were associated with worse mortality based on univariate modeling in patients treated with SSRS; on multivariate analysis, PRISM Group (HR 2.28, p = 0.03) and systemic disease progression (HR 2.67, p = 0.03) remained significant. Four patients (10%) developed compression deformity and one patient (2%) developed radiation neuritis. CONCLUSION: SSRS provides durable local control in patients with metastatic hepatobiliary malignancies, with higher BED necessary to ensure excellent LC. PRISM scoring is a promising prognostic tool to aid SSRS patient selection.

The utility of quantitative CT radiomics features for improved prediction of radiation pneumonitis.

PURPOSE: The purpose of this study was to explore gains in predictive model performance for radiation pneumonitis (RP) using pretreatment CT radiomics features extracted from the normal lung volume. METHODS: A total of 192 patients treated for nonsmall cell lung cancer with definitive radiotherapy were considered in the current study. In addition to clinical and dosimetric data, CT radiomics features were extracted from the total lung volume defined using the treatment planning scan. A total of 6851 features (15 clinical, 298 total lung and heart dosimetric, and 6538 image features) were gathered and considered candidate predictors for modeling of RP grade ≥3. Models were built with the least absolute shrinkage and selection operator (LASSO) logistic regression and applied to the set of candidate predictors with 50 iterations of tenfold nested cross-validation. RESULTS: In the current cohort, 30 of 192 patients (15.6%) presented with RP grade ≥3. Average cross-validated AUC (CV-AUC) using only the clinical and dosimetric parameters was 0.51. CV-AUC was 0.68 when total lung CT radiomics features were added. Analysis with the entire set of available predictors revealed seven different image features selected in at least 40% of the model fits. CONCLUSIONS: We have successfully incorporated CT radiomics features into a framework for building predictive RP models via LASSO logistic regression. Addition of normal lung image features produced superior model performance relative to traditional dosimetric and clinical predictors of RP, suggesting that pretreatment CT radiomics features should be considered in the context of RP prediction.

Sparing of normal tissues with volumetric arc radiation therapy for glioblastoma: single institution clinical experience.

BACKGROUND: Patients with glioblastoma multiforme (GBM) require radiotherapy as part of definitive management. Our institution has adopted the use of volumetric arc therapy (VMAT) due to superior sparing of the adjacent organs at risk (OARs) compared to intensity modulated radiation therapy (IMRT). Here we report our clinical experience by analyzing target coverage and sparing of OARs for 90 clinical treatment plans. METHODS: VMAT and IMRT patient cohorts comprising 45 patients each were included in this study. For all patients, the planning target volume (PTV) received 50 Gy in 30 fractions, and the simultaneous integrated boost PTV received 60 Gy. The characteristics of the two patient cohorts were examined for similarity. The doses to target volumes and OARs, including brain, brainstem, hippocampi, optic nerves, eyes, and cochleae were then compared using statistical analysis. Target coverage and normal tissue sparing for six patients with both clinical IMRT and VMAT plans were analyzed. RESULTS: PTV coverage of at least 95% was achieved for all plans, and the median mean dose to the boost PTV differed by only 0.1 Gy between the IMRT and VMAT plans. Superior sparing of the brainstem was found with VMAT, with a median difference in mean dose being 9.4 Gy. The ipsilateral cochlear mean dose was lower by 19.7 Gy, and the contralateral cochlea was lower by 9.5 Gy. The total treatment time was reduced by 5 min. The difference in the ipsilateral hippocampal D100% was 12 Gy, though this is not statistically significant (P = 0.03). CONCLUSIONS: VMAT for GBM patients can provide similar target coverage, superior sparing of the brainstem and cochleae, and be delivered in a shorter period of time compared with IMRT. The shorter treatment time may improve clinical efficiency and the quality of the treatment experience. Based on institutional clinical experience, use of VMAT for the treatment of GBMs appears to offer no inferiority in comparison to IMRT and may offer distinct advantages, especially for patients who may require re-irradiation.

Lung Size and the Risk of Radiation Pneumonitis.

PURPOSE: The purpose of this study was to identify patient populations treated for non-small cell lung cancer (NSCLC) who may be more at risk of radiation pneumonitis. METHODS AND MATERIALS: A total of 579 patients receiving fractionated 3D conformal or intensity modulated radiation therapy (IMRT) for NSCLC were included in the study. Statistical analysis was performed to search for cohorts of patients with higher incidences of radiation pneumonitis. In addition to conventional risk factors, total and spared lung volumes were analyzed. The Lyman-Kutcher-Burman (LKB) and cure models were then used to fit the incidence of radiation pneumonitis as a function of lung dose and other factors. RESULTS: Total lung volumes with a sparing of less than 1854 cc at 40 Gy were associated with a significantly higher incidence of radiation pneumonitis at 6 months (38% vs 12% for patients with larger volumes, P<.001). This patient cohort was overwhelmingly female and represented 22% of the total female population of patients and nearly 30% of the cases of radiation pneumonitis. An LKB fit to normal tissue complication probability (NTCP) including volume as a dose modifying factor resulted in a dose that results in a 50% probability of complication for the smaller spared volume cohort that was 9 Gy lower than the fit to all mean lung dose data and improved the ability to predict radiation pneumonitis (P<.001). Using an effective dose parameter of n=0.42 instead of mean lung dose further improved the LKB fit. Fits to the data using the cure model produced similar results. CONCLUSIONS: Spared lung volume should be considered when treating NSCLC patients. Separate dose constraints based on smaller spared lung volume should be considered. Smaller spared lung volume patients should be followed closely for signs of radiation pneumonitis.

Survival and toxicity following sequential multimodality treatment including whole abdominopelvic radiotherapy for patients with desmoplastic small round cell tumor.

BACKGROUND AND PURPOSE: Desmoplastic small round cell tumor (DSRCT) is a rare, aggressive malignancy. We report survival rates and toxicity associated with sequential multimodality treatment including whole abdominopelvic radiation therapy (WART). MATERIAL AND METHODS: Medical records of 32 patients with DSRCT treated at our institution were reviewed. Patients underwent chemotherapy, cytoreductive surgery with hyperthermic intraperitoneal chemoperfusion (HIPEC), followed by WART with intensity-modulated radiation or volumetric-modulated arc therapy. RESULTS: Median overall survival (OS) was 60months. After 18months of follow-up, 20 patients (62.5%) had disease recurrence and median disease-free survival (DFS) was 10months. Median time to extrahepatic abdominal failure was 19.4months. Factors affecting time to local progression included liver metastases at diagnosis, and an interval of greater than 5.6months between diagnosis and HIPEC or greater than 2.1months between HIPEC and WART. None of these factors altered OS. Grade 3 or higher toxicities occurred in 84% of patients. CONCLUSIONS: WART following chemotherapy, surgical cytoreduction and HIPEC is an aggressive treatment for DSRCT patients and can result in severe side effects. Our median OS of 5years is favorable compared to prior studies, despite a median DFS of only 10months, which may be due to improved salvage therapies.

In-phantom dose verification of prostate IMRT and VMAT deliveries using plastic scintillation detectors.

The goal of this work was to demonstrate the feasibility of using a plastic scintillation detector (PSD) incorporated into a prostate immobilization device to verify doses in vivo delivered during intensity-modulated radiation therapy (IMRT) and volumetric modulated-arc therapy (VMAT) for prostate cancer. The treatment plans for both modalities had been developed for a patient undergoing prostate radiation therapy. First, a study was performed to test the dependence, if any, of PSD accuracy on the number and type of calibration conditions. This study included PSD measurements of each treatment plan being delivered under quality assurance (QA) conditions using a rigid QA phantom. PSD results obtained under these conditions were compared to ionization chamber measurements. After an optimal set of calibration factors had been found, the PSD was combined with a commercial endorectal balloon used for rectal distension and prostate immobilization during external beam radiotherapy. This PSD-enhanced endorectal balloon was placed inside of a deformable anthropomorphic phantom designed to simulate male pelvic anatomy. PSD results obtained under these so-called "simulated treatment conditions" were compared to doses calculated by the treatment planning system (TPS). With the PSD still inserted in the pelvic phantom, each plan was delivered once again after applying a shift of 1 cm anterior to the original isocenter to simulate a treatment setup error.The mean total accumulated dose measured using the PSD differed the TPS-calculated doses by less than 1% for both treatment modalities simulated treatment conditions using the pelvic phantom. When the isocenter was shifted, the PSD results differed from the TPS calculations of mean dose by 1.2% (for IMRT) and 10.1% (for VMAT); in both cases, the doses were within the dose range calculated over the detector volume for these regions of steep dose gradient. Our results suggest that the system could benefit prostate cancer patient treatment by providing accurate in vivo dose reports during treatment and verify in real-time whether treatments are being delivered according to the prescribed plan.

Reproducibility and genital sparing with a vaginal dilator used for female anal cancer patients.

PURPOSE: Acute vulvitis, acute urethritis, and permanent sexual dysfunction are common among patients treated with chemoradiation for squamous cell carcinoma of the anal canal. Avoidance of the genitalia may reduce sexual dysfunction. A vaginal dilator may help delineate and displace the vulva and lower vagina away from the primary tumor. The goal of this study was to evaluate the positional reproducibility and vaginal sparing with the use of a vaginal dilator. MATERIALS AND METHODS: Ten female patients treated with IMRT for anal cancer were included in this study. A silicone vaginal dilator measuring 29 mm in diameter and 114 mm in length was inserted into the vagina before simulation and each treatment. The reproducibility of dilator placement was investigated with antero-posterior and lateral images acquired daily. Weekly cone beam CT (CBCT) imaging was used to confirm coverage of the GTV, which was typically posterior and inferior to the dilator apex. Finally, a planning study was performed to compare the vaginal doses for these 10 patients to a comparable group of 10 female patients who were treated for anal cancer with IMRT without vaginal dilators. RESULTS: The absolute values of the location of the dilator apex were 7.0 ± 7.8mm in the supero-inferior direction, 7.5 ± 5.5 mm in the antero-posterior, and 3.8 ± 3.1mm in the lateral direction. Coverage of the GTV and CTV was confirmed from CBCT images. The mean dose to the vagina was lower by 5.5 Gy, on average, for the vaginal dilator patients, compared to patients treated without vaginal dilators. CONCLUSION: The vaginal dilator tended to be inserted more inferiorly during treatment than during simulation. For these ten patients, this did not compromise tumor coverage. Combined with IMRT treatment planning, use of a vaginal dilator could allow for maximum sparing of female genitalia for patients undergoing radiation therapy for anal cancer.

Liquid scintillator for 2D dosimetry for high-energy photon beams.

Complex radiation therapy techniques require dosimetric verification of treatment planning and delivery. The authors investigated a liquid scintillator (LS) system for application for real-time high-energy photon beam dosimetry. The system was comprised of a transparent acrylic tank filled with liquid scintillating material, an opaque outer tank, and a CCD camera. A series of images was acquired when the tank with liquid scintillator was irradiated with a 6 MV photon beam, and the light data measured with the CCD camera were filtered to correct for scattering of the optical light inside the liquid scintillator. Depth-dose and lateral profiles as well as two-dimensional (2D) dose distributions were found to agree with results from the treatment planning system. Further, the corrected light output was found to be linear with dose, dose rate independent, and is robust for single or multiple acquisitions. The short time needed for image acquisition and processing could make this system ideal for fast verification of the beam characteristics of the treatment machine. This new detector system shows a potential usefulness of the LS for 2D QA.

Respiratory gating with EPID-based verification: the MDACC experience.

We have investigated the feasibility and accuracy of using a combination of internal and external fiducials for respiratory-gated image-guided radiotherapy of liver tumors after screening for suitable patients using a mock treatment. Five patients were enrolled in the study. Radio-opaque fiducials implanted adjacent to the liver tumor were used for daily online positioning using either electronic portal or kV images. Patient eligibility was assessed by determining the degree of correlation between the external and internal fiducials as analyzed during a mock treatment. Treatment delivery was based on the modification of conventional amplitude-based gating. Finally, the accuracy of respiratory-gated treatment using an external fiducial was verified offline using the cine mode of an electronic portal imaging device. For all patients, interfractional contribution to the random error was 2.0 mm in the supero-inferior direction, which is the dominant direction of motion due to respiration, while the interfractional contribution to the systematic error was 0.9 mm. The intrafractional contribution to the random error was 1.0 mm. One of the significant advantages to this technique is improved patient set-up using implanted fiducials and gated imaging. Daily assessment of images acquired during treatment verifies the accuracy of the delivered treatment and uncovers problems in patient set-up.

Patient dosimetry for total body irradiation using single-use MOSFET detectors.

We studied the usefulness of a new type of solid-state detector, the OneDose single-use MOSFET (metal oxide semiconductor field effect transistor) dosimeter, for entrance dose measurements for total body irradiation (TBI). The factory calibration factors supplied by the manufacturer are applicable to conventional radiotherapy beam arrangements and therefore may not be expected to be valid for TBI dosimetry because of the large field sizes and extended source-to-axis distances used. OneDose detectors were placed under a 1-cm thick bolus at the head, neck, and umbilicus of 9 patients undergoing TBI procedures. Thermoluminescent dosimeters (TLDs) were placed beside the detectors. We found that the OneDose readings differed from the TLD readings by 4.6% at the head, 1.7% at the neck, and 3.9% at the umbilicus, with corresponding standard deviations of 3.9%, 2.2%, and 2.7%. For all patient measurements, 95% of the OneDose readings fell within 3.3% +/- 6.0% of the TLD readings. Anthropomorphic phantom measurements showed differences of -0.1% at the neck and -1.2% midway between the phantom's carina and umbilicus. Our results suggest that these detectors could be used for TBI quality assurance monitoring, although TLDs should remain the standard when critical dose measurements are performed. If OneDose detectors are to be used for TBI, the use of more than one at each location is strongly recommended. Because the detectors are designed for single use, they cannot be individually calibrated. However, to obtain institution-specific correction factors for better applicability to TBI dosimetry, measurements of several detectors taken from a particular lot could also be obtained in phantom with the TBI geometry configurations used for patient treatment.

Transient noise characterization and filtration in CCD cameras exposed to stray radiation from a medical linear accelerator.

Charge coupled devices (CCDs) are being increasingly used in radiation therapy for dosimetric purposes. However, CCDs are sensitive to stray radiation. This effect induces transient noise. Radiation-induced noise strongly alters the image and therefore limits its quantitative analysis. The purpose of this work is to characterize the radiation-induced noise and to develop filtration algorithms to restore image quality. Two models of CCD were used for measurements close to a medical linac. The structure of the transient noise was first characterized. Then, four methods of noise filtration were compared: median filtering of a time series of identical images, uniform median filtering of single images, an adaptive filter with switching mechanism, and a modified version of the adaptive switch filter. The intensity distribution of noisy pixels was similar in both cameras. However, the spatial distribution of the noise was different: The average noise cluster size was 1.2 +/- 0.6 and 3.2 +/- 2.7 pixels for the U2000 and the Luca, respectively. The median of a time series of images resulted in the best filtration and minimal image distortion. For applications where time series is impractical, the adaptive switch filter must be used to reduce image distortion. Our modified version of the switch filter can be used in order to handle nonisolated groups of noisy pixels.

4D-CT imaging with synchronized intravenous contrast injection to improve delineation of liver tumors for treatment planning.

We have developed a tumor-specific protocol for the 4D-CT imaging of liver tumors using synchronized intravenous (IV) contrast injection to improve the accuracy of tumor delineation for treatment planning. Most liver metastases and cholangiocarcinomas can be imaged in the portal venous phase, while hepatocellular carcinomas are most visible in the delayed phase. Combined 4D-CT imaging with synchronized IV contrast allows for both enhancement of tumor contrast and coverage over the entire breathing cycle.