Feasibility study of total marrow lymphoid irradiation with volumetric modulated arc therapy: clinical implementation in a tertiary care center.

PURPOSE: Total marrow lymphoid irradiation (TMLI) with volumetric modulated arc therapy (VMAT) is challenging due to large treatment fields with multiple isocenters, field matching at junctions, and targets being surrounded by many organs at risk. This study aimed to describe our methodology for safe dose escalation and accurate dose delivery of TMLI treatment with the VMAT technique based on early experience at our center. MATERIALS AND METHODS: Computed tomography (CT) scans were acquired in head-first supine and feet-first supine orientations for each patient with an overlap at mid-thigh. VMAT plans were generated for 20 patients on the head-first CT images with either three or four isocenters in the Eclipse treatment planning system (Varian Medical Systems Inc., Palo Alto, CA) and the treatment was delivered in a Clinac 2100 C/D linear accelerator (Varian Medical Systems Inc., Palo Alto, CA). RESULTS: Five patients were treated with a prescription dose of 13.5 Gy in 9 fractions and 15 patients were treated with an escalated dose of 15 Gy in 10 fractions. The mean doses to 95% of the clinical target volume (CTV) and planning target volume (PTV) were 14.3 ± 0.3 Gy and 13.6 ± 0.7 Gy for the prescription doses of 15 Gy, and 13 ± 0.2 Gy and 12.3 ± 0.3 Gy for the prescription doses of 13.5 Gy, respectively. Mean dose to the lung in both schedules was 8.7 ± 0.6 Gy. The overall time taken to execute the treatment plans was approximately 2 h for the first fraction and 1.5 h for subsequent fractions. The average in-room time of 15.5 h per patient over 5 days leads to potential changes in the regular treatment schedules for other patients. CONCLUSION: This feasibility study highlights the methodology adopted for safe implementation of TMLI with the VMAT technique at our institution. Escalation of dose to the target with adequate coverage and sparing of critical structures was achieved with the adopted treatment technique. Clinical implementation of this methodology at our center could serve as a practical guide to start the VMAT-based TMLI program safely by others who are keen to start this service.

In-vivo dose measurements with MOSFET dosimeters during MV portal imaging.

BACKGROUND: The purpose of this study was to investigate the feasibility of MOSFET dosimeter in measuring eye dose during 2D MV portal imaging for setup verification in radiotherapy. MATERIALS AND METHODS: The in-vivo dose measurements were performed by placing the dosimeters over the eyes of 30 brain patients during the acquisition of portal images in linear accelerator by delivering 1 MU with the field sizes of 10 × 10 cm2 and 15 × 15 cm2. RESULTS: The mean doses received by the left and right eyes of 10 out of 30 patients when both eyes were completely inside the anterior portal field were found to be 2.56 ± 0.2 cGy and 2.75 ± 0.2, respectively. Similarly, for next 10 patients out of the same 30 patients the mean doses to left and right eyes when both eyes were completely out of the anterior portal fields were found to be 0.13 ± 0.02 cGy and 0.17 ± 0.02 cGy, respectively. The mean doses to ipsilateral and contralateral eye for the last 10 patients when one eye was inside the anterior portal field were found to be 3.28 ± 0.2 cGy and 0.36 ± 0.1 cGy, respectively. CONCLUSION: The promising results obtained during 2D MV portal imaging using MOSFET have shown that this dosimeter is well suitable for assessing low doses during imaging thereby enabling to optimize the imaging procedure using the dosimetric data obtained. In addition, the documentation of the dose received by the patient during imaging procedure is possible with the help of an in-built software in conjunction with the MOSFET reader module.

Dosimetric and clinical advantages of adapting the DIBH technique to hybrid solitary dynamic portal radiotherapy for left-sided chest-wall plus regional nodal irradiation.

To evaluate the dosimetric and clinical advantages of using deep-inspiration breath-hold (DIBH) technique in hybrid solitary dynamic portal radiotherapy (hSDPRT) for left-sided chest-wall plus regional nodal irradiation and to demonstrate a simplified strategy for preclinical commissioning and calibration of DIBH-gating technique. Fifteen patients with left-sided breast cancer who underwent postmastectomy radiotherapy using hSDPRT were retrospectively evaluated. Two sets of planning-CT images were acquired for each patient, one with free/normal breathing and the other with DIBH. The hSDPRT plans were computed to deliver about 85% of the prescribed dose using static open fields and 15% of dose using a less complex solitary dynamic field. The dosimetric differences between the paired samples were compared using the Wilcoxon signed-rank test. For clinical commissioning of gated treatments, a respiratory simulator equipped with a microcontroller was programmed to simulate free-breathing and DIBH-patterns using a custom-developed android application. While both the hSDPRT plans displayed identical target coverage on both the image-sets, the DIBH technique resulted in statistically significant differences in various dose-volume metrics of heart, left-anterior-descending artery, and ipsilateral-lung structures. The hSDPRT plan with DIBH entails reduced total monitor unit (354.9 ± 13.6 MU) and breath-hold time ranging from 2.9 ± 0.3 to 13.7 ± 0.8 seconds/field, along with an acceptable impact on overall machine throughput. DIBH is a feasible method to effectively address the delivery uncertainty and produce substantial sparing of heart and lung when combined with hSDPRT. Streamlined procedures for commissioning and calibration of DIBH-gating technique are essential for more efficient clinical practice.

A new strategy for craniospinal axis localization and adaptive dosimetric evaluation using cone beam CT.

BACKGROUND AND AIM: Computational complexities encountered in craniospinal irradiation (CSI) have been widely investigated with different planning strategies. However, localization of the entire craniospinal axis (CSA) and evaluation of adaptive treatment plans have traditionally been ignored in CSI treatment. In this study, a new strategy for CSI with comprehensive CSA localization and adaptive plan evaluation has been demonstrated using cone beam CT with extended longitudinal field-of-view (CBCTeLFOV). MATERIALS AND METHODS: Multi-scan CBCT images were acquired with fixed longitudinal table translations (with 1 cm cone-beam overlap) and then fused into a single DICOM-set using the custom software coded in MatLab™. A novel approach for validation of CBCTeLFOV was demonstrated by combined geometry of Catphan-504 and Catphan-604 phantoms. To simulate actual treatment scenarios, at first, the end-to-end workflow of CSI with VMAT was investigated using an anthropomorphic phantom and then applied for two patients (based on random selection). RESULTS: The fused CBCTeLFOV images were in excellent agreement with planning CT (pCT). The custom developed software effectively manages spatial misalignments arising out of the uncertainties in treatment/setup geometry. Although the structures mapped from pCT to CBCTeLFOV showed minimal variations, a maximum spatial displacement of up to 1.2 cm (and the mean of 0.8 ± 0.3 cm) was recorded in phantom study. Adaptive plan evaluation of patient paradigms showed the likelihood of under-dosing the craniospinal target. CONCLUSION: Our protocol serves as a guide for precise localization of entire CSA and to ensure adequate dose to the large and complex targets. It can also be adapted for other complex treatment techniques such as total-marrow-irradiation and total-lymphoid-irradiation.

Trajectory log file sensitivity: A critical analysis using DVH and EPID.

AIM: The aim of this study was to investigate the sensitivity of the trajectory log file based quality assurance to detect potential errors such as MLC positioning and gantry positioning by comparing it with EPID measurement using the most commonly used criteria of 3%/3 mm. MATERIALS AND METHODS: An in-house program was used to modified plans using information from log files, which can then be used to recalculate a new dose distribution. The recalculated dose volume histograms (DVH) were compared with the originals to assess differences in target and critical organ dose. The dose according to the differences in DVH was also compared with dosimetry from an electronic portal imaging device. RESULTS: In all organs at risk (OARs) and planning target volumes (PTVs), there was a strong positive linear relationship between MLC positioning and dose error, in both IMRT and VMAT plans. However, gantry positioning errors exhibited little impact in VMAT delivery. For the ten clinical cases, no significant correlations were found between gamma passing rates under the criteria of 3%/3 mm for the composite dose and the mean dose error in DVH (r < 0.3, P > 0.05); however, a significant positive correlation was found between the gamma passing rate of 3%/3 mm (%) averaged over all fields and the mean dose error in the DVH of the VMAT plans (r = 0.59, P < 0.001). CONCLUSIONS: This study has successfully shown the sensitivity of the trajectory log file to detect the impact of systematic MLC errors and random errors in dose delivery and analyzed the correlation of gamma passing rates with DVH.

Validation of Delivery Consistency for Intensity-Modulated Radiation Therapy and Volumetric-Modulated Arc Therapy Plans.

The delivery consistency of a Varian Edge linear accelerator over the entire course of treatment for nasopharynx carcinoma (NPC) and prostate cancer intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) treatment plans was investigated using four different approaches. Three NPCs and three prostate plans were delivered in 34 and 29 consecutive days, respectively, using a Varian Edge equipped with a 120 high-definition (HD) multileaf collimator (MLC). All deliveries were measured with an electronic portal imaging device (EPID), and MapCheck2 and ArcCheck commercial systems with gamma analysis used to compare the results of all daily measurements against the pretreatment patient-specific quality assurance. The daily log files generated were also assessed for differences between the actual and planned doses using an in-house program to replace the original values in the DICOM plan files with the delivered parameter values from the log file, and then exporting the plans back to the treatment planning system for reconstruction of the actual dose delivered. The trajectory log file and EPID methods showed very good agreement, with minimal deviations between the daily delivered and reference doses. However, comparisons of the MapCheck2 and ArcCheck with the EPID revealed statistically significant differences (P < 0.001, one-tailed) with greater daily fluctuations, raising concerns over the performance, and reliability of the MapCheck2 and ArcCheck systems when being used to identify IMRT and VMAT plans with poor dosimetric accuracy. We conclude that the Varian Edge linear accelerator equipped with a 120 HD MLC can consistently deliver IMRT and VMAT plans over the entire treatment course.

A study on the effect of detector resolution on gamma index passing rate for VMAT and IMRT QA.

The main objectives of this study are to (1) analyze the sensitivity of various gamma index passing rates using different types of detectors having different resolutions and (2) investigate the sensitivity of various gamma criteria in intensity-modulated radiation therapy (IMRT) and volumetrically modulated arc therapy (VMAT) quality assurance (QA) for the detection of systematic multileaf collimator (MLC) errors using an electronic portal imaging device (EPID) and planar (MapCheck2) and cylindrical (ArcCheck) diode arrays. We also evaluated whether the correlation between the gamma passing rate (%GP) and the percentage dose error (%DE) of the dose-volume histogram (DVH) metrics was affected by the finite spatial resolution of the array detectors. We deliberately simulated systematic MLC errors of 0.25 mm, 0.50 mm, 0.75 mm, and 1 mm in five clinical nasopharyngeal carcinoma cases, thus creating 40 plans with systematic MLC errors. All measurements were analyzed field by field using gamma criteria of 3%/3 mm, 3%/2 mm, 3%/1 mm, and 2%/2 mm, with a passing rate of 90% applied as the action level. Our results showed that 3%/1 mm is the most sensitive criterion for the detection of systematic MLC errors when using EPID, with the steepest slope from the best-fit line and an area under the receiver operating characteristic (ROC) curve >0.95. With respect to the 3%/1 mm criterion, a strong correlation between %GP and %DE of the DVH metrics was observed only when using the EPID. However, with respect to the same criteria, a 0.75 mm systematic MLC error can go undetected when using MapCheck2 and ArcCheck, with an area under the ROC curve <0.75. Furthermore, a lack of correlation between %GP and %DE of the DVH metrics was observed in MapCheck2 and ArcCheck. In conclusion, low-spatial resolution detectors can affect the results of a per-field gamma analysis and render the analysis unable to accurately separate erroneous and non-erroneous plans. Meeting these new sensitive criteria is expected to ensure clinically acceptable dose errors.

Is the Deep Inspiration Breath-Hold Technique Superior to the Free Breathing Technique in Cardiac and Lung Sparing while Treating both Left-Sided Post-Mastectomy Chest Wall and Supraclavicular Regions?

AIMS: To evaluate the efficacy of the deep inspirational breath-hold (DIBH) technique and its dosimetric advantages over the free breathing (FB) technique in cardiac (heart and left anterior descending artery [LAD]) and ipsilateral lung sparing in left-sided post-mastectomy field-in-field conformal radiotherapy. DIBH is highly reproducible, and this study aims to find out its dosimetric benefits over FB. MATERIALS AND METHODS: Nineteen left-sided mastectomy patients were immobilized using breast boards with both arms positioned above the head. All patients had 2 sets of planning CT images (one in FB and another in DIBH) with a Biograph TruePoint HD CT scanner in the same setup. DIBH was performed by tracking the respiratory cycles using a Varian Real-Time Position Management system. The target (chest wall and supraclavicular region), organs at risk (OARs; ipsilateral lung, contralateral lung, heart, LAD, and contralateral breast), and other organs of interests were delineated as per the RTOG (Radiation Therapy Oncology Group) contouring guidelines. The single-isocenter conformal fields in the field treatment plans were generated with the Eclipse Treatment Planning System (Varian Medical Systems) for both FB and DIBH images, and the doses to the target and OARs were compared. The standard fractionation regimen of 50 Gy in 25 fractions over a period of 5 weeks was used for all patients in this study. RESULTS AND DISCUSSION: The target coverage parameters (V95, V105, V107, and D_mean) were found to be 97.8 ± 0.9, 6.1 ± 3.4, 0.2 ± 0.3, and 101.9 ± 0.5% in the FB plans and 98.1 ± 0.8, 6.1 ± 3.2, 0.2 ± 0.3, and 101.9 ± 0.4% in the DIBH plans, respectively. The plan quality indices (conformity index and homogeneity index) also showed 1.3 ± 0.2 and 0.1 for the FB plans and 1.2 ± 0.3 and 0.1 for the DIBH plans, respectively. There was a significant reduction in dose to the heart in the DIBH plans compared to the FB plans, with p values of nearly 0 for the V5, V10, V25, V30, and D_mean dosimetric parameters. The difference in ipsilateral lung doses between FB and DIBH showed statistically significant p values, and the differences in mean doses were found to be 7, 15.7, 11.8, and 10.7% for V5, V20, V30, and D_mean, respectively. There was a significant reduction in dose to the LAD in the DIBH compared to the FB plans. CONCLUSIONS: DIBH resulted in significant reductions in doses to the heart, LAD, and lungs, since with this technique there was an increase in the distance between the target and the OARs. With appropriate patient selection and adequate training, the DIBH technique is acceptable and achievable for radiotherapy to the chest, and therefore should be considered for all suitable patients, as this could result in fewer radiotherapy-related complications. However, this technique is time-consuming, since the setup is complex, results in an increased time for treatment delivery, and needs patient cooperation and technical expertise.

A study of Winston-Lutz test on two different electronic portal imaging devices and with low energy imaging.

Stereotactic radiosurgery requires sub-millimetre accuracy in patient positioning and target localization. Therefore, verification of the linear accelerator (linac) isocentre and the laser alignment to the isocentre is performed in some clinics prior to the treatment using the Winston-Lutz (W-L) test with films and more recently with images obtained using the electronic portal imaging devices (EPID). The W-L test is performed by acquiring EPID images of a radio-opaque ball of 6 mm diameter (the W-L phantom) placed at the isocentre of the linac at various gantry and table angles, with a predefined small square or circular radiation beam. In this study, the W-L test was performed on two linacs having EPIDs of different size and resolution, viz, a TrueBeam™ linac with aS1000 EPID of size 40 × 30 cm(2) with 1024 × 768 pixel resolution and an EDGE™ linac having an EPID of size 43 × 43 cm(2) with pixel resolution of 1280 × 1280. In order to determine the displacement of the radio-opaque ball centre from the radiation beam centre of the W-L test, an in-house MATLAB™ image processing code was developed using morphological operations. The displacement in radiation beam centre at each gantry and couch position was obtained by determining the distance between the radiation field centre and the radio-opaque ball centre for every image. Since the MATLAB code was based on image processing that was dependent on the image contrast and resolution, the W-L test was also compared for images obtained with different beam energies. The W-L tests were performed for 6 and 8 MV beams on the TrueBeam™ linac and for 2.5 and 6 MV beams on the EDGE™ linac with a higher resolution EPID. It was observed that the images obtained with the EPID of higher resolution resulted in same accuracy in the determination of the displacement between the centres of the radio-opaque ball and the radiation beam, and significant difference was not observed with images acquired with different energies. It is concluded that the software based on morphological operations provided an accurate estimation of the displacement of the ball centre from the radiation beam center.

Results of a Conservative Dose Plan Linear Accelerator-Based Stereotactic Radiosurgery for Pediatric Intracranial Arteriovenous Malformations.

OBJECTIVE: To evaluate the obliteration rate and clinical outcome following linear accelerator (LINAC)-based stereotactic radiosurgery (SRS) for intracranial arteriovenous malformation (AVM) in pediatric patients (age ≤18 years). METHODS: Factors associated with the obliteration rate and neurologic complications were studied retrospectively in pediatric patients who underwent LINAC-based SRS for AVM between June 1995 and May 2014. RESULTS: The study cohort comprised 36 males and 33 females, with a median age at the time of SRS of 14 years (range, 7-18 years). The mean AVM volume was 8.5 ± 8.7 cc (range, 0.6-41.8 cc). The median marginal dose of radiation delivered was 15 Gy (range, 9-20 Gy). Magnetic resonance imaging (MRI) demonstrated complete obliteration of the AVM in 44 of the 69 patients (63.8%), at a mean follow up of 27.5 months (range, 12-90 months). On subgroup analysis, 41 of the 53 AVMs of ≤14 cc in volume (77.3%) were obliterated. AVMs with a modified AVM radiosurgery score <1 had significantly shorter obliteration times from the time of SRS (P = .006). On multivariate analysis, the mean marginal dose of radiation delivered to the AVM was the sole significant predictor of obliteration (odds ratio, 1.6; 95% confidence interval, 1 to 2.4). CONCLUSIONS: A modest median marginal dose of 15 Gy (16 Gy in the obliterated AVM group vs. 12 Gy in the nonobliterated group) resulted in an obliteration rate of 66.7% after LINAC-based SRS for intracranial AVM, with low rate.

Hyper-fractionated Intensity Modulated Radiation Therapy (HF-IMRT) in Head and Neck Cancer: The Technical Feasibility and Results of a Short Clinical Series.

Among various altered fractionation schedules, only hyper-fractionation has proven increased local control in head and neck cancers. MARCH (Metanalyses of Hyperfractionated or Accelerated radiotherapy in Head and neck cancer) concluded that hyper-fractionated radiotherapy in head and cancers had a survival benefit. This study attempts to combine the benefits of hyper-fractionation with the tissue sparing qualities of intensity modulated radiotherapy. Three patients with advanced oro-pharyngeal cancers were treated with HF-IMRT (Hyperfractionated-IMRT) (2 oropharynx, 1 hypopharynx). Two phase treatment planning with phase I prescribed to high risk volume (HRV) and intermediate risk volume (IRV), 60Gy in 50 fractions at 1.2Gy per fraction, 2 fractions/day, 6-8 h apart. The low risk volume (LRV) received 55Gy to the 95% volume at 1.1Gy per fraction in the same 50 fractions. In phase II, HRV alone was prescribed 1960cGy in 20 fractions over two weeks. Total dose to HRV was 7960cGy in 7 wk. No concurrent chemotherapy was given. Treatment was completed as planned (<60 days; break of 11 days was due to radiation toxicity). Only one patient had grade III toxicity. All three required diet modifications, an average weight loss of 3 kg and no hospitalization required during treatment. This pilot study shows the feasibility of an effective hyper-fractionation with IMRT for head and neck cancers. A Phase II trial is required to prove its efficacy.

Evaluation of on-board imager cone beam CT hounsfield units for treatment planning using rigid image registration.

PURPOSE: To evaluate the on-board imager cone beam CT (OBI-CBCT) Hounsfield units (HUs) for treatment planning. MATERIALS AND METHODS: The HU-electron density (eD) calibration for CBCT, the CATphan504 phantom was used, and the CBCT HU (HUCBCT) consistency was studied by analyzing the CBCT images of Rando phantom and compared with planning CT. The latter study was also performed on CBCT images of 10 H&N patients. For comparison, the structures contoured and treatment plans generated on CT were transferred on to the CBCT after registration. The treatment plans were compared using gamma (g) index analysis and the plan comparison dose volume histograms (DVHPlanComp). RESULTS: Although the HU-eD calibration curves of both the planning CT and CBCT were found to be linear, differences in mean HU values were found in the region of interest (ROI) corresponding to Acrylic, Derlin, and Teflon, viz., 144 ± 11 HU, 193 ± 5 HU, and 257 ± 7 HU respectively. For all the cases, the consistency and reproducibility of HUCBCT values for low density medium agreed the HU CT except at regions of high density. Overall g-evaluation showed more than 94% pixels pass rate and DVH results showed small difference in the DVHPlanComp, Rando, and large differences in DVHPlanComp, patient for structures contoured at peripheral regions (PV) of CBCT images. CONCLUSIONS: We conclude that the pixel-to-pixel HU corrections for entire range of eD are not necessary for OBI-CBCT images. Application of local correction in the high-density and penumbral regions would facilitate the use of CBCT images for routine treatment planning.

Extracranial doses in stereotactic and conventional radiotherapy for pituitary adenomas.

The purpose of this study is to determine the extracranial dose in patients treated for pituitary adenoma with conventional and stereotactic radiotherapy (SRT). Twelve patients receiving treatment with radiation for pituitary adenoma were selected. Six patients underwent SRT, and six patients underwent conventional radiotherapy. Extracranial doses were measured with pre-irradiation annealed lithium fluoride thermoluminscent dosimetry (TLD) chips. The chips were wrapped and placed on the patients' skin, over each eyelid, the thyroid, chest, and scrotum for males and over the suprapubic region for females. Postradiation annealing was done, and the TLDs were read in a TLD reader system. The results were analyzed using the Wilcoxon matched-pairs signed rank test by SPSS, version 6.01. The doses to the thyroid, center, and gonads were significantly higher (74.62 +/- 9.12 mrad, 65.42 +/- 9.35 mrad, and 58.42 +/- 5.36 mrad, respectively) in patients receiving SRT than in conventional radiotherapy portals (69.45 +/- 21.19 mrad, 38.33 +/- 19.44 mrad, and 31.41 +/- 18.25 mrad). But the average doses to the right eye (84.84 +/- 8.80 mrad) and to the left eye (85.68 +/- 5.82 mrad) in the stereotactic group were less when compared with the patients treated with conventional radiotherapy, who received 127.5 +/- 37.90 mrad and 117.29 +/- 34.01 mrad, respectively. In conclusion, SRT is definitely superior to conventional radiotherapy as far as dose to the surrounding normal structures is concerned. The higher extracranial doses in SRT seem to be within the acceptable range; however, the clinical significance of this is still unclear and needs longer followup.

Adaptation of radiation field analyser (RFA) as optical CT scanner for gel dosimetry.

Optical scanning is one of the emerging evaluation tools used for obtaining dose distributions in gel dosimetry. A radiation field analyzer adapted into an optical CT scanner to evaluate an irradiated Fricke gel has been already reported by others. This prototype optical CT scanner functions like a first generation x-ray CT scanner in the translate-rotate fashion. A similar scanner was constructed in our department for optical scanning of irradiated FX gel. At first, an aquarium was constructed and fitted into the water phantom of the RFA with provision to place the gel phantom to be scanned along with a light source and detector. The movements of the RFA were utilized to scan the gel phantom. A scan of a cuvette filled with colored solution was carried out and the resulting images were reconstructed and profiles obtained to evaluate the working of the optical scanner. A scan of the gel phantom was then obtained to evaluate the performance of the scanner. Thus a radiation field analyzer (DYNASCAN) was successfully adapted to an optical scanner to evaluate Fricke gels in our department.

Intra-operative dosimetry of trans-rectal ultrasound guided I prostate implants using C-arm fluoroscopic images.

Permanent implantation of radioactive seeds is a viable and effective therapeutic option widely used today for early-stage prostate cancer. The implant technique has improved considerably during the recent years due to the use of image guidance; however, real-time dose distributions would allow potential cold spots to be assessed and additional seeds added. In this study, we investigate the use of a conventional C-arm fluoroscopy unit for image acquisition and evaluation of dose distribution immediately after the implant. The phantom study indicates that it is possible to obtain seed positions within ±2 mm. A pilot study carried out with three patients indicated that it is possible to obtain seed positions and calculate the dose distribution with C-arm fluoroscopy and about 95% of the seeds were reconstructed within ±2 mm. The results could be further improved with better digital imaging.

Optimization of the imaging protocol of an X-ray CT scanner for evaluation of normoxic polymer gel dosimeters.

X-ray computer tomography (CT) has previously been reported as an evaluation tool for polymer gel (PAG) dosimeters. In this study, the imaging protocol of a Siemens Emotion X-ray CT scanner was optimized to evaluate PAGAT normoxic gel dosimeters. The scan parameters were optimized as 130 kV and 150 mA with a slice thickness of 3 mm for smaller fields and 5 mm for larger fields of irradiation. The number of images to be averaged to reduce noise to an acceptable level was concluded to be 25. It was also concluded that the total monomer concentration required is 7% with 10 mM THP to obtain a maximum change in CT number at dose levels up to 15 Gy for evaluation with X-ray CT. Optimal scan parameters may vary with X-ray CT scanner. Hence the imaging protocol of each scanner to be used for evaluating polymer gels requires individual optimization for the purposes of gel dosimetry evaluation.

Stereotactic radiosurgery for brain lesions: an observation and follow-up.

Stereotactic radiosurgery (SRS) is a technique for obliterating intracranial targets that are inaccessible or unsuitable for open surgical techniques. By means of well-collimated beams of ionizing radiation, a high-dose, single fraction of radiation is delivered to a defined volume of tissue. The entrance and exit doses are distributed in such a way that tissue outside the target is minimally affected. Treatment effects are seen on scans or angiograms after several months or a few years; consequently, follow-up scans are necessary. The first 72 patients who underwent SRS at the Department of Neurological Sciences and Radiation Therapy, Christian Medical College and Hospital were followed. Of the 72 treated, 35 had arteriovenous malformations, while 37 had brain tumors. Of the 37 patients with brain tumors, 14 had meningioma and 17 had acoustic neuroma. Six patients had other lesions such as pineal tumor, hemangioblastoma, astrocytoma, or metastasis. Of 72 patients, 43 came for follow-up. Twenty-three of the followed-up patients showed improvement; 10 clinically and radiologically remained the same, and 2 died due to recurrence. Of 43 patients, 3 continue to have cranial nerve deficit. Four patients were later found to have central necrosis and clinical deterioration. Observation of outcomes following SRS helps neuroscience nurses identify home healthcare strategies such as chest care, eye care, facial massage, and exercises along with the other specific nursing care. Although nursing care has become more technically oriented, the patient's physical, educational, spiritual, and emotional needs must be addressed.