Dose–Volume Analysis of Stereotactic Irradiation for Lung Tumors

Stereotactic irradiation (STI) of lung tumors may be accomplished with a linear accelerator by administering several noncoplaner arcs of a narrow beam focused at the center of target volume with a better immobilization device than conventional radiotherapy. The shape of the radiation distribution produced by this technique is affected by the field size, the number of arcs, the separation angles of the arcs, and the location of the tumor. The influence of these parameters on the resulting radiation distributions was analyzed by computing dose–volume histograms (DVH) for a typical lung. Dose–volume functions were computed for: (1) 1–12 arcs; (2) 20–45° separation angles of arc, (3) 80°–160° of gantry roration; and (4) 5 tumor locations using 4 × 4 cm² rectangular fields. Analysis was based on the hypothetical set up without obstacles, such as the head and arms, and then extended to the practical set up, which is usable in daily practice. Dose–volume statistics showed that five non-coplanar 120° arcs and one 80° arc at different six positions of patient couch with a 30° separation between arcs may be one of the reasonable techniques for irradiation of tumors at the approximate center of the right lung. For tumors situated at more peripheral locations, smaller volume of lung receives dose of 20% to 90% of prescribed dose. Our study provides a basis for further analysis of STI for lung cancer and has the potential to be a treatment strategy for this disease.     

Dosimetric comparison of CyberKnife with other radiosurgical modalities for an ellipsoidal target

OBJECTIVE: To compare treatment plans obtained with the CyberKnife (CK) (Accuray, Inc., Sunnyvale, CA) with those of other commonly used radiosurgical modalities, such as the gamma knife (GK), linear accelerator multiple arcs, conformally shaped static fields, and intensity-modulated radiotherapy (IMRT). METHODS: An ellipsoidal simulated target was chosen centrally located in a three-dimensional model of a patient's head acquired with magnetic resonance or computed tomographic imaging. It was 25 mm in diameter and 35 mm long. The aims of treatment plans were 100% target volume coverage with an appropriate isodose line, minimum radiation dose to normal tissue, and clinically acceptable delivery. These plans were evaluated by use of a dose-volume histogram and other commonly used radiosurgical parameters such as target coverage, homogeneity index, and conformity index. RESULTS: All selected treatment modalities were equivalent in providing full target coverage. For dose homogeneity, all modalities except for multiple isocenter plans for GK (homogeneity index, 2.0) were similar (homogeneity index, congruent with 1.25). Dose conformity was essentially equivalent for all treatment plans except for IMRT, which had a slightly higher value (conformity index, congruent with 1.27). There was a substantial variation in the radiation dose to normal tissue between the studied modalities, particularly at the lower dose levels. CONCLUSION: CK plans seemed to be more flexible for a given target size and shape. For a target of limited volume and essentially of any shape, one could obtain similarly good conformal dosimetry with CK and GK. For a regular-shaped but other than spherical target, homogeneous dose distribution could be obtained with all selected modalities except for multiple isocenters, linear accelerator multiple arcs, or GK. Both IMRT and conformally shaped static fields offered good alternative treatment modalities to CK, GK, or linear accelerator multiple arc radiosurgery, with slightly inferior dosimetry in conformity (IMRT).     

减小非小细胞肺癌三维适形放射治疗靶体积可行性剂量学研究

目的从剂量学探讨减小非小细胞肺癌三维适形放射治疗照射体积的可行性。方法32例非小细胞肺癌患者均做2个放射治疗计划：常规照射野三维适形放射治疗计划和小野三维适形放射治疗计划,用剂量体积直方图评估肿瘤靶区剂量和正常组织受照剂量。结果小野三维适形放射治疗仍能满足肿瘤靶区剂量的要求,亚临床灶的最小剂量、最大剂量和平均剂量分别为50．93Gy、54．60Gy和（52．37±1．02）Gy。与常规适形野相比,小野适形放疗减少了患侧肺、脊髓和食管的平均剂量（P〈0．05）。结论缩小非小细胞肺癌三维适形放射治疗照射野能满足肿瘤靶区剂量的需要,同时降低了正常组织的受照剂量,可在临床开展相关研究。     

A simple scoring ratio to index the conformity of radiosurgical treatment plans. Technical note

A conformity index is a measure of how well the volume of a radiosurgical dose distribution conforms to the size and shape of a target volume. Because the success of radiosurgery is related to the extremely conformal irradiation of the target, an accurate method for describing this parameter is important. Existing conformity ratios and indices used in radiosurgery are reviewed and criticized. It will be demonstrated that previously proposed measurements of conformity can, under certain conditions, give false perfect scores. A new conformity index is derived that gives an objective score of conformity for a treatment plan and gives no false scores. An analysis of five different treatment plans is made using both the existing scoring methods and the new conformity index.     

Comparison of intensity modulated radiotherapy and dynamic three-dimensional conformal radiotherapy with regard to dose distribution and sparing of organs at risk

Dose escalation to the target while sparing the organs at risk near the lesion has been difficult over the last decade. However, recent radiotherapy techniques can deliver more sophisticated doses to the target. This study evaluated whether intensity modulated radiotherapy can deliver more homogeneous and conformal doses to the target than dynamic three-dimensional conformal radiotherapy while sparing organs at risk near the lesion in 13 patients with central nervous system tumors and other tumors around the central nervous system. Dynamic three-dimensional conformal radiotherapy and intensity modulated radiotherapy plans were calculated and dose distributions were compared for all patients with regard to the planning target volume and organs at risk. The plan of intensity modulated radiotherapy was significantly superior to that of dynamic three-dimensional conformal radiotherapy in target dose conformity (p = 0.0006) and organs at risk sparing (p = 0.0257). Intensity modulated radiotherapy could deliver more homogeneous and conformal doses to the target than dynamic three-dimensional conformal radiotherapy with sparing organs at risk near the lesion and may improve local control of radioresistant tumors via dose escalation.     

Early range of motion of the scorpio non-restrictive geometry cruciate-retaining total knee system

Flexion following total knee arthroplasty in the US population generally falls between 100° and 120°. Because of these relatively low flexion arcs, total knee arthroplasty prosthetic designs emerged allowing “high flexion” (≥125°). We hypothesized that a high-flexion implant design, Scorpio Non-Restrictive Geometry cruciate-retaining knee prosthesis, would allow clinical early maximum flexion of at least 125°. A prospective observational cohort study enrolled 87 unselected patients (94 knees) evaluated preoperation and 3 months and 1 year postoperation for clinical flexion, arc of motion, and Knee Society scores. At 1 year, 67% of knees had improved flexion and 23% achieved flexion of at least 125°. Clinically, flexion improved by 6.9° and total arc of motion improved by 10.6° from preoperation to 1-year postoperation. Although this high-flexion design allows increased flexion, many patients fail to achieve flexion of at least 125°.     

Robotic whole body stereotactic radiosurgery: clinical advantages of the Cyberknife integrated system

Radiosurgery is defined as the delivery of high doses of ionising radiation, in mono- or hypo- fractionated treatments, to destroy tumours or focal areas of pathology. The clinical requirements of designing a radiosurgical treatment system include providing: a) a highly precise beam delivery to targets located throughout the body, b) a highly conformal dose distribution, c) the ability to irradiate both small and/or large complex-shaped lesions while minimising the dose to adjacent radiosensitive tissues and d) the ability to interactively track lesion motion due to normal patient motion. To accomplish this, the CyberKnife radiosurgery system has pioneered in this area by taking advantage of the inherent geometrical targeting precision of a commercial arm-based robotic system carrying a compact X-band linear accelerator and integrated with X-ray imaging and visualisation feedback systems. The arm-mounted linear accelerator, equipped with patient specific anatomical models, registered to the patient in real-time with image guidance, dynamically and safely delivers conformal and homogeneous radiation for therapeutic benefit. This paper details the components of the CyberKnife system and their integration in the clinical workflow of radiosurgery.     

Adenomas of the pituitary gland and postoperative 3D conformal external beam radiation therapy

Aim-Background

Adenomas of the pituitary gland are defined as microadenomas or macroadenomas. The main symptoms are hormonal dysfunctions, visual dysfunctions and headache. Treatment modalities include medical management, surgery and external beam radiotherapy (3D EBRT). The risk of recurrence is higher when surgery is not followed by postoperative radiation therapy.

Objectives-Methods

During the period 2010–2011, five patients with pituitary adenoma received 3D conformal beam radiotherapy with a multileaf collimator (MLC) on a linear accelerator. Three patients were diagnosed with macroadenoma of the pituitary gland and received 3D conformal EBRT just one month after surgery. The total dose was 45Gy with involved fields. Two patients with microadenoma of the pituitary gland with local recurrence received RT one year after surgery, with a dose of 50.4–54 Gy with involved fields.

Results

Post radiotherapy, at 6-month, one and two-year follow-up, the patients who had received 3D EBRT 1 month after surgery displayed decreased Prolactin and GH secretion, and had normal visual field testing. After radiotherapy, contrast-enhanced MRI of the pituitary gland showed no evidence of recurrence. The patients who were given 3D EBRT (with recurrence) one year after surgery also displayed improvement, but with less of a decrease in ACTH and cortisol secretion. (Sy Cushing)

Conclusions

An adenoma of the pituitary gland requires therapy for a longer period of time in terms of medical management, surgery, and radiotherapy. Surgical management that is immediately followed by 3D EBRT gives better results than surgery alone. The results for patients who receive late post-op RT are less than ideal, and the risk of recurrence in such cases is higher.     

Stereotactic radiosurgery to treat presumed Rathke's cleft cysts

Abstract Objective. Stereotactic radiosurgery (SRS) has been developed as a clinical treatment method for certain brain tumours that does not need craniotomy. As a more accurate radiation technique, SRS can deliver a relatively large dose of stereotactic radiation to a conformal target with less normal brain tissue irradiated in a single treatment. The aim of this study is to evaluate the therapeutic effects of SRS for Rathke's cleft cysts (RCCs). Methods. SRS was performed using a rotating gamma ray unit in seven selected patients with symptomatic RCCs diagnosed upon typical MR imaging combined with clinical manifestation. The patients included one male and six females with an age range from 25 to 63 years (mean 43.4 years). Five patients presented with headache, three with menstrual disorder or infertility and one with vision impairment. No other endocrine dysfunction was observed. SRS was performed in the patients with a central dose varied from 22.6 to 40 Gy (mean 32.5 Gy) and a peripheral dose from 9 to 20 Gy (mean 13.4 Gy). Results. The patients were followed up for 11-105 months (mean 38.6 months) after SRS. All symptoms that presented before treatment were relieved within 3-6 months post-SRS and no endocrine dysfunction was developed during the follow-up period. MR imaging demonstrated that the RCCs were completely disappeared in five cases and significantly shrunken in the other two cases. No recurrence was observed in any cases during the follow-up. Conclusion. This study demonstrates that SRS can treat RCCs effectively without evident side effects.     

C-Arm Multi-Axis Rotation Stereotactic Linac Radiosurgery System

We developed a C-arm multi-axis, stereotactic linear accelerator radiosurgical system combined with 3-dimensional (3D) dose planning software. The linac beam generator is mounted on a C-arm frame that allows rotation parallel and diagonal to the patient table. As a result of the new structural design, the positional deviation of the beam from mechanical isocenter during rotation of the gantry is almost less than 0.5 mm. The system can provide 3D stereotactic radiosurgery using precessional convergent irradiation (PCI) without movement of the patient table, which improves accuracy of the irradiation. A satisfactory dose gradient suitable for radiosurgery with fewer arcs was achieved by PCI than was possible with noncoplanar multi-converging arcs (MCA). The 3D dose planning system can accurately optimize the dose plan even for an irregularly shaped target. We have treated 60 cases since 1996 with a reduction of total treatment time.     

High dose rate brachytherapy in the treatment of prostate cancer

The optimal treatment of patients with localized prostate cancer remains controversial. Significant clinical data are available, however, demonstrating that patients treated with radiation therapy (RT) have a significantly better outcome as the dose to the gland is increased. What remains debatable, however, is how to best deliver these higher doses of RT without significantly increasing normal tissue toxicities. Conformal high dose rate brachytherapy (C-HDR BT) represents an alternative means of precise dose delivery that offers similar tumoricidal effects as three-dimensional (3D) conformal external beam radiotherapy (EBRT) or permanent interstitial prostate seed implants with potential additional advantages. Since C-HDR BT consists of temporarily placing afterloading needles or catheters directly into the prostate gland under real-time ultrasound guidance, a steep dose gradient between the prostate and adjacent normal tissues can be generated that is minimally affected by organ motion and edema or treatment setup uncertainties. The ability to control the amount of time the single HDR radioactive source "dwells" at each position along the length of each brachytherapy catheter further enhances the conformity of the dose. In addition, recent radiobiological data on prostate cancer treatment suggest that C-HDR BT should produce tumor control and late normal tissue side effects that are at least as good as achieved with conventional fractionation, with the additional possibility that acute side effects might be reduced. Published data from several groups performing C-HDR BT as boosts in patients with locally advanced disease have supported these assumptions. Combined with the physical advantages discussed above, C-HDR BT should provide similar tumor control as 3D conformal EBRT with the added advantages of reduced treatment times, less acute toxicity, and no additional technological requirements to account and correct for treatment setup uncertainties and organ motion. Due to the success of C-HDR BT as boost treatment in locally advanced disease, this form of radiation treatment has recently been applied to low-risk prostate cancer patients as an alternative brachytherapy technique to permanent interstitial seed implantation. Advantages in this setting include an improved ability to define and deliver the prescribed dose, a significantly shortened treatment schedule compared to 3D conformal EBRT, and the fact that patients are not radioactive after implantation.     

Curative external beam radiotherapy for prostate carcinoma: results in 231 patients treated in Lyon.

BACKGROUND: Radical prostatectomy and external beam radiation therapy (EBRT) are the mainstays of treatment of prostate cancer with curative intent. The possible development of radiation proctitis and rectal bleeding are major concerns when using EBRT. Recently, conformal radiotherapy has been introduced in an attempt to improve the results of EBRT. This paper presents an overview of the Lyon experience using standard EBRT with doses of 68 Gy, and reports the preliminary results of a study of conformal radiotherapy with dose escalation. METHODS: From 1981 to 1995, EBRT was used to treat 231 patients with localized adenocarcinomas of the prostate. The dose of EBRT was 68 Gy/34 fractions/7 weeks using a four-field box technique with 18-MeV photons. A feasibility study of conformal radiotherapy was commenced in 1996. To date, 145 patients have been treated with doses escalating from 68 to 80 Gy. RESULTS: In the EBRT group of 231 patients, the 5-year overall survival was 80.3%. Anorectal function was scored as excellent in 90% of patients. Rectal bleeding was seen in 14.3% of patients and required local treatment in only seven. In the group treated with conformal radiotherapy, the preliminary results indicate good early tolerance. CONCLUSION: The curative treatment of patients with prostate cancer using EBRT gives good long-term survival with low rectal toxicity. Conformal radiotherapy appears to be an interesting approach to improve local control and perhaps survival.     

S-Ketamine Anesthesia Increases Cerebral Blood Flow in Excess of the Metabolic Needs in Humans

Background: Animal studies have demonstrated neuroprotective properties of S-ketamine, but its effects on cerebral blood flow (CBF), metabolic rate of oxygen (CMRO2), and glucose metabolic rate (GMR) have not been comprehensively studied in humans.

Methods: Positron emission tomography was used to quantify CBF and CMRO2 in eight healthy male volunteers awake and during S-ketamine infusion targeted to subanesthetic (150 ng/ml) and anesthetic (1,500-2,000 ng/ml) concentrations. In addition, subjects' GMRs were assessed awake and during anesthesia. Whole brain estimates for cerebral blood volume were obtained using kinetic modeling.

Results: The mean +/- SD serum S-ketamine concentration was 159 +/- 21 ng/ml at the subanesthetic and 1,959 +/- 442 ng/ml at the anesthetic levels. The total S-ketamine dose was 10.4 mg/kg. S-ketamine increased heart rate (maximally by 43.5%) and mean blood pressure (maximally by 27.0%) in a concentration-dependent manner (P = 0.001 for both). Subanesthetic S-ketamine increased whole brain CBF by 13.7% (P = 0.035). The greatest regional CBF increase was detected in the anterior cingulate (31.6%; P = 0.010). No changes were detected in CMRO2. Anesthetic S-ketamine increased whole brain CBF by 36.4% (P = 0.006) but had no effect on whole brain CMRO2 or GMR. Regionally, CBF was increased in nearly all brain structures studied (greatest increase in the insula 86.5%; P < 0.001), whereas CMRO2 increased only in the frontal cortex (by 15.7%; P = 0.007) and GMR increased only in the thalamus (by 11.7%; P = 0.010). Cerebral blood volume was increased by 51.9% (P = 0.011) during anesthesia.     

Miniature multileaf collimator as an alternative to traditional circular collimators for stereotactic radiosurgery and stereotactic radiotherapy

PURPOSE: To evaluate the miniature multileaf collimator (MMLC) as an alternative to traditional circular collimators for radiosurgery. MATERIALS AND METHODS: 'Circular' fields were created with the Radionics MMLC (leaf width 3.53 mm at isocenter). Beam data, including tissue maximum ratios, output factors, penumbrae and isodose distributions of these fields were measured. These were compared to the Radionics circular collimators traditionally used for radiosurgery. The MMLC data were input to the XKnife Treatment Planning System. Treatment plans were completed and evaluated using both the MMLC 'circular' fields and the circular collimators. RESULTS: MMLC fields using 3, 5, 7, 9, 11, and 13 leaves on each side of the Radionics MMLC were created to approximate circular fields. The TMRs are essentially identical to those of comparable-size circular collimators. Measured at isocenter at 5-cm depth for 6 MV, the 80-20% penumbra widths are comparable to circular collimators, but are increased by as much as 1 mm at the leaf intersections (steps) where scalloping occurs. Isodose distributions were matched to those of circular collimators with comparable 50% isodose widths. Treatment plans for the MMLC 'circular' fields with four arcs (totaling 360 degrees) are essentially identical to those of comparable circular collimators. Dose-volume histograms revealed clinically insignificant differences between the two in doses to the target, to the volume surrounding the target, and to adjacent critical normal tissues. There is very little discrepancy between the dose distribution calculated with the approximated MMLC fields and with those of simulated arcs with the actual MMLC fields. CONCLUSIONS: With the MMLC simulating circular fields, dose distributions may be obtained which are essentially identical to comparable-size circular collimators. The mechanical accuracy of the MMLC is as good as that of the circular collimators, and the leakage dose is less. The diameter of 'circular' fields is limited by the MMLC leaf width to 1 cm and greater in increments of 7 mm. Attention needs to be paid to mechanical collisions because the MMLC is bulkier than the circular collimators.     

A retrospective analysis concerning physical aspects and clinical dosimetry in radiosurgery

The authors have reviewed their experience with treatments of small intracranial lesions by unconventionally fractionated stereotactic radiotherapy using a 4 MV photon beam. Treatment is carried out by multiple non coplanar arc irradiation obtained rotating the target, while kept at the isocentre of a Linac, around a vertical axis. The outmost concentration of the dose within the target volume enables consistent reduction of the amount of the absorbed dose by critical structures of the intact brain. They analyse the dose distribution and the method to optimise the choice of the therapeutic dose. Finally, some radiobiological considerations are presented.     

Study on esophageal cancer radiotherapy dosimetry and position verification for volumetric modulated arc therapy

BackgroundThis study analyzed the respective advantages and disadvantages by comparing volumetric modulated arc therapy (VMAT) and intensity modulated radiotherapy (IMRT) on the dose distribution and position verification distribution characteristics in esophageal cancer radiotherapy, in order to provide the reference for the clinical radiotherapy technology optimization of esophageal cancer.MethodsA total of 56 cases of patients with esophageal cancer were selected and applied to the Pinnacle three-dimensional radiation treatment planning system (TPS), in order to design a VMAT plan and IMRT plan under the guidance of image-guided radiotherapy (IGRT). The dosimetry and position verification difference were compared between the two groups.ResultsRevealed that the target dose distribution of the VMAT plan and IMRT plan meets the requirements in clinical dosimetry for all 56 patients in this study. Under the premise of similar target coverage, the conformal index (CI) of the VMAT plan, homogeneity index (HI), target volume, BODY-PTV radiated volume and spinal cord D_max, bilateral lung V5, V20 and mean lung dose (MLD), monitor unit (MU) and treatment time (TT), as well as position verification and others, were obviously superior to those in the IMRT plan; and the difference was statistically significant.ConclusionCBCT guided VMAT is a potential effective treatment for esophageal cancer and may be more effective and safer than IMRT.