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H M Kooy

Publications and source records attributed to H M Kooy.

At least 19 recordsLinked to original sources
PubMed2004

Advantage of protons compared to conventional X-ray or IMRT in the treatment of a pediatric patient with medulloblastoma.

PURPOSE: To compare treatment plans from standard photon therapy to intensity modulated X-rays (IMRT) and protons for craniospinal axis irradiation and posterior fossa boost in a patient with medulloblastoma. METHODS: Proton planning was accomplished using an in-house 3D planning system. IMRT plans were developed using the KonRad treatment planning system with 6-MV photons. RESULTS: Substantial normal-tissue dose sparing was realized with IMRT and proton treatment of the posterior fossa and spinal column. For example, the dose to 90% of the cochlea was reduced from 101.2% of the prescribed posterior fossa boost dose from conventional X-rays to 33.4% and 2.4% from IMRT and protons, respectively. Dose to 50% of the heart volume was reduced from 72.2% for conventional X-rays to 29.5% for IMRT and 0.5% for protons. Long-term toxicity with emphasis on hearing and endocrine and cardiac function should be substantially improved secondary to nontarget tissue sparing achieved with protons. CONCLUSION: The present study clearly demonstrates the advantage of conformal radiation methods for the treatment of posterior fossa and spinal column in children with medulloblastoma, when compared to conventional X-rays. Of the two conformal treatment methods evaluated, protons were found to be superior to IMRT.

Cerebellar Neoplasms↗
PubMed2004

Accurate Monte Carlo simulations for nozzle design, commissioning and quality assurance for a proton radiation therapy facility.

Monte Carlo dosimetry calculations are essential methods in radiation therapy. To take full advantage of this tool, the beam delivery system has to be simulated in detail and the initial beam parameters have to be known accurately. The modeling of the beam delivery system itself opens various areas where Monte Carlo calculations prove extremely helpful, such as for design and commissioning of a therapy facility as well as for quality assurance verification. The gantry treatment nozzles at the Northeast Proton Therapy Center (NPTC) at Massachusetts General Hospital (MGH) were modeled in detail using the GEANT4.5.2 Monte Carlo code. For this purpose, various novel solutions for simulating irregular shaped objects in the beam path, like contoured scatterers, patient apertures or patient compensators, were found. The four-dimensional, in time and space, simulation of moving parts, such as the modulator wheel, was implemented. Further, the appropriate physics models and cross sections for proton therapy applications were defined. We present comparisons between measured data and simulations. These show that by modeling the treatment nozzle with millimeter accuracy, it is possible to reproduce measured dose distributions with an accuracy in range and modulation width, in the case of a spread-out Bragg peak (SOBP), of better than 1 mm. The excellent agreement demonstrates that the simulations can even be used to generate beam data for commissioning treatment planning systems. The Monte Carlo nozzle model was used to study mechanical optimization in terms of scattered radiation and secondary radiation in the design of the nozzles. We present simulations on the neutron background. Further, the Monte Carlo calculations supported commissioning efforts in understanding the sensitivity of beam characteristics and how these influence the dose delivered. We present the sensitivity of dose distributions in water with respect to various beam parameters and geometrical misalignments. This allows the definition of tolerances for quality assurance and the design of quality assurance procedures.

Algorithms↗
PubMed2001

Stereotactic radiotherapy for pediatric intracranial germ cell tumors.

PURPOSE: Intracranial germ cell tumors are rare, radiosensitive tumors seen most commonly in the second and third decades of life. Radiotherapy alone has been the primary treatment modality for germinomas, and is used with chemotherapy for nongerminomatous tumors. Stereotactic radiotherapy techniques minimize the volume of surrounding normal tissue irradiated and, hence, the late radiation morbidity. This study reports our experience with stereotactic radiotherapy in this group of tumors. METHODS AND MATERIALS: Between December 1992 and December 1998, 18 patients with intracranial germ cell tumors were treated with stereotactic radiotherapy. A total of 23 histologically proven tumors were treated. Thirteen patients had a histologic diagnosis of germinoma, and 5 patients had germinoma with nongerminomatous elements. Of those patients with a histologic diagnosis of germinoma, 5 had multiple midline tumors. The median age of the patients was 12.9 years (range, 5.6-17.5 years). RESULTS: A boost using stereotactic radiotherapy was delivered to 19 tumors following whole-brain radiation in 8 cases and craniospinal radiation in 11 cases. Three tumors were treated with stereotactic radiotherapy to the tumor volume alone following chemotherapy, and 1 tumor received a boost using stereotactic radiosurgery following craniospinal radiation. A median dose of 2520 cGy (range, 1500-3600) cGy was given to the whole brain, and a median dose of 2160 (range, 2100-2600) cGy was given to the spinal field. The median boost dose to the tumor was 2600 (range, 2160-3600) cGy, given by stereotactic radiotherapy delivered to the 95% isodose line. At a median follow-up time of 40 (range, 12-73) months, no local or marginal recurrences were reported in patients with germinoma. Two patients with nongerminomatous tumors have relapsed. One had elevation of tumor markers only at 37 months following treatment, and the other had persistent disease following chemotherapy and radiation therapy. Eight patients documented pituitary-hypothalamic dysfunction; in 7 (87.5%) of these patients, the dysfunction was present before commencing radiotherapy. Four patients (22%) developed newly diagnosed diabetes insipidus following surgery. Three patients (17%) received antidepressant medication at follow-up. CONCLUSION: Our series shows that stereotactic radiotherapy is achievable and well tolerated in this group of patients. Longer follow-up is required to fully assess the impact on long-term toxicity. Psychologic assessment of mood and affect should be performed as part of routine follow-up in this group of adolescent children.

Adolescent↗
PubMed2000

A software system for interventional magnetic resonance image-guided prostate brachytherapy.

OBJECTIVE: Current prostatic brachytherapy implant procedures use ultrasound imaging for geometric guidance during surgery, with pre-surgical planning based on ultrasound images and post-surgical dosimetry based on computed tomography (CT). This procedure suffers from the poor soft-tissue contrast of ultrasound and CT and problems inherent in the repositioning of the patient at surgery. We have designed and implemented an integrated real-time imaging and treatment-planning software system that combines the superior soft-tissue contrast of magnetic resonance (MR) images with the real-time acquisition of those images for localization, verification, and dosimetric purposes. The system permits the surgeon and patient to complete all phases of treatment in one setting. MATERIALS AND METHODS: We utilize an intra-operative MR unit that permits real-time imaging and stereotactic localization during a surgical procedure. Our software system integrates with the unit and features (i) a calibration schema to calibrate the prostatic surgical implant template within the unit, (ii) full volumetric data acquisition of the prostate, (iii) interactive three-dimensional (3D) treatment planning with volumetric dose evaluation, and (iv) geometric and dosimetric feedback during the surgical procedure. We utilize a software architecture that uses mediators between the abstract data types, or objects. These mediators communicate state changes in individual objects (e.g., a change in a catheter position) to other objects (e.g., a dose-volume histogram) that depend on these changes. A consistent 3D representation of the treatment volumes allows interactive reconstruction of the volumes on arbitrary MR image sections and real-time dose computations. RESULTS: We have successfully implemented the system clinically and have treated 143 patients (as of August 2000). The system supports four clinical phases. The first consists of calibrating the implant template with respect to the patient's anatomy and the MR unit. The second consists of acquiring a complete volumetric MR data set of the prostatic volume. The third consists of delineating the treatment volume (often a sub-volume of the prostate) and the dose-limiting critical volumes. These volumes are used in determining the surgical treatment plan based on catheter and seed placement in the prostate and a dosimetric evaluation of all volumes. The final phase consists of implanting the catheters with the radioactive seeds, where each catheter is imaged and compared to the planned position of the catheter, thus allowing a direct comparison, and possible adjustment, of the implanted versus planned catheter position. CONCLUSIONS: The system is highly interactive, and has great flexibility in its design, maintainability, and clinical practice. The system provides an efficient model to support the surgical procedure. The system significantly improves the diagnostic information provided to the clinician and the treatment planner and the geometric accuracy of the surgical procedure compared to ultrasound procedures. The system allows excellent critical structure sparing, both through interactive placement of the catheters with high geometric accuracy and through the definition of the actual sub-prostatic volumes possible with MR.

Brachytherapy↗
PubMed1999

Computerized design of target margins for treatment uncertainties in conformal radiotherapy.

PURPOSE: We describe a computerized method of determining target margins for beam aperture design in conformal radiotherapy plans. MATERIALS AND METHODS: The method uses previously measured data from a population of patients to simulate setup error and organ motion in the patient currently being planned. Starting with a clinical target volume (CTV) and nontarget organs from the patient's planning CT scan, the simulation is repeated many times to produce a spatial probability distribution for each organ in the treatment machine coordinate system. This is used to determine a prescribed dose volume (PDV), defined as the volume to receive the prescribed dose, which encompasses the CTV while restricting the volume of nontarget organs within it, according to planner-specified values. The PDV is used to design beam apertures using a conventional margin for beam penumbra. RESULTS: The method is applied to 6-field prostate conformal treatment plans, in which the PDV encloses the prostate and seminal vesicles while limiting the enclosed rectal wall volume. The effect of organ motion is assessed by applying the plans on subsequent CT scans of the same patients, calculating probabilities for tumor control (TCP) and normal tissue complication (NTCP), and comparing with plans designed from a physician-drawn planning target volume (PTV). Although prostate TCP and rectal wall NTCP are found to be similar in the two sets of plans, TCP for the seminal vesicles is significantly higher in the PDV-based plans. CONCLUSIONS: The method can improve the dose conformality of treatment plans by incorporating population-based measurements of treatment uncertainties and consideration of nontarget tissues in the design of nonuniform target margins.

Computer Simulation↗
PubMed1999

Quantification and predictors of prostate position variability in 50 patients evaluated with multiple CT scans during conformal radiotherapy.

PURPOSE: To determine the extent and predictors for prostatic motion in a large number of patients evaluated with multiple CT scans during radiotherapy, and evaluate the implications of these data on the design of appropriate treatment margins for patients receiving high-dose three-dimensional conformal radiotherapy. MATERIALS AND METHODS: Fifty patients underwent four serial computerized tomography (CT) scans, consisting of an initial planning scan and subsequent scans at the beginning, middle, and end of the treatment course. Each scan was performed with the patient in the prone treatment position within an immobilization device used during therapy. Contours of the prostate and seminal vesicles were drawn on the axial CT slices of each scan, and the scans were matched by alignment of the pelvic bones with a chamfer matching algorithm. Using the contour information, distributions of the displacement of the organ center of mass and organ border from the planning position were determined separately for the prostate and seminal vesicles in each of the three principle directions: anterior-posterior (AP), superior-inferior (SI) and left-right (LR). Each distribution was fitted to a normal (Gaussian) distribution to determine confidence limits in the center of mass and border displacements and thereby evaluate for the optimal margins needed to contain target motion. RESULTS: The most common directions of displacement of the prostate center of mass (COM) were in the AP and SI directions and were significantly larger than any LR movement. The mean prostate COM displacement (+/- 1 standard deviation, SD) for the entire population was -1.2 +/- 2.9 mm, -0.5 +/- 3.3 mm and -0.6 +/- 0.8 mm in the, AP and SI and LR directions respectively (negative values indicate posterior, inferior or left displacement). The mean (+/- 1 SD) seminal vesicle COM displacement for the entire population was - 1.4 +/- 4.9 mm, 1.3 +/- 5.5 mm and -0.8 +/- 3.1 mm in the AP and SI and LR directions, respectively. The data indicate a tendency for the population towards posterior displacements of the prostate from the planning position and both posterior and superior displacements of the seminal vesicles. AP movement of both the prostate and seminal vesicles were correlated with changes in rectal volume (P = 0.0014 and < 0.0001, respectively) more than with changes in bladder volume (P = 0.030 for seminal vesicles and 0.19 for prostate). A logistic regression analysis identified the combination of rectal volume > 60 cm3 and bladder volumes > 40 cm3 as the only predictor of large ( > 3 mm) systematic deviations for the prostate and seminal vesicles (P = 0.05) defined for each patient as the difference between organ position in the planning scan and mean position as calculated from the three subsequent scans. CONCLUSIONS: Prostatic displacement during a course of radiotherapy is more pronounced among patients with initial planning scans with large rectal and bladder volumes. Such patients may require more generous margins around the CTV to assure its enclosure within the prescription dose region. Identification and correction of patients with large systematic errors will minimize the extent of the margin required and decrease the volume of normal tissue exposed to higher radiation doses.

Artifacts↗
PubMed1999

Treatment of patients with primary glioblastoma multiforme with standard postoperative radiotherapy and radiosurgical boost: prognostic factors and long-term outcome.

OBJECT: To assess the value of stereotactic radiosurgery (SRS) as adjunct therapy in patients suffering from glioblastoma multiforme (GBM), the authors analyzed their experience with 78 patients. METHODS: Between June 1988 and January 1995, 78 patients underwent SRS as part of their initial treatment for GBM. All patients had undergone initial surgery or biopsy confirming the diagnosis of GBM and received conventional external beam radiotherapy. Stereotactic radiosurgery was performed using a dedicated 6-MV stereotactic linear accelerator. Thirteen patients were alive at the time of analysis with a median follow-up period of 40.8 months. The median length of actuarial survival for all patients was 19.9 months. Twelve- and 24-month survival rates were 88.5% and 35.9%, respectively. Patient age and Radiation Therapy Oncology Group (RTOG) class were significant prognostic indicators according to univariate analysis (p < 0.05). Twenty-three patients aged younger than 40 years had a median survival time of 48.6 months compared with 55 older patients who had 18.2 months (p < 0.001). Patients in this series fell into RTOG Classes III (27 patients), IV (29 patients), or V (22 patients). Class III patients had a median survival time of 29.5 months following diagnosis; this was significantly longer than median survival times for Classes IV and V, which were 19.2 and 18.2 months, respectively (p = 0.001). Only patient age (< 40 years) was a significant prognostic factor according to multivariate analysis. Acute complications were unusual and limited to exacerbation of existing symptoms. There were no new neuropathies secondary to SRS. Thirty-nine patients (50%) underwent reoperation for symptomatic necrosis or recurrent tumor. The rate of reoperation at 24 months following SRS was 54.8%. CONCLUSIONS: The addition of a radiosurgery boost appears to confer a survival advantage to selected patients.

Actuarial Analysis↗
PubMed1998

Real-time magnetic resonance image-guided interstitial brachytherapy in the treatment of select patients with clinically localized prostate cancer.

PURPOSE: This study was performed to establish the dose-localization capability and acute toxicity of a real-time intraoperative magnetic resonance (MR) image-guided approach to prostate brachytherapy in select patients with clinically localized prostate cancer. METHODS AND MATERIALS: Nine patients with 1997 American Joint Commission on Cancer (AJCC) clinical stage T1cNxM0 prostate cancer, prostate-specific antigen (PSA) < 10 ng/ml, biopsy Gleason score not exceeding 3 + 4, and endorectal coil MR stage T2 disease were enrolled into this study. The prescribed minimum peripheral dose was 160 Gy to the clinical target volume (CTV), which was the MR-defined peripheral zone (PZ) of the prostate gland. Using a real-time 0.5 Tesla intraoperative MR imaging unit, 5-mm image planes were obtained throughout the prostate gland. The PZ of the prostate gland, anterior rectal wall, and prostatic urethra were identified on the T2 weighted axial images by an MR radiologist. An optimized treatment plan for catheter insertion was generated intraoperatively. Each catheter containing the 125Iodine sources was placed under real-time MR guidance to ensure that its position in the coronal, sagittal, and axial planes was in agreement with the planned trajectory. Real-time dose- volume histogram analyses were used intraoperatively to optimize the dosimetry. RESULTS: For the 9 study patients, 89-99% (median 94%) of the CTV received a minimum peripheral dose of 160 Gy and > or = 95% of the volume of the prostatic urethra and 42-89% (median 70%) of the volume of the anterior rectal wall received doses that were below the reported tolerance. All patients voided spontaneously within 3 h after discontinuation of the Foley catheter and no patient required more than a limited course (< or = 3 weeks) of oral alpha-1 blockers for postimplant urethritis. CONCLUSIONS: Real-time MR-guided interstitial radiation therapy provided the ability to achieve the planned optimized dose-volume histogram profiles to the CTV and healthy juxtaposed structures intraoperatively, with minimal acute morbidity.

Aged↗
PubMed1998

Linac radiosurgery at the Joint Center for Radiation Therapy.

The Joint Center for Radiation Therapy (JCRT) has treated intra-cranial lesions with high-dose single fraction stereotactic radiosurgery (SRS) since 1986 and with multi-fraction stereotactic radiotherapy (SRT) since 1992. This paper describes the JCRT techniques for treatment planning and delivery for SRS, and to a limited extent for SRT. LINAC quality assurance, treatment delivery, and patient management for stereotactic radiosurgery and stereotactic radiotherapy technique are closely related at the JCRT, although differences exist. An historical retrospective of our experience with stereotactic techniques including imaging modalities, treatment planning techniques, optimization methods, and treatment delivery is presented. Three treatment planning approaches, single isocenter, multiple isocenter, and micro-jaw field shaping are used to demonstrate the capabilities and technical dosimetric features of each approach. The major planning differences and clinical of each technique are described. From our experience, lesions less than 3.0 cm in maximum extent are well treated with circular fields using either a single or multiple isocenter configuration. Lesions greater than 3.0 cm in maximum extent usually benefit from field shaping using the micro-jaws. For these large lesions, the shaped field approach typically improves the dose homogeneity as well as reduces the amount of healthy brain irradiated. Our physicians choose between the three techniques to meet the desired clinical outcome the patient's situation requires.

Boston↗
PubMed1998

A stereotactic radiation therapy device for retinoblastoma using a noncircular collimator and intensity filter.

The proximity of the lens to the retina makes the treatment of retinoblastoma a challenge for external beam radiation therapy. The approximately 1 mm separation between the posterior edge of the lens and the anterior region of the retina causes a trade-off between coverage of the entire retina and excessive dose to the lens. A stereotactic, LINAC based, lens sparing technique for treating retinoblastoma is presented. The technique uses noncoplanar arcs with the lens at isocenter. A special noncircular collimator blocks the lens but it also causes the dose distribution to vary across the retina. A fluence modulation filter is used to reduce the dose inhomogeneity across the target. The resulting dose distribution is roughly hemispheric, providing both anterior coverage of the retina and lens blocking unlike conventional techniques. The method used to develop the collimator and filter assembly is presented. Dosimetry of the assembly was carried out using radiochromic film, and the results were entered in a treatment planning system. The dose distribution as measured in a phantom is provided and compared to calculations.

Equipment Design↗
PubMed1997

Optimized beam planning for linear accelerator-based stereotactic radiosurgery.

PURPOSE: Current treatment planning for linear accelerator-based stereotactic radiosurgery and radiotherapy is a lengthy and iterative procedure. The planner has to manually select the beam arcs and carefully consider many different selections to ensure target volume coverage while sparing dose to critical organs. In this article we report an optimization procedure that can automatically select the beam arcs based on geometric and dosimetric analysis of the treatment parameters. METHODS AND MATERIALS: The optimization problem is introduced by using a Beam's Eye View (BEV) map where a pattern of lines represents a beam arc combination for a treatment plan. The collection of all possible treatment plans is described by using the concept of phase space where each point corresponds to a particular configuration of the system under consideration, and in this case, a particular beam arc combination. A geometric reduction of the phase space is performed by excluding static beam ports that irradiate too much critical organs and too little target volume. The phase space is further reduced by excluding beam arc combinations that do not comply with treatment convenience considerations and established planning experiences. These reductions significantly reduces the number of beam arc combinations to be considered and thus dramatically simplifies the computational complexity. The method of simulated annealing is then used to the reduced phase space to select the set of beam arcs that provides the best surface dose distribution for the target volume. The optimization procedure is applied to a radiosurgery case to compare the optimized beam arcs with the previously manually planned beam arcs. The procedure is also applied to 10 randomly selected cases for a comparison in terms of tissue-volume ratio calculations. RESULTS: The system is a highly automated beam arc planning tool for stereotactic radiosurgery and stereotactic radiotherapy. Its interactive nature allows the planner to rapidly consider many treatment plans to search for the best option. For the case presented, it is shown that the optimized beams substantially reduce the dose to the postrema. The tissue-volume ratio calculations demonstrate that the optimization often produces clinically superior treatment plans than the manual beam planning method. CONCLUSIONS: Our method of phase space reduction proves to be very useful in approaching the complex problem of treatment planning optimization. Not only does it substantially reduce the number of beam arcs that need to be considered, but it also simplifies the evaluation of the beam arc options. Both of these greatly reduce the computational complexity of the optimization and make the procedure fast and efficient. Moreover, the reduction of phase space adds another layer of interaction between the user and the beam selection procedure, so that the optimization process is well controlled and thus very effective.

Brain Neoplasms↗
PubMed1997

Beam shaping for conformal fractionated stereotactic radiotherapy: a modeling study.

PURPOSE: The patient population treated with fractionated stereotactic radiotherapy (SRT) is significantly different than that treated with stereotactic radiosurgery (SRS). Generally, lesions treated with SRT are larger, less spherical, and located within critical regions of the central nervous system; hence, they offer new challenges to the treatment planner. Here a simple, cost effective, beam shaping system has been evaluated relative to both circular collimators and an ideal dynamically conforming system for effectiveness in providing conformal therapy for these lesions. METHODS AND MATERIALS: We have modeled a simple system for conformal arc therapy using four independent jaws. The jaw positions and collimator angle are changed between arcs but held fixed for the duration of each arc. Eleven previously treated SRT cases have been replanned using this system. The rectangular jaw plans were then compared to the original treatment plans which used circular collimators. The plans were evaluated with respect to tissue sparing at 100%, 80%, 50%, and 20% of the prescription dose. A plan was also done for each tumor in which the beam aperture was continuously conformed to the beams eye view projection of the tumor. This was used as an ideal standard for conformal therapy in the absence of fluence modulation. RESULTS: For tumors with a maximum extent of over 3.5 cm the rectangular jaw plans reduced the mean volume of healthy tissue involved at the prescription dose by 57% relative to the circular collimator plans. The ideal conformal plans offered no significant further improvement at the prescription dose. The relative advantage of the rectangular jaw plans decreased at lower isodoses so that at 20% of the prescription dose tissue involvement for the rectangular jaw plans was equivalent to that for the circular collimator plans. At these isodoses the ideal conformal plans gave substantially better tissue sparing. CONCLUSION: A simple and economical field shaping device has been shown to provide all of the beam shaping advantage of a hypothetical ideal dynamically conforming system at the prescription level. This system may be immediately implemented in the clinic. It offers a substantial advantage over the currently used circular collimators in the high dose region with equivalent performance in the low dose region.

Humans↗
PubMed1997

Comparison of miniature multileaf collimation (MMLC) with circular collimation for stereotactic treatment.

PURPOSE: A prototype Miniature Multi-Leaf Collimator (MMLC) designed specifically for radiosurgery and small field radiotherapy has been fabricated and evaluated at the University of Texas M. D. Anderson Cancer Center (UTMDACC). This work demonstrates the advantages of a computer-controlled MMLC vs. conventional circular collimation for the treatment of an irregularly shaped target volume in the brain. METHODS AND MATERIALS: Two patient treatments were selected for this comparison from 38 intracranial tumors treated with radiosurgery at UTMDACC from 8/6/91 to 5/10/94. Target contours and critical structures defined for one of the patients was used to create a simulated target volume and critical structures in a spherical head phantom. Computer simulations were performed using traditional single isocenter treatment with a circular collimator for a set of six arcs. The same arc paths were used to compute the dose distribution for the MMLC and conformed beam geometries were defined using a three-dimensional (3D) treatment planning system with beam's eye view capabilities. Then, the calculated dose distribution for a single isocenter, conformal treatment was delivered to the spherical head phantom under static conditions by shaping the MMLC to conform the target volume shape projected as a function of couch rotation and gantry angle. Planar dose distributions through the target volume were measured using therapy verification film located in the phantom. The measurements were used to verify that the 3D treatment planning system was capable of simulating the MMLC technique. For the second patient with a peanut-shaped tumor, the 3D treatment planning calculations were used to compare dose distributions for the MMLC and for traditional single and multiple isocenter treatments using circular collimators. The resulting integral dose-volume histograms (DVHs) for the target volume, normal brain, and critical structures for the three treatment techniques were compared. RESULTS: (a) Analysis of the film dosimetry data exemplified the degree of conformation of the high-dose region to the target shape that is possible with a computer-controlled MMLC. (b) Comparison of measured and calculated dose distributions indicates that the 3D treatment planning system can simulate the MMLC treatment. (c) Comparison of DVHs from the single isocenter MMLC and circular collimator treatments shows similar coverage of the target volume with increased dose to the brain for circular collimation (4). Comparison of DVHs from the single isocenter MMLC with the multiple isocenter circular collimator treatment approach shows a more inhomogeneous dose distribution through the target volume and increased dose to the brain for the latter. CONCLUSION: Dosimetry data for single isocenter treatments using computer-controlled field shaping with a MMLC demonstrate the ability to conform the dose distribution to an irregularly shaped target volume. DVHs validated that the single isocenter MMLC treatment is preferable to both single and multiple isocenter, circular collimator treatment because it provides a more uniform dose distribution to an irregularly shaped target volume and reduces the dose to surrounding brain tissue for the example cases.

Adenocarcinoma↗
PubMed1997

A numerical simulation of organ motion and daily setup uncertainties: implications for radiation therapy.

PURPOSE: In radiotherapy planning, the clinical target volume (CTV) is typically enlarged to create a planning target volume (PTV) that accounts for uncertainties due to internal organ and patient motion as well as setup error. Margin size clearly determines the volume of normal tissue irradiated, yet in practice it is often given a set value in accordance with a clinical precedent from which variations are rare. The (CTV/PTV) formalism does not account for critical structure dose. We present a numerical simulation to assess (CTV) coverage and critical organ dose as a function of treatment margins in the presence of organ motion and physical setup errors. An application of the model to the treatment of prostate cancer is presented, but the method is applicable to any site where normal tissue tolerance is a dose-limiting factor. METHODS AND MATERIALS: A Monte Carlo approach was used to simulate the cumulative effect of variation in overall tumor position, for individual treatment fractions, relative to a fixed distribution of dose. Distributions of potential dose-volume histograms (DVHs), for both tumor and normal tissues, are determined that fully quantify the stochastic nature of radiotherapy delivery. We introduce the concept of Probability of Prescription Dose (PoPD) isosurfaces as a tool for treatment plan optimization. Outcomes resulting from current treatment planning methods are compared with proposed techniques for treatment optimization. The standard planning technique of relatively large uniform margins applied to the CTV, in the beam's eye view (BEV), was compared with three other treatment strategies: (a) reduced uniform margins, (b) nonuniform margins adjusted to maximize normal tissue sparing, and (c) a reduced margin plan in which nonuniform fluence profiles were introduced to compensate for potential areas of reduced dose. RESULTS: Results based on 100 simulated full course treatments indicate that a 10 mm CTV to PTV margin, combined with an additional 5 mm dosimetric margin, provides adequate CTV coverage in the presence of known treatment uncertainties. Nonuniform margins can be employed to reduce dose delivered to normal tissues while preserving CTV coverage. Nonuniform fluence profiles can also be used to further reduce dose delivered to normal tissues, though this strategy does result in higher dose levels delivered to a small volume of the CTV and normal tissues. CONCLUSIONS: Monte Carlo-based treatment simulation is an effective means of assessing the impact of organ motion and daily setup error on dose delivery via external beam radiation therapy. Probability of Prescription Dose (PoPD) isosurfaces are a useful tool for the determination of nonuniform beam margins that reduce dose delivered to critical organs while preserving CTV dose coverage. Nonuniform fluence profiles can further alter critical organ dose with potential therapeutic benefits. Clinical consequences of this latter approach can only be assessed via clinical trials.

Algorithms↗
PubMed1996

Fractionated stereotactic radiotherapy for the treatment of acoustic neuromas: preliminary results.

PURPOSE: To evaluate the efficacy and toxicity of fractionated, stereotactic radiotherapy (SRT) for acoustic neuromas. METHODS AND MATERIALS: Twelve patients with acoustic neuroma were treated with SRT between June 1992 and October 1994. Follow-up ranged from 16-44 months. Patient age ranged from 27-70 (median: 45). Eight patients were treated with primary SRT and four patients were treated after primary surgical intervention for recurrent [3] or persistent [1] disease. Tumor volumes were 1.2-18.4 cm3 (median: 10.1 cm3). Collimator sizes ranged from 30-50 mm (median: 37.5). Tumors received 1.8 Gy/day normalized to the 95% isodose line. Patients received a minimum prescribed dose of 54 Gy in 27-30 fractions over a 6-week period. RESULTS: After a median follow-up of 26.5 months, local control was obtained in 12 out of 12 lesions. Tumor regression was noted in three patients, and tumor stabilization was found in the remaining nine patients. No patient developed a new cranial nerve deficit. One patients developed worsening of preexisting Vth cranial neuropathy and another experienced a decrease in hearing. However, all nine patients with useful hearing prior to SRT maintained useful hearing at last follow-up. CONCLUSIONS: Stereotactic radiotherapy provided excellent local control without new cranial nerve deficits. These results must be viewed as tentative in nature because of the small number of patients and the short median follow-up period.

Adult↗
PubMed1995

Stereotactic radiosurgery for the definitive, noninvasive treatment of brain metastases.

BACKGROUND: The spread of systemic cancer to the brain is a common complication for cancer patients. Conventional radiotherapy offers modest palliation, and surgery is helpful only for the patient with a single metastasis in an accessible location. Stereotactic radiosurgery, a technique that permits the precise delivery of a high dose of radiation to a small intracranial target while sparing the surrounding normal brain, has been used as an alternative treatment for brain metastases. PURPOSE: Our medical center's 7-year experience with radiosurgery for metastases was reviewed to establish the effectiveness of the treatment and to understand the prognoses in patients so treated. METHODS: Retrospective analysis of hospital records, from 248 consecutive patients (421 lesions) that were treated with radiosurgery between May 1986 and May 1993, was performed. Patients were only excluded for a Karnofsky performance score of less than 70, evidence of acute neurologic deterioration, or tumor diameter more than 4 cm. Median follow-up was 26.2 months. Seventy-six percent of patients had recurrent disease, 69% had evidence of systemic disease, 69% had a single metastasis. Treatment was performed using a 6-MeV linear accelerator. The median tumor volume was 3 cm3. The median treatment dose was 1500 cGy. Whole brain radiotherapy was given to all newly diagnosed patients. Patients were followed by neurological examination and neuroimaging at regular intervals. Local control of disease was defined as a lack of progression of solid-contrast enhancement on computed tomography scan or magnetic resonance imaging. RESULTS: Median overall survival from radiosurgery was 9.4 months. The absence of active systemic disease, younger than 60 years of age, two or fewer lesions, and female sex were significantly associated with increased survival (two-sided P < .05). Actuarial local control rates were approximately 85% at 1 year and 65% at 2 years. Factors associated with a significantly decreased local control rate were location below the tentorium, recurrent tumor, and larger tumor volume (two-sided P < .05). Radioresponsive and radioresistant tumor types had similar control rates. The median drop in Karnofsky performance score at 1 year was 10%. CONCLUSIONS: The results of this retrospective analysis show that radiosurgery is an effective, minimally invasive outpatient treatment option for small intracranial metastases. Results of this study also indicate that radiosurgery not only provides local control rates equivalent to those from surgical series but is also effective in treating patients with surgically inaccessible lesions, with multiple lesions, or with tumor types that are resistant to conventional treatment.

Adolescent↗