The use of film dosimetry of the penumbra region to improve the accuracy of intensity modulated radiotherapy.

Accurate measurements of the penumbra region are important for the proper modeling of the radiation beam for linear accelerator-based intensity modulated radiation therapy. The usual data collection technique with a standard ionization chamber artificially broadens the measured beam penumbrae due to volume effects. The larger the chamber, the greater is the spurious increase in penumbra width.

Clinical application of intensity-modulated radiotherapy for locally advanced cervical cancer.

Intensity-modulated radiotherapy (IMRT) offers technical advantages over conventional external beam radiotherapy (CXRT) that might prove clinically advantageous in the management of gynecologic malignancies. Especially in the case of locally advanced cervical cancer, IMRT provides an opportunity to improve the therapeutic ratio by allowing a selective combination of normal tissue dose reduction and/or concomitant integrated boost dose to the tumor. The clinical and biologic rationale for IMRT in this setting is presented here, and pertinent technical considerations such as the delineation of relevant clinical and planning target volumes are discussed.

Technical considerations in the application of intensity-modulated radiotherapy as a concomitant integrated boost for locally-advanced cervix cancer.

The technical aspects of IMRT applied to cervix cancer are discussed in this paper, as well as issues related to tumor delineation, target volume definitions, inverse planning, and IMRT delivery. A theoretical example illustrating how IMRT can accurately mimic dose distributions obtained using conventional planning plus HDR brachytherapy is also shown. The notion of clinical optimization parameters is introduced to account for the radiation delivery variables, which affect the overall treatment time.

The effect of high-dose-rate brachytherapy dwell sequence on cell survival.

Purpose: During a high-dose-rate (HDR) brachytherapy treatment, as the source steps through different dwell positions, the dose rate at any fixed point within the implant varies, because the distance between the point and the source continually changes. The instantaneous dose rate may vary by a factor of 100 or more, in a complex dwell position sequence. Two different points which receive the same total dose may have received that dose with a very different sequence of dose rates.

A Monte Carlo study of radiation transport through multileaf collimators.

Due to the significant increase in the number of monitor units used to deliver a dynamic IMRT treatment, the total MLC leakage (transmission plus scatter) can exceed 10% of the maximum in-field dose. To avoid dosimetric errors, this leakage must be accurately accounted for in the dose calculation and conversion of optimized intensity patterns to MLC trajectories used for treatment delivery. In this study, we characterized the leaf end transmission and leakage radiation for Varian 80- and 120-leaf MLCs using Monte Carlo simulations.

Dosimetric validation for multileaf collimator-based intensity-modulated radiotherapy: a review.

The creation of intricate dose distributions produced by intensity-modulated radiotherapy (IMRT) depends on complex planning systems and specialized mechanical devices. The many possible sources of inaccuracy and the complexity of the dose maps themselves require that a substantial effort be made to ensure that calculated and delivered dose distributions agree. This review provides an overview of the current status of the validation of dose predictions of IMRT planning systems by comparisons with measurements.

Monte Carlo dose calculations for dynamic IMRT treatments.

Dose calculations for intensity modulated radiation therapy (IMRT) face new challenges due to the complex leaf geometry and time dependent nature of the delivery. A fast method of particle transport through a dynamic multileaf collimator (MLC) geometry that accounts for photon attenuation and first-scattered Compton photon production has been incorporated into an existing Monte Carlo code used for patient dose calculations. Dosimetric agreement between calculation and measurement for two photon energies and MLC types is within experimental error for the sliding window tests.

Biologic treatment planning for high-dose-rate brachytherapy.

Purpose: Interstitial brachytherapy treatment plans are conventionally optimized with respect to total target dose and dose homogeneity, which does not account for the biologic effects of dose rate. In an HDR implant, with a stepping source, the dose rate dramatically changes during the course of treatment, depending on location, as the source moves from dwell position to dwell position. These widely varying dose rates, together with the related sequencing of the dwell positions, may impart different biologic effects at points receiving the same total dose.

Interstitial high-dose-rate brachytherapy boost: the feasibility and cosmetic outcome of a fractionated outpatient delivery scheme.

Purpose: To evaluate the feasibility, potential toxicity, and cosmetic outcome of fractionated interstitial high dose rate (HDR) brachytherapy boost for the management of patients with breast cancer at increased risk for local recurrence.

Methods And Materials: From 1994 to 1996, 18 women with early stage breast cancer underwent conventionally fractionated whole breast radiotherapy (50-50.4 Gy) followed by interstitial HDR brachytherapy boost.

A method for determining multileaf collimator transmission and scatter for dynamic intensity modulated radiotherapy.

The main purpose of this work is to demonstrate a practical means of determining the leaf transmission and scatter characteristics of a multileaf collimator (MLC) pertinent to the commissioning of dynamic intensity modulated radiotherapy, especially for the sweeping window technique. The data are necessary for the conversion of intensity distributions produced by intensity-modulated radiotherapy optimization systems into trajectories of MLC leaves for dynamic delivery. Measurements are described for two, tungsten alloy MLCs: a Mark II 80-leaf MLC on a Varian 2100C accelerator and a Millenium 120-leaf MLC on a Varian 2100EX accelerator.

Dynamic splitting of large intensity-modulated fields.

The aims of this paper are to describe a method of splitting large intensity-modulated fields that cannot be delivered as a single field and to verify the accuracy of our method. Some multi-leaf collimators may be operated in the dynamic mode to deliver intensity-modulated radiation treatments (IMRT) using the 'sliding window' technique. In this technique each pair of leaves sweeps over the treatment field while the beam is on.

Internal mammary node coverage: an investigation of presently accepted techniques.

Purpose: Recent publications have generated a renewed interest in regional nodal treatment to include the ipsilateral supraclavicular and internal mammary nodes (IMN). The purpose of this study is to evaluate three presently accepted treatment techniques for coverage of the intact breast and ipsilateral lymph node regions and to construct recommendations regarding the utilization of these techniques.

Methods And Materials: Anatomic data were obtained from five randomly selected patients with computerized tomography (CT) in treatment position.

The impact of electron transport on the accuracy of computed dose.

The aim of this work was to investigate the accuracy of dose predicted by a Batho power law correction, and two models which account for electron range: A superposition/convolution algorithm and a Monte Carlo algorithm. The results of these models were compared in phantoms with cavities and low-density inhomogeneities. An idealized geometry was considered with inhomogeneities represented by regions of air and lung equivalent material.

The impact of fluctuations in intensity patterns on the number of monitor units and the quality and accuracy of intensity modulated radiotherapy.

The purpose of this work is to examine the potential impact of the frequency and amplitude of fluctuations ("complexity") in intensity distributions on intensity-modulated radiotherapy (IMRT) dose distributions. The intensity-modulated beams are efficiently delivered using a multileaf collimator (MLC). Radiation may be delivered through a continuous (dynamic mode) or discrete (step-and-shoot) sequence of windows formed by the leaves.

Clinical use of a digital simulator for rapid setup verification in high dose rate brachytherapy.

Purpose: Fractionated high dose rate (HDR) brachytherapy provides a number of technical advantages over conventional implant therapy in that (a) it can be carried out on an outpatient basis, (b) personnel exposure is reduced to insignificant levels, and (c) patient motion during irradiation is minimized, resulting in a more accurate delivery of the planned radiation dose distribution to the target and critical structures. The patient discomfort associated with the repeated applicator insertions and/or treatment setups can be alleviated to the extent that the setup time is held to a minimum. This work describes the use of a prototype digital simulator to obtain fast, high-quality digital images for rapid setup verification.

Optical properties of experimental prostate tumors in vivo.

The optical properties of tumor tissue provide important information for optimizing treatment plans in photodynamic therapy, especially when interstitial application by multiple fibers is planned. Near infrared light, required to activate novel photosensitizers, should facilitate improved light penetrance of tumor tissue compared with 630 nm light used for activating Photofrin II. We have measured light energy fluence rates for 630 and 789 nm light along radial tracks from a single laterally diffusing optical fiber centrally implanted into Dunning R3327-AT and R3327-H rat prostate tumors in anesthetized rats.

Analysis of tissue optical coefficients using an approximate equation valid for comparable absorption and scattering.

New photosensitizers activated by longer wavelengths than 630 nm light used with Photofrin II are under evaluation by various groups for the treatment of malignancies. Any increase in tumour volume destroyed by these agents as compared to Photofrin II will be partly determined by tissue penetrance at the longer wavelengths. Attenuation coefficients were measured for various tissues at 630 nm and the more penetrative near infrared wavelength of 789 nm.

Non-invasive monitoring of photodynamic therapy with 99technetium HMPAO scintigraphy.

The effect of photodynamic therapy (PDT) on tumour perfusion in both anaplastic (R3327-AT) and well differentiated (R3327-H) Dunning prostatic tumours was studied using the radiopharmaceutical 99Technetium hexamethylpropyleneamine oxime (99mTc-HMPAO). Tumours in the left flanks of rats (Copenhage x Fischer, F1 hybrids) were treated with interstitial PDT when their volumes reached 2-3 cm3. Qualitative and quantitative data from pre- and post-PDT scintigraphy revealed a light-dose-dependent shut-down of tumour perfusion which was also time-dependent.

Nuclear magnetic resonance spectroscopy and sensitizer-adduct measurements of photodynamic therapy-induced ischemia in solid tumors.

Dunning R3327-AT prostate carcinomas growing in Fischer X Copenhagen rats were treated with interstitial photodynamic therapy (PDT--15 mg/kg Photofrin II 4 hours before illumination with 630-nm light via four parallelly implanted optical fibers) at different light intensities. Forty to 60 minutes after treatment, 31P-nuclear magnetic resonance spectra of tumors in anesthetized animals were obtained at 2.35 Tesla using surface coil localization.

The effectiveness of short-term versus long-term exposures to Photofrin II in killing light-activated tumor cells.

Asynchronous populations of mouse EMT-6 tumor cells were exposed to various doses of 630-nm light in slowly stirred aerobic suspensions after both short-term and long-term exposures to Photofrin II. All survival curves are characterized by a "threshold" light dose below which no cell inactivation occurs followed by a steep light-dose response. Both the shoulder widths and the inactivation curve slopes are functions of Photofrin II concentration.

Oxygen dependency of tumor cell killing in vitro by light-activated Photofrin II.

Asynchronous populations of mouse EMT-6 tumor cells were treated with Photofrin II and exposed to various doses of 630 nm light in slowly stirred suspensions which had been equilibrated with various concentrations of oxygen. Survival curves were generated with cells exposed to 20 micrograms/ml Photofrin II in tissue culture medium for 1 h, a procedure which made it possible to remove more than 50% of the drug by washing. It is expected that under these conditions the drug would be loosely bound to cell surface and plasma membranes and in the cellular cytosol.

Photodynamic therapy dosimetry in postmortem and in vivo rat tumors and an optical phantom.

Dosimetry in photodynamic therapy as currently practiced is empirical in that it does not account for optical properties of the target lesion. However, since light attenuation in tissue is unpredictable, measurements of optical properties are needed to ensure optimal light dose delivery. Further improvements in the uniformity of light dose distribution in tumors can be afforded by implanting multiple light sources.

Optical dosimetry for interstitial photodynamic therapy.

An approach to photodynamic treatment of tumors is the interstitial implantation of fiber optic light sources. Dosimetry is critical in identifying regions of low light intensity in the tumor which may prevent tumor cure. We describe a numerical technique for calculating light distributions within tumors, from multiple fiber optic sources.

Neodymium:YAG laser therapy for infiltrating bladder cancer.

There were 32 high risk patients with stages T2 to T4 bladder cancer treated with neodymium:YAG laser irradiation to the tumor base after cautery resection between July 1981 and October 1986. All 12 patients with stage T2 disease followed for 6 to 78 months had no recurrence locally although 4 had stage T1 recurrences elsewhere in the bladder. Of 14 stage T3 cancer patients 8 demonstrated tumor persistence locally but 3 were well 4 to 24 months later without local recurrence (all stage T3a) and 3 were alive 14 to 24 months later with stage T1 recurrences.