Clinical experience with intensity modulated radiation therapy (IMRT) in prostate cancer.

The very first cornerstone paper on intensity-modulated radiation therapy (IMRT) was published in Physics in Medicine and Biology, and many seminal IMRT works have since appeared in this journal. Today IMRT is a widely used clinical treatment modality in many countries. This contribution to the 50th anniversary issue reviews the physical, mathematical, and technological milestones that have facilitated the clinical implementation and success of IMRT. In particular, the basic concepts and developments of both IMRT treatment planning ('inverse planning') and the delivery of cone-beam IMRT with a multileaf collimator from a fixed number of static beam directions are discussed. An outlook into the future of IMRT concludes the paper.

/pdf/imrt-a-review-and-preview-1y2jcgmsfk.pdf

IMRT: a review and preview.

IMRT. General Considerations.Rotation IMRT. Tomotherapy. IMRT Using a Multileaf Collimator.IMRT. Clinical Implementation and Associated Issues. 3D Planning for CFRT Including IMRT. References. Index.

Intensity-modulated radiation therapy

IMRT treatment plans for step-and-shoot delivery have traditionally been produced through the optimization of intensity distributions (or maps) for each beam angle. The optimization step is followed by the application of a leaf-sequencing algorithm that translates each intensity map into a set of deliverable aperture shapes. In this article, we introduce an automated planning system in which we bypass the traditional intensity optimization, and instead directly optimize the shapes and the weights of the apertures. We call this approach “direct aperture optimization.” This technique allows the user to specify the maximum number of apertures per beam direction, and hence provides significant control over the complexity of the treatment delivery. This is possible because the machine dependent delivery constraints imposed by the MLC are enforced within the aperture optimization algorithm rather than in a separate leaf-sequencing step. The leaf settings and the aperture intensities are optimized simultaneously using a simulated annealing algorithm. We have tested direct aperture optimization on a variety of patient cases using the EGS4/BEAM Monte Carlo package for our dose calculation engine. The results demonstrate that direct aperture optimization can produce highly conformal step-and-shoot treatment plans using only three to five apertures per beam direction. As compared with traditional optimization strategies, our studies demonstrate that direct aperture optimization can result in a significant reduction in both the number of beam segments and the number of monitor units. Direct aperture optimization therefore produces highly efficient treatment deliveries that maintain the full dosimetric benefits of IMRT.

Direct aperture optimization: a turnkey solution for step-and-shoot IMRT.

Purpose : To implement radiotherapy with intensity-modulated beams, based on the inverse method of treatment design and using a multileaf collimation system operating in the dynamic mode. Methods and Materials : An algorithm, based on the inverse technique, has been integrated into the radiotherapy treatment-planning computer system in our Center. This method of computer-assisted treatment design was used to derive intensity-modulated beams to optimize the boost portion of the treatment plan for a patient with a T1c cancer of the prostate. A dose of 72 Gy (in 40 fractions) was given with a six-field plan, and an additional 9 Gy (in five fractions) with six intensity-modulated beams. The intensity-modulated fields were delivered using dynamic multileaf collimation 1 , that is, individual leaves were in motion during radiation delivery, with the treatment machine operating in the clinical mode. Exhaustive quality assurance measurement and monitoring were carried out to ensure safe and accurate implementation. Results : Dose distribution and dose-volume histogram of the inverse method boost plan and of the composite (72 Gy primary + 9 Gy boost) plan were judged clinically acceptable. Compared to a manually designed boost plan, the inverse treatment design gave improved conformality and increased dose homogeneity in the planning target volume. Film and ion chamber dosimetry, performed prior to the first treatment, indicated that each of the six intensity-modulated fields was accurately produced. Thermoluminescent dosimeter (TLD) measurements performed on the patient confirmed that the intended dose was delivered in the treatment. In addition, computer-aided treatment-monitoring programs assured that the multileaf collimator (MLC) position file was executed to the specified precision. In terms of the overall radiation treatment process, there will likely be labor savings in the planning and the treatment phases. Conclusions : We have placed into clinical use an integrated system of conformal radiation treatment that incorporated the inverse method of treatment design and the use of dynamic multileaf collimation to deliver intensity-modulated beams. The system can provide better treatment design, which can be implemented reliably and safely. We are hopeful that improved treatment efficacy will result.

Conformal radiation treatment of prostate cancer using inversely-planned intensity-modulated photon beams produced with dynamic multileaf collimation.

Purpose: A method for modulating beam fluence from a linear accelerator is discussed. The beam modulation is accomplished remotely using a multileaf collimator and does not require entering the treatment room. Methods and Materials: The multileaf collimator is used to define a series of field shapes that are superimposed at a fixed gantry angle to produce any desired fluence pattern. A heuristic technique for deriving the field shapes and corresponding monitor unit settings is described. The technique has been tested on randomly generated fluence distributions and on distributions with a limited number of peaks and valleys. The second type of distribution more closely simulates fluence patterns obtained with dose optimization software. Estimates of the time required to use this approach to treat a four-field plan are given and compared to the technique of placing a physical compensator in each beam. Results: It has been demonstrated that complex fluence patterns within a 15 × 15 cm2 field can be achieved with less than 20 fields. Estimates show that this technique is faster than entering the treatment room to change physical compensators. Some limitations of the method are discussed. Conclusion: Optimized distributions that conform the dose to irregularly shaped target volumes that wrap around critical structures are possible using superimposed multileaf fields. A method for defining the field shapes is presented.

Combining multileaf fields to modulate fluence distributions.

The use of superimposed multileaf fields to modulate beam intensity

Computer aided design and fabrication of electron and photon compensators

Correlation of CT information with simulation and portal radiographs

Dosimetric considerations for a new type of Cs-137 gynecological applicator

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