TA13-Recent Advances in Radiotherapy Treatment Techniques

By David Huang, PhD, DABR

Chief Physicist

Memorial Sloan-Kettering Cancer Center @ Mercy Medical Center

It is well accepted that local tumor control and normal tissue complications have sigmoidally shaped dose-response curves. The success of radiotherapy is highly depends on the radiosensitivity of the particular tumor being treated relative to that of the surrounding normal tissues. For tumor sites where the tumor control curve is less steep than the normal tissue complication curve, the high doses required for tumor cure may cause unacceptable normal tissue complications. The goal of radiotherapy is to sufficiently separate the dose-response curves of local tumor control and normal tissues complication, and also the total volume of normal tissue irradiated.

During the past two decades, advances in radiological imaging and computer technology have significantly enhanced our ability to achieve this goal through the development of three-dimensional image-based conformal therapy (3DCRT). Intensity-modulated radiation therapy (IMRT) is an especially advanced method of 3DCRT that utilizes sophisticated computer controlled radiation beam delivery to improve the conformality of the dose distribution to the shape of the tumor. This is achieved by varying beam intensities within each beam portal, as opposed to uniform beam intensities as in conventional 3DCRT. IMRT usually also incorporates computerized inverse treatment plan (ITP) optimization as opposed to the manual optimization techniques of conventional 3DCRT. Both 3DCRT and IMRT utilize sophisticated strategies for patient immobilization and positioning, image-guided treatment planning, and computer enhanced treatment verification. In the heart of these techniques is advanced computer technology and 3D patient imaging with CT, MR and/or PET.

In the radiosurgery community, they are also benefited from the advances in radiological imaging and computer technology and robotic technology. The Linac based radiosurgery moves from cone-collimator system to mini-MLC system which makes the prescribed dose more conformal to the target volume while sparing more surrounding normal tissues. For Gamma Knife, the newer APS (Automatic Positioning System) make it possible to use smaller helmet sizes with larger number of shots. This approach does improve the dose conformality with reasonable treatment time. Besides, the marriage of Robotic technology and imaging technology produces a unique machine, Cyberknife, for Sterotactic Radiosurgery/Radiotherapy field. To some extents, Cyberknife is a “true” Image-guided-radiotherapy (IGRT) machine.

Brachytherapy has advantages to place the radiation source directly to the tumor and to have shorter treatment course as compared to the external beam therapy. In addition to imaging improvement such as 3D ultrasound image, the introduction of robotic technology may improve the precise execution and optimization of entry ports for the needles. It makes seed implant procedure for prostate cancer more accuracy and more acceptable. And, hopefully, it will improve the outcome of treatment as well.

In my talks, besides the clinic application of IMRT techniques for various sites, I will address the advances in radiotherapy treatment techniques in the fields of Sterotactic Radiosurgery/Radiotherapy and prostate seed implant procedure. I would also like to cover the newer treatment unit for radiotherapy, such as Cyberknife and Tomotherapy, in my talk.  

Indeed, IMRT and other advanced treatment techniques in radiotherapy are great techniques for radiotherapy; however, we should not neglect the importance of comprehensive QA procedure for these new techniques. Without a comprehensive QA program, from image acquisition, treatment plan design, treatment delivery, to outcome follow-up, patient may not be benefited from these techniques. Besides, there are some limitations for these techniques which one should realize when implementing these advanced techniques in clinic. Furthermore, to make these techniques better for the cancer patients, future developments/improvements are needed for them. The developments/improvements include, but not limit to, target delineation, organ motion, plan biological evaluation model etc.