Three-dimensional conformal radiation therapy Conference Paper

  


Author: Leibel, S. A.
Title: Three-dimensional conformal radiation therapy
Conference Title: 35th Annual Meeting of the National Council on Radiation Protection and Measurement (NCRP)
Abstract: Failure to control localized cancer results from resistance of tumor clonogens to the maximal dose levels feasible with conventional radiotherapy techniques. Because of difficulties in precisely identifying the location of tumors using traditional radiation therapy planning methods, large safety margins were used in the past to ensure that the tumor was encompassed in its entirety. These safety margins encroached into normal tissue structures. To avoid severe side effects, it was necessary to restrict the tumor dose to the tolerance level of the normal tissues. Three-dimensional conformal radiation therapy (3D-CRT) is an approach to overcome this problem. Using sophisticated computer algorithms to calculate the dose at each point in the entire 3D space of the irradiated tissues, 3D-CRT targets a prescribed dose to the tumor, conforming to its spatial configuration. Concomitantly, the dose to surrounding normal tissues is kept at a minimum, decreasing the risk of normal tissue complications. This, in turn, permits an increase in tumor dose, expected to improve local tumor control. As a proof-in-principle, studies in patients with localized prostate cancer have demonstrated that dose escalation is feasible, and a relationship of dose to tumor response and long-term therapeutic outcome has been established. Further, despite the use of high dose levels, the overall rate of clinically relevant radiation-induced toxicities was reduced when compared to conventional radiotherapeutic approaches. To further improve the dose distribution, intensity modulated radiation therapy (IMRT) has been developed. This advanced 3D-CRT approach permits the high dose radiation volume to be exquisitely shaped to the cancerous area and sculpted around adjacent normal organs, allowing higher, more effective, doses to be delivered to tumors without increasing the side effects of treatment. A novel technique of computer-aided optimization is used for inverse treatment planning in which the intensities of individual rays within the radiation beam are iteratively adjusted to satisfy predefined dose specifications to the tumor and normal tissues. The result is a series of intensity modulated beams which configure dose distribution patterns that respond to the prescribed dose specifications. The system for delivery of intensity modulated beams uses multileaf collimators in a dynamic mode to produce the required dose distribution. IMRT is being implemented for treatment of prostate, head and neck, and breast cancers and for brain tumors. New methods of biological imaging are being integrated into the planning of radiation treatment. Using resonance spectroscopy and positron emission tomography, regions of rapid proliferation, hypoxia and high clonogen burden can be identified within the tumor. IMRT may permit "dose painting" to selectively increase the dose to more aggressive or less radiosensitive regions within the tumor. This approach represents a new frontier in 3D-CRT.
Keywords: algorithm; normal tissue; metastatic; planning; localized prostate-cancer; dose-volume; dissemination; multileaf collimators; clinical-experience; histograms; tumor-control probability; complication probabilities; beam irradiation
Journal Title Radiation Protection in Medicine: Contemporary Issues
Volume: 21
Conference Dates: 1999 Apr 7-8
Conference Location: Arlington, VA
ISBN: 0-929600-62-6
Publisher: Natl Council Radiation Protection Measurements  
Date Published: 1999-01-01
Start Page: 229
End Page: 260
Language: English
ACCESSION: WOS:000173048200012
PROVIDER: wos
Notes: Proceedings Paper -- 35th Annual Meeting of the National-Council-on-Radiation-Protection-and-Measurement -- APR 07-08, 1999 -- ARLINGTON, VA -- Natl Council Radiat Protect -- 7910 WOODMONT AVE, SUITE 1016, BETHESDA, MD 20814 USA -- Source: Wos