Does the evidence support the enthusiasm over 3D conformal radiation therapy and dose escalation in the treatment of prostate cancer

INTRODUCTIONPowerful X-ray computed tomography (CT) simulation andthree-dimensional radiation therapy treatment planning(3D-RTP) systems have now been commercially availablefor nearly a decade and are rapidly replacing the conven-tional radiation therapy X-ray simulator and two-dimen-sional (2D) dose planning process in many clinics. In addi-tion, the latest generation of medical linear accelerators hassophisticated computer-controlled multileaf collimator sys-tems that provide beam intensity modulation features capa-ble of precise shaping of dose distributions.These advanced systems have spurred the implementa-tion of three-dimensional conformal radiation therapy (3D-CRT) and intensity-modulated radiation therapy (IMRT)techniques, in which the high-dose region is conformedmuch more closely to the patient’s target volume, reducingthe volume of normal tissues receiving a high dose. Severalsingle institutions (1–4) and one cooperative group, theRadiation Therapy Oncology Group (RTOG) (5, 6), havealready reported on their early clinical experience in the useof 3D-CRT and/or IMRT for the treatment of prostatecancer, and the results are encouraging. These reports havegenerated signiﬁcant enthusiasm in the community practicefor the treatment of prostate cancer using 3D-CRT. How-ever, the article by Levitt and Khan questions whether theevidence supports the enthusiasm over 3D-CRT and doseescalation in the treatment of prostate cancer. They con-clude, “Until we have solid long-term evidence on the trueclinical potential of this new technology, let us not rush tojudgment, but exercise caution, diligence, and thoughtful-ness in using this new technology to treat our patients” (7).Unfortunately, in reaching this conclusion, the authors de-liver a message that is clouded at times and seems to bemore “anti-technology” than focused on the real issue ofconcern when adopting 3D-CRT/IMRT, i.e., urging thepractitioner to become better educated and trained in the useof what is clearly an improved technology.Three-dimensional planning is not just an add-on to thecurrent radiation therapy planning process. Rather, it repre-sents a radical change in practice, particularly for the radi-ation oncologist. The 2D treatment planning approach, orwhat Levitt and Khan call standard radiation therapy (SRT)(7), emphasizes the use of a conventional simulator fordesigning beam portals based on standardized beam ar-rangement techniques, bony landmarks visualized on planarradiographs, and “the use of generous margins to assureadequate coverage of the target volume while minimizingdose to critical normal structures” (7). Clearly, the SRTapproach, with its use of generous margins, is challenged totruly minimize dose to normal structures for the individualprostate cancer patient.In contrast to the SRT approach, three-dimensional (3D)treatment planning emphasizes an image-based virtual sim-ulation approach for objectively deﬁning tumor and criticalstructure volumes for the individual patient. A critical ques-tion is (and always has been) how well the tumor volumeand normal tissue volumes can be deﬁned for speciﬁc tumorproblems. This new technology does put new demands onthe radiation oncologist to specify target volumes and crit-ical structures with far greater precision. Note the 3D ap-proach does not necessarily result in smaller treatment vol-umes for all sites! We will come back to this point later.Moreover, this new technology also places new demands onthe radiation oncology physicist to ensure adequate qualityassurance measures are in place to accommodate the new3D-CRT process: e.g., the need for new precision in tumorimaging, patient setup reproducibility, organ motion assess-ment, and treatment delivery veriﬁcation.The use of the terms 2D and 3D as descriptors for theplanning process continues to cause some confusion in theradiation oncology community. One should recognize thatplanning the cancer patient’s treatment is, and always hasbeen, a 3D problem (at least in regard to the spatial distri-bution of dose); when we refer to 2D planning, we refer tothe process and tools used. Three-dimensional treatment