|
Advertisement |
|
|
||
 |
|
|||||
|
|||||
|
 |
||||||
|
||||||
|
||||||
|
Journal of Clinical Oncology, Vol 26, No 4 (February 1), 2008: pp. 688 © 2008 American Society of Clinical Oncology. DOI: 10.1200/JCO.2007.15.0524
Potential and Limitations of Intensity-Modulated Radiotherapy in Anal CancerDepartment of Radiation Oncology, University of Würzburg, Würzburg, Germany To the Editor: I read with great interest the recent article by Salama et al1 on their experience with intensity-modulated radiotherapy (IMRT) combined with standard concomitant chemotherapy (mostly fluorouracil/mitomycin) in 53 patients with anal cancer. At 18 months, they reported actuarial colostomy-free survival and local control rates of 83.7% and 83.9%, as well as what they considered a favorable toxicity profile compared with published data. The authors based their treatment approach on the observation that IMRT has been proven to spare critical normal tissues while maintaining good tumor control due to sharp dose gradients in other tumor entities. In contrast to the situation in other sites where critical structures to be spared by IMRT are adjacent to the tumor-bearing organ (eg, prostate cancer/rectum, head and neck cancer/parotid gland), the anus/perianal region itself can be considered to be a tumor-bearing organ and critical structure at the same time. This may limit the potential of IMRT to reduce toxicity and preserve long-term organ function (eg, continence and quality of life), which are important end points in anal cancer treatment2: IMRT in anal cancer may be particularly useful to spare bladder and small bowel when treating a "concave" volume encompassing the anus and distal rectum and the external iliac and inguinal nodes. The relative dose to the anal sphincter and distal rectum, however, should not be reduced in IMRT compared with less advanced radiotherapy techniques. In fact, the authors state that bolus material was used over the inguinal areas, indicating that skin sparing was not desired in the nodal part of the target volume. If reduction of skin dose was aimed at in the perianal region — this would be indicated by the reportedly reduced rates of acute dermatologic toxicity — this raises concerns about the dose coverage of the direct peritumoral area. Although the planned total doses of 50 to 54 Gy were moderate, a treatment break for toxicity was permitted by the treating physician in 42% of patients. Prolonged overall treatment times can have detrimental effects on local control in anal cancer,3 and IMRT should have the potential to reduce the necessity to interrupt the treatment. To further specify the potential benefits of IMRT in anal cancer, it would be interesting to determine if IMRT is also suitable for tumors of the anal margin or if the method should be applied only to anal canal tumors. Another important point for discussion is whether bolus material should be used to guarantee a sufficient surface dose in the direct perianal region. The early results of the present IMRT series regarding local control appear similar, but not necessarily favorable compared with modern series of 3D-conformal radiotherapy. For instance, Vuong et al4 recently reported a 5-year local control rate of 85.1% in 62 consecutive patients of nearly similar stage distribution after chemoradiotherapy with 54 Gy delivered with no treatment interruptions at all and a low rate of grade 3 acute skin toxicity. Although long-term results for local control, anorectal function and quality of life in the cohort of Salama et al will be of great interest, further development of IMRT in anal cancer should aim to avoid the still frequent treatment breaks and to exclude the potential risk of underdosage in the direct perianal region. AUTHOR'S DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST The author(s) indicated no potential conflicts of interest. REFERENCES
1. Salama JK, Mell LK, Schomas DA, et al: Concurrent chemotherapy and intensity-modulated radiation therapy for anal canal cancer patients: A multicenter experience. J Clin Oncol 25:4581-4586, 2007 2. Vordermark D, Sailer M, Flentje M, et al: Curative-intent radiation therapy in anal carcinoma: Quality of life and sphincter function. Radiother Oncol 52:239-243, 1999[CrossRef][Medline] 3. Graf R, Wust P, Hildebrandt B, et al: Impact of overall treatment time on local control of anal cancer treated with radiochemotherapy. Oncology 65:14-22, 2003[CrossRef][Medline] 4. Vuong T, Kopek N, Ducruet T, et al: Conformal therapy improves the therapeutic index of patients with anal cancer treated with combined chemotherapy and external beam radiotherapy. Int J Radiat Oncol Biol Phys 67:1394-1400, 2007[Medline]
Related Reply
Related Article
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
|||||||||||
|
|||||||||||
|
|
Copyright © 2008 by the American Society of Clinical Oncology, Online ISSN: 1527-7755. Print ISSN: 0732-183X
|
