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External-beam radiation therapy alone
External-Beam Radiation Therapy Alone C. Shun WongandJamesD. Brierley Surgery with or without adjuvant radiation therapy and chemotherapy is the standard treatment for patients with resectable rectal carcinoma. Many patients, however, are medically unfit or simply refuse surgery that could result in a colostomy. This article reviews the results of external-beam radiation therapy alone for selected patients with rectal carcinoma and its role in preserving anorectal function. For patients with mobile tumors, a 5-year survival and local relapse-free rate of 30% and 25%, respectively, can be expected after external-beam radiation therapy alone, and 60% remain
colostomy free. Results of radiation therapy alone in patients with fixed or unresectable tumors are poor. Although more than a third of patients remain colostomy-free, only 5% of patients survive 5 years. In patients with mobile rectal carcinomas that are not amenable to sphincter-preserving surgery, who are unfit medically for radical surgery, or who refuse a colostomy, external-beam radiation therapy offers the reality of sphincter preservation and the possibility of longterm tumor control.
urgery is the standard management of patients with localized rectal carcinoma. Reviews of the surgical management of rectal carcinoma have suggested that the overall 5-year survival rate for patients who have apparently complete resection is about 50%.1,2 Despite modern surgical techniques that have reduced the frequency of colostomies,3 a colostomy cannot always be avoided. There is an expanding literature on the use of external-beam radiation therapy combined with sphincter-preservation surgical resection in an attempt to preserve the anorectal function. For patients with small and superficial tumors of the distal rectum, good results can be achieved by local excision with or without radiation therapy. 4,5 Similarly, endocavitary radiation therapy can be used. 6-8 For patients with larger or more advanced tumors, the combination of adjuvant radiation therapy and low anterior resection with coloanal anastomosis offers the reality of radical sphincterpreserving surgery9 -u The role of these techniques in the management of rectal carcinoma is described elsewhere in this issue in detail. Only 3% to 5% of patients, however, have lesions that are suitable for conservative surgical resection or endocavitary radiation therapy. ~ Many patients are not fit for radical surgery because of age or concomitant medical conditions. Many patients may simply refuse surgery if it results in a permanent colostomy. This article describes the results of external-beam radiation therapy alone in the management of patients with localized rectal carcinoma. The focus is
principally on its role in patients who have potentially resectable rectal carcinoma and who for one reason or another are not candidates for surgical resection. The role of external-beam radiation therapy in sphincter preservation for patients with localized but unresectable tumors and locally recurrent cancer is also reviewed.
S
From the Department o/Radiation OncologT,PrincessMargaret Hospital, University of Toronto, Toronto, Ontario. Address reprint requests to C. Shun Wong;MD, FRCPC, Department of Radiation Oncology, Princess Margaret Hospital, 610 University Ave, Townto, Ontario, MSG 2M9. Copyright 9 1998 by W.B. Saunders Company 1053-4296/98/0801-000258.00/0
Copyright 9 1998 by W.B. Saunders Company
Primary Resectable Rectal Carcinoma Although it had been previously suggested that adenocarcinoma of the rectum was essentially radioresistant, 12 Wang and Schulz 13 reported that in 58 patients with tumor confined to the pelvis and treated with radical radiation therapy, 2 survived 5 years or more after external-beam radiation therapy alone. In a report by James and Schofield, ~429 of 42 patients with fixed unresectable rectal carcinoma underwent laparotomy after pelvic irradiation therapy. In three of these cases, there was no residual tumor in the operative specimen. These studies showed that external-beam radiation therapy alone can produce long-term cancer control or complete responses in selected patients with rectal carcinoma. Most reports have described the use of externalbeam radiation therapy alone in patients with unresectable or locally recurrent disease. Many of these patients underwent attempted resection after radiation therapy. There are limited data on the use of external-beam radiation therapy alone in the management of rectal cancer that is potentially resectable. In a series of 113 patients with rectal cancer managed by radiation therapy, described by Overgaard et al, 15 only 2 were considered medically inoperable; in both cases, however, the tumor was described as large and fixed, suggesting that the tumor was also unresectable. Taylor et a116 described a series of 243 patients with rectal cancer treated with external-beam radiation therapy. Seventy-four patients had radical radia-
Seminars in Radiation Oncvlogp, Vol 8, No 1 (Janua?y), 1998:pp 3-12
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WongandBrierley
tion therapy, 33 for recurrent disease and 30 for unresectable disease. Only ll patients had tumors described as potentially resectable and were given radiation therapy because the patients were not considered fit tbr radical surge~T. A complete response of 38% was observed in these 11 patients. The 2-year survival was 55%, but none survived 5 years. Results of external-beam radiation therapy alone for rectal cancer were reported earlier by Williams and Horwitz, 17 who described 2 of 5 patients with small tumors and 10 of 21 patients with tumors involving the whole rectal wall surviving 2 years after external-beam radiation therapy alone. Rousseau et a118gave 50 to 65 Gy and observed complete response in three of five tumors clinically confined to the bowel wall. For tumors that had extended through the bowel wall, the complete response rate was 11% (3 of 28). After a median dose of 68 Gy over 8.5 weeks, AmaMc et a119described a 3-year survival rate of 36% (5 of 14) in patients with tumors that by clinical examination were considered to have extended through the rectal wall.
Princess Margaret Hospital Experience The most extensive experience on the use of externalbeam radiation therapy alone in the primary management of rectal cancer has been reported by investigators from the Princess Margaret Hospital. In the first of three reports, Rider 2~ described the results of 65 patients treated between 1958 and 1969. In a subsequent article, Cummings et a121 reported on another 133 patients treated between 1970 and 1977, 56 of whom had mobile tumors. In our most recent report, Brierley et a122 described the results of 229 patients treated between 1978 and 1987, 134 of whom were considered to have mobile or potentially resectable
disease. All patients had biopsy-proven adenocarcinoma of the rectum. These patients were selected for primary radiation therapy because the tumor was unresectable in the opinion of the surgeon, the patient was medically unfit for radical surgery, the patient had refused to have a colostomy, or a combination of these factors. At the Princess Margaret Hospital, since 1978, a rectal tumor has been classified as fixed when the tumor cannot be moved separately from the extrarectal tissues, partially fixed when the tumor and the rectal wall do not move freely, and mobile when the tumor is fully mobile in all directions. Among the 229 patients reported in our most recent article, the tumor was mobile in 97, partially fixed in 37, fixed in 77, and not assessable for mobility in 18. In this study, the most frequently used fractionation schedule was 50 Gy in 20 fractions in 4 weeks but varied from 40 Gy in 10 fractions in two sessions each of five treatments in 1 week separated by a 2- to 4-week split to 60 Gy in 30 fractions in 6 weeks. Radiation therapy was delivered with cobalt 60 or 18 to 25 MV photons. The most frequently used technique was a four-field box (83 patients). The fields used were designed to cover the primary tumor, perirectal tissues, and pelvic nodes from approximately the level of the first sacral vertebra to 3 to 5 cm below the lowermost palpable edge of the tumor. The overall actuarial 5-year survival from the start of radiation therapywas 27%. The 5-year smMval was 48% for those with mobile tumors and 27% for those with partially fixed tumors. Patients with fixed tumors had a 5-year survival of only 4% (P < .0001) compared with mobile and partially fixed tumors (Fig 1). These results were similar to the 5-year survival rates of 38% and 2% in our previous cohort of
100 80
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Figure 1. Actuarial survival of 229 patients with mobile (97), partially fixed (37), and tixed (77) rectal carcinoma treated with external-beam radiation therapy.
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Figure 2. Barium enema view of a circumferential mobile carcinoma (A) before external-beam radiation therapy and (B) 6 months after radiation therapy. patients with mobile and fixed tumors treated between 1970 and 1977. 91 When a multivariate Cox proportional hazard model was performed, only age less than the median of 75 (P = .001) and absence of tumor fixation (P = .001) were predictors of better survival. Patient gender, tumor grade, tumor description, and tumor location from the anal verge were not significant prognostically for overall survival. Forty-eight (50%) of the mobile, 11 (30%) of the partially fixed; and 7(9%) of the tixed tumors responded completely after radiation therapy (Fig 2).
The rate of tumor regression after radiation therapy was slow. Regression was complete by 4 months in only 60% of the 66 patients in whom a complete response was documented but was complete in more than 90% by 9 months (Fig 3). There was no relationship between the time taken for a rectal cancer to involute completely and the risk of later relapse. The slow regression of rectal carcinoma after external-beam radiation therapy has also been reported by Papillon, 23 who recommended waiting 2 months to allow maximal tumor regression before a
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Figure 3. Time to remission from the start of radiation therapy for 66 patients clinically assessed as having responded completely.
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decision regarding surgical resection versus conservative treatment, such as intracavitary irradiation. Of 59 mobile and partially fixed tumors that went into complete remission, 24 later relapsed locally. Five of seven fixed tumors that were considered to have regressed completely also later relapsed. The principal site of failure was at the location of the primary tumor. Only 3 patients developed distant metastases without evidence of local disease, although both local and distant failure occurred in 52 patients. Brierley et a124have combined data from all three reports (1958-1987), specifically to assess whether prolongation of treatment time was an adverse prognostic factor for local control after external-beam radiation therapy. For the purpose of that analysis, patients treated since 1978 who had mobile or partially fixed tumors were classified together as having mobile tumors. Thus, all tumors were classified as mobile or fixed or, if they were beyond the reach of the examining finger, as mobility unknown. Factors assessed included patient's age, gender, tumor annularity, tumor mobility, total dose, overall treatment time, presence or absence of treatment interruption, and length of treatment interruption. The duration of local control was calculated from the date of first radiation therapy treatment. In total, there were data on local control in 353 patients. A total of 112 patients (32%) went into complete remission, but 47 later relapsed locally. At 5 years, the actuarial local control rate for mobile tumors was 24% and for fixed tumors was 7% (Fig 4). Only tumor fixation was an adverse prognostic factor fbr local control (P = .02) in a multivariate Cox regression analysis (Table 1). For the 171 patients with mobile tumors, none of the factors was significant in predict-
ing local control after external-beam radiation therapy. Of the 229 patients treated between 1978 and 1987, 50 underwent salvage surgery for persistent (43) or recurrent (7) disease. These included 13 patients with fixed tumors who also had salvage surgery. Although it appears to be contradictory that 37 patients initially not treated by surge~T because of refusal or being medically unfit later had salvage surgery, this is because either their condition improved or, in the face of failure of radiation therapy, the surgeon and the patient were willing to accept the increased risk of radical surgery or the necessity of a colostomy. Forty-six of the 50 patients had complete resection without apparent residual disease after surgery. The 5-year actuarial survival rates after surgery for patients with tumor that had been mobile, partially fixed, and fixed before radiation therapy were 59%, 30%, and 23% respectively. These results show the feasibility of salvage surgery after the failure of radiation therapy (Fig 5). Although not all of these patients would have required a colostomy if treated with surgery, it may be assumed that if external-beam radiation therapy is given to patients with potentially resectable tumors and who refuse surgery, 30% achieve sustained local control and avoid a colostomy. Furthermore, not all patients who have persistent or locally recurrent tumor develop obstruction or obstructive symptoms requiring a colostomy. Of the 229 patients in our third study, 17 had a defunctioning colostomy before radiation therapy. None of these was closed subsequently. Of 212 who did not have a colostomy before radiation therapy, 69 later required a defunctioning colostomy or a colostomy as part of salvage surgery.
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Figure 4. Local relapse-flee Fixed
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rate (LRFR) for patients with mobile (171) and f~ed (159) rectal carcinoma treated by external-beam radiation therapy alone.
External-BeamRadiation TherapyAlone
or 4 acute toxicity. Significant late toxicity occurred in 4 of 229 patients. Two patients developed skin ulcers (one required a graft), and one patient developed ureteric stenosis requiring stenting. The fourth patient developed a persistent perineal ulcer and subsequent sacral osteomyelitis from which he died. No patient treated by three- or four-field technique developed grade 3 or 4 late toxicity. No apparent increase in morbidity was observed in patients who underwent salvage surgery. There are limited prospective data on the late effects of radiation therapy on anorectal function. 25,26 We have not systematically assessed anorectal function after radiation therapy, although patients in whom local control was achieved appeared to have normal sphincter function. Our experience with this fractionation schedule during the period of 1970 through 1977 suggests that 50 Gy in 20 fi'actions is likely to be close to rectal tolerance, particularly if a large volume of the pelvis is treated by a parallel pair technique. 21
Table 1. Prognostic Factors Entered Into an Analysis of Association With Local Control in 353 Patients With Primary Rectal Carcinoma Managed by External-Beam Radiation Therapy Alone Cox
Factors
Univariate Analysis
Fixation Annular Treatment length* Interruptiont Gender Age Dose
Multivariate Analysis
.0001 .0001 .02 .03 NS NS NS
7
.02 NS NS NS NS NS NS
*Defined as prolonged treatment time above the median of 30 days. ~'Definedas the presence of a treatment interruption, planned or unplanned. The 5-year actuarial colostomy-free rates fbr 212 patients who did not have a colostomy before radiation therapy were 63% for mobile tumors, 48% for partially fixed tumors, and 37% for fixed tumors (Fig 6). The external-beam radiation therapy was generally well tolerated. Acute proctitis and perineal discomfort usually responded rapidly to symptomatic management. During the period of 1970 through 1977, when most patients were treated with parallelopposed anterior-posterior fields, 2 of 123 patients died shortly after treatment of radiation enteritis. 21 During the subsequent period of 1978 through 1987, when most patients were treated with multiple fields, five patients (2%) developed R T O G / E C O G grade 3
Combined External-Beam and Intracavitary Radiation Therapy or Implant Superficial and small distal rectal carcinomas that carry a low risk of lymph node metastases can be treated adequately by local excision with or without external-beam radiation therapy. 4,5,27,2a These early lesions can also be managed effectively by intracavitary radiation therapy with local control of 90%. 6-8 The latter technique is particularly attractive for
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20 Figure 5. Actuarial survival from date of surgery for 50 patients who had salvage surgery for persistent or recurrent carcinoma after externalbeam radiation therapy.
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elderly and frail patients who are at high risk for surgery including local excision. 6 For more advanced lesions, a combination of external-beam and intracavitary radiation therapy or interstitial implant has been used in a number of centers. Papillon 23 used this technique in 67 patients with tumors measuring more than 4 cm or showing slight extrarectal extension. Patients were initially given an external-beam dose of 30 Gy in 10 daily fractions over 12 days using a 120-degree arc rotation through a 9 • 12 cm sacral field, giving a dose of 35 to 39 Gy to the tumor. This was followed 2 months later either by intracavitary radiation of 25 Gy or an iridium 192 implant of 20 to 30 Gy. A 5-year smMval of 60% was reported, with 40 patients remaining tumor-free. Patients who remained disease-free were described to have normal anal function. A similar combined approach of an intracavitary boost of two to three applications of 30 Gy each given 6 weeks after external-beam radiation therapy of 45 Gy in 25 fractions was reported by Kodner et a129 For mobile tumors measuring less than 3 cm, 11 of 13 patients achieved local control. For tethered tumors or lesions measuring greater than 3 cm, 14 of 20 patients achieved local control. 99,3~ Gdrard et aP 1 used a combination of initial intracavitary treatment (70 Gy/3 fractions) followed by external-beam radiation therapy in a concomitant boost schedule (39 Gy/13 fractions and 4 Gy/4 fractions boost) in 29 patients. In 21 of 29 patients, an iridium 192 implant (20 Gy/22 h) was performed 6 weeks after externalbeam radiation therapy. Patients were staged by transrectal ultrasound with 19 lesions described as exceeding 3 cm. Survival at 5 years was 68%, and 21 of 29 patients achieved local control. Five of 21
6. Colostomy-ffee
rate in 212 p a t i e n t s w i t h rectal carcinoma who underwent
external-beam radiation therapy and had not undergone colostomybefore treatment.
patients who received iridium 192 boost developed rectal necroses. These results suggest that a combination of external-beam radiation therapy and intracavitary boost or interstitial implant can produce local control of about 70% for selected patients with distal rectal cancer. The better local control rates reported in these studies compared with those after externalbeam radiation therapy alone 21,~2 may simply reflect the smaller tumor bulk in patients, which allows the use of intracavitary boost or implant after externalbeam radiation therapy.
Primary Unresectable Rectal Carcinoma Although tumor fixation is not synonymous with unresectability, it is generally assumed that most, if not all, fixed tumors are technically unresectable. 32 Fixed rectal tumors are generally managed by radiation therapy alone or in combination of surgical resection after radiation therapy. Results of externalbeam radiation therapy for fixed rectal tumors are disappointing. Our results of a local control rate of only 7% and median survival of 18 months in patients with fixed rectal carcinomas are similar to those reported in other series33,15,33-36 These results show that external-beam radiation therapy alone is unlikely to be associated with long-term control for tumors clinically fixed to the extrarectM tissues. Nonetheless, the colostomy-ffee rate of 70% at 18 months (Fig 6) in our own series suggests that a significant number of these patients have preservation of anorectal function despite the presence of progressive local disease. There is general agreement in the literature that a better survival is achieved in patients who are able
External-Beam Radiation TherapyAlone
to undergo complete resection subsequent to radiation therapy. In our series from the Princess Margaret Hospital, 2~ 13 of 77 patients classified as having fixed tumor had salvage surgery after external-beam radiation therapy of 50 Gy in 20 fractions. The actuarial 5-year survival rate was 23% tbr these patients. Resectability rates of fixed rectal cancer after radiation therapy are variable and range tk~om 30% to 65% in the literature and probably reflect the differences in selection criteria used to define rcsectability. 32,37-39Because external-beam radiation therapy alone rarely results in long-term control of clinically fixed rectal carcinoma, it should be part of a planned preoperative regimen or be palliative in intent. The role of preoperative radiation therapy in sphincter preservation of patients with rectal carcinoma is discussed elsewhere in this issue. Locally Recurrent Rectal Carcinoma External-beam radiation therapy is frequently used in the treatment of patients in whom local recurrence develops after previous surgical resection and in whom no prior adjuvant radiation therapy has been used. It is generally recognized that symptoms such as pain and bleeding respond well to radiation therapy, whereas palliation of other pelvic symptoms such as neurological deficit, urinary symptoms, and rectal discharge is achieved less fi-equently. Partial or complete tumor regression is rarely reported after external-beam radiation therapy alone. 15,4~ Few patients with locally recurrent rectal carcinoma survive 5 years after external-beam radiation therapy alone. In our series of 519 patients with locally recurrent rectal carcinoma treated principally by external-beam radiation therapy from the Princess Margaret Hospital, the 5-year survival was 5% with a median survival of 14 months. The median time to local or pelvic disease progression was only 5 months. Similarly disappointing results have been reported in other series. 15,3944These results suggest that palliation of pelvic symptoms after radiation therapy is maintained only for a brief period equivalent to a third of the remaining life span of the patients. Similar to patients with primary unresectable tumors, improved survival and local control in patients with local recurrence have generally been reported in the subset of patients who are able to undergo complete surgical resection? 2,45 Undoubtedly, these patients represent a highly selected group of patients with better prognosis. There is, however, general agreement in the literature that surgery or
9
combined surgery and radiation therapy has a major impact on local control and smvival and should be offered to these patients with potentially resectable recurrence. There are limited data on the role of externalbeam radiation therapy alone for patients who develop local recurrence after previous sphincterpreserving surgery. About 10% of patients develop local recurrence after local excision, 27,28,47and abdominal perineal resection is generally considered the standard salvage management, with about 50% who suffer local failure remaining disease-free after salvage surgery. 47,48 We have reported a series of 37 patients who received external-beam radiation therapy alone for local recurrence after previous local excision o r electrocoagulation. 49 In 4 patients, the local recurrence was fixed in the pelvis, whereas the recurrence was considered mobile and potentially resectable in the remaining 33 patients. These patients either had refused to have a salvage abdominal perineal resection or were considered to be poor candidates for radical surgery because of intercurrent medical illness or advancing age and were managed by external-beam radiation therapy alone. The 5-year survival and local control rates were 20% and 15% after radiation therapy for local recurrence. For patients who received a dose of 50 Gy or more, the survival and local control rates were 35% and 40% at 5 years. These results were similar to those we reported in patients with mobile primary rectal carcinoma managed by external-beam radiation therapy alone 21,22 and suggest that selected patients with locally recurrent rectal cancer with small tumor bulk are potentially curable with radiation therapy alone. Attempts to improve the results of external-beam radiation therapy with chemotherapy have not produced any definite benefit over radiation therapy alone. The encouraging early results by Moertel et al 5~ have not been reproduced in a number of subsequent studies. The combination of chemotherapy using drugs such as 5-fluorouracil with radiation therapy have generally resulted in an increase in toxicity from the cytotoxic drugs or radiation therapy.46, 51-56
Conclusions We recommend radical external-beam radiation therapy in patients with rectal cancer if the patient is medically unfit for surgery or refuses surgery that would result in a colostomy and if the tumor is not
Figure 7. Simulation films of (A) posteroanterior and (g) lateral fields for a course of external-beam radiation therapy for a circumferential, partially fixed rectal carcinoma.
External-Beam Radiation TherapyAlone
suitable for local excision or intracavitary radiation therapy. O u r c u r r e n t radiation t h e r a p y prescription is 50 Gy t u m o r dose in 20 fractions over 4 weeks by a three- or four-field technique. T h e a n a t o m i c e x t e n t of the t u m o r is assessed by digital e x a m i n a t i o n , sigmoidoscopy, c o m p u t e d t o m o g r a p h y scan, and rectal barium. T h e fields used are designed to cover the p r i m a r y t u m o r and p e r i r e c t a l tissues and nodes w i t h a 3- to 5-cm margin. N o a t t e m p t is m a d e to e n c o m pass all the l y m p h n o d e - b e a r i n g tissues t h a t m a y be r e m o v e d at surgery because the resulting v o l u m e would result in u n a c c e p t a b l e toxicity. T h e radiation t h e r a p y fields (Fig 7) usually e x t e n d from: 1. Superior field border, 3 to 5 cm above the tumor. 2. Inferior field border, 3 cm below the inferior m a r g i n of the t u m o r , sparing the p e r i n e u m if possible. 3. L a t e r a l field borders, bony margins of the t r u e pelvis, or 3 c m lateral to the tumor. 4. Posterior field border, 2 cm posterior to the a n t e r i o r aspect of the sacral hollow. 5. A n t e r i o r field border, 3 c m anterior to the t u m o r . E x t e r n a l - b e a m radiation therapy can eradicate a p p r o x i m a t e l y 25% of rectal cancers that are mobile or partially fixed, but in patients w i t h fixed tumors, the control rate with e x t e r n a l - b e a m radiation t h e r a p y alone is poor. In patients with mobile or partially fixed t u m o r s who refuse a colostomy or for w h o m sphincter-preserving surgery is not possible, externalb e a m radiation t h e r a p y m a y be a valid option. For patients with fixed rectal cancers, high-dose externalb e a m radiation t h e r a p y should be part of a p l a n n e d preoperative r e g i m e n or be palliative in intent.
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29. Kodner IJ, Gilley, Shemesh EL, et ah Radiation therapy as definitive treatment for selected invasive rectal cancer. Surgery 114:850-856, 1993 30. Myerson RJ, Walz BJ, Kodner IJ, et ah Endocavitary radiation therapy for rectal cancer: Results with and without external beam. Endoc Hypertherm Oncol 5:195-209, I989 31. G4rard JP, Roy P, Coquard R, et ah Combined curative radiation therapy alone in (T1) T2-3 rectal adenocarcinoma: A pilot study of 29 patients. Radiother Onco138:131-137, 1996 32. Buhre LM, Mulder NH, OldhoffJ, et al: The clinical staging of rectal cancer in patients treated by preoperative radiotherapy. Clin Oncol 6:157-161, 1994 33. Minsky BD, Cohen AM, Enker WE, et al: Radiation therapy for unresectable rectal cancer. Int J Radiat Oncol Biol Phys 21:1283-1289, 1991 34. Nordman E, Gronroos M, Aho AJ, et al: Inoperable and recurrent carcinoma of the rectum and rectosigmoid: Aspects of radiation treatment and prognosis. Ann Clin Gynecol 66:265-268, 1977 35. Tierie AH: Radiotherapy in marginal resectable and nonresectable rectum cancer. Radiol Clin 47:222-227, 1978 36. Urdaneta-Lafee N, Kligeman MM, Knowiton AH: Evaluation of palliative irradiation therapy in rectal carcinoma. Radiology 104:673-677, 1992 37. Doseretz DE, Gunderson LL, Hedberg S, et al: Preoperative irradiation for unresectable rectal and rectosigmoid carcinomas. Cancer 52:814-818, 1983 38. Zorzitto M, Germanson T, Cummings BJ, et al: A method of clinical prognostic staging for patients with rectal cancer. Dis Colon Rectum 25:759-765, 1982 39. Mohiuddin M, Regine WF, Marks G: Prognostic significance of tumor fLxation of rectal carcinoma: Implications for adjunctive radiation therapy. Cancer 78:717-722, 1996 40. Ciatto S, Pacini P: Radiation therapy of recurrence of carcinoma of the rectum and sigmoid after surgery. Acta Radiol Onco121:105-109, 1982 41. Dobrowsky W, Schmid AP: Radiotherapy of presacral recurrence following radical surgery tot rectal carcinoma. Dis Colon Rectum 28:917-919, 1985 42. Frykholm GS, Pahlman L, Glimelins B: Treatment of local recurrences of rectal carcinoma. Radiother Oncol 34:185-194, 1995 43. Lybeert MLM, Martijn H, De Neve W, et ah Radiotherapy for locoregional relapses of rectal carcinoma after initial radical surgery: Definite but limited influence on relapse-free survival and smwival. IntJ Radiat Oncol Biol Phys 24:241-246, 1997
44. Murdock MG, Kramer S: Cobalt 60 therapy in the management of perineal recurrence from carcinoma of rectum and colon. AJR Am J Roentgenol 91:149-153, 1964 45. Villalon AH, Green D: The use of radiotherapy for pelvic recurrence following abdominoperineal resection for carcinoma of the rectum: A 10 year experience. Aust N Z J Surg 51:149-151, 1981 46. Rominger CJ, Gelber DG, Gunderson LL, et al: Radiation therapy alone or in combination with chemotherapy in the treatment of residual or inoperable carcinoma of the rectum and rectosigmoid or pelvic recurrence following colorectal surgery. AmJ Clin Oncol 8:118-t27, 1985 47. WhitewayJ, Nicholls RJ, Morson BC: The role of surgical local excision in the treatment of rectal cancer. B r J Surg 72:694697, 1985 48. Wong CS, Stern H, Cummings BJ: Local excision and postoperative radiotherapy for rectal cancer. Int J Radiat Oncol Biol Phys 25:669-675, 1993 49. Wong CS, Cummings BJ, Keane TJ, et ah Results of external beam irradiation for rectal carcinomas locally recurrent after local excision or electrocoagulation. Radiother Oncol 22:145148, 1991 50. Moertel CG, Childs DS, Reitemeier RJ, et al: Combined 5-fluorouracil and supervoltage radiation therapy of locally unresectable gastrointestinal cancer. Lancet 2:865-867, t969 51. Arnott SJ: The value of combined 5-fluorouracil and x-ray therapy in the palliation of locally recurrent and inoperable rectal carcinoma. Clin Radio126:177-181, 1975 52. DanjotLx CE, Gelber RO, Catton GE, et al: Combination chemo-radiotherapy for residual, recurrent or inoperable carcinoma of the rectum: ECOG study (Est 3276). I n t J Radiat Oncol Biol Phys I h765-771, 1985 53. Dunst J: Radiotherapy versus radiotherapy plus 5-FU in inoperable or recurrent rectal cancer. Strahlentherapie und Onkologie 170:245-146, 1994 54. Millington E: The combined treatment of carcinoma of the rectum with cobalt and chemotherapy. AJR A m J Roentgenol 96:635-639, 1966 55. Vongtama V, Douglas HO, Moore RH, et ah End results of radiation therapy alone and combination with 5-fluorouracil in colorectal cancers. Cancer 36:2020-2025, 1975 56. Wong CS, Cummings BJ, Keane TJ, et ah Combined radiation therapy, mitomycin C, and 5-fluorouracil for locally recurrent rectal carcinoma: Results of a pilot study. IntJ Radiat Oncol Biol Phys 21:1291-1296, 1991
colostomy free. Results of radiation therapy alone in patients with fixed or unresectable tumors are poor. Although more than a third of patients remain colostomy-free, only 5% of patients survive 5 years. In patients with mobile rectal carcinomas that are not amenable to sphincter-preserving surgery, who are unfit medically for radical surgery, or who refuse a colostomy, external-beam radiation therapy offers the reality of sphincter preservation and the possibility of longterm tumor control.
urgery is the standard management of patients with localized rectal carcinoma. Reviews of the surgical management of rectal carcinoma have suggested that the overall 5-year survival rate for patients who have apparently complete resection is about 50%.1,2 Despite modern surgical techniques that have reduced the frequency of colostomies,3 a colostomy cannot always be avoided. There is an expanding literature on the use of external-beam radiation therapy combined with sphincter-preservation surgical resection in an attempt to preserve the anorectal function. For patients with small and superficial tumors of the distal rectum, good results can be achieved by local excision with or without radiation therapy. 4,5 Similarly, endocavitary radiation therapy can be used. 6-8 For patients with larger or more advanced tumors, the combination of adjuvant radiation therapy and low anterior resection with coloanal anastomosis offers the reality of radical sphincterpreserving surgery9 -u The role of these techniques in the management of rectal carcinoma is described elsewhere in this issue in detail. Only 3% to 5% of patients, however, have lesions that are suitable for conservative surgical resection or endocavitary radiation therapy. ~ Many patients are not fit for radical surgery because of age or concomitant medical conditions. Many patients may simply refuse surgery if it results in a permanent colostomy. This article describes the results of external-beam radiation therapy alone in the management of patients with localized rectal carcinoma. The focus is
principally on its role in patients who have potentially resectable rectal carcinoma and who for one reason or another are not candidates for surgical resection. The role of external-beam radiation therapy in sphincter preservation for patients with localized but unresectable tumors and locally recurrent cancer is also reviewed.
S
From the Department o/Radiation OncologT,PrincessMargaret Hospital, University of Toronto, Toronto, Ontario. Address reprint requests to C. Shun Wong;MD, FRCPC, Department of Radiation Oncology, Princess Margaret Hospital, 610 University Ave, Townto, Ontario, MSG 2M9. Copyright 9 1998 by W.B. Saunders Company 1053-4296/98/0801-000258.00/0
Copyright 9 1998 by W.B. Saunders Company
Primary Resectable Rectal Carcinoma Although it had been previously suggested that adenocarcinoma of the rectum was essentially radioresistant, 12 Wang and Schulz 13 reported that in 58 patients with tumor confined to the pelvis and treated with radical radiation therapy, 2 survived 5 years or more after external-beam radiation therapy alone. In a report by James and Schofield, ~429 of 42 patients with fixed unresectable rectal carcinoma underwent laparotomy after pelvic irradiation therapy. In three of these cases, there was no residual tumor in the operative specimen. These studies showed that external-beam radiation therapy alone can produce long-term cancer control or complete responses in selected patients with rectal carcinoma. Most reports have described the use of externalbeam radiation therapy alone in patients with unresectable or locally recurrent disease. Many of these patients underwent attempted resection after radiation therapy. There are limited data on the use of external-beam radiation therapy alone in the management of rectal cancer that is potentially resectable. In a series of 113 patients with rectal cancer managed by radiation therapy, described by Overgaard et al, 15 only 2 were considered medically inoperable; in both cases, however, the tumor was described as large and fixed, suggesting that the tumor was also unresectable. Taylor et a116 described a series of 243 patients with rectal cancer treated with external-beam radiation therapy. Seventy-four patients had radical radia-
Seminars in Radiation Oncvlogp, Vol 8, No 1 (Janua?y), 1998:pp 3-12
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WongandBrierley
tion therapy, 33 for recurrent disease and 30 for unresectable disease. Only ll patients had tumors described as potentially resectable and were given radiation therapy because the patients were not considered fit tbr radical surge~T. A complete response of 38% was observed in these 11 patients. The 2-year survival was 55%, but none survived 5 years. Results of external-beam radiation therapy alone for rectal cancer were reported earlier by Williams and Horwitz, 17 who described 2 of 5 patients with small tumors and 10 of 21 patients with tumors involving the whole rectal wall surviving 2 years after external-beam radiation therapy alone. Rousseau et a118gave 50 to 65 Gy and observed complete response in three of five tumors clinically confined to the bowel wall. For tumors that had extended through the bowel wall, the complete response rate was 11% (3 of 28). After a median dose of 68 Gy over 8.5 weeks, AmaMc et a119described a 3-year survival rate of 36% (5 of 14) in patients with tumors that by clinical examination were considered to have extended through the rectal wall.
Princess Margaret Hospital Experience The most extensive experience on the use of externalbeam radiation therapy alone in the primary management of rectal cancer has been reported by investigators from the Princess Margaret Hospital. In the first of three reports, Rider 2~ described the results of 65 patients treated between 1958 and 1969. In a subsequent article, Cummings et a121 reported on another 133 patients treated between 1970 and 1977, 56 of whom had mobile tumors. In our most recent report, Brierley et a122 described the results of 229 patients treated between 1978 and 1987, 134 of whom were considered to have mobile or potentially resectable
disease. All patients had biopsy-proven adenocarcinoma of the rectum. These patients were selected for primary radiation therapy because the tumor was unresectable in the opinion of the surgeon, the patient was medically unfit for radical surgery, the patient had refused to have a colostomy, or a combination of these factors. At the Princess Margaret Hospital, since 1978, a rectal tumor has been classified as fixed when the tumor cannot be moved separately from the extrarectal tissues, partially fixed when the tumor and the rectal wall do not move freely, and mobile when the tumor is fully mobile in all directions. Among the 229 patients reported in our most recent article, the tumor was mobile in 97, partially fixed in 37, fixed in 77, and not assessable for mobility in 18. In this study, the most frequently used fractionation schedule was 50 Gy in 20 fractions in 4 weeks but varied from 40 Gy in 10 fractions in two sessions each of five treatments in 1 week separated by a 2- to 4-week split to 60 Gy in 30 fractions in 6 weeks. Radiation therapy was delivered with cobalt 60 or 18 to 25 MV photons. The most frequently used technique was a four-field box (83 patients). The fields used were designed to cover the primary tumor, perirectal tissues, and pelvic nodes from approximately the level of the first sacral vertebra to 3 to 5 cm below the lowermost palpable edge of the tumor. The overall actuarial 5-year survival from the start of radiation therapywas 27%. The 5-year smMval was 48% for those with mobile tumors and 27% for those with partially fixed tumors. Patients with fixed tumors had a 5-year survival of only 4% (P < .0001) compared with mobile and partially fixed tumors (Fig 1). These results were similar to the 5-year survival rates of 38% and 2% in our previous cohort of
100 80
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Mobile 40 Partially fixed 20 - Fixed I
I
I
I
1 2 3 4 Time from date of radiation therapy (years)
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Figure 1. Actuarial survival of 229 patients with mobile (97), partially fixed (37), and tixed (77) rectal carcinoma treated with external-beam radiation therapy.
External-Beam Radiation TherapyAlone
5
Figure 2. Barium enema view of a circumferential mobile carcinoma (A) before external-beam radiation therapy and (B) 6 months after radiation therapy. patients with mobile and fixed tumors treated between 1970 and 1977. 91 When a multivariate Cox proportional hazard model was performed, only age less than the median of 75 (P = .001) and absence of tumor fixation (P = .001) were predictors of better survival. Patient gender, tumor grade, tumor description, and tumor location from the anal verge were not significant prognostically for overall survival. Forty-eight (50%) of the mobile, 11 (30%) of the partially fixed; and 7(9%) of the tixed tumors responded completely after radiation therapy (Fig 2).
The rate of tumor regression after radiation therapy was slow. Regression was complete by 4 months in only 60% of the 66 patients in whom a complete response was documented but was complete in more than 90% by 9 months (Fig 3). There was no relationship between the time taken for a rectal cancer to involute completely and the risk of later relapse. The slow regression of rectal carcinoma after external-beam radiation therapy has also been reported by Papillon, 23 who recommended waiting 2 months to allow maximal tumor regression before a
100
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80 60 40
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Figure 3. Time to remission from the start of radiation therapy for 66 patients clinically assessed as having responded completely.
0
2 4 6 Time from date of radiation therapy (months)
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WongandBrierley
decision regarding surgical resection versus conservative treatment, such as intracavitary irradiation. Of 59 mobile and partially fixed tumors that went into complete remission, 24 later relapsed locally. Five of seven fixed tumors that were considered to have regressed completely also later relapsed. The principal site of failure was at the location of the primary tumor. Only 3 patients developed distant metastases without evidence of local disease, although both local and distant failure occurred in 52 patients. Brierley et a124have combined data from all three reports (1958-1987), specifically to assess whether prolongation of treatment time was an adverse prognostic factor for local control after external-beam radiation therapy. For the purpose of that analysis, patients treated since 1978 who had mobile or partially fixed tumors were classified together as having mobile tumors. Thus, all tumors were classified as mobile or fixed or, if they were beyond the reach of the examining finger, as mobility unknown. Factors assessed included patient's age, gender, tumor annularity, tumor mobility, total dose, overall treatment time, presence or absence of treatment interruption, and length of treatment interruption. The duration of local control was calculated from the date of first radiation therapy treatment. In total, there were data on local control in 353 patients. A total of 112 patients (32%) went into complete remission, but 47 later relapsed locally. At 5 years, the actuarial local control rate for mobile tumors was 24% and for fixed tumors was 7% (Fig 4). Only tumor fixation was an adverse prognostic factor fbr local control (P = .02) in a multivariate Cox regression analysis (Table 1). For the 171 patients with mobile tumors, none of the factors was significant in predict-
ing local control after external-beam radiation therapy. Of the 229 patients treated between 1978 and 1987, 50 underwent salvage surgery for persistent (43) or recurrent (7) disease. These included 13 patients with fixed tumors who also had salvage surgery. Although it appears to be contradictory that 37 patients initially not treated by surge~T because of refusal or being medically unfit later had salvage surgery, this is because either their condition improved or, in the face of failure of radiation therapy, the surgeon and the patient were willing to accept the increased risk of radical surgery or the necessity of a colostomy. Forty-six of the 50 patients had complete resection without apparent residual disease after surgery. The 5-year actuarial survival rates after surgery for patients with tumor that had been mobile, partially fixed, and fixed before radiation therapy were 59%, 30%, and 23% respectively. These results show the feasibility of salvage surgery after the failure of radiation therapy (Fig 5). Although not all of these patients would have required a colostomy if treated with surgery, it may be assumed that if external-beam radiation therapy is given to patients with potentially resectable tumors and who refuse surgery, 30% achieve sustained local control and avoid a colostomy. Furthermore, not all patients who have persistent or locally recurrent tumor develop obstruction or obstructive symptoms requiring a colostomy. Of the 229 patients in our third study, 17 had a defunctioning colostomy before radiation therapy. None of these was closed subsequently. Of 212 who did not have a colostomy before radiation therapy, 69 later required a defunctioning colostomy or a colostomy as part of salvage surgery.
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Figure 4. Local relapse-flee Fixed
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Years from date of radiation therapy (years)
rate (LRFR) for patients with mobile (171) and f~ed (159) rectal carcinoma treated by external-beam radiation therapy alone.
External-BeamRadiation TherapyAlone
or 4 acute toxicity. Significant late toxicity occurred in 4 of 229 patients. Two patients developed skin ulcers (one required a graft), and one patient developed ureteric stenosis requiring stenting. The fourth patient developed a persistent perineal ulcer and subsequent sacral osteomyelitis from which he died. No patient treated by three- or four-field technique developed grade 3 or 4 late toxicity. No apparent increase in morbidity was observed in patients who underwent salvage surgery. There are limited prospective data on the late effects of radiation therapy on anorectal function. 25,26 We have not systematically assessed anorectal function after radiation therapy, although patients in whom local control was achieved appeared to have normal sphincter function. Our experience with this fractionation schedule during the period of 1970 through 1977 suggests that 50 Gy in 20 fi'actions is likely to be close to rectal tolerance, particularly if a large volume of the pelvis is treated by a parallel pair technique. 21
Table 1. Prognostic Factors Entered Into an Analysis of Association With Local Control in 353 Patients With Primary Rectal Carcinoma Managed by External-Beam Radiation Therapy Alone Cox
Factors
Univariate Analysis
Fixation Annular Treatment length* Interruptiont Gender Age Dose
Multivariate Analysis
.0001 .0001 .02 .03 NS NS NS
7
.02 NS NS NS NS NS NS
*Defined as prolonged treatment time above the median of 30 days. ~'Definedas the presence of a treatment interruption, planned or unplanned. The 5-year actuarial colostomy-free rates fbr 212 patients who did not have a colostomy before radiation therapy were 63% for mobile tumors, 48% for partially fixed tumors, and 37% for fixed tumors (Fig 6). The external-beam radiation therapy was generally well tolerated. Acute proctitis and perineal discomfort usually responded rapidly to symptomatic management. During the period of 1970 through 1977, when most patients were treated with parallelopposed anterior-posterior fields, 2 of 123 patients died shortly after treatment of radiation enteritis. 21 During the subsequent period of 1978 through 1987, when most patients were treated with multiple fields, five patients (2%) developed R T O G / E C O G grade 3
Combined External-Beam and Intracavitary Radiation Therapy or Implant Superficial and small distal rectal carcinomas that carry a low risk of lymph node metastases can be treated adequately by local excision with or without external-beam radiation therapy. 4,5,27,2a These early lesions can also be managed effectively by intracavitary radiation therapy with local control of 90%. 6-8 The latter technique is particularly attractive for
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20 Figure 5. Actuarial survival from date of surgery for 50 patients who had salvage surgery for persistent or recurrent carcinoma after externalbeam radiation therapy.
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elderly and frail patients who are at high risk for surgery including local excision. 6 For more advanced lesions, a combination of external-beam and intracavitary radiation therapy or interstitial implant has been used in a number of centers. Papillon 23 used this technique in 67 patients with tumors measuring more than 4 cm or showing slight extrarectal extension. Patients were initially given an external-beam dose of 30 Gy in 10 daily fractions over 12 days using a 120-degree arc rotation through a 9 • 12 cm sacral field, giving a dose of 35 to 39 Gy to the tumor. This was followed 2 months later either by intracavitary radiation of 25 Gy or an iridium 192 implant of 20 to 30 Gy. A 5-year smMval of 60% was reported, with 40 patients remaining tumor-free. Patients who remained disease-free were described to have normal anal function. A similar combined approach of an intracavitary boost of two to three applications of 30 Gy each given 6 weeks after external-beam radiation therapy of 45 Gy in 25 fractions was reported by Kodner et a129 For mobile tumors measuring less than 3 cm, 11 of 13 patients achieved local control. For tethered tumors or lesions measuring greater than 3 cm, 14 of 20 patients achieved local control. 99,3~ Gdrard et aP 1 used a combination of initial intracavitary treatment (70 Gy/3 fractions) followed by external-beam radiation therapy in a concomitant boost schedule (39 Gy/13 fractions and 4 Gy/4 fractions boost) in 29 patients. In 21 of 29 patients, an iridium 192 implant (20 Gy/22 h) was performed 6 weeks after externalbeam radiation therapy. Patients were staged by transrectal ultrasound with 19 lesions described as exceeding 3 cm. Survival at 5 years was 68%, and 21 of 29 patients achieved local control. Five of 21
6. Colostomy-ffee
rate in 212 p a t i e n t s w i t h rectal carcinoma who underwent
external-beam radiation therapy and had not undergone colostomybefore treatment.
patients who received iridium 192 boost developed rectal necroses. These results suggest that a combination of external-beam radiation therapy and intracavitary boost or interstitial implant can produce local control of about 70% for selected patients with distal rectal cancer. The better local control rates reported in these studies compared with those after externalbeam radiation therapy alone 21,~2 may simply reflect the smaller tumor bulk in patients, which allows the use of intracavitary boost or implant after externalbeam radiation therapy.
Primary Unresectable Rectal Carcinoma Although tumor fixation is not synonymous with unresectability, it is generally assumed that most, if not all, fixed tumors are technically unresectable. 32 Fixed rectal tumors are generally managed by radiation therapy alone or in combination of surgical resection after radiation therapy. Results of externalbeam radiation therapy for fixed rectal tumors are disappointing. Our results of a local control rate of only 7% and median survival of 18 months in patients with fixed rectal carcinomas are similar to those reported in other series33,15,33-36 These results show that external-beam radiation therapy alone is unlikely to be associated with long-term control for tumors clinically fixed to the extrarectM tissues. Nonetheless, the colostomy-ffee rate of 70% at 18 months (Fig 6) in our own series suggests that a significant number of these patients have preservation of anorectal function despite the presence of progressive local disease. There is general agreement in the literature that a better survival is achieved in patients who are able
External-Beam Radiation TherapyAlone
to undergo complete resection subsequent to radiation therapy. In our series from the Princess Margaret Hospital, 2~ 13 of 77 patients classified as having fixed tumor had salvage surgery after external-beam radiation therapy of 50 Gy in 20 fractions. The actuarial 5-year survival rate was 23% tbr these patients. Resectability rates of fixed rectal cancer after radiation therapy are variable and range tk~om 30% to 65% in the literature and probably reflect the differences in selection criteria used to define rcsectability. 32,37-39Because external-beam radiation therapy alone rarely results in long-term control of clinically fixed rectal carcinoma, it should be part of a planned preoperative regimen or be palliative in intent. The role of preoperative radiation therapy in sphincter preservation of patients with rectal carcinoma is discussed elsewhere in this issue. Locally Recurrent Rectal Carcinoma External-beam radiation therapy is frequently used in the treatment of patients in whom local recurrence develops after previous surgical resection and in whom no prior adjuvant radiation therapy has been used. It is generally recognized that symptoms such as pain and bleeding respond well to radiation therapy, whereas palliation of other pelvic symptoms such as neurological deficit, urinary symptoms, and rectal discharge is achieved less fi-equently. Partial or complete tumor regression is rarely reported after external-beam radiation therapy alone. 15,4~ Few patients with locally recurrent rectal carcinoma survive 5 years after external-beam radiation therapy alone. In our series of 519 patients with locally recurrent rectal carcinoma treated principally by external-beam radiation therapy from the Princess Margaret Hospital, the 5-year survival was 5% with a median survival of 14 months. The median time to local or pelvic disease progression was only 5 months. Similarly disappointing results have been reported in other series. 15,3944These results suggest that palliation of pelvic symptoms after radiation therapy is maintained only for a brief period equivalent to a third of the remaining life span of the patients. Similar to patients with primary unresectable tumors, improved survival and local control in patients with local recurrence have generally been reported in the subset of patients who are able to undergo complete surgical resection? 2,45 Undoubtedly, these patients represent a highly selected group of patients with better prognosis. There is, however, general agreement in the literature that surgery or
9
combined surgery and radiation therapy has a major impact on local control and smvival and should be offered to these patients with potentially resectable recurrence. There are limited data on the role of externalbeam radiation therapy alone for patients who develop local recurrence after previous sphincterpreserving surgery. About 10% of patients develop local recurrence after local excision, 27,28,47and abdominal perineal resection is generally considered the standard salvage management, with about 50% who suffer local failure remaining disease-free after salvage surgery. 47,48 We have reported a series of 37 patients who received external-beam radiation therapy alone for local recurrence after previous local excision o r electrocoagulation. 49 In 4 patients, the local recurrence was fixed in the pelvis, whereas the recurrence was considered mobile and potentially resectable in the remaining 33 patients. These patients either had refused to have a salvage abdominal perineal resection or were considered to be poor candidates for radical surgery because of intercurrent medical illness or advancing age and were managed by external-beam radiation therapy alone. The 5-year survival and local control rates were 20% and 15% after radiation therapy for local recurrence. For patients who received a dose of 50 Gy or more, the survival and local control rates were 35% and 40% at 5 years. These results were similar to those we reported in patients with mobile primary rectal carcinoma managed by external-beam radiation therapy alone 21,22 and suggest that selected patients with locally recurrent rectal cancer with small tumor bulk are potentially curable with radiation therapy alone. Attempts to improve the results of external-beam radiation therapy with chemotherapy have not produced any definite benefit over radiation therapy alone. The encouraging early results by Moertel et al 5~ have not been reproduced in a number of subsequent studies. The combination of chemotherapy using drugs such as 5-fluorouracil with radiation therapy have generally resulted in an increase in toxicity from the cytotoxic drugs or radiation therapy.46, 51-56
Conclusions We recommend radical external-beam radiation therapy in patients with rectal cancer if the patient is medically unfit for surgery or refuses surgery that would result in a colostomy and if the tumor is not
Figure 7. Simulation films of (A) posteroanterior and (g) lateral fields for a course of external-beam radiation therapy for a circumferential, partially fixed rectal carcinoma.
External-Beam Radiation TherapyAlone
suitable for local excision or intracavitary radiation therapy. O u r c u r r e n t radiation t h e r a p y prescription is 50 Gy t u m o r dose in 20 fractions over 4 weeks by a three- or four-field technique. T h e a n a t o m i c e x t e n t of the t u m o r is assessed by digital e x a m i n a t i o n , sigmoidoscopy, c o m p u t e d t o m o g r a p h y scan, and rectal barium. T h e fields used are designed to cover the p r i m a r y t u m o r and p e r i r e c t a l tissues and nodes w i t h a 3- to 5-cm margin. N o a t t e m p t is m a d e to e n c o m pass all the l y m p h n o d e - b e a r i n g tissues t h a t m a y be r e m o v e d at surgery because the resulting v o l u m e would result in u n a c c e p t a b l e toxicity. T h e radiation t h e r a p y fields (Fig 7) usually e x t e n d from: 1. Superior field border, 3 to 5 cm above the tumor. 2. Inferior field border, 3 cm below the inferior m a r g i n of the t u m o r , sparing the p e r i n e u m if possible. 3. L a t e r a l field borders, bony margins of the t r u e pelvis, or 3 c m lateral to the tumor. 4. Posterior field border, 2 cm posterior to the a n t e r i o r aspect of the sacral hollow. 5. A n t e r i o r field border, 3 c m anterior to the t u m o r . E x t e r n a l - b e a m radiation therapy can eradicate a p p r o x i m a t e l y 25% of rectal cancers that are mobile or partially fixed, but in patients w i t h fixed tumors, the control rate with e x t e r n a l - b e a m radiation t h e r a p y alone is poor. In patients with mobile or partially fixed t u m o r s who refuse a colostomy or for w h o m sphincter-preserving surgery is not possible, externalb e a m radiation t h e r a p y m a y be a valid option. For patients with fixed rectal cancers, high-dose externalb e a m radiation t h e r a p y should be part of a p l a n n e d preoperative r e g i m e n or be palliative in intent.
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