Chemoradiation or Brachytherapy for Rectal Cancer

Locally advanced rectal carcinoma continues to be a major oncologic problem in the United States with approximately 40,000 new cases diagnosed in 2011. For stage II/III rectal carcinoma, adjuvant chemoradiation and total mesorectal excision (TME) represent the major treatment advances that have increased cure rates over the past 30 years.

In the setting of TME, a landmark phase III German trial of stage II/III rectal cancer patients established neoadjuvant 5FU-based chemoradiation (NCRT) as standard of care over the same regimen given post-operatively. The preoperative arm showed superior local control (6% vs. 13% p=0.006), a complete pathologic response of 8%, a higher rate of sphincter preservation and less grade 3 toxicity compared to post-operative treatment. However, disease-free and overall survival (76% versus 74%, respectively) were no different because of the high rate of distant metastasis occurring in over 1/3 of patients (5yr DM 36 vs 38%,p=0.84). Importantly, those attaining a pathologic complete response had a decreased rate of distant metastasis and improved disease-free survival. Drawbacks to the regimen include acute grade 3 or 4 toxicity in 27% of patients, low compliance rates with postoperative chemotherapy (27 - 50%), and an overall decline in anorectal function shown by long-term studies.

Given the excellent locoregional control reported in TME surgical series, several trials have investigated whether certain patients may be spared preoperative radiotherapy. Two large randomized trials by Dutch and British investigators showed that a short preoperative course of hypofractionated EBRT (25 Gy in 5 fractions) followed by TME surgery decreased locoregional recurrence by 2/3 as compared to patients treated with TME surgery alone. In the Dutch trial, patients with mid and distal rectal cancers were most likely to benefit from radiotherapy. In these patients, preoperative radiation was shown to decrease locoregional recurrence by 5-fold (10% to 2%); however, the hypofractionated preoperative EBRT regimen was associated with a significant increase in acute and chronic morbidity. Indeed, the Dutch study revealed that irradiated patients, when compared to surgery alone, had more perineal wound healing problems after abdominoperineal resection (29% vs. 19%), worsening deterioration of anal sphincter dysfunction, and more severe long-term effects related to sexual functioning both in males (p=0.004) and females (p<0.002). Additionally, colleagues have reported a consistent negative impact on bowel function in those patients undergoing sphincter preservation. In reviewing the long-term data of the Swedish short course preoperative EBRT rectal cancer trial, Birgisson also reported a higher incidence of secondary tumors (9.5%) in patients treated with preoperative radiation when compared to patients having surgery alone (4.3%).

Modern approaches to address the risk of distant metastasis and poor compliance with adjuvant systemic chemotherapy (following NCRT) have incorporated newer effective chemotherapy agents earlier in the treatment protocol. For example, oxaliplatin has been one of the most widely studied agents as a result of its proven efficacy when combined with 5-fluorouracil and leucovorin (FOLFOX) both in the metastatic and adjuvant settings for colon cancer. Initial phase II studies with the addition of oxaliplatin to standard 5-FU based NCRT appeared to show improved pathologic complete response rates compared to standard NCRT. However, two phase III trials clearly show that the addition of oxaliplatin during 5FU-based NCRT does not significantly improve pathologic complete response, locoregional control, distant metastasis or survival but does increase acute grade 3-4 toxicity by two to three-fold.

One approach to limit toxicity from external beam radiotherapy is the use of intensity modulated radiation therapy (IMRT). IMRT can limit radiation dose to normal rectum (above and below the tumor) and surrounding organs at risk (OARs) such as bladder and sexual organs. IMRT utilizes multiple beams of radiation to treat the rectal tumor plus a margin and limits dose to OARs. While IMRT decreases radiation dose to normal structures, it requires an additional 2-3 cm margin for microscopic extension (clinical treatment volume=CTV), set-up error, and rectal motion (planning treatment volume=PTV). Furthermore, IMRT still requires 5-6 weeks of radiation with concurrent chemotherapy, is substantially more expensive than conformal radiation, and is especially prohibitive in countries where access to technology necessary for IMRT is limited. Based on the preliminary results of RTOG 0822 and others, it still remains to be determined whether IMRT confers a statistically significant improvement in pCR, toxicity rates and QOL relative to standard NCRT.

A novel approach to limit radiation toxicity is the use of high dose rate endorectal brachytherapy (Endo-HDR). Endo-HDR involves the placement of a silicon multicatheter applicator within the rectum to deliver large doses to the rectal tumor and mesorectum with rapid dose fall off to the surrounding organs. An Iridium 192 high dose rate brachytherapy source attached to a wire is inserted into each catheter to deliver a high dose of radiation therapy the tumor. High dose rate brachytherapy has been well established in various malignancies (prostate, uterine, sarcoma, head and neck) to escalate radiation dose to the tumor over a short period of time while sparing normal tissue. Compared with NCRT and IMRT, Endo-HDR delivers treatment internally to the tumor without having to pass through surrounding normal tissue and organs. It requires smaller margins (CTV/PTV=~1 cm) on the tumor since the applicator is positioned under fiducial guidance over the tumor without need for a margin for organ motion allowing greater sparing of OARs. Furthermore, the area of the rectum exposed to high dose radiotherapy is surgically removed at the time of resection which further minimizes chronic toxicity. Important structures that may be spared include bone marrow, small bowel, bladder, the autonomic nerves, sexual organs, anal sphincter and skin. Considering that 1/3 of patients will develop metastases, limiting bone marrow toxicity may contribute to better compliance with systemic treatment and allow for a better treatment strategy to target systemic recurrence. Another distinct advantage of Endo-HDR is the shortened treatment time (1 versus 6 weeks). Endo-HDR therefore provides a major logistic advantage for patients who may benefit from neoadjuvant therapy but who are geographically distant from radiation centers, elderly, or medically infirmed.