The organs at risk, including the small bowel, bladder, prostate, uterus, and bilateral femurs were contoured accordingly. When the clinical target volume overlapped the small bowel, the clinical target volume was manually trimmed to reduce the exposure of the small bowel. The planning target volume was not modified when it overlapped the organs at risk.

Treatment parameters

For four-field box radiotherapy, the prescribed dose was delivered to the field isocenter. The dose weightings (ratios) for the anterior-posterior opposed beams and bilaterally opposed beams were either 1:1 or 6:4. For volumetric modulated arc therapy, ten patients had two partial arcs and two patients had three partial arcs. We used the volumetric modulated arc therapy technique with partial arcs by excluding gantry angles between 120° and 240° to treat patients in the prone position on a belly board, mainly to reduce the radiation dose to the urinary bladder and small bowels. This planning method helps achieve conformity of targets and simultaneously spares the critical organs.

Chemotherapy

All patients received bevacizumab (5 mg/kg given every 2 to 3 weeks, for a median of five cycles) and oxaliplatin, 5-fluorouracil, and leucovorin (FOLFOX: 5-fluorouracil 1600 to 2800 mg/m2, oxaliplatin 40 to 85 mg/m2, and leucovorin 300 mg/m2; every 2 to 3 weeks for a median of five cycles), except that one patient was only given 5-fluorouracil, owing to old age.

Surgery

Total mesorectal excision was performed 6 to 8 weeks after the completion of concurrent chemoradiotherapy. Rectum and pelvic lymphatics were removed. The surgical technique was either abdominoperineal resection or low anterior resection. Total mesorectal excisions were conducted laparoscopically in 13 patients.

Measurement of setup errors

Image-guided tools were used to measure the absolute values of displacements in the superior-inferior, left-right, and anterior-posterior directions. For patients receiving volumetric modulated arc therapy, we used cone-beam computed tomography with an Elekta Synergy® X-ray volume imaging system (Elekta Oncology System Ltd., Crawley, West Sussex, UK) in all patients to evaluate setup errors. Approximately 650 projections were collected during a 360° rotation of the gantry in a clockwise direction. All cone-beam computed tomograms were compared with simulation computed tomograms using the pelvic bony structure as a reference. Electronic portal images were used in those receiving three-dimensional conformal radiotherapy. We compared the electronic portal images with digitally reconstructed radiographs from computed tomograms, by using the pelvic bony landmarks including the sacral edge and the pelvic ring, to measure and correct setup errors. With the average displacements from each patient, a group average was calculated for each of these three directions.

Toxicity and outcome assessments

Toxicity was evaluated weekly during concurrent chemoradiotherapy and was graded using The pre-concurrent chemoradiotherapy biopsy sample and post-concurrent chemoradiotherapy surgical tissues were stained immunohistochemically using monoclonal antibodies against CD34 (Dako Denmark A/S, Glostrup, Denmark), Akt (Cell Signaling Technology Inc., Danvers, MA, USA), epidermal growth factor receptor (Dako Denmark A/S, Glostrup, Denmark), and vascular endothelial growth factor receptor 2 (Cell Signaling Technology Inc., Danvers, MA, USA). The slices were reviewed by an experienced pathologist at our institution.

Statistical analysis

The statistical analysis was conducted using IBM SPSS statistics v.20.0 (IBM Corp., Armonk, NY, USA). Fisher’s exact test was used for the analysis of contingency tables. Student’s P <0.05.

Results

Patient characteristics

Twelve patients with stage IIA to IVA rectal adenocarcinoma treated with neoadjuvant concurrent chemoradiotherapy and bevacizumab from March 2010 to March 2012 were prospectively enrolled in this study and were treated in the prone position with volumetric modulated arc therapy (prone volumetric modulated arc therapy). We also retrospectively collected details of all patients treated with neoadjuvant concurrent chemoradiotherapy and bevacizumab before the new technique was used and identified six patients, who all received four-field box radiotherapy in the supine position (supine box). The median follow-up time was 22.4 and 34.2 months in the prone volumetric modulated arc therapy and supine box cohorts, respectively. Patient characteristics (Table 1) included clinical T3 or T4 disease (n =14), and tumor location within 5 cm above the anal verge (P =0.12, 0.25, and 0.22, respectively).

Toxicities

The most common acute toxicities during concurrent chemoradiotherapy (Table 2) were grade 1 or 2 anal pain and anemia. Grade 3 toxicity was observed in three patients (two patients with neutropenia and one with diarrhea). There was no febrile neutropenia that required hospitalization. No difference in treatment-related toxicity (except bowel toxicity) was evident between the supine-position box and prone-position volumetric modulated arc therapy groups. Five of the six (83%) patients in the historical cohort and two of the twelve (17%) patients in the prone volumetric modulated arc therapy group experienced grade ≥2 diarrhea (P =0.005, 0.002, and 0.0006, respectively). The dose distribution (one representative patient from each group) and the average dose-small bowel volume histogram for each group are shown in Figure 1.

Surgical outcome

All 12 patients receiving prone volumetric modulated arc therapy treatment completed neoadjuvant concurrent chemoradiotherapy with bevacizumab and received total mesorectal excision. Two patients in the supine box cohort refused surgery. Pathological responses, including a pathological complete response rate of 33.3%, are shown in Table 3. Postoperative complications included one perianal abscess formation and one postoperative wound infection, and both resolved after treatment. There was no between-cohort difference in pathological response (1/4 in the supine box group versus 4/12 in the prone volumetric modulated arc therapy group, Owing to the few pathological samples for immunohistochemical study, we combined the two cohorts for analysis. Postoperative pathology specimens were available in thirteen patients, while nine of them also had pre-concurrent chemoradiotherapy specimens. Expression of CD34 was upregulated in the tumor area after concurrent chemoradiotherapy in six of seven patients with less than pathological complete response and zero of two patients with pathological complete response (In this prospective study combined with historical comparison, we proposed the technical advantage of using volumetric modulated arc therapy in patients prone-positioned on a belly board, and reported the early pathological and clinical results for combined treatment with bevacizumab and neoadjuvant concurrent chemoradiotherapy in locally advanced rectal cancer. We demonstrated that the prone volumetric modulated arc therapy technique resulted in less toxicity and possibly better pathological response and clinical outcome. To our knowledge, this is the first report on survival outcome and local or distant disease control by neoadjuvant volumetric modulated arc therapy in rectal cancer. This technique allows the concomitant use of oxaliplatin and bevacizumab, which were previously shown to improve pathological response in randomized trials. Although acceptable, the magnitude of setup errors required the use of image-guided procedures for treatment.

A previous study using preoperative bevacizumab with FOLFOX and supine box radiotherapy found postoperative complications including delayed healing, leak or abscess, ischemic colonic reservoir, and fistula in 36% of patients [10]. Our patients had a much lower complication rate (only 2 of 12 patients) and a more reasonable postoperative hospital stay (7 to 24 days). An Austrian group terminated the patient accrual of a phase II trial combining bevacizumab and capecitabine with three-field radiotherapy because two of eight patients (25%) experienced grade 3 diarrhea and intestinal bleeding [11]. In our study, bowel toxicity was much reduced; the mean small bowel volume receiving more than 45 Gy was as small as 24.8 ml. Moreover, the toxicity profile of our prone volumetric modulated arc therapy approach was much lower than that in previous studies and that of our supine box approach. This improvement is beneficial for patients with locally advanced rectal cancer, as well as selected stage IV patients [20]. Of note, neoadjuvant chemotherapy without routine use of radiotherapy was found in a pilot study, and was well tolerable with no radiation-related side effects [21].

Compared with box techniques, step-and-shoot intensity-modulated radiation therapy provides superior planning target volume coverage, dose homogeneity, and conformity; it decreases the volume of small bowel exposed to radiation, but requires a longer delivery time [12]. Staying in the prone position on a belly board for such a long treatment period might increase the magnitude of setup errors. Volumetric modulated arc therapy is capable of dose delivery in a shorter timeframe. In our study, the average delivery time was as short as 285 s, suggesting a lower intrafraction motion error.

It was shown that a collapsed cone convolution algorithm might underestimate the dose in water medium after the photon beam traversed an air gap [19]. Special attention was suggested for possible setup errors and internal organ motion. We did not override the density of rectal gas (if present) during the planning phase. According to our imaging guidance protocol in this study, we used cone-beam computed tomography frequently to monitor for setup error and internal organ motion. We did not observe much change in rectal lumen during the radiotherapy course.

Volumetric modulated arc therapy provided superior target coverage compared with three-dimensional conformal radiotherapy and even step-and-shoot intensity-modulated radiation therapy in two studies on rectal cancer and anal cancer [14, 15]. Both studies used the supine position. Our volumetric modulated arc therapy approach used the prone position, which further reduced the volume of small bowel exposed to radiation. One dosimetric study from Italy showed that the same volumetric modulated arc therapy approach (compared with three- or four-field radiotherapy) reduces small bowel exposure to radiation, and (compared with intensity-modulated radiation therapy) shortens treatment time [22]. However, unlike our study, this study did not investigate clinical outcome (toxicities, magnitude of setup errors, pathological responses, or survivals).

Compared with the traditional four-field box technique, intensity-modulated radiation therapy or volumetric modulated arc therapy irradiates a smaller pelvic area, mainly the lymphatic region and the peritumoral area. The issue of radiotherapy precision by intensity-modulated radiation therapy or volumetric modulated arc therapy has not been well addressed in rectal cancer. Pelvic lymphatics are technically challenging sites to irradiate using intensity-modulated radiation therapy or volumetric modulated arc therapy. Our use of image guidance and the corresponding data on setup errors support our claim of accurate volumetric modulated arc therapy delivery. Our results showed only three patients with pathologically involved lymph nodes after concurrent chemoradiotherapy, and seven of ten patients with initial clinical node-positive disease had an N-downstaging response after volumetric modulated arc therapy.

Our study revealed increased expression of CD34 (possibly associated with increased microvessel density) after concurrent chemoradiotherapy, and increased expression of Akt before and after concurrent chemoradiotherapy. The increased expression of Akt after radiotherapy is compatible with previous reports [2325]. The data on CD34 expression after treatment with bevacizumab have been inconsistent [26, 27]. Our study revealed a trend toward lower pathological complete response rate in patients with CD34 upregulation after concurrent chemoradiotherapy. The increase in CD34 expression after concurrent chemoradiotherapy might represent a response of the tumor to treatment. Given the small number of patients in our study, the true correlation of these markers with the therapeutic response will require further investigation.

The limitations of this study include small patient number, limited follow-up interval, and retrospective comparison with a previously used supine box technique. Pre-concurrent chemoradiotherapy and post-concurrent chemoradiotherapy tumor tissues were only available from nine patients for evaluation of the therapeutic response using potential biomarkers. All these limitations might bias the comparison and endpoints. Although it had a small number of cases, our study implied that prone-position volumetric modulated arc therapy has less bowel toxicity and effectively controls primary tumor and nodal disease. Consequently, a prospective trial of this method (the second cohort) has been initiated in our institution. Serial magnetic resonance imaging, which was associated with histopathological responses [28], was also been performed in the trial. Further patient enrollment and follow-up are needed to confirm our early clinical success.

Conclusions

Using volumetric modulated arc therapy in the prone position combined with bevacizumab or other novel targeted agents for locally advanced rectal cancer treatment is feasible and safe, achieves a satisfactory pathological response and preliminary disease control, and helps reduce bowel toxicity.

Abbreviations

FOLFOX:

(leucovorin, fluorouracil, and oxaliplatin)

N:

node

T:

tumor.

Declarations

This study was supported by the National Science Council, Execute Yuan, Taiwan, ROC (grant numbers: NSC 103-2314-B-002-133-MY3 and NSC 102-2628-B-002-049-MY3), and by Liver Disease Prevention & Treatment Research Foundation, Taiwan.

Authors' original submitted files for images

Below are the links to the authors’ original submitted files for images.
12957_2014_1808_MOESM1_ESM.tifAuthors’ original file for figure 2

All authors declare that they have no competing interests.

CCW conceived the study, participated in its design, and drafted the manuscript. JTL performed all surgery and helped to collect data. CLT participated in study design, statistical analysis, and manuscript editing. YHC participated in study design and data collection. YLL helped to deliver chemotherapy and collect data. CTS analyzed the immunohistochemical specimens. JCC participated in study design, coordinated the study, and revised the manuscript. All authors read and approved the final manuscript.

Authors’ Affiliations

(1)
Department of Oncology, National Taiwan University Hospital Yun-Lin Branch, Yun-Lin, Taiwan
(2)
Graduate Institute of Epidemiology and Preventive Medicine, College of Public Health, National Taiwan University, Taipei, Taiwan
(3)
Department of Surgery, National Taiwan University Hospital, Taipei, Taiwan
(4)
Department of Oncology, National Taiwan University Hospital, Taipei, Taiwan
(5)
Department of Pathology, National Taiwan University Hospital, Taipei, Taiwan
(6)
Graduate Institute of Oncology, National Taiwan University College of Medicine, Taipei, Taiwan
(7)
Division of Radiation Oncology, Department of Oncology, National Taiwan University Hospital, No.7, Chung Shan S. Rd., Taipei, 10002, Taiwan

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