Cumulative Rectal Dose Research Articles

Feasibility of helical tomotherapy for radical dose retreatment in pelvic area: a report of 4 cases.

To retrospectively determine acute toxicity and local control in patients with recurrence after definitive radiotherapy for prostate, bladder and rectal carcinoma. Between September 2009 and March 2010, 4 patients with a prior history of pelvic radiotherapy were treated with helical tomotherapy. The prior course of radiotherapy was given for prostate cancer in 2 patients, bladder carcinoma in 1 patient and rectal carcinoma in 1 patient. The median prescribed dose of the prior course of radiotherapy was 6320 cGy (range, 5000-7600), and the median elapsed time between the first and second course was 17 months (range, 4-73). The total prescribed dose for tomotherapy retreatment was 60 Gy in 3 patients and 50 Gy in 1 patient. Hormone therapy was administered to 2 patients before and during radiation. No patient underwent surgical resection. The cumulative mean dose to the rectum ranged from 3813 to 6058 cGy; cumulative rectal maximum dose to 1 cc ranged from 6475 to 8780 cGy. Regarding the bladder, the cumulative mean dose was between 4384 and 7612 cGy; cumulative maximum dose to 1 cc ranged from 7560 to 9790 cGy. All patients completed the re-irradiation course. Acute genitourinary toxicity (RTOG scale) was grade 0 in 3 patients and grade 1 in 1 patient; acute gastrointestinal toxicity was grade 0 in 3 patients and grade 1 in 1 patient. With a median follow-up of 9 months (range, 7-12), late toxicity was G0 in all patients. Three patients showed partial response with computed tomography or magnetic resonance imaging, and 1 had a PSA decrease. Re-irradiation with helical tomotherapy was well tolerated, with low rates of acute and late toxicity. It can be therefore considered a useful tool to improve local control in patients previously treated with radiotherapy. However, a larger number of patients and a longer follow-up are required to assess retreatment safety.

Simultaneous Integrated Parametrial/Sidewall Boosts for Cervical Cancer: Late Toxicity and Outcomes.

The purpose of this study was to evaluate the safety of intensity-modulated radiotherapy (IMRT) with simultaneous integrated boost (SIB) to the parametrium/paracervical tissue among women with locally advanced cervical cancer. In this IRB approved retrospective study, women with intact cervical cancer treated in a single institution with definitive radiation therapy followed by brachytherapy (BT) boost from 2011 through 2016 were identified. Women treated with SIB technique to either one or both parametria were included. Acute and late toxicities (defined by the CTCAE v 4.0), recurrences (local, sidewall, and distant), and overall survival were analyzed via the Kaplan Meier method. Forty-three women with bulky stage IB1-IVB cervical cancer were treated with curative intent radiotherapy from May 2011 to June 2016 (IB1 n=2, IB2 n=7, IIB n=22, IIIA n=2, IIIB n=9, IVB n=1). All women received external beam radiotherapy (EBRT) to the whole pelvis (45-51.4 Gy/ 24-25 fractions) as well as a unilateral or bilateral parametrial boosts (53.6-60 Gy/ 24-25 fractions) given with SIB technique. Nodal disease received additional dose in 35 women (55-70 Gy/ 24-36 fractions). All women except for one received concurrent cisplatin. At the conclusion of EBRT, brachytherapy was delivered to a total goal EQD2 dose of 75-87Gy. Median follow-up time was 25.2 months. Rates of acute grade ≥2 gastrointestinal (GI), genitourinary (GU), and hematologic (heme) toxicities were 39.5%, 7.0%, and 55.8% respectively; acute grade ≥3 toxicities were 7.0%, 2.3%, and 16.3% respectively. There were no acute grade 4 toxicities. Two-year rates of late grade ≥2 GI and GU toxicities were 33.5% and 10.4% respectively; two-year late grade ≥ 3 toxicities were 12.0% and 6.2% respectively. There were two grade 4 GI toxicities, both rectovaginal fistulas. Two-year overall survival and local control rates were 82.1% and 89.4% respectively. Univariate analysis showed a significant association between late grade ≥ 3 GI toxicity and BT rectal D2cc dose (p=0.041, HR=1.210, 95% CI 1.008-1.453). Patients with cumulative rectal D2cc EQD2 dose ≥75Gy had a significantly higher rate of late grade ≥ 3 GI and GU sequelae compared to those <75Gy (66.7% vs. 2.5% with p=0.001 and 66.7% vs. 0% with p=0.004, respectively). IMRT-SIB is a feasible technique allowing for dose escalation to the parametria and sidewall, with overall toxicity rates similar to conventional technique. Late GI toxicity appears to be highly dependent upon cumulative rectal dose; when the rectal D2cc was below 75Gy EQD2, toxicity rates were low. If SIB technique is considered in the low pelvis, it may be prudent to consider strict adherence to rectal dose constraints at brachytherapy.

OC-0360: Dose warping uncertainties for the cumulative rectal wall dose from brachytherapy in cervical cancer

OC-0360: Dose warping uncertainties for the cumulative rectal wall dose from brachytherapy in cervical cancer

Total Rectal Dose Estimated From Radical External Beam and Intracavitary Radiation Therapy for Uterine Cervical Cancer Using Deformable Image Registration Method

Patients with uterine cervical cancer are generally treated with both intracavitary brachytherapy (ICBT) and external beam radiotherapy (EBRT) using a midline block in Japan. However the actual total dose delivered to the rectum is hard to calculate, because the location of the high dose region may not be identical for each fraction. To calculate the cumulative dose more accurately, we have adapted the deformable image registration (DIR) method and analyzed the difference between the cumulative rectal dose by adding rectal D2cc (simple rectal D2cc) and the cumulative rectal D2cc estimated on the basis of DIR (DIR-based rectal D2cc).

The association of rectal equivalent dose in 2 Gy fractions (EQD2) to late rectal toxicity in locally advanced cervical cancer patients who were evaluated by rectosigmoidoscopy in Faculty of Medicine, Chiang Mai University.

PurposeTo evaluate association between equivalent dose in 2 Gy (EQD2) to rectal point dose and gastrointestinal toxicity from whole pelvic radiotherapy (WPRT) and intracavitary brachytherapy (ICBT) in cervical cancer patients who were evaluated by rectosigmoidoscopy in Faculty of Medicine, Chiang Mai University.Materials and MethodsRetrospective study was designed for the patients with locally advanced cervical cancer, treated by radical radiotherapy from 2004 to 2009 and were evaluated by rectosigmoidoscopy. The cumulative doses of WPRT and ICBT to the maximally rectal point were calculated to the EQD2 and evaluated the association of toxicities.ResultsThirty-nine patients were evaluated for late rectal toxicity. The mean cumulative dose in term of EQD2 to rectum was 64.2 Gy. Grade 1 toxicities were the most common findings. According to endoscopic exam, the most common toxicities were congested mucosa (36 patients) and telangiectasia (32 patients). In evaluation between rectal dose in EQD2 and toxicities, no association of cumulative rectal dose to rectal toxicity, except the association of cumulative rectal dose in EQD2 >65 Gy to late effects of normal tissue (LENT-SOMA) scale ≥ grade 2 (p = 0.022; odds ratio, 5.312; 95% confidence interval, 1.269-22.244).ConclusionThe cumulative rectal dose in EQD2 >65 Gy have association with ≥ grade 2 LENT-SOMA scale.

Tumor and normal tissue dosimetry changes during MR-guided pulsed-dose-rate (PDR) brachytherapy for cervical cancer

Background and purposeTo analyze systematic changes in tumor and normal tissue anatomy and dosimetry using serial MR imaging during pulsed dose rate brachytherapy (PDR BT) for cervical cancer. Material and methodsForty-three patients with cervical cancer underwent MR-guided PDR BT using an intrauterine applicator alone after external beam radiotherapy. MR imaging was repeated on days 2 and 3 of treatment and the day 1 plan was applied to the re-contoured volumes. ResultsThe mean uterine volume and mean HR CTV increased during treatment. This resulted in a decrease in the mean HR CTV D90 relative to the day 1 planned dose. There was no change in the mean bladder volume during treatment but the mean rectal volume increased. This correlated with an increase in the mean rectal dose. There were four local recurrences. There was no apparent relationship between either the planned or the delivered HR CTV D90 and local recurrence. There was only one case of late bladder toxicity but nine patients developed late rectal toxicity. The cumulative rectal dose during treatment was a better predictor of late rectal toxicity than the planned dose. ConclusionsSignificant changes in tumor and normal tissue anatomy and dosimetry can occur during PDR BT and should be tracked and corrected using serial imaging and plan adaptation, especially when the day 1 tumor or normal tissue doses are close to the planning constraints.

Feasibility of helical tomotherapy for radical dose retreatment in pelvic area: A report of 4 cases

To retrospectively determine acute toxicity and local control in patients with recurrence after definitive radiotherapy for prostate, bladder and rectal carcinoma. Between September 2009 and March 2010, 4 patients with a prior history of pelvic radiotherapy were treated with helical tomotherapy. The prior course of radiotherapy was given for prostate cancer in 2 patients, bladder carcinoma in 1 patient and rectal carcinoma in 1 patient. The median prescribed dose of the prior course of radiotherapy was 6320 cGy (range, 5000-7600), and the median elapsed time between the first and second course was 17 months (range, 4-73). The total prescribed dose for tomotherapy retreatment was 60 Gy in 3 patients and 50 Gy in 1 patient. Hormone therapy was administered to 2 patients before and during radiation. No patient underwent surgical resection. The cumulative mean dose to the rectum ranged from 3813 to 6058 cGy; cumulative rectal maximum dose to 1 cc ranged from 6475 to 8780 cGy. Regarding the bladder, the cumulative mean dose was between 4384 and 7612 cGy; cumulative maximum dose to 1 cc ranged from 7560 to 9790 cGy. All patients completed the re-irradiation course. Acute genitourinary toxicity (RTOG scale) was grade 0 in 3 patients and grade 1 in 1 patient; acute gastrointestinal toxicity was grade 0 in 3 patients and grade 1 in 1 patient. With a median follow-up of 9 months (range, 7-12), late toxicity was G0 in all patients. Three patients showed partial response with computed tomography or magnetic resonance imaging, and 1 had a PSA decrease. Re-irradiation with helical tomotherapy was well tolerated, with low rates of acute and late toxicity. It can be therefore considered a useful tool to improve local control in patients previously treated with radiotherapy. However, a larger number of patients and a longer follow-up are required to assess retreatment safety.

Variability of Marker-Based Rectal Dose Evaluation in HDR Cervical Brachytherapy

In film-based intracavitary brachytherapy for cervical cancer, position of the rectal markers may not accurately represent the anterior rectal wall. This study was aimed at analyzing the variability of rectal dose estimation as a result of interfractional variation of marker placement. A cohort of five patients treated with multiple-fraction tandem and ovoid high-dose-rate (HDR) brachytherapy was studied. The cervical os point and the orientation of the applicators were matched among all fractional plans for each patient. Rectal points obtained from all fractions were then input into each clinical treated plan. New fractional rectal doses were obtained and a new cumulative rectal dose for each patient was calculated. The maximum interfractional variation of distances between rectal dose points and the closest source positions was 1.1 cm. The corresponding maximum variability of fractional rectal dose was 65.5%. The percentage difference in cumulative rectal dose estimation for each patient was 5.4%, 19.6%, 34.6%, 23.4%, and 13.9%, respectively. In conclusion, care should be taken when using rectal markers as reference points for estimating rectal dose in HDR cervical brachytherapy. The best estimate of true rectal dose for each fraction should be determined by the most anterior point among all fractions.

SU‐FF‐J‐139: Cumulative Dose to the Rectal Wall and Implications for Prostate IGRT Treatment Planning

Purpose: To investigate the effect of daily variation in rectal volume and shape on dose to the anterior rectal wall in prostate IMRT. Method and Materials: A patient data set was used, consisting of a planning image and a sequence of treatment images (in‐room CTs) acquired over the course of IGRT. 5‐beam IMRT plans (prescription dose 46 Gy) were generated using three different daily treatment CTs as the planning image, with rectal volumes of 77 cc, 89 cc, and 158 cc. For each plan, the daily treatment dose was computed under optimal prostate alignment on all daily images. Dose to the rectal wall was then accumulated to a single image using a landmark‐registered deformable model to determine correspondence. The planned and cumulative rectal wall dose distributions were displayed in a rendered 3D surface display for comparison. Results: The only substantial change in the peak rectal dose occurred when the treatment was planned on the day with the most distended rectum, when the delivered peak dose was ∼5% less than that planned. For the other two planning images, with a medium or small rectum, the change in dose to the hot spot was less than 2%. Examination of each day showed that the rectal wall was closest to the prostate on the day with the largest rectum, so that, when the rectal constraints were satisfied for that case, the resulting dose distributions had a lower maximum on other days for which there was separation between the two organs. The surface displays indicated some spreading of dose due to organ motion. Conclusion: With growing accuracy of prostate setup, the relative motion of other organs may merit separate consideration in planning. A study extending this work to images from 5 patients is under way.

Poster - Thurs Eve-13: Modeling the effect of organ motion on cumulative rectal dose using EUD.

A rigid body model and electronic serial portal imaging (EPI) data were used to generate the cumulative dose distribution for the rectum incorporating organ motion during IMRT. The impact of rectal motion was assessed via NTCP and TCP based on equivalent uniform dose per fraction (EUDf ). The rectal positional variations were measured fraction-to-fraction from MV EPI for 20 prostate patients implanted with gold seeds. Five-field (5F) and seven-field (7F) IMRT plans for prostate patients were constructed with prescribed dose 78 Gy/39 fractions using a Pinnacle3 treatment planning system. EUD increased in 45% of the patients with greater than 2.5% increase for 5% of the patients. While EUD decreased in 55% of the patients with greater than 2.5% decrease for 10% of the patients. The amplitudes of EUDf increase and decrease are correlated with the dose gradient. Higher dose gradients lead to higher rectal EUDf change. The rectal NTCP decreases for half of the patients and increases for the other for both 5F and 7F plans. The NTCP decreased with the increasing of dose gradient between the prostate and rectum for 5F and 7F IMRT plans. The correlation coefficient for the rectal NTCP and the dose gradient is - 0.71. The increase or decrease of rectal cumulative dose depends on the dose gradient, motion amplitude and frequency in AP direction. EUDf is a useful QA parameter for interpreting the biological impact of geometric uncertainties on the static dose distribution. Rectal NTCP is patient dependent and must be determined individually.

MO-D-AUD B-07: Analysis of Rectal Dose Variability Due to Inter-Fractional Variations of Rectal Marker Positioning in Film-Based HDR Cervical Brachytherapy

Purpose: In film-based intracavitary brachytherapy for cervical cancer, rectal dose is usually computed using rectal markers. Position of the markers may not accurately represent the anterior rectal wall. The study is to retrospectively analyze the variability of rectal dose due to variations of marker placement in a multi-fractionated HDR treatment regimen. Method and Materials: A cohort of five patients, total 18 applications, treated with multiple-fraction tandem/ovoid HDR brachytherapy was studied. To correlate the rectal points from different fractions to the same coordinate system, the cervical os point and the orientation of the applicators were manually matched. With the applicator matching, rectal points obtained from other fractions were input into the original treatment plan for each application. A rectal dose was then calculated from all the possible rectal points. The fractional rectal doses were summed as the new cumulative rectal dose for each patient, which was compared with the original cumulative rectal dose. The reproducibility of the results was also analyzed by repeating the matching procedure. Results: The maximum inter-fractional variation of distances between rectal dose points and the closest source positions was 1.1 cm and the corresponding maximum variability of fractional rectal dose was 65.5%. The percentage difference in cumulative rectal dose estimation for each patient was 5.1%, 16.4%, 25.7%, 18.9%, 12.2%, respectively. Overall reproducibility of the results was within 1.8%. Conclusion: Our results show underestimation of the rectal dose caused by variations of rectal marker positioning relative to the anterior rectal wall, which should be taken into consideration in film-based HDR cervical brachytherapy. By manually matching the rectal points into the same treatment plan, one may minimize the possibility of underestimating the rectal dose. We will also anticipate a more accurate approach for evaluating rectal doses in HDR intracavitary brachytherapy with the emerging 3-D volume imaging based treatment planning.

SU-GG-T-419: IMRT Prostate: Cumulative Rectal Dose Incorporating Rectal Motion

Purpose: For prostate IMRT, a rigid body model and serial portalimaging data were used to generate the cumulative dose distribution for the rectum incorporating internal organ motion by using equivalent uniform dose per fraction (EUDf). The impact of the rectal movement on NTCP over the course of treatment was evaluated. Method and Materials: The rectal positional variations were measured fraction‐to‐fraction from MV portalimaging for 20 prostate patients implanted with gold seeds. The rectal dose change per fraction can be expressed as EUDf variation. Five‐field (5F) and seven‐field (7F) IMRT plans for prostate patients were made with prescribed dose 78 Gy/39 fractions using a Pinnacle3treatment planning system with 15 MV x‐rays. The evaluation was performed by comparing the fractional dose‐volume histogram, the rectal EUDf and NTCP with and without internal organ motion. Results: The increase or decrease of cumulative rectal EUD over the course of treatment depends on the motion amplitude and frequency in the anterior or the posterior directions. EUD increased in 45% of the patients with greater than 2.5% increase for 5% of the patients. EUD decreased in 55% of the patients with greater than 2.5% decrease for 10% of the patients. The rectal NTCP decreases for half of the patients and increases for the other for both 5F and 7F plans in this group. Comparing 5F and 7F plan for the same patient, NTCP is lower for 7F plan compared to 5F plan with and without considering rectal movement. Conclusion: EUDf is a useful QA parameter for interpreting the biological impact of geometric uncertainties on the static dose distribution. The increase or decrease of the cumulative rectal dose depended on the motion amplitude and frequency in the anterior or the posterior direction and rectal NTCP is patient dependent and must be determined individually.

WE‐D‐BRA‐04: Problems Associated with IMRT Combined with a Single Fraction, 4D, High Dose Partial Prostate Boost

Purpose: There is a growing body of evidence that suggests that dose escalation will be beneficial in the treatment of prostate cancer. Specifically, dose escalation to areas of the prostate demonstrating high clonogenic cell density through MR spectroscopy or direct biopsy may improve treatment outcome. However, the surrounding normal structures and the movement of the prostate during treatment limit the dose that can be delivered safely. The purpose of this work is to describe a method to limit the dose to critical structures, namely, the rectum, during routine IMRT delivery to the prostate allowing for a dose escalated boost to be delivered to the areas in need. Methods &amp; Materials: Patients are being accrued to an in‐house protocol in which 76 Gy is delivered to the entire prostate PTV via IMRT. An IMRT boost to the high disease density region(s) is then delivered in a single fraction that brings the dose to a biological equivalent of 94 Gy. Active tracking is employed throughout using implanted Calypso Beacons. This allows for a decrease in the PTV margins for the initial IMRT regime and subsequent increased rectal sparing. To evaluate the effects on the rectum a series of 8 prostate CT data sets were chosen for varying CTV volume (38–214 cc). The original, clinically used plans were compared to those generated by decreasing the PTV margins from our standard 8mm (5mm posteriorly) to uniform 3mm expansions. The number of beam directions as well as input constraints for the rectum was kept constant. Our routine clinical acceptance criteria were applied to all. Isoeffective dose calculations (EQD2) were employed to determine the appropriate boost dose. Appropriate composite plans were generated assuming 2 Gy fractions for the entire treatment. Additionally, EQD2 calculations were performed and composite plans generated for cumulative rectal dose. Results: For the initial IMRT plans the average volume of rectum receiving 65 Gy and 40 Gy decreased from 14.9 to 6.3% and 33.1 to 23%, respectively, by decreasing the PTV margins to 3mm. A review of our initial data for patients implanted with Calypso transponders indicates that the prostate drifts during treatment by &gt;3 mm for 103 seconds per average treatment (8–17 minutes). Assuming an α/β of 2.0 for the prostate, a single fraction boost dose of 7.5 Gy results in an equivalent of 94 Gy. This boost will also effect the rectum in a similar manner, assuming appropriate α/β corrections. Conclusions: It is possible to deliver a high dose, single fraction boost to high tumor density regions of the prostate by using active tracking and PTV reduction. However, the effects on critical structures such as the rectum need to be evaluated with respect to our routine acceptance criteria and known side effect rates. It is hoped that this technique will result in improved outcome for patients with unfavorable disease characteristics.Educational Objectives:1. To understand issues related to combining “boost” plans to conventional IMRT plans.2. To be exposed to active organ tracking and the implications for normal tissue sparing.

Predictors of severe gastrointestinal toxicity after external beam radiotherapy and interstitial brachytherapy for advanced or recurrent gynecologic malignancies

The aim of this retrospective review of patients with gynecologic malignancies treated with external beam radiotherapy (EBRT) and interstitial brachytherapy was to determine the rate of Grade > or =2 rectovaginal fistula and Grade > or =4 small bowel obstruction as defined by the National Cancer Institute Common Toxicity Criteria for Adverse Events, version 3.0. Thirty-six patients with primary and recurrent gynecologic cancers were treated with EBRT and interstitial brachytherapy. Median doses to tumor, bladder, and rectum were 75 Gy, 61 Gy, and 61 Gy, respectively. A univariate analysis was performed to identify variables that correlated with toxicity. At median follow-up of 19 months, the 3-year risk of small bowel obstruction was 6%. Those patients with prior abdomino-pelvic surgery who received EBRT with antero-posterior fields had higher rates of obstruction than patients without prior abdomino-pelvic surgery or those who received EBRT with four fields (50% vs. 0%, p < 0.0001). The 3-year risk of rectovaginal fistula was 18% and was significantly higher in patients who received >76 Gy to the rectum compared with those who received < or =76 Gy (100% vs. 7%, p = 0.009). Patients treated with EBRT and interstitial brachytherapy after abdomino-pelvic surgery should receive EBRT with four fields and the cumulative rectal dose should be < or =76 Gy.

Dosimetric factors predicting severe radiation-induced bowel complications in patients with cervical cancer: combined effect of external parametrial dose and cumulative rectal dose

ObjectiveThe purpose of this study was to analyze dosimetric factors of radiation-induced severe bowel complications among patients with cervical cancer. MethodsWe reviewed 297 patients of stage IB–IVA cervical cancer managed by curative-intent radiotherapy from May 1993 through December 1997. Whole-pelvic irradiation of external beam radiation therapy (EBRT) (34.2–48.6 Gy/19–27 fractions) was delivered to all patients. Two hundred and three patients received additional bilateral parametrial boost (3.6–18 Gy/2–10 fractions). High dose-rate (HDR) intracavitary brachytherapy (ICBT), 16–24 Gy/5 fractions to Point A, was given after external irradiation. Cumulative rectal biologically effective dose (CRBED) at rectal reference point was determined by summation of EBRT and ICBT component. ResultsThe 5-year incidences of Grade 3–4 enterocolitis and proctitis were 10% and 7%, respectively. Both complications were associated with external parametrial dose (PMD) and CRBED. Interaction of CRBED and PMD was noted in multivariate analysis of enterocolitis (P < 0.001) and proctitis (P < 0.001). In CRBED ≥ 100 Gy3 group, PMD was an independent factor in enterocolitis (P = 0.010) and proctitis (P = 0.039). In PMD ≥ 54 Gy group, CRBED was an independent factor in enterocolitis (P = 0.003) and proctitis (P = 0.036). Patients with both PMD ≥ 54 Gy and CRBED ≥ 100 Gy3 had higher incidence of 5-year enterocolitis (26%) (P < 0.001) and proctitis (17%) (P < 0.001) than other dose groups. ConclusionRadiation-induced severe bowel complications are association on both high PMD and high CRBED. We do not suggest both external PMD ≥ 54 Gy and CRBED ≥ 100 Gy3 for treatment of cervical cancer due to unacceptably high incidence of severe bowel complications.

The prediction of late rectal complications following the treatment of uterine cervical cancer by high-dose-rate brachytherapy

Purpose: This study aimed to correlate patient, treatment, and dosimetric factors with the risk of late rectal sequelae in patients with uterine cervical cancer treated with external beam radiation therapy (EBRT) and high dose rate intracavitary brachytherapy (HDRICB). Methods and Materials: From September 1992 to December 1995, a total of 128 patients with uterine cervical cancer, who were treated and survived more than 12 months, were evaluated. After EBRT with 40–44 Gy/20–22 Fr/4–5 weeks to the whole pelvis, the dose was boosted up to 54–58 Gy with central shielding for patients with bilateral parametria of Stage IIb or greater. HDRICB consisted of three to four insertions at doses of 5–7.2 Gy (to Point A) at intervals of 1 week. Patient and treatment factors were analyzed using logistic regression analysis and the cumulative rectal biologic equivalent dose (CRBED) was calculated. Results: After 30–75 months of follow-up (median, 43 months), 38 patients (29.7%) had late rectal sequelae. Patients who had Stage IIb–IVa disease, cumulative rectal dose (external RT + total ICRU rectal dose) greeater than 65 Gy, or age greater than 70 years had a high risk of developing late rectal sequelae. When 110 Gy was used as the cut-off value, 19.6% (10 of 51) of patients whose CRBED was less than 110 Gy had rectal complications, while 36.4% (28/77) of patients whose CRBED was greater than 110 Gy developed rectal complications. Conclusion: Risk factors of late rectal complications were advanced stage, age greater than 70 years, and cumulative rectal dose of greater than 65 Gy.