Unique role of proximal rectal dose in late rectal complications for patients with cervical cancer undergoing high-dose-rate intracavitary brachytherapy

Correlation analysis of CT-based rectal planning dosimetric parameters with in vivo dosimetry of MOSkin and PTW 9112 detectors in Co-60 source HDR intracavitary cervix brachytherapy

Intracavitary cervical brachytherapy delivers high doses of radiation to the target tissue and a portion of these doses will also hit the rectal organs due to their close proximity. Rectal dose can be evaluated from dosimetric parameters in the treatment planning system (TPS) and in vivo (IV) dose measurement. This study analyzed the correlation between IV rectal dose with selected volume and point dose parameters from TPS. A total of 48 insertions were performed and IV dose was measured using the commercial PTW 9112 semiconductor diode probe. In 18 of 48 insertions, a single MOSkin detector was attached on the probe surface at 50 mm from the tip. Four rectal dosimetric parameters were retrospectively collected from TPS; (a) PTW 9112 diode maximum reported dose (RP_max) and MOSkin detector, (b) minimum dose to 2 cc (D_2cc), (c) ICRU reference point (ICRU_r), and (d) maximum dose from additional points (R_max). The IV doses from both detectors were analyzed for correlation with these dosimetric parameters. This study found a significantly high correlation between IV measured dose from RP_max (r = 0.916) and MOSkin (r = 0.959) with TPS planned dose. The correlation between measured RP_max with both D_2cc and R_max revealed high correlation of r > 0.7, whereas moderate correlation (r = 0.525) was observed with ICRUr. There was no significant correlation between MOSkin IV measured dose with D_2cc, ICRU_r and R_max. The non-significant correlation between parameters was ascribable to differences in both detector position within patients, and dosimetric volume and point location determined on TPS, rather than detector uncertainties.

Evaluation of Volumetric Doses of Organs at Risk in Carcinoma Cervix Patients with HDR Intracavitary Brachytherapy and Comparison of CT-based and Conventional Plans

Background:

Brachytherapy treatment planning in cervix carcinoma patients using two dimensional (2D) orthogonal images provides only point dose estimates while CT-based planning provides volumetric dose assessment helping in understanding the correlation between morbidity and the dose to organs at risk (OARs) and treatment volume.

Objective:

Aim of present study is to compare International Commission on Radiation Units and Measurements Report 38 (ICRU 38) reference point doses to OARs with volumetric doses using 2D images and CT images in patients with cervical cancer.

Material and Methods:

In this prospective study, 20 patients with cervical cancer stages (IIB-IIIB) were planned for a brachytherapy dose of 7Gy per fraction for three fractions using 2D image-based treatment plan and CT-based plan. ICRU 38 points for bladder and rectum were identified on both 2D image-based plan and CT-based plan and doses (D_ICRU) at these points were compared to the minimum dose to 2cc volume (D_2cc) of bladder and rectum receiving the highest dose.

Results:

D_2cc bladder dose was 1.60 (±0.67) times more than D_ICRUb bladder dose whereas D_2cc rectum dose was 1.13±0.40 times D_ICRUr. Significant difference was found between D_ICRUb and D_2cc dose for bladder (p=.0.016) while no significant difference was seen between D_ICRUr and D_2cc dose for rectum (p=0.964).

Conclusion:

The study suggests that ICRU 38 point doses are not the true representation of maximum doses to OARs. CT-based treatment planning is more a reliable tool for OAR dose assessment than the conventional 2D radiograph-based plan.

American Brachytherapy Task Group Report: A pooled analysis of clinical outcomes for high-dose-rate brachytherapy for cervical cancer

PURPOSE

Advanced imaging used in combination with brachytherapy (BT) has revolutionized the treatment of patients with cervical cancer. We present a comprehensive review of the literature for definitive radiation with high-dose-rate (HDR) BT. In addition, we investigate potential outcome improvement with image-based brachytherapy (IBBT) compared to studies using traditional Point A dosing. This review extensively investigates acute and late toxicities.

METHODS AND MATERIALS

This study reviews the literature from 2000 to 2015 with an emphasis on modern approaches including concurrent chemotherapy (chemoRT), radiation, and HDR BT and IBBT. Descriptive statistics and pelvic control (PC), disease-free survival (DFS), and overall survival (OS) outcomes were calculated using weighted means to report pooled analysis of outcomes.

RESULTS

Literature search yielded 16 prospective, 51 retrospective studies that reported survival outcomes, and 13 retrospective studies that focused on acute and late toxicity outcomes regardless of applicator type. There are 57 studies that report Point A dose specification with 33 having chemoRT, and 10 studies that use IBBT, 8 with chemoRT. Patients receiving radiation and chemoRT with HDR BT in the prospective studies, with >24 months followup, rates of PC were: for RT: 73%, SD: 11; CRT: 82%, SD: 8; DFS-RT: 55%, SD: 10; CRT: 65%, SD: 7; OS-RT: 66%, SD: 7; CRT: 70%, SD: 11. In the retrospective studies, the PC rates (weighted means) for the radiation and chemoradiation outcomes are 75% vs. 80%, and for DFS, the values were 55% vs. 63%, respectively. Comparing patients receiving chemoRT and IBBT to traditional Point A dose specification, there is a significant improvement in PC (p < 0.01) and DFS (p < 0.01) with IBBT. The range of genitourinary late toxicity reported for radiation was Grade 3: 1-6% and for chemoRT 2-20%. The range of late gastrointestinal toxicity for radiation was Grade 3: 4-11% and for chemoRT, 1-11%. For the late gynecologic toxicity, only 1 of the 16 prospective trials report a Grade 1-2 of 17% for radiation and 9% for chemoRT effects.

CONCLUSIONS

We present concise outcomes of PC, DFS, OS, and toxicity for cervical cancer patients treated with chemoradiation and HDR BT. Our data suggest an improvement in outcomes with the use of IBBT compared with traditional Point A dose prescriptions. In conclusion, HDR BT is a safe, effective modality when combined with IBBT.

The usefulness of fleet rectal enemas on high-dose-rate intracavitary cervical cancer brachytherapy. A prospective trial

Purpose

To evaluate the effects of rectal enemas on rectal doses during radical high-dose-rate (HDR) intracavitary cervical brachytherapy (BT).

Material and methods

Twenty patients suffering from cervical cancer and treated with external beam radiotherapy and HDR-BT were included in a prospective trial. The first brachytherapy fraction was considered the basal status, and patients were instructed to self-administer two rectal cleansing enemas before the second fraction. Dose-volume histogram (DVH) values were generated for the rectum and correlated with rectal volume variation. Brachytherapy was carried out with a Fletcher or Utrecht applicator.

Results

No significant rectal volume differences were observed between fractions with or without rectal enemas (without, 52.64 ± 15.92 cc; with, 53.16 ± 19.28 cc). There was a significant correlation between both rectal volumes (r = 0.722, p = 0.001). No significant differences were observed in analyzed DVH parameters (median values: ΔD_0.1cc, 4.17 vs. 3.61 Gy; ΔD_1cc, 3.23 vs. 2.87 Gy; ΔD_2cc, 2.9 vs. 2.54 Gy; ΔD_5cc, 2.35 vs. 2.05 Gy, for no enema and enema fraction, respectively). No significant rectal volume differences nor DVH parameter differences were observed according the applicator type.

Conclusions

Our rectal enemas protocol prior to HDR-BT was ineffective in significantly modifying rectal DVH parameters. No differences were observed according to the type of applicator used.

The effect of leg position on the dose distribution of intracavitary brachytherapy for cervical cancer: 3D computerised tomography plan evaluation and in vivo dosimetric study

Purpose

To evaluate the impact of leg position on the dose distribution during intracavitary brachytherapy for cervical cancer.

Patients and methods

This prospective study was performed on 11 women with cervical cancer who underwent intracavitary brachytherapy. After insertion of the brachytherapy applicator, two sets of computed tomography slices were taken including pelvis, one with straight leg and one with leg flexion position with knee support. The dose (7 Gy) was prescribed to point A. The radiotherapy plan was run on the Plato Planning Software System V14·1 to get the dose distributions. Also, rectum and bladder doses were measured for both leg positions during the treatment. The doses and volumes of organs were compared via the Wilcoxon signed-rank test by using Statistical Package for the Social Sciences 11·5 statistical software.

Results

No significant difference regarding the dose distributions and volumes of target, sigmoid and bladder due to leg position was observed, either on 3D planning or on in vivo dose measurements. However, there were significant differences for 25 and 50% isodose coverage of rectum in favour of straight leg position (p=0·026). There were no significant differences regarding maximum doses in any critical organ.

Conclusion

Difference in leg position caused only a small change in rectum dose distribution and did not cause any other change in either dose distributions or in vivo measured doses of both target and critical organs during cervical brachytherapy. Straight leg position appears better with regard to rectum dose.

CT based 3-dimensional treatment planning of intracavitary brachytherapy for cancer of the cervix: comparison between dose-volume histograms and ICRU point doses to the rectum and bladder

BACKGROUND

CT based brachytherapy allows 3-dimensional (3D) assessment of organs at risk (OAR) doses with dose volume histograms (DVHs). The purpose of this study was to compare computed tomography (CT) based volumetric calculations and International Commission on Radiation Units and Measurements (ICRU) reference-point estimates of radiation doses to the bladder and rectum in patients with carcinoma of the cervix treated with high-dose-rate (HDR) intracavitary brachytherapy (ICBT).

MATERIALS AND METHODS

Between March 2011 and May 2012, 20 patients were treated with 55 fractions of brachytherapy using tandem and ovoids and underwent post-implant CT scans. The external beam radiotherapy (EBRT) dose was 48.6 Gy in 27 fractions. HDR brachytherapy was delivered to a dose of 21 Gy in three fractions. The ICRU bladder and rectum point doses along with 4 additional rectal points were recorded. The maximum dose (DMax) to rectum was the highest recorded dose at one of these five points. Using the HDR plus 2.6 brachytherapy treatment planning system, the bladder and rectum were retrospectively contoured on the 55 CT datasets. The DVHs for rectum and bladder were calculated and the minimum doses to the highest irradiated 2cc area of rectum and bladder were recorded (D2cc) for all individual fractions. The mean D2cc of rectum was compared to the means of ICRU rectal point and rectal DMax using the Student's t-test. The mean D2cc of bladder was compared with the mean ICRU bladder point using the same statistical test .The total dose, combining EBRT and HDR brachytherapy, were biologically normalized to the conventional 2 Gy/fraction using the linear-quadratic model. (α/β value of 10 Gy for target, 3 Gy for organs at risk).

RESULTS

The total prescribed dose was 77.5 Gy α/β10. The mean dose to the rectum was 4.58 ± 1.22 Gy for D 2cc, 3.76 ± 0.65 Gy at D ICRU and 4.75 ± 1.01 Gy at DMax. The mean rectal D 2cc dose differed significantly from the mean dose calculated at the ICRU reference point (p<0.005); the mean difference was 0.82 Gy (0.48 -1.19 Gy). The mean EQD2 was 68.52 ± 7.24 Gy α/β3 for D 2cc, 61.71 ± 2.77 Gy α/β3 at D ICRU and 69.24 ± 6.02 Gy α/β3 at DMax. The mean ratio of D 2cc rectum to D ICRU rectum was 1.25 and the mean ratio of D 2cc rectum to DMax rectum was 0.98 for all individual fractions. The mean dose to the bladder was 6.00 ± 1.90 Gy for D 2cc and 5.10 ± 2.03 Gy at D ICRU. However, the mean D 2cc dose did not differ significantly from the mean dose calculated at the ICRU reference point (p=0.307); the mean difference was 0.90 Gy (0.49-1.25 Gy). The mean EQD2 was 81.85 ± 13.03 Gy α/β3 for D 2cc and 74.11 ± 19.39 Gy α/β3 at D ICRU. The mean ratio of D 2cc bladder to D ICRU bladder was 1.24. In the majority of applications, the maximum dose point was not the ICRU point. On average, the rectum received 77% and bladder received 92% of the prescribed dose.

CONCLUSIONS

OARs doses assessed by DVH criteria were higher than ICRU point doses. Our data suggest that the estimated dose to the ICRU bladder point may be a reasonable surrogate for the D 2cc and rectal DMax for D 2cc. However, the dose to the ICRU rectal point does not appear to be a reasonable surrogate for the D 2cc.

Dosimetric evaluation of manually and inversely optimized treatment planning for high dose rate brachytherapy of cervical cancer

BACKGROUND

To compare five inverse treatment planning methods with the conventional manually optimized planning approach for brachytherapy of cervical cancer with respect to dosimetric parameters.

MATERIAL AND METHODS

Eighteen cervical cancer patients treated with magnetic resonance imaging (MRI)-guided high dose rate (HDR) brachytherapy were included in this study. Six plans were created for each of the 4 HDR brachytherapy fractions for each patient: 1 manually optimized and 5 inversely planned. Three of these were based on inverse planning simulated annealing (IPSA) with and without extra constraints on maximum doses of the target volume, and different constraints on doses to the organs at risk (OARs). In addition there were two plans based on dose to target surface points. The resulting dose-volume histograms were analyzed and compared from the dosimetric point of view by quantifying specific dosimetric parameters, such as clinical target volume (CTV) D₉₀, CTV D₁₀₀, conformal index (COIN), and D₂cm3 for rectum, bladder and the sigmoid colon.

RESULTS

Manual optimization led to a mean target coverage of 78.3% compared to 87.5%, 91.7% and 82.5% with the three IPSA approaches (p < 0.001). Similar COIN values for manual and inverse optimization were found. The manual optimization led to better results with respect to the dose to the OARs expressed as D₂cm3. Overall, the best results were obtained with manual optimization and IPSA plans with volumetric constraints including maximum doses to the target volume.

CONCLUSIONS

Dosimetric evaluation of manual and inverse optimization approaches is indicating the potential of IPSA for brachytherapy of cervical cancer. IPSA with constraints of maximum doses to the target volume is closer related to manual optimization than plans with constraints only to minimum dose to the target volume and maximum doses to OARs. IPSA plans with proper constraints performed better than those based on dose to target surface points and manually optimized plans.

Definitive radiotherapy for uterine cervix cancer: long term results for patients treated in the period from 1998 till 2002 at the Institute of Oncology Ljubljana

Background

The aim of this retrospective study was to analyse results of the two-dimensional (2D) uterine cervix cancer treatment at the Institute of Oncology Ljubljana from 1998 till 2002, before the three-dimensional (3D) approach was introduced in our clinical practice.

Methods

Ninety-eight patients with the following FIGO stage distribution were analysed: 10% IB, 7% IIA, 37% IIB, 4% IIIA and 42% IIIB. The influence of age, haemoglobin level, histology, grade, stage, lymph node status, cumulative point A dose, and an overall treatment time on the survival and local control (LC) were evaluated. Acute and late side effects were assessed.

Results

Five and 8-year overall survival (OS), disease specific survival (DSS) and LC rate were as follows: 47.2% and 43.0%, 54.7% and 53.4%, 74.9% and 72.5%, respectively. Point A dose and histology of the tumour influenced OS, positive lymph nodes DSS and point A dose LC rate. Probability of grade three and four late complications in the first five years was 7.1% for gastrointestinal tract and 3.3% for genitourinary system and vagina.

Conclusions

Point A dose was independent predictor of OS and LC rate, lymph node status predicted DSS, while histology of the tumour influenced OS.

Endoscopic findings of rectal mucosal damage after pelvic radiotherapy for cervical carcinoma: correlation of rectal mucosal damage with radiation dose and clinical symptoms

PURPOSE

To describe chronic rectal mucosal damage after pelvic radiotherapy (RT) for cervical cancer and correlate these findings with clinical symptoms and radiation dose.

MATERIALS AND METHODS

Thirty-two patients who underwent pelvic RT were diagnosed with radiation-induced proctitis based on endoscopy findings. The median follow-up period was 35 months after external beam radiotherapy (EBRT) and intracavitary radiotherapy (ICR). The Vienna Rectoscopy Score (VRS) was used to describe the endoscopic findings and compared to the European Organization for Research and Treatment of Cancer (EORTC)/Radiation Therapy Oncology Group (RTOG) morbidity score and the dosimetric parameters of RT (the ratio of rectal dose calculated at the rectal point [RP] to the prescribed dose, biologically effective dose [BED] at the RP in the ICR and EBRT plans, α/β = 3).

RESULTS

Rectal symptoms were noted in 28 patients (rectal bleeding in 21 patients, bowel habit changes in 6, mucosal stools in 1), and 4 patients had no symptoms. Endoscopic findings included telangiectasia in 18 patients, congested mucosa in 20, ulceration in 5, and stricture in 1. The RP ratio, BEDICR, BEDICR+EBRT was significantly associated with the VRS (RP ratio, median 76.5%; BEDICR, median 37.1 Gy3; BEDICR+EBRT, median 102.5 Gy3; p < 0.001). The VRS was significantly associated with the EORTC/RTOG score (p = 0.038).

CONCLUSION

The most prevalent endoscopic findings of RT-induced proctitis were telangiectasia and congested mucosa. The VRS was significantly associated with the EORTC/RTOG score and RP radiation dose.

Stereotactic body radiation therapy via helical tomotherapy to replace brachytherapy for brachytherapy-unsuitable cervical cancer patients - a preliminary result

Aim

To review the experience and to evaluate the results of stereotactic body radiation therapy (SBRT) via helical tomotherapy (HT), for the treatment of brachytherapy-unsuitable cervical cancer.

Methods

Between September 1, 2008 to January 31, 2012, nine cervical cancer patients unsuitable for brachytherapy were enrolled. All of the patients received definitive whole pelvic radiotherapy with or without chemotherapy, followed by SBRT via HT.

Results

The actuarial locoregional control rate at 3 years was 78%. The mean biological equivalent dose in 2-Gy fractions of the tumor, rectum, bladder, and intestines was 76.0 ± 7.3, 73.8 ± 13.2, 70.5 ± 10.0, and 43.1 ± 7.1, respectively. Only two had residual tumors after treatment, and the others were tumor-free. Two patients experienced grade 3 acute toxicity: one had diarrhea; and another experienced thrombocytopenia. There were no grade 3 or 4 subacute toxicities. Three patients suffered from manageable rectal bleeding in months 11, 14, and 25, respectively. One stage I VA patient experienced fistula formation in month 3.

Conclusion

SBRT via HT provides the possibility for treatment of locally advanced cervical cancer in patients who are unsuitable for brachytherapy. Long-term follow up and enrollment of more such patients to receive SBRT via the HT technique are warranted.

Impact of 3D image-based PDR brachytherapy on outcome of patients treated for cervix carcinoma in France: results of the French STIC prospective study

PURPOSE

In 2005 a French multicentric non randomized prospective study was initiated to compare two groups of patients treated for cervix carcinoma according to brachytherapy (BT) method: 2D vs 3D dosimetry. The BT dosimetric planning method was chosen for each patient in each center according to the availability of the technique. This study describes the results for 705 out of 801 patients available for analysis.

PATIENTS AND METHODS

For the 2D arm, dosimetry was planned on orthogonal X-Rays using low dose rate (LDR) or pulsed dose rate (PDR) BT. For the 3D arm, dosimetry was planned on 3D imaging (mainly CT) and performed with PDR BT. Each center could follow the dosimetric method they were used to, according to the chosen radioelement and applicator. Manual or graphical optimization was allowed.

PATIENTS AND METHODS

Three treatment regimens were defined: Group 1: BT followed by surgery; 165 patients (2D arm: 76; 3D arm: 89); Group 2: EBRT (+chemotherapy), BT, then surgery; 305 patients (2D arm: 142; 3D arm: 163); Group 3: EBRT (+chemotherapy), then BT; 235 patients, (2D arm: 118; 3D arm: 117).

PATIENTS AND METHODS

The DVH parameters for CTVs (High Risk CTV and Intermediate Risk CTV) and organs at risk (OARs) were computed as recommended by GYN GEC ESTRO guidelines. Total doses were converted to equivalent doses in 2Gy fractions (EQD2). Side effects were prospectively assessed using the CTCAEv3.0.

RESULTS

The 2D and 3D arms were well balanced with regard to age, FIGO stage, histology, EBRT dose and chemotherapy. For each treatment regimen, BT doses and volumes were comparable between the 2D and 3D arms in terms of dose to point A, isodose 60 Gy volume, dose to ICRU rectal points, and TRAK.

RESULTS

Dosimetric data in the 3D arm showed that the dose delivered to 90% of the High Risk CTV (HR CTV D90) was respectively, 81.2Gy(α/β10), 63.2Gy(α/β10) and 73.1Gy(α/β10) for groups 1, 2 and 3. The Intermediate Risk (IR) CTV D90 was respectively, 58.5Gy(α/β10), 57.3Gy(α/β10) and 61.7Gy(α/β10) for groups 1, 2 and 3. For the OARs, doses delivered to D2cc ranged 60-70Gy(α/β3) for the bladder, 33-61Gy(α/β3) for the rectum, and 44-58Gy(α/β3) for the sigmoid according to the regimen.

RESULTS

At 24 months, local relapse-free survival was 91.9% and 100% in group 1, 84.7% and 93% in group 2, 73.9% and 78.5% in group 3; grade 3-4 toxicity rate was 14.6% and 8.9% in group 1, 12.5% and 8.8% in group 2, and 22.7% and 2.6% in group 3 for 2D and 3D arm.

CONCLUSION

This multicentric study has shown that 3D BT is feasible and safe in routine practice. It has improved local control with half the toxicity observed with 2D dosimetry. The combined treatment with radiotherapy and surgery was more toxic than definitive radiotherapy. For patients with advanced tumors, it is necessary to improve coverage of target volumes without raising toxicity.

Reporting and validation of gynaecological Groupe Euopeen de Curietherapie European Society for Therapeutic Radiology and Oncology (ESTRO) brachytherapy recommendations for MR image-based dose volume parameters and clinical outcome with high dose-rate brachytherapy in cervical cancers: a single-institution initial experience

OBJECTIVE

The objectives are to report the dosimetric analysis, preliminary clinical outcome, and comparison with published data of 3-dimensional magnetic resonance-based high dose rate brachytherapy (BT) in cervical cancer.

MATERIALS AND METHODS

The data set of 24 patients with cervical cancer treated with high dose-rate brachytherapy applications was analyzed. All patients received radiation with or without chemotherapy (10 patients received concomitant chemoradiation). Point A, International Commission on Radiation Units and Measurement (ICRU) point doses, and Groupe Europeen de Curietherapie-European Society for Therapeutic Radiology and Oncology dose volume parameters, namely, high-risk clinical target volume (HR-CTV), D90 and D100 doses, and dose to D0.1cc and D2cc, for rectum, bladder, and sigmoid, were calculated and correlated.

RESULTS

Mean ± SD HR-CTV was 45.2 ± 15.8 cc. The mean ± SD point A dose was 73.4 ± 4.5 Gy (median, 74.3 Gy) total biologically equivalent dose in 2 Gy per fraction (EQD2), whereas mean ± SD D90 doses were 70.9 ± 10.6 GyEQD2 (median, 68). The mean ± SD ICRU rectal and bladder points were 63.5 ± 8.1 and 80.4 ± 34.4 GyEQD2, respectively. The D0.1cc and D2cc for rectum were 66.0 ± 9.9 GyEQD2 (median, 64.5) and 57.8 ± 7.7 GyEQD2 (median, 58.8), for bladder 139.1 ± 54.7 GyEQD2 (median, 131.9) and 93.4 ± 24.6 GyEQD2 (median, 91), and sigmoid were 109.4 ± 45.2 GyEQD2 (median, 91) and 74.6 ± 19.6 GyEQD2 (median, 69.6). With a median follow-up of 24 months, 3 patients had local nodal failure, 1 had right external iliac nodal failure, and 1 had left supraclavicular nodal failure.

CONCLUSIONS

The 3-D magnetic resonance image-based high dose-rate brachytherapy approach in cervical cancers is feasible. In our experience, the HR-CTV volumes are large, and D0.1cc and D2cc doses to bladder and sigmoid are higher than published literature so far.

Comparison of intracavitary brachytherapy and stereotactic body radiotherapy dose distribution for cervical cancer

PURPOSE

To compare the dose distribution characteristics of stereotactic body radiotherapy (SBRT) with intracavitary high-dose-rate (HDR) brachytherapy in patients with cervical carcinoma.

METHODS AND MATERIALS

HDR intracavitary brachytherapy treatment plans for 11 women with cervical carcinoma were evaluated in this analysis. The total HDR brachytherapy dose was 28Gy given in four fractions. HDR brachytherapy was delivered with the microSelectron HDR therapy unit (Nucletron B. V., Veenendaal, The Netherlands). SBRT plans for each patient were generated with MultiPlan for CyberKnife Robotic Radiosurgery System (Accuray Inc., Sunnyvale, CA). The dose distributions, dose-volume histograms, and maximum dose points of the target and critical organs were recorded for both plans.

RESULTS

SBRT yielded significantly better target coverage; the median target coverage for the 100% isodose line was 50.7% for HDR brachytherapy plans, whereas it was 99.1% for SBRT plans. The dose distributions for critical organs were similar in both types of plans. The exceptions were the 25% isodose being significantly better in brachytherapy plans for rectum, and the 100% isodose exposure being higher in brachytherapy plans for rectum, bladder, and sigmoid colon. Some significant differences were also found in maximum doses received by a 2-cc volume of bladder in favor of SBRT plans. In addition, maximum bone marrow doses were significantly higher in SBRT plans.

CONCLUSION

SBRT plans achieved better target coverage and better dose distributions to critical organs except bone marrow compared with HDR brachytherapy plans in patients with locally advanced cervical cancer.

Can point doses predict volumetric dose to rectum and bladder: a CT-based planning study in high dose rate intracavitary brachytherapy of cervical carcinoma?

OBJECTIVE

Point doses, as defined by the International Commission on Radiation Units and Measurements (ICRU), are classically used to evaluate doses to the rectum and bladder in high dose rate intracavitary brachytherapy (HDR-ICBT) in cervical cancer. Several studies have shown good correlation between the ICRU point doses and the volumetric doses to these organs. In the present study we attempted to evaluate whether this correlation could be used to predict the volumetric doses to these organs.

METHODS

A total of 150 HDR-ICBT insertions performed between December 2006 and June 2008 were randomly divided into two groups. Group A (n=50) was used to derive the correlation between the point and volumetric doses using regression analysis. This was tested in Group B (n=100) insertions using studentised residuals and Bland-Altman plots.

RESULTS

Significant correlations were obtained for all volumetric doses and ICRU point doses for rectum and bladder in Group A insertions. The strongest correlation was found for the dose to 2 cc volumes (D(2cc)). The correlation coefficients for bladder and rectal D(2cc) versus the respective ICRU point doses were 0.82 and 0.77, respectively (p<0.001). Statistical validation of equations generated in Group B showed mean studentised residual values of 0.001 and 0.000 for the bladder and rectum. However, Bland-Altman analysis showed that the error range for these equations for bladder and rectum were ±64% and ±41% of the point A dose, respectively, which makes these equations unreliable for clinical use.

CONCLUSION

Volumetric imaging is essential to obtain proper information about volumetric doses.

Hypofractionated extracranial stereotactic radiotherapy boost for gynecologic tumors: a promising alternative to high-dose rate brachytherapy

The purpose of this study is to report toxicity and outcome results in patients with gynaecological tumours treated with a final boost using extra-cranial stereotactic radiotherapy (SRT) with a linac-based micro-multileaf collimator technique as an alternative to high-dose rate brachytherapy (HDR-BT). Since January 2002, 26 patients with either endometrial (n = 17) or cervical (n = 9) cancer were treated according to this protocol: 45-50.4 Gy external radiotherapy (RT) to the pelvic +/- para-aortic regions followed by a final SRT boost of 2 x 7 Gy to the vaginal vault (4-7 day interval between fractions). Median age was 62 years (37-74 range). Fifteen patients were diagnosed with adenocarcinoma, 7 with squamous-cell carcinoma, and 4 with sarcoma. FIGO stage I (n = 17), stage II (n = 7), and stage III (n = 2). Toxicity was scored according to RTOG/EORTC criteria. No severe (> grade-3) acute urinary or low-gastrointestinal (GI) toxicity was observed during treatment and up to 3 months after treatment completion. Moderate (grade < or = 3) acute urinary or low-GI toxicity was observed in 23% and 35% of patients, respectively. After a median follow-up of 47 months (4-77, range), late urinary, low-GI, and sexual > or = grade-2 (worst score) has been reported in 4%, 12% and 29.4% of patients, respectively. The 3-year loco-regional failure-free and overall survival rates were 96% and 95%, respectively. Preliminary results on feasibility, tolerance, and outcome with SRT are encouraging and may be considered a sound alternative to HDR-BT for gynecologic tumors.

Exploring the potential of mixed-source brachytherapy for the treatment of cervical cancer using high-dose rate 192Ir and/or 50 kV electronic sources

PURPOSE

In this study, computer modeling was used to compare the relative doses with the bladder, rectum, and bowel when two different brachytherapy modalities were used to treat cervical cancer with a tandem and ovoid applicator. A standard high-dose rate (HDR) (192)Ir treatment plan was compared with a "mixed-source" brachytherapy (MSB) treatment plan in which a 50 kV electronic brachytherapy X-ray source was substituted for (192)Ir as the tandem source.

METHODS AND MATERIALS

A total of 15 three-dimensional CT data sets from cervical cancer patients previously treated with tandem and ovoid applicator were evaluated for the study. Bladder, rectum, bowel, and target volumes were contoured and separate treatment plans were created for MSB and HDR (192)Ir applications. Dose-volume histograms were analyzed for each organ at risk.

RESULTS

The mean %V(25) for the bladder was 43% vs. 70% for MSB and HDR (192)Ir methods, respectively. Similarly, for the rectum mean %V(25) was 34% vs. 48% for MSB and HDR (192)Ir. For the bowel, the mean %V(25) was 28% vs. 43% for the MSB and HDR (192)Ir methods, respectively. In 16 of 45 organs at risk, %D(2 cc) values were higher for MSB than HDR (192)Ir.

CONCLUSIONS

MSB is capable of providing target coverage to the cervix, uterus, and paracervical regions equivalent to that provided by HDR (192)Ir, while significantly reducing the overall dose to the bladder, rectum, and bowel. This reduction is associated with small regions of increased dose in a significant proportion of patients.

Late effects after radiotherapy for locally advanced cervical cancer: comparison of two brachytherapy schedules and effect of dose delivered weekly

PURPOSE

To compare the severe late effects (Grade 3 or greater) for two groups of cervical cancer patients treated with the same external beam radiotherapy and two high-dose-rate intracavitary brachytherapy regimens and to investigate the influence of the dose delivered each week.

METHODS AND MATERIALS

For 120 patients, intracavitary brachytherapy was delivered with 33.6 Gy in eight fractions to Point A (HD group), and for 119, intracavitary brachytherapy was delivered with 29.4 Gy in seven fractions to Point A (LD group). The cumulative incidence of severe gastrointestinal and genitourinary late effects were calculated for both dose groups using Kaplan-Meier survival analysis. This method was also used to explore whether the number of weeks with different dose levels could predict the cumulative incidence of late effects.

RESULTS

The actuarial rate of developing severe gastrointestinal morbidity at 7 years was 10.7% and 8.3% for HD and LD groups, respectively. The rate for genitourinary morbidity was 6.6% for the HD group and 5.0% for the LD group, respectively. No significant difference was found between the two groups. The analyses showed that a marginally significant increase occurred in severe gastrointestinal complications as the number of weeks with a physical dose >20 Gy increased in the HD group (p = .047).

CONCLUSION

To establish dose-response relationships for late complications, three-dimensional imaging and dose-volume histogram parameters are needed. We found some indications that 20 Gy/wk is an upper tolerance level when the dose to the International Commission on Radiation Units and Measurements rectum point is 81 Gy(alpha/beta=3) (isoeffective [equivalent] dose of 2-Gy fractions). However, additional investigations using three-dimensional data are needed.

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.

MRI-guided 3D optimization significantly improves DVH parameters of pulsed-dose-rate brachytherapy in locally advanced cervical cancer

PURPOSE

To compare dose-volume histogram parameters of standard Point A and magnetic resonance imaging-based three-dimensional optimized dose plans in 21 consecutive patients who underwent pulsed-dose-rate brachytherapy (PDR-BT) for locally advanced cervical cancer.

METHODS AND MATERIALS

All patients received external beam radiotherapy (elective target dose, 45 Gy in 25-30 fractions; tumor target dose, 50-60 Gy in 25-30 fractions). PDR-BT was applied with a tandem-ring applicator. Additional ring-guided titanium needles were used in 4 patients and a multichannel vaginal cylinder in 2 patients. Dose planning was done using 1.5 Tesla T(1)-weighted and T(2)-weighted paratransversal magnetic resonance imaging scans. T(1)-weighted visible oil-containing tubes were used for applicator reconstruction. The prescribed standard dose for PDR-BT was 10 Gy (1 Gy/pulse, 1 pulse/h) for two to three fractions to reach a physical dose of 80 Gy to Point A. The total dose (external beam radiotherapy plus brachytherapy) was normalized to an equivalent dose in 2-Gy fractions using alpha/beta = 10 Gy for tumor, alpha/beta = 3 Gy for normal tissue, and a repair half-time of 1.5 h. The goal of optimization was dose received by 90% of the target volume (D(90)) of > or =85 Gy(alpha/beta10) in the high-risk clinical target volume (cervix and remaining tumor at brachytherapy), but keeping the minimal dose to 2 cm(3) of the bladder and rectum/sigmoid at <90 and <75 Gy(alpha/beta3), respectively.

RESULTS

Using three-dimensional optimization, all dose-volume histogram constraints were met in 16 of 21 patients compared with 3 of 21 patients with two-dimensional library plans (p < 0.001). Optimization increased the minimal target dose (D(100)) of the high-risk clinical target volume (p < 0.007) and decreased the minimal dose to 2 cm(3) for the sigmoid significantly (p = 0.03). For the high-risk clinical target volume, D(90) was 91 +/- 8 Gy(alpha/beta10) and D(100) was 76 +/- 5 Gy(alpha/beta10). The minimal dose to 2 cm(3) for the bladder, rectum, and sigmoid was 73 +/- 6, 67 +/- 6, and 69 +/- 6 Gy(alpha/beta3), respectively.

CONCLUSION

The results of our study have shown that magnetic resonance imaging-guided optimization of PDR-BT for locally advanced cervical cancer significantly improved the dose-volume histogram parameters.

High Dose-Rate Intracavitary Brachytherapy for Cervical Carcinomas With Lower Vaginal Infiltration

PURPOSE

This report presents the clinical applications of an automated treatment-planning program of high-dose-rate intracavitary brachytherapy (HDR-ICBT) for advanced uterine cervical cancer infiltrating the parametrium and the lower vagina.

METHODS AND MATERIALS

We adopted HDR-ICBT under optimized dose distribution for 22 cervical cancer patients with tumor infiltration of the lower half of the vagina. All patients had squamous cell carcinoma with International Federation of Gynecology and Obstetrics clinical stages IIB-IVA. After whole pelvic external beam irradiation with a median dose of 30.6 Gy, a conventional ICBT was applied as "pear-shaped" isodose curve. Then 3-4 more sessions per week of this new method of ICBT were performed. With a simple determination of the treatment volume, the cervix-parametrium, and the lower vagina were covered automatically and simultaneously by this program, that was designated as "utero-vaginal brachytherapy". The mean follow-up period was 87.4 months (range, 51.8-147.9 months).

RESULTS

Isodose curve for this program was "galaxy-shaped". Five-year local-progression-free survival and overall survival rates were 90.7% and 81.8%, respectively. Among those patients with late complications higher than Grade 2 Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer morbidity score, only one (4.5%) developed severe proctitis.

CONCLUSIONS

Because of the favorable treatment outcomes, this treatment-planning program with a simplified target-volume based dosimetry was proposed for cervical cancer with lower vaginal infiltration.

Late Rectal Complications Evaluated by Computed Tomography–Based Dose Calculations in Patients With Cervical Carcinoma Undergoing High-Dose-Rate Brachytherapy

PURPOSE

To investigate the efficacy of dose calculations at the computed tomography (CT)-based rectal point (CTRP) as a predictive factor for late rectal complications in patients with cervical carcinoma who were treated with a combination of high-dose-rate intracavitary brachytherapy and external beam radiotherapy.

METHODS AND MATERIALS

Ninety-two patients with uterine cervical carcinoma undergoing definitive radiotherapy alone were retrospectively analyzed. The median follow-up time for all patients was 32 months (range, 13-60 months). The cumulative biologically effective dose (BED) was calculated at the rectal reference point as defined by the International Commission on Radiation Units and Measurements Report 38 (BED(RP)) and at the CTRP (BED(CTRP)). Late rectal complications were recorded according to the Radiation Therapy Oncology Group grading system.

RESULTS

The late rectal complications were distributed as follows: Grade 0, 68 patients (74%); Grade 1, 20 patients (22%); Grade 2, 4 patients (4%). Univariate analysis showed that BED(RP), BED(CTRP), RP dose/point A dose ratio, and CTRP dose/point A dose ratio were significantly correlated with late rectal complications (p < 0.05). On multivariate analysis, patients with a rectal BED(CTRP) >/=140 Gy(3) presented with significantly greater frequency of rectal complications (p = 0.031).

CONCLUSIONS

The present results suggest that BED(CTRP) is a useful predictive factor for late rectal complications.

Computed Tomography-Based High-Dose-Rate Intracavitary Brachytherapy for Uterine Cervical Cancer: Preliminary Demonstration of Correlation Between Dose–Volume Parameters and Rectal Mucosal Changes Observed by Flexible Sigmoidoscopy

PURPOSE

To compare the dose-volume histogram (DVH) parameters obtained by three-dimensional gynecologic brachytherapy planning with the rectosigmoid mucosal changes observed by flexible sigmoidoscopy.

METHODS AND MATERIALS

Between January 2004 and July 2005, 71 patients with International Federation of Gynecology and Obstetrics Stage IB-IIIB uterine cervical cancer underwent computed tomography-based high-dose-rate intracavitary brachytherapy. The total dose (external beam radiotherapy [RT] plus intracavitary brachytherapy) to the International Commission of Radiation Units and Measurements rectal point (ICRU(RP)) and DVH parameters for rectosigmoid colon were calculated using the equivalent dose in 2-Gy fractions (alpha/beta = 3 Gy). Sigmoidoscopy was performed every 6 months after RT, with the 6-scale scoring system used to determine mucosal changes.

RESULTS

The mean values of the DVH parameters and ICRU(RP) were significantly greater in patients with a score of > or =2 than in those with a score <2 at 12 months after RT (ICRU(RP), 71 Gy(alpha/beta3) vs. 66 Gy(alpha/beta3), p = 0.02; D(0.1cc), 93 Gy(alpha/beta3) vs. 85 Gy(alpha/beta3), p = 0.04; D(1cc), 80 Gy(alpha/beta3) vs. 73 Gy(alpha/beta3), p = 0.02; D(2cc), 75 Gy(alpha/beta3) vs. 69 Gy(alpha/beta3), p = 0.02). The probability of a score of > or =2 showed a significant relationship with the DVH parameters and ICRU(RP) (ICRU(RP), p = 0.03; D(0.1cc), p = 0.05; D(1cc), p = 0.02; D(2cc), p = 0.02).

CONCLUSION

Our preliminary data have shown that DVH values of the rectosigmoid colon obtained by computed tomography-based three-dimensional brachytherapy planning are reliable and predictive of score > or =2 rectosigmoid mucosal changes.

Image-based three-dimensional treatment planning of intracavitary brachytherapy for cancer of the cervix: Dose-volume histograms of the bladder, rectum, sigmoid colon, and small bowel

PURPOSE

The purpose of this study was to evaluate dose-volume histograms (DVHs) of bladder, rectum, sigmoid colon, and small bowel using image-based three-dimensional treatment planning for intracavitary brachytherapy.

METHODS AND MATERIALS

Between 2001 and 2003, 22 patients with cancer of the cervix (1 IB1, 5 IB2, 11 IIB, 5 IIIB) were treated with computerized tomography (CT)-compatible high-dose-rate intracavitary applicators and underwent postimplant pelvic CT scans with the applicator in place. The volumes of organs at risk were digitized. For radiography-based planning, International Commission on Radiation Units and Measurements (ICRU) bladder and rectum point doses were calculated. For the CT-based planning, the DVHs were computed for the bladder, rectum, sigmoid colon, and small bowel. To compare doses to organs at risk, the minimum dose in 2.0cm(3) volume receiving the highest dose (D(2)) was determined from DVHs. These D(2) doses were compared with radiography-based ICRU point doses.

RESULTS

The mean ICRU bladder point dose (401cGy) was markedly underestimated compared to the mean bladder D(2) dose (484cGy). However, the mean ICRU rectal point dose (412cGy) did not differ significantly from the mean rectal D(2) dose (373cGy). The most frequent organ receiving the highest D(2) dose was the sigmoid colon in 9 of 22 patients (41%) followed by the rectum in 7 of 22 patients (32%) and small bowel in 6 of 22 patients (27%).

CONCLUSIONS

From CT-based three-dimensional (3-D) evaluation, the ICRU bladder point dose was substantially lower than bladder D(2) dose. Special attention should also be given to the areas of proximal rectum and sigmoid colon due to more frequent high D(2) dose in these areas.

Dosimetric evaluation of a newly designed low dose rate brachytherapy applicator for treatment of cervical cancer with extension into the lower vagina

Currently, patients having cervical cancer with extension into the lower vagina are being treated with a combination of the Fletcher–Suit applicator, which treats the cervix, and a vaginal cylinder, which treats the lower vagina. With this method, patients receive two separate implants—a procedure that creates greater uncertainty in the dose distribution and unnecessary patient inconvenience.

To reduce the uncertainty of the dose delivery and to eliminate patient inconvenience, a new applicator was designed and fabricated at the University of Kentucky for treatment of cervical cancer extending into the lower vagina. In addition, the geometric design of the new device allows for treatment of cervical cancer without extension into the lower vagina and simultaneously provides advantages relative to the commonly used Fletcher–Suit applicator.

The dosimetric characteristics of this new applicator (hereafter called Meigooni applicator) were determined using experimental procedures. The measurements were performed using tissue‐equivalent phantom material (Solid Water: Gammex RMI, Middleton, WI) that was machined to accommodate the applicator and LiF thermoluminescent dosimetry chips. The applicator was loaded with C137s brachytherapy sources in a standard loading scheme. A similar experimental procedure was performed using the currently available Fletcher–Suit mini‐ovoid applicator. The results obtained with each applicator were compared with the values calculated by two commercially available treatment planning systems.

The experiments showed that the Meigooni applicator allows for safe single treatment of cervical cancer that has extended into the lower vagina, eliminating the need for two separate treatment techniques. Moreover, the Meigooni applicator can function as an alternative to the Fletcher–Suit applicator for the treatment of patients with cervical cancer.

PACS number: 87.53.Jw

Dosimetric parameters that predict late rectal complications after curative radiotherapy in patients with uterine cervical carcinoma

BACKGROUND

Late rectal complication (LRC) was a major late complication in patients with uterine cervical carcinoma who were treated with a combination of external beam radiotherapy (EBRT) and high-dose-rate intracavitary irradiation (HDR-ICR). For the current study, the authors retrospectively evaluated dosimetric parameters that were correlated with LRC > or = Grade 2 in patients with uterine cervical carcinoma who were treated with curative radiotherapy, and they analyzed the appropriate dose estimates to the rectum that were predictive for LRC > or = Grade 2.

METHODS

Between July 1994 and September 2002, 157 patients who were diagnosed with Stage IB-IIIB cervical carcinoma and were treated with definitive radiotherapy were included. EBRT (41.4-66 grays [Gy] in 23-33 fractions) to the whole pelvis was delivered to all patients, with midline shielding performed after a 36-50.4 Gy external dose. HDR-ICR (21-39 Gy in 6-13 fractions to Point A) was administered at a rate of 2 fractions weekly after midline shielding of EBRT. LRC was scored using Radiation Therapy Oncology Group criteria. The total biologically effective dose (BED) at specific points, such as Point A (BED(Point A)), rectal point (BED(RP)), and maximal rectal point (BED(MP)), was determined by a summation of the EBRT and HDR-ICR components, in which the alpha/beta ratio was set to 3. Analyzed parameters included patient age, tumor size, stage, concurrent chemotherapy, ICR fraction size, RP ratio (dose at the rectal point according to the Point A dose), MP ratio (dose at the maximal rectal point according to the Point A dose), EBRT dose, BED(Point A), BED(RP), and BED(MP).

RESULTS

The 5-year actuarial overall rate of LRC > or = Grade 2 in all patients was 18.4%. Univariate analysis showed that the RP ratio, MP ratio, EBRT dose, BED(Point A), BED(RP), and BED(MP) were correlated with LRC > or = Grade 2 (P < 0.05). Multivariate analysis showed that, of all clinical and dosimetric parameters evaluated, only BED(RP) was correlated with LRC > or = Grade 2 (P = 0.009). The 5-year actuarial rate of LRC > or = Grade 2 was 5.4% in patients with a BED(RP) < 125 Gy(3) and 36.1% in patients with a BED(RP) > or = 125 Gy(3) (P < 0.001).

CONCLUSIONS

BED(RP) was a useful dosimetric parameter for predicting the risk of LRC > or = Grade 2 and should be limited to < 125 Gy(3) whenever possible to minimize the risk of LRC > or = Grade 2 in patients with uterine cervical carcinoma who are treated with a combination of EBRT and HDR-ICR. Cancer 2005.

Fractionated stereotactic radiotherapy boost for gynecologic tumors: an alternative to brachytherapy?

PURPOSE

A brachytherapy (BT) boost to the vaginal vault is considered standard treatment for many endometrial or cervical cancers. We aimed to challenge this treatment standard by using stereotactic radiotherapy (SRT) with a linac-based micromultileaf collimator technique.

METHODS AND MATERIALS

Since January 2002, 16 patients with either endometrial (9) or cervical (7) cancer have been treated with a final boost to the areas at higher risk for relapse. In 14 patients, the target volume included the vaginal vault, the upper vagina, the parametria, or (if not operated) the uterus (clinical target volume [CTV]). In 2 patients with local relapse, the CTV was the tumor in the vaginal stump. Margins of 6-10 mm were added to the CTV to define the planning target volume (PTV). Hypofractionated dynamic-arc or intensity-modulated radiotherapy techniques were used. Postoperative treatment was delivered in 12 patients (2 x 7 Gy to the PTV with a 4-7-day interval between fractions). In the 4 nonoperated patients, a dose of 4 Gy/fraction in 5 fractions with 2 to 3 days' interval was delivered. Patients were immobilized in a customized vacuum body cast and optimally repositioned with an infrared-guided system developed for extracranial SRT. To further optimize daily repositioning and target immobilization, an inflated rectal balloon was used during each treatment fraction. In 10 patients, CT resimulation was performed before the last boost fraction to assess for repositioning reproducibility via CT-to-CT registration and to estimate PTV safety margins around the CTV. Finally, a comparative treatment planning study between BT and SRT was performed in 2 patients with an operated endometrial Stage I cancer.

RESULTS

No patient developed severe acute urinary or low-intestinal toxicity. No patient developed urinary late effects (>6 months). One patient with a vaginal relapse previously irradiated to the pelvic region presented with Grade 3 rectal bleeding 18 months after retreatment. A second patient known to suffer from irritable bowel syndrome presented with Grade 1 abdominal pain after treatment. The estimated PTV margins around the CTV were 9-10 mm with infrared marker registration. External SRT succeeded in improving dose homogeneity to the PTV and in reducing the maximum dose to the rectum, when compared to BT.

CONCLUSION

These results suggest that the use of external SRT to deliver a final boost to the areas at higher risk for relapse in endometrial or cervical cancer is feasible, well tolerated, and may well be considered an acceptable alternative to BT.

Comparative study of reference points by dosimetric analyses for late complications after uniform external radiotherapy and high-dose-rate brachytherapy for cervical cancer

PURPOSE

This study aimed to correlate and compare the predictive values of rectal and bladder reference doses of uniform external beam radiotherapy without shielding and high-dose-rate intracavitary brachytherapy (HDRICB) with late sequelae in patients with uterine cervical cancer.

METHODS AND MATERIALS

Between September 1992 and December 1998, 154 patients who survived more than 12 months after treatment were studied. Initially, they were treated with 10-MV X-rays (44 to 45 Gy/22 to 25 fractions over 4 to 5 weeks) to the whole pelvis, after which HDRICB was performed using (192)Ir remote afterloading at 1-week intervals for 4 weeks. The standard prescribed dose for each HDRICB was 6.0 Gy to point A. Patient- and treatment-related-factors were evaluated for late rectal complications using logistic regression modeling.

RESULTS

The probability of rectal complications showed better correlation of dose-response with increasing total ICRU (International Committee on Radiotherapy Units and Measurements) rectal dose. Multivariate logistic regression demonstrated a high risk of late rectal sequelae in patients who developed rectal complications (p = 0.0001;relative risk, 15.06;95% CI, 2.89 approximately 43.7) and total ICRU rectal dose greater than 16 Gy (p = 0.02;relative risk, 2.07;95% CI, 1.13 approximately 4.55). The high risk factors for bladder complications were seen in patients who developed rectal complications (p = 0.0001;relative risk, 15.2;95% CI, 2.81 approximately 44.9) and total ICRU bladder dose greater than 24 Gy (p = 0.02;relative risk, 8.93;95% CI, 1.79 approximately 33.1).

CONCLUSION

This study demonstrated the predictive value of ICRU rectal and bladder reference dosing in HDRICB for patients receiving uniform external beam radiation therapy without central shielding. Patients who had a total ICRU rectal dose greater than 16 Gy, or a total ICRU bladder dose over 24 Gy, were at risk of late sequelae.