Optimization of high dose-rate cervix brachytherapy; Part I: Dose distribution

Aiming for 100% Local Control in Locally Advanced Cervical Cancer: The Role of Complex Brachytherapy Applicators and Intraprocedural Imaging

The use of brachytherapy for the treatment of gynecologic malignancies, particularly cervical cancer, has a long and rich history that is nearly as long as the history of radiation oncology itself. From the first gynecologic brachytherapy treatments in the early 20th century to the modern era, significant transformation has occurred driven largely by advancements in technology. The development of high-dose rate sources, remote afterloaders, novel applicators, and 3-dimensional image guidance has led to improved local control, and thus improved survival, solidifying the role of brachytherapy as an integral component in the treatment of locally advanced cervical cancer. Current research efforts examining novel magnetic resonance imaging sequences, active magnetic resonance tracking, and the application of hydrogel aim to further improve local control and reduce treatment toxicity.

A review of nonstandardized applicators digitization in Nucletron™ HDR procedures

The major errors in HDR procedures were failures to enter the correct treatment distance, which could be caused by either entering wrong transmission lengths or imprecisely digitizing the dwelling positions. Most of those errors were not easily avoidable by enhancing the HDR management level because they were caused by implementations of nonstandardized applicators utilizing transmission tubes of different lengths in standard HDR procedures. We performed this comprehensive study to include all possible situations with different nonstandardized applicators that frequently occurred in HDR procedures, provide corresponding situations with standard applicator as comparisons, list all possible errors and in planning, clarify the confusions in offsets setting, and provide mathematical and quantitative solutions for each given scenarios. Training on HDR procedures with nonstandardized applicators are normally not included in most residential program for medical physics, thus this study could be meaningful in both clinical and educational purpose. At precision of 1 mm, our study could be used as the essential and practical reference for finding the correct treatment length as well as locating the accurate dwelling positions in any HDR procedure with nonstandardized applicators.

Dosimetric advantages of using multichannel balloons compared to single-channel cylinders for high-dose-rate vaginal cuff brachytherapy

PURPOSE

To evaluate the dosimetric advantages of using multichannel balloons (MCBs) vs. single-channel cylinders (SCCs) for high-dose-rate vaginal cuff brachytherapy.

METHODS AND MATERIALS

A total of 91 consecutive high-dose-rate vaginal cuff brachytherapy including 45 MCB and 46 SCC treatments were reviewed. The clinical target volume (CTV) was defined as a 0.5-cm uniform expansion of the applicator surface from vaginal apex for 3 cm. For dosimetric comparison, we normalized prescription dose per fraction to 700 cGy and optimized each plan to cover at least 90% of CTV. CTV-1 cm, the true vaginal cuff volume, was defined as proximal 1 cm of CTV from vaginal apex. Four quality indices including conformity index (CI), dose homogeneity index, dose nonuniformity index, and overdose index were compared.

RESULTS

The CTV and CTV-1 cm were significantly larger for MCB cases compared to SCC cases. Evaluating CTV coverage, the mean dose homogeneity index and dose nonuniformity index were superior for MCB than SCC. No differences were noted regarding CI and overdose index between MCB and SCC cases. However, focusing on CTV-1 cm, the difference of CI became significant in favor of MCB cases. In addition, the mean point dose at 0.5-cm depth from the apex was significantly lower in SCC cases compared to cases by MCB treatment, indicating inadequate vaginal apex coverage by SCC treatment.

CONCLUSIONS

Compared to SCC, MCB treats a larger volume and offers a more conformal and homogeneous target coverage. In addition, a lower dose at the vaginal apex due to SCCs source anisotropy can be minimized.

Safety aspects of pulsed dose rate brachytherapy: analysis of errors in 1,300 treatment sessions

PURPOSE

To determine the safety of pulsed-dose-rate (PDR) brachytherapy by analyzing errors and technical failures during treatment.

METHODS AND MATERIALS

More than 1,300 patients underwent treatment with PDR brachytherapy, using five PDR remote afterloaders. Most patients were treated with consecutive pulse schemes, also outside regular office hours. Tumors were located in the breast, esophagus, prostate, bladder, gynecology, anus/rectum, orbit, head/neck, with a miscellaneous group of small numbers, such as the lip, nose, and bile duct. Errors and technical failures were analyzed for 1,300 treatment sessions, for which nearly 20,000 pulses were delivered. For each tumor localization, the number and type of occurring errors were determined, as were which localizations were more error prone than others.

RESULTS

By routinely using the built-in dummy check source, only 0.2% of all pulses showed an error during the phase of the pulse when the active source was outside the afterloader. Localizations treated using flexible catheters had greater error frequencies than those treated with straight needles or rigid applicators. Disturbed pulse frequencies were in the range of 0.6% for the anus/rectum on a classic version 1 afterloader to 14.9% for orbital tumors using a version 2 afterloader. Exceeding the planned overall treatment time by >10% was observed in only 1% of all treatments. Patients received their dose as originally planned in 98% of all treatments.

CONCLUSIONS

According to the experience in our institute with 1,300 PDR treatments, we found that PDR is a safe brachytherapy treatment modality, both during and outside of office hours.

Potential of dose optimisation in MRI-based PDR brachytherapy of cervix carcinoma

BACKGROUND AND PURPOSE

In this study on PDR treatment planning of utero-vaginal carcinoma, we analysed the dosimetry of traditional X-ray based plans as it presents on MR images. The potential gain of MRI-based dose optimisation was assessed.

PATIENTS AND METHODS

Sixteen patients boosted with PDR brachytherapy after external beam therapy were included. The clinical X-ray based plans were projected on MR images. The GTV, HR-CTV and IR-CTV were retrospectively contoured, as well as the bladder, rectum and sigmoid colon. The dose in the critical organs and target coverage was investigated. In a second phase, the plans were manually optimised using the MR information. The objectives were to lower the dose in the critical organs (<or= 85 Gy(alphabeta3) for bladder, <or= 75 Gy(alphabeta3) for rectum and sigmoid colon) and to increase the HR-CTV dose to D90 >or= 85 Gy(alphabeta10).

RESULTS

In the X-ray based plans, D(2cc) in bladder and sigmoid colon exceeded the tolerance doses in 10/16 and 7/16 patients, respectively. Coverage of the IR-CTV with the 60 Gy(alphabeta10) was acceptable. D90 of the HR-CTV was below 85 Gy(alphabeta10) in 13 out of 16 patients. After optimisation, the dose constraints in the OAR were not exceeded anymore in any patient. The average D(2cc) dose reduction was 7+/-6 Gy(alphabeta3) in the bladder and 7+/-4 Gy(alphabeta3) in the sigmoid colon for those patients in which the dose constraint was initially exceeded. In addition, an average dose increase of 3 Gy(alphabeta10) was accomplished in the HR-CTV.

CONCLUSIONS

MRI-based dose optimisation can play an important role to reduce the dose delivered to the critical organs and to improve target coverage.

Cervical brachytherapy utilizing ring applicator: Comparison of standard and conformal loading

PURPOSE

Afterloading high-dose-rate brachytherapy (HDR) treatment of cervical cancer with cross-sectional imaging and three-dimensional (3D) reconstruction offers opportunities for individualized conformal treatment planning rather than fixed point-A dosimetry.

METHODS AND MATERIALS

Between June 2003 and September 2004, 15 patients with FIGO Stage 1B-4A cervical carcinoma, median age 56 years, were treated with radical external-beam radiotherapy to pelvis, including paraortic nodes if positive on staging investigations. Fourteen patients received concurrent cisplatin chemotherapy. All patients received HDR brachytherapy administered by intrauterine tube and ring applicator. Clinical target volume (CTV) and organs at risk (OAR)--rectum, bladder, and small bowel--were outlined from postinsertion CT planning scans. Planning target volume (PTV) was derived by use of 2-mm to 3-mm 3D expansion. A standard plan was produced that delivered 6 Gy to point A, and a second plan delivered 6 Gy to PTV. Constraints were defined for the OAR: bladder, 6 Gy; rectum, 5 Gy; and small bowel, 5 Gy. Dosimetric comparison was performed by use of the Baltas conformal index (COIN).

RESULTS

Mean COIN values were 0.39 for conformal plans and 0.33 for standard plans (p = 0.001); mean D95 values were 4.79 Gy and 4.50 Gy, respectively.

CONCLUSION

The majority of patients achieved a plan closer to ideal for coverage of PTV, with minimization of radiation received by normal tissues for conformal loading measured by COIN compared with fixed point-A prescription that used the cervical ring applicator.

Comparison of traditional low-dose-rate to optimized and nonoptimized high-dose-rate tandem and ovoid dosimetry

PURPOSE

Few dose specification guidelines exist when attempting to perform high-dose-rate (HDR) dosimetry. The purpose of this study was to model low-dose-rate (LDR) dosimetry, using parameters common in HDR dosimetry, to achieve the "pear-shape" dose distribution achieved with LDR tandem and ovoid applications.

METHODS AND MATERIALS

Radiographs of Fletcher-Suit LDR applicators and Nucletron "Fletcher-like" HDR applicators were taken with the applicators in an idealized geometry. Traditional Fletcher loadings of 3M Cs-137 sources and the Theratronics Planning System were used for LDR dosimetry. HDR dosimetry was performed using the Nucletron Microselectron HDR UPS V11.22 with an Ir-192 source. Dose optimization points were initially located along a line 2 cm lateral to the tandem, beginning at the tandem tip at 0.5-cm intervals, ending at the sail, and optimized to 100% of the point A dose. A single dose optimization point was also placed laterally from the center of each ovoid equal to the radius of the ovoid (ovoid surface dose). For purposes of comparison, dose was also calculated for points A and B, and a point located 1 cm superior to the tandem tip in the plane of the tandem, (point F). Four- and 6-cm tandem lengths and 2.0-, 2.5-, and 3.0-cm ovoid diameters were used for this study. Based on initial findings, dose optimization schemes were developed to best approximate LDR dosimetry. Finally, radiographs were obtained of HDR applications in two patients. These radiographs were used to compare the optimization schemes with "nonoptimized" treatment plans.

RESULTS

Calculated doses for points A and B were similar for LDR, optimized HDR, and nonoptimized HDR. The optimization scheme that used tapered dose points at the tandem tip and optimized a single ovoid surface point on each ovoid to 170% of point A resulted in a good approximation of LDR dosimetry. Nonoptimized HDR resulted in higher doses at point F, the bladder, and at points lateral to the tandem tip than both the optimized plan or the LDR plan.

CONCLUSION

Optimized HDR allows specification of dose to points of interest, can approximate LDR dosimetry, and appears superior to nonoptimized HDR treatment planning, at least at the tandem tip. An optimization scheme is presented that approximates LDR dosimetry.

The American Brachytherapy Society recommendations for high-dose-rate brachytherapy for carcinoma of the endometrium

PURPOSE

To develop recommendations for use of high-dose-rate (HDR) brachytherapy in patients with endometrial cancer.

METHODS

A panel of members of the American Brachytherapy Society (ABS) performed a literature review, supplemented their clinical experience, and formulated recommendations for endometrial HDR brachytherapy.

RESULTS

The ABS endorses the National Comprehensive Cancer Network (NCCN) guidelines for indications for radiation therapy for patients with endometrial cancer and the guidelines on HDR quality assurance of the American Association on Physicists in Medicine (AAPM). The ABS made specific recommendations for HDR applicator selection, insertion techniques, target volume definition, dose fractionation, and specifications for postoperative adjuvant vaginal cuff therapy, for vaginal recurrences, and for medically inoperable primary endometrial cancer patients. The ABS recommends that applicator selection should be based on patient and target volume geometry. The dose prescription point should be clearly specified. The treatment plan should be optimized to conform to the target volume whenever possible while recognizing the limitations of computer optimization. Suggested doses were tabulated for treatment with HDR alone, and in combination with external beam radiation therapy (EBRT), when applicable. For intravaginal brachytherapy, the largest diameter applicator should be selected to ensure close mucosal apposition. Doses should be reported both at the vaginal surface and at 0.5-cm depth irrespective of the dose prescription point. For vaginal recurrences, intracavitary brachytherapy should be restricted to patients with nonbulky (< 0.5-cm thick) disease. Patients with bulky (> 0.5-cm thick) recurrences should be treated with interstitial techniques. For medically inoperable patients, an appropriate applicator that will allow adequate irradiation of the entire uterus should be selected.

CONCLUSION

Recommendations are made for HDR brachytherapy for endometrial cancer. Practitioners and cooperative groups are encouraged to use these recommendations to formulate their treatment and dose reporting policies. This will lead to meaningful comparisons of reports from different institutions and lead to advances and appropriate use of HDR.

Management of stage I-B, II-A, and II-B carcinoma of the cervix with high-dose-rate brachytherapy: initial results of an institutional clinical trial

In 1989, the University of Miami began a program incorporating high-dose-rate (HDR) brachytherapy into the definitive treatment of patients with invasive carcinoma of the cervix. Patients received an average total dose to point A of 5,511 cGy (range 4,280-6,360 cGy) in an average of 57 days (range 39-84 days). An analysis of the first 24 cases found 11 FIGO Stage I-B, four Stage II-A, and nine Stage II-B tumors. At the end of all radiation therapy, 19/24 patients' tumors (79.2%) had undergone a clinical complete response (CR). With median follow-up of 26 months (range 14-63 months), three have relapsed locally, two regionally, and six in extrapelvic sites. Almost two-thirds of all failures occurred in patients with tumors >4 cm, who also took more than 8 weeks to complete their treatment. Overall 2-year actuarial survival for the entire study group is approximately 74%. A univariate analysis determined that clinical stage (P = 0.02), overall treatment time (P = 0.03), tumor size (P = 0.05), and response at the end of therapy (P = 0.005) were significant prognostic factors. Multivariate analysis showed that tumor response to therapy was the most important prognosticator of outcome (P = 0.001). Besides five cases of apical vaginal stenosis, there have been no reported chronic complications in this cohort of patients. A prospectively randomized trial is recommended to compare the efficacy of HDR vs. low-dose-rate brachytherapy in cervical carcinoma.

Dose determination in high dose-rate brachytherapy

Although high dose-rate brachytherapy with a single, rapidly moving radiation source is becoming a common treatment modality, a suitable formalism for determination of the dose delivered by a moving radiation source has not yet been developed. At present, brachytherapy software simulates high dose-rate treatments using only a series of stationary sources, and consequently fails to account for the dose component delivered while the source is in motion. We now describe a practical model for determination of the true, total dose administered. The algorithm calculates both the dose delivered while the source is in motion within and outside of the implanted volume (dynamic component), and the dose delivered while the source is stationary at a series of fixed dwell points. It is shown that the dynamic dose element cannot be ignored because it always increases the dose at the prescription points and, in addition, distorts the dose distribution within and outside of the irradiated volume. Failure to account for the dynamic dose component results in dosimetric errors that range from significant (> 10%) to negligible (< 1%), depending on the prescribed dose, source activity, and source speed as defined by the implant geometry.