Dose-dependent differential effects of low and pulsed dose-rate brachytherapy in a radioresistant syngenic rat prostate tumour model

PURPOSE: To study the response of the Dunning prostate carcinoma (R3327-AT1 subline) to continuous low dose-rate (CLDR) and pulsed dose-rate (PDR) brachytherapy. MATERIALS AND METHODS: After subcutaneous tumour transplantation into the thigh of the Copenhagen rat, doses of 0, 20, 30, 40 and 50 Gy were applied to the tumour surface (tumour diameter 9+/-1mm). Eight animals were irradiated per dose group and exposure condition. Interstitial PDR ((192)Ir source, 37 GBq) and CLDR ((192)Ir seed, 150 MBq) brachytherapy were carried out with 0.75 Gy/pulse h(-1) and a dose-rate of 0.75Gyh(-1), respectively. Treatment response was assessed in terms of growth delay expressed as the time (T(5)) required for each tumour to reach five times the initial tumour volume. RESULTS: The median T(5) times for the CLDR groups (in the order: control, 20, 30, 40, 50 Gy) were 12 (12), 54.5 (21), 64.5 (31), 85.5 (51), and 65 (47.5) days. Values after PDR brachytherapy are given in parentheses and resulted in a significantly impaired tumour growth delay (log-rank test) in the 20Gy (p =0.006) and 30 Gy (p =0.036) groups. No significant difference was found in the 40-50 Gy dose range. CONCLUSIONS: In contrast to previous results and predictions of biological models we observed dose-dependent differential effects of PDR and CLDR brachytherapy with reduced efficacy of PDR in the lower dose range.     

Comparison of 60Cobalt and 192Iridium Sources in High Dose Rate Afterloading Brachytherapy

PURPOSE: (60)Co sources with dimensions identical to those of (192)Ir have recently been made available in clinical brachytherapy. A longer half time reduces demands on logistics and quality assurance and perhaps costs. MATERIAL AND METHODS: Comparison of the physical properties of (60)Co and (192)Ir with regard to brachytherapy. RESULTS: Required activities for the same air kerma rate are lower by a factor of 2.8 for (60)Co. Differential absorption in tissues of different densities can be neglected. Monte Carlo calculations demonstrate that integral dose due to radial dose fall off is higher for (192)Ir in comparison to (60)Co within the first 22 cm from the source (normalization at 1 cm). At larger distances this relationship is reversed. CONCLUSION: Clinical examples for intracavitary and interstitial applications however, show practically identical dose distributions in the treatment volume.     

American Brachytherapy Society consensus guidelines for locally advanced carcinoma of the cervix. Part III: low-dose-rate and pulsed-dose-rate brachytherapy

PurposeTo develop a guideline for quality practice of low-dose-rate (LDR) and pulsed-dose-rate (PDR) brachytherapy for locally advanced cervical cancer.MethodsMembers of the American Brachytherapy Society (ABS) with expertise in cervical cancer brachytherapy formulated updated guidelines for LDR and PDR brachytherapy for locally advanced (International Federation of Gynecology and Obstetrics [FIGO] Stages IB2–IVA) cervical cancer based on literature review and clinical experience.ResultsThe ABS strongly recommends the use of brachytherapy as a component of the definitive treatment of locally advanced cervical carcinoma. Precise applicator placement is necessary to maximize the probability of achieving local control without major side effects. The ABS recommends a cumulative delivered dose of approximately 80–90 Gy for definitive treatment. Dosimetry must be performed after each insertion before treatment delivery. The dose delivered to point A should be reported for all intracavitary brachytherapy applications regardless of treatment planning technique. The ABS also recommends adoption of the Groupe Européen de Curiethérapie-European Society for Therapeutic Radiology and Oncology guidelines for contouring, image-based treatment planning and dose reporting. Interstitial brachytherapy may be considered for a small proportion of patients whose disease cannot be adequately encompassed by intracavitary application and should be performed by practitioners with special expertise in these procedures. Quality management measures must be performed, and follow-up information should also be obtained.ConclusionsUpdated ABS guidelines are provided for LDR and PDR brachytherapy for locally advanced cervical cancer. Practitioners and cooperative groups are encouraged to use these guidelines to formulate their clinical practices and to adopt dose-reporting policies that are critical for outcome analysis.     

Daytime pulsed dose rate brachytherapy as a new treatment option for previously irradiated patients with recurrent oesophageal cancer

The aim of this study was to evaluate the feasibility, effects, and toxicity of pulsed dose rate (PDR) brachytherapy for re-irradiation of oesophageal carcinoma. A total of 16 patients (median age 67 years) with inoperable recurrences from oesophageal cancer after primary radio-(chemo)-therapy (median 50 Gy) were re-irradiated using PDR brachytherapy ((192)Ir, 37 GBq). Treatment was carried out on an outpatient basis applying a weekly 5 Gy daytime schedule (0.5 Gy pulse(-1) h(-1), total dose 15-20 Gy). The dose was prescribed 10 mm from the mid-dwell position and encompassed the clipped tumour extension with 2 cm margins. The use of clips for delineation of tumour extent and catheter movement during irradiations was evaluated. All 61 PDR treatments were applied safely. The median catheter movement was 5 mm, range 2-12 mm. After a median follow-up of 8 months, three patients had a complete and five a partial remission. Body weight increased in 5 of 16 (31%) and was stable in 4 of 16 (25%) patients, respectively. The median grade 2 (RTOG/EORTC) dysphagia-free survival was 17 months. Seven patients experienced grade 1, five grade 2, and one grade 3 late toxicity. Three patients with uncontrolled locoregional disease showed grade 4 complications (oesophago-tracheal fistulae (n=2), fatal arterial bleeding (n=1). Daytime PDR brachytherapy proved to be feasible and provided effective palliation. Toxicity remains a major problem. Thus, total dose should be restricted to <15 Gy in this palliative situation.     

Dose-dependent differential effects of low and pulsed dose-rate brachytherapy in a radioresistant syngenic rat prostate tumour model

Purpose : To study the response of the Dunning prostate carcinoma (R3327-AT1 subline) to continuous low dose-rate (CLDR) and pulsed dose-rate (PDR) brachytherapy. Materials and methods : After subcutaneous tumour transplantation into the thigh of the Copenhagen rat, doses of 0, 20, 30, 40 and 50 Gy were applied to the tumour surface (tumour diameter 9 ±1mm). Eight animals were irradiated per dose group and exposure condition. Interstitial PDR (192 Ir source, 37 GBq) and CLDR (192 Ir seed, 150 MBq) brachytherapy were carried out with 0.75 Gy/pulse h -1 and a dose-rate of 0.75Gyh -1, respectively. Treatment response was assessed in terms of growth delay expressed as the time (T 5) required for each tumour to reach five times the initial tumour volume. Results : The median T 5 times for the CLDR groups (in the order: control, 20, 30, 40, 50 Gy) were 12 (12), 54.5 (21), 64.5 (31), 85.5 (51), and 65 (47.5) days. Values after PDR brachytherapy are given in parentheses and resulted in a significantly impaired tumour growth delay (log-rank test) in the 20Gy (p =0.006) and 30 Gy (p =0.036) groups. No significant difference was found in the 40-50 Gy dose range. Conclusions : In contrast to previous results and predictions of biological models we observed dose-dependent differential effects of PDR and CLDR brachytherapy with reduced efficacy of PDR in the lower dose range.     

American Brachytherapy Society–Groupe Européen de Curiethérapie–European Society of Therapeutic Radiation Oncology (ABS-GEC-ESTRO) consensus statement for penile brachytherapy

PurposeTo develop a consensus statement between the American Brachytherapy Society (ABS) and Groupe Européen de Curiethérapie/European Society for Therapeutic Radiation and Oncology (GEC-ESTRO) for the use of brachytherapy in the primary management of carcinoma of the penis.Methods and MaterialsThe American Brachytherapy Society and Groupe Européen de Curiethérapie/European Society for Therapeutic Radiation and Oncology convened a group of expert practitioners and physicists to develop a statement for the use of ¹⁹²Ir in low-dose-rate (LDR), pulse-dose-rate, and high-dose-rate (HDR) brachytherapy for penile cancer.ResultsDecades of brachytherapy experience with LDR ¹⁹²Ir wire and pulse-dose-rate ¹⁹²Ir sources for this rare malignancy indicate a penile preservation rate of 70% at 10 years postimplant. Chief morbidities remain stenosis of the urethral meatus and soft tissue ulceration at the primary site. Nonhealing ulceration can be successfully managed with various measures including hyperbaric oxygen treatment. HDR brachytherapy implant procedures are technically similar to LDR. The optimal HDR dose and fractionation schemes are being developed.ConclusionsThe good tumor control rates, acceptable morbidity, and functional organ preservation warrant recommendation of brachytherapy as the initial treatment for invasive T1, T2, and selected T3 penile cancers.     

Intracavitary dosimetry of a high-activity remote loading device with oscillating source

Dosimetric experiments have been carried out in order to obtain the dose distribution in water around a Fletcher applicator loaded by a Buchler system containing two 137Cs 148 GBq (4 Ci) sources and one 192Ir 740 GBq (20 Ci) source. The mechanical system which controls the movement of the 192Ir source and the resulting motion of the source are described. The dose distribution around the sources was measured photographically and by a PWT Normal 0.22 cm3 ionisation chamber. The absolute dose rate was measured along the lateral axes of the sources. The measurements of exposure in water near the sources were corrected for the effect due to the finite volume of the chamber. The "quantisation method" described by Cassell (1983) was utilised to calculate the variation of the dose rate along the lateral axes of the sources. The dose distribution around both 192Ir and 137Cs sources was found to be spherical for angles greater than 40 degrees from the longitudinal axes of the sources. A simple algorithm fitting the data for the moving 192Ir source is proposed. A program written in FORTRAN IV and run on a Univac 1100/80 computer has been used to plot dose distributions on anatomical data obtained from CT images. The uncertainties of the measurements and calculations have been examined and the greatest error has been found to be 5.5%. The clinical significance of the treatment method is discussed.     

LDR vs. HDR brachytherapy for localized prostate cancer: the view from radiobiological models

PURPOSE: Permanent LDR brachytherapy and temporary HDR brachytherapy are competitive techniques for clinically localized prostate radiotherapy. Although a randomized trial will likely never be conducted comparing these two forms of brachytherapy, a comparative radiobiological modeling analysis proves useful in understanding some of their intrinsic differences, several of which could be exploited to improve outcomes. METHODS AND MATERIALS: Radiobiological models based upon the linear quadratic equations are presented for fractionated external beam, fractionated (192)Ir HDR brachytherapy, and (125)I and (103)Pd LDR brachytherapy. These models incorporate the dose heterogeneities present in brachytherapy based upon patient-derived dose volume histograms (DVH) as well as tumor doubling times and repair kinetics. Radiobiological parameters are normalized to correspond to three accepted clinical risk factors based upon T-stage, PSA, and Gleason score to compare models with clinical series. Tumor control probabilities (TCP) for LDR and HDR brachytherapy (as monotherapy or combined with external beam) are compared with clinical bNED survival rates. Predictions are made for dose escalation with HDR brachytherapy regimens. RESULTS: Model predictions for dose escalation with external beam agree with clinical data and validate the models and their underlying assumptions. Both LDR and HDR brachytherapy achieve superior tumor control when compared with external beam at conventional doses (<70 Gy), but similar to results from dose escalation series. LDR brachytherapy as boost achieves superior tumor control than when used as monotherapy. Stage for stage, both LDR and current HDR regimens achieve similar tumor control rates, in agreement with current clinical data. HDR monotherapy with large-dose fraction sizes might achieve superior tumor control compared with LDR, especially if prostate cancer possesses a high sensitivity to dose fractionation (i.e., if the alpha/beta ratio is low). CONCLUSIONS: Radiobiological models support the current clinical evidence for equivalent outcomes in localized prostate cancer with either LDR or HDR brachytherapy using current dose regimens. However, HDR brachytherapy dose escalation regimens might be able to achieve higher biologically effective doses of irradiation in comparison to LDR, and hence improved outcomes. This advantage over LDR would be amplified should prostate cancer possess a high sensitivity to dose fractionation (i.e., a low alpha/beta ratio) as the current evidence suggests.     

Modeling of the direction modulated brachytherapy tandem applicator using the Oncentra Brachy advanced collapsed cone engine

PurposeThe direction modulated brachytherapy (DMBT) magnetic resonance–compatible tandem applicator, made from a tungsten alloy rod, has six symmetric peripheral grooves, designed specifically to enhance intensity modulation capacity through achieving directional radiation dose profiles. In this work, the directional dose distributions of the DMBT tandem were modeled and calculated with the Oncentra Brachy advanced collapsed cone engine (ACE), which was validated against Monte Carlo (MC) calculations.Methods and MaterialThe prototype 3D tandem applicator model was created for use in the Oncentra Brachy treatment planning system. The ¹⁹²Ir source was placed inside a DMBT tandem in one and six channels as a single dwell position (DP) per channel with the same index length, as well as 1 DP in a standard tandem. Dose distributions were calculated in a water medium by both ACE and MC and compared.ResultsFor 1DP/6DP inside the DMBT and 1DP inside the standard tandem, respectively, the mean dose differences were 3.5/3.3% and <2.8% with the range of 0.1%–6.5%/0.2%–5% and 0.1%–5%, between ACE and MC, respectively.ConclusionsThe DMBT tandem is successfully modeled in a commercial treatment planning system. The ACE algorithm is capable of accurately calculating highly directional dose distributions generated by a dense tungsten alloy contained within the DMBT tandem, with agreements achieved within <3.5%.     

Single dose irradiation response of pig skin: a comparison of brachytherapy using a single, high dose rate iridium-192 stepping source with 200 kV X-rays

An experimental brachytherapy model has been developed to study acute and late normal tissue reactions as a tool to examine the effects of clinically relevant multifractionation schedules. Pig skin was used as a model since its morphology, structure, cell kinetics and radiation-induced responses are similar to human skin. Brachytherapy was performed using a microSelectron high dose rate (HDR) afterloading machine with a single stepping source and a custom-made template. In this study the acute epidermal reactions of erythema and moist desquamation and the late dermal reactions of dusky mauve erythema and necrosis were evaluated after single doses of irradiation over a follow-up period of 16 weeks. The major aims of this work were: (a) to compare the effects of iridium-192 (192Ir) irradiation with effects after X-irradiation; (b) to compare the skin reactions in Yorkshire and Large White pigs; and (c) to standardize the methodology. For 192Ir irradiation with 100% isodose at the skin surface, the 95% isodose was estimated at the basal membrane, while the 80% isodose covered the dermal fat layers. After HDR 192Ir irradiation of Yorkshire pig skin the ED50 values (95% isodose) for moderate/severe erythema and moist desquamation were 24.8 Gy and 31.9 Gy, respectively. The associated mean latent period (+/- SD) was 39 +/- 7 days for both skin reactions. Late skin responses of dusky mauve erythema and dermal necrosis were characterized by ED50 values (80% isodose) of 16.3 Gy and 19.5 Gy, with latent periods of 58 +/- 7 days and 76 +/- 12 days, respectively. After X-irradiation, the incidence of the various skin reactions and their latent periods were similar. Acute and late reactions were well separated in time. The occurrence of skin reactions and the incidence of effects were comparable in Yorkshire and Large White pigs for both X-irradiation and HDR 192Ir brachytherapy. This pig skin model is feasible for future studies on clinically relevant multifractionation schedules in a brachytherapy setting.     

5-Year Results of Pulsed Dose Rate Brachytherapy Applied as a Boost after Breast-Conserving Therapy in Patients at High Risk for Local Recurrence from Breast Cancer

PURPOSE: The aim of this study was to evaluate effect, toxicity, and cosmesis of a prospectively applied pulsed dose rate (PDR) brachytherapy boost schedule in patients with stage I/II/IIIa invasive breast cancer. PATIENTS AND METHODS: A total of 113 patients were treated after breast-conserving surgery (BCS) and external beam radiotherapy (median 50 Gy, range 46-52). The boost dose was graded in accordance to the pathologic tumor characteristics: 20-25 Gy: incomplete resection (n = 34), vascular invasion (n = 27), close margin resection (n = 41); 15 Gy: T2G3 stage (n = 11). PDR brachytherapy (37 GBq, (192)Ir source) was carried out after geometric volume optimization with 1 Gy/pulse/h. The implantation and dose specification were performed similar to the rules of the Paris system. RESULTS: The overall local failure rate after a median follow-up of 61 months was 4.4% (5/113). The actuarial 5- and 8-year local recurrence-free survival rates were 95% and 93%, respectively. Cosmesis was rated by 90% of the patients as excellent or good. 14/113 patients experienced grade III (all caused by planar telangiectasia) and none of the patients grade IV late toxicity of the skin (RTOG/EORTC). A boost dose of 25 Gy resulted in a significantly higher rate of late toxicity (Fisher's exact test, p < 0.01). CONCLUSIONS: PDR brachytherapy is safe, effective, and provides good cosmesis. A CLDR breast boost can be replaced by PDR brachytherapy without significant loss of therapeutic ratio.     

CT-Guided Interstitial Brachytherapy of Primary and Secondary Lung Malignancies

BACKGROUND AND PURPOSE: CT-guided interstitial brachytherapy of primary lung malignancies and pulmonary metastases represents a novel interventional technique, combining conventional high-dose-rate (HDR) iridium-192 ((192)Ir) brachytherapy with modern CT guidance for applicator positioning and computer-aided 3-D radiation treatment planning. The purpose of this study was to assess safety and efficacy of this technique. PATIENTS AND METHODS: 30 patients with 83 primary or secondary lung malignancies were recruited in a prospective nonrandomized trial (Table 1). After catheter positioning under CT fluoroscopy, a spiral CT was acquired for treatment planning (Figure 1). All but two patients received a defined single dose (coverage > 99%) of at least 20 Gy from a (192)Ir source in HDR technique. RESULTS: Adverse effects were nausea (n = 3, 6%), minor (n = 6, 12%) and one major pneumothorax (2%). Post intervention, no changes of vital capacity and forced expiratory volume could be detected. The median follow-up period was 9 months (1-21 months) with a local tumor control of 91% at 12 months (Figure 2). CONCLUSION: CT-guided interstitial brachytherapy proved to be safe and effective for the treatment of primary and secondary lung malignancies.     

Low-dose-rate vs. high-dose-rate intracavitary brachytherapy for carcinoma of the cervix: The University of Alabama at Birmingham (UAB) experience

PURPOSE: To review the clinical outcome retrospectively of cervical cancer patients treated definitively with either high-dose-rate (HDR) or low-dose-rate (LDR) brachytherapy. METHODS AND MATERIALS: One hundred sixty patients (44 Stage I, 83 Stage II, and 33 Stage III) were treated from 1990 to 2000 with curative intent for carcinoma of the cervix. One hundred three LDR patients were compared to 57 HDR patients. Two groups were treated during the same period. An external beam dose of 45 Gy to the entire pelvis was delivered at 1.8 Gy per fraction to most patients before the first intracavitary insertion in both groups. Brachytherapy was delivered in one to two LDR implants or four to five HDR implants at 6 Gy per fraction. The prescribed dose to Point A for LDR was at least 80-85 Gy. Patient characteristics were similar for each cohort. Point A doses were similar for each stage. The primary endpoints assessed were survivals and failure sites. Endpoints were estimated using the Kaplan-Meier method and comparisons between treatment groups were performed using the log-rank test. RESULTS: The median followup was 48 months for the LDR group and 59 months for the HDR group. For all stages combined and stage for stage in both groups, there was no statistically significant difference in locoregional control, cause-specific survival, and overall survival for LDR compared with HDR. Locoregional control and overall survival were 78% and 60% for LDR compared to 76% and 55% for HDR at 3 years, respectively (p = 0.96 and p = 0.48). Median cause-specific survival values for LDR vs. HDR were 71 and 81 months, respectively (p = 0.62). The cause-specific survival for LDR patients was 62% compared with 59% for HDR patients at 3 years. For Stage IB2, II, and III LDR patients, cause-specific survival rates were 62%, 67%, and 45%, compared to 67%, 57%, and 33% for HDR at 3 years, respectively (p = 0.75, p = 0.95, and p = 0.48). For patients with a recorded site of first failure, the most common site was locoregional (56%) and then distant metastases (26%). Eight patients who were cancer free developed late complications requiring surgical intervention. Two patients were in the HDR group (3.5%) and 5 in the LDR group (4.8%). CONCLUSIONS: Similar outcome was observed for LDR compared with HDR intracavitary brachytherapy for the entire cohort. In this review, HDR group was not inferior to LDR group in advanced stages. This is likely because our patients were treated with brachytherapy after a high dose of external pelvic radiotherapy in both LDR and HDR patients.     

Dosimetric study of the applications of intracavitary radiotherapy using a remote-loading device with mobile sources

This paper deals with the dosimetric aspects of remote-controlled afterloading irradiation devices used in brachytherapy. An afterloading device (Gammamed III) is available at Varese Regional Hospital, for intracavitary radiation therapy (low-dose rate). In the Gammamed afterloading method the radioactive sources contained in an applicator are introduced into the patient's body. This device is based on the principle of stepwise movement of three 137Cs radioactive sources (1.48; 2.96; 1.48 GBq). The results are here presented of a dosimetric study on the correspondence between algorithm for calculating isodose distributions in intracavitary treatment and experimental measurements in a phantom. Doses around the moving source were measured using thermoluminescent LiF-100 dosimeters (1 x 1 x 6 mm). Measurements were taken in a polystyrene phantom. Isodose distributions were estimated by reading the optical density of radiographic films. Doses were found to range around the calculated values within +/- 4% (with thermoluminescent dosimeters) and within +/- 8% (with films). The close agreement between the experimental and the calculated doses confirmed the acceptability of the dose distribution calculation model for the moving sources, and the Gammamed reliability.     

Is simulation necessary for each high-dose-rate tandem and ovoid insertion in carcinoma of the cervix?

PURPOSE: To evaluate the dose variation in high-dose-rate (HDR) intracavitary brachytherapy for cancer of the cervix when treatment planning is performed prior to each applicator insertion versus when the initial plan is used for each treatment. METHODS AND MATERIALS: Fourteen patients with carcinoma of the cervix were treated with chemoradiotherapy followed by five intracavitary tandem and ovoid insertions of 600 cGy/fraction. We modified the actual plans to calculate the dose each dose point would have received using only the treatment plan created for the initial fraction. RESULTS: An increase in the percent dose to the rectum, bladder, and vaginal surface of 5%, cGy (p = 0.038), 6% (p = 0.006), and 11%, respectively, were observed when the initial treatment plan was used versus using the optimized treatment plan for each insertion. The greatest single change resulted in a percent increase of 35%, 30%, and 45% to the rectum, bladder, and vaginal surface points, respectively. CONCLUSIONS: Increased dose to at-risk structures occurred when individualized treatment planning was not performed. Since a significant increase in dose to the rectum (p = 0.038) and bladder (p = 0.006) was obtained without customized treatment planning, we continue to advocate individualized treatment planning in HDR tandem and ovoid insertions for the treatment of cervix cancer.     

Radical radiotherapy with high-dose-rate brachytherapy for uterine cervix cancer long-term results

The aim of this is to report the results of radical radiotherapy in carcinoma of the cervix treated by high-dose rate (HDR) intracavitary brachytherapy and external beam radiotherapy (XRT) at a single centre in Singapore. This is a retrospective analysis of 106 consecutive cases with histologically proven cervical cancer, treated by HDR brachytherapy and XRT at the Mount Elizabeth Hospital from 1990 to 1993. External beam radiotherapy to the pelvis was delivered with 6 MV photons, to 45-50.4 Gy in 1.8 Gy fractions. High-dose-rate brachytherapy comprised two to three applications of an intrauterine tandem with paired ovoids, to a median dose of 18 Gy to point 'A', carried out during XRT. All 106 patients completed treatment. Their ages ranged from 32 to 80 years (median 57 years). Most patients presented with stage II or III disease (44 and 37%, respectively) and with squamous cell carcinoma (91%). Median follow-up time was 59 months (range 2-169 months). The 5-year relapse-free survival rate across all stages was 71%. The corresponding overall survival rate was 69%. Local control was achieved in 86 patients (81%); six patients had residual disease (6%), and 14 patients had local recurrence (13%). Fourteen patients developed metastatic disease (13%). On univariate analysis, tumour stage, haemoglobin level, number of brachytherapy treatments and overall treatment time were found to be prognostic factors for overall survival. Late complications were mild (Radiation Therapy Oncology Group score 1-2), except for one patient with grade 4 rectal toxicity. The complication rates were 8, 14 and 45%, respectively, for the rectum, bladder and vagina (stenosis). The use of two to three fractions of HDR intracavitary brachytherapy in addition to pelvic XRT achieves good outcomes.     

Role of Interstitial PDR Brachytherapy in the Treatment of Oral and Oropharyngeal Cancer

PURPOSE: To evaluate the role of pulsed-dose-rate interstitial brachytherapy (PDR IBT) in patients with head-and-neck malignancies. PATIENTS AND METHODS: From October 1997 to December 2003, 236 patients underwent PDR IBT for head-and-neck cancer at the authors' department. 192 patients received brachytherapy as part of their curative treatment regimen after minimal non-mutilating surgery, 44 patients were treated with irradiation alone. 144 patients had sole IBT (median D(REF) = 56 Gy), in 92 patients IBT procedures (median D(REF) = 24 Gy) were performed in combination with external irradiation. The pulses (0.4-0.7 Gy/h) were delivered 24 h a day with a time interval of 1 h between two pulses. The analysis of tumor control, survival and treatment-related toxicity was performed after a median follow-up of 26 months (6-75 months). RESULTS: At the time of analysis permanent local tumor control was registered in 208 of 236 patients (88%). At 5 years overall survival and local recurrence-free survival of the entire group were 82-73% and 93-83% for T1/2, and 56% and 83% for T3/4, respectively. Soft-tissue necrosis was seen in 23/236 patients (9.7%) and bone necrosis in 17/236 patients (7.2%). No other serious side effects were observed. CONCLUSION: PDR IBT with 0.4-0.7 Gy/h and 1 h between pulses is safe and effective. These results confirm that PDR IBT of head-and-neck cancer is comparable with low-dose-rate (LDR) brachytherapy - equally effective and less toxic.     

A precise and simple isodose-volume-based verification method for HDR and LDR brachytherapy plans

PURPOSEThe American Association of Physicists in Medicine (AAPM) code of practice for brachytherapy physics recommends performing an independent treatment time calculation. For this we implemented an easy to use isodose-based verification method for HDR (high-dose-rate) and LDR (low-dose-rate) brachytherapy plans.MATERIAL AND METHODSDose-volume-based methods have been developed for Ir-192-based high-dose-rate (HDR) and I-125 prostate low-dose-rate (LDR) brachytherapy. They allow checking the integral dwell time or activity when the volume of a suitable isodose is known. The verification method was validated for 55 clinical HDR and 243 clinical LDR plans.RESULTSFor HDR brachytherapy, the mean absolute difference between the estimated and calculated integral dwell time was 0.8% ± 1.0% (n = 30) with a single-source path and 2.7% ± 1.1% (n = 25) for multiple source paths. The corresponding value for LDR brachytherapy was 1.8% ± 2.0% (n = 243). In HDR brachytherapy, the verification method depends slightly on the plan class when considering one or more than one source paths. Good agreement between the estimated and calculated integral dwell times was obtained based on the 2 Gy isodose. Unlike HDR brachytherapy, the parameters used in the verification method for LDR brachytherapy plan verification strongly depend on the type of seed distribution. So, we recommend using an isodose at the prescribed dose for prostate HDR therapy.CONCLUSIONSIsodose-based verification methods are precise, do not presuppose dedicated tools, and are simple to implement in clinical practice.     

Effect of brachytherapy technique and patient characteristics on cervical cancer implant dosimetry

Our purpose was to evaluate the relationship between brachytherapy technique and patient characteristics on dose to organs-at-risk (OARs) in patients undergoing high dose rate (HDR) brachytherapy for cervical cancer. From 1998 to 2008, 31 patients with cervical cancer with full dosimetric data were identified who received definitive external-beam radiation and HDR brachytherapy with tandem and ovoid applicators. Doses were recorded at point A, the International Commission on Radiation Units and Measurements (ICRU)-38 rectal point, the ICRU-38 bladder point, the vaginal surface, and the pelvic sidewall. Generalized estimating equations were used to determine the significance of changes in OAR to point A dose ratios with differences in brachytherapy technique or patient characteristics. Patients underwent a median of 5 brachytherapy procedures (range, 3 to 5), with a total of 179 procedures for 31 patients. For all brachytherapy treatments, the average ratios between the doses for the rectal, bladder, vaginal surface, and pelvic sidewall reference points to those at point A were 0.49, 0.59, 1.15, and 0.17, respectively. In general, decreased OAR dose was associated with a lower stage, younger age, increased ovoid size, increased tandem length, and earlier implant number. Increased tandem curvature significantly increased bladder dose and decreased rectal dose. Intravenous anesthesia usage was not correlated with improved dosimetry. This study allowed identification of patient and procedure characteristics influencing OAR dosing. Although the advent of 3-dimensional (3D) image-guided brachytherapy will bring new advances in treatment optimization, the actual technique involved at the time of the brachytherapy implant procedure will remain important.