Single-channel Applications Research Articles

Dosimetry and safety of single-channel applicators for intracavitary brachytherapy in cervical cancer

High-dose-rate intracavitary brachytherapy plays a crucial role in achieving local control in the treatment of unresectable uterine cervical cancer. In this treatment approach, the single-channel applicator (SCA) offers a simpler structure for implantation compared to the fletcher applicator set (FAS), easing the treatment planning. To evaluate the dosimetry and safety of the SCA for intracavitary brachytherapy in cervical cancer, the present study aims to assess its dose distribution in relation to the FAS. In this study, we compared the physical and dosimetric characteristics of the inferential reference points (A, cervix; B, bladder; and R, rectum) of the SCA to those obtained with tandem and FAS dosing. Dosimetric characteristics and dose distributions in a Chinese female anthropomorphic phantom were evaluated using RGD-3B thermoluminescent dosimetry. The SCA generated an oblate, pear-shaped dose distribution curve, resulting in a reduced high-dose area along the bladder-rectum axis. Compared to the tandem, the SCA resulted in dose reductions of 21% and 17% at the bladder and rectum, respectively. When compared to the FAS, the dosing with the SCA at the bladder and rectum did not show significant differences concerning the occurrence of severe toxic effects. The SCA demonstrated a dose distribution curve similar to the standard FAS but not the tandem. The results of the present study indicate that both SCA and FAS showed equally acute toxicity and resulted in late injuries to the rectum and bladder. Nevertheless, the SCA’s simpler structure, which allows for more convenient placement and planning, warrants further clinical investigations to assess its efficacy and practical application.

Multichannel two-gradient direction filtered reference least mean square algorithm for output-constrained multichannel active noise control

Multichannel active noise control is a proven and long-standing technique for achieving a large zone of quiet in enclosures and open spaces. In practice, the multichannel active noise control system encounters more significant output saturation nonlinearity than the single-channel system as a result of the increased number of multiple output amplifiers, which not only degrades noise reduction performance but also compromises system stability. Conventional output-saturation solutions are mainly designed for single-channel applications, and their high computational complexity prevents them from being extended to multichannel systems. Hence, this paper proposes a novel two-gradient direction multichannel filtered reference least mean square (FxLMS) method that effectively avoids the saturation problem by restricting the output to the desired range and marginally increasing the computation over the conventional Multichannel FxLMS algorithm. In addition, this paper investigates the step sizes of the algorithm and proposes a computation-efficient variable step-size strategy to reduce further the steady-state error caused by the varying gradient directions. Finally, the efficacy of the proposed algorithm is demonstrated through numerical simulations using measured primary and secondary paths.

PO18: The 3-Year Results of Phase II Trial of Brachytherapy with Single-Channel Applicator for Cervical Carcinoma

Purpose: To evaluate whether the patent single-channel applicator(China Patent number:200710050108.1), which was modified from the traditional tandem applicator and wrapped with a oval-shield alloy around the source channel, has the same clinical efficacy and safety as the standard Fletcher-type applicator in the high-dose-rate brachytherapy for carcinoma of the cervix.

PO18: The 3-Year Results of Phase II Trial of Brachytherapy with Single-Channel Applicator for Cervical Carcinoma

PO18: The 3-Year Results of Phase II Trial of Brachytherapy with Single-Channel Applicator for Cervical Carcinoma

The 2-year Results of Phase II Clinical Trial of Brachytherapy with Single-Channel Applicator For Cervical Carcinoma

To evaluate whether the patent single-channel applicator( China Patent number:200710050108.1), which was modified from the traditional tandem applicator and wrapped with an oval-shield alloy around the source channel, has the same clinical efficacy and safety as the standard Fletcher-type applicator in the high-dose-rate brachytherapy for carcinoma of the cervix. This was a single blind, prospective, parallel randomized trial. This trial was registered in the Chinese Clinical Trial Registry (No. ChiCTR-TRC-12002321). All the eligible patients were randomized by random computer generation to 1 of 2 treatment groups: the Fletcher applicator group or the patent single-channel applicator group. Patients in both groups were treated with concurrent cisplatin chemotherapy and external beam radiotherapy(EBRT) followed by HDR brachytherapy (not includingⅡa1). Whole pelvis irradiation was given with 6-MV photons via a four-field box variants or anterior and posterior parallel fields. The standard prescribed dose was 46 to 50 Gy, consisting of 23 to 25 fractions 5 to 6 weeks apart. Five to six fractions with a dose of 7 Gy per fraction of intracavitary brachytherapy at point A once a week were designed for all patients after the third week of pelvic irradiation. This regimen gives a total equivalent dose in 2-Gy fractions (EQD2) of 80-90 Gy to Point A. Chemotherapy was given with intravenous cisplatin 40 mg/m2 once a week during the EBRT. The acute toxicities and the late toxicities were evaluated according to the RTOG grading scale. The Kaplan-Meier analysis was used to compare the overall survival (OS), the Progression-Free-Survival (PFS) and the locoregional failure-free survival (LRFFS). From December 1st 2011 to February 2017, 299 patients with pathologically confirmed International Federation of Gynecology and Obstetrics (FIGO 2009) stage Ⅰb2-Ⅳa carcinoma of the cervix were randomly assigned to the Fletcher applicator group(n=150) and the single-channel group (n=149). All but eight patients were treated with concurrent chemoradiotherapy. Up to February 2019, all the patients had achieved a minimum follow-up of 2 years. The 2-year OS, PFS and LRFSS was 81.4%, 77.7% and 79.5% for the Fletcher group, and for the single-channel group was 88.2%, 83.6% and 87.0%, respectively. The seriousness of acute treatment-related toxicities was similar in the two groups. The cumulative rate of late rectal complications for Grade 3-4 in the Fletcher group and the single-channel group was 4.0% and 5.4%, respectively. The cumulative rate of Grade 3-4 bladder complications was 1.3% for the Fletcher group and 0.7% for the single-channel group. The 2-year results of our study shows that the patent single-channel intracavitary applicator may be able to provide a protection for the rectum and bladder, and seems to have the same clinical efficacy as the standard Fletcher type three-channel applicator in the high-dose-rate brachytherapy for carcinoma of the cervix.

Early Interim Results of a Phase 2Clinical Trial of Brachytherapy With Single-Channel Applicator for Cervical Carcinoma

To evaluate whether a single-channel intracavitary applicator ( China Patent number:200710050108.1) which transformed from a traditional tandem applicator with a oval-shaped shield maded of high density alloy has the same clinical efficacy and safety as the standard Fletcher-type applicator in the high-dose-rate(HDR) brachytherapy for carcinoma of the cervix. From December 1st 2011 to December 1st 2014, 112 patients with cervix cancer were randomly assigned to the Patent applicator group (n=54) and the Fletcher applicator group(n=58). All but seven patients with early stage were treated with concurrent cisplatin chemotherapy and external beam radiotherapy (EBRT) followed by HDR brachytherapy. Whole pelvis irradiation was given with 6-MV photons via a four-field box variants or anterior and posterior parallel fields. The standard prescribed dose was 46 to 50 Gy, consisting of 23 to 25 fractions 5 to 6 weeks apart. Five to six fractions with a dose of 7 Gy per fraction of intracavitary brachytherapy at point A once a week were designed for all patients after the third week of pelvic irradiation.This regimen gives a total equivalent dose in 2-Gy fractions (EQD2) of 80-90 Gy to Point A. Chemotherapy was given with intravenous cisplatin 40 mg/m2 once a week during the EBRT. The acute toxicities and the late toxicities were evaluated according to the RTOG grading scale. The Kaplan-Meier analysis was used to compare the overall survival (OS), the progression-Free-Survival (PFS) and the local control (LC). The 2-year OS rate in the two groups was 72.4% in the Fletcher group and 83.2% in the Patent group, respectively. The 2-year PFS rate was 69.0% in the Fletcher group and 79.4% in the Patent group. The 2-year LC rate was 72.4% in the Fletcher group and 79.4% in the Patent group. The seriousness of acute treatment-related toxicities was similar in the two groups. 34 (58.6%) patients in the Fletcher group and 29 (53.7%) in the Patent group had Grade 3–4 hematologic toxicity. No Grade 4 nonhematologic toxicity was observed in the two groups. 5 (8.6%) patients in the Fletcher group and 10 (18.5%) in the Patent group had Grade 3 acute gastrointestinal toxicity. Grade 3 acute rectal reaction and genitourinary effect for the Fletcher group was both 1.7%, and for the Patent group was both 1.9%. The cumulative rate of late rectal complications for Grade 3–4 in the Fletcher group and the Patent group was 5.2% and 1.9%, respectively. The bladder late complications rate of Grade 3–4 was 1.7% for the Fletcher group, and no patients in the Patent group had serious bladder late complications． The early interim results of our study have shown that the patent single-channel intracavitary applicator may be able to provide a protection for the rectum and bladder, and has the same clinical efficacy as the standard Fletcher type three-channel applicator in the HDR brachytherapy for carcinoma of the cervix. Further studies are needed to assess long-term outcomes and associated toxicities.

Applications of MOSkin dosimeters for quality assurance in gynecological HDR brachytherapy: An in-phantom feasibility study

In vivo dosimetry (IVD) is an excellent mode of treatment verification and detection of possible overexposures. A feasibility study was conducted to evaluate a proposed IVD procedure for gynecological HDR brachytherapy procedure quality assurance. MOSkin dosimeters were selected due to their small size and capability of measuring steep dose gradients, such as those relevant in HDR brachytherapy procedures. Two in-phantom experiments measuring dose with MOSkins at the position simulating the rectal wall were conducted employing a cylindrical single channel applicator and a multichannel applicator. Three MOSkins were incorporated onto a rectal catheter, which was then attached to the applicator, separated by a small wooden plaque, simulating the vaginal to rectal wall distance and fixing catheter position. This setup was inserted into a water phantom and three treatment plans prescribing 300 cGy to 3 different targets were assigned with various dose distributions. Each treatment was administered three times, and doses measured by the MOSkins were recorded. Doses measured by the MOSkins were within 5% of the dose determined by the treatment planning system (TPS), ranging between 208 and 332 cGy, depending on dosimeter position on the rectal catheter. The overall average dose difference between measured and TPS values was 2.09% ± 1.15% (ranging between 0.83 and 4.27%, with measured values always higher than TPS dose), subdivided in 1.40 ± 0.37% and 2.79 ± 1.27% for single and multichannel applicator experiments, respectively. An overall dose agreement between the TPS and measured values, detector reproducibility, and practicality of the rectal catheter demonstrated the suitability of the proposed method for in vivo real time QA purposes in gynecological HDR brachytherapy.

Contemporary Toxicity Profile of Breast Brachytherapy Versus External Beam Radiation After Lumpectomy for Breast Cancer

We compared toxicities after brachytherapy versus external beam radiation therapy (EBRT) in contemporary breast cancer patients. Using MarketScan healthcare claims, we identified 64,112 women treated from 2003 to 2012 with lumpectomy followed by radiation (brachytherapy vs EBRT). Brachytherapy was further classified by multichannel versus single-channel applicator approach. We identified the risks and predictors of 1-year infectious and noninfectious postoperative adverse events using logistic regression and temporal trends using Cochran-Armitage tests. We estimated the 5-year Kaplan-Meier cumulative incidence of radiation-associated adverse events. A total of 4522 (7.1%) patients received brachytherapy (50.2% multichannel vs 48.7% single-channel applicator). The overall risk of infectious adverse events was higher after brachytherapy than after EBRT (odds ratio [OR]=1.21; 95% confidence interval [CI] 1.09-1.34, P<.001). However, over time, the frequency of infectious adverse events after brachytherapy decreased, from 17.3% in 2003 to 11.6% in 2012, and was stable after EBRT at 9.7%. Beyond 2007, there were no longer excess infections with brachytherapy (P=.97). The overall risk of noninfectious adverse events was higher after brachytherapy than after EBRT (OR=2.27; 95% CI 2.09-2.47, P<.0001). Over time, the frequency of noninfectious adverse events detected increased: after multichannel brachytherapy, from 9.1% in 2004 to 18.9% in 2012 (Ptrend=.64); single-channel brachytherapy, from 12.8% to 29.8% (Ptrend<.001); and EBRT, from 6.1% to 10.3% (Ptrend<.0001). The risk was significantly higher with single-channel than with multichannel brachytherapy (hazard ratio=1.32; 95% CI 1.03-1.69, P=.03). Of noninfectious adverse events, 70.9% were seroma. Seroma significantly increased breast pain risk (P<.0001). Patients with underlying diabetes, cardiovascular disease, and treatment with chemotherapy had increased infectious and noninfectious adverse events. The 5-year incidences of fat necrosis, breast pain, and rib fracture were slightly higher after brachytherapy than after EBRT (13.7% vs 8.1%, 19.4% vs 16.0%, and 1.6% vs 1.3%, respectively), but the risks were not significantly different for multichannel versus single-channel applicators. Toxicities after breast brachytherapy were distinct from those after EBRT. Temporal toxicity trends may reflect changing technology and evolving practitioner experience with brachytherapy.

Use of a Flexible Inflatable Multi-Channel Applicator for Vaginal Brachytherapy in the Management of Gynecologic Cancer.

Evaluate use of novel multi-channel applicator (MC) Capri™ to improve vaginal disease coverage achievable by single-channel applicator (SC) and comparable to Syed plan simulation. Twenty-eight plans were evaluated from four patients with primary or recurrent gynecologic cancer in the vagina. Each received whole pelvis radiation, followed by three weekly treatments using HDR brachytherapy with a 13-channel MC. Upper vagina was treated to 5 mm depth to 1500 cGy/3 fractions with a simultaneous integrated boost totaling 2100 cGy/3 fractions to tumor. Modeling of SC and Syed plans was performed using MC scans for each patient. Dosimetry for MC and SC plans was evaluated for PTV700 cGy coverage, maximum dose to 2 cm(3) to bladder, rectum, as well as mucosal surface points. Dosimetry for Syed plans was calculated for PTV700 cGy coverage. Patients were followed for treatment response and toxicity. Dosimetric analysis between MC and SC plans demonstrated increased tumor coverage (PTV700 cGy), with decreased rectal, bladder, and contralateral vaginal mucosa dose in favor of MC. These differences were significant (p < 0.05). Comparison of MC and Syed plans demonstrated increased tumor coverage in favor of Syed plans which were not significant (p = 0.71). Patients treated with MC had no cancer recurrence or ≥grade 3 toxicity. Use of MC was efficacious and safe, providing superior coverage of tumor volumes ≤1 cm depth compared to SC and comparable to Syed implant. MC avoids excess dose to surrounding organs compared to SC, and potentially less morbidity than Syed implants. For tumors extending ≤1 cm depth, use of MC represents an alternative to an interstitial implant.

High-Performance Single Photon Avalanche Diode Array and Integrated Electronics for Time Correlated Single Photon Counting

Time Correlated Single Photon Counting (TCSPC) is a very effective measurement technique to perform the analysis of extremely weak and fast, periodical light signals. Based on the detection of single photons and on the measure of their arrival time within the period of the signal, TCSPC technique is increasingly widespread in a large number of fields, from medicine to chemistry and biology, and in a large number of applications such as single molecule fluorescence spectroscopy, fluorescence imaging, and laser scanning microscopy.Nowadays, most of the high-performance TCSPC systems are focused on single channel applications and the use of multiple parallel acquisition chains is necessary to obtain a multidimensional system, , with very high costs and large occupied areas. It is therefore necessary to develop new acquisition systems based, on the one hand, on detectors with high quantum efficiency and suitable for parallel operation, and, on the other hand, on electronics intrinsically designed to simultaneously acquire data from multiple channels. Concerning the first aspect, Single Photon Avalanche Diodes (SPADs) proved to be a valid alternative to PMTs in many applications, from quantum cryptography to astrophysics and biology.Recent systems for single-photon timing applications typically present a trade-off between number of channels and performance: the higher the number of channels, the poorer the obtained performance on each channel.In order to overcome this trade-off, in this work we present the development of the detector and the electronics necessary to develop photon timing systems featuring a large number of channels in conjunction with high performance. Starting from the SPAD developed in our lab in the last years, it is important to develop all the integrated electronics to extract and elaborate the timing information. First of all, a circuit capable of reading directly the avalanche current coming from the detectors is of the utmost importance in order to achieve a very high temporal resolution while minimizing the crosstalk between adjacent channels. Thus, a fully integrated trans-impedance stage has been designed in 180nm Si-Ge with a gigahertz bandwidth in order to obtain few tens of picoseconds full width at half maximum resolution and negligible crosstalk between different channels. Secondly, a fully integrated array of high performance time-to-amplitude converters (TAC) has been designed. In fact, in any TCSPC application one of the most important section in the acquisition chain is the time measurement block. Three main performances are required in the time measure to reconstruct the analyzed signal without introducing distortions: a high temporal resolution (in the order of few tens of picoseconds), a differential nonlinearity (DNL) of few percent of the histogram channel width and a high measurement rate (in the Megahertz order).Finally, in order to develop a fully parallel and compact TCSPC system, resource sharing is mandatory. To achieve thisgoal an integrated chip capable of routing the signal coming from the trans-impedance stage towards the timemeasurement circuit has been designed in 180nm Si-Ge technology. Since the probability of detecting a photon during one excitation cycle in any TCSPC measurement is far less than one, we have designed the routing logic to connect theSPAD to one of the TAC converters only if a photon has been detected, thus allowing the system to have a number ofTAC converters lower than the detectors one.The design of these three main blocks in conjunction with fully custom high efficiency SPAD arrays opens the way to the development of a TCSPC acquisition system that can feature both a very high number of parallel channels and very high performance.

Clinical Outcomes for 3-Dimensional High-Dose-Rate Vaginal Brachytherapy Using an Intravaginal Multichannel Cylinder: Improving Dosimetry to Decrease Toxicity for Primary and Recurrent Vaginal Cancers

Brachytherapy is an integral part of vaginal cancer treatment, delivered via either interstitial or a standard single-channel vaginal cylinder applicator. Recently, we along with others have published dosimetric studies showing improved organ-at-risk (OAR) sparing with a multichannel vaginal cylinder over the standard single-channel applicator. However, whether these dosimetric advantages afforded by a multi-channel cylinder applicator translate into clinical meaningful outcomes is unknown.

Dosimetric Comparison of 3-Dimensional Planning Techniques Using an Intravaginal Multichannel Balloon Applicator for High-Dose-Rate Gynecologic Brachytherapy

To study the dosimetric differences of various channel combinations of the Capri vaginal applicator. The Capri consists of a single central channel (R1), an inner array of 6 channels (R2), and an outer array of 6 channels (R3). Three-dimensional plans were simulated for 6 channel arrangements (R1, R2, R12, R13, R23, and R123). Treatment plans were optimized to the applicator surface or 5-mm depth while minimizing dose to organs at risk (OARs: bladder, rectum, sigmoid, and urethra). The clinical target volume (CTV) was defined as a 5-mm circumferential shell extending 4 cm in length around the applicator. Clinical target volume coverage (Dmean, D90, V100, and V150) and OAR doses (D0.1 cm3, D1 cm3, D2 cm3, and Dmean) were compared. A comparison between the Capri (R123) and a conventional single-channel applicator was also done. Statistical significance (P value<.05) was evaluated with a 2-tailed t test. When prescribing to 5-mm depth, CTV coverage using all 13 channels (R123) versus a single channel (R1) was similar; however, when prescribing to the surface there were differences (P<.0001) in all CTV metrics except for the V150. The R1 plans had higher doses to all OARs compared with R123 plans (P<.007). Doses to OARs were not significantly different between R23 and R123 plans (P=.05-.95), and CTV coverage differences were on the order of 1%. Capri R123 plans provided slightly lower CTV D90 and Dmean but equivalent OAR doses with smaller standard deviations compared with conventional cylinder plans for both prescriptions. The Capri multichannel applicator provides equivalent target coverage at 5-mm depth, with significantly reduced dose to OARs relative to using a single channel. Optimal plans can be achieved using R12 (lowest V150) or R123 or R23 (lowest OAR doses).

SU-D-213AB-02: Optimal Design of Multichannel Vaginal Cylinder Applicators for High Dose Rate Brachytherapy.

To determine the optimal location of catheters in multichannel vaginal applicators to appropriately cover the vaginal cuff target and minimize dose to the organs at risk (OARs) and hot spots in the target. A new multichannel vaginal applicator with a diameter of 30 mmconsists of a single central catheter and an outer array of eight catheters. A total of 20 plans were generated from 5 patients by using different outer catheter locations at r = 4, 8, and 12 mm. The target was defined as a 5 mmcircumferential shell extending 4 cm in length around the applicator, excluding the bladder, rectum, and bowel. An inverse planning simulated annealing algorithm and graphical optimization was applied to ensure the prescription dose (7.0 Gy per fraction) covered >97% of the target and minimized dose to the OARs. Target coverage (D90 and V100), hot spots (V150 and V200), and OAR doses (D0.1cc, D1cc, and D2cc) from the various catheter placements were compared to single catheter plans. By study design all plans had the same target coverage D90 (105.0- 108.3%) and V100 (97.1-97.2%). The V150 and V200 were 16.1% and 3.4% (r=0mm), 17.3% and 4.2% (r=4mm), 20.1% and 2.2% (r=8mm), and 30.1% and 6.0% (r=12mm). The DO.1cc to the OARs from the various catheter placements at r = 4, 8, and 12 mm was reduced by 4.0%, 8.6%, 11.9% (bladder), 7.4%, 13.2%, and 17.4% (rectum), when compared to the central catheter plans. Multichannel vaginal applicators provide better dosimetry than single channel applicator. The catheter array located closest to the applicator surface most significantly reduces dose tothe OARs at the expense of larger hot spots in the target. The array in the middle of the applicator radius provides significantly decreased dose to the OARs and gave relatively smaller hot spots.

Dual optimal filters for parameter estimation of a multivariate autoregressive process from noisy observations

This study deals with the estimation of a vector process disturbed by an additive white noise. When this process is modelled by a multivariate autoregressive (M-AR) process, optimal filters such as Kalman or H∞ filter can be used for prediction or estimation from noisy observations. However, the estimation of the M-AR parameters from noisy observations is a key issue to be addressed. Off-line or iterative approaches have been proposed recently, but their computational costs can be a drawback. Using on-line methods such as extended Kalman filter and sigma-point Kalman filter are of interest, but the size of the state vector to be estimated is quite high. In order to reduce this size and the resulting computational cost, the authors suggest using dual optimal filters. In this study, the authors propose to extend to the multi-channel case the so-called dual Kalman or H∞ filters-based scheme initially proposed for single-channel applications. The proposed methods are first tested with a synthetic M-AR process and then with an M-AR process corresponding to a mobile fading channel. The comparative simulation study the authors carried out with existing techniques confirms the effectiveness of the proposed methods.

SU‐E‐T‐381: Dosimetric Analysis of Patients Treated with Accelerated Partial Breast Irradiation Using the Mammosite® and SAVI Applicators

Purpose: To present dosimetric data for patients undergoing Accelerated Partial Breast Irradiation (APBI) using the Mammosite® and Strut‐Adjusted Volume Implant (SAVI) applicators. Methods: We have treated 35 patients with Accelerated Partial Breast Irradiation (APBI) using high dose rate brachytherapy. These patients were treated per guidelines specified in the NSABP B‐39/RTOG 0413 protocol. The patients undergoing APBI have been treated with Mammosite® applicator (N=20) and SAVI applicator (N=15). The Mammosite® applicator used for all 20 patients was a single channel applicator. Single or multiple dwell positions were used as warranted by the type of balloon used and other clinical factors. The SAVI Applicator is a single‐entry, multi‐catheter device available in different sizes with 7, 9 and 11 catheters. The use of multiple catheters facilitates dose sculpting to improve treatment plan quality as well as reduce the skin dose. Each treatment plan was evaluated for conformance of the dose to the PTV using commonly used dosimetric parameters. These parameters included balloon/cavity volume, PTV volume, V90, V100, V150 and V200. Results: The median V90 for the treatment plans delivered using the Mammosite® applicator was 99.7% (96.7%–99.8%) whereas it was 98.8% (96%–100.0%) for the patients treated with the SAVI applicator. Other data including the V100, V150, V200 and skin dose will be presented. The impact/ importance of the data presented is that it provides useful information about the range of dosimetric parameters to be expected in treatment planning of APBI cases using these applicators. Conclusions: : Our results indicate that both the Mammosite® and SAVI applicators allow treatment planning and delivery of APBI per the guidelines specified in the NSABP B‐39/RTOG 0413 protocol.

An Inter-comparison of Differing Applicators for HDR Vaginal Cuff Brachytherapy with a Focus on the Potential Use of the Contura Device

HDR brachytherapy is commonly used for vaginal cuff treatment. The vast majority of radiation therapy facilities, according to a recent ABS survey, used the single channel HDR vaginal cylinder. The potential use and efficacy of Mammosite balloon in HDR vaginal cuff brachytherapy (VCB) has been recently reported. The major disadvantage to using a single channel applicator is the pronounced anisotropy seen at the vaginal apex. In this study, we have evaluated and inter-compared the single channel 3 cm diameter HDR cylinder, the 4-channel Wright vaginal applicator, the single lumen Hologic Mammosite, and the multi lumen Senorex Contura brachytherapy balloon in VCB.

SU-FF-T-33: 3D Conformal Brachytherapy for Partial Breast Irradiation

Purpose: Partial‐breast brachy irradiation following the lumpectomy is effective in treatment women with early‐stage breast cancer and is being broadly implemented in clinic. However, the current popular radiation treatments are limited to treat regularly shaped, spherical or ellipsoid, targets with strictly defined skin and rib distances. In reality, many treatment targets cannot be defined perfectly spherical or ellipsoid due to the irregularly shaped lumpectomy cavity and/or skin distance or nearby critical organ limits. In such cases, the 3D conformal brachytherapy becomes necessary. Methods and Materials: Multiple channel breast brachytherapy applicator is used to replace the single channel applicator for 3D conformal brachytherapy. Patient is CT scanned with slice thickness at 1 mm. The target and critical organs are delineated by radiation oncologist and planning staff. Brachytherapy source dwell positions and dwell time are the parameters for treatment planning optimization. The inverse planning and graphic optimization of Plato treatment planning system (Nucletron, Columbia, Maryland) are utilized to achieve conformal radiation dose to the target and spare the critical organs.Treatment plans are evaluated based on the isodose curves displayed on top of CTimages, the dose conformality to the target and the dose volume histograms of target and critical organs.Results: Clinic cases with irregularly shaped targets and/or short skin distance, or closely located critical organs are planned and treated with 3D conformal brachytherapy. All the plans are achieved with satisfied dose distribution, i.e. good dose conformality to the target and sparing of critical organs. The after treatment following up demonstrates successful radiation treatment and good control of patient skin reaction. Conclusion: The 3D conformal brachytherapy for partial breast irradiation allow us to better treat the irregularly shaped targets and spare the critical organs. It also releases the restrictions of skin distance and air cavity volume in the selection of patients.

The importance of applicator design for intraluminal brachytherapy of rectal cancer

An important aspect of designing an applicator for radiation treatment of rectal cancer is the ability to minimize dose to the mucosa and noninvolved parts of the rectum wall. For this reason we investigated a construction of a flexible multichannel applicator with several channels placed along the periphery of a cylinder and a construction of a rigid cylinder with a central channel and interchangeable shields. Calculations of the dose gradient, dose homogeneity in the tumor, and shielding ability were performed for the two applicators in question. Furthermore, the influence on dose distribution around a flexible multichannel applicator from an unintended off-axis positioning of the source inside a bent channel was investigated by film measurements on a single bent catheter. Calculations showed that a single-channel applicator with interchangeable shields yields a higher degree of shielding and has a better dose homogeneity in the tumor volume than that of a multi-channel applicator. A single-channel applicator with interchangeable shields was manufactured, and the influence of different size of shield angle on dose rate in front of and behind the shields was measured. While dose rate in front of the shield and shielding ability are closely independent of the size of the shield angle when measured 1 cm from the applicator surface, dose rate in more distant volumes will to some extent be influenced by shield angle due to volume scatter conditions.

Focus on Data Acquisition

Focus on Data Acquisition

On the origin of strongly conducting states in thin insulator films : A. Szymanski. Electron. Technol.4, No. 4 (1971), p. 15

To study the dosimetric differences of various channel combinations of the Capri vaginal applicator.The Capri consists of a single central channel (R1), an inner array of 6 channels (R2), and an outer array of 6 channels (R3). Three-dimensional plans were simulated for 6 channel arrangements (R1, R2, R12, R13, R23, and R123). Treatment plans were optimized to the applicator surface or 5-mm depth while minimizing dose to organs at risk (OARs: bladder, rectum, sigmoid, and urethra). The clinical target volume (CTV) was defined as a 5-mm circumferential shell extending 4 cm in length around the applicator. Clinical target volume coverage (Dmean, D90, V100, and V150) and OAR doses (D0.1 cm3, D1 cm3, D2 cm3, and Dmean) were compared. A comparison between the Capri (R123) and a conventional single-channel applicator was also done. Statistical significance (P value <.05) was evaluated with a 2-tailed t test.When prescribing to 5-mm depth, CTV coverage using all 13 channels (R123) versus a single channel (R1) was similar; however, when prescribing to the surface there were differences (P<.0001) in all CTV metrics except for the V150. The R1 plans had higher doses to all OARs compared with R123 plans (P<.007). Doses to OARs were not significantly different between R23 and R123 plans (P=.05-.95), and CTV coverage differences were on the order of 1%. Capri R123 plans provided slightly lower CTV D90 and Dmean but equivalent OAR doses with smaller standard deviations compared with conventional cylinder plans for both prescriptions.The Capri multichannel applicator provides equivalent target coverage at 5-mm depth, with significantly reduced dose to OARs relative to using a single channel. Optimal plans can be achieved using R12 (lowest V150) or R123 or R23 (lowest OAR doses).