PURPOSE:To evaluate the dosimetric impact of rotational setup errors in stereotactic body radiotherapy (SBRT) treatment of liver tumors and to investigate whether translational shifts can compensate for rotation. METHODS AND MATERIALS:The positioning accuracy in 20 patients with liver malignancies treated with SBRT was reevaluated offline by matching the patients' cone-beam computed tomography (CT) scans (n=75) to the planning CT scans and adjusting the 3 rotational angles (pitch, roll, and yaw). Systematic and random setup errors were calculated. The dosimetric changes caused by rotational setup errors were quantified for both simulated and observed patient rotations. Dose distributions recalculated on the rotated CT scans were compared with the original planned doses. Translational corrections were simulated based on manual translational registration of the rotated images to the original CT scans. The correction efficacy was evaluated by comparing the recalculated plans with the original plans. RESULTS:The systematic rotational setup errors were -0.06° ± 0.68°, -0.29° ± 0.62°, and -0.24° ± 0.61°; the random setup errors were 0.80°, 1.05°, and 0.61° for pitch, roll, and yaw, respectively. Analysis of CBCT images showed that 56.0%, 14.7%, and 1.3% of treated fractions had rotational errors of >1°, >2°, and >3°, respectively, in any one of the rotational axes. Rotational simulations demonstrated that the reduction of gross tumor volume (GTV) coverage was <2% when rotation was <3°. Recalculated plans using actual patient roll motions showed similar reduction (<2%) in GTV coverage. Translational corrections improved the GTV coverage to within 3% of the original values. For organs at risk (OAR), the dosimetric impact varied case by case. CONCLUSION:Actual rotational setup errors in SBRT for liver tumors are relatively small in magnitude and are unlikely to affect GTV coverage significantly. Translational corrections can be optimized to compensate for rotational setup errors. However, caution regarding possible dose increases to OAR needs to be exercised.

PURPOSE:To evaluate the dosimetric impact of lung tissue in Ir-192 APBI.MATERIAL AND METHODS:In a 40 × 40 × 40 cm(3) water tank, an Accelerated Partial Breast Irradiation (APBI) brachytherapy balloon inflated to 4 cm diameter was situated directly below the center of a 30 × 30 × 1 cm(3) solid water slab. Nine cm of solid water was stacked above the 1 cm base. A parallel plate ion chamber was centered above the base and ionization current measurements were taken from the central HDR source dwell position for channels 1, 2, 3 and 5 of the balloon. Additional ionization data was acquired in the 9 cm stack at 1 cm increments. A comparable data set was also measured after replacing the 9 cm solid water stack with cork slabs. The ratios of measurements in the two phantoms were calculated and compared to predicted results of a commercial treatment planning system.RESULTS:Lower dose was measured in the cork within 1 cm of the cork/solid water interface possibly due to backscatter effects. Higher dose was measured beyond 1 cm from the cork/solid water interface, increasing with path length up to 15% at 9 cm depth in cork. The treatment planning system did not predict either dose effect.CONCLUSIONS:This study investigates the dosimetry of low density material when the breast is treated with Ir-192 brachytherapy. HDR dose from Ir-192 in a cork media is shown to be significantly different than in unit density media. These dose differences are not predicted in most commercial brachytherapy planning systems. Empirical models based on measurements could be used to estimate lung dose associated with HDR breast brachytherapy.

ENWEndNote BIBJabRef, Mendeley RISPapers, Reference Manager, RefWorks, Zotero AMA Slessinger E, Pepin E, Zhao Q, Zhao L, Das I. Physics ContributionsDose correction in lung for HDR breast brachytherapy. Journal of Contemporary Brachytherapy. 2012;4(2):106-110. doi:10.5114/jcb.2012.29367. APA Slessinger, E., Pepin, E., Zhao, Q., Zhao, L., & Das, I. (2012). Physics ContributionsDose correction in lung for HDR breast brachytherapy. Journal of Contemporary Brachytherapy, 4(2), 106-110. https://doi.org/10.5114/jcb.2012.29367 Chicago Slessinger, Eric, Eric Pepin, Qingya Zhao, Li Zhao, and Indra Das. 2012. "Physics ContributionsDose correction in lung for HDR breast brachytherapy". Journal of Contemporary Brachytherapy 4 (2): 106-110. doi:10.5114/jcb.2012.29367. Harvard Slessinger, E., Pepin, E., Zhao, Q., Zhao, L., and Das, I. (2012). Physics ContributionsDose correction in lung for HDR breast brachytherapy. Journal of Contemporary Brachytherapy, 4(2), pp.106-110. https://doi.org/10.5114/jcb.2012.29367 MLA Slessinger, Eric et al. "Physics ContributionsDose correction in lung for HDR breast brachytherapy." Journal of Contemporary Brachytherapy, vol. 4, no. 2, 2012, pp. 106-110. doi:10.5114/jcb.2012.29367. Vancouver Slessinger E, Pepin E, Zhao Q, Zhao L, Das I. Physics ContributionsDose correction in lung for HDR breast brachytherapy. Journal of Contemporary Brachytherapy. 2012;4(2):106-110. doi:10.5114/jcb.2012.29367.

Purpose A study was conducted to determine the dosimetric effects resulting from air pockets and high atomic number (Z) contrast medium within a multichannel breast brachytherapy device. Material and methods A 5-6 cm diameter Contura (SenoRx) brachytherapy device was inflated using 37 cm3 of saline. Baseline dose falloff from an HDR Iridium-192 source was measured with the Iridium source centered in the central channel and an anterior off-center channel. Data were collected at distances from 1 to 50 mm. Comparison studies were conducted with identically inflated volume containing varied air pocket volumes (1-4 cm3) and concentrations of contrast solution (3%, 6%, and 9% by volume). Dose perturbation factors (DPF) were computed and evaluated. Results Dose perturbations due to air pockets and contrast solutions were observed. As the volume of air increased, the DPF increased by approximately 2.25%/cm3. The effect was consistent for both channels. The contrast effects were more complex. The 3% contrast media had minimal dose perturbation. The 6% contrast solution caused dose reduction of 1.0% from the central channel but 1.5% dose increase from the anterior channel. The 9% contrast solution caused dose reductions by 4.0% (from central channel) and 3.0% (from anterior channel). The DPF from all contrast solutions moderated with increasing distance. Conclusions Dose perturbations due to air pockets and high-Z contrast solution can be significant. It is important to control these effects to avoid dose errors.

PURPOSE: Suboptimal dosage evaluated from postimplant dosimetry of prostate brachytherapy creates conundrum that needs resolution. This pilot study was undertaken to explore the feasibility of summing and visualizing radiation dosage from multimodality treatment.METHODS AND MATERIALS: Four weeks after (125)I permanent prostate seed implant, CT scans were performed on the whole pelvis of patients using our standard protocol for prostate planning. The acquired CT data sets were reconstructed using different sizes of field of view (FOV). The images with limited FOV focusing on prostate were imported into Variseed (Varian Medical Systems, Inc., Palo Alto, CA) for postimplant evaluation, whereas images with full FOV were imported to Eclipse (Varian Medical Systems, Inc., Palo Alto, CA) treatment planning system (TPS) for future managements, that is, for external beam salvage.RESULTS: The dose matrix resulted from the postimplant dosimetry was exported from Variseed in standard DICOM format and imported into Eclipse TPS. The brachytherapy dose matrix was registered with the patient images with full FOV in Eclipse TPS. Targets for dose boost were defined based on the isodose curves generated from brachytherapy. An external photon beam plan was successfully generated to deliver dose for selected underdose regions.CONCLUSION: Accurate external beam radiation treatment planning can be accomplished using our planning protocols when inadequate brachytherapy dose delivery occurs. The proposed technique can be used to safely deliver additional external radiation dose using intensity-modulated radiation therapy technique after suboptimal brachytherapy procedure. (C) 2011 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.

PURPOSE:Low-dose-rate (LDR) brachytherapy is an integral treatment modality in radiation oncology. Clinical efficacy is based on experience with manual source loading and continuous dose delivery. With remote afterloading technology, sources may be loaded and unloaded during the treatment course to prevent radiation exposure to nursing staff members and visitors. The aim of this study was to investigate treatment interruptions in terms of frequency and duration as well as extension of the overall treatment time period. The potential clinical impact of treatment interruptions was also considered.MATERIALS AND METHODS:The treatment records of 20 patients who underwent brachytherapy in the Indiana University Department of Radiation Oncology administered with a Selectron LDR remote afterloader were reviewed. Results were tabulated and analysis performed with respect to 1) the number of interruptions, 2) delay time, 3) delay time (T(d)) as a function of total implant time (T), 4) the time of day that each interruption occurred, and 5) the time in minutes of each individual interruption.RESULTS:The mean number of interruptions was 44.9 per patient, (range, 24-76), with a mean prescription implantation duration of 45.7 hours and a mean actual treatment time of 51.2 hours resulting in a mean interruption time of 6.4 minutes per treatment hour. The number of interruptions was standardized and divided by the number of prescribed dose in grays, translating to 1.2 to 3.7 interruptions per gray delivered, with a mean of 1.6, resulting in an average T(d) of 11.21% (range, 7.35%-17.12%).CONCLUSION:Significant interruptions are frequent using remote afterloading LDR techniques, reducing the effective dose rate. Careful monitoring of such interruptions is warranted.

PURPOSE: A process for prostate high-dose-rate (HDR) brachytherapy was developed and implemented successfully in the community hospital setting. The practical aspects of the program are reviewed and may serve as a foundation for clinics interested in offering this clinical service.METHODS AND MATERIALS: A generic needle distribution geometry was established to accommodate target volumes of variable size. A system to identify and assign treatment channels to each implant needle was devised. The computerized tomography (CT) based treatment planning was used with dose constraints defined for sensitive structures and target uniformity. Implant needle stability was promoted by supporting the patient on a CT compatible padded sliding board. A process that aligns dwell position to CT imaging without the use of radiographic markers was followed. Graphical optimization of dwell times was used to generate the treatment dose distributions.RESULTS: Prostate HDR brachytherapy as a boost or as monotherapy has been offered in a program that has evolved over the past 8 years. Practical aspects of the program promote its feasibility and precision. Collaboration with commercial entities has also led to the development of products that support the technique.CONCLUSIONS: Prostate HDR brachytherapy offers a relatively high degree of dose distribution control in comparison with other prostate radiotherapy modalities. The practical aspects described offer assurance to achieve that goal. (C) 2010 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.

PURPOSE:The purpose of this report is to describe the clinical implementation and evaluation of an interstitial remote afterloading device for multichannel intracavitary brachytherapy. METHODS AND MATERIALS:Two 15-channel low dose rate devices were adapted for use with Fletcher-Suit tandem and ovoids and Simon-Heyman capsules. The technical records for 103 intracavitary brachytherapy procedures performed from February 1989 through February 1991 were reviewed. RESULTS:Isodose distributions from fixed source trains for Microselectron low dose rate gynecologic applicators closely approximate standard manual afterloading sources and applicators. Device malfunctions occurred in 51% (53 out of 103) of the procedures. Malfunctions by applicator type were 70% (51 out of 73) for tandem, ovoids, and capsules, 12% (2 out of 17) for tandem and ovoids, and none (0 out of 13) for ovoids only. The most common malfunction occurred during source transfer. Total implant time was prolonged 0 to 4% by malfunction and 10% by patient care interruptions, depending on applicator type. CONCLUSION:The adaptation of the Microselectron device for multichannel gynecologic intracavitary brachytherapy results in similar dose distributions as standard manual after loading sources and a decreased radiation exposure to nursing personnel. The system has a high rate of malfunctions but a low overall prolongation of implant time due to malfunction.

PURPOSE:The independent collimator feature in medical linear accelerators can define radiation fields that are asymmetric with respect to the flattening filter and oblique to the incident surface. Prior to clinical implementation, it is necessary to evaluate the dosimetry of this non-standard treatment delivery technique. An investigation of the independent collimator dosimetry for 6 MV and 18 MV x-ray beams has been undertaken. METHODS AND MATERIALS:Dose to tissue in free space, percent depth dose and dose distribution were measured and compared to that for symmetric field collimation. RESULTS:The dosimetry results were consistent for both photon modes. Dose in free space with asymmetric collimation can be calculated from the corresponding symmetric field dose in free space to within 1.2 +/- 0.7% by applying an appropriate off-axis factor. Asymmetric field percent depth dose differs from symmetric field percent depth dose on average by 1.1 +/- 0.7% for 6 MV and by 0.7 +/- 0.5% for 18 MV for field sizes ranging from 5 x 5 to 20 x 20, centered 3 cm and 10 cm off-axis. The measured isodose curves demonstrate divergence effects and reduced doses (less than 3%) adjacent to the field edge closest to the flattening filter center. This dose asymmetry result is identical to that from secondary collimation. CONCLUSION:The methodology for clinical implementation of the independent collimator feature is straightforward. However, accurate representation of the isodose distributions by commercial radiotherapy treatment planning systems requires special dose calculation algorithms.

A new afterloadable gynecological intracavitary applicator has been designed and is now in use for the treatment of a wide range of vaginal, cervical, and endometrial cancers in a single application, with a dose distribution that more closely matches the prescribed treatment than previous methods. The plexiglass applicator consists of a bulbous section that is inserted up to the vaginal apex and loaded with right and left ovoid sources. The distal portion is cylindrical with a central channel for tandem sources. A straight tandem is used when the target volume extends to the vaginal apex, but an intrauterine tandem can also be used. Extensive dosimetric and radiographic evaluations were performed to guide design refinements and to validate the surface dose predictions of the brachytherapy treatment planning system. The final applicator design delivers 110-120 cGy/hr to the vaginal apex surface and 95-100 cGy/hr to the distal vaginal surfaces when loaded with a 144.6 U (20 mgRaEq) cesium tube in each ovoid channel and 72.3, 72.3, and 144.6 U (10, 10, and 20 mgRaEq) cesium tubes in the vaginal cylinder channel. A system for treatment dose specification has been established that includes dose tables for manually calculating surface doses to reference points. A dose distribution comparison with a sequential colpostat-vaginal cylinder treatment demonstrates that dose delivery is more precise and uniform with this new applicator.

Proceedings of the 34th Annual ASTRO Meeting 295 scatter decreases from 7% for Cobalt-60 and 12% for 6 MV to 0.5% for both energies.The loss of backscatter dose remains relatively constant as field size increases, with Cobalt-60 doses lower by approximately 5% and 6 MV doses lower by approximately 8%.

PURPOSE:To define the adequacy of the electron beam therapy in the treatment of advanced cervical adenopathy in patients with head and neck cancers. MATERIALS AND METHODS:Twelve patients with N2 or N3 jugulodigastric lymphadenopathy received primary radiation therapy with or without chemotherapy for definitive control of their disease.The common technique of opposed lateral portals for the initial phase of treatment was used.The portals were then reduced to spare the spinal cord, and nodal disease lying behind the plane of the spinal cord was boosted with electron beam therapy.Electron energies ranged from 8-12 MeV with the majority of patients receiving 10 MeV electrons prescribed to dmax.The cervical lymph nodes were then outlined on diagnostic CT scans with the aid of a head and neck radiologist.The relationship of the nodal volume with respect to adequate coverage with electron beam therapy was then analyzed.Adequate coverage was defined as all disease encompassed by the 90% isodose line.Spinal cord tolerance was defined as the 10% isodose line or lower reaching the spinal cord.

Under the auspices of NCI contracts, four institutions have collaborated to assess the accuracy of the pixel-based dose calculation methods they employ for external photon treatment planning. The approach relied on comparing calculations using each group's algorithm with measurements in phantoms of increasing complexity. The first set of measurements consisted of ionization chamber measurements in water phantoms in normally incident square fields, an elongated field, a wedged field, a blocked field, and an obliquely incident beam. The second group of measurements was carried out using thermoluminescent dosimeters in phantoms designed to investigate the effects of surface curvature, high density heterogeneities, and low density heterogeneities. The final study tested the entire treatment planning system, including CT data conversion, in an anthropomorphic phantom. Overall, good agreement between calculation and measurements was found for all algorithms. Regions in which discrepancies were observed are pointed out, areas for algorithm improvement are identified and the clinical import of algorithm accuracy is discussed.

The comparison of a predicted portal dose image, calculated during treatment planning, with the measured image obtained during treatment is proposed as an approach to verify the correct implementation of a patient treatment plan. The comparison inherently verifies both the geometric alignment and the dose delivered. Feasibility studies were conducted with 60Co irradiation of a modular plastic phantom, an anthropomorphic phantom and a patient with lung cancer. Calculations were made with the 3-dimensional scatter ray-trace Delta Volume method. Calculated distributions and/or selected points of transmitted dose correction factors were compared with measurements made with TLD, scanning ionization chamber and film. For the two phantom studies, excellent agreement, usually to within 3%, was achieved when positioning of the phantoms were accurate. The patient study showed that selected point comparisons were inadequate in identifying the cause of errors when disagreement occurred. Simple subtraction of the calculated and measured images showed a 4 mm translational misalignment. The results are encouraging and demonstrate that portal dose images can be used to detect large geometric and dosimetric discrepancies between treatment plan calculations and measurements. The results also show that perfect verification is virtually impossible in the clinical situation. More work is required to use the verification information for improving the estimation of dose to the patient.

Between 1976 and 1982, 293 patients were treated for carcinoma of the uterine cervix at Washington University by definitive radiotherapy consisting of external beam therapy and two standard Fletcher-Suit applications (tandem plus vaginal colpostats). In ninety-nine patients (34%) mini-colpostats (MC) were used for one or both of their intracavitary insertions while 194 (66%) patients were treated twice with regular Fletcher-Suit colpostats (RC). The frequency of MC use was related to the age and parity of the patients. The distribution by stage of MC and RC groups was not significantly different. Pelvic failure in the MC group was similar to that of the RC group (21% vs 24%). Five-year disease-free survival was also similar between the two groups: 86% vs 80% Stage IB, 57% vs 61% Stage IIA, 47% vs 52% Stage IIB, and 27% vs 45% Stage III for MC and RC groups, respectively. The rate of major complications (grade 3) was 15% in the MC group and 8% in the RC group (p = 0.08). Careful phantom dosimetric studies in both types of colpostats and correlations of dose distributions at various points in the pelvis with frequency of rectal and bladder complications were carried out. The bladder and rectum received a 5–10% higher mean radiation dose (Gy) in the MC group than in the RC group despite lower overall exposure (milligram-hours). Thermoluminescent dosimetry in a polystyrene phantom demonstrates that approximately 10% higher doses are delivered to the bladder, rectum, and point A with an MC system as compared to an RC system, for constant exposure in mgh. Phantom measurements of a newer MC with bladder and rectal shielding demonstrate no influence on the bladder and rectal point dose at a source separation of 3 cm; midline points of the bladder and rectum are not within the full shadow of the shields even if the colpostats are flush with the tandem. Implications for therapy are discussed.