Dosimetric comparison of brachytherapy sources for high-dose-rate treatment of endometrial cancer: (192)Ir, (60)Co and an electronic brachytherapy source.

OBJECTIVE: To compare high-dose-rate (HDR) brachytherapy systems with (192)Ir, (60)Co and electronic brachytherapy source (EBS) for treatment of endometrial cancers. METHODS: Two additional plans were generated per patient fraction using a (60)Co source and Xoft-EBS on 10 selected patients, previously treated with a vaginal cylinder applicator using a (192)Ir source. Dose coverage of "PTV_CYLD", a 5-mm shell surrounding the cylinder, was evaluated. Doses to the following organs at risk (OARs) the rectum, bladder and sigmoid were evaluated in terms of V35% and V50%, the percentage volume receiving 35% and 50% of the prescription dose, respectively, and D2cm(3), the highest dose to a 2-cm(3) volume of an OAR. RESULTS: Xoft-EBS reduces doses to all OARs in the lower dose range, but it does not always provide better sparing of the rectum in higher dose range as does evaluation using D2cm3. V150% and V200% for PTV_CYLD was up to four times greater for Xoft-EBS plans than for plans generated with (192)Ir or (60)Co. Surface mucosal (vaginal cylinder surface) doses were also 23% higher for Xoft-EBS than for (192)Ir or (60)Co plans. CONCLUSION: Xoft-EBS is a suitable HDR source for vaginal applicator treatment with advantages of reducing radiation exposure to OARs in the lower dose range, while simultaneously increasing the vaginal mucosal dose. ADVANCES IN KNOWLEDGE: This work presents newer knowledge in dosimetric comparison between (192)Ir or (60)Co and Xoft-EBS sources for endometrial vaginal cylinder HDR planning.

Modeling treatment couches in the Pinnacle treatment planning system: Especially important for arc therapy.

This study is to demonstrate the importance and a method of properly modeling the treatment couch for dose calculation in patient treatment using arc therapy. The 2 treatment couch tops-Aktina AK550 and Elekta iBEAM evo-of Elekta LINACs were scanned using Philips Brilliance Big Bore CT Simulator. Various parts of the couch tops were contoured, and their densities were measured and recorded on the Pinnacle treatment planning system (TPS) using the established computed tomography density table. These contours were saved as organ models to be placed beneath the patient during planning. Relative attenuation measurements were performed following procedures outlined by TG-176 as well as absolute dose comparison of static fields of 10 × 10 cm(2) that were delivered through the couch tops with that calculated in the TPS with the couch models. A total of 10 random arc therapy treatment plans (5 volumetric-modulated arc therapy [VMAT] and 5 stereotactic body radiation therapy [SBRT]), using 24 beams, were selected for this study. All selected plans were calculated with and without couch modeling. Each beam was evaluated using the Delta(4) dosimetry system (Delta(4)). The Student t-test was used to determine statistical significance. Independent reviews were exploited as per the Imaging and Radiation Oncology Core head and neck credentialing phantom. The selected plans were calculated on the actual patient anatomies with and without couch modeling to determine potential clinical effects. Large relative beam attenuations were noted dependent on which part of the couch top beams were passing through. Substantial improvements were also noted for static fields both calculated with the TPS and delivered physically when the couch models were included in the calculation. A statistically significant increase in agreement was noted for dose difference, distance to agreement, and γ-analysis with the Delta(4) on VMAT and SBRT plans. A credentialing review showed improvement in treatment delivery after couch modeling with both thermoluminescent dosimeter doses and film analysis. Furthermore, analysis of treatment plans with and without using the couch model showed a statistically significant reduction in planning target volume coverage and increase in skin dose. In conclusion, ignoring the treatment couch, a common practice when generating a patient treatment plan, can overestimate the dose delivered especially for arc therapy. This work shows that explicitly modeling the couch during planning can meaningfully improve the agreement between calculated and measured dose distributions. Because of this project, we have implemented the couch models clinically across all treatment plans.

Medical Physics Residency Consortium: collaborative endeavors to meet the ABR 2014 certification requirements.

In 2009, Mary Bird Perkins Cancer Center (MBPCC) established a Radiation Oncology Physics Residency Program to provide opportunities for medical physics residency training to MS and PhD graduates of the CAMPEP-accredited Louisiana State University (LSU)-MBPCC Medical Physics Graduate Program. The LSU-MBPCC Program graduates approximately six students yearly, which equates to a need for up to twelve residency positions in a two-year program. To address this need for residency positions, MBPCC has expanded its Program by developing a Consortium consisting of partnerships with medical physics groups located at other nearby clinical institutions. The consortium model offers the residents exposure to a broader range of procedures, technology, and faculty than available at the individual institutions. The Consortium institutions have shown a great deal of support from their medical physics groups and administrations in developing these partnerships. Details of these partnerships are specified within affiliation agreements between MBPCC and each participating institution. All partner sites began resident training in 2011. The Consortium is a network of for-profit, nonprofit, academic, community, and private entities. We feel that these types of collaborative endeavors will be required nationally to reach the number of residency positions needed to meet the 2014 ABR certification requirements and to maintain graduate medical physics training programs.

Development of a standardized method for contouring the lumbosacral plexus: a preliminary dosimetric analysis of this organ at risk among 15 patients treated with intensity-modulated radiotherapy for lower gastrointestinal cancers and the incidence of radiation-induced lumbosacral plexopathy.

PURPOSE: To generate a reproducible step-wise guideline for the delineation of the lumbosacral plexus (LSP) on axial computed tomography (CT) planning images and to provide a preliminary dosimetric analysis on 15 representative patients with rectal or anal cancers treated with an intensity-modulated radiotherapy (IMRT) technique. METHODS AND MATERIALS: A standardized method for contouring the LSP on axial CT images was devised. The LSP was referenced to identifiable anatomic structures from the L4-5 interspace to the level of the sciatic nerve. It was then contoured retrospectively on 15 patients treated with IMRT for rectal or anal cancer. No dose limitations were placed on this organ at risk during initial treatment planning. Dosimetric parameters were evaluated. The incidence of radiation-induced lumbosacral plexopathy (RILSP) was calculated. RESULTS: Total prescribed dose to 95% of the planned target volume ranged from 50.4 to 59.4 Gy (median 54 Gy). The mean (± standard deviation [SD]) LSP volume for the 15 patients was 100 ± 22 cm(3) (range, 71-138 cm(3)). The mean maximal dose to the LSP was 52.6 ± 3.9 Gy (range, 44.5-58.6 Gy). The mean irradiated volumes of the LSP were V40Gy = 58% ± 19%, V50Gy = 22% ± 23%, and V55Gy = 0.5% ± 0.9%. One patient (7%) was found to have developed RILSP at 13 months after treatment. CONCLUSIONS: The true incidence of RILSP in the literature is likely underreported and is not a toxicity commonly assessed by radiation oncologists. In our analysis the LSP commonly received doses approaching the prescribed target dose, and 1 patient developed RILSP. Identification of the LSP during IMRT planning may reduce RILSP. We have provided a reproducible method for delineation of the LSP on CT images and a preliminary dosimetric analysis for potential future dose constraints.

Comparison of intensity-modulated radiotherapy using helical tomotherapy and segmental multileaf collimator-based techniques for nasopharyngeal carcinoma: dosimetric analysis incorporating quality assurance guidelines from RTOG 0225.

Intensity-modulated radiotherapy (IMRT) treatment plans generated by segmental multileaf collimator (SMLC) and helical tomotherapy (HT) techniques for patients with nasopharyngeal carcinoma were compared using standardized criteria proposed by Radiation Therapy Oncology Group (RTOG) protocol 0225. The goal was to deliver a prescribed dose of 70 Gy to at least 95% of the planning target volume (PTV) encompassing gross tumor, and 59.4 Gy and 50.4 Gy, respectively, to areas at high and low risk for microscopic disease, over 33 treatments while respecting constraints to organs at risk (OAR). HT-IMRT significantly reduced dose to the contralateral parotid gland and improved dose homogeneity to the PTVs. Mean doses to the inner and middle ears were also reduced by 18% and 24%, respectively, on the ipsilateral side, and 24%, and 35%, respectively, on the contralateral side using HT-IMRT compared to SMLC-IMRT. Additionally, HT-IMRT reduced mean doses to brainstem (p = 0.02), larynx (p = 0.03), and oral cavity (p = 0.03). These findings suggest that HT-IMRT may be of improve the therapeutic ratio in the radiotherapeutic treatment of nasopharyngeal carcinoma.

Late esophageal toxicity after radiation therapy for head and neck cancer.

BACKGROUND: The aim of this study was to determine the incidence of esophageal toxicity after radiation therapy for head and neck cancer. METHODS: The records of 211 patients treated by radiation therapy for head and neck cancer were reviewed to identify those with dysphagia lasting more than 90 days after therapy. Late toxicity criteria established by the Radiation Therapy Oncology Group were used to score the symptoms. RESULTS: The incidence of grade 3+ esophageal toxicity at 3 and 6 months was 30% and 19%, respectively. The rate of gastrotomy-tube dependence at 3 and 6 months was 20% and 11%, respectively. Hypopharyngeal and unknown primary site (p = .01, for both), T4 disease (p = .01), and the use of concurrent chemotherapy (p = .001) were associated with grade 3+ esophageal toxicity and stricture formation. CONCLUSION: A significant proportion of patients exhibit symptoms of esophageal toxicity after radiation therapy for head and neck cancer. Therefore, preventive strategies need further investigation.

Initial clinical experience with helical tomotherapy for head and neck cancer.

BACKGROUND: To report a single-institutional experience with the use of helical tomotherapy (HT)-based intensity-modulated radiotherapy (IMRT) for head and neck cancer. METHODS: Seventy-seven consecutive patients were treated with HT for squamous cell carcinoma of the head and neck to a median dose of 66 Gy (range, 60 to 72 Gy). Megavoltage CT scans were obtained as part of an image-guided registration protocol for patient alignment before each treatment. Concurrent chemotherapy was administered to 48 patients (62%). RESULTS: The 2-year estimates of overall survival, local-regional control, and disease-free survival were 82%, 77%, and 71%, respectively. Spatial evaluation of local-regional failures revealed that 16 of the 18 patients who progressed in the primary site or neck failed in the high-dose planning target volume (PTV). CONCLUSIONS: HT appears to achieve clinical outcomes comparable to contemporary series reporting on IMRT for head and neck cancer.

Comparison of peripheral dose from image-guided radiation therapy (IGRT) using kV cone beam CT to intensity-modulated radiation therapy (IMRT).

PURPOSE: The growing use of IMRT with volumetric kilovoltage cone-beam computed tomography (kV-CBCT) for IGRT has increased concerns over the additional (typically unaccounted) radiation dose associated with the procedures. Published data quantify the in-field dose of IGRT and the peripheral dose from IMRT. This study adds to the data on dose outside the target area by measuring peripheral CBCT dose and comparing it with out-of-field IMRT dose. MATERIALS AND METHODS: Measurements of the CBCT peripheral dose were made in an anthropomorphic phantom with TLDs and were compared to peripheral dose measurements for prostate IMRT, determined with MOSFET detectors. RESULTS: Doses above 1cGy (per scan) were found outside the CBCT imaged volume, with 0.2cGy at 25 cm from the central axis. IMRT peripheral dose was 1cGy at 20 cm and 0.4cGy at 25 cm (per fraction). CONCLUSIONS: An appreciable dose can be found beyond the edge of the IGRT field; of similar order of magnitude as peripheral dose from IMRT (mGy), and approximately half the dose delivered to the same point from the IMRT treatment (0.2cGy c.f. 0.4cGy 25 cm from the isocenter). This shows that peripheral dose, as well as the in-field dose from CBCT, needs to be taken into account when considering long term care of radiation oncology patients.