Retrospective analysis of reduced energy switching and room switching times on throughput efficiency of a multi-room proton therapy center.

OBJECTIVE: To quantify how a control software upgrade changed beam delivery times and impacted efficiency and capacity of a multiroom proton therapy center. METHODS: A four-room center treating approximately 90 patients/day, treating for approximately 7 years with optimized operations, underwent a software upgrade which reduced room and energy switching times from approximately 30 to 20 s and approximately 4 s to ~0.5 s, respectively. The center uses radio-frequency identification data to track patient treatments and has software which links this to beam delivery data extracted from the treatment log server. Two 4-month periods, with comparable patient volume, representing periods before and after the software change, were retrospectively analyzed. RESULTS: A total of 16,168 and 17,102 fields were analyzed. For bilateral head and neck and prostate patients, the beam waiting time was reduced by nearly a factor of 3 and the beam delivery times were reduced by nearly a factor of 2.5. Room switching times were reduced more modestly. Gantry capacity has increased from approximately 30 patients to 40-45 patients in a 16-h daily operation. CONCLUSIONS: Many proton centers are striving for increased efficiencies. We demonstrated that reductions in energy and room switching time can significantly increase center capacity. Greater potential for further gains would come from improvements in setup and imaging efficiency. ADVANCES IN KNOWLEDGE: This paper provides detailed measured data on the effect on treatment times resulting from reducing energy and room switching times under controlled conditions. It helps validate the models of previous investigations to establish treatment capacity of a proton therapy center.

Brachial plexus contouring with CT and MR imaging in radiation therapy planning for head and neck cancer.

With the increasing use of intensity-modulated radiation therapy (IMRT) for the treatment of head and neck cancer, radiation oncologists are expected to have an in-depth knowledge of the computed tomographic (CT) and magnetic resonance (MR) imaging anatomy of this region to be able to accurately characterize tumor extent and define organs at risk for potential radiation injury. The brachial plexus is a complex anatomic structure in the head and neck adjacent to diseased nodes and elective nodal volumes (ie, nodal areas that are prophylactically treated because they are at high risk for micrometastatic disease) and should, therefore, be carefully identified and contoured at CT prior to IMRT planning. A number of multi-institutional protocols mandate contouring the brachial plexus as an "avoidance structure" (ie, a structure or volume that is at risk for complications of radiation therapy) in the planning of head and neck radiation therapy, and, although little information exists on the best method of doing so consistently, contouring may be facilitated with fusion CT-MR imaging software. With three-dimensional conformal radiation therapy, the brachial plexus is not routinely contoured; therefore, its dose limits are not evaluated in treatment planning. In contrast, with IMRT, tolerance doses can be set to limit the maximum dose to the brachial plexus to 60 Gy in most radiation protocols, although the true radiation tolerance dose in patients with head and neck cancer has been mentioned only sporadically in the literature. Additional studies will be required to determine if identification of the brachial plexus as an avoidance structure prior to radiation therapy planning improves treatment outcome in patients with head and neck cancer and reduces long-term toxicity in this structure.

Distinguishing post-treatment changes from recurrent disease in cholangiocarcinoma: a case report.

INTRODUCTION: Three-dimensional techniques for radiotherapy have expanded possibilities for partial volume liver radiotherapy. Characteristic, transient radiographic changes can occur in the absence of clinical radiation-induced liver disease after hepatic radiotherapy and must be distinguished from local recurrence. CASE PRESENTATION: In this report, we describe computed tomography changes after chemoradiotherapy for cholangiocarcinoma as an example of collaboration to determine the clinical significance of the radiographic finding. CONCLUSION: Because of improved three-dimensional, conformal radiotherapy techniques, consultation across disciplines may be necessary to interpret post-treatment imaging findings.

A cone beam CT-Based Study for Clinical Target Definition Using Pelvic Anatomy During Postprostatectomy Radiotherapy.

PURPOSE: There are no accepted guidelines for target volume definition for online image-guided radiation therapy (IGRT) after radical prostatectomy (RP). This study used cone beam CT (CBCT) imaging to generate information for use in post-RP IGRT. METHODS AND MATERIALS: The pelvic anatomy of 10 prostate cancer patients undergoing post-RP radiation therapy (RT) to 68.4 Gy was studied using CBCT images obtained immediately before treatment. Contoured bladder and rectal volumes on CBCT images were compared with planning CT (CT(ref)) volumes from seminal vesicle stump (SVS) to bladder-urethral junction. This region was chosen to approximate the prostatic fossa (PF) during a course of post-RP RT. Anterior and posterior planning target volume margins were calculated using ICRU report 71 guidelines, accounting for systematic and random error based on bladder and rectal motion, respectively. RESULTS: A total of 176 CBCT study sets obtained 2 to 5 times weekly were analyzed. The rectal and bladder borders were reliably identified in 166 of 176 (94%) of CBCT images. Relative to CT(ref), mean posterior bladder wall position was anterior by 0.1 to 1.5 mm, and mean anterior rectum wall position was posterior by 1.6 to 2.7 mm. Calculated anterior margin as derived from bladder motion ranged from 5.9 to 7.1 mm. Calculated posterior margin as derived from rectal motion ranged from 8.6 to 10.2 mm. CONCLUSIONS: Normal tissue anatomy was definable by CBCT imaging throughout the course of post-RP RT, and the interfraction anteroposterior motion of the bladder and rectum was studied. This information should be considered in devising post-RP RT techniques using image guidance.