Monitoring Intrafraction Motion of the Prostate During Radiation Therapy: Suggested Practice Points From a Focused Review.

PURPOSE: External beam radiation therapy to the prostate is typically delivered after verification of prostatic position with image guidance. Prostate motion can occur during the delivery of each radiation treatment between the time of localization imaging and completion of treatment. The objective of this work is to review the literature on intrafraction motion (IFM) of the prostate during radiation therapy and offer clinical recommendations on management. METHODS AND MATERIALS: A comprehensive literature review was conducted on prostate motion during prostate cancer radiation therapy. Information was organized around 3 key clinical questions, followed by an evidence-based recommendation. RESULTS: IFM of the prostate during radiation therapy is typically ≤3 mm and is unlikely to compromise prostate dosimetry to a clinically meaningful degree for men treated in a relatively short treatment duration with planning target volume (PTV) margins of ≥3 to 5 mm. IFM of 5 mm or more has been observed in up to ∼10% of treatment fractions, with limited dosimetric effect related to the infrequency of occurrence and longer fractionation of therapy. IFM can be monitored in continuous or discontinuous fashion with a variety of imaging platforms. Correction of IFM may have the greatest value when tighter PTV margins are desired (such as with stereotactic body radiation therapy or intraprostatic nodule boosting), ultrahypofractionated courses, or when treatment time exceeds several minutes. CONCLUSIONS: This focused review summarizes literature and provides practical recommendations regarding IFM in the treatment of prostate cancer with external beam radiation therapy.

Fully automated planning and delivery of hippocampal-sparing whole brain irradiation.

The goal of this study is to fully automate the treatment planning and delivery process of hippocampal-sparing whole brain irradiation (HS-WBRT) by combining a RapidPlan (RP) knowledge-based planning model and HyperArc (HA) technology. Additionally, this study compares the dosimetric performance of RapidPlan-HyperArc (RP-HA) treatment plans with RP plans and volumetric modulated arc therapy (VMAT) plans. Ten patients previously treated with HS-WBRT using conventional VMAT were re-planned using RP-HA technique and RP model for HS-WBRT. Treatment plans were generated for 30Gy in 3Gy fractions using 6MV photon beam on a TrueBeam linear accelerator (Varian Medical Systems, Palo Alto, CA) equipped with high definition multileaf collimator (HDMLC). Target coverage, homogeneity index (HI), Paddick Conformity index (CI), dose to organs-at-risk (OARs) provided by the 3 planning modalities were compared, and a paired t-test was performed. Total number of monitor units (MU), effective planning time and beam-on-time time were reported and evaluated for each plan. RP-HA plans achieved on average a 4% increase in D98% of PTV, a 26% improvement in HI, a 2.3% increase in CI, when compared to RP plans. Furthermore, RP-HA plans provided on average 11% decrease in D100% of hippocampi when compared to VMAT plans. All RP-HA plans were generated in less than 30 minutes while RP plans took 40 minutes and VMAT plans required on average 9 hours to complete. Regarding beam-on-time time, it was estimated that RP-HA plans take on average 5 minutes to deliver while RP and VMAT plans require 6.5 and 10 minutes, respectively. RP-HA method provides fully automated planning and delivery for HS-WBRT. The auto-generated plans together with automated treatment delivery allow standardization of plan quality, increased efficiency and ultimately improved patient care.

Failure mode and effects analysis of linac-based liver stereotactic body radiotherapy.

PURPOSE: Although stereotactic body radiation therapy (SBRT) is an attractive noninvasive approach for liver irradiation, it presents specific challenges associated with respiration-induced liver motion, daily tumor localization due to liver deformation, and poor visualization of target with respect to adjacent normal liver in computed tomography (CT). We aim to identify potential hazards and develop a set of mitigation strategies to improve the safety of our liver SBRT program, using failure mode and effect analysis (FMEA). MATERIALS AND METHODS: A multidisciplinary group consisting of two physicians, three physicists, two dosimetrists, and two therapists was formed. A process map covering ten major stages of the liver SBRT program from the initial diagnosis to posttreatment follow-up was generated. A total of 102 failure modes (FM), together with their causes and effects, were identified. The occurrence (O), severity (S), and lack of detectability (D) were independently scored using a scale from 1 (lowest risk) to 10 (largest risk). The ranking was done using the risk probability number (RPN) defined as the product of average O, S, and D numbers for each mode. Two fault tree analyses were performed. The failure modes with the highest RPN values as well as highest severity score were considered for investigation and a set of mitigation strategies was developed to address these. RESULTS: The median RPN (RPNmed ) values for all modes ranged from of 9 to 105 and the highest median S score (Smed ) was 8. Fourteen FMs were identified to be significant by both RPNmed and Smed (top ten RPNmed ranked and highest Smed FMs) and 12 of them were considered for risk mitigation efforts. The remaining two were omitted due to either sufficient checks already in place, or lack of practical mitigation strategies. Implemented measures consisted of five physics tasks, two physician tasks, and three workflow changes. CONCLUSIONS: The application of FMEA to our liver SBRT program led to the identification of potential FMs and allowed improvement measures to enhance the safety of our clinical practice.

Stereotactic Radiation for Palliation of Skull Base Recurrences of Salivary Gland Carcinomas: Implications for Tumor Targeting.

Background Approximately 3 to 13% of salivary carcinomas recur at the skull base. We report our experience treating these recurrences with stereotactic radiation. Methods In total, 14 patients with skull base recurrence of salivary gland carcinoma were identified. Patient characteristics, treatment parameters, response to treatment, local recurrence-free/overall survival, and patterns of failure were studied. Results All 12 symptomatic patients experienced palliation of symptoms. Two grade 3 toxicities were observed. Local recurrence-free survival after skull base treatment was 28 months (74 months after allowing for additional course of salvage radiotherapy). Overall survival was 153 months from primary diagnosis and 67 months from first skull base failure. Of 13 treatment failures, 8 occurred at margins; the rest were infield. All intracranial failures occurred along meningeal surfaces. Conclusions Stereotactic radiation provides well-tolerated palliation for the majority of patients, but with a high rate of local failure. Due to the propensity for meningeal failures, we suggest increasing margins along the meningeal surfaces when treating these patients.

3D CT-based volumetric dose assessment of 2D plans using GEC-ESTRO guidelines for cervical cancer brachytherapy.

PURPOSE: To investigate two-dimensional (2D) radiograph-based plans using three-dimensional (3D) dose-volume histogram (DVH) parameters following guidelines from Gynecologic GEC-ESTRO Working Group (GEC-ESTRO). METHODS AND MATERIALS: Nineteen high-dose-rate (HDR) fractions from 8 patients were studied. Prescription was 45 Gy from external beam radiation therapy plus 30 Gy in five fractions from HDR using tandem and ring/ovoids. Both radiographs and CT scan were obtained. Treatment was planned using radiographs following American Brachytherapy Society (ABS) guidelines. Retrospective evaluation of above 2D plans on a 3D volumetric basis was achieved by generating CT image-based 3D plans using same dwell times. RESULTS: In 2D plans, International Commission on Radiation Units and Measurement (ICRU) bladder and rectal point doses were 3.8+/-0.4 and 3.0+/-0.5 Gy, respectively. In 3D plans, rectum D(2 cc) is 4.0+/-1.0 Gy and bladder D(2 cc) is 5.4+/-0.9 Gy. Position of actual hottest spot in 3D rectum volume was close to the position of ICRU rectal point. ICRU bladder point did not match with the actual hottest spot in 3D bladder volume. In 2D plans, H-point dose was 5.8+/-0.2 Gy. In 3D plans, dose to CT-based cervix (D(90)) reduced from 7.1 to 4.2 Gy as the cervical volume increased from 12 to 39 cc. Average D(2 cc)/ICRU dose ratio was calculated to be 1.36/1.01 for bladder/rectum, respectively. CONCLUSIONS: The DVH analysis of 2D plans revealed a suboptimal coverage of CT-based cervix and a negative correlation between coverage and cervical size. Rectum dose to 2 cc weakly correlated with ICRU point dose. Currently published constraint for bladder in 3D planning is tighter than ABS guidelines in past 2D planning.