Brendan M. Prendergast

Plan quality and treatment planning technique for single isocenter cranial radiosurgery with volumetric modulated arc therapy

PURPOSE To demonstrate plan quality and provide a practical, systematic approach to the treatment planning technique for single isocenter cranial radiosurgery with volumetric modulated arc therapy (VMAT; RapidArc, Varian Medical systems, Palo Alto, CA). METHODS AND MATERIALS Fifteen patients with 1 or more brain metastases underwent single isocenter VMAT radiosurgery. All plans were normalized to deliver 100% of the prescription dose to 99%-100% of the target volume. All targets per plan were treated to the same dose. Plans were created with dose control tuning structures surrounding targets to maximize conformity and dose gradient. Plan quality was evaluated by calculation of conformity index (CI = 100% isodose volume/target volume) and homogeneity index (HI = maximum dose/prescription dose) scores for each target and a Paddick gradient index (GI = 50% isodose volume/100% isodose volume) score for each plan. RESULTS The median number of targets per patient was 2 (range, 1-5). The median number of non-coplanar arcs utilized per plan was 2 (range, 1- 4). Single target plans were created with 1 or 2 non-coplanar arcs while multitarget plans utilized 2 to 4 non-coplanar arcs. Prescription doses ranged from 5-16 Gy in 1-5 fractions. The mean conformity index was 1.12 (± SD, 0.13) and the mean HI was 1.44 (± SD, 0.11) for all targets. The mean GI per plan was 3.34 (± SD, 0.42). CONCLUSIONS We have outlined a practical approach to cranial radiosurgery treatment planning using the single isocenter VMAT platform. One or 2 arc single isocenter plans are often adequate for treatment of single targets, while 2-4 arcs may be more advantageous for multiple targets. Given the high plan quality and extreme clinical efficiency, this single isocenter VMAT approach will continue to become more prevalent for linac-based radiosurgical treatment of 1 or more intracranial targets and will likely replace multiple isocenter techniques.

Flattening filter-free linac improves treatment delivery efficiency in stereotactic body radiation therapy

Stereotactic body radiation therapy (SBRT) employs precision target tracking and image‐guidance techniques to deliver ablative doses of radiation to localized malignancies; however, treatment with conventional photon beams requires lengthy treatment and immobilization times. The use of flattening filter‐free (FFF) beams operating at higher dose rates can shorten beam‐on time, and we hypothesize that it will shorten overall treatment delivery time. A total of 111 lung and liver SBRT cases treated at our institution from July 2008 to July 2011 were reviewed and 99 cases with complete data were identified. Treatment delivery times for cases treated with a FFF linac versus a conventional dose rate linac were compared. The frequency and type of intrafraction image guidance was also collected and compared between groups. Three hundred and ninety‐one individual SBRT fractions from 99 treatment plans were examined; 36 plans were treated with a FFF linac. In the FFF cohort, the mean (± standard deviation) treatment time (time elapsed from beam‐on until treatment end) and patients immobilization time (time from first alignment image until treatment end) was 11.44 (± 6.3) and 21.08 (± 6.8) minutes compared to 32.94 (± 14.8) and 47.05 (± 17.6) minutes for the conventional cohort (p<0.01 for all values). Intrafraction‐computed tomography (CT) was used more often in the conventional cohort (84% vs. 25%; p<0.05), but use of orthogonal X‐ray imaging remained the same (16% vs. 19%). For lung and liver SBRT, a FFF linac reduces treatment and immobilization time by more than 50% compared to a conventional linac. In addition, treatment with a FFF linac is associated with less physician‐ordered image guidance, which contributes to further improvement in treatment delivery efficiency. PACS number: 87.55.‐x

Intensity-modulated Radiation Therapy for Anal Cancer: Results From a Multi-Institutional Retrospective Cohort Study.

Objectives:To assess toxicity and efficacy of intensity-modulated radiation therapy (IMRT) for anal cancer. Methods:Records of 152 patients were reviewed retrospectively from multiple institutions. Data on disease control and toxicity were collected as well as patient and treatment characteristics. Acute (<6 mo) and late (≥6 mo) severe toxicity (grade ≥3) were graded. Four patients were excluded due to the presence of metastatic disease or stage TX. Late toxicity data were available for 120 patients. Results:Median cumulative IMRT dose was 51.25 Gy (median, 28 fractions). All but 2 patients received chemotherapy. With median follow-up of 26.8 months, local control at 3 years was 87%, worse for patients with T3-T4 than T1-T2 disease on univariate analysis (79% vs. 90%; P=0.04). Regional control, distant control, and overall survival were 97%, 91%, and 87%, respectively, at 3 years. Nodal status was associated with regional control, distant control, and overall survival (P<0.01 for each). Most common severe acute toxicity was hematologic (41%), skin (20%), and gastrointestinal tract (11%). Two grade 5 toxicities occurred (hematologic and gastrointestinal tract). Severe late toxicity affected skin (1%) and gastrointestinal tract (3%). Conclusions:IMRT with chemotherapy resulted in excellent local control. Although T stage predicted worse local control, most T3-T4 disease was controlled with IMRT. Nodal status predicted regional and distant control and overall survival. Severe toxicity was acceptable.

Effects of flattening filter-free and volumetric-modulated arc therapy delivery on treatment efficiency

Flattening filter‐free (FFF) beams are available on an increasing number of commercial linear accelerators. FFF beams have higher dose rates than flattened beams of equivalent energy which can lead to increased efficiency of treatment delivery, especially in conjunction with increased FFF beam energy and arc‐based delivery configurations. The purpose of this study is to quantify and assess the implications of improved treatment efficiency for several FFF delivery options on common types of linac applicable radiotherapy. Eleven characteristic cases representative of a variety of clinical treatment sites and prescription doses were selected from our patient population. Treatment plans were generated for a Varian TrueBeam linear accelerator. For each case, a reference plan was created using DMLC IMRT with 6 MV flat beams. From the same initial objectives, plans were generated using DMLC IMRT and volumetric‐modulated arc therapy (VMAT) with 6 MV FFF and 10 MV FFF beams (max. dose rates of 1400 and 2400 MU/min, respectively). The plans were delivered to a phantom; beam‐on time, total treatment delivery time, monitor units (MUs), and integral dose were recorded. For plans with low dose fractionations (1.8–2.0 & 3.85 Gy/fraction), mean beam‐on time difference between reference plan and most efficient FFF plan was 0.56 min (41.09% decrease); mean treatment delivery time difference between the reference plan and most efficient FFF plan was 1.54 min (range: 0.31–3.56 min), a relative improvement of 46.1% (range: 29.2%‐59.2%). For plans with high dose fractionations (16–20 Gy/fraction), mean beam‐on time difference was 6.79 min (74.9% decrease); mean treatment delivery time difference was 8.99 min (range: 5.40–13.05 min), a relative improvement of 71.1% (range: 53.4%‐82.4%). 10 MV FFF VMAT beams generated the most efficient plan, except in the spine SBRT case. The distribution of monitor unit counts did not vary by plan type. In cases where respiratory motion management would be applicable, 10 MV FFF DMLC IMRT reduced beam‐on time/field to less than 12 sec. FFF beams significantly reduced treatment delivery time. For radiosurgical doses, the efficiency improvement for FFF beams was clinically significant. For conventional fractionation, a large improvement in relative treatment delivery time was observed, but the absolute time savings were not likely to be of clinical value. In cases that benefit from respiratory motion management, beamon/field was reduced to a time for which most patients can comfortably maintain deep inspiratory breath hold. PACS numbers: 87.55.D‐, 87.55.de, 87.56.bd, 87.56.N‐

Novel setup techniques for radiation treatment of severely obese patients with cervical cancer

The prevalence of overweight (body mass index [BMI] N 25 kg/m2) and obesity (BMI N30 kg/m2) in the United States currently exceeds two-thirds of the adult population. Obesity and severe obesity (BMI N 40 kg/m2) may impact the management of early-stage cervical cancer, where surgical resection is often the preferred treatment.1 Due to medical comorbidities and surgical risks, these patients are often not considered surgical candidates, and definitive radiation or chemoradiation may be the only curative option. Although most patients with inoperable cervical cancer are physically able to undergo a computed tomographic (CT) simulation and subsequent radiation treatment, patients with severe obesity and large abdominopelvic girth may present obstacles in simulation, treatment planning and dosimetry, and treatment delivery. Potential clinical problems include weight in excess of simulator or treatment table limits, girth in excess of CT bore or field of view,2 poor image quality secondary to tissue attenuation, creating an accurate body contour, achieving an acceptable dose distribution and heterogeneity index given the confines of beam arrangement and body thickness, gantry clearance issues, issues with patient setup and verification, and reliability of external fiducials. In this study, we report