Faculty Bibliography

PURPOSE/OBJECTIVE:This study evaluated the extent of prostate displacement during SBRT on an MRI Linac using comprehensive motion management (CMM) and identified variables associated with intrafraction motion (IFM). METHODS:212 patients with clinically localized prostate cancer were treated with 5-fraction SBRT on a 1.5 T MR-Linac where IFM was continuously tracked and gated by CMM. Pre-beam positional shifts were identified from MRI registration prior to beam delivery. Intrafraction positional variability during beam delivery was evaluated, and multivariable analysis identified variables associated with IFM. RESULTS:In 614 fractions (62.7%), a > 1.5 mm pre-beam positional shift led to an adapt-to-position (ATP) plan correction. Mean anterior-posterior and superior-inferior pre-beam shifts were 2.2 mm and 2.1 mm, respectively. For 962 evaluable fractions, the median beam-on-time was 13.7 min with a mean duty cycle of 95.8%. Sustained > 3 mm displacement was observed in 520 fractions (54.1%) with a median cumulative duration of 24 s; >5 mm displacement was observed in 209 fractions (21.7%) with a median duration of 12.4 s. The ATS + ATP workflow was associated with reduced odds of sustained > 3 mm motion (p = 0.035), while older age was associated with increased odds (p = 0.011). CONCLUSIONS:Significant prostate shifts can occur immediately prior to and during radiation beam delivery, frequently exceeding applied margins and potentially leading to tumor underdosage. Continuous motion tracking and gating during prostate SBRT is an important tool in reducing IFM and enhance treatment delivery accuracy.

PURPOSE/OBJECTIVE(S)/OBJECTIVE:Radiation therapy (RT) positioning and planning are vital to minimizing toxicity in patients with synchronous bilateral breast cancer (SBBC). We studied clinical outcomes and setup reproducibility in SBBC patients treated in the prone position. MATERIALS/METHODS/METHODS:This retrospective study analyzed SBBC patients treated prone between 2012-2022. Demographics, clinical RT dose/field, dosimetry, on-treatment imaging, toxicity, and outcomes data were collected. RT delivery was standardized, with left breast treated first. After 2014, radiochromic (GaF) films were placed fractions 1-5 to evaluate field overlap, prompting re-simulation or re-planning if consistent overlap was detected. Positional shifts during setup were collected for bilateral whole breast irradiation (WBI) and partial breast irradiation (PBI). RESULTS:45 patients were included. Median age was 67 years old and median follow-up was 64 months. 35, 5, and 5 patients received bilateral WBI (1 with low axilla), bilateral PBI, a combination of WBI and PBI, respectively. The most common WBI dose was 40.5 Gy, with a simultaneous tumor bed boost to 48 Gy. PBI patients received 30 Gy in 5 fractions (n=4) or 40.05 Gy in 15 fractions (n=1). All patients who developed grade 2 (17.7%) and grade 3 (2%) dermatitis received bilateral WBI except for 1. 6 patients had acute dermatitis in the sternal area with overlap on GaF seen in 2 patients. Of 20 patients with late toxicity follow-up, 25% had late grade 1-2 dermatitis (20% received WBI). One patient recurred locally and distantly. Mean positional shifts were mostly sub-centimeter or sub-degree. Only 10% of patients had field overlap on GaF. CONCLUSION/CONCLUSIONS:To our knowledge, this is the first study examining patients treated for SBBC in the prone position. Prone bilateral RT is feasible with minimal shifts and overlap. However, higher rates of acute dermatitis occurred in bilateral WBI patients (vs. PBI), and overlap wasn't seen on GaF in all patients who developed midline dermatitis.

PURPOSE/OBJECTIVE:To commission a beam model in ClearCalc (Radformation Inc.) for use as a secondary dose calculation algorithm and to implement its use into an adaptive workflow for an MR-linear accelerator. METHODS:A beam model was developed using commissioning data for an Elekta Unity MR-linear accelerator and entered into ClearCalc. The beam model consisted of absolute dose calculation settings, output factors, percent depth-dose (PDD) curves, mutli-leaf collimator (MLC) transmission and dose leaf gap error, and cryostat corrections. Beam profiles were hard-coded by the manufacturer into the beam model and were compared with Monaco-derived profiles. The beam model was tested by comparing point doses in a homogenous phantom obtained through measurements using an ionization chamber in water, Monaco, and ClearCalc for various field sizes, source-surface distances (SSDs), and point locations. Additional testing including point dose verification for test plans using a heterogeneous phantom and patient plans. Post clinical implementation, performance of ClearCalc was evaluated for the first 41 patients treated, which included 215 adaptive plans. RESULTS:PDDs generated using ClearCalc fell within 1.2% of measurements. Field profile comparison between ClearCalc and Monaco showed an average pass rate of 98% using a 3%/3 mm gamma criteria. Measured cryostat corrections used in the beam model showed a maximum deviation from unity of 1.4%. Point dose and field monitor units (MUs) comparisons in a homogenous phantom (N = 22), heterogeneous phantoms (N = 22), and patient plans (N = 57) all passed with a threshold of 5%/5MU. Clinically, ClearCalc was implemented as a physics check post adaptive planning completed prior to beam delivery. Point dose and field MUs showed good agreement at a 5%/5MU threshold for prostate stereotactic body radiation therapy (SBRT), pelvic lymph nodes, rectum, and prostate and lymph node plans. DISCUSSION/CONCLUSIONS:This work demonstrated commissioning and clinical implementation of ClearCalc into an adaptive planning workflow. No primary or adaptive plan failures were reported with proper beam model testing.

PURPOSE/OBJECTIVE:The American Association of Physicists in Medicine Radiation Oncology Medical Physics Education Subcommittee (ROMPES) has updated the radiation oncology physics core curriculum for medical residents in the radiation oncology specialty. METHODS AND MATERIALS/METHODS:Thirteen physicists from the United States and Canada involved in radiation oncology resident education were recruited to ROMPES. The group included doctorates and master's of physicists with a range of clinical or academic roles. Radiation oncology physician and resident representatives were also consulted in the development of this curriculum. In addition to modernizing the material to include new technology, the updated curriculum is consistent with the format of the American Board of Radiology Physics Study Guide Working Group to promote concordance between current resident educational guidelines and examination preparation guidelines. RESULTS:The revised core curriculum recommends 56 hours of didactic education like the 2015 curriculum but was restructured to provide resident education that facilitates best clinical practice and scientific advancement in radiation oncology. The reference list, glossary, and practical modules were reviewed and updated to include recent literature and clinical practice examples. CONCLUSIONS:ROMPES has updated the core physics curriculum for radiation oncology residents. In addition to providing a comprehensive curriculum to promote best practice for radiation oncology practitioners, the updated curriculum aligns with recommendations from the American Board of Radiology Physics Study Guide Working Group. New technology has been integrated into the curriculum. The updated curriculum provides a framework to appropriately cover the educational topics for radiation oncology residents in preparation for their subsequent career development.

We compiled a sampling of the treatment techniques of intensity-modulated total body irradiation, total marrow irradiation and total marrow and lymphoid irradiation utilized by several centers across North America and Europe. This manuscript does not serve as a consensus guideline, but rather is meant to serve as a convenient reference for centers that are considering starting an intensity-modulated program.

Breast re-irradiation (reRT) after breast-conserving surgery (BCS) using external beam radiation is an increasingly used salvage approach for women presenting with recurrent or new primary breast cancer. However, radiation technique, dose and fractionation as well as eligibility criteria differ between studies. There is also limited data on efficacy and safety of external beam hypofractionation and accelerated partial-breast irradiation (APBI) regimens. This paper reviews existing retrospective and prospective data for breast reRT after BCS, APBI reRT outcomes and delivery at our institution and the need for a randomized controlled trial using shorter courses of radiation to better define patient selection for different reRT fractionation regimens.

Accelerated partial breast irradiation (APBI) is increasingly used to treat select patients with early stage breast cancer. However, radiation technique, dose and fractionation as well as eligibility criteria differ between studies. This has led to controversy surrounding appropriate patients for APBI and an assessment of the toxicity and cosmetic outcomes of APBI as compared to whole breast irradiation (WBI). This paper reviews existing data for APBI, APBI delivery at our institution, and ongoing research to better define patient selection, treatment delivery, dosimetric considerations and toxicity outcomes.

We present the case of a 56-year-old female with a diagnosis of acute T-cell lymphoblastic leukemia who received myeloablative conditioning for bone marrow transplant with total body irradiation (TBI) using volumetric modulated arc therapy (VMAT) to the upper body and anterior-posterior/posterior-anterior (AP/PA) open fields to the lower body followed by hematopoietic stem cell transplant. Her clinical course was complicated by high-grade pulmonary toxic effects 55 days after treatment that resulted in death. We discuss the case, planning considerations by radiation oncologists and radiation physicists, and the multidisciplinary medical management of this patient.