40 Gray in 5 Fractions for Salvage Reirradiation of Spine Lesions Previously Treated With Stereotactic Body Radiotherapy.

BACKGROUND AND PURPOSE: A retrospective single-center analysis of the safety and efficacy of reirradiation to 40 Gy in 5 fractions (reSBRT) in patients previously treated with stereotactic body radiotherapy to the spine was performed. METHODS: We identified 102 consecutive patients treated with reSBRT for 105 lesions between 3/2013 and 8/2021. Sixty-three patients (61.8%) were treated to the same vertebral level, and 39 (38.2%) to overlapping immediately adjacent levels. Local control was defined as the absence of progression within the treated target volume. The probability of local progression was estimated using a cumulative incidence curve. Death without local progression was considered a competing risk. RESULTS: Most patients had extensive metastatic disease (54.9%) and were treated to the thoracic spine (53.8%). The most common regimen in the first course of stereotactic body radiotherapy was 27 Gy in 3 fractions, and the median time to reSBRT was 16.4 months. At the time of simulation, 44% of lesions had advanced epidural disease. Accordingly, 80% had myelogram simulations. Both the vertebral body and posterior elements were treated in 86% of lesions. At a median follow-up time of 13.2 months, local failure occurred in 10 lesions (9.5%). The 6- and 12-month cumulative incidences of local failure were 4.8% and 6%, respectively. Seven patients developed radiation-related neuropathy, and 1 patient developed myelopathy. The vertebral compression fracture rate was 16.7%. CONCLUSION: In patients with extensive disease involvement, reSBRT of spine metastases with 40 Gy in 5 fractions seems to be safe and effective. Prospective trials are needed to determine the optimal dose and fractionation in this clinical scenario.

Validation of the bladder neck as an important organ at risk in prostate seed brachytherapy based on D2cc: A single-institution, retrospective review.

Purpose: International guidelines recommend urethral dose volume constraints to minimize the risk of urinary toxicity after prostate brachytherapy. An association between dose to the bladder neck (BN) and toxicity has previously been reported, and we sought to evaluate the impact of this organ at risk on urinary toxicity, based on intra-operative contouring. Material and methods: Rates of acute and late urinary toxicity (AUT and LUT, respectively) were graded according to CTCAE version 5.0 for 209 consecutive patients who underwent low-dose-rate (LDR) brachytherapy monotherapy, with approximately equal numbers treated before and after we began routinely contouring the BN. AUT and LUT were compared in patients treated before and after we began contouring the OAR, and also for those treated after we began contouring who had a D2cc of greater than or less than 50% prescription dose. Results: AUT and LUT fell after intra-operative BN contouring was instituted. Rates of grade ≥ 2 AUT fell from 15/101 (15%) to 9/104 (8.6%), p = 0.245. Grade ≥ 2 LUT decreased from 32/100 (32%) to 18/100 (18%), p = 0.034. Grade ≥ 2 AUT was observed in 4/63 (6.3%) and 5/34 (15%) of those with a BN D2cc >/≤ 50%, respectively, of prescription dose. Corresponding rates for LUT were 11/62 (18%) and 5/32 (16%). Conclusions: There were lower urinary toxicity rates for patients treated after we commenced routine intra-operative contouring of the BN. No clear relationship was observed between dosimetry and toxicity in our population.

Stereotactic Magnetic Resonance-Guided Adaptive Radiation Therapy (SMART) for Abdominopelvic Oligometastases.

PURPOSE: Stereotactic body radiation therapy can be an effective treatment for oligometastases. However, safe delivery of ablative radiation is frequently limited by the proximity of mobile organs sensitive to high radiation doses. The goal of this study was to determine the feasibility, safety, and disease control outcomes of stereotactic magnetic resonance-guided adaptive radiation therapy (SMART) in patients with abdominopelvic oligometastases. METHODS AND MATERIALS: We identified 101 patients with abdominopelvic oligometastases, including 20 patients enrolled on phase 1 protocols, who were consecutively treated with SMART on a 0.35T magnetic resonance linear accelerator (MR linac) at a single institution from October 2019 to September 2021. Local control and overall survival were analyzed using the Kaplan-Meier method. RESULTS: Overall, 114 tumors were treated. The most common histology was prostate adenocarcinoma (60 tumors [53.5%]), and 65 sites (57.0%) were centered in the pelvis. Ninety-one sites (79.8%) were treated to 8 Gy × 5, and 49 (43.0%) were treated with breath-hold respiratory gating. Online adaptation resulted in a clinically significant improvement in coverage or organ sparing in 86.6% of delivered fractions. The median time required for adaptation was 24 minutes, and the median time in the treatment room was 58 minutes. With median follow-up of 11.4 months, the 12-month local control was 93% and was higher for prostate adenocarcinoma versus other histologies (100% vs 84%; P = .009). The 12-month overall survival was 96% and was higher for prostate adenocarcinoma versus other histologies (100% vs 91%; P = .046). Three patients (3.0%) developed grade 3 toxic effects (colonic hemorrhage at 3.4 months and urinary tract obstructions at 10.1 and 18.4 months, respectively). CONCLUSIONS: In this study, SMART was feasible, safe, and effective for delivering ablative radiation therapy to abdominopelvic metastases. Adaptive planning was necessary in the large majority of cases. The advantages of SMART warrant its further investigation as a standard option for the treatment of abdominopelvic oligometastases.

Personalized Treatment Selection Leads to Low Rates of Local Salvage Therapy for Bone Metastases.

PURPOSE: Local therapy for patients with nonspine bone metastases is evolving, with data supporting the use of single-fraction treatments, and more recently, showing possible benefit from stereotactic body radiation therapy (SBRT). However, the rate of local salvage therapy (LST) after each technique has not been characterized in real-world clinic settings where patients are selected at physician discretion. We examined rates of LST in patients with nonspine bone metastases. METHODS AND MATERIALS: We reviewed records of RT for nonspine bone metastases at our institution from January 1, 2016, to December 31, 2018. We defined LST as the first occurrence of RT or surgery for oncologic progression to a bone metastasis after initial RT. Cumulative incidence functions for retreatment were generated. We conducted multivariate analysis to identify variables associated with LST. RESULTS: A total of 1754 patients were analyzed, with median follow-up of 16.2 months (range, 0-36.8 months). Of all episodes of RT, 51.5% were multifraction external beam radiation therapy (EBRT), 7.0% were single-fraction EBRT, and 41.4% were SBRT. Altogether, 88 patients (5.0%) required LST, with an incidence at 6 months of 2.5%. Incidence of LST at 6 months was 2.1% for SBRT, 5.3% for single-fraction conventional regimens, and 2.4% for multifraction conventional regimens (P = .26). Patients of younger age, who had a higher Karnofsky performance status, and/or who had lesions in the pelvis had a higher risk of retreatment. CONCLUSIONS: In this large institutional cohort, the rate of LST was low, with no difference between RT techniques. The findings indicated that SBRT for patients at high risk for treatment failure may reduce the rate of retreatment overall. When treatment modality was selected based on patient characteristics, rates of LST were lower than when treatment was randomly selected.

A novel dynamic arc treatment planning solution to reduce dose to small bowel in preoperative radiotherapy for rectal cancer.

Preoperative radiotherapy or combined chemoradiotherapy for locally advanced rectal cancer (LARC) can cause acute and late gastrointestinal (GI) side-effects. There is thought to be a dose-volume relationship between small bowel irradiation and the development of these effects. A planning study was undertaken to compare small bowel sparing for a range of 3D conformal and dynamic arc planning solutions. A planning study was carried out for 20 LARC patients. Organs at risk (OAR) contoured included bowel loops and peritoneal space (PS). For each of the 20 patients, 5 plans were created: (1) standard 3D conformal plan; (2) standard dual dynamic arc plan; (3) dual dynamic arc plan with 90° avoidance sector through the anterior portion of the patient; (4) dual dynamic arc plan with an anterior avoidance structure in the optimizer; (5) dual dynamic arc plan with both an anterior avoidance structure and an avoidance sector. The prescription was 50.4 Gy in 28 fractions to the planning target volume (PTV). Five Dose Volume Levels (DVLs; V15 Gy, V20 Gy, V25 Gy, V35 Gy, V40 Gy, and V50.4 Gy) for bowel and PS were selected. The DVLs were compared between the plans using Friedman Tests and Wilcoxon Signed Rank Tests. Comparison of the 5 plans revealed that a dual dynamic arc plan containing both an anterior avoidance sector and structure significantly improved the dose to the bowel compared to a standard 3D conformal plan and to a standard dual dynamic arc plan. This improvement was achieved while maintaining PTV coverage. This novel dual dynamic arc planning technique that uses both an avoidance sector and structure reduces the dose to the bowel and PS, which may lead to a reduction in GI toxicity.