MR-Guided Radiotherapy for Prostate Cancer

Contains fulltext : 229889.pdf (publisher's version ) (Open Access)External beam radiotherapy remains the primary treatment modality for localized prostate cancer. The radiobiology of prostate carcinoma lends itself to hypofractionation, with recent studies showing good outcomes with shorter treatment schedules. However, the ability to accurately deliver hypofractionated treatment is limited by current image-guided techniques. Magnetic resonance imaging is the main diagnostic tool for localized prostate cancer and its use in the therapeutic setting offers anatomical information to improve organ delineation. MR-guided radiotherapy, with daily re-planning, has shown early promise in the accurate delivery of radiotherapy. In this article, we discuss the shortcomings of current image-guidance strategies and the potential benefits and limitations of MR-guided treatment for prostate cancer. We also recount present experiences of MR-linac workflow and the opportunities afforded by this technology

Patterns of Utilization and Clinical Adoption of 0.35 MR-Guided Radiation Therapy in the United States — Understanding the Transition to Adaptive, Ultra-Hypofractionated Treatments

Magnetic resonance imaging-guided radiation therapy (MRgRT) utilization is rapidly expanding worldwide, driven by advanced capabilities including continuous intrafraction visualization, automatic triggered beam delivery, and on-table adaptive replanning. Our objective was to describe patterns of 0.35T-MRgRT utilization in the United States (US) among early adopters of this novel technology. Anonymized administrative data from all US 0.35T-MRgRT treatment systems were extracted for patients completing treatment from 2014-2020. Detailed treatment information was available for all 0.35T-MR Linac system and some cobalt system patients. Most cobalt patients were included in total only. 17 systems at 16 centers treated 5,733 patients, delivering 40,171 fractions (fractions unavailable for 1,225 cobalt patients), of which 6,244 (15.5%) were adapted. Thirteen centers (81.3%) had treated for > = 1 year, of which 9 treated > 100 patients/year and 6 treated > 150 patients/year. Ultra-hypofractionation (1-5 fractions) was delivered for 72.9% of all patients. The proportion of fractions adapted in patients receiving ultra-hypofractionation was 28.6%, with an average of 3.2 adapted fractions per course. The most commonly treated tumor types were pancreas (20.7%), liver (16.5%), prostate (12.5%), breast (11.5%), and lung (9.4%), respectively, with significantly increased number of fractions delivered from 2018-2020 compared to 2014-2017 for each (pancreas: 5,161 vs. 1,155; liver: 3,597 vs. 921; prostate: 5,795 vs. 1,398; breast: 2,221 vs. 1,876; lung: 2,589 vs. 660). The compound annual growth rate (CAGR) in the number of patients was 59.5%, growing from 111 in 2014 to 1,830 in 2020. Ultra-hypofractionation increased from 31.8% of all treated MR-Linac patients in 2014 to 87.0% in 2020 (n = 1,576/1,811). The proportion of adapted fractions in all patients and ultra-hypofractionation patients increased from 0% in the first two years to 24.3% (n = 3,071/12,639) and 33.8% (n = 2,677/7,911) respectively, by the end of 2020. No patient had adaptive treatment in 2014 although adaptive replanning steadily increased over time. For example, in 2020 vs. 2018 the proportion of adaptive fractions was highest for pancreas (60.6% vs. 50.8%), liver (17.8% vs. 9.9%), and lung (17.8% vs. 1.8%) cancers. This is the first comprehensive study reporting patterns of utilization among early adopters of a 0.35T-MRgRT system in the US. Intrafraction MR guidance, advanced motion management, and increasing adoption of adaptive RT has accelerated a transition to ultra-hypofractionation regimens. MRgRT has been predominantly used to treat abdominal and pelvic tumors, and increasingly with adaptive replanning, which is a radical departure from legacy radiotherapy practices

Potential impact of 68Ga-PSMA-11 PET/CT on the planning of definitive radiation therapy for prostate cancer

Standard-of-care imaging for initial staging of prostate cancer (PCa) underestimates disease burden. Prostate-specific membrane antigen (PSMA) PET/CT detects PCa metastasis with superior accuracy, having a potential impact on the planning of definitive radiation therapy (RT) for nonmetastatic PCa. Our objectives were to determine how often definitive RT planning based on standard target volumes covers 68Ga-PSMA-11 PET/CT-defined disease and to assess the potential impact of 68Ga-PSMA-11 PET/CT on definitive RT planning. Methods: This was a post hoc analysis of an intention-totreat population of 73 patients with localized PCa without prior local therapy who underwent 68Ga-PSMA PET/CT for initial staging as part of an investigational new drug trial. Eleven of the 73 were intermediate- risk (15%), 33 were high-risk (45%), 22 were very-highrisk (30%), and 7 were N1 (9.5%). Clinical target volumes (CTVs), which included the prostate, seminal vesicles, and (in accord with the Radiation Therapy Oncology Group consensus guidelines) pelvic lymph nodes (LNs), were contoured on the CT portion of the PET/CT images by a radiation oncologist masked to the PET findings. 68Ga-PSMA-11 PET/CT images were analyzed by a nuclear medicine physician. 68Ga-PSMA-11-positive lesions not covered by planning volumes based on the CTVs were considered to have a major potential impact on treatment planning. Results: All patients had one or more 68Ga-PSMA-11-positive primary prostate lesions. Twenty-five (34%) and 7 (9.5%) of the 73 patients had 68Ga-PSMA- 11-positive pelvic LN and distant metastases, respectively. The sites of LN metastases in decreasing order of frequency were external iliac (20.5%), common iliac (13.5%), internal iliac (12.5%) obturator (12.5%), perirectal (4%), abdominal (4%), upper diaphragm (4%), and presacral (1.5%). The median size of the LN lesions was 6 mm (range, 4-24 mm). RT planning based on the CTVs covered 69 (94.5%) of the 73 primary lesions and 20 (80%) of the 25 pelvic LN lesions, on a per-patient analysis. Conclusion: 68Ga-PSMA-11 PET/CT had a major impact on intended definitive RT planning for PCa in 12 (16.5%) of the 73 patients whose RT fields covered the prostate, seminal vesicles, and pelvic LNs and in 25 (37%) of the 66 patients whose RT fields covered the prostate and seminal vesicles but not the pelvic LNs