Online adaptive radiotherapy potentially reduces toxicity for high-risk prostate cancer treatment

Abstract

Background and purpose: With daily, MR-guided online adapted radiotherapy (MRgART) it may be possible to reduce the PTV in pelvic RT. This study investigated the potential reduction in normal tissue complication probability (NTCP) of MRgART compared to standard radiotherapy for high-risk prostate cancer. Materials and methods: Twenty patients treated with 78 Gy to the prostate and 56 Gy to elective pelvic lymph nodes were included. VMAT plans were generated with standard clinical PTV margins. Additionally to the planning MR, patients had three MRI scans during treatment to simulate an MRgART. A reference plan with PTV margins determined for MRgART was created per patient and adapted to each of the following MRs. Adapted plans were warped to the planning MR for dose accumulation. The standard plan was rigidly registered to each adaptation MR before it was warped to the planning MR for dose accumulation. Dosimetric impact was compared by DVH analysis and potential clinical effects were assessed by NTCP modeling. Results: MRgART yielded statistically significant lower doses for the bladder wall, rectum and peritoneal cavity, compared to the standard RT, which translated into reduced median risks of urine incontinence (DNTCP 2.8%), urine voiding pain (DNTCP 2.8%) and acute gastrointestinal toxicity (DNTCP 17.4%). Mean population accumulated doses were as good or better for all investigated OAR when planned for MRgART as standard RT. Conclusion: Online adapted radiotherapy may reduce the dose to organs at risk in high-risk prostate cancer patients, due to reduced PTV margins. This potentially translates to significant reductions in the risks of acute and late adverse effects.

A Prospective Study of Stereotactic Body Radiotherapy (SBRT) with Concomitant Whole-Pelvic Radiotherapy (WPRT) for High-Risk Localized Prostate Cancer Patients Using 1.5 Tesla Magnetic Resonance Guidance: The Preliminary Clinical Outcome

“…Despite the lack of previous MRgSBRT studies for direct comparisons of clinical outcome, our preliminary clinical outcome seemed to be well aligned with the simulation results by Christiansen et al [ 47 ], although slightly larger PTV margins were applied in our study. Long-term clinical outcome of our study will be presented with further follow-up.…”

“…Recently, a simulation study by Christiansen et al [ 47 ] showed that online adaptive MRgRT might reduce the dose to the surrounding tissues compared to standard RT for HR-PC patients by allowing tighter PTV margins to both the prostate (3 mm, 4 mm, and 5 mm in R-L, S-I, and A-P) and pelvic lymph node (uniform 2 mm) CTVs. Such observed reductions in doses to OARs could translate to reduced risks of acute GI toxicity and late bladder toxicity.…”

“…The better visualization of on-the-day anatomies by daily MR images at each fraction also facilitates online plan adaptation without fiducial markers to achieve superior targets coverage and sparing organs at risk (OARs) [ 46 ]. A recent simulation study suggested that online adapted MRgRT may reduce the dose to organs at risk (OARs) in HR-PC patients due to the reduced PTV margins derived from inter-fractional daily MRI, which potentially translates to toxicity reduction [ 47 ]. However, to date, the reports of clinical outcomes of MRgSBRT with concomitant WPRT in HR-PC remain sparse.…”

Assessment of planning target volume margins in 1.5 T magnetic resonance‐guided stereotactic body radiation therapy for localized prostate cancer

“…Given a considerably long treatment time in MRgSBRT, it is reasonable to conclude that a posterior margin of 3 mm and an SI margin of 5 mm might need to be slightly increased to achieve adequate PTV coverage in the absence of intrafractional motion monitoring. Compared with previously published data for gantry-based SBRT 15 and MRgRT on MR-Linac, 29 the present data show a smaller AP margin, but a larger SI margin, thus a more pronounced margin in the SI direction. This could be due to the endorectal balloon used in our protocol for MRgSBRT, as the rectum wall distension might be suppressed by the inserted rectal balloon, resulting in consistent rectum shape through the treatment course.…”

Assessment of a Therapeutic X-ray Radiation Dose Measurement System Based on a Flexible Copper Indium Gallium Selenide Solar Cell

“…Radiation therapy is one of the primary treatments for cancer. Recently, various radiation therapy techniques such as image-guided radiotherapy and adaptive radiotherapy have been adopted by clinics to deliver highly conformal doses to tumors while sparing normal tissues [ 1 , 2 , 3 , 4 ].…”