Session Item

We aimed to develop and implement Volumetric Modulated Arc Therapy (VMAT) for Total Marrow Irradiation (TMI) in our clinic to enable selective dose-escalation to the marrow for patients with hematologic malignancies.

VMAT-TMI was recently commissioned at our institution (Raystation-Mosaiq environment). After literature review and consults with outside institutions, patient selection criteria as well as dosimetric constraints for both targets and normal tissues were established through consensus between radiation oncologists, medical oncologists, and medical physicists. Treatment planning studies were performed with multiple VMAT and 3D isocenters. Isocenter selections, junction settings, calculation properties, beam parameter settings, multi-isocenter co-optimization strategies, and dose computation on both head- and feet-first supine CT scans were explored. The necessary immobilization devices and ancillary equipment were identified. We developed patient setup and image guidance techniques to support a ≤1 cm PTV margin while simultaneously minimizing treatment setup time. End-to-end testing using the CIRS ATOM male adult phantom was conducted to test the feasibility of the entire treatment planning and treatment delivery process. To inform the allowable patient shifts, robustness analysis was performed by offsetting the isocenters by ± 0.2, 0.5, and 1.0 cm in all 3 directions, and shifting one isocenter independently versus shifting multiple isocenters together (with distance between isocenters maintained). VMAT-TMI as a component of transplant conditioning was conducted on an IRB-approved protocol and all patients provided informed consent for treatment.

To date, 3 patients have been successfully treated with VMAT-TMI at our institution. All 3 patients tolerated the procedure well. The target prescription dose was 1200 cGy in 4 fractions. TMI was planned with VMAT for the body (6 to 12 overlapping arcs with 3 to 6 isocenters) and 3D conformal radiotherapy for the legs. Raystation was capable of co-optimization on the head-first supine scan using the background dose from the 3D plan on the feet-first supine scan. PTV D90% was 1069 ± 102 cGy (bones D90% = 1156 ± 67 cGy). Mean doses to the lungs, kidneys, brain, heart, and liver were 622 ± 28 cGy, 461 ± 49 cGy, 487 ± 25 cGy, 543 ± 23 cGy, 546 ± 6 cGy, respectively. To confirm each patient’s setup reproducibility, a verification simulation CT scan was acquired, and a dry run was performed. The clinical plans remained robust as evaluated on the verification scans. For daily treatments, isocenter shifts were allowed in the superior-inferior direction only, and the relevant dosimetric parameters could be met for discrepancies up to ± 1.0 cm when the distance between isocenters were maintained.

We have developed and implemented VMAT-TMI in our clinic (Raystation-Mosaiq environment), thereby expanding the radiotherapy options in the multidisciplinary management of patients with hematologic malignancies.