Implementing safe and robust Total Marrow Irradiation using Helical Tomotherapy – A practical guide

Abstract

Total Marrow Irradiation (TMI) with Helical Tomotherapy is a radiotherapy treatment technique that targets bone marrow and sanctuary sites prior to stem cell or bone marrow transplantation (SCT/BMT). TMI is a complex procedure that involves several critical steps that all need to be carefully addressed for a successful implementation, such as dose homogeneity in field junctions, choice of target margins, integrity of treatment and backup planning. In this work we present our solution for a robust and reproducible workflow throughout the treatment chain and data for twenty-three patients treated to date. Material & Methods: Patients were immobilized in a whole body vacuum cushion and thermoplastic mask. CTscanning and treatment were performed in two parts with field matching at the upper thigh. Target consisted of marrow containing bone and sanctuary sites. Lungs, kidneys, bowel, heart and liver were defined as organs at risk (OAR). A fast surface scanning system was used to position parts of the body not covered by the imaging system (MVCT) as well as to reduce treatment time. Results: All patients completed their treatment and could proceed with SCT/BMT. Doses to OARs were significantly reduced and target dose homogeneity was improved compared to TBI. Robustness tests performed on field matching and patient positioning support that the field junction technique is adequate. Replacing MVCT with optical surface scanning reduced the treatment time by 25 min per fraction. Conclusion: The methodology presented here has shown to provide a safe, robust and reproducible treatment for Total Marrow Irradiation using Tomotherapy.

Total marrow and lymphoid irradiation with helical tomotherapy: A practical implementation report

“…Lung D50 achieved in our patients was relatively higher compared to other published series of TMLI [8][9][10]17] and this is possibly due to differences in target delineation, margins and differences in target coverage goals. Varying margins to the chest wall target have been used by investigators which were based either on geometric expansion ranging from 0-10 mm [9,18] or based on chest wall motion [18]. Our coverage goal of 95% of dose to 98% of CTV was higher than the 85% set by others (9) possibly explaining higher lung D50.…”

“…We have used two sets of CT scans and plans with complementary dose gradient across the junction similar to the one described by Haraldsson, et al [18] for TMI. Planning and optimization processes were similar except that we allowed a lengthier junction to ensure plan robustness.…”

Leaf Open Time Sinogram (LOTS): A novel approach for Patient specific quality assurance of Total marrow irradiation

“…However, the practice of TBI has witness a steady decline as a result of radiation induced toxicity and alternative use of only chemotherapy based conditioning regimens. Profoundly, several investigators have reported the feasibility of selective irradiation of total marrow (TMI) and lymphatic (TMLI), using volumetric modulated arc therapy (VMAT) and more conveniently with helical tomotherapy (HT) [4][5][6][7]. TMI have shown a signi cant reduction of dose to organs at risk (OAR) as compared to TBI thereby reducing radiation induced toxicity [5,6,8,9] with encouraging complete response rate [9].…”

“…The treatment planning of TMI/TMLI using either HT or VMAT is complicated due to extensive and complex irregular shape target volume requiring highly modulated beam intensity, multiple isocenters and eld junctions. HT has been the most preferred high precision treatment modality for TMI/TMLI owing to its ability to treat a maximum length of 135 cm at a time requiring zero or one junction to treat the entire target volume as compared to 4-5 junctions in VMAT [4][5][6][7]. Pre-treatment veri cation of dose delivery in the entire target volume is of paramount importance to ensure accurate delivery of dose to the patient.…”

“…All the commercially available active or passive detectors for patient speci c quality assurance (PSQA) have limited longitudinal and lateral dimensions of 20-25 cm to verify highly modulated mega treatment elds from TMI/TMLI especially for HT delivery. The feasibility of different detector arrays (2D or 3D) arranged in planar, hexagonal, circular and helical have been investigated for section by section dose veri cation of TBI/TMI plans [7,10,11]. Takahashi Y and Hui K S [12] developed a simple inhouse whole body phantom to verify TMI treatment plan of up to 110 cm in HT using three ionization chambers and three radiochromic lms.…”