Multimodality Image Guided Total Marrow Irradiation and Verification of the Dose Delivered to the Lung, PTV, and Thoracic Bone in a Patient: A Case Study

Abstract

This work reports our initial experience using multimodality image guidance to improve total marrow irradiation (TMI) using helical tomotherapy. We also monitored the details of the treatment delivery to glean information necessary for the implementation of future adaptive processes. A patient with metastatic Ewing's sarcoma underwent MRI, and bone scan imaging prior to TMI. A whole body kilovoltage CT (kVCT) scan was obtained for intensity modulated TMI treatment planning, including a boost treatment to areas of bony involvement. The delivered dose was estimated by using MVCT images from the helical tomotherapy treatment unit, compared to the expected dose distributions mapped onto the kVCT images. Clinical concerns regarding patient treatment and dosimetric uncertainties were also evaluated. A small fraction of thoracic bone volume received lower radiation dose than the prescribed dose. Reconstructed planned treatment volume (PTV) and the dose delivered to the lung were identical to planned dose. Bone scan imaging had a higher sensitivity for detecting skeletal metastasis compared to MR imaging. However the bone scan lacked sufficient specificity in three dimensions to be useful for planning conformal radiation boost treatments. Inclusion of appropriate imaging modalities improves detection of metastases, which allows the possibility of a radiation dose boost to metastases during TMI.Conformal intensity modulated radiation therapy via helical tomotherapy permitted radiation delivery to metastases in the skull with reduced dose to brain in conjunction with TMI. While TMI reduces irradiation to the lungs, onboard megavoltage computed tomography (MVCT) to verify accurate volumetric dose coverage to marrow-containing thoracic bones may be essential for successful conformal TMI treatment.

Dose Escalation of Total Marrow Irradiation in High-Risk Patients Undergoing Allogeneic Hematopoietic Stem Cell Transplantation

“…We used TMI to deliver highly focused radiation to the skeleton, which is a large and complex anatomical structure. Given this, it was essential to assure that patient positioning within the irradiation unit was accurate over the course of multiple treatments lasting for either 5 or 6 days in both small children and large adults which requires careful attention to patient positioning with each treatment 19 . Secondly, the BED provides a biological equivalent reference to compare the various strategies of TMI dose escalation with standard TBI.…”

“…General anesthesia was used for pediatric patients unable to follow commands due to the risk of large body motion which could result in delivery of irradiation to incorrect anatomical sites. A technique was previously developed to use WB MVCT images to calculate the irradiation dose delivered during TMI, taking into consideration the subtle change in patient positioning and was implemented in this trial 19,20 . The delivered skeletal and pulmonary doses were verified with the original treatment plan.…”

Preclinical Assessment of Volumetric Modulated Arc Therapy for Total Marrow Irradiation

“…A similar approach was followed by Aydogan et al (7). More seminal investigations were performed by groups looking at approaches bases on helical tomotherapy (HT) (8)(9)(10)(11)(12)(13). Shueng et al (8) showed that HT allowed a dose reduction to OARs from 21% to 74% with respect to TBI.…”

“…Radiation treatment was associated to chemotherapy with melphalan. Hui et al (9,10) showed that with TMI the dose to OARs might be reduced by 35-70% of the prescribed dose using HT, through a feasibility study on a phantom and with the treatment of a single case. The City of Hope group (Duarte, CA, USA) (11)(12)(13) reported on both simulation studies and treatment of 21 patients with HT.…”

Feasibility of intrafraction whole-body motion tracking for total marrow irradiation

“…31 One of the main aims for the recently developed total marrow irradiation (TMI) method is to reduce radiation dose to lungs to control lung toxicity. 5,6,32 At present, safety margins around the thoracic bone are kept the same (approximately 1.5 cm) for all directions because of limited knowledge of the directional chest wall motion. Breathing motion data shows a relatively larger variation in the diaphragm, in comparison to the apex and thoracic regions of the chest.…”