Radiation-induced CT number changes in GTV and parotid glands during the course of radiation therapy for nasopharyngeal cancer

Abstract

Objective: To investigate the changes in CT number (CTN) in gross tumour volume (GTV) and organs at risk (OARs) during the course of radiation therapy (RT) for nasopharyngeal cancer (NPC). Methods: Daily megavoltage CT (MVCT) data collected from 30 patients with NPC treated with a prescription dose of 70 Gy in 30-33 fractions using helical tomotherapy were retrospectively analyzed. The contours of GTV and OARs on daily MVCTs were obtained by populating the planning contours from planning CT to daily MVCTs with manual editing, if necessary. The changes of GTV and OAR volumes and the histograms of CTN in the GTV and OARs during the course of RT delivery were analyzed. Results: Volumes of GTV and parotid glands were reduced during the course of radiation treatment, with an average shrinkage rate of 0.23% per day (range, 0.02-0.8%) and 1.2% per day (range, 0.2-2.3%), respectively. The mean CTN changes in GTV and ipsilateral and contralateral parotid glands were reduced by 52 6 35 HU, 18 6 20 HU and 17 6 22 HU, respectively. For GTV, the CTN and GTV volume decreases were found to be correlated with each other (p , 0.0001). No noticeable CTN change was found in the spinal cord and non-specified tissue irradiated with low doses. Conclusion: The CTN changes in GTV and parotids are measurable during the delivery of fractionated radiotherapy for NPC, were associated with the doses received (the number of fractions delivered) and were patient specific. Advances in knowledge: The CTN change during radiotherapy is dose dependent and is measurable for NPC.

In-vivo Comparison of 18F-FLT uptake, CT Number, Tumor Volume in Evaluation of Repopulation during Radiotherapy for Lung cancer

“…Comparison test also failed to detect a good correlation between TV change and CTN as well as 18 F-FLT uptake during the present study time frame. This result was in coincidence with the previous reports111518. Mayer et al .…”

“…found a fair correlation between CTN reductions and radiation doses for a subset of Head and Neck cancer (HNC) patients. Similar results had also been observed by Xu et al 18,. that the CTN change during radiotherapy was dose dependent and was measurable for NPC, implying that the CTN might be an indicator to monitor tumor growth during treatment.…”

“…But what we should notice is that TV changes are sometimes too small or happen too late to timely provide accurate and useful information of tumor growth for RT re-planning. More and more studies have discovered the potential of CT to observe the molecular biological features of tumors15181920. The study conducted by Mayer et al .…”

Technical Note: Is bulk electron density assignment appropriate for MRI-only based treatment planning for lung cancer?

“…The integration of MRI with radiation therapy (RT) offers the potential ability for tumor tracking and/or respiratory gated delivery techniques, which could be advantageous in treating lung tumors . These advanced features combined with on‐board MRI imaging will improve the management of tumor/organ motion during delivery and the assessment of treatment response …”

“…5,6 These advanced features combined with on-board MRI imaging will improve the management of tumor/organ motion during delivery and the assessment of treatment response. [7][8][9] A major limitation in the exclusive use of MRI for treatment planning is the lack of a relationship between the MRI signal intensity (I MRI ) and electron density (ED), which is necessary for dose calculations. One method to address this issue is to assign bulk ED or relative ED (rED) to each organ, tissue or target necessary for the planning a specific value that is assumed uniform throughout the delineated structure.…”