Repeat CT imaging and replanning during the course of IMRT for head-and-neck cancer

Hansen, Eric K.; Bucci, M. Kara; Quivey, Jeanne M.; Weinberg, Vivian; Xia, Ping

doi:10.1016/j.ijrobp.2005.07.957

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Volume 64, Issue 2 , Pages 355-362, 1 February 2006

Repeat CT imaging and replanning during the course of IMRT for head-and-neck cancer

The paper was presented orally at the 46th Annual Meeting of the American Society for Therapeutic Radiology and Oncology (ASTRO), Atlanta, GA, October 4, 2004.

Eric K. Hansen, M.D.
- Department of Radiation Oncology, University of California, San Francisco, San Francisco, CA, USA
M. Kara Bucci, M.D.
- Department of Radiation Oncology, University of California, San Francisco, San Francisco, CA, USA
Jeanne M. Quivey, M.D.
- Department of Radiation Oncology, University of California, San Francisco, San Francisco, CA, USA
Vivian Weinberg, Ph.D.
- Comprehensive Cancer Center Biostatistics Core, University of California, San Francisco, San Francisco, CA, USA
Ping Xia, Ph.D.
- Department of Radiation Oncology, University of California, San Francisco, San Francisco, CA, USA
- Reprint requests to: Ping Xia, Ph.D., Department of Radiation Oncology, University of California, San Francisco, 1600 Divisadero Street, Suite H-1031, San Francisco, CA 94143-1708. Tel: (415) 353-7175; Fax: (415) 353-9883

Received 19 October 2004; received in revised form 1 July 2005; accepted 6 July 2005. published online 26 October 2005.

Purpose: Many patients with head-and-neck (H&N) cancer have tumor shrinkage and/or weight loss during the course of radiotherapy. We conducted this retrospective study to determine the dosimetric effects of repeat computed tomography (CT) imaging and replanning during the course of intensity-modulated radiotherapy (IMRT) on both normal tissues and target volumes.

Methods and Materials: A retrospective chart review identified 13 patients with H&N cancer treated with IMRT who had repeat CT imaging and replanning during the course of radiotherapy. The first IMRT plan for each patient was generated based on the original planning CT scan acquired before the start of treatment. Because of tumor shrinkage or weight loss during radiotherapy, a second CT scan was acquired, and a new plan was generated and used to complete the course of IMRT. CT–CT fusion was used to correct patient positioning differences between the scans. By using a commercial inverse IMRT planning system, a hybrid IMRT plan was generated for each patient by applying the beam configurations of the first IMRT plan (including the intensity profile of each beam) to the anatomy of the second CT scan. The dose–volume histograms of the actual and hybrid IMRT plans were compared using analysis of variance methods for repeated measures.

Results: All patients had locally advanced, nonmetastatic Stage III or IV disease, including 6 nasopharynx, 6 oropharynx, and 1 unknown primary site. All patients were treated with concurrent platinum-based chemotherapy. When replanning vs. not replanning was compared, the hybrid IMRT plans (without replanning) demonstrated reduced doses to target volumes and increased doses to critical structures. The doses to 95% (D₉₅) of the planning target volumes of the gross tumor volume (PTV_GTV) and the clinical target volume (PTV_CTV) were reduced in 92% of patients, by 0.8–6.3 Gy (p = 0.02) and 0.2–7.4 Gy (p = 0.003), respectively. The maximum dose (D_max) to the spinal cord increased in all patients (range, 0.2–15.4 Gy; p = 0.003) and the brainstem D_max increased in 85% of patients without replanning (range, 0.6–8.1 Gy; p = 0.007).

Conclusions: Repeat CT imaging and replanning during the course of IMRT for selected patients with H&N cancer is essential to identify dosimetric changes and to ensure adequate doses to target volumes and safe doses to normal tissues. Future prospective studies with larger sample sizes will help to determine criteria for repeat CT imaging and IMRT replanning for H&N cancer patients undergoing radiotherapy.

Keywords: Head-and-neck cancer , Intensity-modulated radiotherapy , Imaging , Radiotherapy planning