Dosimetric and volumetric effects of end expiration breath hold radiotherapy for oesophageal cancer
Christopher Mayhew,
United Kingdom
PO-1858
Abstract
Dosimetric and volumetric effects of end expiration breath hold radiotherapy for oesophageal cancer
Authors: Christopher Mayhew1, Jeyaanth Venkatasai2, Marina Khan3, Benson Leung3, Kasia Owczarczyk2, Georgios Ntentas1
1Guy's and St Thomas' NHS Foundation Trust, Department of Medical Physics, London, United Kingdom; 2Guy's and St Thomas' NHS Foundation Trust, Department of Oncology, London, United Kingdom; 3Guy's and St Thomas' NHS Foundation Trust, Department of Radiotherapy, London, United Kingdom
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Purpose or Objective
Respiratory gating using end expiration breath hold (EEBH) radiotherapy has the potential to reduce tumour motion during treatment in tumours near the diaphragm. This may obviate the need for an internal target volume (ITV), and reduce the dose to organs at risk (OAR) such as the heart, lungs and liver by repositioning them with respect to the target volume compared to free-breathing (FB) radiotherapy using 4DCT. The aim of our study was to evaluate the dosimetric and volumetric effects of EEBH in patients with oesophageal cancer undergoing (chemo)radiotherapy.
Material and Methods
Thus far, 12 lower third oesophageal cancer patients have been planned for, using volumetric modulated arc therapy (VMAT) in both FB and EEBH scans. For patients treated in EEBH, clinicians created a new set of target volumes on the FB scans and vice-versa. New treatment plans were retrospectively generated for the non-clinical CT & structure set. The plans were optimised and evaluated in order to be comparable to the original clinical plan. All plans were reviewed and approved by clinicians using the same criteria. Paired t-tests were performed to examine within-patient volumetric and dosimetric differences.
Results
Of the 12 patients, 10 were male and two female with a median age of 73.5 years. 10 patients presented at stage T3 and two at T2, with the prevailing histology being adenocarcinoma (10/12). 11 were treated with EEBH and one in FB. Volumetrically, we observed a mean PTV volume reduction of 61.8cc [p=0.002] for EEBH plans compared to FB (Table 1). Heart/PTV overlap volumes were reduced by 1.21% [p=0.024] and Lung/PTV overlap volumes by 0.28% [p=0.010] between EEBH and FB plans. Dosimetrically, mean heart doses reduced by 0.75Gy [p=0.231] with EEBH but not with statistical significance, with lung and liver mean dose reductions of 0.61Gy [p=0.086] and 0.76Gy [p=0.096] respectively.
Table 1 – Average volumetric and dosimetric results for comparison between EEBH and FB for lower oesophagus RT
| Mean PTV Volume
/cc
(Range)
| Mean Heart/PTV Overlap Volume as a percentage of heart volume /%
| Mean Lung/PTV Overlap Volume as a percentage of lung volume /%
| Mean Liver/PTV Overlap Volume as a percentage of liver volume /%
| Mean Heart Dose /Gy
| Mean Lung Dose /Gy
| Mean Liver Dose /Gy
|
EEBH
| 381.1
(132.0-821.0)
| 4.20
| 0.29
| 1.29
| 17.85
| 7.26
| 10.65
|
FB
| 442.9 (153.8-904.8)
| 5.42
| 0.57
| 1.53
| 18.61
| 7.87
| 11.41
|
Difference (p-value)
| 61.8
(0.002)
| 1.21
(0.024)
| 0.280
(0.010)
| 0.246
(0.266)
| 0.751
(0.231)
| 0.609
(0.086)
| 0.763
(0.096)
|
Conclusion
Our study is one of the first to examine the dosimetric and volumetric effects of the EEBH technique in patients with oesophageal cancer. EEBH presents a promising method for reducing PTV volumes, as well as OAR doses. This, combined with the increased stability in motion that EEBH assures, compared to that of FB, may show EEBH as an effective breathing technique for optimising radiotherapy for oesophageal cancer treatment. Further work is ongoing to investigate the significance of current results in a larger patient cohort.