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Published on: July 3, 2014
Three-dimensional heart dose reconstruction to estimate normal tissue complication probability after breast
R J W Louwe1, M Wendling, M B van Herk
1Department of Radiation Oncology, The Netherlands Cancer Institute/Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands. r.louwe@rther.umcn.nl
Insights
This study demonstrates electronic imaging portal device (EPID) dosimetry for accurate in vivo heart dose verification during breast cancer radiotherapy. This method enables reliable estimation of normal tissue complication probability for late cardiac mortality, even without 3D CT data.
Area of Science:
- Radiation Oncology
- Medical Physics
- Radiotherapy Dosimetry
Background:
- Cardiac irradiation is a significant concern in breast cancer radiotherapy, potentially leading to long-term complications.
- Accurate assessment of heart dose is crucial for minimizing radiation-induced cardiac mortality.
- Three-dimensional (3D) treatment planning, while beneficial, is not always feasible due to data limitations (e.g., lack of CT scans).
Purpose of the Study:
- To investigate the feasibility of 3D reconstruction of actual heart dose using electronic imaging portal device (EPID) dosimetry.
- To enable independent verification of heart dose and calculation of dose-volume histograms (DVHs) without requiring planning CT data.
- To estimate the normal tissue complication probability (NTCP) for late excess cardiac mortality based on EPID-derived heart doses.
Main Methods:
- Reconstruction of patient dose from treatment portal images at the radiological midsurface.
- Combination with a geometrical heart model to calculate DVHs and NTCP.
- Comparison of EPID dosimetry results with 3D treatment planning system (TPS) calculations, film dosimetry, and ionization chamber measurements in an anthropomorphic phantom and in fifteen breast cancer patients.
Main Results:
- EPID-reconstructed heart dose agreed within 1.5% with TPS calculations in the lung/heart region.
- The average difference in NTCP values between the EPID method and TPS calculations was 0.1% ± 0.3% for phantom and patient data.
- EPID dosimetry yielded lower average NTCP values (0.9%) compared to the Hurkmans et al. method (2.2%) for in vivo measurements.
Conclusions:
- EPID dosimetry is a suitable method for in vivo verification of heart dose in breast cancer radiotherapy.
- The approach allows for the incorporation of actual heart dose into NTCP estimations for late excess cardiac mortality.
- This study presents the first use of portal dosimetry for calculating DVH and NTCP for an organ at risk.
Abstract:
Irradiation of the heart is one of the major concerns during radiotherapy of breast cancer. Three-dimensional (3D) treatment planning would therefore be useful but cannot always be performed for left-sided breast treatments, because CT data may not be available. However, even if 3D dose calculations are available and an estimate of the normal tissue damage can be made, uncertainties in patient positioning may significantly influence the heart dose during treatment. Therefore, 3D reconstruction of the actual heart dose during breast cancer treatment using electronic imaging portal device (EPID) dosimetry has been investigated. A previously described method to reconstruct the dose in the patient from treatment portal images at the radiological midsurface was used in combination with a simple geometrical model of the irradiated heart volume to enable calculation of dose-volume histograms (DVHs), to independently verify this aspect of the treatment without using 3D data from a planning CT scan. To investigate the accuracy of our method, the DVHs obtained with full 3D treatment planning system (TPS) calculations and those obtained after resampling the TPS dose in the radiological midsurface were compared for fifteen breast cancer patients for whom CT data were available. In addition, EPID dosimetry as well as 3D dose calculations using our TPS, film dosimetry, and ionization chamber measurements were performed in an anthropomorphic phantom. It was found that the dose reconstructed using EPID dosimetry and the dose calculated with the TPS agreed within 1.5% in the lung/heart region. The dose-volume histograms obtained with EPID dosimetry were used to estimate the normal tissue complication probability (NTCP) for late excess cardiac mortality. Although the accuracy of these NTCP calculations might be limited due to the uncertainty in the NTCP model, in combination with our portal dosimetry approach it allows incorporation of the actual heart dose. For the anthropomorphic phantom, and for fifteen patients for whom CT data were available to test our method, the average difference between the NTCP values obtained with our method and those resulting from the dose distributions calculated with the TPS was 0.1% +/- 0.3% (1 SD). Most NTCP values were 1%-2% lower than those obtained using the method described by Hurkmans et al. [Radiother. Oncol. 62, 163-171 (2002)], using the maximum heart distance determined from a simulator image as a single pre-treatment parameter. A similar difference between the two methods was found for twelve patients using in vivo EPID dosimetry; the average NTCP value obtained with EPID dosimetry was 0.9%, whereas an average NTCP value of 2.2% was derived using the method of Hurkmans et al. The results obtained in this study show that EPID dosimetry is well suited for in vivo verification of the heart dose during breast cancer treatment, and can be used to estimate the NTCP for late excess cardiac mortality. To the best of our knowledge, this is the first study using portal dosimetry to calculate a DVH and NTCP of an organ at risk.
