Abstract
Simple SummaryThermoBrachyTherapy, a combination therapy where radiation and heat are simultaneously applied using needle-shaped applicators from within the target, is a potentially very effective treatment for prostate cancer. When radiation and thermal therapies are applied, the dose coverage of each treatment is preplanned without considering the combined effect of the two dose distributions. In this study, we propose a method to automatically plan the thermal dose in such a treatment, based on the combined effect with the radiation. Furthermore, we apply the method on 10 patients and compare the treatment to a brachytherapy-only treatment plan. In this way, we show that, with properly optimized ThermoBrachyTherapy, we can provide equivalent combined dose coverages to the prostate, while reducing the dose delivered to critical organs surrounding the prostate, which might translate to reduced toxicity of the treatment.In high-dose-rate brachytherapy (HDR-BT) for prostate cancer treatment, interstitial hyperthermia (IHT) is applied to sensitize the tumor to the radiation (RT) dose, aiming at a more efficient treatment. Simultaneous application of HDR-BT and IHT is anticipated to provide maximum radiosensitization of the tumor. With this rationale, the ThermoBrachyTherapy applicators have been designed and developed, enabling simultaneous irradiation and heating. In this research, we present a method to optimize the three-dimensional temperature distribution for simultaneous HDR-BT and IHT based on the resulting equivalent physical dose (EQDphys) of the combined treatment. First, the temperature resulting from each electrode is precomputed. Then, for a given set of electrode settings and a precomputed radiation dose, the EQDphys is calculated based on the temperature-dependent linear-quadratic model. Finally, the optimum set of electrode settings is found through an optimization algorithm. The method is applied on implant geometries and anatomical data of 10 previously irradiated patients, using reported thermoradiobiological parameters and physical doses. We found that an equal equivalent dose coverage of the target can be achieved with a physical RT dose reduction of 20% together with a significantly lower EQDphys to the organs at risk (p-value < 0.001), even in the least favorable scenarios. As a result, simultaneous ThermoBrachyTherapy could lead to a relevant therapeutic benefit for patients with prostate cancer.
Highlights
High-dose-rate brachytherapy (HDR-BT) is a well-established treatment option in localized prostate cancer treatment [1]
Radiobiological clinical data have shown that prostate cancer, in contrast to most tumor sites, has a very low α/β ratio (α/β = 0.9–2.2 Gy) [2]. This is a value very close to or lower than the α/β of nearby organs at risk (OAR), with the urethra estimated at an α/β = 0.5–1 Gy [3] and the rectum estimated at an α/β = 1.6–3.1 Gy [4], depending on the considered toxicity endpoint. This very low α/β ratio is the reason that radiotherapy for prostate cancer is aimed towards hypofractionation, with extensive use of HDR-BT as a boost to external beam radiation therapy (EBRT) or even as a standalone therapy [5,6]
We have developed novel ThermoBrachytherapy (TBT) applicators that enable the simultaneous application of HDR-BT and capacitive coupled radiofrequency (CC-RF) interstitial heating [25]
Summary
High-dose-rate brachytherapy (HDR-BT) is a well-established treatment option in localized prostate cancer treatment [1]. Radiobiological clinical data have shown that prostate cancer, in contrast to most tumor sites, has a very low α/β ratio (α/β = 0.9–2.2 Gy) [2] This is a value very close to or lower than the α/β of nearby organs at risk (OAR), with the urethra estimated at an α/β = 0.5–1 Gy [3] and the rectum estimated at an α/β = 1.6–3.1 Gy [4], depending on the considered toxicity endpoint. This very low α/β ratio is the reason that radiotherapy for prostate cancer is aimed towards hypofractionation, with extensive use of HDR-BT as a boost to external beam radiation therapy (EBRT) or even as a standalone therapy (monotherapy) [5,6]. Ultrahypofractionated HDR-BT monotherapy is currently not recommended in higher-risk patients [10,11]
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