Biological dose summation of external beam radiotherapy for the whole breast and image-guided high-dose-rate interstitial brachytherapy boost in early-stage breast cancer

Determining Combined Modality Dosimetric Constraints by Integration of IMRT and LDR Prostate Brachytherapy Dosimetry and Correlation with Toxicity

Purpose

Intermediate- and high-risk prostate cancer patients undergoing combination external beam radiation therapy (EBRT) and low dose rate (LDR) brachytherapy have demonstrated increased genitourinary (GU) toxicity. We have previously demonstrated a method to combine EBRT and LDR dosimetry. In this work, we use this technique for a sample of patients with intermediate- and high-risk prostate cancer, correlate with clinical toxicity, and suggest preliminary summed organ-at-risk constraints for future investigation.

Methods and Materials

Intensity modulated EBRT and ¹⁰³Pd-based LDR treatment plans were combined for 138 patients using biological effective dose (BED) and deformable image registration. GU and gastrointestinal (GI) toxicity were compared with combined dosimetry for the urethra, bladder, and rectum. Differences between doses in each toxicity grade were assessed by analysis of variance (α = 0.05). Combined dosimetric constraints are proposed using the mean organ-at-risk dose, subtracting 1 standard deviation for a conservative recommendation.

Results

The majority of our 138-patient cohort experienced grade 0 to 2 GU or GI toxicity. Six grade 3 toxicities were noted. Mean prostate BED D90 (± 1 standard deviation) was 165.5±11.1 Gy. Mean urethra BED D10 was 230.3±33.9 Gy. Mean bladder BED was 35.2±11.0 Gy. Mean rectum BED D2cc was 85.6±24.3 Gy. Significant dosimetric differences between toxicity grades were found for mean bladder BED, bladder D15, and rectum D50, but differences between individual means were not statistically significant. Given the low incidence of grade 3 GU and GI toxicity, we propose urethra D10 <200 Gy, rectum D2cc <60 Gy, and bladder D15 <45 Gy as preliminary dose constraints for combined modality therapy.

Conclusions

We successfully applied our dose integration technique to a sample of patients with intermediate- and high-risk prostate cancer. Incidence of grade 3 toxicity was low, suggesting that combined doses observed in this study were safe. We suggest preliminary dose constraints as a conservative starting point to investigate and escalate prospectively in a future study.

Comparison of Breast Cancer Radiotherapy Techniques Regarding Secondary Cancer Risk and Normal Tissue Complication Probability - Modelling and Measurements Using a 3D-Printed Phantom

Background

Radiotherapy after breast-conserving therapy is a standard postoperative treatment of breast cancer, which can be carried out with a variety of irradiation techniques. The treatment planning must take into consideration detrimental effects on the neighbouring organs at risk-the lung, the heart, and the contralateral breast, which can include both short- and long-term effects represented by the normal tissue complication probability and secondary cancer risk.

Patients and Methods

In this planning study, we investigate intensity-modulated (IMRT) and three-dimensional conformal (3D-CRT) radiotherapy techniques including sequential or simultaneously integrated boosts as well as interstitial multicatheter brachytherapy boost techniques of 38 patients with breast-conserving surgery retrospectively. We furthermore develop a 3D-printed breast phantom add-on to allow for catheter placement and to measure the out-of-field dose using thermoluminescent dosimeters placed inside an anthropomorphic phantom. Finally, we estimate normal tissue complication probabilities using the Lyman-Kutcher-Burman model and secondary cancer risks using the linear non-threshold model (out-of-field) and the model by Schneider et al. (in-field).

Results

The results depend on the combination of primary whole-breast irradiation and boost technique. The normal tissue complication probabilities for various endpoints are of the following order: 1%-2% (symptomatic pneumonitis, ipsilateral lung), 2%-3% (symptomatic pneumonitis, whole lung), and 1%-2% (radiation pneumonitis grade ≥ 2, whole lung). The additional relative risk of ischemic heart disease ranges from +25% to +35%. In-field secondary cancer risk of the ipsilateral lung in left-sided treatment is around 50 per 10,000 person-years for 20 years after exposure at age 55. Out-of-field estimation of secondary cancer risk results in approximately 5 per 10,000 person-years each for the contralateral lung and breast.

Conclusions

In general, 3D-CRT shows the best risk reduction in contrast to IMRT. Regarding the boost concepts, brachytherapy is the most effective method in order to minimise normal tissue complication probability and secondary cancer risk compared to teletherapy boost concepts. Hence, the 3D-CRT technique in combination with an interstitial multicatheter brachytherapy boost is most suitable in terms of risk avoidance for treating breast cancer with techniques including boost concepts.

Unresectable bulky chest wall recurrent breast cancer controlled with CT-guided interstitial high-dose-rate brachytherapy and external beam radiotherapy with adjuvant hormonal therapy - case report

Purpose

Bulky chest wall recurrence after mastectomy presents a therapeutic challenge because of high-dose of radiation required to control the disease, and its proximity to low-tolerance organs at risk. We report a case of successful computed tomography (CT)-guided high-dose-rate (HDR) salvage interstitial brachytherapy (ISBT) boost.

Material and methods

A 70-year-old female initially presented with a tumor in right breast, and was treated with mastectomy and adjuvant chemotherapy, followed by hormonal therapy for 5 years without adjuvant radiotherapy. In 2018, 20 years after the initial treatment, she developed unresectable chest wall recurrence that measured 10.5 cm × 7.3 cm × 4.5 cm, with bone and parietal pleura invasion. Biopsy revealed invasive pleomorphic lobular carcinoma [estrogen receptor (ER)-positive, progesterone receptor (PR)-negative, HER2-negative]. There was no evidence of metastatic disease.

Results

The patient underwent external beam radiotherapy (EBRT) plus ISBT. After EBRT of 50 Gy in 25 fractions was completed, CT-guided ISBT was performed as an outpatient treatment. HDR dose was 16 Gy delivered in 2 fractions with 2 implants. Dose was prescribed to gross tumor volume. ISBT plans were created using inverse planning simulated annealing (IPSA) algorithm. Gross tumor volume D_90% plus EBRT dose was 82 Gy equivalent dose of 2 Gy (EQD₂), assuming α/β of 4 for breast carcinoma. The patient continued on hormonal therapy. At the 30-month follow-up, the patient remains in remission. The tumor could not be detected by magnetic resonance imaging (MRI) or positron emission tomography (PET). There were no severe treatment-related complications.

Conclusions

CT-guided HDR ISBT boost can be a useful modality in individualizing treatment strategies for breast cancer patients with unresectable bulky chest wall recurrence.