[Radiobiology in brachytherapy]

Stereotactic Radiation Therapy versus Brachytherapy: Relative Strengths of Two Highly Efficient Options for the Treatment of Localized Prostate Cancer

Stereotactic body radiation therapy (SBRT) has become a valid option for the treatment of low- and intermediate-risk prostate cancer. In randomized trials, it was found not inferior to conventionally fractionated external beam radiation therapy (EBRT). It also compares favorably to brachytherapy (BT) even if level 1 evidence is lacking. However, BT remains a strong competitor, especially for young patients, as series with 10-15 years of median follow-up have proven its efficacy over time. SBRT will thus have to confirm its effectiveness over the long-term as well. SBRT has the advantage over BT of less acute urinary toxicity and, more hypothetically, less sexual impairment. Data are limited regarding SBRT for high-risk disease while BT, as a boost after EBRT, has demonstrated superiority against EBRT alone in randomized trials. However, patients should be informed of significant urinary toxicity. SBRT is under investigation in strategies of treatment intensification such as combination of EBRT plus SBRT boost or focal dose escalation to the tumor site within the prostate. Our goal was to examine respective levels of evidence of SBRT and BT for the treatment of localized prostate cancer in terms of oncologic outcomes, toxicity and quality of life, and to discuss strategies of treatment intensification.

Stereotactic Ablative Brachytherapy: Recent Advances in Optimization of Radiobiological Cancer Therapy

Brachytherapy (BT), a type of focal anti-cancer radiotherapy, delivers a highly focused radiation dose to localized tumors, sparing surrounding normal tissues. Recent technological advances have helped to increase the accuracy of BT and, thus, improve BT-based cancer treatment. Stereotactic ablative brachytherapy (SABT) was designed to improve the ablative effect of radiation, which was achieved via improved image guidance, and calculation of ablative dose, shorter treatment duration, and better organ preservation. Recently collected data characterized SABT as having the potential to cure various early-stage cancers. The method provides higher tumor control rate levels that were previously achievable only by surgical resection. Notably, SABT is suitable for application with unresectable malignancies. However, the pathological assessment of SABT irradiated tumors is limited due to difficulties in specimen acquisition. Prostate, lung, liver, and gynecological cancers are the most commonly reported SABT-treated malignancies. This study will give an overview of SABT, focusing on the advances in SABT optimization, and provide insights on the future benefits of the combined application of SABT with cancer immunotherapies.

[Brachytherapy: When needs overtake care offer]

Brachytherapy has the unique characteristic of being able to deliver high doses to a very localized volume, and remains one of the radiotherapy techniques that has an unparalleled therapeutic index. However, its use has been declining in the past years. Globally, only 55 to 88 % of patients with locally advanced cervical cancer benefit from utero-vaginal brachytherapy, despite the fact that it is proven to enhance both progression-free and overall survival. A decline in the use of low dose rate brachytherapy has likewise been described in the treatment of low-risk and favorable intermediate-risk prostate cancers. Several factors could explain this. First, the radiation oncologists who have the proficiency to perform brachytherapy seems to be inadequate, as it is a technique that requires training and expertise for optimal applications. In many cancer care centers, the caseload is insufficient to provide this experience. Second, the increasing use of technically advanced external beam radiation therapy, such as intensity modulated radiation therapy, offers an easier substitute with more lucrative benefits, resulting in decreased utilization of brachytherapy. However, when brachytherapy is not delivered, a poorer survival rate is reported in locally advanced cervical cancer, and is suggested in intermediate and high-risk prostate cancer. The increasing level of evidence of treatment with brachytherapy necessitates an improvement in its accessibility by having more radiation oncologists as well as cancer centers equipped to perform the procedure.

Radiobiology of brachytherapy: The historical view based on linear quadratic model and perspectives for optimization

Most preclinical studies examining the radiobiology of brachytherapy have focused on dose rate effects. Scarcer data are available on other major parameters of therapeutic index, such as cell cycle distribution, repopulation or reoxygenation. The linear quadratic model describes the effect of radiotherapy in terms of normal tissue or tumour response. It allows some comparisons between various irradiation schemes. This model should be applied cautiously for brachytherapy, because it relies on cell death analysis only, and therefore partially reflects the biological effects of an irradiation. Moreover, the linear quadratic model validity has not been demonstrated for very high doses per fraction. A more thorough analysis of mechanisms involved in radiation response is required to better understand the true effect of brachytherapy on normal tissue. The modulation of immune response is one promising strategy to be tested with brachytherapy. A translational approach applied to brachytherapy should lead to design trials testing pharmacological agents modulating radiation response, in order to improve not only local control, but also decrease the risk of distant failure. Here we review the radiobiology of brachytherapy, from the historical view based on linear quadratic model to recent perspectives for biological optimization.

High dose rate brachytherapy for prostate cancer: A prospective toxicity evaluation of a one day schedule including two 13.5 Gy fractions

BACKGROUND AND PURPOSE

High dose-rate (HDR) brachytherapy (BT) provides a highly conformal method of dose delivery to the prostate. The purpose of this study is to prospectively determine the toxicity of the treatment protocol of 13.5 Gy × 2 fractions.

MATERIALS AND METHODS

From 2010 through 2017, 119 patients with low (71%) or intermediate-risk prostate cancer were prospectively treated in a single institute with HDR-BT at 13.5 Gy × 2 fractions within one day. Median follow-up time was 4.4 years.

RESULTS

Actuarial rates of no biochemical evidence of disease, overall survival and metastasis-free survival for all patients were 96%,98% and 98%, respectively. The cumulative incidence of acute grade 2 and 3 genitourinary (GU) toxicity was 9% and 2%, respectively. The corresponding incidences of late GU toxicity were 18% and 1%. No grade ≥4 of either type of toxicity was detected. Multivariate analysis showed that having higher international prostate symptom score (IPSS; P = 0.041) or higher V₂₀₀ (P = 0.013) was associated with a higher risk of experiencing any grade of acute GU toxicity. In addition, patients having a higher IPSS (P = 0.019) or a higher V₁₅₀ (P = 0.033) were associated with a higher grade >1 acute GU toxicity.

CONCLUSIONS

The findings of this study show that HDR-BT 13.5 Gy × 2 as monotherapy was safe and effective for prostate cancer patients with low-intermediate risk.

Interstitial high-dose-rate brachytherapy in eyelid cancer

PURPOSE

To report the experience and the outcomes of interstitial high-dose-rate (HDR) brachytherapy (BT) of eyelid skin cancer at the Department of Radiotherapy of Hospital de Santa Maria in Lisbon.

METHODS AND MATERIALS

Seventeen patients (pts; mean age, 73.75 years) who underwent eyelid interstitial HDR BT with an (192)Ir source between January 2011 and February 2013 were analyzed. Lesions were basal (94%) and squamous (6%) cell carcinomas, on lower (88%) or upper (6%) eyelids, and on inner canthus (6%). T-stage was Tis (6%), T1 (46%), T2 (36%), and T3a (12%). The purpose of BT was radical (12%), adjuvant to surgery (71%), or salvage after surgery (18%). The BT implant and treatment planning were based on the Stepping Source Dosimetry System. The median total dose was 42.75 Gy (range, 32-50 Gy), with a median of 10 fractions (range, 9-11 fractions), twice daily, 6 h apart. The median V100 was 2.38 cm(3) (range, 0.83-5.59 cm(3)), and the median V150 was 1.05 cm(3) (range, 0.24-3.12 cm(3)).

RESULTS

At a median followup of 40 months (range, 7-43 months), the local control was 94.1%. There was one local recurrence and one non-related death. The BT was well tolerated. Madarosis was the most common late effect (65% of pts) and was related with higher values of V100 (p = 0.027). Cosmetic outcomes were good and excellent in 70% of pts.

CONCLUSIONS

Interstitial HDR BT is a feasible and safe technique for eyelid skin cancers, with good local control. Recurrent lesions and higher volumes receiving the prescribed dose were associated with worse outcomes.

Biological effects of low-dose-rate irradiation of pancreatic carcinoma cells in vitro using 125I seeds

AIM: To determine the mechanism of the radiation-induced biological effects of ¹²⁵I seeds on pancreatic carcinoma cells in vitro.

METHODS: SW1990 and PANC-1 pancreatic cancer cell lines were cultured in DMEM in a suitable environment. Gray’s model of iodine-125 (¹²⁵I) seed irradiation was used. In vitro, exponential phase SW1990, and PANC-1 cells were exposed to 0, 2, 4, 6, and 8 Gy using ¹²⁵I radioactive seeds, with an initial dose rate of 12.13 cGy/h. A clonogenic survival experiment was performed to observe the ability of the cells to maintain their clonogenic capacity and to form colonies. Cell-cycle and apoptosis analyses were conducted to detect the apoptosis percentage in the SW1990 and PANC-1 cells. DNA synthesis was measured via a tritiated thymidine (³H-TdR) incorporation experiment. After continuous low-dose-rate irradiation with ¹²⁵I radioactive seeds, the survival fractions at 2 Gy (SF2), percentage apoptosis, and cell cycle phases of the SW1990 and PANC-1 pancreatic cancer cell lines were calculated and compared.

RESULTS: The survival fractions of the PANC-1 and SW1990 cells irradiated with ¹²⁵I seeds decreased exponentially as the dose increased. No significant difference in SF2 was observed between SW1990 and PANC-1 cells (0.766 ± 0.063 vs 0.729 ± 0.045, P < 0.05). The ¹²⁵I seeds induced a higher percentage of apoptosis than that observed in the control in both the SW1990 and PANC-1 cells. The rate of apoptosis increased with increasing radiation dosage. The percentage of apoptosis was slightly higher in the SW1990 cells than in the PANC-1 cells. Dose-dependent G2/M cell-cycle arrest was observed after ¹²⁵I seed irradiation, with a peak value at 6 Gy. As the dose increased, the percentage of G2/M cell cycle arrest increased in both cell lines, whereas the rate of DNA incorporation decreased. In the ³H-TdR incorporation experiment, the dosimetry results of both the SW1990 and PANC-1 cells decreased as the radiation dose increased, with a minimum at 6 Gy. There were no significant differences in the dosimetry results of the two cell lines when they were exposed to the same dose of radiation.

CONCLUSION: The pancreatic cancer cell-killing effects induced by ¹²⁵I radioactive seeds mainly occurred via apoptosis and G2/M cell cycle arrest.

[Pulsed-dose rate brachytherapy in cervical cancers: why, how?]

The end of the production of 192 iridium wires terminates low dose rate brachytherapy and requires to move towards pulsed-dose rate or high-dose rate brachytherapy. In the case of gynecological cancers, technical alternatives exist, and many teams have already taken the step of pulsed-dose rate for scientific reasons. Using a projector source is indeed a prerequisite for 3D brachytherapy, which gradually installs as a standard treatment in the treatment of cervical cancers. For other centers, this change implies beyond investments in equipment and training, organizational consequences to ensure quality.

[How to prepare the brachytherapy of the future]

For more than a century, brachytherapy has been a treatment of choice for delivering a high dose in a small volume. However, over the past 15 years, this irradiation technique has stalled. Even so, brachytherapy allows the delivery of the right dose at the right place by dispensing with target volume motion and repositioning. The evolution of brachytherapy can be based on a road-map including at least the following three points: the acquisition of clinical evidence, teaching and valuation of the procedures. The evolution of brachytherapy will be also impacted by technological considerations (end of the production of low dose rate 192 iridium wires). Regarding the evolution toward a personalized treatment, brachytherapy of the future should take its place as a partner of other modern external beam radiation techniques, be performed by experimented actors (physicians, physicists, technicians, etc.) who received adequate training, and be valued in proportion to the delivered medical service.