Halftime for repair of sublethal damage in normal bladder and rectum: an analysis of clinical data from cervix brachytherapy

Safety and Efficacy of Brachytherapy in Inoperable Endometrial Cancer

Background/Objectives: Radiotherapy represents the only treatment option for patients with inoperable endometrial cancer (EC). The aim of our study was to evaluate the efficacy and safety of brachytherapy (BT) in this selected patient population. Methods: Between 1990 and 2019, 18 patients with inoperable EC in stage FIGO I-IV were treated with intracavitary brachytherapy using the "Heyman Packing technique". BT was performed either as sole PDR- or HDR-brachytherapy with a median cumulative dose up to 60.0 Gy (67.9 Gy EQD2 α/β = 3Gy) and 34.0 Gy (75.6 Gy EQD2 α/β = 3Gy), respectively. Results: The median follow-up was 46 months (6-219). The mean age was 71 years. The 5-year cumulative local recurrence rate (CLRR) for the whole cohort was 27.3%. The 5-year overall survival (OS), distant metastasis-free survival (DMFS), and disease-free survival (DFS) were 51%, 79%, and 69%. The 5-year DFS for low-, intermediate-, and high-risk EC was 89%, 50%, and 44% (p = 0.51). No significant difference in DFS was observed in patients over 70 (p = 0.526). No late side effects of grade > 1 were documented. Conclusions: Brachytherapy for inoperable EC is a safe and effective treatment option, offering good local control and OS with minimal toxicity. Moreover, brachytherapy effectively controls hemoglobin-relevant bleeding. Therefore, BT should be considered a viable alternative to non-curative treatment strategies in gynecological multidisciplinary conferences.

Biological effective dose in analysis of rectal dose in prostate cancer patients who underwent a combination therapy of VMAT and LDR with hydrogel spacer insertion

This study aimed to evaluate rectal dose reduction in prostate cancer patients who underwent a combination of volumetric modulated arc therapy (VMAT) and low‐dose‐rate (LDR) brachytherapy with insertion of hydrogel spacer (SpaceOAR). For this study, 35 patients receiving hydrogel spacer and 30 patients receiving no spacer were retrospectively enrolled. Patient was treated to doses of 45 Gy to the primary tumor site and nodal regions over 25 fractions using VMAT and 100 Gy to the prostate using prostate seed implant (PSI). In VMAT plans of patients with no spacer, mean doses of rectal wall were 43.6, 42.4, 40.1, and 28.8 Gy to the volume of 0.5, 1, 2, and 5 cm³, respectively. In patients with SpaceOAR, average rectal wall doses decreased to 39.0, 36.9, 33.5, and 23.9 Gy to the volume of 0.5, 1, 2, and 5 cm³, respectively (p < 0.01). In PSI plans, rectal wall doses were on average 78.5, 60.9, 41.8, and 14.8 Gy to the volume of 0.5, 1, 2, and 5 cm³, respectively, in patients without spacer. In contrast, the doses decreased to 34.5, 28.4, 20.6 (p < 0.01), and 8.5 Gy (p < 0.05) to rectal wall volume of 0.5, 1, 2, and 5 cm³, respectively, in patient with SpaceOAR. To demonstrate rectal sum dose sparing, dose‐biological effective dose (BED) calculation was accomplished in those patients who showed >60% overlap of rectal volumetric doses between VMAT and PSI. In patients with SpaceOAR, average BED_sum was decreased up to 34%, which was 90.1, 78.9, 65.9, and 40.8 Gy to rectal volume of 0.5, 1, 2, and 5 cm³, respectively, in comparison to 137.4, 116.7, 93.0, and 50.2 Gy to the volume of 0.5, 1, 2, and 5 cm³, respectively, in those with no spacer. Our result suggested a significant reduction of rectal doses in those patients who underwent a combination of VMAT and LDR with hydrogel spacer placement.

DIFFERENCE IN DEGREE OF SUB-LETHAL DAMAGE RECOVERY BETWEEN CLINICAL PROTON BEAMS AND X-RAYS

Fractionated proton beam radiotherapy is spreading worldwide these days. However, biological data of sub-lethal damage recovery (SLDR) after proton irradiation is not known yet. We here conducted split-dose experiments (20-360 min intervals) to clarify SLDR kinetics, and also compared the kinetics between cells with different repairability of DNA double-strand breaks. CHO and 51D1 cell lines but not V3 cell line showed significant SLDR, which reached plateau in 4-6 h. The recovery rates and recovery halftime of SLDR after X-rays were significantly higher and shorter than proton beams for CHO and 51D1 cells, respectively. Additionally, the frequency of remaining gamma-H2AX foci after two fractions was remarkably higher for X-rays than proton beams. These data suggest that there is a difference between proton beam and X-rays in SLDR and the retained DNA double-strand breaks after split-dose irradiation.

Radiobiological dose calculation parameters for cervix cancer brachytherapy: A systematic review

The GEC-ESTRO recommendation in cervical cancer treatment planning, including external beam radiotherapy and brachytherapy boosts, is to use radiobiological dose calculations. Such calculations utilize the linear-quadratic model to estimate the effect of multiple cellular response factors and dose delivery parameters. The radiobiological parameters utilized in these calculations are literature values estimated based on clinical and experimental results. However, the impact of the uncertainties associated with these parameters is often not fully appreciated. This review includes a summary of the radiobiological dose calculation (for both high-dose-rate and pulsed-dose-rate brachytherapy boost treatments) for cervical cancer and a compilation of the reported values of the associated parameters. As discrepancies exist between conventionally recommended and published values, equivalencies between current brachytherapy boosts may be imprecise and could create underappreciated uncertainties in the radiobiological dose calculations. This review highlights these uncertainties by calculating the radiobiological dose delivered by the brachytherapy boost when assuming different radiobiological parameter values (within the range reported by previous research). Furthermore, conventional treatment planning does not consider the effects of proliferation of the tumor over the treatment time, which can significantly decrease its radiobiological dose and can introduce an additional variance of over 7 Gy₁₀. Further investigation of uncertainties in parameter values and modifications of current dose models could improve the accuracy of radiobiological dose calculation.

Focal or whole-gland salvage prostate brachytherapy with iodine seeds with or without a rectal spacer for postradiotherapy local failure: How best to spare the rectum?

PURPOSE

Salvage prostate permanent implant (sPPI) for postradiation local failure provides high rates of biochemical control. The cumulative dose delivered to the prostate and the rectum is still unknown.

METHODS AND MATERIALS

We reviewed the postimplant CT-based dosimetry of 18 selected patients who underwent sPPI with (125)I seeds for isolated biopsy-proven local failure several years after external beam radiation therapy. Ten patients had whole-prostate sPPI, and 8 patients had multiparametric MRI-based focal sPPI. In 8 patients, hyaluronic acid (HA) gel was injected into the prostate-rectum space.

RESULTS

The median cumulative biological effective dose after EBRT + sPPI for the prostate and the rectum was higher in patients treated with whole-gland sPPI than in patients treated with focal sPPI (313.5 Gy2 vs. 174.4 Gy2; p = 0.06 and 258.1 Gy3 vs. 172.6 Gy3; p < 0.01, respectively). The median D0.1cc for the rectum was significantly lower in patients who had HA gel: 63.3 Gy (29.0-78.3) vs. 83.9 Gy (34.9-180.0) (p = 0.04).

CONCLUSIONS

Cumulative prostate and rectum biological effective doses were lower with focal sPPI. D0.1cc delivered to the rectum was significantly lower with HA gel, while there was no difference between focal or whole-gland plans.

Ku-dependent non-homologous end-joining as the major pathway contributes to sublethal damage repair in mammalian cells

PURPOSE

Sublethal damage repair (SLDR) is a type of repair that occurs in split-dose irradiated cells, which was discovered more than 50 years ago. However, due to conflicting reported data, it remains unclear which DNA double-strand break (DSB) repair pathway, non-homologous end-joining (NHEJ) repair, homologous recombination repair (HRR) or both, contributes to SLDR, particularly in human cells. We were interested in clarifying this question.

METHODS AND MATERIALS

Mammalian cell lines, including human, mouse and Chinese hamster ovary (CHO) cell lines, wild type, deficient in NHEJ or HRR were irradiated with either single dose or two split doses at 2- or 4-h intervals. The clonogenic assay was used to evaluate these cell radiosensitivities.

RESULTS

All wild-type or HRR-deficient cells (including human, mouse and CHO cells) showed a higher survival rate after exposure to split-dose versus single-dose radiation; however, all classical NHEJ-deficient cells (including human, mouse and hamster cells) did not show any apparent sensitivity changes between single-dose and split-dose irradiation.

CONCLUSION

Classical NHEJ mainly contributes to SLDR in mammalian cells (including human cells). These results have the potential to improve radiotherapy.

Monte Carlo Calculation of Radioimmunotherapy with (90)Y-, (177)Lu-, (131)I-, (124)I-, and (188)Re-Nanoobjects: Choice of the Best Radionuclide for Solid Tumour Treatment by Using TCP and NTCP Concepts

Radioimmunotherapy has shown that the use of monoclonal antibodies combined with a radioisotope like ¹³¹I or ⁹⁰Y still remains ineffective for solid and radioresistant tumour treatment. Previous simulations have revealed that an increase in the number of ⁹⁰Y labelled to each antibody or nanoobject could be a solution to improve treatment output. It now seems important to assess the treatment output and toxicity when radionuclides such as ⁹⁰Y, ¹⁷⁷Lu, ¹³¹I, ¹²⁴I, and ¹⁸⁸Re are used. Tumour control probability (TCP) and normal tissue complication probability (NTCP) curves versus the number of radionuclides per nanoobject were computed with MCNPX to evaluate treatment efficacy for solid tumours and to predict the incidence of surrounding side effects. Analyses were carried out for two solid tumour sizes of 0.5 and 1.0 cm radius and for nanoobject (i.e., a radiolabelled antibody) distributed uniformly or nonuniformly throughout a solid tumour (e.g., Non-small-cell-lung cancer (NSCLC)). ⁹⁰Y and ¹⁸⁸Re are the best candidates for solid tumour treatment when only one radionuclide is coupled to one carrier. Furthermore, regardless of the radionuclide properties, high values of TCP can be reached without toxicity if the number of radionuclides per nanoobject increases.

Radiobiological comparison of two radiotherapy treatment techniques for high-risk prostate cancer

BACKGROUND

To make a radiobiological comparison, for high risk prostate cancer (T3a, PSA > 20 ng/ml or Gleason > 7) of two radiotherapy treatment techniques. One technique consists of a treatment in three phases of the pelvic nodes, vesicles and prostate using a conventional fractionation scheme of 2 Gy/fraction (SIMRT). The other technique consists of a treatment in two phases that gives simultaneously different dose levels in each phase, 2 Gy/fraction, 2.25 Gy/fraction and 2.5 Gy/fraction to the pelvic nodes, vesicles and prostate, respectively (SIBIMRT).

MATERIALS AND METHODS

The equivalent dose at fractionation of 2 Gy (EQD2), calculated using the linear quadratic model with α/β prostate = 1.5 Gy, was the same for both treatment strategies. For comparison the parameters employed were D95, mean dose and Tumour Control Probabilities for prostate PTV and D15, D25, D35, D50, mean dose and Normal Tissue Complication Probabilities for the rectum and bladder, with physical doses converted to EQD2. Parameters were obtained for α/β prostate = 1.5, 3 and 10 Gy and for α/β oar = 1, 2, 3, 4, 6 and 8.

RESULTS

For prostate PTV, both treatment strategies are equivalent for α/β prostate = 1.5 Gy but for higher α/β prostate, EQD2 and TCP, decrease for the SIBIMRT technique. For the rectum and bladder when α/β oar ≤ 2 Gy, EQD2 and NTCP are lower for the SIMRT technique or equal in both techniques. For α/β oar ≥ 2-3 Gy, EQD2 and NTCP increase for the SIMRT treatment.

CONCLUSIONS

A comparison between two radiotherapy techniques is presented. The SIBIMRT technique reduces EQD2 and NTCP for α/β oar from 2 to 8 Gy.

Prognostic factors for acute toxicity in prostate cancer patients treated with high-dose hypofractionated radiotherapy

PURPOSE

To prospectively study acute genitourinary (GU) and gastrointestinal (GI) toxicity during hypofractionated radiotherapy.

PATIENTS AND MATERIALS

One-hundred and seventy-one consecutive men with cT1-T3cN0cM0 prostate cancer were treated at 2.6 Gy/fraction to a total dose of 67.6 for low risk (EQD2 = 79 Gy) and 70.2 Gy for intermediate-high risk (EQD2 = 82 Gy) over 5.2-5.4 weeks (α/β 1.5). Acute toxicity was scored according to RTOG/EORTC toxicity extended criteria after completing a 22-item questionnaire (basal, weekly, at 6 months).

RESULTS

Minimum and median follow-up were 36 and 54.2 months, respectively. GU toxicity grades 0, 1, 2 and 3 were found in 30.4, 37, 32 and 0.6 % of patients, respectively. The figures for grades 0, 1, 2 and 3 GI toxicity were 66, 24, 10 and 0 %. The highest degree of acute reactions was reached at 4-5 weeks. At 6 months, 15 % of patients had GU toxicity (11 % grade 1, 4 % grade 2) and 5.8 % GI toxicity (5.3 % grade 1, 0.5 % grade 2). Multivariate analysis shows that bladder volume receiving ≥65 Gy (V 65) is associated with an increased risk of GU complications (p = 0.017, HR = 1.143, 95 % CI = 1.025-1.276), while history of TURP is linked to lower risk (p = 0.002, HR = 0.310, 95 % CI 0.004-0.370). Mean rectal dose (p = 0.013, HR = 1.089, 95 % CI 1.018-1.116) and total dose (p = 0.019, HR = 0.734, 95 % CI 0.567-0.950) are significantly related to GI toxicity.

CONCLUSIONS

This 5-week dose-escalation hypofractionated radiotherapy schedule that uses 3D-conformal radiotherapy without IGRT has resulted in <1 % grade 3 acute complications. Our study suggests that reducing the mean rectal dose and the bladder V 65 helps prevent acute toxicity. TURP before radiotherapy was associated with lower acute GU toxicity.

Providing a fast conversion of total dose to biological effective dose (BED) for hybrid seed brachytherapy

Optimization of permanent seed implant brachytherapy plans for treatment of prostate cancer should be based on biological effective dose (BED) distributions, since dose does not accurately represent biological effects between different types of sources. Currently, biological optimization for these plans is not feasible due to the amount of time necessary to calculate the BED distribution. This study provides a fast calculation method, based on the total dose, to calculate the BED distribution. Distributions of various numbers of hybrid seeds were used to calculate total dose distributions, as well as BED distributions. Hybrid seeds are a mixture of different isotopes (in this study ¹²⁵I and ¹⁰³Pd). Three ratios of hybrid seeds were investigated: 25/75, 50/50, and 75/25. The total dose and BED value from each voxel were coupled together to produce graphs of total dose vs. BED. Equations were then derived from these graphs. The study investigated four types of tissue: bladder, rectum, prostate, and other normal tissue. Equations were derived from the total dose – BED correspondence. Accuracy of conversion from total dose to BED was within 2 Gy; however, accuracy of conversion was found to be better for high total dose regions as compared to lower dose regions. The method introduced in this paper allows one to perform fast conversion of total dose to BED for brachytherapy using hybrid seeds, which makes the BED‐based plan optimization practical. The method defined here can be extended to other ratios, as well as other tissues that are affected by permanent seed implant brachytherapy (i.e., breast).

PACS number: 87.55.de

Pulsed brachytherapy: a modelled consideration of repair parameter uncertainties and their influence on treatment duration extension and daytime-only "block-schemes"

OBJECTIVES

The radiobiological modelling of all types of protracted brachytherapy is susceptible to uncertainties in the values of tissue repair parameters. Although this effect has been explored for many aspects of pulsed brachytherapy (PB), it is usually considered within the constraint of a fixed brachytherapy treatment time. Here the impact of repair parameter uncertainty is assessed for PB treatments of variable duration. The potential use of "block-schemes" (blocks of PB pulses separated by night-time gaps) is also investigated.

METHODS

PB schedule constraints are based on the cervical cancer protocols of the Royal Marsden Hospital (RMH), but the methodology is applicable to any combination of starting schedule and treatment constraint. Calculations are performed using the biologically effective dose (BED) as a tissue-specific comparison metric. The ratio of normal tissue BED to tumour BED is considered for PB regimens with varying total pulse numbers and/or "block-schemes".

RESULTS

For matched brachytherapy duration, PB has a good "window of opportunity" relative to the existing RMH continuous low dose rate (CLDR) practice for all modelled repair half-times. The most clear-cut route to radiobiological optimisation of PB is via modest temporal extension of the PB regimen relative to the CLDR reference. This option may be practicable for those centres with scope to extend their relatively short CLDR treatment durations.

CONCLUSION

Although daytime-only "block-scheme" PB for cervical cancer has not yet been employed clinically, the possibilities appear to be theoretically promising, providing the overall (external beam plus brachytherapy) treatment duration is not extended relative to current practice, such that additional tumour repopulation becomes a concern.

Radioimmunotherapy with radioactive nanoparticles: biological doses and treatment efficiency for vascularized tumors with or without a central hypoxic area

PURPOSE

Radioactive atoms attached to monoclonal antibodies are used in radioimmunotherapy to treat cancer while limiting radiation to healthy tissues. One limitation of this method is that only one radioactive atom is linked to each antibody and the deposited dose is often insufficient to eradicate solid and radioresistant tumors. In a previous study, simulations with the Monte Carlo N-Particle eXtended code showed that physical doses up to 50 Gy can be delivered inside tumors by replacing the single radionuclide by a radioactive nanoparticle of 5 nm diameter containing hundreds of radioactive atoms. However, tumoral and normal tissues are not equally sensitive to radiation, and previous works did not take account the biological effects such as cellular repair processes or the presence of less radiosensitive cells such as hypoxic cells.

METHODS

The idea is to adapt the linear-quadratic expression to the tumor model and to determine biological effective doses (BEDs) delivered through and around a tumor. This BED is then incorporated into a Poisson formula to determine the shell control probability (SCP) which predicts the cell cluster-killing efficiency at different distances "r" from the center of the tumor. BED and SCP models are used to analyze the advantages of injecting radioactive nanoparticles instead of a single radionuclide per vector in radioimmunotherapy.

RESULTS

Calculations of BED and SCP for different distances r from the center of a solid tumor, using the non-small-cell lung cancer as an example, were investigated for 90Y2O3 nanoparticles. With a total activity of about 3.5 and 20 MBq for tumor radii of 0.5 and 1.0 cm, respectively, results show that a very high BED is deposited in the well oxygenated part of the spherical carcinoma.

CONCLUSIONS

For either small or large solid tumors, BED and SCP calculations highlight the important benefit in replacing the single beta-emitter 90Y attached to each antibody by a 90Y2O3 nanoparticle.

Technology Insight: Combined external-beam radiation therapy and brachytherapy in the management of prostate cancer

External-beam radiation therapy (EBRT) combined with brachytherapy is an attractive treatment option for selected patients with clinically localized prostate cancer. This therapeutic strategy offers dosimetric coverage if local-regional microscopic disease is present and provides a highly conformal boost of radiation to the prostate and immediate surrounding tissues. Either low-dose-rate (LDR) permanent brachytherapy or high-dose-rate (HDR) temporary brachytherapy can be combined with EBRT; such combined-modality therapy (CMT) is typically used to treat patients with intermediate-risk to high-risk, clinically localized disease. Controversy persists with regard to indications for CMT, choice of LDR or HDR boost, isotope selection for LDR, and integration of EBRT and brachytherapy. Initial findings from prospective, multicenter trials of CMT support the feasibility of this strategy. Updated results from these trials as well as those of ongoing and new phase III trials should help to define the role of CMT in the management of prostate cancer. In the meantime, long-term expectations for outcomes of CMT are based largely on the experience of single institutions, which demonstrate that CMT with EBRT and either LDR or HDR brachytherapy can provide freedom from disease recurrence with acceptable toxicity.

Stereotactic body radiotherapy for localized prostate cancer: interim results of a prospective phase II clinical trial

PURPOSE

The radiobiology of prostate cancer favors a hypofractionated dose regimen. We report results of a prospective Phase II clinical trial of stereotactic body radiotherapy (SBRT) for localized prostate cancer.

METHODS AND MATERIALS

Forty-one low-risk prostate cancer patients with 6 months' minimum follow-up received 36.25 Gy in five fractions of 7.25 Gy with image-guided SBRT alone using the CyberKnife. The early (<3 months) and late (>6 months) urinary and rectal toxicities were assessed using validated quality of life questionnaires (International Prostate Symptom Score, Expanded Prostate Cancer Index Composite) and the Radiation Therapy Oncology Group (RTOG) toxicity criteria. Patterns of prostate-specific antigen (PSA) response are analyzed.

RESULTS

The median follow-up was 33 months. There were no RTOG Grade 4 acute or late rectal/urinary complications. There were 2 patients with RTOG Grade 3 late urinary toxicity and none with RTOG Grade 3 rectal complications. A reduced rate of severe rectal toxicities was observed with every-other-day vs. 5 consecutive days treatment regimen (0% vs. 38%, p = 0.0035). A benign PSA bounce (median, 0.4 ng/mL) was observed in 12 patients (29%) occurring at 18 months (median) after treatment. At last follow-up, no patient has had a PSA failure regardless of biochemical failure definition. Of 32 patients with 12 months minimum follow-up, 25 patients (78%) achieved a PSA nadir </=0.4 ng/mL. A PSA decline to progressively lower nadirs up to 3 years after treatment was observed.

CONCLUSIONS

The early and late toxicity profile and PSA response for prostate SBRT are highly encouraging. Continued accrual and follow-up will be necessary to confirm durable biochemical control rates and low toxicity profiles.