Minimal toxicity after proton beam therapy for prostate and pelvic nodal irradiation: results from the proton collaborative group REG001-09 trial

Proton versus photon therapy for high-risk prostate cancer with dose escalation of dominant intraprostatic lesions: a preliminary planning study

Background and purpose

This study aimed to investigate the feasibility of safe-dose escalation to dominant intraprostatic lesions (DILs) and assess the clinical impact using dose-volume (DV) and biological metrics in photon and proton therapy. Biological parameters defined as late grade ≥ 2 gastrointestinal (GI) and genitourinary (GU) derived from planned (D P) and accumulated dose (D A) were utilized.

Materials and methods

In total, 10 patients with high-risk prostate cancer with multiparametric MRI-defined DILs were investigated. Each patient had two plans with a focal boost to the DILs using intensity-modulated proton therapy (IMPT) and volumetric-modulated arc therapy (VMAT). Plans were optimized to obtain DIL coverage while respecting the mandatory organ-at-risk constraints. For the planning evaluation, DV metrics, tumor control probability (TCP) for the DILs and whole prostate excluding the DILs (prostate-DILs), and normal tissue complication probability (NTCP) for the rectum and bladder were calculated. Wilcoxon signed-rank test was used for analyzing TCP and NTCP data.

Results

IMPT achieved a higher Dmean for the DILs compared to VMAT (IMPT: 68.1 GyRBE vs. VMAT: 66.6 Gy, p < 0.05). Intermediate-high rectal and bladder doses were lower for IMPT (p < 0.05), while the high-dose region (V60 Gy) remained comparable. IMPT-TCP for prostate-DIL were higher compared to VMAT (IMPT: 86%; α/β = 3, 94.3%; α/β = 1.5 vs. VMAT: 84.7%; α/β = 3, 93.9%; α/β = 1.5, p < 0.05). Likewise, IMPT obtained a moderately higher DIL TCP (IMPT: 97%; α/β = 3, 99.3%; α/β = 1.5 vs. VMAT: 95.9%; α/β = 3, 98.9%; α/β = 1.5, p < 0.05). Rectal D A-NTCP displayed the highest GI toxicity risk at 5.6%, and IMPT has a lower GI toxicity risk compared to VMAT-predicted Quantec-NTCP (p < 0.05). Bladder D P-NTCP projected a higher GU toxicity than D A-NTCP, with VMAT having the highest risk (p < 0.05).

Conclusion

Dose escalation using IMPT is able to achieve a high TCP for the DILs, with the lowest rectal and bladder DV doses at the intermediate-high-dose range. The reduction in physical dose was translated into a lower NTCP (p < 0.05) for the bladder, although rectal toxicity remained equivalent.

Proton therapy planning and image-guidance strategies within a randomized controlled trial for high-risk prostate cancer

The Danish Prostate Cancer Group is launching the randomized trial, PROstate PROTON Trial 1 (NCT05350475), that compares photons and protons to the prostate and pelvic lymph nodes in treatment of high-risk prostate cancer. The aim of the work described in this paper was, in preparation of this trial, to establish a strategy for conventionally fractionated proton therapy of prostate and elective pelvic lymph nodes that is feasible and robust. Proton treatments are image-guided based on gold fiducial markers and on-board imaging systems in line with current practice. Our established proton beam configuration consists of four coplanar fields; two posterior oblique fields and two lateral oblique fields, chosen to minimize range uncertainties associated with penetrating a varying amount of material from both treatment couch and patient body. Proton plans are robustly optimized to ensure target coverage while keeping normal tissue doses as low as is reasonably achievable throughout the course of treatment. Specific focus is on dose to the bowel as a reduction in gastrointestinal toxicity is the primary endpoint of the trial. Strategies have been established using previously treated patients and will be further investigated and evaluated through the ongoing pilot phase of the trial.

Late Toxicity of Moderately Hypofractionated Intensity-Modulated Proton Therapy Treating the Prostate and Pelvic Lymph Nodes for High-Risk Prostate Cancer

PURPOSE

To evaluate late gastrointestinal (GI) and genitourinary (GU) toxicity of moderately hypofractionated intensity modulated proton therapy (IMPT) targeting the prostate and pelvic lymph nodes.

METHODS AND MATERIALS

A target accrual of 56 patients with high-risk or unfavorable intermediate risk prostate cancer were enrolled into a prospective study (ClinicalTrials.gov: NCT02874014) of moderately hypofractionated IMPT. IMPT with pencil beam scanning was used to deliver 6750 and 4500 cGy relative biological effectiveness in 25 daily fractions simultaneously to the prostate and pelvic lymph nodes, respectively. All received androgen deprivation therapy. Late GI and GU toxicity was prospectively assessed using Common Terminology Criteria for Adverse Events version 4.0, at baseline, weekly during radiation therapy, 3-month postradiation therapy, and then every 6 months. Actuarial rates of late GI and GU toxicity were estimated using Kaplan-Meier method.

RESULTS

Median age was 75.5 years. Fifty-four patients were available for late toxicity evaluation. Median follow-up was 43.9 months (range, 16-66). The actuarial rate of late grade ≥2 GI toxicity at both 2 and 3 years was 7.4% (95% confidence interval [CI], 0.2%-14.2%). The actuarial rate of late grade 3 GI toxicity at both 2 and 3 years was 1.9% (95% CI, 0%-5.4%). One patient experienced grade 3 GI toxicity with proctitis. The actuarial rate of late grade ≥2 GU toxicity was 20.5% (95% CI, 8.9%-30.6%) at 2 years, and 29.2 % (95% CI, 15.5%-40.7%) at 3 years. None had grade 3 GU toxicity. The presence of baseline GU symptoms was associated with a higher likelihood of experiencing late grade 2 GU toxicity.

CONCLUSIONS

A moderately hypofractionated IMPT targeting the prostate and regional pelvic lymph nodes was generally well tolerated. Patients with pre-existing GU symptoms had a higher rate of late grade 2 GU toxicity. A phase 3 study is needed to assess any therapeutic gain of IMPT, in comparison with photon-based radiation therapy.

A Phase II prospective study of hypofractionated proton therapy of prostate and pelvic lymph nodes: Acute effects on patient-reported quality of life

BACKGROUND

The objective of this study was to report acute changes in patient-reported quality of life (PRQOL) using the 26-item Expanded Prostate Index Composite (EPIC-26) questionnaire in a prospective study using hypofractionated intensity-modulated proton beam therapy (H-IMPT) targeting the prostate and the pelvic lymph nodes for high-risk or unfavorable intermediate-risk prostate cancer.

METHODS

Fifty-five patients were enrolled. H-IMPT consisted of 45 GyE to the pelvic lymph nodes and 67.5 GyE to the prostate and seminal vesicles in 25 fractions. PRQOL was assessed with the urinary incontinence (UI), urinary irritative/obstructive symptoms (UO), and bowel function (BF) domains of EPIC-26 questionnaire. Mean changes in domain scores were analyzed from pretreatment to the end of treatment and 3 months posttreatment. A clinically meaningful change (or minimum important change) was defined as a score change > 50% of the baseline standard deviation.

RESULTS

The mean scores of UO, UI, and BF at baseline were 84.6, 91.1, and 95.3, respectively. At the end of treatment, there were statistically significant and clinically meaningful declines in UO and BF scores (-13.5 and -2.3, respectively), while the decline in UI score was statistically significant but not clinically meaningful (-13.7). A clinically meaningful decline in UO, UI, and BF scores occurred in 53.5%, 22.7%, and 73.2% of the patients, respectively. At 3 months posttreatment, all three mean scores showed an improvement, with fewer patients having a clinically meaningful decline in UO, UI, and BF scores (18.4%, 20.5%, and 45.0%, respectively). There was no significant reduction in the mean UO and UI scores compared to baseline, although the mean BF score remained lower than baseline and the difference was clinically meaningful.

CONCLUSIONS

UO, UI, and BF scores of PRQOL declined at the end of H-IMPT. UO and UI scores showed improvement at 3 months posttreatment and were similar to the baseline scores. However, BF score remained lower at 3 months posttreatment with a clinically meaningful decline.

Proton Therapy of Prostate and Pelvic Lymph Nodes for High Risk Prostate Cancer: Acute Toxicity

Purpose

To assess acute gastrointestinal (GI) and genitourinary (GU) toxicities of intensity-modulated proton therapy (IMPT) targeting the prostate/seminal vesicles and pelvic lymph nodes for prostate cancer.

Materials and Methods

A prospective study (ClinicalTrials.gov: NCT02874014), evaluating moderately hypofractionated IMPT for high-risk or unfavorable intermediate-risk prostate cancer, accrued a target sample size of 56 patients. The prostate/seminal vesicles and pelvic lymph nodes were treated simultaneously with 6750 and 4500 centigray radiobiologic equivalent (cGyRBE), respectively, in 25 daily fractions. All received androgen-deprivation therapy. Acute GI and GU toxicities were prospectively assessed from 7 GI and 9 GU categories of the Common Terminology Criteria for Adverse Events (version 4), at baseline, weekly during radiotherapy, and 3-month after radiotherapy. Fisher exact tests were used for comparisons of categorical data.

Results

Median age was 75 years. Median follow-up was 25 months. Fifty-five patients were available for acute toxicity assessment. Sixty-two percent and 2%, respectively, experienced acute grade 1 and 2 GI toxicity. Grade 2 GI toxicity was proctitis. Sixty-five percent and 35%, respectively, had acute grade 1 and 2 GU toxicity. The 3 most frequent grade 2 GU toxicities were urinary frequency, urgency, and obstructive symptoms. None had acute grade ≥ 3 GI or GU toxicity. The presence of baseline GI and GU symptoms was associated with a greater likelihood of experiencing acute GI and GU toxicity, respectively. Of 45 patients with baseline GU symptoms, 44% experienced acute grade 2 GU toxicity, compared with only 10% among 10 with no baseline GU symptoms (P = 0.07). Although acute grade 1 and 2 GI and GU toxicities were common during radiotherapy, most resolved at 3 months after radiotherapy.

Conclusion

A moderately hypofractionated IMPT targeting the prostate/seminal vesicles and regional pelvic lymph nodes was well tolerated with no acute grade ≥ 3 GI or GU toxicity. Patients with baseline GU symptoms had a higher rate of acute grade 2 GU toxicity.

Clinical Efficacy and Safety of Proton and Carbon Ion Radiotherapy for Prostate Cancer: A Systematic Review and Meta-Analysis

BACKGROUND

Carbon ion radiotherapy (CIRT) and proton beam therapy (PBT) are promising methods for prostate cancer, however, the consensus of an increasing number of studies has not been reached. We aimed to provide systematic evidence for evaluating the efficacy and safety of CIRT and PBT for prostate cancer by comparing photon radiotherapy.

MATERIALS AND METHODS

We searched for studies focusing on CIRT and PBT for prostate cancer in four online databases until July 2021. Two independent reviewers assessed the quality of included studies and used the GRADE approach to rate the quality of evidence. R 4.0.2 software was used to conduct the meta-analysis. A meta-regression test was performed based on the study design and tumor stage of each study.

RESULTS

A total of 33 studies including 13 CIRT- and 20 PBT-related publications, involving 54,101, participants were included. The quality of the included studies was found to be either low or moderate quality. Random model single-arm meta-analysis showed that both the CIRT and PBT have favorable efficacy and safety, with similar 5-year overall survival (OS) (94 vs 92%), the incidence of grade 2 or greater acute genitourinary (AGU) toxicity (5 vs 13%), late genitourinary (LGU) toxicity (4 vs 5%), acute gastrointestinal (AGI) toxicity (1 vs 1%), and late gastrointestinal (LGI) toxicity (2 vs 4%). However, compared with CIRT and PBT, photon radiotherapy was associated with lower 5-year OS (72-73%) and a higher incidence of grade 2 or greater AGU (28-29%), LGU (13-14%), AGI (14-19%), and LGI toxicity (8-10%). The meta-analysis showed the 3-, 4-, and 5-year local control rate (LCR) of CIRT for prostate cancer was 98, 97, and 99%; the 3-, 4-, 5-, and 8-year biochemical relapse-free rate (BRF) was 92, 91, 89, and 79%. GRADE assessment results indicated that the certainty of the evidence was very low. Meta-regression results did not show a significant relationship based on the variables studied (P<0.05).

CONCLUSIONS

Currently available evidence demonstrated that the efficacy and safety of CIRT and PBT for prostate cancer were similar, and they may significantly improve the OS, LCR, and reduce the incidence of GU and GI toxicity compared with photon radiotherapy. However, the quantity and quality of the available evidence are insufficient. More high-quality controlled studies are needed in the future.

Elective nodal radiotherapy in prostate cancer

In patients with prostate cancer who have a high risk of pelvic nodal disease, the use of elective whole pelvis radiotherapy is still controversial. Two large, randomised, controlled trials (RTOG 9413 and GETUG-01) did not show a benefit of elective whole pelvis radiotherapy over prostate-only radiotherapy. In 2020, the POP-RT trial established the role of elective whole pelvis radiotherapy in patients who have more than a 35% risk of lymph node invasion (known as the Roach formula). POP-RT stressed the importance of patient selection. In patients with cN1 (clinically node positive) disease or pN1 (pathologically node positive) disease, the addition of whole pelvis radiotherapy to androgen deprivation therapy significantly improved survival compared with androgen deprivation therapy alone, as shown in large, retrospective studies. This patient population might increase in the future because use of the more sensitive prostate-specific membrane antigen PET-CT will become the standard staging procedure. Additionally, the SPORTT trial suggested a benefit of whole pelvis radiotherapy in biochemical recurrence-free survival in the salvage setting. A correct definition of the upper field border, which should include the bifurcation of the abdominal aorta, is key in the use of pelvic radiotherapy. As a result of using modern radiotherapy technology, severe late urinary and intestinal toxic effects are rare and do not seem to increase compared with prostate-only radiotherapy.

Management of Clinically Involved Lateral Lymph Node Metastasis in Locally Advanced Rectal Cancer: A Radiation Dose Escalation Study

Background

Patients with lateral lymph nodes (LLNs) metastasis are not effectively treated with neoadjuvant chemoradiotherapy. This study aimed to compare the efficacy of three neoadjuvant therapeutic regimens, namely, chemotherapy, chemoradiotherapy, and chemoradiotherapy with a dose boost of LLNs, and to identify the optimal approach for treating LLNs metastasis of locally advanced rectal cancer.

Methods

A total of 202 patients with baseline LLNs metastasis (short axis ≥5 mm) and treated with neoadjuvant treatment, followed by radical surgery from 2011 to 2019, were enrolled. The short axis of the LLNs on baseline and restaging MRI were recorded. Survival outcomes were compared.

Results

In the booster subgroup, shrinkage of LLNs was significantly greater than in the neoadjuvant chemotherapy and chemoradiotherapy subgroups (P <0.001), without increasing radiation related side effects (P = 0.121). For patients with baseline LLNs of short axis ≥5 mm in the booster subgroup, the response rate (short axis <5 mm on restaging MRI) was 72.9%, significantly higher than patients in the neoadjuvant chemotherapy subgroup (48.9%, P = 0.007) and higher than for patients in the neoadjuvant chemoradiotherapy group (65.0%), but there was no statistical difference (P = 0.411). The 3-year local recurrence and lateral local recurrence rates were both 2.3% in the dose booster group, which were lower than those of the other two subgroups (local recurrence: P <0.001; lateral local recurrence: P <0.001). The short axis of lateral lymph nodes (≥5 and <5 mm) on restaging MRI was an independent risk factor for prognosis (P <0.05).

Conclusion

Radiation dose boost is an effective way of increasing the response rate and decreasing recurrence rates. The restaging LLNs with short axis ≥5 mm is a predictor of poor prognosis.

Anatomically robust proton therapy using multiple planning computed tomography scans for locally advanced prostate cancer

BACKGROUND

Proton therapy (PT) is sensitive towards anatomical changes that may occur during a treatment course. The aim of this study was to investigate if anatomically robust PT (ARPT) plans incorporating patient-specific target motion improved target coverage while still sparing normal tissues, when applied on locally advanced prostate cancer patients where pelvic irradiation is indicated.

MATERIAL AND METHODS

A planning computed tomography (CT) scan used for dose calculation and two additional CTs (acquired on different days) were used to make patient-specific targets for the ARPT plans on the eight included patients. The plans were compared to a conventional robust PT plan and a volumetric modulated arc therapy (VMAT) photon plan, which were derived from the planning CT (pCT). Worst-case robust optimisation was used for all proton plans with a setup uncertainty of 5 mm and a range uncertainty of 3.5%. Target coverage (V95% and D95%) and normal tissue doses (V5-75 Gy) were evaluated on 6-8 rCTs per patient.

RESULTS

The ARPT plans improved the prostate target coverage for the most challenging patient compared to conventional robust PT plans (20% point increase for V95% and 31 Gy increase for D95%). Across the whole cohort the estimated mean value for V95% was 97% for the ARPT plans and 95% for the conventional robust PT plans. The ARPT plans had a slight, statistically insignificant increase in normal tissue doses compared to the conventional robust proton plans. Compared to VMAT, the ARPT plans significantly reduced the normal tissue doses in the low-to-intermediate dose range.

CONCLUSIONS

While both proton plans reduced the low-to-intermediate normal tissue doses compared to VMAT, ARPT plans improved the target coverage for the most challenging patient without significantly increasing the normal tissue doses compared to conventional robust PT plans.

Strategies to Minimize Late Effects From Pelvic Radiotherapy

During the past 30 years, radiation treatment techniques have significantly improved, from conventional external-beam radiation therapy, to three-dimensional conformal radiation therapy, to current intensity-modulated radiation therapy, benefiting patients who undergo treatment of pelvic malignancies. Modern treatment options also include proton beam irradiation as well as low and high dose rate brachytherapy. Although the acute adverse effects of these modalities are well documented in clinical trials, less well known are the true incidence and optimal management of those late adverse effects that can occur months to years later. In a population of survivors of cancer that is steadily increasing, with many such patients receiving radiotherapy at some time during their disease course, these late effects can become a considerable management and quality-of-life issue. This review will examine the range of late toxicities that can occur from pelvic radiotherapy and explore strategies to prevent and mitigate them.

Robust treatment planning in whole pelvis pencil beam scanning proton therapy for prostate cancer

Whole-pelvis pencil beam scanning (PBS) proton therapy is utilized in both the intact and post-operative settings in patients with prostate cancer. As whole pelvis prostate radiotherapy has traditionally been delivered with standard photon beams, limited evidence and technical descriptions have been reported regarding the use of proton therapy. Here we present two robust three-field treatment planning approaches utilized to maximize target coverage in the presence of anatomic and delivery uncertainties. Both techniques, conventional optimization (CO) and robust optimization (RO), create treatment plans with acceptable target coverage and sparing of organs at risk (OAR). While the RO method is less time intensive and may theoretically allow for superior OAR sparing and improved robustness, the CO method can be implemented by institutions who do not have RO capabilities.

Financial toxicity associated with treatment of localized prostate cancer

Financial toxicity is a broad term to describe the economic consequences and subjective burden resulting from a cancer diagnosis and treatment. As financial toxicity is associated with poor disease outcomes, recognition of this problem and calls for strategies to identify and support those most at risk are increasing. Men with localized prostate cancer face treatment choices including active surveillance, prostatectomy or radiotherapy. The fact that potential patient out-of-pocket costs might influence decision making has rarely been acknowledged and, overall, the risk of financial toxicity for men with localized prostate cancer remains poorly studied. This shortfall requires a work-up in the context of prostate cancer and a multidimensional framework for considering a patient's risk of financial toxicity. The major elements of this framework are direct and indirect costs, patient-specific values, expectations of possible financial burdens, and individual economic circumstances. Current data indicate that total cost patterns probably differ by treatment modality: surgery might have an increased short-term effect, whereas radiotherapy might have an increased long-term risk of financial toxicity. Specific thresholds of patient income levels or out-of-pocket costs that predict risk of financial toxicity are difficult to identify. Compared with other malignancies, prostate cancer might have a lower overall risk of financial toxicity, but persistent post-treatment urinary, bowel or sexual adverse effects are likely to increase this risk.

IMPT versus VMAT for Pelvic Nodal Irradiation in Prostate Cancer: A Dosimetric Comparison

Purpose:

To compare dosimetric data of the organs at risk (OARs) and clinical target volumes (CTVs) between intensity-modulated proton therapy (IMPT) and volumetric-modulated arc therapy (VMAT) for patients undergoing prostate and elective, pelvic lymph node radiotherapy in the setting of unfavorable, intermediate and high-risk prostate carcinoma.

Methods and Materials:

A study of moderately hypofractionated proton therapy (6750 centigray [cGy] in 25 fractions) is in progress for unfavorable, intermediate and high-risk prostate cancer where treatment includes an elective pelvic nodal CTV (4500 cGy in 25 fractions). Ten consecutively accrued patients were the subjects for dose-volume histogram comparison between IMPT and VMAT. Two treatment plans (IMPT and VMAT) were prepared for each patient with predefined planning objectives for target volumes and OARs. The IMPT plans were prepared with 2 lateral beams and VMAT plans with 2 arcs.

Results:

The CTV coverage was adequate for both plans with 99% of CTVs receiving ≥ 100% of the prescription doses. Mean doses to the bladder, rectum, large bowel, and small bowel were lower with IMPT versus VMAT. Mean femoral head dose was greater with IMPT. The percentage of volumes of rectum receiving ≤ 47.5 Gy, large bowel receiving ≤ 27.5 Gy, small bowel receiving ≤ 30 Gy, and bladder receiving ≤ 37.5 Gy was less with IMPT versus VMAT, largely because of reduction in the low-dose “bath” associated with VMAT.

Conclusions:

In the setting of prostate and elective, pelvic nodal radiotherapy for prostate cancer, IMPT can significantly reduce the dose to OARs, in comparison to VMAT, and provide adequate target coverage.

Rectal radiation dose-reduction techniques in prostate cancer: a focus on the rectal spacer

Prostate cancer is the most common cancer in men. External beam radiotherapy by a variety of methods is a standard treatment option with excellent disease control. However, acute and late rectal side effects remain a limiting concern in intensification of therapy in higher-risk patients and in efforts to reduce treatment burden in others. A number of techniques have emerged that allow for high-radiation dose delivery to the prostate with reduced risk of rectal toxicity, including image-guided intensity-modulated radiation therapy, endorectal balloons and various forms of rectal spacers. Image-guided radiation therapy, either intensity-modulated radiation therapy or stereotactic ablative radiation therapy, in conjunction with a rectal spacer, is an efficacious means to reduce acute and long-term rectal toxicity.

Intensity-modulated radiotherapy for whole pelvis irradiation in prostate cancer: A dosimetric and plan robustness study between photons and protons

Purpose

To evaluate the dosimetric impact and plan robustness of using Pencil Beam Scanning (PBS) in patients that requires prophylactic pelvic lymph nodes (PLNs) irradiation for prostate cancer.

Material and methods

Five intermediate to high-risk prostate patients previously treated using volumetric modulated arc therapy (VMAT), were selected for this study. Comparative proton radiotherapy plans were generated, where a three-field intensity modulated proton therapy (IMPT) plan was for the phase 1 planning target volume (PTV1) with PLNs. A technique with two posterior oblique fields using single field uniform dose (SFUD) was used for phase 2 (PTV2) volume, that comprises of the prostate and proximal seminal vesicles (Pro + proxSVs). Plan evaluation was performed on PTV coverage and dose to the organs at risk (OARs) using VMAT plans as a baseline (BL). Robust analysis on clinical target volume (CTV) coverage for the PBS plans was simulated with a 3 and 5 mm setup errors and a 3.5% range uncertainty.

Results

For target coverage, PTV1 and PTV2 showed negligible differences with a comparable homogeneity index (HI) values for both modalities. Proton plans produced a statistically significant lower mean dose to the bladder (32.5 Gy(RBE) vs. 46.5 Gy) and rectum (33.6 Gy(RBE) vs. 42.7 Gy). Dose to the bladder and rectum was equivalent at the high dose region. For the bowel cavity, the mean dose for proton plans were 45% lower compared to VMAT plans. Similarly, proton plans were able to achieve an overall reduction in integral dose for both treatment phase. CTV coverage remained high with all the simulated setup and range errors.

Conclusions

Proposed beam geometries for PTV1 and PTV2 proton plans presented good treatment accuracy with similar target coverage as the VMAT plans. Better sparing of OARs was achieved at the low-medium dose region for the proton plans.