Radiation for Prostate Cancer: Intensity Modulated Radiation Therapy versus Proton Beam

Better preservation of erectile function in localized prostate cancer patients with modern proton therapy: Is it cost-effective?

BACKGROUND

Stereotactic body radiation therapy (SBRT) has gradually been recognized as favorable curative treatment for localized prostate cancer (PC). However, the high rate of erectile dysfunction (ED) after traditional photon-based SBRT remains an ongoing challenge that greatly impacts the quality of life of PC survivors. Modern proton therapy allows higher conformal SBRT delivery and has the potential to reduce ED occurrence but its cost-effectiveness remains uninvestigated.

METHODS

A Markov decision model was designed to evaluate the cost-effectiveness of proton SBRT versus photon SBRT in reducing irradiation-related ED. Base-case evaluation was performed on a 66-year-old (median age of PC) localized PC patient with normal pretreatment erectile function. Further, stratified analyses were performed for different age groups (50, 55, 60, 65, 70, and 75 years) and threshold analyses were conducted to estimate cost-effective scenarios. A Chinese societal willingness-to-pay (WTP) threshold (37,653 US dollars [$])/quality-adjusted life-year [QALY]) was adopted.

RESULTS

For the base case, protons provided an additional 0.152 QALY at an additional cost of $7233.4, and the incremental cost-effectiveness ratio was $47,456.5/QALY. Protons was cost-effective for patients ≤62-year-old at the WTP of China (≤66-year-old at a WTP of $50,000/QALY; ≤73-year-old at a WTP of $100,000/QALY). For patients at median age, once the current proton cost ($18,000) was reduced to ≤$16,505.7 or the patient had a life expectancy ≥88 years, protons were cost-effective at the WTP of China.

CONCLUSIONS

Upon assumption-based modeling, the results of current study support the use of proton SBRT in younger localized PC patients who are previously potent, for better preservation of erectile function. The findings await further validation using data from future comparative clinical trials.

Consensus Statement on Proton Therapy for Prostate Cancer

Proton therapy is a promising but controversial treatment in the management of prostate cancer. Despite its dosimetric advantages when compared with photon radiation therapy, its increased cost to patients and insurers has raised questions regarding its value. Multiple prospective and retrospective studies have been published documenting the efficacy and safety of proton therapy for patients with localized prostate cancer and for patients requiring adjuvant or salvage pelvic radiation after surgery. The Particle Therapy Co-Operative Group (PTCOG) Genitourinary Subcommittee intends to address current proton therapy indications, advantages, disadvantages, and cost effectiveness. We will also discuss the current landscape of clinical trials. This consensus report can be used to guide clinical practice and research directions.

Systematic review of methodology used in clinical studies evaluating the benefits of proton beam therapy

BACKGROUND

Proton beam therapy (PBT) delivers high-energy radiation to target tumours while sparing surrounding normal tissues. The dosimetric advantages of PBT over traditional photon radiotherapy may be clear but the translation of this benefit into clinically meaningful reductions in toxicities and improved quality-of-life (QoL) needs to be determined. Randomised controlled trials (RCTs) are considered the gold standard for generating the highest-level evidence in medicine. The objectives of this systematic review were to provide an overview of published clinical studies evaluating the benefits of PBT, and to examine the methodology used in clinical trials with respect to study design and outcomes.

METHODS

PubMed, EMBASE and Cochrane databases were systematically searched for published clinical studies where PBT was a cancer treatment intervention. All randomised and non-randomised studies, prospective or retrospective, were eligible for inclusion.

RESULTS

In total, 219 studies were included. Prospective studies comprised 89/219 (41%), and of these, the number of randomised phase II and III trials were 5/89 (6%) and 3/89 (3%) respectively. Of all the phase II and III trials, 18/24 (75%) were conducted at a single PBT centre. Over one-third of authors recommended an increase in length of follow up. Research design and/or findings were poorly reported in 74/89 (83%) of prospective studies. Patient reported outcomes were assessed in only 19/89 (21%) of prospective studies.

CONCLUSIONS

Prospective randomised evidence for PBT is limited. The set-up of national PBT services in several countries provides an opportunity to guide the optimal design of prospective studies, including RCTs, to evaluate the benefits of PBT across various disease sites. Collaboration between PBT centres, both nationally and internationally, would increase potential for the generation of practice changing evidence. There is a need to facilitate and guide the collection and analysis of meaningful outcome data, including late toxicities and patient reported QoL.

Hydrogel Spacer Reduces Rectal Dose during Proton Therapy for Prostate Cancer: A Dosimetric Analysis

Purpose

Proton therapy for prostate cancer may reduce bowel dose and risk of bowel symptoms relative to photon-based methods. Here, we determined the effect of using a biodegradable, injectable hydrogel spacer on rectal dose on plans for treating prostate cancer with intensity-modulated proton therapy (IMPT) or passive scattering proton therapy (PSPT).

Materials and Methods

Pairs of IMPT and PSPT plans for 9 patients were created from fused computed tomography/magnetic resonance imaging scans obtained before and after spacer injection. Calculated values of rectal V40, V60, V70, V80, and maximum dose (Dmax) were compared with Wilcoxon signed rank tests. Displacements at the base (BP), midgland (MP), and apex (AP) of the prostate relative to the anterior rectal wall with the spacer in place were averaged for each patient and correlated with V70 by using linear regression models.

Results

The presence of a spacer reduced all dosimetric parameters for both PSPT and IMPT, with the greatest difference in V70, which was 81.1% lower for PSPT-with-spacer than for IMPT-without-spacer. Median displacements at BP, MP, and AP were 12 mm (range 7-19), 2 mm (range 0-4), and 1 mm (range 0-5) without the spacer and 19 mm (range 12-23), 10 mm (range 8-16), and 7 mm (range 2-12) with the spacer. Modest linear trends were noted between rectal V70 and displacement for IMPT-with-spacer and PSPT-with-spacer. When displacement was ≥8 mm, V70 was ≤5.1% for IMPT-with-spacer and PSPT-with-spacer.

Conclusion

Use of biodegradable hydrogel spacers for prostate cancer treatment provides a significant reduction of radiation dose to the rectum with proton therapy. Significant reductions in rectal dose occurred in both PSPT and IMPT plans, with the greatest reduction for IMPT-with-spacer relative to PSPT alone. Prospective studies are ongoing to assess the clinical impact of reducing rectal dose with hydrogel spacers.

Proton therapy for prostate cancer: A review of the rationale, evidence, and current state

Men diagnosed with localized prostate cancer have many curative treatment options including several different radiotherapeutic approaches. Proton radiation is one such radiation treatment modality and, due to its unique physical properties, offers the appealing potential of reduced side effects without sacrificing cancer control. In this review, we examine the intriguing dosimetric rationale and theoretical benefit of proton radiation for prostate cancer and highlight the results of preclinical modeling studies. We then discuss the current state of the clinical evidence for proton efficacy and toxicity, derived from both large claim-based datasets and prospective patient-reported data. The result is that the data are mixed, and clinical equipoise persists in this area. We place these studies into context by summarizing the economics of proton therapy and the changing practice patterns of prostate proton irradiation. Finally, we await the results of a large prospective randomized clinical trial currently accruing and also a large prospective pragmatic comparative study which will provide more rigorous evidence regarding the clinical and comparative effectiveness of proton therapy for prostate cancer.

Early toxicity and patient reported quality-of-life in patients receiving proton therapy for localized prostate cancer: a single institutional review of prospectively recorded outcomes

Background

We report prospectively captured clinical toxicity and patient reported outcomes in a single institutional cohort of patients treated for prostate cancer with proton beam therapy (PBT). This is the largest reported series of patients treated mostly with pencil beam scanning PBT.

Methods

We reviewed 231 patients treated on an IRB approved institutional registry from 2013 to 2016; final analysis included 192 patients with > 1-year of follow-up. Toxicity incidence was prospectively captured and scored using CTCAE v4.0. International Prostate Symptoms Score (IPSS), Sexual Health Inventory for Men (SHIM) score, and Expanded Prostate Cancer Index Composite (EPIC) bowel domain questionnaires were collected at each visit. Univariate Cox regression was used to explore associations of grade 2+ toxicity with clinical, treatment, and dosimetric variables.

Results

Median follow-up was 1.7 years. Grade 3 toxicity was seen in 5/192 patients. No grade 4 or 5 toxicity was seen. Patient reported quality-of-life showed no change in urinary function post-radiation by IPSS scores. Median SHIM scores declined by 3.7 points at 1-year post-treatment without further decrease beyond year 1. On univariate analysis, only younger age (HR = 0.61, p = 0.022) was associated with decreased sexual toxicity. EPIC bowel domain scores declined from 96 at baseline (median) by an average of 5.4 points at 1-year post-treatment (95% CI: 2.5–8.2 points, p < 0.001), with no further decrease over time. Bowel toxicity was mostly in the form of transient rectal bleeding and was associated with anticoagulation use (HR = 3.45, p = 0.002).

Conclusions

Grade 3 or higher toxicity was rare at 2-years after treatment with PBT for localized prostate cancer. Longer follow-up is needed to further characterize late toxicity and biochemical control.

Trial registration

NCT, NCT01255748. Registered 1 January 2013.

Inclusion of a variable RBE into proton and photon plan comparison for various fractionation schedules in prostate radiation therapy

PURPOSE

A constant relative biological effectiveness (RBE) of 1.1 is currently used in proton radiation therapy to account for the increased biological effectiveness compared to photon therapy. However, there is increasing evidence that proton RBE vary with the linear energy transfer (LET), the dose per fraction, and the type of the tissue. Therefore, this study aims to evaluate the impact of disregarding variations in RBE when comparing proton and photon dose plans for prostate treatments for various fractionation schedules using published RBE models and several α/β assumptions.

METHODS

Photon and proton dose plans were created for three generic prostate cancer cases. Three BED_3Gy equivalent schedules were studied, 78, 57.2, and 42.8 Gy in 39, 15, and 7 fractions, respectively. The proton plans were optimized assuming a constant RBE of 1.1. By using the Monte Carlo calculated dose-averaged LET (LET_d ) distribution and assuming α/β values on voxel level, three variable RBE models were applied to the proton dose plans. The impact of the variable RBE was studied in the plan comparison, which was based on the dose distribution, DVHs, and normal tissue complication probabilities (NTCP) for the rectum. Subsequently, the physical proton dose was reoptimized for each proton plan based on the LET_d distribution, to achieve a homogeneous RBE-weighted target dose when applying a specific RBE model and still fulfill the clinical goals for the rectum and bladder.

RESULTS

All the photon and proton plans assuming RBE = 1.1 met the clinical goals with similar target coverage. The proton plans fulfilled the robustness criteria in terms of range and setup uncertainty. Applying the variable RBE models generally resulted in higher target doses and rectum NTCP compared to the photon plans. The increase was most pronounced for the fractionation dose of 2 Gy(RBE), whereas it was of less magnitude and more dependent on model and α/β assumption for the hypofractionated schedules. The reoptimized proton plans proved to be robust and showed similar target coverage and doses to the organs at risk as the proton plans optimized with a constant RBE.

CONCLUSIONS

Model predicted RBE values may differ substantially from 1.1. This is most pronounced for fractionation doses of around 2 Gy(RBE) with higher doses to the target and the OARs, whereas the effect seems to be of less importance for the hypofractionated schedules. This could result in misleading conclusions when comparing proton plans to photon plans. By accounting for a variable RBE in the optimization process, robust and clinically acceptable dose plans, with the potential of lowering rectal NTCP, may be generated by reoptimizing the physical dose. However, the direction and magnitude of the changes in the physical proton dose to the prostate are dependent on RBE model and α/β assumptions and should therefore be used conservatively.

Rectal dose to prostate cancer patients treated with proton therapy with or without rectal spacer

The purpose of this study was to evaluate whether a spacer inserted in the prerectal space could reduce modeled rectal dose and toxicity rates for patients with prostate cancer treated in silico with pencil beam scanning (PBS) proton therapy. A total of 20 patients were included in this study who received photon therapy (12 with rectal spacer (DuraSeal™ gel) and 8 without). Two PBS treatment plans were retrospectively created for each patient using the following beam arrangements: (1) lateral-opposed (LAT) fields and (2) left and right anterior oblique (LAO/RAO) fields. Dose volume histograms (DVH) were generated for the prostate, rectum, bladder, and right and left femoral heads. The normal tissue complication probability (NTCP) for ≥grade 2 rectal toxicity was calculated using the Lyman-Kutcher-Burman model and compared between patients with and without the rectal spacer. A significantly lower mean rectal DVH was achieved in patients with rectal spacer compared to those without. For LAT plans, the mean rectal V70 with and without rectal spacer was 4.19 and 13.5%, respectively. For LAO/RAO plans, the mean rectal V70 with and without rectal spacer was 5.07 and 13.5%, respectively. No significant differences were found in any rectal dosimetric parameters between the LAT and the LAO/RAO plans generated with the rectal spacers. We found that ≥ 9 mm space resulted in a significant decrease in NTCP modeled for ≥grade 2 rectal toxicity. Rectal spacers can significantly decrease modeled rectal dose and predicted ≥grade 2 rectal toxicity in prostate cancer patients treated in silico with PBS. A minimum of 9 mm separation between the prostate and anterior rectal wall yields the largest benefit.

Validation of rectal sparing throughout the course of proton therapy treatment in prostate cancer patients treated with SpaceOAR®

The purpose of this study was to investigate the consistency of rectal sparing using multiple periodic quality assurance computerized tomography imaging scans (QACT) obtained during the course of proton therapy for patients with prostate cancer treated with a hydrogel spacer. Forty-one low- and intermediate-risk prostate cancer patients treated with image-guided proton therapy with rectal spacer hydrogel were analyzed. To assess the reproducibility of rectal sparing with the hydrogel spacer, three to four QACTs were performed for each patient on day 1 and during weeks 1, 3, and 5 of treatment. The treatment plan was calculated on the QACT and the rectum V90%, V75%, V65%, V50%, and V40% were evaluated. For the retrospective analysis, we evaluated each QACT and compared it to the corresponding treatment planning CT (TPCT), to determine the average change in rectum DVH points. We were also interested in how many patients exceeded an upper rectum V90% threshold on a QACT. Finally, we were interested in a correlation between rectum volume and V90%. On each QACT, if the rectum V90% exceeded the upper threshold of 6%, the attending physician was notified and the patient was typically prescribed additional stool softeners or laxatives and reminded of dietary compliance. In all cases of the rectum V90% exceeding the threshold, the patient had increased gas and/or stool, compared to the TPCT. On average, the rectum V90% calculated on the QACT was 0.81% higher than that calculated on the TPCT. The average increase in V75%, V65%, V50%, and V40% on the QACT was 1.38%, 1.59%, 1.87%, and 2.17%, respectively. The rectum V90% was within ± 1% of the treatment planning dose in 71.2% of the QACTs, and within ± 5% in 93.2% of the QACTs. The 6% threshold for rectum V90% was exceeded in 7 out of 144 QACTs (4.8%), identified in 5 of the 41 patients. We evaluated the average rectum V90% across all QACTs for each of these patients, and it was found that the rectum V90% never exceeded 6%. 53% of the QACTs had a rectum volume within 5 cm3 of the TPCT volume, 68% were within 10 cm3. We found that patients who exceeded the threshold on one or more QACTs had a lower TPCT rectal volume than the overall average. By extrapolating patient anatomy from three to four QACT scans, we have shown that the use of hydrogel in conjunction with our patient diet program and use of stool softeners is effective in achieving consistent rectal sparing in patients undergoing proton therapy.

Prostate Cancer Radiation Therapy: What Do Clinicians Have to Know?

Radiotherapy (RT) for prostate cancer (PC) has steadily evolved over the last decades, with improving biochemical disease-free survival. Recently population based research also revealed an association between overall survival and doses ≥ 75.6 Gray (Gy) in men with intermediate- and high-risk PC. Examples of improved RT techniques are image-guided RT, intensity-modulated RT, volumetric modulated arc therapy, and stereotactic ablative body RT, which could facilitate further dose escalation. Brachytherapy is an internal form of RT that also developed substantially. New devices such as rectum spacers and balloons have been developed to spare rectal structures. Newer techniques like protons and carbon ions have the intrinsic characteristics maximising the dose on the tumour while minimising the effect on the surrounding healthy tissue, but clinical data are needed for confirmation in randomised phase III trials. Furthermore, it provides an overview of an important discussion issue in PC treatment between urologists and radiation oncologists: the comparison between radical prostatectomy and RT. Current literature reveals that all possible treatment modalities have the same cure rate, but a different toxicity pattern. We recommend proposing the possible different treatment modalities with their own advantages and side-effects to the individual patient. Clinicians and patients should make treatment decisions together (shared decision-making) while using patient decision aids.

Therapeutic results in elderly patients with prostate cancer: chronological comparison in a single community hospital

Objective: There are few reports of the long-term outcomes of elderly patients with prostate cancer. We analyzed data from our institution from the past 12 years, including the patient history, treatment methods, and prognosis of patients with prostate cancer aged 80 years or more.

Patients and Methods: A total of 179 cases of prostate cancer in patients aged 80 years or more were retrospectively evaluated. We divided them chronologically into groups A, B, C, and D: Group A included 40 cases from 2002–2004; Group B, 48 cases from 2005–2007; Group C, 46 cases from 2008–2010; and Group D, 45 cases from 2011–2013.

Results: Sixty-one (30%) patients changed treatment course. Interestingly, no cancer deaths occurred in the patients who changed treatment course. Although 14 (7.8%) cancer deaths occurred (A: B: C: D = 4: 4: 6: 0, respectively), all occurred in 2011 or later.

Conclusion: In our study, over 50 patients who underwent treatment survived for 5 years or more. By treating prostate cancer in elderly patients when appropriate, we can lower the mortality rate due to prostate cancer. Our results support the active treatment of prostate cancer in elderly patients.

National trends and determinants of proton therapy use for prostate cancer: A National Cancer Data Base study

BACKGROUND

In the current study, the authors sought to both characterize the national trends in proton therapy use for prostate cancer and determine the factors associated with receipt of this limited resource, using what to the best of their knowledge is the largest nationwide cancer registry.

METHODS

The National Cancer Data Base was used to identify 187,730 patients diagnosed with nonmetastatic prostate cancer from 2004 through 2012 who received external beam radiotherapy as their initial form of definitive therapy. Multivariable logistic regression analysis adjusted for sociodemographic and clinical factors was used to identify independent determinants of proton therapy use.

RESULTS

The rate of proton therapy use increased significantly from 2.3% in 2004 to 5.2% in 2011 and 4.8% in 2012 (P value for trend <.0001). Proton therapy for prostate cancer was much more likely to be delivered at an academic compared with nonacademic center and to patients who were white, younger, healthier, from metropolitan areas, from zip codes with higher median household incomes, and who did not have an advanced stage of or high-grade disease (all P<.0001). Compared with white patients, those who were black and Hispanic were found to be significantly less likely to receive proton therapy even after robust multivariable adjustments (adjusted odds ratio, 0.20 [95% confidence interval, 0.18-0.22; P<.0001] and adjusted odds ratio, 0.57 [95% confidence interval, 0.48-0.66; P<.0001], respectively).

CONCLUSIONS

The use of proton therapy to treat patients with prostate cancer more than doubled from 2004 to 2012, with striking racial disparities in its use noted despite robust multivariable adjustments. Long-term follow-up is needed to determine whether the increased use of proton therapy for prostate cancer is justified, and ongoing efforts should be made to ensure equal access to resource-limited oncologic therapies. Cancer 2016;122:1505-12. © 2016 American Cancer Society.