Intermediate-risk prostate cancer patients treated with androgen deprivation therapy and a hypofractionated radiation regimen with or without image guided radiotherapy

Background To evaluate the efficacy of hypofractionated radiotherapy (HyRT) with or without image guided radiotherapy (IGRT) in intermediate risk prostate cancer. Methods 105 patients were treated with HyRT, 43,8 Gy and 54,75 Gy were delivered to the seminal vescicles and to the prostate, respectively; 3,65 Gy/fraction three times weekly. All patients underwent 9 months hormonal therapy. Patient position was verified with daily kV cone beam CT in 69 patients (IGRT group). Acute and late toxicities were evaluated according to RTOG scale. Biochemical relapse was defined using PSA nadir + 2 ng/mL. The data were prospectively collected and retrospectively analyzed to evaluate the efficacy of IGRT. Results After a median follow-up of 31 months the actuarial 3-year bNED was 93,7%. During RT, 10.5% and 7.6% of patients developed ≥Grade 2 rectal and urinary toxicities, respectively. The cumulative incidence of ≥Grade 2 late rectal and urinary toxicities at 3 years were 6,9%, and 10,8%, respectively. The incidence of ≥Grade 2 late rectal toxicities was significant reduced in the IGRT group (1,6% vs. 14,5%, p=0,021). Two patients developed Grade 3 urethral obstruction and one patient developed grade 3 rectal bleeding. Conclusions HyRT represents a well-tolerated treatment able to achieve a high bNED. The use of daily IGRT is beneficial for reducing the incidence of late toxicities.


Background
External Beam Radiotherapy (RT) is one of the therapeutic options for treating prostate cancer. The use of high dose RT with a conventional fractionation delivered conformally to spare as much normal tissue as possible, results in a significant biochemical control with acceptable toxicities [1].
In the past decade hypofractionated radiotherapy (HyRT) has been proposed as an alternative to conventional fractionation. Unlike most tumors, the estimated α/β ratio of prostate cancer is about 1.5 Gy, showing lower value compared to the α/β of surrounding tissues (e.g. rectum) [2]. Prostate cancer, because of its intrinsic slow proliferation, would be more sensitive to fractionations than nearby late-responding tissues. According to the Linear-Quadratic Model (LQM), the use of fewer and larger fractions of radiation instead of the conventional daily fractions of 2 Gy, would lead to an expected therapeutic advantage [3]. Moreover, HyRT is convenient for patients since the overall treatment time is reduced of several weeks depending on the higher dose per fraction, as well as for costs reduction of the health care system.
Randomized phase 3 trials comparing HyRT vs. conventional RT were carried out in late 1990s, but results are not conclusive because total doses used both in the control arm (64-66 Gy) and in the hypofractionated arm (biological equivalent dose of 62-67 Gy) are considered to be below the current standard [4,5]. The recent report on clinical outcome of the RTOG 9406 trial, concluded that dose-escalated 3D-CRT yields favorable outcomes for localized prostate cancer [6]. In the past decade differents fractionations have been explored in several randomized and non-randomized trials with good biochemical control and with acceptable acute and late toxicity profile [7][8][9]. Furthermore, the progress in radiotherapy techniques capable to spare healthy tissues allowing a dose-escalation such as intensity modulated RT (IMRT), stereotactic body RT (SBRT) or the use of image-guided RT (IGRT) would probably lead to a better clinical outcome [10][11][12][13][14][15].
To assess this issue, in 2007 we started a study using a novel HyRT regimen with or without IGRT for intermediate risk prostate carcinoma. A preliminary report regarding acute toxicity on 62 patients enrolled was previously published [16]. In the present paper, the authors assessed acute and late toxicity rates and provide survivals data in a cohort of 105 intermediate risk patients. Subgroups' analysis was also performed to evaluate any difference related to the use or not of daily IGRT in terms of toxicity or biochemical no evidence of disease (bNED).

Patients' characteristics
Between March 2007 and June 2011, 105 consecutive patients affected by intermediate risk prostate cancer were prospectively enrolled. Under an IRB-approved protocol the data were prospectively collected and retrospectively analyzed to evaluate the efficacy of IGRT in terms of toxicities and bNED. Written consent was obtained from all patient. All patients had histologically confirmed diagnosis and Gleason Score definition using transrectal ultrasound (TRUS) guided biopsies. The pre-treatment evaluation included patients' complete history, physical examination with digital rectal examination (DRE), blood tests including PSA level, total body computed tomography (CT) scan with iodine-based contrast and 99mTc bone scan. TRUS was employed for local staging in the early group of patients included (n=36, non-IGRT group), while multiparametric magnetic resonance imaging (MRI) of the pelvis including diffusion-weighted imaging (DWI) and dynamic contrast-enhanced study (DCE-MRI) was obtained in the following group of patients (n=69, IGRT group).
According to the National Comprehensive Cancer Network (NCCN) guidelines, intermediate risk group includes patients with any clinical T2b-T2c prostate cancer, Gleason Score equal to 7 or pre-treatment PSA value ranging from 10 to 20 ng/mL [17].

Simulation and treatment
Prior to simulation, patients were educated to empty the rectum and fill the bladder. All patients were immobilized in the supine position with feet fixation. A pre-treatment CT planning with 2.5 mm slices from the anal verge to the L5-S1 interface was performed. Planning CT images were fused with the multiparametric MRI to better delineate the Clinical Target Volume (CTV) in the IGRT group (n=69). The CTV1 included the prostate plus seminal vesicles (SSVV) and the CTV2 the prostate alone. Planning Target Volumes (PTV1 and PTV2, respectively) were generated adding a 8 mm margin in all directions except in the posterior direction where a 6 mm expansion was adopted in the non-IGRT group (n=36). A 5 mm expansion in all direction was used for the IGRT group. Indeed, the use of daily CBCT permit to reduce set-up errors as well the internal margin due to the interfraction motion of the prostate. The margin of 5 mm has been chosen to encompass the intrafraction movement also taking into account the deformation of the target as well as of the organ at risk (i.e. bladder and rectum) during the treatment.
The whole rectum from the anus to the sigmoid flexure, bladder, femoral heads and penile bulb were contoured as organs at risk.
A 3D conformal radiotherapy (3D-CRT) plan on the Eclipse planning system (Varian, Palo Alto, CA) was performed using 5 coplanar fields. Treatment was delivered by a linear accelerator using 15 MV photons. Thus the PTV1 received 43.8 Gy in 12 fractions (3.65 Gy per fraction) and the PTV2 received 54.75 Gy in 15 fractions, three times a week. According to the LQM this RT regimen is biologically equivalent to 80.5 Gy in 2 Gy fractions assuming a α/β ratio of 1.5 Gy. This regimen is also equivalent to 72.8 Gy in 2 Gy fractions assuming a α/β ratio of 3 Gy for late responding tissue. The overall treatment time has been chosen based on studies on acute mucosal toxicity in head and neck cancers showing that a BED10 over 60 Gy may be associated with a higher acute toxicity rate [2]. Thus, with the aim to maintain the acute toxicity rate and the consequential late damage low, we decided not to shorten below 5 weeks the overall treatment time. [18]. Dose-volume constraints were as follows: V45<35% and V52<25% for the rectum; V40<50% for the bladder. Patient position was verified using electronic portal imaging device (EPID) in the non-IGRT group, while the IGRT group underwent daily kV cone-beam CT (CBCT).
Neoadjuvant, concomitant and adjuvant hormonal therapy (HT) was started 3 months before RT. The HT consisted in anti-androgen or LHRH-analogue according to the treating physician's preference and was administered to all patients.

Toxicity and follow-up
Follow up was performed every 3 months for the first year and every 6 months afterwards. Toxicities were prospectively assessed according to the Radiation Therapy Oncology Group (RTOG) scale for acute and late adverse effects at each follow-up [19]. In general, the occurrence of symptoms not requiring medications or an increased in magnitude of baseline symptoms were considered as Grade 1 toxicities. Grade 2 toxicities were considered as the occurrence of symptoms requiring new medications (e.g. antidiarrheal drugs) or increase of previously prescribed medication or symptoms requiring a single surgical intervention (i.e. single laser coagulation). Grade 3 toxicities were defined as the occurrence of symptoms requiring surgery (i.e. TURP or permanent catheter or bleeding requiring ≥2 laser coagulation). Late toxicities were defined as occurring after 90 days from the completion of treatment. Erectile dysfunction was also evaluated using the following question from the Sexual Adjustment Questionnaire: "When sexually excited, are you able to get an erection?" at baseline, 3 months after RT and 1 year after HT. The five levels of response were: always, almost always, sometimes, almost never, never, not applicable/not answer [20].

Statistical analysis
The biochemical failure was defined as the PSA nadir + 2 ng/mL according to the Phoenix criteria [21]. Overall survival (OS), disease specific survival (DSS), bNED and the cumulative incidence of ≥ Grade 2 late toxicity were calculated to the event using the Kaplan-Meier method. In the subgroups' analysis acute toxicities between the IGRT and non-IGRT series were compared using the chi-square test. Differences in bNED as well the cumulative incidence of ≥ Grade2 late toxicities between the two groups were evaluated with log-rank test. Statistical analyses were performed using SPSS statistical software package version 13.0 (SPSS, Inc., Chicago, IL). A p-value of less than 0.05 was considered to be statistically significant.
After a median follow-up of 31 months (range, 6-64 months), the actuarial 3-year BFS was 93,7% ( Figure 1). The median follow-up was 50 months (range, 7-64 months) and 25 months (range, 6-43 months) for non-IGRT and IGRT patients, respectively. Five patients developed biochemical failure: 3 patients were found to have metastasis to loco-regional lymph nodes and 2 patients had bone metastasis. Subsequently, all these patients (n=5) were submitted to total Androgen Deprivation Therapy (ADT). Patients with regional lymph nodes received salvage radiation therapy based on 18FCholine-PET/TC. Patients with bone metastasis received palliative radiation treatment. Then, PSA levels normalization was obtained in 3 patients (node metastasis: 2 patients; bone metastasis: 1 patient). One patient with lymph-node metastasis did not respond to ADT plus RT and underwent taxane-based chemotherapy that is still ongoing. The other patient with bone metastasis died because of systemic disease progression. Six patients died from intecurrent disease without evidence of prostate cancer. The 3-year OS was 95% and the 3-years DSS 98,2% (Figure 1). No differences were found in BFS between the two groups of patients (91,3% vs. 94,3%; p=0,413).

Acute toxicities
During RT, 15.2% of the patients developed Grade 1 GI toxicity and 10.5% developed ≥ Grade 2 GI toxicity. At 3 months after RT, 4 patients had Grade 1 GI toxicities and only 1 patient had a Grade 2 proctitis. Acute GU   toxicities during RT were recorded as follows: 47.6% experienced Grade 1 toxicities and 7.6% experienced ≥ Grade 2 toxicities. At 3 months after RT, 31.4% had Grade 1 GU toxicities and 2.9% had ≥ Grade 2 GU toxicities. None had grade 3-4 acute toxicities (Table 2).

Sexual function
At baseline, 46.6% was always (21.9%) or almost always (24.8%) able to have an erection, while at the first followup, only the 10.5% of patients was always (1.9%) or almost always (8.6%) able to have an erection. After 1 year from the end of HT there was a partial recovery of sexual function (17.1% always or almost always) ( Table 4).

Discussion
Hypofractionated radiotherapy represents an attractive therapeutic option for tumors with low proliferation grade such as prostate cancer. The difference in α/β ratio between the tumor itself and surrounding normal tissues may lead to a therapeutic gain as well as an advantage for the patient and the health care system because the reduced overall duration of the treatment.
In the last decade, several randomized trial compared HyRT vs. conventional RT showing good toxicity rates and local control but only in a few studies was an adequate dose delivered [4,5,7,10].
Dearnaley et al. compared a conventional schedule of 74 Gy in 37 fractions with two hypofractionated highdose intensity-modulated schedules with a total dose 60 Gy or 57 Gy, delivered in 20 or 19 fractions of 3 Gy per fraction, respectively [10]. All patients were also submitted to receive ADT for 4-6 months. The cumulative rates of late GI and GU toxicities ≥ Grade 2 showed not statistically significant differences between the three groups while survival analysis was not reported.
Arcangeli et al. randomized 168 high-risk prostate cancer patients to receive HyRT (62 Gy in 20 fractions, 4 fractions/week) or conventionally fractionated (80 Gy in 40 fractions) three-dimensional conformal radiotherapy to the prostate and seminal vesicles [7]. All patients were also submitted to 9 months-ADT started 2 months before RT. The reported ≥ Grade 2 GI and GU late toxicities were similar in both groups, while the 4-year actuarial freedom from biochemical failure was significantly different for patients treated with HyRT vs. conventional fractionation (82% vs. 60%, respectively; p = 0.004).
The use of HyRT in prostate cancer patients has also been investigated in several recent phase II studies that demonstrated good biochemical control rates depending on risk stratification and acceptable toxicities (≥ Grade 2 GU and GI late toxicities ranging from 3% to 25%) [8,9,[11][12][13]22]. Therefore, further randomized studies are needed to confirm these data. In the present study, 5.7% patients experienced ≥ Grade 2 GI toxicity and 9.5% patients had ≥ Grade 2 GU toxicity. Our results are comparable to those reported in the literature.
Zelefsky et al. found that high-dose IGRT is associated with a low rate of late urinary toxicity and with an improvement in biochemical tumor control among highrisk patients [23]. Differently, in our study the use of IGRT was associated to a decreased late GI toxicity and combined late GI plus GU toxicities. Such different results obtained by Zelefsky et al. can be explained by the use of IMRT instead of 3D-CRT, a technique able to spare the bladder neck that is responsible of late GU toxicities after radiotherapy. On the contrary, the reduction in late GI toxicities we observed are possibly due to several factors such as: the role of MRI during the planning that reduced the CTV, the reduced PTV margin, and the daily CBCT that decreased set-up errors. Acute toxicity rates were similar in both groups, even if a trend of significance for better outcome was found regarding the incidence of acute GI toxicity in favor of IGRT.
The association of ADT to HyRT is still an open question. A preliminary report of the French trial GETUG 14 regarding patients affected by intermediate-risk cancer treated with dose escalated RT vs. dose escalated RT plus short course ADT showed a statistically significant increased 3-year biochemical progression-free survival; no   Kupelian et al. found that the use of hormonal therapy before or after HyRT (70 Gy at 2.5 Gy per fraction) was an independent predictor of a worse outcome [13]. However, to determine the exact role of HT in the era of HyRT in intermediate-risk prostate cancer randomized trials are needed. The strength of this paper is that a novel HyRT schedule was examined in 105 patients affected by intermediaterisk prostate cancer. The majority of studies on prostate cancer includes different categories of risk making the results not generalizable. Indeed, it should be taken into account that intermediate-risk prostate cancer itself would represent a clinically non-uniform group of disease characterized by a wide range of clinical behavior [26].
On the other hand, there are several limits of this study including the low median follow-up and the different RT technique used. Moreover, the study was unpowered to detect differences in terms of acute toxicities between the two groups of patients, probably due to the small number of patients treated without IGRT. Despite these limits we found a clearly advantage of using daily IGRT in HyRT in terms of reduced ≥ Grade 2 late toxicities.

Conclusions
In conclusion, the HyRT schedule represents a welltolerated treatment with acceptable rates of both acute and late toxicity, able to achieve a high bNED in intermediate-risk prostate cancer; but a longer follow-up is needed. The use of daily IGRT is beneficial for reducing the incidence of late toxicities but further studies are required to confirm these results.