Salvage Reirradiation for Locally Recurrent Prostate Cancer: Results From a Prospective Study With 7.2 Years of Follow-Up.

PURPOSE: There are no well-established re-treatment options for local recurrence after primary curative radiation therapy for prostate cancer (PCa), as prospective studies with long-term follow-up are lacking. Here, we present results from a prospective study on focal salvage reirradiation with external-beam radiation therapy with a median follow-up of 7.2 years. MATERIALS AND METHODS: From 2013 to 2017, 38 patients with biopsy-proven locally recurrent PCa >2 years after previous treatment and absence of grade 2-3 toxicity from the first course of radiation were included. The treatment was 35 Gy in five fractions to the MRI-based target volume and 6 months of androgen-deprivation therapy starting 3 months before radiation. The Phoenix criteria defined biochemical recurrence-free survival (bRFS), and toxicity was scored according to Radiation Therapy Oncology Group criteria. RESULTS: Median age was 70 years, and median time from primary radiation to prostate-specific antigen (PSA) recurrence was 83 months. The actuarial 2-year and 5-year bRFS were 81% (95% CI, 69 to 94) and 58% (95% CI, 49 to 74), respectively. The actuarial 5-year local recurrence-free survival was 93% (95% CI, 82 to 100), metastasis-free survival was 82% (95% CI, 69 to 95), and overall survival was 87% (95% CI, 76 to 98). Two patients (5%) had durable grade 3 genitourinary toxicity, one combined with GI grade 3 toxicity. A PSA doubling time ≤6 months at salvage, a Gleason score >7, and a PSA nadir ≥0.1 ng/mL predicted a worse outcome. CONCLUSION: Reirradiation with EBRT for locally recurrent PCa after primary curative radiation therapy is clinically feasible and demonstrated a favorable outcome with acceptable toxicity in this prospective study with long-term follow-up.

Clinical iterative model development improves knowledge-based plan quality for high-risk prostate cancer with four integrated dose levels.

BACKGROUND: Manual volumetric modulated arc therapy (VMAT) treatment planning for high-risk prostate cancer receiving whole pelvic radiotherapy (WPRT) with four integrated dose levels is complex and time consuming. We have investigated if the radiotherapy planning process and plan quality can be improved using a well-tuned model developed through a commercial system for knowledge-based planning (KBP). MATERIAL AND METHODS: Treatment plans from 69 patients treated for high-risk prostate cancer with manually planned VMAT were used to develop an initial KBP model (RapidPlan, RP). Prescribed doses were 50, 60, 67.5, and 72.5 Gy in 25 fractions to the pelvic lymph nodes, prostate and seminal vesicles, prostate gland, and prostate tumour(s), respectively. This RP model was in clinical use from July 2019 to February 2020, producing another set of 69 clinically delivered treatment plans for a new patient group, which were used to develop a second RP model. Both models were validated on an independent group of 40 patients. Plan quality was compared by D 98% and the Paddick conformity index for targets, mean dose (D mean) and generalised equivalent uniform dose (gEUD) for bladder, bowel bag and rectum, and number of monitor units (MU). RESULTS: Target coverage and conformity was similar between manually created and RP treatment plans. Compared to the manually created treatment plans, the final RP model reduced average D mean and gEUD with 2.7 Gy and 1.3 Gy for bladder, 1.2 Gy and 0.9 Gy for bowel bag, and 2.7 Gy and 0.8 Gy for rectum, respectively (p < .05). For rectum, the interpatient variation (i.e., 95% confidence interval) of DVHs was reduced by 23%. CONCLUSION: KBP improved plan quality and consistency among treatment plans for high-risk prostate cancer. Model tuning using KBP-based clinical plans further improved model outcome.

Ten-Year Results From a Phase II Study on Image Guided, Intensity Modulated Radiation Therapy With Simultaneous Integrated Boost in High-Risk Prostate Cancer.

PURPOSE: There is no consensus on how to treat high-risk prostate cancer, and long-term results from hypofractionated radiation therapy are lacking. We report 10-year results after image guided, intensity modulated radiation therapy with hypofractionated simultaneous integrated boost and elective pelvic field. METHODS AND MATERIALS: Between 2007 and 2009, 97 consecutive patients with high-risk prostate cancer were included, treated with 2.7 to 2.0 Gy × 25 Gy to the prostate, seminal vesicles, and elective pelvic field. Toxicity was scored according to Radiation Therapy Oncology Group criteria and biochemical disease-free survival (BFS) defined by the Phoenix definition. Patients were subsequently divided into 3 groups: high risk (HR; n = 32), very high risk (VHR; n = 50), and N+/s-prostate-specific antigen (PSA) ≥100 (n = 15). Differences in outcomes were examined using Kaplan-Meier analyses. RESULTS: BFS in the patients at HR and VHR was 64%, metastasis-free survival 80%, prostate cancer-specific survival 90%, and overall survival (OS) 72%. VHR versus HR subgroups demonstrated significantly different BFS, 54% versus 79% (P = .01). Metastasis-free survival and prostate cancer-specific survival in the VHR group versus HR group were 76% versus 87% (P = .108) and 74% versus 100% (P = .157). Patients reaching nadir PSA <0.1 (n = 80) had significantly better outcomes than the rest (n = 17), with BFS 70% versus 7% (P < .001). Acute grade 2 gastrointestinal tract (GI) and genitourinary tract (GU) toxicity occurred in 27% and 40%, grade 3 GI and GU toxicity in 1% and 3%. Late GI and GU grade 2 toxicity occurred in 1% and 8%. CONCLUSIONS: High-risk prostate cancer patients obtained favorable 10-year outcomes with low toxicity. There were significantly better results in the HR versus the VHR group, both better than the N+/PSA ≥100 group. A nadir PSA value < 0.1 predicted good prognosis.

Impact of positive surgical margins on secondary treatment, palliative radiotherapy and prostate cancer-specific mortality. A population-based study of 13 198 patients.

BACKGROUND: The results of studies evaluating the impact of positive surgical margins on prostate cancer-specific mortality have been inconsistent. We, therefore, evaluated the impact of surgical margin status on subsequent secondary treatment, palliative radiotherapy, and prostate cancer-specific mortality. METHODS: A total of 14 837 men treated with radical prostatectomy (RP) during the period 2001 to 2015 were identified from the Cancer Registry of Norway. Of those, 13 198 (89%) patients had complete data on the preoperative prostate-specific antigen level, pathological T-category, Gleason score in the prostatectomy specimen, and margin status. Multivariable Cox proportional hazards models were used to evaluate the risk, and flexible parametric models for the cumulative incidence were fitted to predict the probabilities of secondary treatment (salvage radiotherapy or prophylactic breast radiation), palliative radiotherapy, and prostate cancer-specific mortality. RESULTS: After a median follow-up time of 5.2 years (3591 patients with ≥8 years of follow-up), positive surgical margins (PSMs) were independently predictive of secondary treatment (hazard ratio [HR] = 2.43, 95% confidence interval [CI] = 2.21-2.66) and palliative radiotherapy (HR = 1.45, 95% CI = 1.03-2.05). After 10 years, the absolute increased risk for palliative radiotherapy in patients with PSMs after RP varied between 0.1% in pT2 tumors with a Gleason score of 6, to 12% for pT3b tumors with a Gleason score of 9 to 10. PSMs were not independently associated with prostate cancer-specific mortality (HR = 1.14, 95% CI = 0.82-1.59). CONCLUSION: PSMs were associated with increased application of secondary treatment and palliative radiotherapy but were not predictive of prostate cancer-specific mortality. As the use of palliative radiotherapy was only marginally increased in patients with PSMs and the lowest-risk disease characteristics, avoiding PSMs may be of greatest prognostic relevance in patients with higher-risk disease characteristics.

Statistical motion modelling for robust evaluation of clinically delivered accumulated dose distributions after curative radiotherapy of locally advanced prostate cancer.

BACKGROUND AND PURPOSE: Planned doses are used as surrogate for the actually delivered dose in radiotherapy. We have estimated the delivered dose in a dose-escalation trial of locally advanced prostate cancer by statistical dose-accumulation and by DVH-summation, and compared to planned dose. MATERIALS AND METHOD: Prescribed dose-escalation to the prostate was 67.5 Gy/25fr., corresponding to 81GyEQD2 assuming α/ß = 1.5. The 21 patients had three targets (i.e. CTV67.5 + 2 mm, CTV60 + 5 mm, CTV50 + 10 mm) irradiated by a simultaneous-integrated-boost technique. Analysis was based on 213 CT scans and 5-years of follow-up. For statistical dose-accumulation, we modelled 10000 possible treatment courses based on planned dose and deformation-vector-fields from contour-based registration. For DVH-summation we recalculated dose on repeat-CTs and estimated median D98%/EUD. Groups with/without disease recurrence were compared. RESULTS: Discrepancies between planned and accumulated dose were mostly seen for CTV67.5, where under-dosage was found at different locations in the prostate in 12/21 patients. Delivered dose-escalation (D98%) was on average 73.9GyEQD2 (range: 68.3-78.7GyEQD2). No significant difference in accumulated-D98% was found in patients with (n = 8) and without (n = 13) recurrence (p > 0.05). Average D98%/EUD with statistical dose-accumulation vs DVH-summation was significantly different in CTV60, CTV50, rectum and bladder but not in CTV67.5. CONCLUSION: The planned dose escalation was not received by more than half-of-the patients. Robustness of the prostate target (CTV67.5) should therefore be better prioritized in these patients given the low toxicity profile. Estimates of delivered dose were less conservative for dose-accumulation due to interaction of random organ motion with the dose matrix.

Risk of radiation-induced secondary rectal and bladder cancer following radiotherapy of prostate cancer.

BACKGROUND: An elevated risk of radiation-induced secondary cancer (SC) has been observed in prostate cancer patients after radiotherapy (RT), rising to as high as one in 70 patients with more than 10 years follow-up. In this study we have estimated SC risks following RT with both previous and contemporary techniques, including proton therapy, using risk models based on different dose-response relationships. MATERIAL AND METHODS: RT plans treating the prostate and seminal vesicles with either conformal radiotherapy (CRT), volumetric modulated arc therapy (VMAT) or intensity-modulated proton therapy (IMPT) were created for 10 patients. The risks of radiation-induced cancer were estimated for the bladder and rectum using dose-response models reflecting varying degrees of cell sterilisation: a linear model, a linear-plateau model and a bell-shaped model also accounting for fractionated RT. RESULTS: The choice of risk models was found to rank the plans quite differently, with the CRT plans having the lowest SC risk using the bell-shaped model, while resulting in the highest risk applying the linear model. Considering all dose-response scenarios, median relative risks of VMAT versus IMPT were 1.1-1.7 for the bladder and 0.9-1.8 for the rectum. Risks of radiation-induced bladder and rectal cancers were lower from VMAT if exposed at 80 years versus IMPT if exposed at 50 years. CONCLUSIONS: The SC risk estimations for the bladder and rectum revealed no clear relative relationship between the contemporary techniques and CRT, with divergent results depending on choice of model. However, the SC risks for these organs when using IMPT were lower or comparable to VMAT. SC risks could be assessed when considering referral of prostate cancer patients to proton therapy, taking also general patient characteristics, such as age, into account.

Prediction of rectum and bladder morbidity following radiotherapy of prostate cancer based on motion-inclusive dose distributions.

BACKGROUND AND PURPOSE: In radiotherapy (RT) of prostate cancer the key organs at risk (ORs) - the rectum and the bladder - display considerable motion, which may influence the dose/volume parameters predicting for morbidity. In this study we compare motion-inclusive doses to planned doses for the rectum and bladder and explore their associations with prospectively recorded morbidity. MATERIALS AND METHODS: The study included 38 prostate cancer patients treated with hypo-fractionated image-guided intensity-modulated RT that had an average of nine repeat CT scans acquired during treatment. These scans were registered to the respective treatment planning CT (pCT) followed by a new dose calculation from which motion-inclusive dose distributions were derived. The pCT volumes, the treatment course averaged volumes as well as the planned and motion-inclusive doses were associated with acute and late morbidity (morbidity cut-off: ≥ Grade 2). RESULTS: Acute rectal morbidity (observed in 29% of cases) was significantly associated with both smaller treatment course averaged rectal volumes (population median: 75 vs. 94 cm(3)) and the motion-inclusive volume receiving doses close to the prescription dose (2 Gy-equivalent dose of 76 Gy). CONCLUSION: Variation in rectum and bladder volumes leads to deviations between planned and delivered dose/volume parameters that should be accounted for to improve the ability to predict morbidity following RT.