Dosimetric feasibility of moderately hypofractionated/dose escalated radiation therapy for localised prostate cancer with intensity-modulated proton beam therapy using simultaneous integrated boost (SIB-IMPT) and impact of hydrogel prostate-rectum spacer

Purpose

To examine the dosimetric feasibility of hypofractionated/dose escalated radiation therapy in patients with localized prostate carcinoma using simultaneous integrated boost intensity-modulated proton beam therapy (SIB-IMPT) in absence or presence of prostate-rectum spacer.

Methods

IMPT technique was implemented in 23 patients with intermediate- and high-risk prostate cancer treated at West German Proton Therapy Centre from March 2016 till June 2018, using SIB technique prescribing 60 GyRBE and 72 GyRBE in 30 fractions to PTV1 (prostate and seminal vesicle) and PTV2 boost (prostate and proximal seminal vesicle), respectively. In 15 patients, a transperineal injection of hydrogel was applied prior to radiotherapy to increase the distance between prostate and rectum. Planning and all treatments were performed with a 120 ml fluid-filled endorectal balloon customised daily for each patient. For each patient, 2 lateral IMPT beams were implemented taking a field-specific range uncertainty (RU) into account. Dose volume histograms (DVH) were analyzed for PTV2, PTV2 with range uncertainty margin (PTV2RU), rectum, bladder, right/left femoral heads, and penile bulb. For late rectal toxicities, the normal tissue complication probabilities (NTCP) were calculated using different biological models. A DVH- and NTCP-based dosimetric comparison was carried out between non-spacer and spacer groups.

Results

For the 23 patients, high-quality plans could be achieved for target volume and for other organs at risk (OARs). For PTV2, the V_107% was 0% and the D_max did not exceed 106.2% of the prescribed dose. The volume PTV2RU covered by 95% of the dose ranged from 96.16 to 99.95%. The conformality index for PTV2RU was 1.12 ± 0.057 and the homogeneity index (HI) was 1.04 ± 0.014. Rectum D_max and rectal volume receiving 73–50 Gy could be further reduced for the spacer-group. Significant reductions in mean and median rectal NTCPs (stenosis/necrosis, late rectal bleeding ≥ 2, and late rectal toxicities ≥ 3) were predicted for the spacer group in comparison to the non-spacer group.

Conclusion

Hypofractionated/dose escalated radiotherapy with SIB-IMPT is dosimetrically feasible. Further reduction of the rectal volumes receiving high and medium dose levels (73–50 Gy) and rectal NTCP could be achieved through injection of spacers between rectum and prostate.

Radiation toxicity in prostate cancer patients

Prostate cancer (PC) is the most frequent male tumor, accounting for about one-third of all cancers in men. Since survival is often favorable regardless of therapy, treatment decisions may depend on therapy-specific health outcomes. The majority of men initially diagnosed with localized PC ultimately die with, rather than of, their disease. As a result, men who are diagnosed will live many years with the treatment's sequelae. The major therapeutic strategies include radical prostatectomy or external beam radiotherapy. Radiotherapy is one of the curative treatment options. The tumor dose-response relationship has been studied and is widely accepted. The unsatisfactory local control with doses < 70 Gy led to dose escalation using highly precise radiotherapy techniques - three-dimensional conformal radiotherapy and intensity-modulated radiotherapy enabling the delivery of high radiation doses up to 74 - 78 Gy. Bowel, rectal and urinary toxicities are the principal limiting factors in delivering a high dose. Acute symptoms include a change in bowel habits, urgency, and fecal incontinence. The most commonly reported late toxicities were chronic diarrhea, proctitis, or rectal bleeding. Several factors have been associated with increased gastrointestinal toxicity such as larger bowel volume receiving high doses, the patient's age, diabetes, and concomitant use of androgen deprivation therapy. Bladder damage resulting from acute radiation toxicity is manifested as radiation cystitis (frequent urination and dysuric disorders). Smoking, previous abdominopelvic surgeries and the use of diuretics significantly affect the occurrence of acute genitourinary toxicity grade ≥ 2. Risk factors for the development of late genitourinary complications are higher radiation dose, previous urinary problems, transurethral interventions, and acute genitourinary complications. It is essential to strike a balance between the therapeutic benefits and radiotherapy side effects. Severe late complications significantly reduce the quality of life (QOL) of PC survivors. Early detection and proper evaluation of complications are especially important in increasing the patient's QOL.

Systematic Review of the Relationship between Acute and Late Gastrointestinal Toxicity after Radiotherapy for Prostate Cancer

A small but meaningful percentage of men who are treated with external beam radiation therapy for prostate cancer will develop late gastrointestinal toxicity. While numerous strategies to prevent gastrointestinal injury have been studied, clinical trials concentrating on late toxicity have been difficult to carry out. Identification of subjects at high risk for late gastrointestinal injury could allow toxicity prevention trials to be performed using reasonable sample sizes. Acute radiation therapy toxicity has been shown to predict late toxicity in several organ systems. Late toxicities may occur as a consequential effect of acute injury. In this systematic review of published reports, we found that late gastrointestinal toxicity following prostate radiotherapy seems to be statistically and potentially causally related to acute gastrointestinal morbidity as a consequential effect. We submit that acute gastrointestinal toxicity may be used to identify at-risk patients who may benefit from additional attention for medical interventions and close follow-up to prevent late toxicity. Acute gastrointestinal toxicity could also be explored as a surrogate endpoint for late effects in prospective trials.

Moderate Hypofractionated Protracted Radiation Therapy and Dose Escalation for Prostate Cancer: Do Dose and Overall Treatment Time Matter?

PURPOSE

This was a retrospective study of 2 sequential dose escalation regimens of twice-weekly 4 Gy/fractions hypofractionated intensity modulated radiation therapy (IMRT): 56 Gy and 60 Gy delivered within a protracted overall treatment time (OTT) of 6.5 and 7 weeks, respectively.

METHODS AND MATERIALS

163 prostate cancer patients with cT1c-T3a disease and nodal involvement risk ≤20% (Roach index) were treated twice weekly to the prostate ± seminal vesicles with 2 sequential dose-escalated IMRT schedules: 56 Gy (14 × 4 Gy, n=81) from 2003 to 2007 and 60 Gy (15 × 4 Gy, n=82) from 2006 to 2010. Patient repositioning was made with bone matching on portal images. Gastrointestinal (GI) and genitourinary (GU) toxicities were scored according to the Common Terminology Criteria for Adverse Events version 3.0 grading scale.

RESULTS

There were no significant differences regarding the acute GU and GI toxicities in the 2 dose groups. The median follow-up times were 80.2 months (range, 4.5-121 months) and 56.5 months (range, 1.4-91.2 months) for patients treated to 56 and 60 Gy, respectively. The 5-year grade ≥2 late GU toxicity-free survivals with 56 Gy and 60 Gy were 96 ± 2.3% and 78.2 ± 5.1% (P=.001), respectively. The 5-year grade ≥2 late GI toxicity-free survivals with 56 Gy and 60 Gy were 98.6 ± 1.3% and 85.1 ± 4.5% (P=.005), respectively. Patients treated with 56 Gy showed a 5-year biochemical progression-free survival (bPFS) of 80.8 ± 4.7%, worse than patients treated with 60 Gy (93.2 ± 3.9%, P=.007). A trend for a better 5-year distant metastasis-free survival was observed among patients treated in the high-dose group (95.3 ± 2.7% vs 100%, P=.073, respectively). On multivariate analysis, only the 60-Gy group predicted for a better bPFS (P=.016, hazard ratio = 4.58).

CONCLUSIONS

A single 4-Gy additional fraction in patients treated with a hypofractionated protracted IMRT schedule of 14 × 4 Gy resulted in a similar and minimal acute toxicity, in worse moderate to severe urinary and GI late effects, but a significantly better biochemical control.

Transformation of physical DVHs to radiobiologically equivalent ones in hypofractionated radiotherapy analyzing dosimetric and clinical parameters: a practical approach for routine clinical practice in radiation oncology

Purpose. The purpose of this study was to transform DVHs from physical to radiobiological ones as well as to evaluate their reliability by correlations of dosimetric and clinical parameters for 50 patients with prostate cancer and 50 patients with breast cancer, who were submitted to Hypofractionated Radiotherapy. Methods and Materials. To achieve this transformation, we used both the linear-quadratic model (LQ model) and the Niemierko model. The outcome of radiobiological DVHs was correlated with acute toxicity score according to EORTC/RTOG criteria. Results. Concerning the prostate radiotherapy, there was a significant correlation between RTOG acute rectal toxicity and D₅₀ (P < 0.001) and V₆₀ (P = 0.001) dosimetric parameters, calculated for α/β = 10 Gy. Moreover, concerning the breast radiotherapy there was a significant correlation between RTOG skin toxicity and V_≥60 dosimetric parameter, calculated for both α/β = 2.3 Gy (P < 0.001) and α/β = 10 Gy (P < 0.001). The new tool seems reliable and user-friendly. Conclusions. Our proposed model seems user-friendly. Its reliability in terms of agreement with the presented acute radiation induced toxicity was satisfactory. However, more patients are needed to extract safe conclusions.