A method to estimate composite doses for organs at risk in prostate cancer patients treated with EBRT in combination with HDR BT

Methodology of dose calculation for external beam radiation combined with high dose rate brachytherapy in the era of 3-dimensional treatment planning system

Intracavitary application of brachytherapy (BT) sources followed by external beam radiation is essential for the local treatment of carcinoma of the cervix, postate, and nasopharynx. Dose distribution of external beam radiation plus BT can be challenging for the planning system because of their dose calculation by 2 different treatment planning system (TPS). The aims of this study were to introduce a novel iterative method of dose calculation preformed in the Pinnacle plan and evaluate a combined dose distribution for external beam radiation and BT.Because it is often the goal of the planner to produce plan with uniform dose throughout the target volume and normal tissue, we present an Iridium-192 calculation program using American Association of Physicists in Medicine Task Group 43 formula and export it to other commercialized TPS though the combined dose distribution of external beam radiation and BT can be shown. To illustrate such an improved procedure, we present the treatment plans of 2 patients treated with external beam radiation plus BT.Dose distribution of the single BT source were calculated with the Plato post loading TPS and the program model, and the results of 2 methods were similar. A nasopharyngeal case and a cervical case were shown in Pinnacle with this program. The total dose distribution of BT combined with EBRT was showed in compute tomography images. And the corresponding dose volume histogram figures could be displayed correctly in Pinnacle TPS.We demonstrated a novel iterative method of dose calculation preformed in the Pinnacle plan to produce a combined dose distribution for external beam radiation and BT. We used it to evaluate the dose of target volume and normal tissues in the treatment of external beam radiation plus BT.

Pudendal nerve injury impairs anorectal function and health related quality of life measures ≥2 years after 3D conformal radiotherapy for prostate cancer

PURPOSE

To compare GI symptoms, measures of generic and disease specific health related quality of life (HRQoL), anorectal and pudendal nerve function and anal sphincter morphology between (i) patients ≥2 years after 3D conformal radiotherapy (3D-CRT)±high dose rate (HDR) brachytherapy for carcinoma of the prostate and aged matched patients before radiotherapy and (ii) symptomatic and asymptomatic patients ≥2 years after 3D-CRT ± HDR brachytherapy.

MATERIAL AND METHODS

Methodology included: (i) modified LENT-SOMA scales for GI symptoms, (ii) EORTC QLQ-C30 and EORTC QLQ-PR25 questionnaires for generic and disease specific HRQoL, (iii) anorectal manometry and terminal motor latency for anorectal and pudendal nerve function and (iv) endorectal ultrasound for anal sphincter morphology. GI symptoms, parameters of HRQoL, anorectal and pudendal nerve function and anal sphincter morphology were compared using Mann-Whitney's U, unpaired t and χ² tests.

RESULTS

Impairment of HRQoL bowel symptoms in the patients ≥2 years after 3D-CRT ± HDR brachytherapy was associated with worse anorectal motor and sensory function, internal and external anal sphincter morphology and 5× greater prevalence of pudendal nerve dysfunction compared with age matched patients before radiotherapy. Symptomatic patients had worse (i) HRQoL measures including global quality of life and bowel and urinary symptom scores, (ii) rectal bleeding, fecal urgency and incontinence scores and (iii) a 2× higher prevalence of pudendal nerve dysfunction compared with asymptomatic patients. Rectal and anal (i) V 40 Gy >65%, (ii) Dmax >60 Gy, (iii) pudendal nerve Dmax >60 Gy and (iv) Anal V 60 Gy >40% were associated with a greater prevalence of pudendal nerve dysfunction.

CONCLUSIONS

3D-CRT ± HDR brachytherapy for prostate carcinoma, impairs late functional measures including HRQoL, anorectal and pudendal nerve function. Rectal, anal and pudendal nerve radiation dose constraints are proposed for reducing the prevalence of pudendal nerve dysfunction.

Urinary bladder dose-response relationships for patient-reported genitourinary morbidity domains following prostate cancer radiotherapy

BACKGROUND AND PURPOSE

Radiotherapy (RT) induced genitourinary (GU) morbidity is typically assessed by physicians as single symptoms or aggregated scores including symptoms from various domains. Here we apply a method to group patient-reported GU symptoms after RT for localized prostate cancer based on their interplay, and study how these relate to urinary bladder dose.

MATERIALS AND METHODS

Data were taken from two Scandinavian studies (N=207/276) including men treated with external-beam RT (EBRT) to 78/70Gy (2Gy/fraction; median time-to-follow-up: 3.6-6.4y). Within and across cohorts, bladder dose-volume parameters were tested as predictors for GU symptom domains identified from two study-specific questionnaires (35 questions on frequency, incontinence, obstruction, pain, urgency, and sensory symptoms) using univariate and multivariate logistic regression analysis (MVA) with 10-fold cross-validation. Performance was evaluated using Area Under the Receiver Operating Characteristic Curve (Az).

RESULTS

For the identified Incontinence (2-5 symptoms), Obstruction (3-5 symptoms), and Urgency (2-7 symptoms) domains, MVA demonstrated that bladder doses close to the prescription doses were the strongest predictors for Obstruction (Az: 0.53-0.57) and Urgency (Az: 0.60). For Obstruction, performance increased for the across cohort analysis (Az: 0.61-0.64).

CONCLUSIONS

Our identified patient-reported GU symptom domains suggest that high urinary bladder doses, and increased focus on both obstruction and urgency is likely to further add to the understanding of GU tract RT responses.