Anorectal function and radiation dose to pelvic floor muscles after primary treatment for anal cancer.

BACKGROUND AND PURPOSE: Chemoradiotherapy is the primary treatment for localized anal cancer (AC). This treatment offers high rates of cure and organ preservation. Radiotherapy can however, result in late persisting anorectal dysfunction, with anal incontinence, urge and clustering. Correlation of radiation doses to pelvic substructures and functional outcome is not well described in AC. We correlated patient reported anorectal function to radiation doses to sphincters and pelvic floor muscles. MATERIALS AND METHODS: Patients treated with (chemo)radiotherapy for AC were asked to fill out LARS (lower anterior resection syndrome) questionnaires at follow-up. We compared patients with no LARS (score 0-19) and patients with major LARS (30-42) as well as individual LARS questions to specific radiation doses to sphincters, levators and puborectal muscles. RESULTS: Thirty-six patients were included, 18 with no LARS and 18 with major LARS. Gender, age, TNM stage, PTV, chemotherapy, time to LARS score (mean 660 and 749 days) were comparable between the two groups. LARS symptoms, occurring at least once per week, were reported between 25-55.7%, and poorer LARS outcome was associated to worse quality of life. Dose to sphincter complex (Dmean, V50Gy and D90%) differed significantly between patients with no and major LARS (p = 0.048, 0.035 and 0.02 respectively). Further, D90% to the sphincter complex was significantly higher in patients who had accidental leakage of stool, (p = 0.044). CONCLUSION: Patients treated with (chemo)radiotherapy for AC show high frequency of patient reported anorectal dysfunction. Specific doses to the sphincters could become a useful predictor of anal incontinence and major LARS and incorporated into future radiotherapy planning studies.

Pelvic insufficiency fractures, dose volume parameters and plan optimization after radiotherapy for rectal cancer.

Pelvic insufficiency fractures (PIF) is a known but under-acknowledged late effect of pelvic radiotherapy. In rectal cancer, studies describing incidence of PIF and relation to dose volume relationships are lacking. The aim of this study was (i) to analyse dose volume histograms (DVH) from pelvic bones in patients with and without PIF, and (ii) to determine bone sparing capacity of 2 and 3 arc volumetric arc therapy (VMAT), intensity modulated radiotherapy (IMRT) and proton beam therapy (PBT), in rectal cancer patients treated with chemoradiotherapy (CRT). MATERIAL AND METHODS: Patients treated with CRT for primary rectal cancer underwent a 3-year pelvic MRI for identification of PIFs. Bone structures were retrospectively delineated, and DVHs were re-calculated. Comparative planning was done with 2 (original) and 3 arc VMAT, fixed field IMRT and PBT plans. RESULTS: 27 patients (18 men, mean age 64 years) were included and PIFs were identified in 9 (33%), most (n = 6) had multiple fracture sites. In general, patients with PIFs received higher doses to pelvic bones, and V30 Gy to the sacroiliac joint was non-significantly higher in patients with PIF 68.5% (60.1-69.3 IQR) vs. 56% (54.1-66.6 IQR), p = 0.064. Comparative planning showed that especially 3 arc VMAT and proton beam therapy could be optimized for bone. CONCLUSIONS: Patients, treated with VMAT based CRT for rectal cancer, have high rates of PIFs after 3 years. Patients with PIFs tended to have received higher doses to sacroiliac joints. Comparative planning demonstrated most pronounced bone sparing capacity of 3 arc VMAT and with PBT having the potential to further lower doses. These results should be validated in larger and preferably prospective cohorts.

Robust dose planning objectives for mesorectal radiotherapy of early stage rectal cancer - A multicentre dose planning study.

BACKGROUND AND PURPOSE: Organ preservation strategies are increasingly being explored for early rectal cancer. This requires revision of target volumes according to disease stage, as well as new guidelines for treatment planning. We conducted an international, multicentre dose planning study to develop robust planning objectives for modern radiotherapy of a novel mesorectal-only target volume, as implemented in the STAR-TReC trial (NCT02945566). MATERIALS AND METHODS: The published literature was used to establish relevant dose levels for organ at risk (OAR) plan optimisation. Ten representative patients with early rectal cancer were identified. Treatment scans had mesorectal target volumes as well as bowel cavity, bladder and femoral heads outlined, and were circulated amongst the three participating institutions. Each institution produced plans for short course (SCRT, 5 × 5 Gy) and long course (LCRT, 25 × 2 Gy) treatment, using volumetric modulated arc therapy on different dose planning systems. Optimisation objectives for OARs were established by determining dose metric objectives achievable for ≥90% of plans. RESULTS: Sixty plans, all fulfilling target coverage criteria, were produced. The planning results and literature review suggested optimisation objectives for SCRT: V 10Gy < 180 cm3, V 18Gy < 110 cm3, V 23Gy < 85 cm3 for bowel cavity; V 21Gy < 15% and V 25Gy < 5% for bladder; and V 12.5Gy < 11% for femoral heads. Corresponding objectives for LCRT: V 20Gy < 180 cm3, V 30Gy < 130 cm3, V 45Gy < 90 cm3 for bowel cavity; V 35Gy < 22% and V 50Gy < 7% for bladder; and V 25Gy < 15% for femoral heads. Constraints were validated across all three institutions. CONCLUSION: We utilized a multicentre planning study approach to develop robust planning objectives for mesorectal radiotherapy for early rectal cancer.