Early-stage Favourable Anal Cancer: A Retrospective Analysis of Clinical Outcomes of a Moderately Low Dose Elective Nodal Intensity-modulated Radiotherapy Schedule

Effective Organs-at-Risk Dose Sparing in Volumetric Modulated Arc Therapy Using a Half-Beam Technique in Whole Pelvic Irradiation

BACKGROUND

Although there are some controversies regarding whole pelvic radiation therapy (WPRT) due to its gastrointestinal and hematologic toxicities, it is considered for patients with gynecological, rectal, and prostate cancer. To effectively spare organs-at-risk (OAR) doses using multi-leaf collimator (MLC)'s optimal segments, potential dosimetric benefits in volumetric modulated arc therapy (VMAT) using a half-beam technique (HF) were investigated for WPRT.

METHODS

While the size of a fully opened field (FF) was decided to entirely include a planning target volume in all beam's eye view across arc angles, the HF was designed to use half the FF from the isocenter for dose optimization. The left or the right half of the FF was alternatively opened in VMAT-HF using a pair of arcs rotating clockwise and counterclockwise. Dosimetric benefits of VMAT-HF, presented with dose conformity, homogeneity, and dose-volume parameters in terms of modulation complex score, were compared to VMAT optimized using the FF (VMAT-FF). Consequent normal tissue complication probability (NTCP) by reducing the irradiated volumes was evaluated as well as dose-volume parameters with statistical analysis for OAR. Moreover, beam-on time and MLC position precision were analyzed with log files to assess plan deliverability and clinical applicability of VMAT-HF as compared to VMAT-FF.

RESULTS

While VMAT-HF used 60%-70% less intensity modulation complexity than VMAT-FF, it showed superior dose conformity. The small intestine and colon in VMAT-HF showed a noticeable reduction in the irradiated volumes of up to 35% and 15%, respectively, at an intermediate dose of 20-45 Gy. The small intestine showed statistically significant dose sparing at the volumes that received a dose from 15 to 45 Gy. Such a dose reduction for the small intestine and colon in VMAT-HF presented a significant NTCP reduction from that in VMAT-FF. Without sacrificing the beam delivery efficiency, VMAT-HF achieved effective OAR dose reduction in dose-volume histograms.

CONCLUSIONS

VMAT-HF led to deliver conformal doses with effective gastrointestinal-OAR dose sparing despite using less modulation complexity. The dose of VMAT-HF was delivered with the same beam-on time with VMAT-FF but precise MLC leaf motions. The VMAT-HF potentially can play a valuable role in reducing OAR toxicities associated with WPRT.

Management of locally advanced anal canal carcinoma with intensity-modulated radiotherapy and concurrent chemotherapy

The best curative option for locally advanced (stages II-III) squamous-cell carcinomas of the anal canal (SCCAC) is concurrent chemo-radiotherapy delivering 36-45 Gy to the prophylactic planning target volume with an additional boost of 14-20 Gy to the gross tumor volume with or without a gap-period between these two sequences. Although 3-dimensional conformal radiotherapy led to suboptimal tumor coverage because of field junctions, this modality remains a standard of care. Recently, intensity-modulated radiotherapy (IMRT) techniques improved tumor coverage while decreasing doses delivered to organs at risk. Sparing healthy tissues results in fewer severe acute toxicities. Consequently, IMRT could potentially avoid a gap-period that may increase the risk of local failure. Furthermore, these modalities reduce severe late toxicities of the gastrointestinal tract as well as better functional conservation of anorectal sphincter. This report aims to critically review contemporary trends in the management of locally advanced SCCAC using IMRT and concurrent chemotherapy.

Modern intensity-modulated radiotherapy with image guidance allows low toxicity rates and good local control in chemoradiotherapy for anal cancer patients

PURPOSE

To report outcomes of a population of anal cancer patients treated with modern intensity-modulated radiotherapy and daily image-guided radiotherapy techniques.

METHODS

We analyzed data of 155 patients consecutively treated with intensity-modulated radiotherapy +/- chemotherapy in three radiotherapy departments. One hundred twenty-two patients presented a stage II-IIIA disease. Chemotherapy was administered in 138 patients, mainly using mitomycin C and 5-fluorouracil (n = 81). All patients received 36 Gy (1.8 Gy/fraction) on the pelvic and inguinal nodes, on the rectum, on the mesorectum and on the anal canal, and a sequential boost up to a total dose of 59.4 Gy (1.8 Gy/fraction) on the anal canal and on the nodal gross tumor volumes.

RESULTS

Median follow-up was 38 months (interquartile range 12-51). Toxicity data were available for 143 patients: 22% of them presented a G3+ acute toxicity, mainly as moist desquamation (n = 25 patients) or diarrhea (n = 10). Three patients presented a late grade 3 gastrointestinal toxicity (anal incontinence). No grade 4 acute or late toxicity was recorded. Patients treated with fixed-gantry IMRT delivered with a sliding window technique presented a significantly higher risk of acute grade 3 (or more) toxicity compared to those treated with VMAT or helical tomotherapy (38.5 vs 15.3%, p = 0.049). Actuarial 4-year local control rate was 82% (95% CI 76-91%).

CONCLUSIONS

Modern intensity-modulated radiotherapy with daily image-guided radiotherapy is effective and safe in treating anal cancer patients and should be considered the standard of care in this clinical setting.