Dose planning objectives in anal canal cancer IMRT: the TROG ANROTAT experience

Patterns of the use of advanced radiation therapy techniques for the management of bone metastases and the associated factors in Victoria

INTRODUCTION

To describe the pattern of the use of advanced radiation therapy (RT) techniques, including intensity-modulated RT (IMRT), volumetric modulated arc therapy (VMAT), and stereotactic body RT (SBRT) for the management of bone metastases (BM), and the associated factors in Victoria.

METHODS

We used a population-based cohort of patients from the state-wide Victorian Radiotherapy Minimum Data Set (VRMDS) who received RT for BM between 2012 and 2017. The primary outcome was proportion of RT courses using advanced RT techniques. The Cochran-Armitage test for trend was used to evaluate temporal trend in advanced RT use. Multinomial logistic regression was used to identify factors associated with advanced RT use.

RESULTS

A total of 18,158 courses of RT were delivered to 10,956 patients-16,626 (91.6%) courses were 3D conformal RT, 857 (4.7%) IMRT/VMAT and 675 (3.7%) SBRT. There was a sharp increase in IMRT/VMAT use from <1% in 2012-2015, to 10.1% in 2016 and 16.3% in 2017 (P-trend < 0.001). Increase in SBRT use was more gradual, from 1.2% in 2012 to 4.8% in 2016 and 5.5% in 2017 for SBRT (P-trend<0.001). In multivariate analyses, year of RT was the strongest predictor of IMRT/VMAT use (OR = 41; 95%CI = 25-67; P < 0.001, comparing 2012-2013 and 2016-2017). Primary tumour type (prostate cancer) was the strongest predictor of SBRT use (OR = 6.07; 95% CI = 4.19-8.80; P < 0.001).

CONCLUSION

Overall, there was increasing trend in the use of advanced RT techniques for BM in Victoria, with a distinct pattern for IMRT/VMAT compared with SBRT - SBRT uptake was more gradual while IMRT/VMAT uptake was abrupt, occurring contemporaneously with Medicare Benefit Scheme funding changes in 2016.

A first radiotherapy application of functional bulboclitoris anatomy, a novel female sexual organ-at-risk, and organ-sparing feasibility study

OBJECTIVE

The bulboclitoris (clitoris and vestibular bulbs) is the primary organ responsible for female sexual arousal and orgasm. Effects of radiotherapy on the bulboclitoris are unknown, as its structure/function has yet to be described in radiotherapy, and it overlaps only partially with the external genitalia structure. Our aim was to: describe bulboclitoris structure, function and delineation; compare volume of and dose delivered to the bulboclitoris vs external genitalia; and, compare bulboclitoris-sparing IMRT (BCS-IMRT) to standard IMRT (S-IMRT) to determine reoptimization feasibility.

METHODS

Our expert team (anatomist, pelvic radiologist, radiation oncologist) reviewed bulboclitoris anatomy and developed contouring guidance for radiotherapy. 20 female patients with anal cancer treated with chemoradiation were analyzed. Sexual organs at risk (OARs) included the external genitalia and the bulboclitoris. Volumes, dice similarity coefficients (DSCs) and dose received using S-IMRT were compared. Plans were reoptimized using BCS-IMRT. Dose-volume histograms (DVHs) for PTVs and all OARs were compared for BCS-IMRT vs S-IMRT.

RESULTS

Bulboclitoris structure, function and delineation are described herein. The bulboclitoris occupies 20cc (IQR:12-24), largely distinct from the external genitalia (DSC <0.05). BCS-IMRT was superior to S-IMRT in reducing the dose to the bulboclitoris, with the greatest reductions in V30 and V40, with no significant changes in dose to other OARs or PTV 1/V95.

CONCLUSION

The bulboclitoris can be contoured on planning imaging, largely distinct from the external genitalia. Compared with S-IMRT, BCS-IMRT dramatically reduced dose to the bulboclitoris in anal cancer planning. BCS-IMRT might safely reduce sexual toxicity compared with standard approaches.

ADVANCES IN KNOWLEDGE

The structure and function of the bulboclitoris, the critical primary organ responsible for female sexual arousal and orgasm, has yet to be described in the radiotherapy literature. Structure, function and delineation of the bulboclitoris are detailed, delineation and bulboclitoris-sparing IMRT were feasible, and sparing reduces the dose to the bulboclitoris nearly in half in female patients receiving IMRT for anal cancer, warranting further clinical study.

Dosimetric comparison of helical tomotherapy and VMAT for anal cancer: A single institutional experience

To compare the dosimetric results of helical tomotherapy (HT) and volumetric arc therapy (VMAT) in the treatment of anal cancer. Plans were created for 20 (n = 20) patients treated for anal cancer using HT and 2 arc VMAT. Dosimetric comparison was assessed for doses to targets and organs at risk (small bowel, bladder, external genitalia, and femoral heads). Delivery time and dosimetric verification results were also compared. HT showed a higher V95% for both primary and nodal targets (V95% increase by 0.5% to 1.3%; p = ≤0.05). No differences were seen in V105%, V107%, or V110 % between techniques. HT provided better sparing of the small bowel for dose levels V30, V35, and V40 (p = 0.005, 0.001, and 0.030), but was similar at higher doses. Similarly HT provided better bladder dose at V35 only (p = 0.020). Doses to femoral heads and genitalia were similar. Delivery time was higher for the HT plans (4.58 ± 1.1 min) than VMAT (3.13 ± 0.2 minutes) (p = 0.011). Dose verification results were 99.5 ± 0.9% and 100 ± 0% (HT, n = 6) vs 95.0 ± 3.1% and 99.2 ± 0.8% (VMAT, n = 20) for global gamma criteria 3%/3 mm and 4%/4 mm, respectively. Both HT and VMAT produced high quality plans that frequently met most of the dose objectives apart from genitalia V20, V40, bladder V35, and V50. Although absolute dose differences were small, the PTV V95%, small bowel V30, V35, and V40 and bladder V35 were statistically better in the HT plans. VMAT provided a shorter delivery time by 1.45 minutes; however, our HT plans were more likely to pass tighter plan dose verification criteria than VMAT.

The impact of contour variation on tumour control probability in anal cancer

BACKGROUND

While intensity modulated radiotherapy (IMRT) has been widely adopted for the treatment of anal cancer (AC), the added contour complexity poses potential risks. This study investigates the impact of contour variation on tumour control probability (TCP) when using IMRT for AC.

METHODS

Nine Australian centres contoured a single computed tomography dataset of a patient with AC. The same optimised template-based IMRT planning protocol was applied to each contour set to generate nine representative treatment plans and their corresponding dose volume histograms. A geometric analysis was performed on all contours. The TCP was calculated for each plan using the linear quadratic and logitEUD model.

RESULTS

The median concordance index (CI) for the bladder, head and neck of femur, bone marrow, small bowel and external genitalia was 0.94, 0.88, 0.84, 0.65 and 0.65, respectively. The median CI for the involved nodal, primary tumour and elective clinical target volumes were 0.85, 0.77 and 0.71, respectively. Across the nine plans, the TCP was not significantly different. Variation in TCP between plans increased as tumour cell load increased or radiation dose decreased.

CONCLUSIONS

When using IMRT for AC, contour variations generated from a common protocol within the limits of minor deviations do not appear to have a significant impact on TCP. Contouring variations may be more critical with increasing tumour cell load or reducing radiotherapy dose.

Adjuvant external beam radiotherapy after therapeutic groin lymphadenectomy for patients with melanoma: a dosimetric comparison of three-dimensional conformal and intensity-modulated radiotherapy techniques

Radiotherapy after lymph node dissection is recommended in high-risk melanoma cases. The aim of this study is to assess whether intensity-modulated radiotherapy (IMRT) offers advantages over three-dimensional conformal radiotherapy (3DCRT) in the groin nodal basin. Fifteen consecutively treated patients (5 3DCRT and 10 IMRT) were selected. Optimized theoretical plans using the other modality were created - enabling direct comparisons of 3DCRT and IMRT. Target volume and organs at risk constraints were assessed as achieved or as having minor (≤5%) or major (>5%) deviations. The Wilcoxon signed-rank test was used to compare the dose received from each patient plan (3DCRT vs. IMRT), whereas the Mann-Whitney U-test was used to compare clinical plans with theoretical plans. Fisher's exact test was used to compare categorical data. Target coverage was achievable in most patients (major deviations - 1 IMRT and 3 3DCRT). Conformity index improved with IMRT - median 0.65, range 0.48-0.81, versus median 0.44, range 0.29-0.60 for 3DCRT; P value less than 0.001. All 3DCRT plans had major deviations for femoral head/neck constraints. Twelve and 13 IMRT plans achieved the high (V42<5%) and low (V36<35%) constraints; P value less than 0.001. IMRT delivered statistically significant lower doses to small bowel volumes up to 40 ml. There were no differences in beam numbers used nor dosimetric endpoints measured when clinical plans were compared with theoretical plans. IMRT appears to allow superior conformity of dose to the target volume while relatively sparing the adjacent the bowel and femoral head/neck. This may reduce toxicity while maintaining control rates.