Dosimetric effects of prone immobilization devices on skin in intensity-modulated radiation therapy for gynecologic cancer: a retrospective study

doi:10.21203/rs.3.rs-3771109/v1

Objective

The dose perturbation effect of immobilization devices is often overlooked in intensity-modulated radiation therapy (IMRT) for gynecologic cancer. This retrospective study assessed the dosimetric effects of a prone immobilization device combined with a belly board (PIDBB) on the skin.

Methods

We recruited 63 women with gynecologic cancer undergoing postoperative IMRT at our institute. A 0.3 cm thick skin contour and body contours with or without PIDBB system were outlined for each patient. Dose calculations were performed for the two sets of contours using the same plan, named Plan₋ and Plan₊, respectively. The accuracy of calculated doses was verified by gafchromic EBT3 film and anthropomorphic phantom.

Results

The V_{40 Gy}, V_{30 Gy}, V_{20 Gy}, V_{15 Gy} and D_mean of skin increased by 56.94%, 65.48%, 53.12%, 41.91%, and 1.91%, respectively. Even after excluding the effect of prescription dose coverage, the V_{40 Gy}, V_{30 Gy}, V_{20 Gy}, V_{15 Gy} and D_mean of skin still increased by 46.90%, 92.07%, 72.81%, 52.25%, and 18.06%, respectively. No significant differences were observed in doses to other organs at risk. The EBT3 measurements showed that the skin dose map to the anthropomorphic phantom was 23.66% higher than that calculated by the treatment planning system without the PIDBB system.

Conclusions

While the PIDBB system effectively reduces the low dose to small intestine, it also induces radiation attenuation, leading to a sharp increase in skin dose, particularly in patients receiving radiation in the groin and perineum area. Therefore, immobilization devices should be included in the external contour to account for dose attenuation and the increment in skin dose.

Trial registration:

This study does not report on interventions in human health care.

gynecologic cancer

intensity-modulated radiation therapy

prone position

prone immobilization devices

skin dose

skin toxicity

PIDBB system

Gynecologic cancer is a prevalent form of cancer among women, ranking fourth in terms of incidence and mortality among female malignant tumors worldwide in 2020 [1]. In China, gynecologic cancer holds the third position among female malignant tumors, with an incidence rate of 23.57 per million population in 2016 [2]. Radiotherapy is a crucial treatment method for gynecologic cancer; however, it can cause damage to normal organs and tissues within the radiation field [3]. Therefore, minimizing the radiation dose to normal tissues is a key consideration in external radiation therapy plans for gynecologic cancer. Several studies have indicated that using the prone position during pelvic tumor radiotherapy can effectively reduce the irradiation volume of the small bowel compared to the supine position [4–5]. However, the prone position requires additional immobilization devices for positioning, and the radiation beam needs to pass through these devices, leading to increased dose attenuation and scattering [6–7].

Previous research has demonstrated that the use of immobilization devices in radiotherapy may result in reduced tumor dose, increased skin dose, and altered dose distribution [8–10]. Nevertheless, no study has yet evaluated the dosimetric effects of prone immobilization devices combined with a belly board (PIDBB) on skin doses in intensity-modulated radiation therapy (IMRT) for gynecologic cancer. Therefore, this study aims to simulate the dosimetric effects of a novel PIDBB on the target area and organs at risk (OARs) using a commercial treatment planning system (TPS). Dose-volumetric parameters and dose difference distribution maps will be calculated and compared to analyze the dosimetric effects of the PIDBB. Additionally, EBT3 films will be calibrated and utilized to measure the skin dose of the hypogastrium when the immobilization devices are employed.

Patient data and setup

This retrospective study included a total of 63 women with cervical or endometrial cancer who underwent adjuvant radiotherapy at the third Affiliated Hospital of Sun Yat-sen University between August 2020 and November 2022. The study has been approved by Medical Ethics Committee of the Third Affiliated Hospital of Sun Yat-sen University (Prot. Number II2023-149-01). The patients' ages ranged from 27 to 74 years, with a median age of 52 years. All patients had a confirmed pathological diagnosis and were eligible for radiotherapy without any contraindications. For immobilization, all patients were positioned in the prone position using the PIDBB system, with their hands raised upward to grip the handle and their chest and abdomen supported by a flat frame. The PIDBB system used in this study (Klarity Inc, Guangzhou, China) consisted of a carbon fiber floor, engineering foam support pad, negative pressure vacuum bag, and thermoplastic film (Fig. 1a). The effectiveness and reproducibility of the PIDBB system were previously validated in our institution [11–12]. Before each fraction of radiotherapy, bladder urine volume measurements were performed for all pelvic patients to ensure accurate positioning. Throughout the simulation and treatment process, all patients maintained the same position. CT images of each patient were acquired using a large aperture CT simulation device (SOMATOM Definition, Siemens Healthiness, Germany, Munich). The scan range extended from the 11th thoracic vertebra to 5 cm below the ischial tuberosity, with a slice thickness of 3mm. The acquired CT images were then transferred to the treatment planning system (Monaco V6.0, Elekta AB, Stockholm, Sweden) via the radiotherapy network for treatment planning (Fig. 1b &1c).

Regions of interest

The gross target volume (GTV) for gynecologic cancer was determined based on gynecological examination and imaging diagnosis. The clinical target volume (CTV) was determined by considering the direct spread and lymph node metastasis pathways specific to cervical or endometrial cancer. The planned target volume (PTV) was obtained by expanding the CTV outward by 5 mm to account for setup errors. The organs at risk (OARs) included the small intestine, colon, rectum, bladder, femoral heads, and skin. The radiation therapy structures were delineated on CT images for all patients by an experienced radiation oncologist, following the guidelines outlined in the National Health Commission of the People's Republic of China Standard Practice for Diagnosis and Treatment of Cervical Cancer (2018 edition), National Health Commission of the People's Republic of China Endometrial Carcinoma Diagnosis and Treatment Specification (2018 edition), and International Commission on Radiation Units and Measurements (ICRU) Report 83 [13]. To evaluate the variation in surface dose caused by the immobilization devices, the skin contour was delineated with a thickness of 3 mm below the skin surface for each patient. In this study, two sets of external body contours were created for each patient: one set included only the patient's body without the PIDBB, while the other set included the patient's external body contours along with the PIDBB.

Treatment planning and dose calculation

The purpose of this study was to evaluate the impact of using a patient-specific bolus (PIDBB) on the dose distribution in multi-beam IMRT plans. The plans were designed using 6 MV X-ray beams from a medical linear accelerator (Synergy, Elekta AB, Stockholm, Sweden). Seven evenly distributed coplanar beams (150°, 100°, 50°, 0°, 310°, 260°, 210°) were used for each plan. The optimization of the plans was performed using the Monte Carlo (MC) algorithm combined with dynamic multi-leaf collimator (dMLC) technology. Each field control number was set to 20, and the calculated grid size was 3 mm × 3 mm × 3 mm. The uncertainty of each control point of the MC algorithm was set at 3%. The maximum and minimum doses were planned according to the recommendations of ICRU Report 83, with dose constraints based on the Quantitative Analyses of Normal Tissue Effects in the Clinic (QUANTEC) guidelines.

Two IMRT plans were generated for each patient, one with the PIDBB (Plan₊) and one without (Plan₋). The prescription dose to the planning target volume (PTV) was 50 Gy, delivered in 25 fractions. To evaluate the skin dose, interference from target coverage was eliminated by renormalizing the dose distribution in Plan₋ and Plan₊ to achieve a clinically desired prescribed dose of V_{50 Gy} = 95%. These renormalized plans were recorded as Plan_− n and Plan_+ n, respectively.

Statistical analysis

Dose-volume histograms (DVHs) are commonly used to assess the dose coverage of PTVs and OARs. In this study, several parameters were used to evaluate the dose distribution within the PTVs. These parameters included the mean dose (D_mean), the homogeneity index (HI), and the conformity index (CI). The HI and CI were calculated using the following formulas[14, 15]:

$$HI=\frac{{D}_{2\%}-{D}_{98\%}}{{D}_{50\%}}$$

1

$$CI=\frac{{V}_{RX}}{{V}_{T}}*\frac{{V}_{RX}}{{V}_{RI}}$$

2

In formula (1), D_2%, D_50%, and D_98% represent the doses received by 2%, 50%, and 98% of the volume of ROI, respectively. According to the ICRU Report 83, D_2% represents the near-maximum dose, while D_98% represents the near-minimum dose within the ROI. A smaller HI value, closer to 0, indicates a more uniform dose distribution within the target volume.

In formula (2), V_T represents the volume of the target, V_RX represents the volume of the target covered by the reference isodose curve (which was set at 100% of the prescribed dose in this study), and V_RI represents the total volume within the reference isodose curve. The CI ranges from 0 to 1, with higher CI values indicating better dose conformity to the target volume.

To assess the impact of the immobilization device on the overall treatment plan, the TPS was used to calculate the perturbation effect. This was done by subtracting Plan- from Plan+, and the average of the parameter differences between the two plans was represented as $\stackrel{-}{D}$ by the following formula (3).

$$\stackrel{-}{D}={\sum }_{1}^{63}\left[{Plan}_{-}-{Plan}_{+}\right]/63$$

3

IBM SPSS Statistics (version 22.0, IBM Corp., Armonk, NY, USA) was used to analyze all data. Paired-samples T tests were employed to determine the significance of the observed differences between Plan₊ and Plan₋ as well as between Plan_+ n and Plan_− n. A p-value of less than 0.05 was considered statistically significant for these differences.

Dose verification of the anthropomorphic phantom

An Alderson Radiation Therapy (ART) anthropomorphic phantom (RSD Inc., USA) and gafchromic EBT3 film (ASHLAND Inc., USA) were used to verify the dose distribution of Plan₋ and Plan₊. The ART phantom used in this study is composed of a tissue-equivalent material that closely resembles the scattering and absorption properties of human tissue. The phantom is horizontally divided into slices that are 2.5 cm thick, replicating the anatomy of the abdomen and pelvis (Fig. 2a). EBT3 films, obtained from the same batch (NO. 09131801) with a calibration dose range of 0-4Gy, were used for dose measurements. These films were cut into appropriate sizes and placed between the transverse slices of the phantom. To simulate the actual patient treatment process, the phantom was immobilized using the PIDBB and scanned using a large aperture CT, similar as a real patient. The actual radiotherapy plan was executed using a linear accelerator, and the dose value of the hypogastrium skin (point A, Fig. 2b) was obtained using the EBT3 film in the ART phantom. The irradiated films were then scanned and imported into FilmQA Pro 2016 software (ASHLAND Inc., USA). In the Monaco TPS, a verification plan was created for Plan₋ to obtain the dose value at point A, using the CT images of the ART phantom as a verification phantom. Similarly, dose values mapped from Plan₊ to point A were obtained. The differences between the dose measured on the irradiated EBT3 film and the TPS calculations from Plan + and Plan- were then determined.

Dose verification of patient-specific quality assurance (QA)

Patient-specific verification QA plays a crucial role in identifying any discrepancies between the calculated and delivered radiation doses. The association of physicists in medicine (AAPM) TG-218 report [16] provides universal action limits for such QA, stating that the γ passing rate should be equal to or greater than 90%, with a criterion of 3%/2mm and a 10% dose threshold. For this study, it is necessary to perform verification QA for both Plan₊ and Plan₋ for a total of 63 patients. This is done to assess the accuracy of radiation delivery to these patients and ensure that the treatment plans are being executed as intended.

Doses in the targets and OARs

The dosimetric differences between Plan₊ and Plan₋ are summarized in Table 1. The DVH curves of PTVs and OARs in Plan₊ shift slightly to the left after considering the fixed device, as depicted in Fig. 3a.Statistical analysis of the DVHs for the 63 patients revealed significant reductions in V_{50 Gy} and V_{49 Gy} of the PTVs by 28.67% and 6.59% (t = 15.57 and 13.98, P < 0.05), respectively. The homogeneity index (HI) of the PTVs increased by 42.86% (t = -13.92, P < 0.05). However, there were no statistically significant differences in the mean dose (D_mean) and conformity index (CI) of the PTVs. V_{40 Gy}, V_{30 Gy}, V_{20 Gy}, V_{15 Gy} and D_mean of the skin were significantly increased by 56.94%, 65.48%, 53.12%, 41.91%, and 1.91% (t = -4.08, -11.81, -19.28, -21.43, and − 20.42, P < 0.05), respectively. The V_{50 Gy}, V_{20 Gy}, and D_mean of other OARs showed slight decreases, as shown in Table 1.

The dosimetric differences between Plan_+ n and Plan_− n are presented in Table 2. After renormalizing the prescribed dose to the clinically desired level (V_50Gy = 95%), there were no statistically significant differences in V_{50 Gy}, V_{49 Gy}, D_mean, HI, and CI of the PTVs. However, the V_{40 Gy}, V_{30 Gy}, V_{20 Gy}, V_{15 Gy} and D_mean of the skin were significantly increased by 46.90%, 92.07%, 72.81%, 52.25%, and 18.06% (t = -5.357, -15.183, -24.590, -24.426, -29.359, P < 0.05), respectively. The V_{50 Gy}, V_{20 Gy}, and D_mean of other OARs showed slight increases, as shown in Fig. 3b.

Table 1

Comparison of dosimetric parameters in 63 cases with or without the immobilization devices (x̄ ± s)
Parameter	Plan-	Plan₊	$\stackrel{-}{\varvec{D}}$	t	P value
PTV
V_{50 Gy} (%)	96.50 ± 1.25	68.83 ± 14.37	27.67 ± 14.10	15.57	0.000
V_{49 Gy} (%)	98.61 ± 0.79	92.11 ± 3.83	6.50 ± 3.69	13.98	0.000
D_mean (cGy)	5 110.27 ± 589.27	5 036.32 ± 38.27	73.95 ± 578.70	1.01	0.314
HI	0.14 ± 0.01	0.08 ± 0.04	-0.06 ± 0.00	-13.92	0.000
CI	0.80 ± 0.11	0.63 ± 0.13	0.16 ± 0.17	7.70	0.000
Skin
V_{40 Gy} (%)	0.62 ± 2.86	0.97 ± 2.79	-0.35 ± 0.68	-4.08	0.000
V_{30 Gy} (%)	2.08 ± 4.79	3.43 ± 4.64	-1.36 ± 0.91	-11.81	0.000
V_{20 Gy} (%)	9.94 ± 7.61	15.22 ± 7.07	-5.28 ± 2.17	-19.28	0.018
V_{15 Gy} (%)	23.96 ± 8.51	34.01 ± 9.28	-10.04 ± 3.72	-21.43	0.000
D_mean (cGy)	1042.83 ± 259.16	1186.63 ± 260.79	-143.80 ± 55.89	-20.42	0.000
Small intestine
V_{50 Gy} (%)	4.32 ± 3.28	2.34 ± 2.45	1.97 ± 1.55	10.10	0.000
V_{20 Gy} (%)	45.49 ± 13.03	43.73 ± 12.97	1.76 ± 5.77	2.42	0.000
D_mean (cGy)	1906.76 ± 423.38	1870.35 ± 413.58	36.41 ± 13.40	21.56	0.000
Colon
V_{50 Gy} (%)	8.98 ± 7.02	4.53 ± 5.45	4.45 ± 2.64	13.37	0.000
D_mean (cGy)	2453.28 ± 495.97	2393.76 ± 482.97	59.52 ± 20.87	22.64	0.000
Femoral heads
D_mean (cGy)	2143.31 ± 366.95	2074.18 ± 337.13	69.14 ± 134.18	4.09	0.000
Bladder
V_{50 Gy} (%)	33.89 ± 7.18	16.52 ± 8.82	17.37 ± 7.94	17.36	0.000
D_mean (cGy)	4404.85 ± 207.16	4259.18 ± 201.49	145.67 ± 30.15	38.35	0.000
Rectum
V_{50 Gy} (%)	31.65 ± 11.22	16.87 ± 9.27	14.78 ± 8.65	13.56	0.000
D_mean (cGy)	4 402.31 ± 293.42	4 281.77 ± 286.92	120.54 ± 35.84	26.70	0.000
Note:$\stackrel{-}{D}={\sum }_{1}^{63}\left[\left({Plan}_{-}\right)-\left({Plan}_{+}\right)\right]/63$
Abbreviations: Plan-, plan generated without immobilization device; Plan+, plan calculated from Plan- with immobilization device taken into accounted; PTV, planning target volume; HI, homogeneity index; CI, conformity index.

Table 2

Comparison of dosimetric parameters in 63 cases after renormalized by V_{50 Gy}=95% (x̄ ± s)
Parameter	Plan_− n	Plan_+ n	$\stackrel{-}{\varvec{D}}$	t	P value
PTV
V_{50 Gy} (%)	95.00 ± 0.00	95.00 ± 0.00	∕	∕	∕
V_{49 Gy} (%)	98.25 ± 0.73	98.42 ± 0.52	-0.18 ± 0.51	-2.81	0.007
D_mean (cGy)	5148.22 ± 29.82	5165.41 ± 25.47	-17.19 ± 10.21	-13.37	0.006
HI	0.02 ± 0.01	0.02 ± 0.01	0.00 ± 0.01	2.83	0.000
CI	0.82 ± 0.04	0.80 ± 0.04	0.02 ± 0.02	7.52	0.000
Skin
V_{40 Gy} (%)	0.60 ± 2.85	1.13 ± 3.04	-0.53 ± 0.78	-5.36	0.000
V_{30 Gy} (%)	2.02 ± 4.78	3.88 ± 4.94	-1.86 ± 0.97	-15.18	0.000
V_{20 Gy} (%)	9.71 ± 7.59	16.78 ± 7.42	-7.07 ± 2.28	-24.59	0.000
V_{15 Gy} (%)	23.54 ± 8.52	35.84 ± 9.58	-12.30 ± 4.00	-24.43	0.000
D_mean (cGy)	1035.68 ± 259.36	1223.72 ± 272.45	-188.03 ± 50.83	-29.36	0.000
Small intestine
V_{50 Gy} (%)	3.85 ± 3.14	4.25 ± 3.20	-0.39 ± 0.41	-7.53	0.000
V_{20 Gy} (%)	45.04 ± 13.04	45.14 ± 13.06	-0.09 ± 5.67	-0.13	0.898
D_mean (cGy)	1893.32 ± 422.08	1917.99 ± 421.89	-24.67 ± 7.85	-24.93	0.000
Colon
V_{50 Gy} (%)	7.51 ± 5.05	7.82 ± 4.95	-0.31 ± 0.53	-4.59	0.000
D_mean (cGy)	2384.90 ± 330.89	2402.67 ± 331.63	-17.77 ± 7.97	-17.69	0.000
Femoral heads
D_mean (cGy)	2133.87 ± 365.61	2143.66 ± 363.90	-9.78 ± 43.03	-1.80	0.076
Bladder
V_{50 Gy} (%)	32.07 ± 7.19	31.00 ± 7.46	1.07 ± 1.46	5.85	0.000
D_mean (cGy)	4374.30 ± 209.88	4368.21 ± 208.19	6.09 ± 17.85	2.71	0.009
Rectum
V_{50 Gy} (%)	29.12 ± 10.35	30.87 ± 11.18	-1.75 ± 1.98	-7.01	0.004
D_mean (cGy)	4371.17 ± 292.16	4386.87 ± 300.88	-15.69 ± 41.37	-3.01	0.000
Note:$\stackrel{-}{D}={\sum }_{1}^{63}\left[\left({Plan}_{-n}\right)-\left({Plan}_{+n}\right)\right]/63$
Abbreviations: Plan-, plan generated without immobilization device; Plan+, plan calculated from Plan- with immobilization device taken into accounted; PTV, planning target volume; HI, homogeneity index; CI, conformity index.

Dose difference distribution map

The differences in dose distribution were calculated by subtracting Plan₊ from Plan_-, as illustrated in Figure 3c. The color gradient from blue to red represented various absolute dose values ranging from -5 Gy to 25 Gy. The dose distributions were significantly affected by both the build-up effect and radiation scattering caused by the immobilization devices. The skin dose in the hypogastrium region increased noticeably by 10 Gy to 25 Gy, while the PTVs in the irradiated area were reduced by approximately 2 Gy (Figure 3c).

Similarly, the differences in dose distribution were calculated by subtracting Plan_+n from Plan_-n, as shown in Figure 3d. The color gradient from blue to red represented different absolute dose values ranging from -5 Gy to 25 Gy. After adjusting the prescribed dose to the clinically desired V_50Gy=95%, there were no significant differences in the PTV coverage areas. However, the skin dose in the hypogastrium region still increased noticeably by 10 Gy to 25 Gy, approximately 2 Gy more than before the adjustment (Figure 3c, 3d).

Dose measurement verification

According to Fig. 4, the EBT3 measurements (18.24 ± 5.85 Gy) on the skin of the lower abdomen were more similar to the Plan₊ calculations (20.26 ± 6.84 Gy) than the Plan_- results (13.90 ± 4.76 Gy). The Plan_-, which did not take into account the immobilization device when calculating the dose distributions on the external contour, underestimated the skin dose by approximately 23.66%.

Dose verification of patient-specific quality assurance

For each Plan- and Plan+ of all patients, the global γ passing rate were calculated. The mean global gamma passing rate was 98.18% ± 1.31% in Plan- set and 89.01% ± 2.90 % in Plan+ set, with 3%/2mm and a 10% dose threshold. Out of the 63 plans, 34 had a pass rate of less than 90%, which means that 54% of the plans, including those with the immobilization device, did not meet the verification criteria.

With the rapid advancement of radiotherapy technology, individual immobilization devices have become widely utilized in clinical practice. These devices not only minimize positioning errors but also ensure the consistency of positioning during intra-fractional and inter-fractional radiotherapy. In the case of patients undergoing postoperative radiotherapy for gynecologic cancer, while supine fixation provides greater comfort, prone fixation has been found to reduce small intestine exposure and the occurrence of gastrointestinal toxicity [17-18]. This is particularly beneficial for obese patients, as prone fixation has been shown to have a smaller margin of error compared to supine fixation [19-20]. It is important to note that the materials used in immobilization devices are not completely transparent to X-rays and can attenuate the delivered dose. Therefore, it is crucial to consider the dosimetric effects of these devices in dose calculations [21, 22]. The AAPM TG-176 report recommends taking into account the influence of fixation devices on dose calculation [23]. However, most commercial medical treatment planning systems do not automatically account for all types of immobilization devices, requiring medical physicists to manually include them in the calculations.

The PIDBB utilized in this study is made up of an engineering plastic support pad, a negative pressure vacuum bag, and a thermoplastic film. All three materials are classified as low density materials, but they can lead to the attenuation of radiation and alterations in the built-up effect, which in turn affects the planned dose distribution. Cheung discovered that the basal layer doses increased from 16% in an open field to 52% of the maximum with a bag thickness of 2.5 cm for a 10 cm × 10 cm field at 6 MV X-ray [24]. Chen examined the dosimetric impact of head and neck fixation devices on the intensity modulation plan for nasopharyngeal cancer. The reduction in prescription dose coverage rate and mean dose to the target volumes was significant, and the increase in skin dose could reach up to an average of 53%, similar to our findings [25]. Lv computed and evaluated the dosimetric effects on the skin of supine immobilization devices for breast cancer in IMRT plans. The data indicated a significant increase in skin dose, particularly in patients who had undergone breast-conservation surgery, with both the V_30Gy and V_40Gy of the skin increasing by more than 10% [26]. In our study, V_{40 Gy}, V_{30 Gy}, and V_{20 Gy} of the skin increased by at least 45%, regardless of the impact on prescription dose coverage. According to the EBT3 measurements, the skin dose on the anthropomorphic phantom’s abdomen and pelvis was 23.66% higher. The occurrence of radiation dermatitis is directly related to the skin dose. Pastores reported that V_{30 Gy} of the skin was the most significant dosimetric predictor of acute radiation dermatitis [27]. The additional dosimetric effects of PIDBB may increase the incidence of acute radiation dermatitis, especially in patients requiring exposure to the inguinal lymph node drainage area or the perineal area. Therefore, it is crucial to carefully consider the use of fixation devices and analyze their pros and cons. Firstly, radiation oncologists need to determine whether the prone position is more advantageous than the supine position for GC patients when choosing fixation devices. Secondly, when radiotherapists perform the planning CT scan, they should use the extended FOV algorithm to reconstruct the CT images, given the large diameter and volume of the PIDBB. Thirdly, when radiation dosimetrists design the plan, they must manually outline the complete PIDBB. Dosimetrists should avoid selecting certain angles in multi-field intensity-modulated planning due to the limitations of the source skin distance in commercial TPS. Fourthly, when physicists conduct patient-specific quality assurance, they need to identify whether the failure to validate the dose is due to the PIDBB. In our study, approximately 54% of plans involving the immobilization device did not meet the verification criteria.

Although this study has yielded positive outcomes, there are certain constraints that need to be addressed in the future. It is essential to expand the sample size of patients and incorporate varying TPS or calculation algorithms, dosimetry techniques, and dose measurements in subsequent studies.

In this study, we performed calculations and evaluations to determine the impact of prone immobilization devices on the skin during intensity-modulated radiation therapy for gynecologic cancer. There was a significant decrease in the rate of prescribed dose coverage and an increase in the average dose to the target areas. The percentage of skin volume receiving 40 Gy, 30 Gy, and 20 Gy increased by more than 45%. To accurately calculate the dose attenuation and skin dose increment in the treatment planning system, the immobilization device should be incorporated within the external body contour.

IMRT: intensity modulated radiation therapy; GC: gynecologic cancer; PIDBB: prone immobilization devices combined with belly board; TPS: treatment planning system; OAR: organs of risk; DMLC: dynamic multi-leaf collimator; GTV: gross target volume; CTV: clinical target volume; PTV : planned target volume; ICRU: international radiation units and measurements; DVH: dose-volume histograms; HI: homogeneity index; CI: conformity index; ART: An Alderson Radiation Therapy; AAPM: association of physicists in medicine;

Acknowledgements

Not applicable.

Authors’ contributions

WDH and LB conceived and designed this study and drafted the manuscript under the supervision of DJ. DJ participated in the design and coordination of the study, and helped to draft the manuscript. YHM selected the patient collective and contoured the reigns of interest. LZH and KFU conducted IMRT plans. WDH, CLX and DJ collected the data and performed the analysis. All authors read and approved the final manuscript.

Funding

This work was jointly supported by the Guangdong Basic and Applied Basic Research Foundation (2021A1515111084).

Availability of data and materials

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Ethics approval and consent to participate

As the data are anonymous and no intervention was happened in the treatment of patient, only verbal informed consent was obtained from participants, this procedure was approved by the of the Third Affiliated Hospital of Sun Yat-sen University Ethics Committee [II2023-149-01].

Consent for publication

The authors have declared that no competing interest exists.

Competing interests

The authors have declared that no competing interest exists.

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No competing interests reported.

Dosimetric effects of prone immobilization devices on skin in intensity-modulated radiation therapy for gynecologic cancer: a retrospective study

Status:

Journal Publication

Version 1

Abstract

Objective

Methods

Results

Conclusions

Trial registration:

Figures

Background

Methods

Patient data and setup

Regions of interest

Treatment planning and dose calculation

Statistical analysis

Dose verification of the anthropomorphic phantom

Dose verification of patient-specific quality assurance (QA)

Results

Doses in the targets and OARs

Discussion

Conclusion

Abbreviations

Declarations

References

Additional Declarations

Status:

Journal Publication

Version 1